CN103401616B - A kind of radio frequency optical transmission system of high linearity and method - Google Patents

Abstract

The invention discloses a radio frequency optical transmission system and method with high linearity, adopts dual parallel electro-optical phase modulators at the transmitting end, and uses two sets of couplers and photoelectric balance detectors at the receiving end to perform coherent balance on two modulation signals respectively Detection, by controlling the power ratio of the light source and the voltage ratio of the radio frequency signal input to the two parallel phase modulators at the transmitting end, so that the powers of the third-order intermodulation components in the two electrical signals detected by the coherent balance of the two modulated signals are equal, and then The third-order intermodulation component can be canceled out by using the electric subtractor to subtract the two electrical signals, and the complete suppression of the third-order intermodulation component can be realized, thereby improving the linearization of the system. At the same time, because the invention adopts the coherent balance detection technology, the sensitivity of the system can be improved, and the relative intensity noise can be reduced, thereby reducing the noise figure of the system.

Description

A high linearity radio frequency optical transmission system and method

technical field

The invention belongs to the technical field of radio frequency optical transmission, and more specifically relates to a high linearity radio frequency optical transmission system and method.

Background technique

The radio frequency optical transmission system is a transmission system that modulates the radio frequency signal and loads it into the optical carrier, and demodulates and restores the radio frequency signal at the receiving end after transmission through the optical fiber. It is an important part of the radio frequency microwave communication system. In recent years, with the rapid development of wireless communication technology, the application requirements of radio frequency optical transmission systems are also increasing rapidly. As a technology with very wide applicability, radio frequency optical transmission system has important application value in civil communication and national defense military, and its application covers radio communication, television broadcasting, radar positioning, telemetry and remote control, satellite communication, electronic warfare and Now it has completely entered various fields such as cellular mobile communication equipment of ordinary families.

The dynamic range of a radio frequency optical transmission system refers to the power range between the minimum signal and the maximum signal that the system can transmit. It is restricted by two key factors: one is the noise of the system, and the other is the nonlinearity of the system. In order to realize a radio frequency optical transmission system with a large dynamic range, lower system noise and higher system linearity are required. In the radio frequency optical transmission system, the most important nonlinear term affecting the nonlinearity of the system is the third-order intermodulation (Third-Order Intermodulation, IMD3) component. Therefore, to achieve high linearity of the system means better suppression of IMD3.

The research work on radio frequency optical transmission system based on electro-optical intensity modulator has a history of more than 30 years. IMD3 suppression technologies for such systems include pre-distortion technology, two intensity modulators connected in parallel, in series, and mixed polarization state technology based on intensity modulators. In the literature [Dual Parallel Modulation Schemes for Low-Distortion Analog Optical Transmission, S.K.Korotky, R.M.DERidder, IEEE Photon.Technol.Lett.Vol.21, no.21, pp.1627—1629, 2009.], the author proposed In the parallel connection scheme of the modulators, the third-order nonlinear distortion can be suppressed by adjusting the ratio of the optical power injected into the two modulators and the voltage ratio of the radio frequency signal, and at the same time adjusting the DC bias points of the two modulators. In literature [Enhanced Spurious-Free Dynamic Range Using Mixed Polarization in Optical Single Sideband Mach-Zehnder Modulator, B.Masella, B.Hraimel, X.Zhang, J.Lightwave TechnoL, vol.27, no.15, pp.3034—3041 ,2009.], the author proposed a hybrid polarization state technology scheme based on intensity modulators, using the characteristics of different polarization states and different modulation efficiencies in the intensity modulator, by adjusting the polarization state of the injected light and the polarization synthesis after the modulator The angle achieves the effect of third-order nonlinear distortion suppression.

However, due to the inherent defects of the electro-optical intensity modulator itself, the nonlinear suppression of the radio-frequency optical transmission system based on the electro-optical intensity modulator has limitations, and the electro-optic intensity modulator requires a sophisticated feedback circuit to control the DC bias voltage to control the modulator transfer function.

The radio-frequency optical transmission system based on the electro-optic phase modulator has become the focus of research in this field in recent years. The electro-optic modulation of the electro-optic phase modulator is to modulate the radio frequency signal to the phase of the optical carrier, which is a good linear process without nonlinear distortion. However, converting phase information into intensity information at the receiving end is a nonlinear process, which still brings nonlinear distortion to the system.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the prior art, provide a high linearity radio frequency optical transmission system and method, adopt dual parallel electro-optic phase modulators at the transmitting end, realize the complete suppression of the third-order intermodulation component through power control, The receiving end adopts coherent balanced detection method to receive, which improves the sensitivity and noise figure of the system.

In order to achieve the purpose of the above invention, the high linearity radio frequency optical transmission system of the present invention includes a transmitting end, a receiving end and an optical fiber, and is characterized in that the transmitting end includes a radio frequency signal source module, a radio frequency power distribution module, a light source module, a first An electro-optic phase modulator, a second electro-optic phase modulator, the receiving end includes a local oscillator light source module, a first optical coupler, a second optical coupler, a first photoelectric balance detector, a second photoelectric balance detector, an electrical subtraction device, of which:

A radio frequency signal source module, used to generate a radio frequency signal S _RF ;

The radio frequency signal power distribution module is used to divide the radio frequency signal S _RF generated by the radio frequency signal source module into two radio frequency signals S ₁ (t) and S ₂ (t), the voltages are V ₁ and V ₂ respectively, and the radio frequency signal S ₁ (t) is sent to the first electro-optic phase modulator, and the radio frequency signal S ₂ (t) is sent to the second electro-optic phase modulator;

The light source module is used to generate two laser light sources L ₁ and L ₂ , which have the same frequency and power respectively P ₁ and P ₂ , and their power ratio P ₁ /P ₂ =(V ₂ /V ₁ ) ³ , the light source L ₁ is sent to the first electro-optic phase modulator, and light source L ₂ is sent to the second electro-optic phase modulator;

The first electro-optic phase modulator is used to phase-modulate the radio frequency signal S ₁ (t) and the light source L ₁ , and the obtained signal light X ₁ is sent to the first coupler at the receiving end through an optical fiber;

The second electro-optical phase modulator is used to phase-modulate the radio frequency signal S ₂ (t) and the light source L ₂ , and the obtained signal light X ₂ is sent to the second coupler at the receiving end through an optical fiber;

The local oscillator light source module is used to generate two laser local oscillator light sources L' ₁ and L' ₂ , the local oscillator light source L' ₁ is coherent with the light source L ₁ , the local oscillator light source L' ₂ is coherent with the light source L ₂ , and the local oscillator light source L' ₁ is sent to the first coupler, and the local oscillator light source L' ₂ is sent to the second coupler;

The first optical coupler is used to couple the signal light X1 with the local oscillator light source L' ₁ , and send the coupled signal _Y1 to the _first photoelectric balance detector;

The second optical coupler is used to couple with the local oscillator light source L' ₂ , and send the coupled signal Y ₂ to the second photoelectric balance detector;

The first photoelectric balance detector is used to convert the signal Y ₁ into an electrical signal T ₁ and send it to the electrical subtractor;

The second photoelectric balance detector is used to convert the signal Y ₂ into an electrical signal T ₂ and send it to the electrical subtractor;

An electrical subtractor, used to subtract two electrical signals to obtain a restored radio frequency signal S

The present invention also provides a radio frequency optical transmission method based on a high linearity radio frequency optical transmission system, which is characterized in that it includes:

S1: The transmitting end divides the radio frequency signal S _RF into two radio frequency signals S ₁ (t) and S ₂ (t), the voltages are V ₁ and V ₂ respectively, and two laser light sources L ₁ and L ₂ are used to pair the radio frequency signals S ₁ (t) and S ₂ (t) perform electro-optic phase modulation, the powers of the two laser sources are P ₁ and P ₂ respectively, and their power ratio P ₁ /P ₂ = (V ₂ /V ₁ ) ³ , the electro-optic After phase modulation, two channels of signal light X ₁ and X ₂ are obtained and transmitted to the receiving end through the optical fiber;

S2: The receiving end receives signal light X ₁ and X ₂ , uses two laser local oscillator light sources L′ ₁ and L′ ₂ to couple and coherently signal light X ₁ and X ₂ respectively, and then obtains two signals Y ₁ and Y ₂ conducts photoelectric balance detection to obtain two electrical signals T ₁ and T ₂ , and subtracts the two electrical signals to obtain the recovered radio frequency signal

The radio frequency optical transmission system and method with high linearity of the present invention adopts dual parallel electro-optic phase modulators at the transmitting end, and uses two sets of couplers and photoelectric balance detectors at the receiving end to perform coherent and balanced detection of the two-way signal light respectively. The terminal controls the relationship between the power ratio of the light source and the voltage ratio of the radio frequency signal input to the two parallel phase modulators, so that the power of the third-order intermodulation component in the two electrical signals detected by the coherent balance of the two signal lights is equal, and then the electrical subtraction method is used The device can cancel the third-order intermodulation component by subtracting the two electrical signals, and realize the complete suppression of the third-order intermodulation component, thereby improving the linearization of the system. At the same time, because the invention adopts the coherent balance detection technology, the sensitivity of the system can be improved, and the relative intensity noise can be reduced, thereby reducing the noise figure of the system.

Description of drawings

Fig. 1 is a kind of specific embodiment structural diagram of the radio frequency optical transmission system of high linearity of the present invention;

Fig. 2 is the schematic diagram of photoelectric balance detection among the present invention;

Fig. 3 is the structural representation of embodiment 1 of the present invention;

Fig. 4 is the structural representation of embodiment 2 of the present invention;

Fig. 5 is a schematic structural view of Embodiment 3 of the present invention;

Fig. 6 is the electrical signal spectrum result that the first balanced detector outputs in the simulation of embodiment 2;

Fig. 7 is the electrical signal spectrum result that the second balance detector outputs in the simulation of embodiment 2;

Fig. 8 is the spectrum result of the electrical signal output by the electrical subtractor in the simulation of Embodiment 2.

Detailed ways

Specific embodiments of the present invention will be described below in conjunction with the accompanying drawings, so that those skilled in the art can better understand the present invention. It should be noted that in the following description, when detailed descriptions of known functions and designs may dilute the main content of the present invention, these descriptions will be omitted here.

FIG. 1 is a structural diagram of a specific embodiment of the high linearity radio frequency optical transmission system of the present invention. As shown in Figure 1, the present invention includes a transmitting end, a receiving end and an optical fiber, wherein the transmitting end includes a radio frequency signal source module 5, a radio frequency power distribution module 4, a light source module 1, a first electro-optic phase modulator 2, a second electro-optic phase modulator device 3, the receiving end includes a local oscillator light source module 6, a first optical coupler 7, a second optical coupler 8, a first photoelectric balance detector 9, a second photoelectric balance detector 10, and an electrical subtractor 11, wherein :

The radio frequency signal source module 5 is configured to generate a radio frequency signal S _RF .

The radio frequency signal power distribution module 4 is used to divide the radio frequency signal S _RF generated by the radio frequency signal source module 5 into two radio frequency signals S ₁ and S ₂ , the voltages are V ₁ and V ₂ respectively, and send the radio frequency signal S ₁ to the first An electro-optic phase modulator ₂ , and the radio frequency signal S2 is sent to a second electro-optic phase modulator 3.

The light source module 1 is used to generate two laser light sources L ₁ and L ₂ , which have the same frequency and power respectively P ₁ and P ₂ , and their power ratio P ₁ /P ₂ =(V ₂ /V ₁ ) ³ , will The light source L ₁ is sent to the first electro-optic phase modulator 2 , and the light source L ₂ is sent to the second electro-optic phase modulator 3 . The light source module 1 may be a combined module of a laser and a beam splitter.

The _first electro-optic phase modulator ₂ is used to perform phase modulation on the radio frequency signal S1 and the light source L1, and the obtained signal light X1 is sent to the _first optical coupler 7 at the receiving end through an optical fiber.

The _second electro-optical phase modulator ₃ is used for phase modulation of the radio frequency signal S2 and the light source L2, and the obtained signal light X2 is sent to the _second optical coupler 8 at the receiving end through an optical fiber.

The local oscillator light source module 6 is used to generate two laser local oscillator light sources L' ₁ and L' ₂ , the local oscillator light source L' ₁ is coherent with the light source L ₁ , the local oscillator light source L' ₂ is coherent with the light source L ₂ , and the local oscillator The light source L′ ₁ is sent to the first optical coupler 7 , and the local oscillator light source L′ ₂ is sent to the second optical coupler 8 .

The first optical coupler 7 is used to couple the signal light X ₁ with the local oscillator light source L′ ₁ and send the coupled signal Y ₁ to the first balanced detector 9 .

The second optical coupler 8 is used to couple the signal light X2 with the local oscillator light source L' ₂ , and send the coupled signal _Y2 to the _second balanced detector 10;

The first photoelectric balance detector 9 is used to convert the signal Y ₁ into an electrical signal T ₁ and send it to the electrical subtractor 11;

The second photoelectric balance detector 10 is used to convert the signal Y ₂ into an electrical signal T ₂ and send it to the electrical subtractor 11;

Electrical subtractor 11, used for subtracting two electrical signals to obtain a restored radio frequency signal

The present invention also provides a radio frequency optical transmission method based on a high linearity radio frequency optical transmission system, which is characterized in that it includes:

S1: The transmitting end divides the radio frequency signal S _RF into two radio frequency signals S ₁ (t) and S ₂ (t), the voltages are V ₁ and V ₂ respectively, and two laser light sources L ₁ and L ₂ are used to pair the radio frequency signals S ₁ (t) and S ₂ (t) perform electro-optic phase modulation, the powers of the two laser sources are P ₁ and P ₂ respectively, and their power ratio P ₁ /P ₂ = (V ₂ /V ₁ ) ³ , the electro-optic After phase modulation, two channels of signal light X ₁ and X ₂ are obtained and transmitted to the receiving end through the optical fiber;

S2: The receiving end receives signal light X ₁ and X ₂ , uses two laser local oscillator light sources L′ ₁ and L′ ₂ to couple and coherently signal light X ₁ and X ₂ respectively, and then obtains two signals Y ₁ and Y ₂ conducts photoelectric balance detection to obtain two electrical signals T ₁ and T ₂ , and subtracts the two electrical signals to obtain the recovered radio frequency signal

The present invention adopts dual parallel electro-optical phase modulators at the transmitting end, and uses coherent balanced detection at the receiving end. The power output of the third-order intermodulation components of the two photoelectrically balanced detectors can be expressed as follows:

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}\mathrm{<span\; class="notranslate">\; the\; th</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 128</span>}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}^{\mathrm{<span\; class="notranslate">\; 6</span>}}{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 6</span>}}{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}$

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}\mathrm{<span\; class="notranslate">\; the\; th</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 128</span>}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}^{\mathrm{<span\; class="notranslate">\; 6</span>}}{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 6</span>}}{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}$

Where P ₁ and P ₂ represent the input optical power of the two electro-optic phase modulators and the input optical power of the two optocouplers, respectively, V ₁ and V ₂ are the RF signal voltages input to the two electro-optic phase modulators respectively, r _d is the photoelectric conversion efficiency of the photoelectric balance detector, α is the insertion loss of the electro-optic phase modulator, V _π is the half-wave voltage of the electro-optic phase modulator, and Z _out is the output impedance of the photoelectric balance detector.

It can be found from the above formula that when the laser output optical power ratio and the RF signal voltage ratio are reasonably controlled, that is, P ₁ /P ₂ =(V ₂ /V ₁ ) ³ , then the two signals can be subtracted at the receiving end, That is to say, the third-order intermodulation distortion is completely canceled, so that good suppression of the third-order nonlinear distortion can be achieved, and the dynamic range is expanded.

The present invention adopts a coherent balanced detection mode at the receiving end. Coherent detection is a commonly used detection method at present. The output power of coherent detection is: P _coherent ＝2a ² P _S P _L R _L , while the output power of traditional direct detection is: P _directly ＝a ² P _S ² R _L ,in are the average power of the signal light and the local oscillator light respectively, and _RL is the load resistance. Usually _PL > _PS , so coherent detection can provide a sufficiently high gain, which is especially effective for weak signal detection.

Balanced detection is a technology that emerges with the development of coherent detection technology. Its main function is to reduce the noise of local lasers. It has been widely used in the field of microwave optical links. Fig. 2 is a schematic diagram of photoelectric balance detection in the present invention. As shown in Figure 2, after the signal light E ₁ (t) and the local oscillator light E ₂ (t) are coherent through the coupler, the coupled signal is obtained, including E ₃ (t) and E ₄ (t), and the input The photoelectric balance detector, the photoelectric balance detector can be equivalent to two photodetectors and an electrical subtractor, and the two detectors perform photoelectric detection on E ₃ (t) and E ₄ (t) respectively, and obtain two electrical signals i ₁ (t) and i ₂ (t), the electrical subtractor subtracts the two electrical signals to obtain the electrical signal i(t)=i ₁ (t)-i ₂ (t).

The balanced detector in the radio frequency optical transmission system of the present invention uses two photodetectors, and since the shot noise is a differential mode signal, more shot noise is introduced than the system using a single detector. However, the relative intensity noise of the laser is a common-mode signal, so balanced detection can reduce the relative intensity noise of the system. If the offset relative intensity noise is greater than the increased shot noise, the noise of the entire system will be reduced, and the noise figure will be reduced.

Example 1

Fig. 3 is a schematic structural diagram of Embodiment 1 of the present invention. As shown in Figure 3, in the present embodiment, at the transmitting end, the radio frequency signal source module 5 produces two sine wave signals whose angular frequencies are ω ₁ and ω ₂ respectively, and the two sine wave signals are combined into one way through an electric coupler Output to the radio frequency signal power distribution module.

The radio frequency signal power distribution module 4 includes a third beam splitter 401 and an electrical attenuator 402, wherein:

The electrical beam splitter 401 is used to split the radio frequency signal S _RF generated by the radio frequency signal source module 5 into two radio frequency signals S ₁ (t) and S ₂ (t).

The electric attenuator 402 is used to adjust the power of the radio frequency signal S ₁ (t) or S ₂ (t). In this embodiment, it is used to change the power of the radio frequency signal S ₂ (t).

In order to facilitate the power distribution of the light source, the power of the two radio frequency signals usually satisfies a predetermined power ratio during power distribution of the radio frequency signal. In this embodiment, the voltage of the radio frequency signal S ₁ (t) is set as V ₁ , and the voltage of the radio frequency signal S ₂ is V ₂ , then the radio frequency signal S ₁ (t) input to the first electro-optic phase modulator 2 and the input of the second electro-optic phase modulator 2 The expressions of the radio frequency signal S ₂ (t) of the phase modulator 3 are respectively:

S ₁ (t)=V ₁ (sin(ω ₁ t)+sin(ω ₂ t)),

S ₂ (t)=V ₂ (sin(ω ₁ t)+sin(ω ₂ t)).

In this embodiment, the light source module 1 uses a laser to generate a light source for beam splitting, including a laser 101 , a first amplifier 102 , a first polarization controller 103 , and a first beam splitter 104 .

The laser 101 is used to generate a laser light source.

The first amplifier 102 is used to amplify the light source generated by the laser 101 . The function of the first amplifier 102 is to better control the power of the light source.

The first polarization controller 103 is configured to adjust the polarization state of the light source, that is, to adjust the polarization of the light source amplified by the first amplifier 102 . The purpose of configuring the polarization controller 103 in the light source module 1 is mainly to determine the polarization state of the light source, so that the local oscillator light source module 6 at the receiving end controls the polarization state of the local oscillator light source to make the local oscillator light source coherent with the signal light received at the receiving end.

The first beam splitter 104 is used to split the light source into two light sources L ₁ and L ₂ , the powers of which are P ₁ and P ₂ respectively, and the power ratio P ₁ /P ₂ =(V ₂ /V ₁ ) ³ . The two light sources L ₁ and L ₂ are sent to the first electro-optic phase modulator 2 and the second electro-optic phase modulator 3 respectively.

The light intensity expressions of the two light sources L ₁ and L ₂ are respectively:

${\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{\sqrt{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\sqrt{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>$

Among them, i is the imaginary unit, and ω ₀ is the angular frequency of the light source.

The first electro-optical phase modulator 2 is used to perform phase modulation on the radio frequency signal S ₁ (t) and the light source L ₁ , and the obtained signal light X ₁ is sent to the first coupler 7 at the receiving end through the optical fiber 12 .

The second electro-optical phase modulator 3 is used for phase-modulating the radio frequency signal S ₂ (t) and the light source L ₂ , and the obtained signal light X ₂ is sent to the second coupler 8 at the receiving end through the optical fiber 12 .

The expressions of the optical field intensity of the signal light output by the two electro-optic phase modulators are:

${\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; PM</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{\sqrt{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; i\&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; i</span>}\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>$

${\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; PM</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\sqrt{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; i</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; i</span>}\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>$

Among them, V _π represents the half-wave voltage of the electro-optic phase modulator, and this parameter is consistent in the two electro-optic phase modulators.

At the receiving end, in this embodiment, the local oscillator light source module 6 uses a local oscillator laser to generate a laser local oscillator light source for beam splitting, including a local oscillator laser 601, a second amplifier 602, a second polarization controller 603, and a second beam splitter device 604, wherein:

The local oscillator laser 601 is used to generate a laser local oscillator light source with the same frequency, propagation direction and light source. The frequency and propagation direction of the local oscillator light source are the same as that of the light source, so that the local oscillator light source and the signal light modulated by the radio frequency signal can be coherent.

The second amplifier 602 is used to amplify the local oscillator light source generated by the local oscillator laser 601 . The function of the second amplifier 102 is to better control the power of the local oscillator light source.

The second polarization controller 603 is configured to modulate the polarization state of the local oscillator light source so that it is in the same polarization direction as the signal light received at the receiving end. The polarization direction of the local oscillator light source and the signal light are the same to ensure that the local oscillator light source and the signal light modulated by the radio frequency signal can be coherent. If during the optical fiber transmission process, the polarization state of the signal light does not change, then the polarization direction of the signal light received at the receiving end is the same as that of the light source used for radio frequency signal modulation, then the second polarization controller 603 performs local oscillator light source When adjusting the polarization state of the light source module, the polarization state of the light source generated by the light source module can be directly compared. Therefore, the optical fiber 12 in the present invention may be a polarization-maintaining optical fiber.

The second beam splitter 604 is used for splitting the local oscillator light source adjusted by the second polarization controller 603 into two beams of local oscillator light source L' ₁ and L' ₂ . The two local oscillator light sources L' ₁ and L' ₂ are sent to the first optical coupler 7 and the second optical coupler 8 respectively. _{In this embodiment, the local oscillator light sources L'1 and} L' _{2 have} the same power as the corresponding light sources L1 and L2.

The expressions of the light field intensity of the two local oscillator light sources L′ ₁ and L′ ₂ are respectively:

${\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{\sqrt{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>$

${\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\sqrt{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; .</span>$

It can be seen that in this embodiment, the light field strengths of the two local oscillator light sources L' ₁ and L' ₂ are consistent with those of the light source.

The first optical coupler 7 is used to couple the signal light X ₁ with the local oscillator light source L′ ₁ , and send the coupled signal Y ₁ to the first photoelectric balance detector 9 .

The second optical coupler 8 is used to couple the signal light X ₂ with the local oscillator light source L′ ₂ and send the coupled signal Y ₂ to the second photoelectric balance detector 10 .

The first photoelectric balance detector 9 is used to convert the signal Y ₁ into an electrical signal T ₁ and send it to the electrical subtractor 11 . The power expression _of the fundamental frequency component in the electrical signal T1 is:

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; RF</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}^{\mathrm{<span\; class="notranslate">\; 6</span>}}{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}$

The power of the third-order intermodulation component is:

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}\mathrm{<span\; class="notranslate">\; the\; th</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 128</span>}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}^{\mathrm{<span\; class="notranslate">\; 6</span>}}{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 6</span>}}{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}$

The second photoelectric balance detector 10 is used to convert the signal Y ₂ into an electrical signal T ₂ and send it to the electrical subtractor 11 . _The power expression of the fundamental frequency component in the electrical signal T2 is:

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; RF</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}$

The power of the third-order intermodulation component is:

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}\mathrm{<span\; class="notranslate">\; the\; th</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 128</span>}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}^{\mathrm{<span\; class="notranslate">\; 6</span>}}{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 6</span>}}{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}$

Electrical subtractor 11, used for subtracting two electrical signals to obtain a restored radio frequency signal It can be seen that since P ₁ /P ₂ =(V ₂ /V ₁ ) ³ in the present invention, the two electrical signals are subtracted by the electrical subtractor 11, the third-order intermodulation components are completely suppressed, and the final recovered radio frequency signal Only the output of the baseband signal remains:

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; RF</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}<span\; class="notranslate">\; .</span>$

Example 2

Fig. 4 is a schematic structural diagram of Embodiment 2 of the present invention. As shown in FIG. 4 , in this embodiment, except for the light source module 1 and the local oscillator light source module 6 , other modules are the same as those in the first embodiment.

The radio frequency signal source module 5 is consistent with Embodiment 1, and produces two sine wave signals whose angular frequencies are ω ₁ and ω ₂ respectively, and the two sine wave signals are combined into one and output to the radio frequency signal power distribution module 4 by an electric coupler .

The radio frequency signal power distribution module 4 includes the third beam splitter 401 and the electric attenuator 402 to carry out beam splitting and power adjustment to the radio frequency signal S _RF generated by the radio frequency signal source module 5. Similarly, in the present embodiment, the radio frequency signal S ₁ ( The voltage at t) is V ₁ , the voltage of the radio frequency signal S ₂ is V ₂ , then the radio frequency signal S ₁ (t) input to the first electro-optical phase modulator 2 and the radio frequency signal S ₂ ( The expressions of t) are respectively:

S ₁ (t)=V ₁ (sin(ω ₁ t)+sin(ω ₂ t)),

S ₂ (t)=V ₂ (sin(ω ₁ t)+sin(ω ₂ t)).

In this embodiment, in addition to the laser 101, the first amplifier 102, the first polarization controller 103, and the first beam splitter 104, the light source module 1 also includes a third beam splitter 105, which converts the Light source splitting. The third optical beam splitter 105 divides the light source generated by the laser 101 into two beams, one of which is used as a light source for signal phase modulation, and the other beam is sent to the local oscillator light source module at the receiving end through an optical fiber as a local oscillator light source. In this embodiment, the third beam splitter 105 splits the light source into two beams, one beam is sent to the first amplifier 102 as a light source, and the other beam is sent to the local oscillator light source module 6 at the receiving end through the optical fiber 12 . In this embodiment, the power of the two light sources obtained by splitting the beams by the third beam splitter 105 is the same.

In the light source module 1 , the first amplifier 102 amplifies the light source obtained by the third beam splitter 105 .

The first polarization controller 103 is configured to adjust the polarization state of the light source, that is, to adjust the polarization of the light source amplified by the first amplifier 102 .

The first beam splitter 104 is used to divide the light source adjusted by the polarization controller 103 into two light sources L ₁ and L ₂ , the powers of which are P ₁ and P ₂ respectively, and the power ratio P ₁ /P ₂ =( V ₂ /V ₁ ) ³ . The two light sources L ₁ and L ₂ are sent to the first electro-optic phase modulator 2 and the second electro-optic phase modulator 3 respectively.

Similarly, the light intensity expressions of the two light sources L ₁ and L ₂ are:

${\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{\sqrt{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\sqrt{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>$

Among them, i is the imaginary unit, and ω ₀ is the angular frequency of the light source.

The first electro-optical phase modulator 2 is used to perform phase modulation on the radio frequency signal S ₁ (t) and the light source L ₁ , and the obtained signal light X ₁ is sent to the first coupler 7 at the receiving end through the optical fiber 12 .

The second electro-optical phase modulator 3 is used for phase-modulating the radio frequency signal S ₂ (t) and the light source L ₂ , and the obtained signal light X ₂ is sent to the second coupler 8 at the receiving end through the optical fiber 12 .

The expressions of the optical field intensity of the signal light output by the two electro-optic phase modulators are:

${\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; PM</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{\sqrt{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; i\&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; i</span>}\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>$

${\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; PM</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\sqrt{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; i</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; i</span>}\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>$

Among them, V _π represents the half-wave voltage of the electro-optic phase modulator, and this parameter is consistent in the two electro-optic phase modulators.

In this embodiment, since the local oscillator light source is generated by the light source module 1 at the transmitting end, there is no need to configure a local oscillator laser in the local oscillator light source module 6. The local oscillator light source module 6 includes a second amplifier 602, a second polarization controller 603 and a second polarization controller 603. Two beam splitters 604, wherein:

The second amplifier 602 is used to amplify the local oscillator light source received from the light source module 1 .

The second polarization controller 603 is configured to modulate the polarization state of the local oscillator light source so that the polarization direction of the signal light received by the receiving end is the same. Similarly, when the optical fiber 12 adopts a polarization-maintaining optical fiber, the polarization state of the signal light received at the receiving end is consistent with the light source used for phase modulation, and the second polarization controller 603 directly controls the polarization state of the light source when adjusting the polarization state of the local oscillator light source. polarization state.

The second beam splitter 604 is used for splitting the local oscillator light source adjusted by the second polarization controller 603 into two beams of local oscillator light source L' ₁ and L' ₂ . The two local oscillator light sources L' ₁ and L' ₂ are sent to the first optical coupler 7 and the second optical coupler 8 respectively. _{In this embodiment, the local oscillator light sources L'1 and} L' _{2 have} the same power as the corresponding light sources L1 and L2.

The expressions of the light field intensity of the two local oscillator light sources L′ ₁ and L′ ₂ are respectively:

${\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{\sqrt{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>$

${\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\sqrt{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; .</span>$

It can be seen that in this embodiment, the light field strengths of the two local oscillator light sources L' ₁ and L' ₂ are consistent with those of the light source.

The first optical coupler 7 is used to couple the signal light X ₁ with the local oscillator light source L′ ₁ , and send the coupled signal Y ₁ to the first photoelectric balance detector 9 .

The second optical coupler 8 is used to couple the signal light X ₂ with the local oscillator light source L′ ₂ and send the coupled signal Y ₂ to the second photoelectric balance detector 10 .

The first photoelectric balance detector 9 is used to convert the signal Y ₁ into an electrical signal T ₁ and send it to the electrical subtractor 11 . The power expression _of the fundamental frequency component in the electrical signal T1 is:

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; RF</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}^{\mathrm{<span\; class="notranslate">\; 6</span>}}{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}$

The power of the third-order intermodulation component is:

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}\mathrm{<span\; class="notranslate">\; the\; th</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 128</span>}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}^{\mathrm{<span\; class="notranslate">\; 6</span>}}{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 6</span>}}{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}$

The second photoelectric balance detector 10 is used to convert the signal Y ₂ into an electrical signal T ₂ and send it to the electrical subtractor 11 . _The power expression of the fundamental frequency component in the electrical signal T2 is:

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; RF</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}$

The power of the third-order intermodulation component is:

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}\mathrm{<span\; class="notranslate">\; the\; th</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 128</span>}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}^{\mathrm{<span\; class="notranslate">\; 6</span>}}{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 6</span>}}{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}$

Electrical subtractor 11, used for subtracting two electrical signals to obtain a restored radio frequency signal

Same as Embodiment 1, since P ₁ /P ₂ =(V ₂ /V ₁ ) ³ , the electrical signals obtained by the two photoelectric balance detectors are finally subtracted by the electrical subtractor 11, and the third-order intermodulation components are completely suppressed , the final recovered RF signal Only the output of the baseband signal remains:

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; RF</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}<span\; class="notranslate">\; .</span>$

Example 3

Fig. 5 is a schematic structural diagram of Embodiment 3 of the present invention. As shown in FIG. 5 , in this embodiment, except for the light source module 1 and the local oscillator light source module 6 , other modules are the same as those in the first embodiment.

At the transmitting end, the radio frequency signal source module 5 is the same as embodiment 1, and produces two sine wave signals whose angular frequencies are ω ₁ and ω ₂ respectively, and the two sine wave signals are combined into one path and output to the radio frequency signal power by an electric coupler. Assign modules.

The radio frequency signal power distribution module 4 includes the third beam splitter 401 and the electric attenuator 402 to carry out beam splitting and power adjustment to the radio frequency signal S _RF generated by the radio frequency signal source module 5. Similarly, in the present embodiment, the radio frequency signal S ₁ ( The voltage at t) is V ₁ , the voltage of the radio frequency signal S ₂ is V ₂ , then the radio frequency signal S ₁ (t) input to the first electro-optical phase modulator 2 and the radio frequency signal S ₂ ( The expressions of t) are respectively:

S ₁ (t)=V ₁ (sin(ω ₁ t)+sin(ω ₂ t)),

S ₂ (t)=V ₂ (sin(ω ₁ t)+sin(ω ₂ t)).

In this embodiment, the light source module 1 uses a laser to generate a light source for beam splitting, including a laser 101 , a first amplifier 102 , a first polarization controller 103 , and a first polarization beam splitter 105 .

The laser 101 is used to generate a laser light source.

The first amplifier 102 is used to amplify the light source generated by the laser 101 . The function of the first amplifier 102 is to better control the power of the light source.

The first polarization controller 103 is configured to adjust the polarization state of the light source, that is, to adjust the polarization of the light source amplified by the first amplifier 102 . In this embodiment, the first polarization controller 103 adjusts the polarization state of the light source to facilitate power distribution of the local oscillator light source in the local oscillator light source module 6 .

The first polarization beam splitter 105 is used to map the light source to the two orthogonal polarization states of the polarization beam splitter 105, and divide it into two beams of light sources L ₁ and L ₂ , the powers of which are P _x and P _y respectively, and their Power ratio P _x /P _y =(V ₂ /V ₁ ) ³ . The two light sources L ₁ and L ₂ are sent to the first electro-optic phase modulator 2 and the second electro-optic phase modulator 3 respectively. _In Embodiments ₁ and ₂ , the polarization states of the light sources L1 and L2 are the same, and in this embodiment, the polarization states _of the light sources L1 and L2 are orthogonal.

The light intensity expressions of the two light sources L ₁ and L ₂ are respectively:

${\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{\sqrt{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\sqrt{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>$

Among them, i is the imaginary unit, and ω ₀ is the angular frequency of the light source.

The first electro-optical phase modulator 2 is used to perform phase modulation on the radio frequency signal S ₁ (t) and the light source L ₁ , and the obtained signal light X ₁ is sent to the first coupler 7 at the receiving end through the optical fiber 12 .

The second electro-optical phase modulator 3 is used for phase-modulating the radio frequency signal S ₂ (t) and the light source L ₂ , and the obtained signal light X ₂ is sent to the second coupler 8 at the receiving end through the optical fiber 12 .

The expressions of the optical field intensity of the signal light output by the two electro-optic phase modulators are:

${\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; PM</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{\sqrt{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; i\&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; i</span>}\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>$

${\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; PM</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\sqrt{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; i</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; i</span>}\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>$

Among them, V _π represents the half-wave voltage of the electro-optic phase modulator, and this parameter is consistent in the two electro-optic phase modulators.

At the receiving end, in this embodiment, the local oscillator light source module 6 uses a local oscillator laser to generate a laser local oscillator light source for beam splitting, including a local oscillator laser 601, a second amplifier 602, a second polarization controller 603, and a polarization beam splitter 605 ,in:

The local oscillator laser 601 is used to generate a laser local oscillator light source with the same frequency, propagation direction and light source.

The second amplifier 602 is used to amplify the local oscillator light source generated by the local oscillator laser 601 .

The second polarization controller 603 is configured to modulate the polarization state of the local oscillator light source to make it the same as the polarization direction of the light source, so as to facilitate the power distribution of the local oscillator light source by the second polarization beam splitter 604 .

The second polarization beam splitter 604 is configured to split the local oscillation light source adjusted by the second polarization controller 603 into two local oscillation light sources L' ₁ and L' ₂ . The two local oscillator light sources L' ₁ and L' ₂ are sent to the first optical coupler 7 and the second optical coupler 8 respectively. _{In this embodiment, the local oscillator light sources L'1 and} L' _{2 have} the same power as the corresponding light sources L1 and L2.

The expressions of the light field intensity of the two local oscillator light sources L′ ₁ and L′ ₂ are respectively:

${\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{\sqrt{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>$

${\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\sqrt{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; .</span>$

It can be seen that in this embodiment, the light field strengths of the two local oscillator light sources L' ₁ and L' ₂ are consistent with those of the light source.

The first optical coupler 7 is used to couple the signal light X ₁ with the local oscillator light source L′ ₁ , and send the coupled signal Y ₁ to the first photoelectric balance detector 9 .

The second optical coupler 8 is used to couple the signal light X ₂ with the local oscillator light source L′ ₂ and send the coupled signal Y ₂ to the second photoelectric balance detector 10 .

The first photoelectric balance detector 9 is used to convert the signal Y ₁ into an electrical signal T ₁ and send it to the electrical subtractor 11 . The power expression _of the fundamental frequency component in the electrical signal T1 is:

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; RF</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}$

The power of the third-order intermodulation component is:

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}\mathrm{<span\; class="notranslate">\; the\; th</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 128</span>}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}^{\mathrm{<span\; class="notranslate">\; 6</span>}}{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 6</span>}}{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}$

The second photoelectric balance detector 10 is used to convert the signal Y ₂ into an electrical signal T ₂ and send it to the electrical subtractor 11 . _The power expression of the fundamental frequency component in the electrical signal T2 is:

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; RF</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}$

The power of the third-order intermodulation component is:

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}\mathrm{<span\; class="notranslate">\; the\; th</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 128</span>}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}^{\mathrm{<span\; class="notranslate">\; 6</span>}}{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 6</span>}}{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}$

Electrical subtractor 11, used for subtracting two electrical signals to obtain a restored radio frequency signal It can be seen that since P _x /P _y =(V ₂ /V ₁ ) ³ in this embodiment, the two electrical signals are subtracted by the electrical subtractor 11, the third-order intermodulation components are completely suppressed, and the final recovered radio frequency signal Only the output of the baseband signal remains:

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; RF</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}<span\; class="notranslate">\; .</span>$

Embodiment 2 is used for simulation. The simulation parameters are: P ₁ = _90mw , P ₂ =10mw, V ₁ =0.2V, V ₂ =0.42V, ω ₁ =10GHz, ω ₂ =12GHz, rd =1.0A/W. Fig. 6 is the result of the electrical signal spectrum output by the first balanced detector in the simulation of Embodiment 2. Fig. 7 is the result of the electrical signal spectrum output by the second balanced detector in the simulation of the second embodiment. Fig. 8 is the spectrum result of the electric signal output by the electric subtractor in the second embodiment. As shown in Figures 6 to 8, when the radio frequency optical transmission system of the present invention is used for the optical carrier transmission of radio frequency signals, the third-order intermodulation components are almost completely suppressed, and the loss of the fundamental frequency signal is very small, so that the linearity of the system can be improved. As it increases, the dynamic range also increases.

Although the illustrative specific embodiments of the present invention have been described above, so that those skilled in the art can understand the present invention, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art, As long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions and creations using the concept of the present invention are included in the protection list.

Claims (10)

1. A radio frequency optical transmission system with high linearity, comprising a transmitting end, a receiving end and an optical fiber, characterized in that, the transmitting end comprises a radio frequency signal source module, a radio frequency power distribution module, a light source module, and the first electro-optic phase modulator , the second electro-optical phase modulator, the receiving end includes a local oscillator light source module, a first optical coupler, a second optical coupler, a first photoelectric balance detector, a second photoelectric balance detector, and an electric subtractor, wherein: A radio frequency signal source module, used to generate a radio frequency signal S _RF ; The radio frequency signal power distribution module is used to divide the radio frequency signal S _RF generated by the radio frequency signal source module into two radio frequency signals S ₁ (t) and S ₂ (t), the voltages are V ₁ and V ₂ respectively, and the radio frequency signal S ₁ (t) is sent to the first electro-optic phase modulator, and the radio frequency signal S ₂ (t) is sent to the second electro-optic phase modulator; The light source module is used to generate two laser light sources L ₁ and L ₂ , which have the same frequency and power respectively P ₁ and P ₂ , and their power ratio P ₁ /P ₂ =(V ₂ /V ₁ ) ³ , the light source L ₁ is sent to the first electro-optic phase modulator, and light source L ₂ is sent to the second electro-optic phase modulator; The first electro-optic phase modulator is used to phase-modulate the radio frequency signal S ₁ (t) and the light source L ₁ , and the obtained signal light X ₁ is sent to the first coupler at the receiving end through an optical fiber; The second electro-optical phase modulator is used to phase-modulate the radio frequency signal S ₂ (t) and the light source L ₂ , and the obtained signal light X ₂ is sent to the second coupler at the receiving end through an optical fiber; The local oscillator light source module is used to generate two laser local oscillator light sources L' ₁ and L' ₂ , the local oscillator light source L' ₁ is coherent with the light source L ₁ , the local oscillator light source L' ₂ is coherent with the light source L ₂ , and the local oscillator light source L' ₁ is sent to the first coupler, and the local oscillator light source L' ₂ is sent to the second coupler; The first optical coupler is used to couple the signal light X1 with the local oscillator light source L' ₁ , and send the coupled signal _Y1 to the _first photoelectric balance detector; The second optical coupler is used to couple the signal light X2 with the local oscillator light source L' ₂ , and send the coupled signal _Y2 to the _second photoelectric balance detector; The first photoelectric balance detector is used to convert the signal Y ₁ into an electrical signal T ₁ and send it to the electrical subtractor; The second photoelectric balance detector is used to convert the signal Y ₂ into an electrical signal T ₂ and send it to the electrical subtractor; Electrical subtractor, used to subtract two electrical signals to obtain a recovered radio frequency signal 2. The radio frequency optical transmission system according to claim 1, wherein the radio frequency signal power distribution module comprises an electrical beam splitter and an electrical attenuator, wherein: An electrical beam splitter, used to divide the radio frequency signal S _RF generated by the radio frequency signal source module into two radio frequency signals S ₁ (t) and S ₂ (t); The electric attenuator is used for adjusting the power of the radio frequency signal S ₁ (t) or S ₂ (t). 3. The radio frequency optical transmission system according to claim 1, wherein the light source module comprises a laser and a first beam splitter, wherein: A laser is used to generate a laser light source; The first beam splitter is used to split the light source into two light sources L ₁ and L ₂ , the powers of which are P ₁ and P ₂ respectively, and the power ratio P ₁ /P ₂ =(V ₂ /V ₁ ) ³ . 4. The radio frequency optical transmission system according to claim 3, wherein the light source module further comprises a first polarization controller connected to the first beam splitter for adjusting the polarization state of the light source generated by the laser. 5. The radio frequency optical transmission system according to claim 3, wherein the first optical beam splitter is a polarization beam splitter. 6. The radio frequency optical transmission system according to claim 3, wherein the light source module further comprises a third beam splitter, which splits the light source generated by the laser, one of which is used as a light source, and the other beam passes through The optical fiber is sent to the local oscillator light source module at the receiving end as the local oscillator light source. 7. The radio frequency optical transmission system according to claim 1, wherein the local oscillator light source module comprises a local oscillator laser, a second polarization controller and a second beam splitter, wherein: The local oscillator laser is used to generate a laser local oscillator light source with the same frequency, propagation direction and light source; The second beam splitter is used to divide the local oscillator light source adjusted by the second polarization controller into two beams of local oscillator light source L' ₁ and L'₂; The second polarization controller is connected with the second optical beam splitter and is used to adjust the polarization state of the local oscillator light source generated by the local oscillator laser. 8. The radio frequency optical transmission system according to claim 7, wherein the second optical beam splitter is a polarization beam splitter. 9. The radio frequency optical transmission system according to any one of claims 1 to 8, wherein the optical fiber is a polarization maintaining optical fiber. 10. A high linearity radio frequency optical transmission method, characterized in that, comprising the following steps: S1: The transmitting end divides the radio frequency signal S _RF into two radio frequency signals S ₁ (t) and S ₂ (t), the voltages are V ₁ and V ₂ respectively, and two laser light sources L ₁ and L ₂ are used to pair the radio frequency signals S ₁ (t) and S ₂ (t) perform electro-optic phase modulation, the powers of the two laser sources are P ₁ and P ₂ respectively, and their power ratio P ₁ /P ₂ = (V ₂ /V ₁ ) ³ , the electro-optic After phase modulation, two channels of signal light X ₁ and X ₂ are obtained and transmitted to the receiving end through the optical fiber; S2: The receiving end receives signal light X ₁ and X ₂ , uses two laser local oscillator light sources L′ ₁ and L′ ₂ to couple and coherently signal light X ₁ and X ₂ respectively, and then obtains two signals Y ₁ and Y ₂ conducts photoelectric balance detection respectively to obtain two electrical signals T ₁ and T ₂ , and subtracts the two electrical signals to obtain the recovered radio frequency signal