CN105933072A - Device for simulating optical link linearization - Google Patents

Abstract

The embodiment of the present invention discloses a device for simulating the linearization of an optical link. The device includes a Mach-Zehnder modulator, a bias control module, a first fiber coupler, a second fiber coupler, a low-pass optical receiver, The photodetector and biaser, the Mach-Zehnder modulator performs intensity modulation on the input radio frequency signal; the first fiber coupler divides the input signal into two signals; the bias control module controls the Mach-Zehnder modulation according to the received signal The second optical fiber coupler divides the input signal into two signals; the low-pass optical receiver filters the received signal; the biaser connects the DC bias voltage with the low-pass optical receiver The filtered AC signal is mixed together as a bias signal for the photodetector; the photodetector multiplies the two received signals. By applying the embodiment of the present invention, nonlinear suppression can be realized.

Description

A device for simulating optical link linearization

technical field

The invention relates to the field of microwave signal optical domain transmission, in particular to a device for simulating the linearization of optical links.

Background technique

Analog Optical Link (APL) is becoming an ideal choice for radio frequency (RF) signal transmission and processing due to its advantages of high bandwidth, low insertion loss and insusceptibility to electromagnetic interference, and has been used in radio over fiber communication (RoF, Radio over Fiber ) system, cable TV and many other aspects have been applied. For analog optical links, bandwidth, gain and dynamic range are the main indicators for evaluating system performance. Since the Mach-Zehnder modulator (MZM) widely used in APL itself has a nonlinear transfer function, the MZM will cause the system to generate intermodulation distortion (IMD). method removed, IMD will eventually limit the dynamic range of the link. Therefore, an important research content to improve the performance of analog optical links is how to linearize the link, suppress IMD, and improve the dynamic range of the entire link.

In the prior art, there is a linearization device for performing optical predistortion by simulating a transmitting end of an optical link. The composition of the device mainly includes two MZM intensity modulators, two polarization beam splitters, a photodetector and other peripheral auxiliary microwave devices. The device makes the two MZM intensity modulators produce third-order intermodulation distortion with the same intensity but opposite phase by reasonably controlling the laser output optical power ratio and radio frequency signal power ratio, so as to ensure that the third-order intermodulation distortion can be completely canceled at the receiving end . Optical power distribution is mainly realized by a polarization controller and a polarization beam splitter. The polarization controller can adjust the polarization state of the input light, and map the input light to two orthogonal polarization states of the beam splitter through the polarization beam splitter. This enables precise distribution of optical power. As for the power distribution ratio of the radio frequency signal, the precise control of the two radio frequency signals is realized through an adjustable microwave attenuator. By controlling the input optical power and the precise allocation of radio frequency signals, the amplitudes of the signal components are unequal, while the amplitudes of the nonlinear components are equal, and the phases of the two signals are opposite.

Due to the difficulty in achieving accurate and stable distribution of optical and radio frequency power in this device, the nonlinear distortion cannot be completely suppressed, and generally there will be residual nonlinearity.

Contents of the invention

The embodiment of the invention discloses a device for simulating the linearization of an optical link, which can suppress nonlinearity. The technical solution is as follows:

The device comprises a Mach-Zehnder modulator, a bias control module, a first fiber coupler, a second fiber coupler, a low-pass optical receiver, a photodetector and a bias,

Wherein, the Mach-Zehnder modulator loads the radio frequency signal obtained from the radio frequency generator onto the optical carrier obtained from the laser to become a signal to be modulated, modulates the signal to be modulated into a first modulated signal, and converts the The first modulation signal is respectively sent to the first fiber coupler;

The first optical fiber coupler divides the first modulated signal into a second modulated signal and a third modulated signal, and sends the second modulated signal to the bias control module, and transmits the third modulated signal delivered to the second fiber optic coupler;

The bias control module controls the Mach-Zehnder modulator to be at a preset bias point according to the second modulation signal;

The second optical fiber coupler divides the third modulated signal into a fourth modulated signal and a fifth modulated signal, and sends the fourth modulated signal to the low-pass optical receiver, and transmits the fifth modulated signal to the low-pass optical receiver. a signal is delivered to the photodetector;

The optical receiver filters the received fourth modulated signal to obtain a sixth modulated signal, and sends the sixth modulated signal to the biaser;

The biaser converts the sixth modulation signal into a seventh modulation signal, and superimposes the DC bias voltage and the seventh modulation signal together to form an eighth modulation signal, and converts the eighth modulation signal delivered to the photodetector;

The photodetector multiplies the fifth modulation signal and the eighth modulation signal to obtain a ninth modulation signal, wherein the ninth modulation signal is a linear signal.

Preferably, the arrival time of the fifth modulation signal and the eighth modulation signal at the photodetector is synchronized.

Preferably, the time synchronization is controlled by controlling the time delay of the first section of optical fiber from the second fiber coupler to the optical receiver and the second time delay from the second fiber coupler to the photodetector. Delay implementation of a segment of fiber.

Preferably, the calculation formula of the time delay is:

$\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; L</span>}}{{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; ln</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}$

Among them, L is the length of the fiber, v _g is the group velocity of the fiber, c is the speed of light in vacuum, and _ng is the group refractive index of the fiber.

Preferably, the radio frequency signal is a dual-tone radio frequency signal, which is a first single-tone radio frequency signal and a second single-tone radio frequency signal, and the low-pass optical receiver includes a low-pass filter, and the low-pass filter The cutoff frequency of the device is the frequency difference between the first single-tone radio frequency signal and the second single-tone radio frequency signal.

Preferably, the bias device includes a capacitor and an inductor.

Preferably, the first fiber coupler is a fiber coupler with a split ratio of 99:1.

Preferably, the second fiber coupler is a fiber coupler with a split ratio of 50:50.

It can be seen from the above technical solution that the embodiment of the present invention provides an analog optical link linearization device, which loads the input radio frequency signal onto the optical carrier through a Mach-Zehnder modulator and converts it into a first modulated signal, and The intensity modulation of the first modulation signal is converted into a second modulation signal; the bias control module controls the Mach-Zehnder modulator to be at a preset bias point; the second modulation signal passes through the first fiber coupler and the second fiber coupler , the second optical fiber coupler sends the fifth modulation signal to the photodetector, and the fourth modulation signal to the low-pass optical receiver; the low-pass optical receiver filters the received signal to obtain the sixth modulation signal, and sends the fourth modulation signal to the low-pass optical receiver. The six modulated signals are sent to the bias device; the bias device generates and converts the sixth modulated signal into the eighth modulated signal, and sends the eighth modulated signal to the photodetector; the photodetector compares the fifth modulated signal with the eighth modulated signal multiply to obtain the ninth modulation signal. It can be seen that in the embodiment of the present invention, the fifth modulation signal is multiplied by the eighth modulation signal through the photodetector, and the Mach-Zehnder modulation can be canceled through the processing of the low-pass optical receiver and the reasonable setting of the bias point and DC bias voltage The intermodulation distortion generated by the device, so as to achieve the suppression of nonlinearity.

Of course, implementing any product or method of the present invention does not necessarily need to achieve all the above-mentioned advantages at the same time.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. Those skilled in the art can also obtain other drawings based on these drawings without creative work.

FIG. 1 is a schematic diagram of a device for simulating optical link linearization provided by an embodiment of the present invention;

Fig. 2 is the spectrogram of the signal that carries out nonlinear third-order intermodulation suppression;

Fig. 3 is the dynamic range figure of the signal that carries out nonlinear third-order intermodulation suppression;

Fig. 4 is the spectrogram of the signal that does not carry out nonlinear third-order intermodulation suppression;

FIG. 5 is a dynamic range diagram of a signal without nonlinear third-order intermodulation suppression.

detailed description

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

Referring to FIG. 1 , a device for simulating optical link linearization provided by an embodiment of the present invention includes the device including a Mach-Zehnder modulator 100, a bias control module 130, a first fiber coupler 110, a second Fiber coupler 120 , low pass optical receiver 140 , photodetector 150 and biaser 160 .

Wherein, the Mach-Zehnder modulator 100 loads the radio frequency signal obtained from the radio frequency generator onto the optical carrier obtained from the laser to become a signal to be modulated, modulates the signal to be modulated into a first modulated signal, and converts the second A modulation signal is respectively sent to the first fiber coupler 110;

The first fiber coupler 110 divides the first modulation signal into a second modulation signal and a third modulation signal, and sends the second modulation signal to the bias control module 130, and sends the third modulation signal to the first modulation signal. Two fiber optic couplers 120;

The bias control module 130 controls the Mach-Zehnder modulator 100 to be at a preset bias point according to the second modulation signal;

The second optical fiber coupler 120 divides the third modulated signal into a fourth modulated signal and a fifth modulated signal, and delivers the fourth modulated signal to the low-pass optical receiver 140, and delivers the fifth modulated signal to the photodetector 150;

The low-pass optical receiver 140 filters the received fourth modulated signal to obtain a sixth modulated signal, and sends the sixth modulated signal to the biaser 160;

The biaser 160 converts the sixth modulation signal into a seventh modulation signal, and superimposes the DC bias voltage and the seventh modulation signal into an eighth modulation signal, and sends the eighth modulation signal to the optoelectronic detector 150;

The photodetector 150 multiplies the fifth modulation signal and the eighth modulation signal to obtain a ninth modulation signal, wherein the ninth modulation signal is a linear signal.

It should be noted that the "first" in the "first fiber coupler 110" and the "second" in the "second fiber coupler 120" provided in the embodiment of the present invention are only for distinguishing the two optical fiber couplings in terms of naming. device, and does not have any limiting meaning.

It should be noted that the Mach-Zehnder modulator 100 provided by the embodiment of the present invention is made by utilizing the electro-optical effect, and is a chirp-free Mach-Zehnder modulator. The Mach-Zehnder modulator 100 is at a preset bias point, which causes the crystal refractive index of the Mach-Zehnder modulator 100 to change, thereby changing the light intensity of the signal to be modulated, and realizing optical millimeter-wave spectrum structures with different light intensities, such as bilateral band, single sideband and suppressed optical carrier double sideband, which can ensure the output of all order sidebands, thereby ensuring that the low-pass optical receiver 140 can extract sideband signals near DC, and ensure that the second optical fiber coupling The third-order intermodulation compensation signal and the distorted signal of the radio frequency signal generated by the joint action of the device 120, the low-pass optical receiver 140, the photodetector 150, and the bias device 160 meet the condition of opposite phases, which is why the embodiment of the present invention can realize the analog One of the key conditions for optical link linearization. The bias angle of the Mach-Zehnder modulator 100 is also at a preset point, which can improve the noise, gain and dynamic range of the analog optical link.

It is not difficult to understand that the photodetector 150 provided by the embodiment of the present invention can realize two functions, one is the function of receiving the optical signal, for example, receiving the eighth modulation signal and the fifth modulation signal, and the other function is to receive Multiplies the optical signal, for example, multiplies the fifth modulation signal and the eighth modulation signal.

In the embodiment of the present invention, the arrival time of the fifth modulation signal and the eighth modulation signal at the photodetector 150 are synchronized.

In the embodiment of the present invention, time synchronization is achieved by controlling the time delay of the first section of optical fiber from the second fiber coupler 120 to the low-pass optical receiver 140 and the time delay from the second fiber coupler 120 to the photodetector 150 Delay implementation of the second segment of fiber.

In the embodiment of the present invention, the calculation formula of the time delay is:

$\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; L</span>}}{{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; ln</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}$

Among them, L is the length of the fiber, v _g is the group velocity of the fiber, c is the speed of light in vacuum, and _ng is the group refractive index of the fiber.

The group velocity and group refractive index of the first section of fiber and the second section of fiber are the same, and the lengths are different. The delay of the first section of fiber is greater than that of the second section of fiber, and the delay of the second section of fiber The time between when the receiver 140 receives the fourth modulated signal and when the photodetector 150 receives the eighth modulated signal is equal to the time delay of the first section of optical fiber. When the time between receiving the fourth modulated signal from the low-pass optical receiver 140 and receiving the eighth modulated signal by the photodetector 150 is fixed, it can be calculated how much longer the first section of optical fiber needs to be than the second section of optical fiber, and the fifth modulated signal It is synchronized with the time when the eighth modulated signal arrives at the photodetector 150 .

In the implementation of the present invention, the radio frequency signal is a dual-tone radio frequency signal, which is respectively the first single-tone radio frequency signal and the second single-tone radio frequency signal. The low-pass optical receiver 140 includes a low-pass filter, and the cut-off of the low-pass filter The frequency is the frequency difference between the first single-tone radio frequency signal and the second single-tone radio frequency signal.

In the embodiment of the present invention, the biaser 160 may include a capacitor and an inductor, but of course it is not limited thereto.

It is not difficult to understand that the capacitor can filter out the DC component in the sixth modulation signal, leaving only the AC component. The input DC bias voltage of the biaser 160 is generated by an external power supply and passed through an inductor to ensure that only a DC component exists in the DC bias voltage. The size of the DC bias voltage is obtained according to the performance test of the responsivity and modulation efficiency of the photodetector 150. Assuming that the DC bias voltage is 1.3V, it means that when the DC bias voltage is 1.3V, the photodetector 150 Good responsivity and modulation efficiency performance can be obtained simultaneously.

The biaser 160 superimposes the DC bias voltage and the seventh modulation signal together to form the eighth modulation signal, then the DC component of the eighth modulation signal is the DC bias voltage, assuming that the DC bias voltage is 1.3V, then the eighth modulation signal The DC component of the eight modulated signals is 1.3V.

In the embodiment of the present invention, the first fiber coupler 110 is a fiber coupler with a splitting ratio of 99:1.

The splitting ratio of the first optical fiber coupler 110 can not only provide a feedback signal to the polarization control module 130, which is used to drive the polarization control module 130 to control and control the Mach-Zehnder modulator 100 to be at a preset bias point, but also ensure that the output Nine modulated signals.

In the embodiment of the present invention, the second fiber coupler 120 is a fiber coupler with a splitting ratio of 50:50.

The light splitting ratio of the second fiber coupler 120 ensures that the power of the fourth modulation signal and the fifth modulation signal are the same.

Those skilled in the art can understand that, the photodetector 150 mixes (that is, multiplies) the fifth modulation signal and the eighth modulation signal, and the nonlinear third-order intermodulation term is suppressed, and the photodetector 150 outputs The ninth modulation signal is a linear signal, which realizes the linearization of the analog optical link.

The following describes the embodiments of the present invention in detail through the functions of each device.

Suppose the RF signal obtained from the RF generator is:

x(t)＝A(t)(cosw ₁ t+cosw ₂ t)

Wherein, A(t) is the amplitude of the RF signal, w ₁ is the angular frequency of the first single-tone RF signal, and w ₂ is the angular frequency of the second single-tone RF signal.

The wavelength of the optical carrier is set to 1550nm by the laser, and the Mach-Zehnder modulator 100 loads the radio frequency signal onto the optical carrier. The transfer function of the Mach-Zehnder modulator 100 is nonlinear, and the transfer function is expressed in a general form, and Taylor series Expanded, the transfer function is:

y=a ₀ +a ₁ x+a ₂ x ² +a ₃ x ³

Wherein, y is the output signal of the Mach-Zehnder modulation 100, and a _i is the coefficient of each order nonlinear component determined by the simulated optical link parameters. It is worth mentioning that under the small signal model, the nonlinear components above the third order can be ignored due to their small amplitude.

The Mach-Zehnder modulator 100 outputs the radio frequency signal after intensity modulation, and the output signal is:

$\begin{array}{c}\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; A</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><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 9</span>}}{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; cosw</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; cosw</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\\ <span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; A</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>\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span>\\ <span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}{\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}{\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span>\\ <span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; A</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>\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; w</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>\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; w</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><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; ...</span>}\end{array}$

In the output signal y, the angular frequency of some signal components is far away from w ₁ or w ₂ , and these signal components are easily filtered out. Therefore, the embodiment of the present invention does not consider these signal components, and the output signal is the first modulation signal for:

${\mathrm{<span\; class="notranslate">\; the\; y</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 9</span>}}{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; cosw</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; cosw</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>$

Wherein, y' is the first modulation signal.

The first modulation signal is divided into a second modulation signal and a third modulation signal through the first fiber coupler 110, and the second modulation signal is sent to the bias control module 130, and the third modulation signal is sent to the second optical fiber coupler 120 .

The light splitting ratio of the first fiber coupler 110 is 99:1, then the second modulation signal is:

${\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 100</span>}}<span\; class="notranslate">\; \&lsqb;</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; A</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><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 9</span>}}{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; cosw</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; cosw</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&rsqb;</span>$

Wherein, y2 is the _second modulation signal.

The third modulation signal is:

${\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 99</span>}}{\mathrm{<span\; class="notranslate">\; 100</span>}}<span\; class="notranslate">\; \&lsqb;</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; A</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><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 9</span>}}{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; cosw</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; cosw</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&rsqb;</span>$

Wherein, y3 is the _third modulation signal.

The bias control module 130 controls the Mach-Zehnder modulator 100 to be at a preset bias point according to the second modulation signal y ₂ .

The second optical fiber coupler 120 divides the third modulated signal into a fourth modulated signal and a fifth modulated signal, and delivers the fourth modulated signal to the low-pass optical receiver 140, and delivers the fifth modulated signal to The photodetector 150 .

The fourth modulation signal is:

${\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 99</span>}}{\mathrm{<span\; class="notranslate">\; 200</span>}}<span\; class="notranslate">\; \&lsqb;</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; A</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><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 9</span>}}{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; cosw</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; cosw</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&rsqb;</span>$

Wherein, y4 is the _fourth modulation signal.

The fifth modulation signal is:

${\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 99</span>}}{\mathrm{<span\; class="notranslate">\; 200</span>}}<span\; class="notranslate">\; \&lsqb;</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; A</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><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 9</span>}}{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; cosw</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; cosw</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&rsqb;</span>$

Wherein, _y5 is the fifth modulation signal.

The low-pass optical receiver 140 filters the received fourth modulated signal to obtain a sixth modulated signal, and sends the sixth modulated signal to the biaser 160 .

The sixth modulation signal is:

${\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; 6</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 99</span>}}{\mathrm{<span\; class="notranslate">\; 200</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span>$

Wherein, y6 is the _sixth modulation signal.

The biaser 160 generates a DC bias voltage and converts the sixth modulation signal into a seventh modulation signal, and superimposes the DC bias voltage and the seventh modulation signal to form an eighth modulation signal, and the eighth modulation signal The signal is fed to the photodetector 150 .

The seventh modulation signal is:

${\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; 7</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 99</span>}}{\mathrm{<span\; class="notranslate">\; 200</span>}}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>$

Wherein, y ₇ is the seventh modulation signal.

The eighth modulation signal is:

${\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 99</span>}}{\mathrm{<span\; class="notranslate">\; 200</span>}}<span\; class="notranslate">\; \&lsqb;</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&rsqb;</span>$

in, is the DC bias voltage, and y ₈ is the eighth modulation signal.

The photodetector 150 multiplies the fifth modulation signal and the eighth modulation signal to obtain a ninth modulation signal.

The ninth modulation signal is:

$\begin{array}{c}{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; 9</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; *</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}}<span\; class="notranslate">\; \&ap;</span>\frac{{\mathrm{<span\; class="notranslate">\; 99</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; 200</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; \&lsqb;</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{<span\; class="notranslate">\; \&prime;</span>}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; cosw</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; cosw</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\\ <span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 9</span>}}{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{<span\; class="notranslate">\; \&prime;</span>}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; cosw</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; cosw</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&rsqb;</span>\end{array}$

It should be noted that because the fifth modulation signal is multiplied by the ninth modulation signal, the output intermodulation product has part of the signal component whose angular frequency is far away from w ₁ or w ₂ , and this part of the signal component can be easily filtered out and can be obtained by Neglect, embodiments of the present invention do not consider these signal components.

It can be seen from the above formula that besides the original two-tone radio frequency signal, the ninth modulated signal also includes its third-order intermodulation distortion component, which is introduced by the existence of A ² (t). when When , the third-order intermodulation nonlinear distortion is completely suppressed, and theoretically linearization can be achieved by optimizing the link parameters a _i . This formula can also be written as The ratio of a ₃ to a ₁ is a customized value, which characterizes the nonlinear index of the transmitting end of the link, and is determined by the performance of the Mach-Zehnder modulator 100 . The key to realize the intermodulation compensation condition is to adjust a ₂ and The ratio of makes it a fixed value of a certain size, is a DC bias voltage provided by an external power supply device. In practical applications, when the DC bias voltage is set to 1.3V, both responsivity and modulation efficiency can be considered. Therefore, the only link characteristic parameter that needs to be adjusted next is a ₂ . _The adjustment of the non-zero value a2 is very critical to the realization of the third _- order intermodulation compensation, and the precise control of a2 can be realized by adjusting the input optical power of the low-pass optical receiver 140 or changing the multiple of the amplifier in the low-pass receiver 140 , so that the system satisfies the intermodulation compensation condition, and finally the ninth modulated signal y ₉ is a linear signal.

The embodiments of the present invention will be described in detail below through application examples.

Assume that the frequency of the first single-tone radio frequency signal is 3.0477GHZ, and the frequency of the second single-tone radio frequency signal is 3.04GHZ. The radio frequency signal is loaded on the optical carrier with a wavelength of 1550nm through the Mach-Zehnder modulator 100, and the Mach-Zehnder modulator The bias angle of 100 is 48 degrees, and a spectrum analyzer is connected to the output end of the photodetector 150 to analyze the spectrum of the ninth modulation signal. The obtained spectrum is shown in Figure 2, and the stray-free dynamic unit obtained 3 shown. In order to illustrate that the present invention performs nonlinear third-order intermodulation suppression on intermodulation distortion, the low-pass optical receiver 140 device in the embodiment of the present invention is not used, and the nonlinear third-order intermodulation distortion is not suppressed. In the photodetector 150 The output end of the output port is connected to a spectrum analyzer to analyze the spectrum of the ninth modulation signal, the obtained spectrum is shown in Figure 4, and the obtained dynamic single range is shown in Figure 5. By comparing Fig. 2 and Fig. 4, the nonlinear third-order intermodulation of the embodiment of the present invention is suppressed by 22dB. By comparing Fig. 3 and Fig. 5, the dynamic range of the 1HZ bandwidth of the embodiment of the present invention is increased to 123.4dB.

Applying the example of the present invention, the fifth modulation signal and the eighth modulation signal are multiplied by the photodetector, and the processing of the optical receiver and the reasonable setting of the bias point and the DC bias voltage can cancel the output generated by the Mach-Zehnder modulator. Intermodulation distortion, so as to achieve the suppression of nonlinearity.

It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is a relationship between these entities or operations. There is no such actual relationship or order between them. Furthermore, the term "comprises", "comprises" or any other variation thereof is intended to cover a non-exclusive inclusion such that a process, method, article or apparatus comprising a set of elements includes not only those elements, but also includes elements not expressly listed. other elements of or also include elements inherent in such a process, method, article, or device. Without further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article or apparatus comprising said element.

Each embodiment in this specification is described in a related manner, the same and similar parts of each embodiment can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the device embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and for relevant parts, please refer to part of the description of the method embodiment.

Those of ordinary skill in the art can understand that all or part of the steps in the implementation of the above method can be completed by instructing related hardware through a program, and the program can be stored in a computer-readable storage medium, referred to herein as Storage media, such as: ROM/RAM, disk, CD, etc.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present invention are included in the protection scope of the present invention.

Claims (8)

1. A device for simulating optical link linearization, characterized in that the device comprises a Mach-Zehnder modulator, a bias control module, a first fiber coupler, a second fiber coupler, a low-pass optical receiver, Photodetectors and biasers; Wherein, the Mach-Zehnder modulator loads the radio frequency signal obtained from the radio frequency generator onto the optical carrier obtained from the laser to become a signal to be modulated, modulates the signal to be modulated into a first modulated signal, and converts the The first modulation signal is respectively sent to the first fiber coupler; The first optical fiber coupler divides the first modulated signal into a second modulated signal and a third modulated signal, and sends the second modulated signal to the bias control module, and transmits the third modulated signal delivered to the second fiber optic coupler; The bias control module controls the Mach-Zehnder modulator to be at a preset bias point according to the second modulation signal; The second optical fiber coupler divides the third modulated signal into a fourth modulated signal and a fifth modulated signal, and sends the fourth modulated signal to the low-pass optical receiver, and transmits the fifth modulated signal to the low-pass optical receiver. a signal is delivered to the photodetector; The optical receiver filters the received fourth modulated signal to obtain a sixth modulated signal, and sends the sixth modulated signal to the biaser; The biaser converts the sixth modulation signal into a seventh modulation signal, and superimposes the DC bias voltage and the seventh modulation signal together to form an eighth modulation signal, and converts the eighth modulation signal delivered to the photodetector; The photodetector multiplies the fifth modulation signal and the eighth modulation signal to obtain a ninth modulation signal, wherein the ninth modulation signal is a linear signal. 2 . The device according to claim 1 , wherein the arrival time of the fifth modulation signal and the eighth modulation signal at the photodetector are synchronized. 3 . 3. The device according to claim 2, wherein the time synchronization is performed by controlling the time delay of the first section of optical fiber from the second optical fiber coupler to the optical receiver and coupling from the second optical fiber The time delay of the second section of optical fiber from the detector to the photodetector is realized. 4. The device according to claim 3, wherein the calculation formula of the time delay is: $\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; L</span>}}{{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; ln</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}$ Among them, L is the length of the fiber, v _g is the group velocity of the fiber, c is the speed of light in vacuum, and _ng is the group refractive index of the fiber. 5. The device according to claim 1, wherein the radio frequency signal is a dual-tone radio frequency signal, which is respectively the first monotone radio frequency signal and the second monotone radio frequency signal, and the low-pass optical receiver includes A low-pass filter, where the cutoff frequency of the low-pass filter is the frequency difference between the first single-tone radio frequency signal and the second single-tone radio frequency signal. 6. The device according to claim 1, wherein the bias device comprises a capacitor and an inductor. 7. The device according to claim 1, wherein the first fiber coupler is a fiber coupler with a splitting ratio of 99:1. 8. The device according to claim 1, wherein the second fiber coupler is a fiber coupler with a splitting ratio of 50:50.