CN107707309B - Microwave photon quadrature mixing method and device based on cascaded phase and polarization modulators - Google Patents

Abstract

The invention discloses a microwave photon quadrature frequency mixing method based on cascaded phase and polarization modulators. In this method, a cascaded phase modulator and a polarization modulator are used to respectively modulate the radio frequency signal and the intrinsic signal on the optical carrier to generate a cascaded modulated signal with a phase difference of 90° between the two vertically polarized modulated signals; The first-order single-sideband signal of the cascaded modulation signal is divided into two paths; and then two analyzers whose polarization direction and the polarization direction of the polarization modulator main axis are at an angle of 90° and 45° are used The two channels of first-order SSB signals are respectively subjected to polarization detection; finally, the two channels of polarization-detected signals are respectively subjected to photoelectric detection and the DC component in the obtained electrical signals is removed to obtain a pair of intermediate frequency signals with the same amplitude and phase quadrature. The invention also discloses a microwave photon quadrature frequency mixing device based on cascaded phase and polarization modulators. Compared with the prior art, the invention has a higher working bandwidth and a more compact and simple structure.

Description

Microwave photon quadrature mixing method and device based on cascaded phase and polarization modulators

technical field

The invention relates to a frequency mixing method, in particular to a microwave photon orthogonal frequency mixing method.

Background technique

Quadrature mixers are used to convert radio frequency signals into a pair of IF signals with equal amplitudes and quadrature phases. Quadrature mixer is an important part of many electronic systems today. It can realize many functions, such as image frequency interference suppression for radar systems, modulation and demodulation of complex formats for communication systems, and realization of measurement systems. phase detection etc.

Compared with electrical quadrature mixers, microwave photonic quadrature mixers have the advantages of large bandwidth and immunity from electromagnetic interference. Therefore, microwave quadrature mixers based on photonic technology have received more and more attention. Existing microwave-photonic quadrature mixers can be divided into four categories. The first type of scheme is based on an electric 90-degree coupler or an electric phase shifter. With the help of an electric 90-degree coupler or an electric phase shifter, the local oscillator signal is divided into two paths that are orthogonal to each other, and then respectively combined with the radio frequency signal Down-conversion is achieved by means of cascaded modulators, the bandwidth of which is limited by electrical devices. The second type of scheme is based on microwave photonic phase shifters, which use some special modulators, such as dual polarization multiplexing Mach-Zehnder modulators, dual-parallel Mach-Zehnder modulators, dual-drive Mach-Zehnder modulators, etc.; By adjusting the DC bias or polarization direction of these modulators, the purpose of microwave photon phase shifting can be achieved. The phase shifter is divided into two paths, and the phases with a phase difference of 90 degrees can be shifted to obtain two paths of intermediate frequency signals that are orthogonal to each other. , the program adjustment process is more complicated. The third type of scheme is based on an optical 90-degree coupler. This scheme uses an optical 90-degree coupler to achieve a 90-degree phase shift difference on the light, and two intermediate frequency signals with a 90-degree difference can be obtained through photoelectric detection; however, The jitter of the environment has a great influence on the stability of the optical 90-degree coupler. The fourth type of scheme is based on the optical delay line, which uses the fiber delay or dispersion effect to artificially introduce different phases between two channels or two optical carriers with different wavelengths; by precisely controlling the delay or dispersion, A 90-degree phase difference can be introduced like an optical 90-degree coupler to achieve quadrature mixing; however, the bandwidth of this solution to maintain quadrature is limited, because the delay or dispersion will change with the radio frequency or local oscillator frequency.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a microwave photon quadrature mixing method and device based on cascaded phase and polarization modulators, which have a higher working bandwidth and a more compact and simple structure.

The present invention specifically adopts the following technical solutions to solve the above technical problems:

Microwave photon quadrature mixing method based on cascaded phase and polarization modulators, using cascaded phase modulators and polarization modulators to modulate the radio frequency signal and the intrinsic signal on the optical carrier, and generate two vertical polarization state modulations A cascaded modulation signal with a phase difference of 90° between the signals; extracting the first-order SSB signal of the cascaded modulation signal and dividing it into two paths; then using the polarization direction and the polarization direction of the polarization modulator axis The two analyzers with angles of 90° and 45° respectively detect the polarization of the two first-order SSB signals; finally, the two analyzed signals are respectively photoelectrically detected and the DC component in the obtained electrical signal is removed , to obtain a pair of IF signals with the same amplitude and quadrature phase.

Further, the method further includes a step of amplifying the cascaded modulation signal or the first-order single sideband signal.

Preferably, an erbium-doped fiber amplifier is used for signal amplification.

Preferably, an optical passband filter is used to extract the first-order single sideband signal of the cascaded modulation signal.

Preferably, a DC blocker is used to remove the DC component in the electrical signal.

Microwave photonic quadrature mixing device based on cascaded phase and polarization modulators, including:

A cascaded modulation unit, which includes a cascaded phase modulator and a polarization modulator, is used to separately modulate the radio frequency signal and the intrinsic signal on the optical carrier to generate a phase difference between two vertical polarization state modulation signals of 90° The cascaded modulation signal;

A single sideband extraction unit, used to extract the first-order single sideband signal of the cascaded modulation signal and divide it into two paths;

A polarization analysis unit is used to analyze the two first-order single sideband signals respectively by using two analyzers whose included angles between the polarization direction and the polarization direction of the polarization modulator are 90° and 45°;

The photoelectric detection output unit is used to perform photoelectric detection on the two channels of polarized signals and remove the DC component in the obtained electrical signals to obtain a pair of intermediate frequency signals with the same amplitude and orthogonal phases.

Further, the SSB extracting unit further includes an amplifier for amplifying the cascaded modulation signal or the first-order SSB signal.

Preferably, the amplifier is an erbium-doped fiber amplifier.

Preferably, the single sideband extraction unit extracts the first-order single sideband signal of the cascaded modulation signal by using an optical passband filter.

Preferably, the photodetection output unit uses a DC blocker to remove the DC component in the electrical signal.

Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

1) The present invention realizes microwave quadrature mixing in the optical domain, avoiding the restriction of the working bandwidth and electromagnetic interference by electrical devices;

2) The present invention utilizes a polarization modulator and a pair of analyzers to simultaneously realize phase and Mach-Zehnder intensity modulation functions, and the structure is simpler;

3) The present invention realizes the amplification and filtering of in-phase (I) and quadrature (Q) road signals through a single erbium-doped fiber amplifier and optical band-pass filter respectively, which not only simplifies the structure, but also avoids the possibility of using different amplifiers or filters. The phase or amplitude mismatch problem brought about.

Description of drawings

Fig. 1 is a schematic diagram of the structural principle of a specific embodiment of the quadrature mixing device of the present invention;

Figure 2 is a pair of 100-MHz IF signals measured by a real-time oscilloscope;

Fig. 3 is a relationship curve between IF signal power, phase mismatch and radio frequency.

Detailed ways

Aiming at the deficiencies of the existing microwave photon quadrature mixing technology, the basic idea of the present invention is to use the structure of cascaded phase modulators and polarization modulators to realize microwave photon down-conversion, and use polarizers with different polarizing directions to A mutually orthogonal phase relationship between a pair of intermediate frequency signals is realized.

Specifically, the microwave photon quadrature mixing device based on cascaded phase and polarization modulators of the present invention includes:

A cascaded modulation unit, which includes a cascaded phase modulator and a polarization modulator, is used to separately modulate the radio frequency signal and the intrinsic signal on the optical carrier to generate a phase difference between two vertical polarization state modulation signals of 90° The cascaded modulation signal;

A single sideband extraction unit, used to extract the first-order single sideband signal of the cascaded modulation signal and divide it into two paths;

A polarization analysis unit is used to analyze the two first-order single sideband signals respectively by using two analyzers whose included angles between the polarization direction and the polarization direction of the polarization modulator are 90° and 45°;

The photoelectric detection output unit is used to perform photoelectric detection on the two channels of polarized signals and remove the DC component in the obtained electrical signals to obtain a pair of intermediate frequency signals with the same amplitude and orthogonal phases.

It should be emphasized that, in the technical solution of the present invention, the front-rear relationship between the phase modulator and the polarization modulator in the cascaded modulation unit can be adjusted arbitrarily. The RF signal can be input to the RF input terminal of the phase modulator, and the local oscillator signal can be input to the RF input terminal of the polarization controller; or vice versa, the local oscillator signal can be input to the RF input terminal of the phase modulator, and the RF signal can be input to the polarization controller. RF input terminal of the device. As long as the phase difference between the two vertically polarized state modulation signals in the output signal is guaranteed to be 90°, this solution has high flexibility.

To improve signal strength, signal amplification can be performed before or after extracting the first-order SSB signal. In order to simplify the structure and avoid phase or amplitude mismatch problems, it is preferable to use the same erbium-doped fiber amplifier and optical band-pass filter to construct the amplification and single-sideband extraction unit for the two cascaded modulation signals.

In order to facilitate the public's understanding, the technical solution of the present invention will be described in detail below with a preferred embodiment of the quadrature mixing device of the present invention and in conjunction with the accompanying drawings:

Fig. 1 shows the basic structure of the quadrature mixing device in this embodiment. As shown in Figure 1, the device includes: a laser, a phase modulator, a polarization modulator, an erbium-doped fiber amplifier, an optical bandpass filter, a beam splitter, an analyzer 1, an analyzer 2, a photodetector 1, Photodetector 2, DC blocker 1, DC blocker 2. As shown in Figure 1, the output end of the laser is connected to the optical carrier input end of the phase modulator; the phase modulator, polarization modulator, erbium-doped fiber amplifier, optical bandpass filter, and beam splitter are cascaded in sequence; one of the beam splitters The output end is connected to the polarizer 1, the photodetector 1, and the DC blocker 1 in turn to form an upper branch; the other output end of the beam splitter is connected to the polarizer 2, the photodetector 2, and the DC blocker 2 in sequence to form a Lower branch.

Load the RF signal and the local oscillator signal to the RF input terminals of the phase modulator and the polarization modulator respectively, and adjust the DC bias of the polarization modulator to make it work in a quadrature bias state, thereby realizing the microwave photon down-conversion function; The optical signal output by the polarization modulator is amplified by the erbium-doped fiber amplifier and the +1 or -1 order sideband is selected by the optical band-pass filter; then, the optical signal passed through the filter is divided into the same two by the optical beam splitter branch; the two-way signals pass through the polarizer, photodetector and DC block successively, the difference is the angle between the polarizing direction of the two-way polarizer and the polarization direction of the polarization modulator axis; among them, the detector on one branch The included angle between the polarization direction of the polarizer and the polarization direction of the main axis of the polarization modulator is 90 degrees; the included angle between the polarization direction of the analyzer on the other branch and the polarization direction of the main axis of the polarization modulator is 45 degrees; finally, the two signals are respectively After the photoelectric detector completes the photoelectric conversion and removes the DC component through the DC blocker, a pair of intermediate frequency signals with the same amplitude and orthogonal phase can be obtained, that is, the function of quadrature mixing is realized.

Let the continuous light wave output by the laser be

E _c (t)＝E ₀ cos(ω _c t). (1)

Where E ₀ is the amplitude of the light wave, and ω _c is the central angular frequency of the light wave.

In a phase modulator loaded with an RF signal, the phase of the laser is modulated by the RF signal. The output of the phase modulator is

E ₁ (t)＝E ₀ cos[ω _c t+β ₁ cos(ω _R t)]. (2)

Among them, β1 is the phase modulation coefficient _of the phase modulator, and ω _R is the angular frequency of the radio frequency signal.

The phase-modulated signal is subjected to secondary modulation in a polarization modulator loaded with a local oscillator signal. The output of the polarization modulator is expressed as

Where _β2 is the phase modulation coefficient of the polarization modulator, ω _L is the angular frequency of the local oscillator signal, is the phase difference between two vertically polarized modulation signals, and its magnitude can be changed by adjusting the DC bias of the polarization modulator.

In the present invention, The value of is set to 90 degrees.

Then, the signal modulated twice by the polarization modulator is amplified by the erbium-doped fiber amplifier, and the +1 or -1 order sideband is selected by the optical bandpass filter. Taking the -1st order sideband as an example, the output of the optical bandpass filter is

where J _n (·) represents the first kind of Bessel function of order n.

The signal passing through the optical bandpass filter is divided into the same two branches by a beam splitter, each branch has a polarizer. Let the angle between the polarization direction of the analyzer and the polarization direction of the polarization modulator axis be α. Without loss of generality, the output of the polarizer is:

E ₂ (t)∝cosα·E _x1 +sinα·E _y1 . (5)

In the upper branch, the included angle between the polarization direction of the analyzer 1 and the polarization direction of the main axis of the polarization modulator is 90 degrees.

At this time, the polarization modulator realizes the function of phase modulation, and the output of analyzer 1 is:

E ₃ (t)∝J ₀ (β ₁ )J ₁ (β ₂ )sin[(ω _c -ω _L )t]-J ₀ (β ₂ )J ₁ (β ₁ )sin[(ω _c -ω _R )t]. (6)

In the lower branch, the included angle between the polarization direction of the analyzer 2 and the polarization direction of the main axis of the polarization modulator is 45 degrees. At this time, the polarization modulator realizes the function of Mach-Zehnder intensity modulation, and the output of the analyzer 2 is:

E ₄ (t)∝J ₀ (β ₁ )J ₁ (β ₂ )cos[(ω _c -ω _L )t-π/4]+J ₀ (β ₂ )J ₁ (β ₁ )cos[(ω _c -ω _R )t+π/4].(7)

Finally, the photodetector 1 and the photodetector 2 respectively convert the output optical signals of the polarizer 1 and the polarizer 2 into electrical signals, and remove the direct current in the obtained electrical signals through the DC blocker 1 and the DC blocker 2 respectively. component, the obtained upper branch output is:

v _I (t)∝J ₀ (β ₁ )J ₁ (β ₂ )J ₀ (β ₂ )J ₁ (β ₁ )cos[(ω _R -ω _L )t]. (8)

The output of the lower branch is:

v _Q (t)∝J ₀ (β ₁ )J ₁ (β ₂ )J ₀ (β ₂ )J ₁ (β ₁ )sin[(ω _R -ω _L )t]. (9)

Comparing the intermediate frequency signals shown in formula (8) and formula (9), it can be seen that the phase difference between the two is 90 degrees, and the amplitude is the same, indicating that the present invention can realize quadrature mixing.

In order to illustrate the effectiveness of the technical solution of the present invention, the present invention has been tested. The device parameters used in the experiment are as follows:

The output wavelength of the laser (TeraXion, PS-NLL-1550.12-040-000-A1) is 1550.12nm, and the output power is 16dBm; the working bandwidth of the phase modulator (EOSPACE, PM-DV5-40-PFA-PFA-LV) is 40GHz ; The polarization modulator (Versawave, PL-40G-3-1550-V-FCP-FCU) has a working bandwidth of 40 GHz; the selected model of the erbium-doped fiber amplifier is: Amonics, AEDFA-35-B-FA; optical bandpass filter The selected model is: Yenista, XTM-50/S; the working bandwidth of the photodetector (Discovery Semiconductors, DSC50S) is 12GHz, and the responsivity is 0.80A/W; the RF signal source is Agilent, E8257D-option 567; the local oscillator signal The source is Agilent, E8257D-option 540.

First, the frequency of the microwave signal output by the RF signal source is set to 25.1GHz, and the power is set to 6dBm; the frequency of the microwave signal output by the local oscillator signal source is set to 25GHz, and the power is set to 10dBm. Figure 2 shows the 100-MHZ IF signal measured with a real-time oscilloscope (Keysight, DSO-X92504A). It can be seen that the amplitudes of the two are equal, and the phases are orthogonal, indicating that the present invention can effectively realize quadrature mixing.

Then, the frequency of the microwave signal output by the radio frequency signal source is sequentially increased from 5 GHz to 40 GHz in steps of 2.5-GHz. Correspondingly, the frequency of the microwave signal output by the local oscillator signal source is always kept 0.1 GHz lower than the frequency of the radio frequency signal. Fig. 3 shows the relation curves of IF signal power, phase mismatch and radio frequency. It can be seen that in the frequency range from 10 to 40 GHz, the phase mismatch is less than 1 degree, and the maximum amplitude imbalance is 1.02 dB. Therefore, the quadrature mixing device of the present invention has a large bandwidth characteristic.

Claims (10)

1. a kind of orthogonal frequency mixing method of microwave photon based on cascade phase and light polarization modulator, which is characterized in that using successively Radiofrequency signal and intrinsic signals are successively modulated on light carrier by cascade phase-modulator and light polarization modulator respectively, generation Cascading the phase difference in modulated signal between two perpendicular polarisation state modulated signals is 90 °；Extract the one of the cascade modulated signal Rank single sideband singal is simultaneously classified as two-way；Then the angle for being polarized direction Yu light polarization modulator main shaft polarization direction is utilized Analyzing is carried out respectively to two-way single order single sideband singal for 90 ° and 45 ° of two analyzers；Finally to signal after two-way analyzing point Photodetection and the DC component in gained electric signal carry out not be removed, obtain that a pair of of amplitude is identical, intermediate frequency of quadrature in phase letter Number.

2. method as described in claim 1, which is characterized in that further include being carried out to cascade modulated signal or single order single sideband singal The step of signal amplifies.

3. method as claimed in claim 2, which is characterized in that carry out signal amplification using erbium-doped fiber amplifier.

4. method as described in claim 1, which is characterized in that extract the one of the cascade modulated signal using light pass filter Rank single sideband singal.

5. method as described in claim 1, which is characterized in that utilize the DC component in block isolating device removal electric signal.

6. a kind of orthogonal mixer device of microwave photon based on cascade phase and light polarization modulator characterized by comprising

Cascade modulation unit comprising successively cascade phase-modulator and light polarization modulator, for successively by radiofrequency signal with Intrinsic signals are modulated on light carrier respectively, the phase in the cascade modulated signal of generation between two perpendicular polarisation state modulated signals Difference is 90 °；

Single-side belt extraction unit, for extracting the single order single sideband singal of the cascade modulated signal and being classified as two-way；

Analyzing unit, for being the two of 90 ° and 45 ° using the angle for being polarized direction and light polarization modulator main shaft polarization direction A analyzer carries out analyzing to two-way single order single sideband singal respectively；

Photodetection output unit, for carrying out photodetection respectively to signal after two-way analyzing and removing in gained electric signal DC component, obtains that a pair of of amplitude is identical, intermediate-freuqncy signal of quadrature in phase.

7. device as claimed in claim 6, which is characterized in that the single-side belt extraction unit further includes amplifier, for grade Join modulated signal or single order single sideband singal carries out signal amplification.

8. device as claimed in claim 7, which is characterized in that the amplifier is erbium-doped fiber amplifier.

9. device as claimed in claim 6, which is characterized in that the single-side belt extraction unit extracts institute using light pass filter State the single order single sideband singal of cascade modulated signal.

10. device as claimed in claim 6, which is characterized in that the photodetection output unit is utilized to be removed using block isolating device DC component in electric signal.