CN111623892A - Adaptive optical fiber type Mach-Zehnder interferometer for time-varying random signal measurement - Google Patents

Abstract

The invention discloses an adaptive fiber type Mach-Zehnder interferometer used for time-varying random signal measurement. The laser emitted laser is coupled into the fiber by the fiber collimator, and transmitted to the electro-optical amplitude modulator through the fiber, The signal sent by the first signal generator is input to the electro-optical amplitude modulator, one end of the first fiber beam splitter receives the signal sent by the electro-optical amplitude modulator, and the other end outputs two signals, one of which passes through the first electro-optical phase modulator, the first The phase shifter is converged to the second fiber beam splitter, and the other path is converged to the second fiber beam splitter through the second electro-optic phase modulator and the second phase shifter in turn, and the first electro-optic phase modulator also receives the second signal generator. The output signal of the second fiber beam splitter outputs two signals through the balanced detector, one is fed back to the first phase shifter through the first phase-locked loop, and the other is fed back to the first phase-shifter through the second phase-locked loop. the second electro-optic phase modulator. Compared with other methods, the present invention has higher estimation accuracy for the time-varying random phase.

Description

Adaptive Fiber Mach-Zehnder Interferometer for Time-Varying Random Signal Measurement

technical field

The invention relates to the field of quantum precision measurement, in particular to an adaptive optical fiber Mach-Zehnder interferometer for measuring time-varying random phase signals.

Background technique

Quantum precision measurement is an important research direction in the field of physics and optics today. To date, optical frequency and phase measurement is one of the measurement techniques with the highest measurement accuracy of all physical quantities. In the field of precision measurement, the measurement of many physical quantities is attributed to the measurement of the phase, so the interferometer has become the most common experimental device in precision measurement, and plays a vital role in basic scientific research and practical engineering applications. For example, the measurement of gravitational waves uses the principle of the optical Michelson interferometer to precisely measure the optical phase caused by space-time changes in general relativity. In addition, using the principle of laser interference, physical quantities such as refractive index and length can be precisely measured, and the coherent characteristics of the laser can be used to make the measurement accuracy very high.

At present, the precision of quantum precision measurement is getting higher and higher, and the measurable physical quantities are quite wide. However, there are still two problems in this type of precision measurement: 1. Quantum measurement is mainly based on the free space system, and the rapid development of information technology in the future requires miniaturization and practicality. 2. Quantum precision measurement mainly focuses on the measurement of fixed signals, while the tracking of random signals and real-time signals is less researched, and the latter research is very important in practical application systems.

The patent "An Optical Fiber Adaptive Balance Zero-beat Measurement System for Measuring Time-varying Phase Signals" is a time-varying phase signal tracking device based on an optical fiber system. The estimation accuracy cannot be further improved, the number of injected photons is about ~10 ⁶ , and the minimum phase estimation variance is only 0.03.

SUMMARY OF THE INVENTION

Purpose of the invention: Aiming at the problem of insufficient estimation accuracy in the prior art, the present invention provides an adaptive fiber-optic Mach-Zehnder interferometer for measuring time-varying random signals. The interferometer can measure time-varying random signals with better estimation accuracy. high.

Technical solution: The adaptive fiber Mach-Zehnder interferometer for time-varying random signal measurement according to the present invention includes a laser, a fiber collimator, a first signal generator, an electro-optical amplitude modulator, and a first fiber beam splitter. device, first electro-optic phase modulator, first phase shifter, second electro-optic phase modulator, second phase shifter, second fiber beam splitter, balanced detector, second signal generator, first phase locked loop and the second phase-locked loop, wherein the laser light emitted by the laser is coupled into the fiber by the fiber collimator, and transmitted to the electro-optical amplitude modulator through the fiber, and the signal sent by the first signal generator is input to the electro-optical Amplitude modulator, one end of the first fiber beam splitter receives the signal sent by the electro-optical amplitude modulator, and the other end outputs two signals, one of which passes through the first electro-optic phase modulator and the first phase shifter in turn and converges to the second fiber beam splitter, the other path is converged to the second fiber beam splitter through the second electro-optic phase modulator and the second phase shifter in sequence, and the first electro-optic phase modulator also receives the signal sent by the second signal generator, so The output signal of the second fiber beam splitter outputs two signals through the balanced detector, one of which is fed back to the first phase shifter through the first phase-locked loop, and the other is fed back to the first phase-shifter through the second phase-locked loop. The second electro-optic phase modulator.

Further, the first phase-locked loop includes a proportional-integral-derivative PID controller and a high-voltage amplifier, and the balance detector, the proportional-integral-derivative PID controller, the high-voltage amplifier and the first phase shifter are connected in sequence.

Further, the second phase-locked loop includes a third signal generator, a phase-locked amplifier, a Kalman filter and a proportional controller, the balanced detector, the third signal generator, the phase-locked amplifier, and the Kalman filter. , the proportional controller and the second electro-optical phase modulator are connected in sequence.

Further, the laser is used to output a free-space continuous wave laser with a narrow line width of 1064 nm. The first signal generator is used to generate a 2.5MHz driving signal. The second signal generator is used for generating a time-varying random signal. The third signal generator is used to generate a reference signal. The electro-optical amplitude modulator, the first electro-optical phase modulator, and the second electro-optical phase modulator are all of waveguide type, and both the first phase shifter and the second phase shifter are of optical fiber type.

Further, the balanced photodetector is composed of two photodiodes with the same gain response, and is used for output after subtracting the photocurrent according to the optical power received by each photodiode.

Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: 1. An all-fiber Mach-Zehnder interferometer suitable for random phase estimation is established, and the two arms of the interferometer are respectively equipped with a signal sensing unit and a signal feedback unit. The two arms of the interferometer are loss-matched and a polarization-maintaining fiber device is used. 2. In the linear Gaussian system of laser interferometric phase measurement, a Kalman filter is formed by a first-order low-pass filter and a proportional amplifier, and a random phase estimation loop is established, which gives the optimal phase estimation value under the minimum variance . 3. A proportional-integral-differentiator is used to construct a slow loop with low frequency and low gain, which is used to offset the phase drift of the interferometer caused by environmental disturbances such as vibration and temperature. At the same time, the method locks the phase difference between the two arms of the interferometer to π/2, and obtains the maximum phase measurement sensitivity. 4. Using modulation transfer technology, the input state of the fiber optic interferometer is amplitude modulated, and the detection signal is demodulated to the low frequency band to realize the low frequency phase measurement. 5. The optical balance detection technology is adopted in the signal detection, which can cancel the common mode noise in the optoelectronic system and further improve the phase tracking accuracy. 6. Compared with the prior art, the method can greatly increase the number of injected photons at the input end of the interferometer to 3.7×10 ¹⁰ , thereby improving the absolute accuracy of random phase estimation.

Description of drawings

1 is a schematic structural diagram of an embodiment of the present invention;

Fig. 2 is the time domain diagram of time-varying random phase estimation;

Figure 3 is a schematic diagram of random phase tracking variance as a function of photon number.

Detailed ways

As shown in FIG. 1 , this embodiment provides an adaptive fiber Mach-Zehnder interferometer for measuring time-varying random signals, including a laser 1 , a fiber collimator 2 , an electro-optical amplitude modulator 3 , and a first signal Generator 4, first fiber beam splitter 5, second signal generator 6, first electro-optic phase modulator 7, first phase shifter 8, second electro-optic phase modulator 9, second phase shifter 10, first Two fiber beam splitters 11, balanced detectors 12, a first phase-locked loop and a second phase-locked loop. The electro-optical amplitude modulator 3 , the first electro-optical phase modulator 7 , and the second electro-optical phase modulator 9 are all of the waveguide type, and the first phase shifter 8 and the second phase shifter 10 are both of the fiber type.

Among them, the laser 1 outputs a free-space continuous wave laser with a narrow line width of 1064 nm, and the emitted laser is coupled into the fiber by the fiber collimator 2, and transmitted to the waveguide type electro-optical amplitude modulator 3 through the fiber, and the first signal generator 4 A 2.5MHz driving signal is provided and loaded into the waveguide type electro-optical amplitude modulator 3 to realize amplitude modulation of the optical field, and the modulated laser light is incident into the first fiber beam splitter 5 .

The first fiber beam splitter 5, the first electro-optical phase modulator 7, the first phase shifter 8, the second electro-optical phase modulator 9, the second fiber-type phase shifter 10, and the second fiber-optic beam splitter 11 together form an optical fiber Type Mach-Zehnder interferometer for tracking measurements of time-varying random phases. Wherein, the first fiber beam splitter 5 and the second fiber beam splitter 11 are both 50/50 fiber beam splitters, and the two lasers output by the first fiber beam splitter 5 enter the first electro-optic phase modulator 7 all the way. The other path enters the first electro-optic phase modulator 9 . The second signal generator 6 outputs a time-varying random signal, which is applied to the first electro-optical phase modulator 7 as a modulation signal, and the first electro-optical phase modulator 7 modulates the phase of the laser signal according to the time-varying random signal, thereby converting the time-varying random The phase information of the signal is loaded into the laser signal, and the laser signal carrying the phase of the time-varying random signal is output. The first phase shifter 8 is an executive device of the first phase-locked loop, which adjusts the phase of the laser carrying random phase information according to the signal fed back by the high-voltage amplifier. The device has a large dynamic adjustment range and can compensate for the phase caused by environmental disturbances. drift, and lock the phase difference between the two arms of the interferometer to π/2. The second electro-optical phase modulator 9 receives another signal output from the first fiber splitter 5 and adaptively adjusts the phase of the input laser signal according to the phase estimation signal output by the proportional controller 18 . The second fiber-type phase shifter 10 has the same structure as the first phase shifter 8, and is used for loss matching of the two arms of the interferometer. The light beams of the two arms of the interferometer interfere at the second fiber beam splitter 11 , and then the interference signal is divided into two paths with a split ratio of 50/50, which is detected and received by the balanced photodetector 12 .

The balanced photodetector 12 is used to detect the laser interference signal. It is composed of two photodiodes with the same gain response. The photocurrent is subtracted and outputted according to the optical power received by each photodiode, thereby deducting the photoelectric system. Common mode noise improves detection accuracy.

The first phase-locked loop and the second phase-locked loop are respectively used to control the relative phase difference between the two arms of the Mach-Zehnder interferometer and capture the estimated phase information. The first phase-locked loop includes a proportional-integral-derivative PID controller 13 and a high-voltage amplifier 14. The first phase-locked loop is fed back to the first phase-locked loop via the proportional-integral-derivative PID controller 13 and the high-voltage amplifier 14 according to the DC signal output by the balance detector 12. The fiber-optic phase shifter 8 forms a low-frequency, low-gain feedback control loop, which is used to offset the phase drift of the interferometer caused by environmental disturbances such as vibration and temperature. At the same time, this method locks the phase difference between the two arms of the interferometer. to π/2 for maximum phase measurement sensitivity. The second phase-locked loop includes a third signal generator 15 , a phase-locked amplifier 16 , a Kalman filter 17 and a proportional controller 18 . demodulate to obtain a photocurrent error signal containing phase estimation information, where the third signal generator 15 provides a reference signal to the lock-in amplifier 16, and the Kalman filter 17 and the proportional controller 18 work together on the photocurrent error signal to perform The estimation is filtered, and the signal is fed back to the second electro-optical phase modulator 9 and output to the oscilloscope 19 at the same time, and the optimal phase estimation value with the minimum estimation variance is obtained by adjusting the gain of the proportional controller 18 .

This embodiment is experimentally verified, and the results are shown in Figures 2 and 3 . Fig. 2 is a time domain diagram of time-varying random phase estimation. The time-varying random signal in Fig. 2(a) is a random signal with a bandwidth of 3 kHz generated by the white noise generated by the second signal generator 6 through a low-pass filter. Fig. 2(b) shows the estimation result output by the proportional controller 18 after Kalman filtering. The comparison shows that the phase estimation method of the present invention has an ideal effect. Figure 3 is a graph of the experimental results of the variance of the phase estimation as a function of the number of injected photons. In the experiment, under different photon numbers, measure and calculate the mean square error of tracking, adjust the gain of Kalman filter, and record the optimal tracking variance. In the experiment, the number of photons reaches 3.7×10 ¹⁰ , and the tracking variance reaches 2.5×10 ^-5 . It can be seen that the phase estimation accuracy of the present invention is very high.

Claims (9)

1. an adaptive fiber type Mach-Zehnder interferometer for time-varying random signal measurement, is characterized in that: comprise laser, fiber collimator, first signal generator, electro-optical amplitude modulator, first fiber beam splitter device, first electro-optic phase modulator, first phase shifter, second electro-optic phase modulator, second phase shifter, second fiber beam splitter, balanced detector, second signal generator, first phase locked loop and the second phase-locked loop, wherein the laser light emitted by the laser is coupled into the fiber by the fiber collimator, and transmitted to the electro-optical amplitude modulator through the fiber, and the signal sent by the first signal generator is input to the electro-optical Amplitude modulator, one end of the first fiber beam splitter receives the signal sent by the electro-optical amplitude modulator, and the other end outputs two signals, one of which passes through the first electro-optic phase modulator and the first phase shifter in turn and converges to the second fiber beam splitter, the other path is converged to the second fiber beam splitter through the second electro-optic phase modulator and the second phase shifter in sequence, and the first electro-optic phase modulator also receives the signal sent by the second signal generator, so The output signal of the second fiber beam splitter outputs two signals through the balanced detector, one of which is fed back to the first phase shifter through the first phase-locked loop, and the other is fed back to the first phase-shifter through the second phase-locked loop. The second electro-optic phase modulator. 2. The self-adaptive fiber-optic Mach-Zehnder interferometer for time-varying random signal measurement according to claim 1, wherein the first phase-locked loop comprises a proportional-integral-derivative PID controller and a high-voltage amplifier; The balance detector, the proportional-integral-derivative PID controller, the high-voltage amplifier and the first phase shifter are connected in sequence. 3. The adaptive fiber Mach-Zehnder interferometer for time-varying random signal measurement according to claim 1, wherein the second phase-locked loop comprises a third signal generator, a phase-locked amplifier, a card Mann filter and proportional controller, the balanced detector, the third signal generator, the lock-in amplifier, the Kalman filter, the proportional controller and the second electro-optical phase modulator are connected in sequence. 4 . The adaptive fiber Mach-Zehnder interferometer for measuring time-varying random signals according to claim 1 , wherein the laser is used to output a free-space continuous-wave laser with a narrow linewidth of 1064 nm. 5 . 5 . The adaptive fiber Mach-Zehnder interferometer for measuring time-varying random signals according to claim 1 , wherein the first signal generator is used to generate a 2.5MHz driving signal. 6 . 6 . The adaptive fiber Mach-Zehnder interferometer for measuring time-varying random signals according to claim 1 , wherein the second signal generator is used to generate time-varying random signals. 7 . 7. The self-adaptive fiber-optic Mach-Zehnder interferometer for time-varying random signal measurement according to claim 1, wherein the balanced photodetector is composed of two photodiodes with the same gain response, It is used to subtract the photocurrent according to the optical power received by each photodiode and then output it. 8 . The adaptive fiber Mach-Zehnder interferometer for measuring time-varying random signals according to claim 1 , wherein the third signal generator is used to generate a reference signal. 9 . 9. The adaptive fiber Mach-Zehnder interferometer for time-varying random signal measurement according to claim 1, characterized in that: the electro-optical amplitude modulator, the first electro-optical phase modulator, and the second electro-optical phase modulator Both the first phase shifter and the second phase shifter are of the optical fiber type.

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