An electrically controlled phase shift device for quantum homodyne detection and a phase shift regulation method thereof

Abstract

The application relates to an electrically controlled phase-shifting device for quantum homodyne detection and a phase shift regulation method thereof, which comprises a first beam splitter, a first interference arm, a second interference arm and a second beam splitter; inputted signal light is split into two beams of signal light by the first beam splitter, one beam of signal light passes through the first interference arm to obtain signal light subjected to phase shift / frequency shift, and the other beam of signal light passes through the second interference arm to obtain signal light not subjected to phase shift / frequency shift; the signal light subjected to phase shift / frequency shift and the signal light not subjected to phase shift / frequency shift are respectively inputted into the second beam splitter and then split into two beams of output light; the frequency difference Delta f s of the signal light generated by the first interference arm is adjusted to regulate the optical phase shift of the electrically controlled phase-shifting device; and the frequency shift amount of the acousto-optic crystal is controlled by the driving frequency, and the fine frequency regulation capability of a digital frequency synthesizer is combined to realize high-precision frequency control of the optical phase shift amount.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of quantum optical homodyne detection, and particularly relates to an electrically controlled phase-shifting device for quantum homodyne detection and a phase shift regulation method thereof. BACKGROUND

[0002] Homodyne detector directly measures the phase-dependent quadrature of the quantum state electric field, which is an important tool for studying optical quantum states. Therefore, homodyne detection can realize continuous variable quantum key distribution schemes with classical and non-classical states; at the same time, this technology also allows phase estimation of quantum states under the Heisenberg limit. However, observing these characteristic information requires maintaining low loss and high phase stability during the input state detection process, and the measured non-classical state effect will be poor under the influence of the environment, such as the change of insertion loss, mode mismatch, phase jitter, etc. This is mainly because in the case of phase mismatch and high insertion loss, the non-classical state will become a classical coherent state with small amplitude, losing the original quantum characteristics. Among these influencing factors, the accuracy and fluctuation of the phase will directly affect the orthogonality of the signal light, thereby significantly affecting the sensitivity of the homodyne detection, because the phase of the intrinsic reference determines which quadrature component is to be measured. Therefore, any instability of the phase will cause fluctuations in the detected signal, which may reduce the sensitivity of the homodyne measurement and limit the ability to accurately extract the quantum information encoded in the phase of the signal light.

[0003] There are many methods to accurately control the phase shift, including optomechanical, thermal-optical or electro-optical, which have been widely used in homodyne detection since the early days of the rapid development of quantum optics. However, these control schemes have inherent defects in frequency control bandwidth and phase shift accuracy. The optomechanical and thermal-optical effect phase shift control is difficult to accurately control the phase shift amount, and the way to adjust the phase shift needs seconds or even longer time. And these two schemes are difficult to cope with the changes of complex environment. And the electro-optical phase adjustment is difficult to maintain the polarization characteristics of the quantum state, which is the basis of quadrature detection. Therefore, it is urgent to find a fast and sensitive method to tune the phase shift to solve the influence of the phase on the quantum homodyne detection technology. SUMMARY

[0004] The present application aims to solve the problems of low control precision and slow adjustment speed of optomechanical and thermal-optical effect phase shift control, and make up for the shortcomings of electro-optical phase adjustment which is difficult to maintain the polarization characteristics of the quantum state. A fast and sensitive method to tune the phase shift is proposed, which takes advantage of the feature that the frequency shift amount of the acousto-optic crystal is controlled by the driving frequency, and combines the fine frequency adjustment ability of the digital frequency synthesizer to realize high-precision frequency control optical phase shift.

[0005] According to a first aspect of the present application, there is provided an electrically controlled phase-shifting device for quantum homodyne detection, comprising: a first beam splitter, a first interference arm, a second interference arm, and a second beam splitter;

[0006] After the input signal light to be measured is split into two beams of signal light by the first beam splitter, one beam of signal light is passed through the first interference arm to obtain signal light with phase / frequency shift, and the other beam of signal light is passed through the second interference arm to obtain signal light without phase / frequency shift; the signal light with phase / frequency shift and the signal light without phase / frequency shift are respectively input into the second beam splitter and then split into two beams of output light;

[0007] The frequency difference Δ f s of the first interference arm to the signal light is adjusted to adjust the optical phase shift of the electrically controlled phase-shifting device.

[0008] Based on the above technical solution, the present application can also be improved as follows.

[0009] Optionally, the first interference arm comprises: a first acousto-optic frequency shifter and a second acousto-optic frequency shifter with fixed spacing; the signal light is passed through the first interference arm to obtain signal light with phase shift.

[0010] The frequency difference Δ f s of the first acousto-optic frequency shifter and the second acousto-optic frequency shifter is adjusted to adjust the optical phase shift of the electrically controlled phase-shifting device.

[0011] The fixed phase shift generated by the first interference arm is Δ n LΔ f s ;

[0012] wherein Δ f s is the difference between the frequency shifts generated by the first acousto-optic frequency shifter and the second acousto-optic frequency shifter, L is the distance between the first acousto-optic frequency shifter and the second acousto-optic frequency shifter, and n is a positive integer.

[0013] Optionally, the second interference arm comprises: a second mirror.

[0014] The other beam of signal light split by the first beam splitter is reflected by the second mirror and then enters the second beam splitter.

[0015] Optionally, the first beam splitter is a first fiber coupler, the first acousto-optic frequency shifter is a first fiber acousto-optic frequency shifter, and the second acousto-optic frequency shifter is a second fiber acousto-optic frequency shifter; the first fiber acousto-optic frequency shifter and the second fiber acousto-optic frequency shifter are connected by a fixed-length delay fiber.

[0016] The second beam splitter is a second fiber coupler that includes a first output terminal and a second output terminal.

[0017] Optionally, the electronically controlled phase-shifting device further includes a frequency drift compensation circuit connected to one of the outputs of the second fiber optic coupler;

[0018] The frequency drift compensation circuit includes: a photodetector, a bandpass filter, a first DDS, a second DDS, a phase detector, a mixer, and a PID controller; the first DDS is used to drive the first fiber optic acousto-optic frequency shifter, and the second DDS is used to drive the second fiber optic acousto-optic frequency shifter.

[0019] The photodetector converts one signal output from the second fiber coupler into an electrical signal, which is then input to the bandpass filter. The bandpass filter separates the signals to obtain the frequency. f s1 -Δ f s +Δ f And input to the phase detector; wherein, f s1 Δ is the frequency shift generated by the first fiber optic acousto-optic frequency shifter. f Frequency drift caused by environmental factors;

[0020] The mixer 406 is based on the output frequency of the first DDS. f s1 and the output frequency of the second DDS f s2 The frequency difference Δ is generated f s And input to the phase detector; wherein, f s2 This refers to the frequency shift generated by the second fiber optic acousto-optic frequency shifter;

[0021] The phase detector is based on the frequency. f s1 -Δ f s +Δ f and the frequency difference Δ f s Generate a frequency signal Δ related to the disturbance. f and the frequency signal Δ f The input is sent to the PID controller;

[0022] The PID controller dynamically adjusts the output frequency of the second DDS based on feedback. f s2 .

[0023] Optionally, the first interference arm comprises: a first double-pass acousto-optic frequency shift optical path and a second double-pass acousto-optic frequency shift optical path; the signal light passes through the first interference arm to obtain frequency-shifted signal light;

[0024] The second beam splitter is a fiber coupler;

[0025] The input signal light to be measured passes through the first double-pass acousto-optic frequency shift optical path to generate 0-order light and 1-order diffraction light, the 1-order diffraction light passes through the first double-pass acousto-optic frequency shift optical path and the second double-pass acousto-optic frequency shift optical path to generate two times of cumulative frequency shift, and then the 0-order light and the 1-order diffraction light pass through the fiber coupler to be divided into two paths and output;

[0026] The frequency difference Δf of the 0-order light and the 1-order diffraction light is changed by adjusting f s The optical phase shift of the electrically controlled phase shift device is adjusted.

[0027] On the basis of the above technical solutions, the application can also be improved as follows.

[0028] Optionally, the first double-pass acousto-optic frequency shift optical path comprises: a circulator, a first double-pass acousto-optic modulator and a fiber mirror;

[0029] After the input signal light to be measured enters through one port of the circulator, the 0-order light and the 1-order diffraction light with frequency shift f are generated after passing through the first double-pass acousto-optic modulator, the 0-order light and the 1-order diffraction light are reflected by the fiber mirror and returned to the first double-pass acousto-optic modulator, the 0-order light and the 1-order diffraction light with frequency shift 2f are obtained, and then the 0-order light and the 1-order diffraction light are output to the second double-pass acousto-optic frequency shift optical path through the other port of the circulator. f s1 f s1

[0030] Optionally, the second double-pass acousto-optic frequency shift optical path comprises: a fiber polarization prism, a second double-pass acousto-optic modulator and a fiber Faraday rotator mirror;

[0031] The 0-order light and the 1-order diffraction light are reflected to the second double-pass acousto-optic modulator through the fiber polarization prism, the 0-order light and the 1-order diffraction light with frequency shift 2f are obtained, and then the 0-order light and the 1-order diffraction light are reflected by the fiber Faraday rotator mirror and returned to the second double-pass acousto-optic modulator, the 0-order light and the 1-order diffraction light with frequency shift 2f+2f are obtained, and then the 0-order light and the 1-order diffraction light are output to the fiber coupler. f s1 f s2 f s1 f s2 The 0-order light and the 1-order diffraction light are coupled and output to the first output signal and the second output signal after being split by the fiber coupler.​​​​​

[0032] Optionally, the electrically controlled phase-shifting device further comprises a frequency drift compensation circuit connected to one of the outputs of the fiber coupler;

[0033] The frequency drift compensation circuit comprises a photodetector, a band-pass filter, a first DDS, a second DDS, a phase detector, a frequency mixer and a PID controller; the first DDS is used to drive the first double-pass acousto-optic modulator, and the second DDS is used to drive the second double-pass acousto-optic modulator;

[0034] The photodetector converts the signal output by the fiber coupler into an electrical signal, which is input into the band-pass filter; the band-pass filter separates the frequency f s1 -Δ f s +Δ f and inputs it into the phase detector; wherein Δ f is the frequency drift caused by the environment;

[0035] The frequency mixer 406 generates the frequency difference Δ f s1 based on the output frequency of the first DDS f s2 and the output frequency of the second DDS f s and inputs it into the phase detector;

[0036] The phase detector generates a frequency signal Δ f s1 -Δ f s +Δ f related to the disturbance based on the frequency f s and the frequency difference Δ f and inputs the frequency signal Δ f into the PID controller;

[0037] The PID controller calculates the feedback dynamic adjustment of the output frequency of the second DDS f s2 .

[0038] According to a third aspect of the present application, a method for regulating an electrically controlled phase-shifting device for quantum homodyne detection is provided, comprising:

[0039] Step 1: generating a linear phase shift / frequency shift of one of the light outputs of the electrically controlled phase-shifting device by adjusting the frequency difference Δ f s .

[0040] Step 2, combine the two light outputs of the electrically controlled phase shifter device and output a quadrature signal.

[0041] The application provides an electrically controlled phase shifter device for quantum homodyne detection and a phase shift control method thereof, and innovatively proposes a method for precisely controlling optical phase shift based on an acousto-optic crystal. The method is characterized in that the frequency shift amount of the acousto-optic crystal is controlled by a driving frequency, and is combined with the fine frequency adjustment capability of a digital frequency synthesizer to realize a new method for high-precision frequency control of optical phase shift. On one hand, the method can suppress the phase change of the homodyne detection optical path caused by environmental disturbance, and on the other hand, the method can reduce the residual phase change caused by the heating effect of active control elements such as a detector and an acousto-optic frequency shifter. Meanwhile, by changing the equivalent length between the two acousto-optic phase shifters, the overall phase shift amount can be controlled, and a controllable phase shift can be realized within several optical periods. The proposed technology opens up a new way for phase control methods. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 FIG. 1 shows a schematic diagram of an embodiment of the structure of an electrically controlled phase shifter device for quantum homodyne detection provided by the application;

[0043] Figure 2 FIG. 2 shows a schematic diagram of the structure of an all-fiber electrically controlled phase shifter device for homodyne detection provided by the application;

[0044] Figure 3 FIG. 3 shows a schematic diagram of the structure of an all-fiber electrically controlled phase shifter device for homodyne detection provided by the application in a quasi-collinear form;

[0045] Figure 4 FIG. 4 shows a schematic diagram of an embodiment of the structure of a frequency drift compensation circuit provided by the application.

[0046] In the drawings, the components represented by the respective reference numerals are listed as follows:

[0047] 101, first beam splitter, 102, first acousto-optic frequency shifter, 103, second acousto-optic frequency shifter, 104, first mirror, 105, second mirror, 106, second beam splitter;

[0048] 201, signal light input end, 202, first fiber coupler, 203, first fiber acousto-optic frequency shifter, 204, delay fiber, 205, second fiber acousto-optic frequency shifter, 206, second fiber coupler, 207, first output end, 208, second output end;

[0049] 301, input signal, 302, circulator, 303, first double-pass acousto-optic modulator, 304, fiber mirror, 305, fiber polarization prism, 306, second double-pass acousto-optic modulator, 307, fiber Faraday rotator mirror, 308, fiber coupler, 309, first output signal, 310, second output signal;

[0050] 401, photodetector, 402, band-pass filter, 403, first DDS, 404, second DDS, 405, phase detector, 406, mixer, 407, PID controller. DETAILED DESCRIPTION

[0051] The principles and features of the present application are described below in conjunction with the accompanying drawings, in which the examples are used to explain the present application and are not intended to limit the scope of the present application.

[0052] Figure 1 An embodiment of the structure of an electrically controlled phase-shifting device for quantum homodyne detection provided by the present application is shown in the accompanying drawings, in conjunction with Figure 1 It can be seen that the embodiment of the electrically controlled phase-shifting device comprises a first beam splitter 101, a first interference arm, a second interference arm, and a second beam splitter 106.

[0053] The input signal light to be measured is split into two beams of signal light after passing through the first beam splitter, one beam of signal light passes through the first interference arm to obtain signal light that has undergone phase shift / frequency shift, and the other beam of signal light passes through the second interference arm to obtain signal light that has not undergone phase shift / frequency shift; the signal light that has undergone phase shift / frequency shift and the signal light that has not undergone phase shift / frequency shift are split into two outputs after inputting into the second beam splitter.

[0054] The frequency difference Δ f s of the first interference arm to the signal light is adjusted to adjust the optical phase shift of the electrically controlled phase-shifting device.

[0055] The electrically controlled phase-shifting device for quantum homodyne detection provided by the present application is based on an asymmetric Mach-Zehnder interferometer, the second interference arm is a non-phase-shifted reference light path, and the first interference arm and the second interference arm form an asymmetric interferometer structure.

[0056] In a possible embodiment, the first interference arm comprises a first acousto-optic frequency shifter and a second acousto-optic frequency shifter with fixed spacing; the signal light passes through the first interference arm to obtain signal light that has undergone phase shift.

[0057] The frequency difference Δ f s of the first acousto-optic frequency shifter and the second acousto-optic frequency shifter is adjusted to adjust the optical phase shift of the electrically controlled phase-shifting device.

[0058] The fixed phase shift generated by the first interference arm is ΔΦ = 2π n LΔ f s .

[0059] wherein Δ f s is the difference between the frequency shift generated by the first acousto-optic frequency shifter and the second acousto-optic frequency shifter, L is the distance between the first acousto-optic frequency shifter and the second acousto-optic frequency shifter, and n is a positive integer.

[0060] In a specific implementation, the first acousto-optic frequency shifter generates a frequency shift of f s1 , and the second acousto-optic frequency shifter generates a frequency shift of f s2 f s1 + Δ f s After passing through the first interference arm, a fixed phase shift controlled by the frequency shift is generated, ΔΦ = 2π n LΔ f s Therefore, for a fixed interference arm length L, by changing the frequency difference between the first acousto-optic frequency shifter 102 and the second acousto-optic frequency shifter 103, the phase of the light passing through the first interference arm can be adjusted.

[0061] The driving module is configured to adjust Δfs to generate a linear phase shift ΔΦ = 2π n LΔ f s The homodyne detection port outputs interference signals with a phase quadrature.

[0062] In a possible embodiment, the second interference arm includes a second mirror.

[0063] The other beam of signal light split by the first beam splitter 101 enters the second beam splitter 106 after being reflected by the second mirror.

[0064] The second interference arm, composed of the second mirror 105 and the second beam splitter 106, does not generate a phase shift. The distance between the first acousto-optic frequency shifter 102 and the second acousto-optic frequency shifter 103 of the first interference arm is a fixed interference arm length. By changing the frequency of the first acousto-optic frequency shifter 102 and the second acousto-optic frequency shifter 103 within the fixed propagation length, the phase of the light passing through the first interference arm can be adjusted, that is, a proportional optical phase shift to the frequency offset can be obtained, instead of the case where the phase shift is proportional to the integral of the frequency offset over time as usual. The signal light passing through different interference arms converges at the second beam splitter 106, and the two beams of signal light passing through the phase shift are evenly divided into two paths, divided into output 1 and output 2, for completing the homodyne detection of the signal. ​

[0065] The application provides an electrically controlled phase-shifting device for quantum homodyne detection, and aims to solve the problems of low control precision and slow adjustment speed of optomechanical and thermal-optical phase shift, and make up for the shortcomings of difficulty in maintaining the polarization characteristics of quantum states by electric-optical phase adjustment, and proposes a fast and sensitive tuning phase shift method, which is based on the feature that the frequency shift amount of the acousto-optic crystal is controlled by the driving frequency, and combines the fine frequency adjustment capability of the digital frequency synthesizer to realize a new method of high-precision frequency control optical phase shift. On one hand, the method can suppress the phase change of the homodyne detection optical path caused by environmental disturbance, and on the other hand, the method can reduce the residual phase change caused by the thermal effect of active control elements such as detectors and acousto-optic frequency shifters. Meanwhile, by changing the equivalent length between the two acousto-optic phase shifters, the overall phase shift amount can be controlled, and the controllable phase shift in several optical periods can be realized. The proposed technology opens up a new way for phase control methods.

[0066] Embodiment 1

[0067] The embodiment 1 provided by the application is an embodiment of the all-fiber electrically controlled phase-shifting device for homodyne detection provided by the application, as shown in the figure. Figure 2 As shown in the figure, the all-fiber electrically controlled phase-shifting device for homodyne detection provided by the application is a structural schematic diagram, which combines Figure 2 It can be known that the all-fiber electrically controlled phase-shifting device for homodyne detection comprises a signal light input end 201, a first fiber coupler 202, a first fiber acousto-optic frequency shifter 203, a delay fiber 204, a second fiber acousto-optic frequency shifter 205, a second fiber coupler 206, a first output end 207 and a second output end 208.

[0068] The signal light to be detected is input through the signal light input end 201, and is divided into two beams through the first fiber coupler 202 and enters two interference arms respectively. The first interference arm comprises the first fiber acousto-optic frequency shifter 203 and the second fiber acousto-optic frequency shifter 205, and the two fiber acousto-optic frequency shifters are connected by the fixed-length delay fiber 204. The output end of the second fiber acousto-optic frequency shifter 205 is connected with the first input end of the second fiber coupler 206. The other output end of the first fiber coupler 202 is connected with the second input end of the second fiber coupler 206 to form the second interference arm. The light signal passes through the first interference arm to produce a phase shift, while the second interference arm does not produce a phase shift, so that the output light for detecting the homodyne signal is generated at the first output end 207 and the second output end 208 of the second fiber coupler.

[0069] Since the 1st-order diffraction light is inevitably coupled back into the optical path due to the influence of the diffraction efficiency of the acousto-optic crystal itself in the double-pass structure, when homodyne detection is finally performed, in addition to the Δ f sIn addition, an extra set of signals will be obtained. f s1 -Δ f s and f s2 -Δ f s This characteristic signal can be filtered out by precisely designed filters, but because it is also sensitive to jitter and stability shifts in the beam propagation path, the change in the characteristic quantity is as follows: f s1 -Δ f s +Δ f and f s2 -Δ f s +Δ f The frequency drift caused by the environment is Δ f Therefore, it can be used to control additional variations caused by the characteristic frequency compensation environment of the DDS. Thus, in one possible embodiment, the electrically controlled phase-shifting device further includes a frequency drift compensation circuit connected to one output of the fiber optic coupler; in another possible embodiment, the electrically controlled phase-shifting device further includes a frequency drift compensation circuit connected to one output of a second fiber optic coupler. Figure 4 The diagram shown is a structural schematic of an embodiment of a frequency drift compensation circuit provided by the present invention. Figure 4 It is known that the frequency drift compensation circuit includes: a photodetector 401, a bandpass filter 402, a first DDS 403, a second DDS 404, a phase detector 405, a mixer 406, and a PID controller 407; the first DDS (Direct Digital Synthesizer) 403 is used to drive the first fiber optic acousto-optic frequency shifter 203, and the second DDS 404 is used to drive the second fiber optic acousto-optic frequency shifter 205.

[0070] The photodetector 401 converts one signal output from the second fiber coupler 206 into an electrical signal, which is then input to the bandpass filter 402. The bandpass filter 402 separates the signals to obtain the frequency. f s1 -Δ f s +Δ f And input to phase detector 405; where, f s1 Δ is the frequency shift generated by the first fiber optic acousto-optic frequency shifter. f Frequency drift caused by environmental factors.

[0071] Mixer 406 is based on the output frequency of the first DDS403 f s1The output frequency of the second DDS404 f s2 Generate frequency difference Δ f s And input to phase detector 405; where, f s2 This is the frequency shift generated by the second fiber optic acousto-optic frequency shifter.

[0072] Phase detector 405 based on frequency f s1 -Δ f s +Δ f and frequency difference Δ f s Generate a frequency signal Δ related to the disturbance. f and the frequency signal Δ f Input to PID controller 407.

[0073] The PID controller 407 dynamically adjusts the output frequency of the second DDS based on operational feedback. f s2 .

[0074] Example 2

[0075] Embodiment 2 of this invention provides an embodiment of a quasi-collinear all-fiber electrically controlled phase-shifting device for zero-difference detection. Embodiment 1 of this invention provides an all-fiber electrically controlled phase-shifting device for zero-difference detection. However, optical path jitter and the accumulation of thermal effects both affect phase stability. The optical path jitter and thermal effect compensation involved are important technical aspects in realizing this technical solution. Embodiment 2 provides a quasi-collinear all-fiber electrically controlled phase-shifting device for zero-difference detection, introducing two transmission paths. The disturbances of the two optical fibers in the environment affect the stability of the system. In order to enhance the stability of the method and device and obtain accurate frequency control phase quantity, this embodiment is designed to address these issues.

[0076] like Figure 3 The diagram shown is a schematic representation of a quasi-collinear, all-fiber, electrically controlled phase-shifting device for zero-difference detection provided by the present invention. Figure 3 It is known that the embodiment of the electronically controlled phase shifter includes: the first interferometer arm includes: a first dual-pass acoustic-optic frequency shifting optical path and a second dual-pass acoustic-optic frequency shifting optical path. The signal light passes through the first interferometer arm to obtain the frequency-shifted signal light.

[0077] The second beam splitter is fiber optic coupler 308.

[0078] The input signal light is input into the first double-pass acousto-optic frequency shift optical path to generate 0-order light and 1st-order diffraction light, and the 1st-order diffraction light is input into the first double-pass acousto-optic frequency shift optical path and the second double-pass acousto-optic frequency shift optical path to generate two times of frequency shift, and then the 0-order light and the 1st-order diffraction light are split into two paths by the fiber coupler.

[0079] The frequency difference Δf between the 0-order light and the 1st-order diffraction light is adjusted by adjusting the driving signal. f s The optical phase of the electrically controlled phase shift device is adjusted.

[0080] In a possible embodiment, the first double-pass acousto-optic frequency shift optical path comprises a circulator 302, a first double-pass acousto-optic modulator 303 and a fiber mirror 304.

[0081] After the input signal 301 is input into one port of the circulator 302, the 0-order light and the 1st-order diffraction light with frequency shift Δf are generated after the input signal 301 passes through the first double-pass acousto-optic modulator 303. f s1 The 0-order light and the 1st-order diffraction light with frequency shift 2Δf are reflected by the fiber mirror 304 and then returned to the first double-pass acousto-optic modulator 303. f s1 The 0-order light and the 1st-order diffraction light with frequency shift 2Δf are output from the other port of the circulator 302 to the second double-pass acousto-optic frequency shift optical path.

[0082] In a possible embodiment, the second double-pass acousto-optic frequency shift optical path comprises a fiber polarization prism 305, a second double-pass acousto-optic modulator 306 and a fiber Faraday rotator mirror 307.

[0083] The 0-order light and the 1st-order diffraction light are reflected by the fiber polarization prism 305 to the second double-pass acousto-optic modulator 306 to generate the 0-order light and the 1st-order diffraction light with frequency shift 2Δf. f s1 The 0-order light and the 1st-order diffraction light with frequency shift 2Δf are reflected by the fiber Faraday rotator mirror 307 and then returned to the second double-pass acousto-optic modulator 306. f s2 The 0-order light and the 1st-order diffraction light with frequency shift 2Δf are output from the other port of the circulator 302 to the second double-pass acousto-optic frequency shift optical path. f s1 The 0-order light and the 1st-order diffraction light with frequency shift 2Δf are output from the other port of the circulator 302 to the second double-pass acousto-optic frequency shift optical path. f s2 The 0-order light and the 1st-order diffraction light with frequency shift 2Δf are output from the other port of the circulator 302 to the second double-pass acousto-optic frequency shift optical path.

[0084] The input signal 301 is input into the first port of the circulator 302, and first passes through the first double-pass acousto-optic modulator 303. f s1and the 0th order does not change. The two beams of light are reflected by the fiber mirror 304 back to the first double-pass AOM, and the 0th order light and the 1st order diffracted light return to the original path without additional phase change, while the 1st order diffracted light is frequency shifted again f s1 , resulting in 2 f s1 frequency shifts, and then injected into the fiber polarization prism 305 after fiber transmission.

[0085] All signals are reflected to the second double-pass AOM 306, where the same physical process as the first double-pass AOM 303 occurs, and the frequency shift is 2 f s2 ; in particular, the fiber Faraday rotator mirror 307 is used instead of the fiber mirror 304, and the rotation angle of the fiber Faraday rotator mirror 307 needs to be precisely adjusted to 90°, so that the second time the polarization passes through the fiber polarization prism 305 after passing through the second double-pass AOM 306, it will be completely transmitted and output; and the frequency-shifted signals pass through this specially designed optical path, and are split by the fiber coupler 308 to be coupled out to the first output signal 309 and the second output signal 310, generating two signal beams for homodyne detection.

[0086] The combination of double-pass AOM and fiber Faraday rotator mirror allows the optical signal to pass through the frequency shifter twice to generate a cumulative frequency shift of 2fs1 and 2fs2; polarization selective transmission is achieved through the fiber polarization prism to suppress back-reflection noise.

[0087] Due to the influence of the diffraction efficiency of the AOM itself, a part of the 1st order diffracted light will inevitably be coupled back into the optical path in the double-pass structure, so in the final homodyne detection, in addition to the required Δ f s , a set of additional signals, f s1 -Δ f s and f s2 -Δ f s will be obtained. f s1 -Δ f s +Δ f and fs2 -Δ f s +Δ f where Δ is the frequency shift caused by the environment f Therefore, the characteristic frequency of the DDS can be used to compensate the additional change caused by the environment, thus, in one possible embodiment, the electrically controlled phase shifting device further comprises a frequency shift compensation circuit connected to one of the outputs of the fiber coupler; in combination Figure 4 It can be seen that the frequency shift compensation circuit comprises a photodetector 401, a band-pass filter 402, a first DDS 403, a second DDS 404, a phase detector 405, a frequency mixer 406 and a PID controller 407; the first DDS 403 is used to drive the first double-pass acousto-optic modulator 303, and the second DDS is used to drive the second double-pass acousto-optic modulator 306.

[0088] The photodetector 401 converts the signal output by the fiber coupler 308 into an electrical signal and inputs the electrical signal into the band-pass filter 402, and the band-pass filter 402 separates the frequency f s1 -Δ f s +Δ f and inputs the frequency difference Δ into the phase detector; where Δ is the frequency shift caused by the environment f

[0089] The frequency mixer 406 generates a frequency difference Δ based on the output frequency f s1 of the first DDS 403 and the output frequency f s2 of the second DDS 404 f s and inputs the frequency difference Δ into the phase detector.

[0090] The phase detector 405 generates a frequency signal Δ related to the disturbance based on the frequency f s1 -Δ f s +Δ f and the frequency difference Δ f s and inputs the frequency signal Δ into the PID controller 407. f f The PID controller 407 calculates a feedback dynamic adjustment of the output frequency s2 of the second DDS to compensate for the frequency signal Δ

[0091] . f f

[0092] In the specific implementation process, f s1 -Δ​​​f s +Δ f The signal contained in the second output signal 310 is first detected by a photodetector 401 carrying the two frequencies and converted into an electrical signal. The electrical signal then passes through a bandpass filter 402 to separate the two signals from other signals. The first DDS 403, used to drive the first fiber optic acousto-optic frequency shifter 203 and the first dual-pass acousto-optic modulator 303, outputs a frequency... f s1 The second DDS404, used to drive the second fiber optic acousto-optic frequency shifter 205 and the second dual-pass acousto-optic modulator 306, outputs a frequency... f s1 A stable Δ is generated in the input mixer 406. f s Two sets of frequencies f s1 -Δ f s +Δ f and Δ f s The input to phase detector 405 will generate a frequency signal Δ related to the disturbance. f , then Δ f The input is fed into the PID controller 407, which performs calculations and provides feedback to control the output frequency of the second DDS 404, compensating for frequency drift caused by disturbances.

[0093] The frequency drift compensation circuit acts as a feedback control unit, detecting the frequency of the disturbance signal at the output terminal. f s1 -Δ f s +Δ f The environmental drift Δ was extracted by the phase detector. f Δ is corrected in real time through PID feedback. f s This ensures that the system phase jitter is <0.01° (RMS).

[0094] Drive frequency difference Δ f s The adjustment range is 1–200MHz, and the phase shift resolution is <0.001°.

[0095] In specific implementations, the electronically controlled phase-shifting device for zero-difference detection provided by this invention can be applied to local oscillator phase locking in continuous variable quantum key distribution (CV-QKD) and Bell state measurement in optical quantum computing.

[0096] Example 4

[0097] The embodiment 4 provided by the application is an embodiment of a homodyne detection phase shift regulation method of an electrically controlled phase shift device for homodyne detection provided by the application, and the regulation method comprises the following steps:

[0098] Step 1, linear phase shift / frequency shift is generated for one of the light outputs of the electrically controlled phase shift device by adjusting the frequency difference Δ f s Step 2, the two light outputs of the electrically controlled phase shift device are combined and an orthogonal signal is output.

[0099] Step 2, the two light outputs of the electrically controlled phase shift device are combined and an orthogonal signal is output.

[0100] When the double-pass structure is adopted, the polarization rotation angle of the Faraday rotator mirror is 90° to ensure signal transmission.

[0101] The electrically controlled phase shift device for quantum homodyne detection and the phase shift regulation method thereof provided by the embodiment of the application innovatively propose a method for accurately controlling optical phase shift based on an acousto-optic crystal, and by virtue of the feature that the frequency shift amount of the acousto-optic crystal is controlled by the driving frequency, the new method of high-precision frequency control optical phase shift is realized by combining the fine frequency adjustment capability of the digital frequency synthesizer. On the one hand, the phase change of the homodyne detection light path caused by environmental disturbance can be suppressed, and on the other hand, the residual phase change caused by the thermal effect of the active control element such as the detector and the acousto-optic frequency shifter can be reduced. At the same time, by changing the equivalent length between the two acousto-optic phase shifters, the overall phase shift amount can also be controlled, and the controllable phase shift in several optical periods can be realized. The proposed technology opens up a new way for phase control methods.

[0102] It should be noted that in the above embodiments, the description of each embodiment has its own emphasis, and the parts not described in detail in a certain embodiment can be referred to the related description of other embodiments.

[0103] Those skilled in the art should understand that the embodiments of the application can be provided as a method, a system, or a computer program product. Therefore, the application can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the application can take the form of a computer program product implemented on one or more computer usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer usable program code.

[0104] The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks. Figure 1 one or more flowcharts and / or blocks Figure 1 means for functionally implementing the steps listed in the flowchart

[0105] These computer program instructions can also be stored in a computer- readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instructions which implement the function specified in the flowchart block or blocks. Figure 1 one or more flowcharts and / or blocks Figure 1 means for functionally implementing the steps listed in the flowchart

[0106] The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks. Figure 1 one or more flowcharts and / or blocks Figure 1 means for functionally implementing the steps listed in the flowchart

[0107] While the preferred embodiments of the application have been described, additional variations and modifications can be employed by those skilled in the art. Therefore, the appended claims are intended to cover all such variations and modifications as falling within the scope of the application.

[0108] It is apparent that a number of modifications and variations of the present application are possible in light of the above teachings. It is therefore intended that the present application covers all such modifications and variations of this application provided they come within the scope of the appended claims and their equivalents.

Claims

1. An electrically controlled phase shift device for quantum homodyne detection, characterized by The electrically controlled phase-shifting device comprises a first beam splitter, a first interference arm, a second interference arm and a second beam splitter; The input signal light is split into two beams by the first beam splitter, one of which is guided through the first interference arm to obtain phase / frequency shifted signal light, and the other is guided through the second interference arm to obtain signal light without phase / frequency shift; the phase / frequency shifted signal light and the signal light without phase / frequency shift are input into the second beam splitter and then split into two beams; by adjusting a frequency difference Δ generated by the first path interference arm pair to the signal light f s adjusting an optical phase shift of the electrically controlled phase shift device; The first interference arm comprises a first fixed-spacing acousto-optic frequency shifter and a second fixed-spacing acousto-optic frequency shifter; the signal light is guided through the first interference arm to obtain phase shifted signal light; by adjusting a frequency difference Δ of the first acousto-optic frequency shifter and the second acousto-optic frequency shifter f s adjusting an optical phase shift of the electronically controlled phase shifting device; The first path interference arm generates a fixed phase shift of ΔΦ = 2π n LΔ f s ; wherein Δ f s is the difference between the frequency shift generated by the first and second acousto-optic frequency shifters, L is the distance between the first and second acousto-optic frequency shifters, and n is a positive integer.

2. The electrically controlled phase shift device of claim 1, wherein The second interference arm comprises a second mirror; The other beam of signal light split by the first beam splitter is reflected by the second mirror and then enters the second beam splitter.

3. The electrically controlled phase shift device of claim 1, wherein, The first beam splitter is a first fiber coupler, the first acousto-optic frequency shifter is a first fiber acousto-optic frequency shifter, and the second acousto-optic frequency shifter is a second fiber acousto-optic frequency shifter; the first fiber acousto-optic frequency shifter and the second fiber acousto-optic frequency shifter are connected by a fixed-length delay fiber; The second beam splitter is a second fiber coupler comprising a first output end and a second output end.

4. The electrically controlled phase shift device of claim 3, wherein, The electrically controlled phase-shifting device further comprises a frequency drift compensation circuit connected to one of the outputs of the second fiber coupler; The frequency drift compensation circuit comprises a photodetector, a bandpass filter, a first DDS, a second DDS, a phase detector, a frequency mixer and a PID controller; the first DDS is used to drive the first fiber acousto-optic frequency shifter, and the second DDS is used to drive the second fiber acousto-optic frequency shifter; The photoelectric detector converts a signal output by the second fiber coupler into an electrical signal input to the band-pass filter, which separates frequencies f s1 -Δ f s +Δ f and input to the phase detector; wherein, f s1 is a frequency shift amount generated by the first fiber acousto-optic frequency shifter, Δ f is a frequency drift caused by the environment; The frequency difference Δ is generated based on the output frequency of the first DDS f s1 and the output frequency of the second DDS f s2 The frequency difference Δ is generated based on the output frequency of the first DDS f s and the output frequency of the second DDS f s2 The frequency difference Δ is generated based on the output frequency of the first DDS The phase detector is based on the frequency f s1 -Δ f s +Δ f and the frequency difference Δ f s generates a disturbance-related frequency signal Δ f and inputs the frequency signal Δ f to the PID controller; The PID controller calculates a feedback dynamic adjustment of the output frequency of the second DDS f s2 .

5. The electrically controlled phase shift device of claim 1, wherein, The first interference arm comprises a first double-pass acousto-optic frequency shifting optical path and a second double-pass acousto-optic frequency shifting optical path; the signal light is guided through the first interference arm to obtain frequency shifted signal light; The second beam splitter is a fiber coupler; The input signal light is guided through the first double-pass acousto-optic frequency shifting optical path to generate 0-order light and 1-order diffracted light; the 1-order diffracted light is subjected to twice cumulative frequency shift by the first double-pass acousto-optic frequency shifting optical path and the second double-pass acousto-optic frequency shifting optical path, and then the 0-order light and the 1-order diffracted light are split into two beams by the fiber coupler; by adjusting the frequency difference Δ between the 0th order light and the 1st order diffracted light f s adjusting the optical phase shift of the electrically controlled phase shifting device.

6. The electrically controlled phase shift device of claim 5, wherein, The first double-pass acousto-optic frequency shifting optical path comprises a circulator, a first double-pass acousto-optic modulator and a fiber mirror; The input signal light enters through one port of the circulator, and after passing through the first double-pass acousto-optic frequency shifter, 0-order light and frequency-shifted 1-order diffracted light are generated f s1 After being reflected by the optical fiber mirror, the 0-order light and the frequency-shifted 1-order diffracted light return to the first double-pass acousto-optic frequency shifter, and 0-order light and frequency-shifted 2-order diffracted light are generated f s1 After passing through the other port of the circulator, the 0-order light and the frequency-shifted 2-order diffracted light are output to the second double-pass acousto-optic frequency shifter.

7. The electrically controlled phase shift device of claim 6, wherein, The second double-pass acousto-optic frequency shifting optical path comprises a fiber polarization prism, a second double-pass acousto-optic modulator and a fiber Faraday rotator mirror; The 0th-order light and the 1st-order diffracted light are reflected by the fiber polarizing prism to the second dual-pass acousto-optic modulator, resulting in 0th-order light and a frequency-shifted 2... f s1 + f s2 The first-order diffracted light, after being reflected by the fiber optic Faraday rotator, returns to the second dual-pass acousto-optic modulator, resulting in the 0th-order light and a frequency shift of 2. f s1 +2 f s2 After the first-order diffracted light is diffracted, it is output to the fiber coupler, and after being split by the fiber coupler, it is coupled and output to the first output signal and the second output signal.

8. The electrically controlled phase shift device of claim 7, wherein, The electrically controlled phase-shifting device further comprises a frequency drift compensation circuit connected to one of the outputs of the fiber coupler; The frequency drift compensation circuit comprises a photodetector, a bandpass filter, a first DDS, a second DDS, a phase detector, a frequency mixer and a PID controller; the first DDS is used to drive the first double-pass acousto-optic modulator, and the second DDS is used to drive the second double-pass acousto-optic modulator; The photoelectric detector converts one of the signals output by the fiber coupler into an electrical signal input to the bandpass filter, which separates the frequencies f s1 -Δ f s +Δ f and inputs them to the phase detector; wherein Δ f is a frequency drift caused by the environment; The mixer is based on the output frequency of the first DDS. f s1 and the output frequency of the second DDS f s2 The frequency difference Δ is generated f s And input to the phase detector; The phase detector is based on the frequency f s1 -Δ f s +Δ f and the frequency difference Δ f s generates a disturbance-related frequency signal Δ f and inputs the frequency signal Δ f to the PID controller; The PID controller calculates a feedback dynamic adjustment of the output frequency of the second DDS f s2 .

9. A method for phase-shift control of homodyne detection of an electrically controlled phase-shifting device for quantum homodyne detection according to any one of claims 1 to 8, characterized in that The control method comprises: Step 1, by adjusting the frequency difference Δ f s causing a linear phase shift / frequency shift of one of the light outputs of the electronically controlled phase shifting device; Step 2, merging the two beams of light output by the electrically controlled phase-shifting device and outputting a quadrature signal.

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