Method and system for suppressing polarization-induced phase noise in weak measurement system

Abstract

The application provides a method and system for suppressing polarization-induced phase noise in a weak measurement system, comprising the following steps: step 1: building a quantum weak measurement optical system based on optical fiber with time division polarization switching function, making the light source emit light pulses at a preset frequency, and using a polarization switch to modulate the polarization state of each incident light pulse at the same frequency; step 2: introducing a reference phase to make the system work within a preset sensitivity and dynamic range; step 3: synchronously controlling the optical path switch through an external clock; step 4: receiving the light pulse through a balanced detector, and obtaining the signal-to-noise ratio of the current output signal through calculation; step 5: if the current signal-to-noise ratio is higher than the preset signal-to-noise ratio, the noise suppression effect is achieved, otherwise, the polarization switching rate is increased, and steps 2-5 are repeated. The application can suppress the polarization-induced phase noise caused by the disturbance of a single-mode optical fiber, and realize high-precision measurement of time-varying parameters.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of weak measurement technology, in particular, to a method and system for suppressing polarization-induced phase noise in a weak measurement system, and more particularly, to a method for suppressing polarization-induced phase noise in a weak measurement system based on an optical fiber. BACKGROUND

[0002] Quantum sensing takes advantage of the characteristics of quantum mechanics, breaking through the limitations of classical sensing, and avoiding the Heisenberg uncertainty principle, which can measure physical quantities more sensitively and accurately, and has much better performance than classical sensing in many technical applications. Weak measurement, as a quantum measurement, is different from strong measurement in that it has minimal interference with the system and can only obtain limited quantum state information. However, when the selection and post-selection act together, weak measurement can obtain amazing measurement results far exceeding the eigenvalues. Since weak measurement was discovered by Aharonov et al. in 1988, it has been applied to various fields and has made a lot of research results, of which the most famous is the ultra-high sensitivity measurement of the spin Hall effect. Although the application of weak measurement technology has made great progress, most of the current research is based on the design and implementation of a free-space platform. Due to cost, stability, portability, and other reasons, it is difficult to apply to practical scenarios. With the development and maturity of optical fiber sensing technology, using optical fiber components instead of free-space components in the system is one of the methods to solve this problem.

[0003] Although optical fibers have many advantages, such as resistance to electromagnetic interference, corrosion resistance, and high stability, their disadvantage of being susceptible to birefringence effects cannot be ignored. In optical fiber sensing, the presence of fiber birefringence can cause polarization-induced phase noise, which is particularly evident in long optical fibers. Especially in weak measurement where the polarization state of light is used as the system state, fiber birefringence becomes a key factor affecting measurement accuracy.

[0004] The patent document with publication number CN101917233B discloses a full-optical phase noise suppression method suitable for coherent detection. In view of the current situation that improving the phase noise characteristics of local oscillator coherent reception requires ultra-low noise performance light sources and complex circuit processing technology, the patent document proposes using a full-optical method to suppress phase noise and improve reception performance. The transmitting end of the patent document uses a pair of optical carriers with correlation characteristics, one of which is loaded with information to obtain signal light, and the other is used as coherent light and combined with the signal light before entering the optical fiber for transmission. The receiving end mixes the extracted signal light and coherent light, and after photoelectric conversion, the signal is demodulated. However, the technical solution and the technical problems solved by the patent document are different from those of the present application.

[0005] The patent document with the publication number CN101453274B discloses a method and device for suppressing noise, and belongs to the field of optical communication. The method comprises the following steps: coupling a degraded signal with pump light, and then modulating to obtain pump light carrying information in the degraded signal; performing differential time delay processing on the pump light carrying information in the degraded signal to obtain two-way vector synthesized pump light with relative time delay; and performing polarization filtering processing on the two-way vector synthesized pump light with relative time delay to suppress "0" code noise. However, the patent document is different from the technical scheme of the present application. SUMMARY

[0006] In view of the defects in the prior art, the purpose of the present application is to provide a method and system for suppressing polarization-induced phase noise in a weak measurement system.

[0007] According to the method for suppressing polarization-induced phase noise in a weak measurement system provided by the present application, the following steps are included:

[0008] Step 1: building a quantum weak measurement optical system based on optical fiber with time division polarization switching function, so that the light source emits light pulses at a preset frequency, and the polarization state of each incident light pulse is modulated by a polarization switch at the same frequency, the pre-selection of the weak measurement system is changed, and the time-varying phase parameter is generated by introducing an external signal in the interaction process;

[0009] Step 2: introducing a reference phase to make the system work within a preset sensitivity and dynamic range;

[0010] Step 3: synchronously controlling the optical path switch by an external clock to make different pre-selections correspond to respective post-selections;

[0011] Step 4: receiving the light pulse by a balanced detector, and calculating the signal-to-noise ratio of the current output signal;

[0012] Step 5: if the current signal-to-noise ratio is higher than the preset signal-to-noise ratio, the noise suppression effect is achieved, otherwise, the polarization switching rate is increased, and steps 2-5 are repeated.

[0013] Preferably, the step 1 specifically includes the following steps:

[0014] Step 1.1: modulating the light pulses output by the light source at a preset frequency into four pre-selection states |i1>, |i2>, |i3>, |i4>, and four light pulses are one period;

[0015] Step 1.2: encoding the signal to be measured into a time-varying phase parameter in the interaction process The interaction process is represented as wherein, is a Stokes polarization operator.

[0016] Preferably, in step 2, a reference phase is inserted by a phase retarder after the interaction is expressed as

[0017] Preferably, when the polarization state of the light pulse is switched at a preset frequency, the four-way weak measurement in a period is regarded as a same weak interaction, and the influence of the fiber birefringence is regarded as a same influence.

[0018] Preferably, step 3 specifically comprises the following steps:

[0019] Step 3.1: synchronously control the polarization switcher and the optical path switcher with an external clock, so that the light pulses of different polarization states enter different post-selection optical paths;

[0020] Step 3.2: the post-selection states of the four post-selection optical paths correspond to the four pre-selection states respectively, expressed as |f1>, |f2>, |f3>, |f4>, and the light pulses of different pre-selection states are projected onto the respective post-selection states.

[0021] Preferably, the switching frequency of the optical path switcher is the same as the polarization switching rate.

[0022] Preferably, in step 4, light intensity is used as a detection index for weak measurement, and the light pulses of different polarization states enter the balanced detector in turn, finally forming time-division four-way weak measurement;

[0023] The light intensity of the output light pulse is expressed as: where I0 is the initial light intensity, U(t) represents the unitary operator of the fiber action system;

[0024] The value of the light intensity of the four-way time-division weak measurement output light pulse is detected by the balanced detector, and a correlation operation is performed:

[0025]

[0026]

[0027] where θ(t) is the rotation angle of the fiber principal axis, and ξ(t) is the phase difference introduced by the fiber birefringence;

[0028] The differential light intensity contrast is obtained by using the ratio of the two light intensity differences:

[0029] The output signal can be obtained from the G value without noise terms by calculation.

[0030] Preferably, the faster the polarization switching rate, the better the noise suppression effect.

[0031] Preferably, the step 5 specifically comprises the following steps:

[0032] Step 5.1: preset a required signal-to-noise ratio SNR S If SNR R is greater than or equal to SNR S , the required effect of suppressing polarization-induced phase noise is achieved.

[0033] Step 5.2: if SNR R is less than SNR S , the polarization switching rate is increased, and steps 2-5 are repeated until the required noise suppression effect is achieved.

[0034] The application also provides a system for suppressing polarization-induced phase noise in a weak measurement system, comprising the following modules:

[0035] Module M1: build a quantum weak measurement optical system based on optical fiber with time division polarization switching function, so that the light source emits light pulses at a preset frequency, and the polarization state of each incident light pulse is modulated by a polarization switch at the same frequency, changes the pre-selection of the weak measurement system, and generates a time-varying phase parameter by introducing an external signal during the interaction process;

[0036] Module M2: introduce a reference phase to make the system work at a preset sensitivity and dynamic range;

[0037] Module M3: control the optical path switcher through an external clock to make different pre-choices correspond to their own post-choices;

[0038] Module M4: receive the light pulse through a balanced detector, and calculate the signal-to-noise ratio of the current output signal;

[0039] Module M5: if the current signal-to-noise ratio is higher than the preset signal-to-noise ratio, the noise suppression effect is achieved, otherwise, the polarization switching rate is increased, and the iteration of modules M2-M5 is repeated.

[0040] Compared with the prior art, the application has the following beneficial effects:

[0041] 1. The application can suppress the polarization-induced phase noise caused by the disturbance of a single-mode optical fiber, and realize high-precision measurement of time-varying parameters;

[0042] 2. The application solves the problem of polarization-induced phase noise caused by the birefringence of optical fiber in the prior art;

[0043] 3. The application increases the applicability of weak measurement technology in practical scenarios. BRIEF DESCRIPTION OF DRAWINGS

[0044] Other features, objects, and advantages of the application will become more apparent from the following detailed description of non-limiting embodiments thereof, when read in connection with the following accompanying drawings:

[0045] Figure 1 Flow chart of the method for suppressing polarization-induced phase noise in the weak measurement system of the present application;

[0046] Figure 2 Schematic diagram of the principle of the present application;

[0047] Figure 3 Flow chart of the feedback regulation of the polarization switching rate of the present application.

[0048] The figure shows:

[0049] Light source 1 First post-selection process 7

[0050] Polarization switch 2 Second post-selection process 8

[0051] External clock 3 Third post-selection process 9

[0052] Interaction process 4 Fourth post-selection process 10

[0053] Reference phase 5 Balanced detector 11

[0054] Optical path switch 6 Computer 12 DETAILED DESCRIPTION

[0055] The present application will be described in detail below with specific embodiments. The following examples will help those skilled in the art to further understand the present application, but do not limit the present application in any form. It should be noted that for those skilled in the art, without departing from the concept of the present application, a number of changes and improvements can be made. These are within the scope of the present application.

[0056] Example 1

[0057] As Figures 1 to 3 shown, the present embodiment provides a method for suppressing polarization-induced phase noise in a weak measurement system, comprising the following steps:

[0058] Step 1: Build a quantum weak measurement optical system based on optical fiber with time division polarization switching function, make the light source emit light pulse with preset frequency, modulate the polarization state of each incident light pulse with the same frequency by polarization switch, change the pre-selection of the weak measurement system, and generate time-varying phase parameter by introducing external signal in the interaction process; Specifically, it includes the following steps:

[0059] Step 1.1: The light pulses output by the light source at a preset frequency are modulated into four pre-selection states |i1>, |i2>, |i3>, |i4> respectively, and four light pulses form a cycle;

[0060] Step 1.2: The signal to be measured is encoded into a time-varying phase parameter in the interaction The interaction process is represented as Wherein, is the Stokes polarization operator.

[0061] Step 2: Introduce a reference phase to make the system work in a preset sensitivity and dynamic range; after the interaction, use the phase retarder to insert the reference phase is represented as

[0062] Step 3: Control the optical path switcher by external clock synchronization to make different pre- selections correspond to respective post- selections; specifically including the following steps:

[0063] Step 3.1: Control the polarization switcher and the optical path switcher by external clock synchronization to make light pulses of different polarization states enter different post-selection light paths;

[0064] Step 3.2: The post-selection states of the four post-selection light paths correspond to the four pre-selection states respectively, represented as |f1>, |f2>, |f3>, |f4>, and the light pulses of different pre-selection states are projected onto the respective post-selection states.

[0065] Step 4: Receive the light pulses by the balanced detector, and calculate the signal-to-noise ratio of the current output signal; use light intensity as the detection index for weak measurement, and different polarization state light pulses enter the balanced detector in turn to finally form time-division four-way weak measurement;

[0066] The light intensity of the output light pulse is represented as: Where I0 is the initial light intensity, U(t) represents the unitary operator of the fiber interaction system;

[0067] The balanced detector is used to detect the values of the four time-division weak measurement output light pulses, and the relevant operations are performed:

[0068]

[0069]

[0070] Where θ(t) is the rotation angle of the optical fiber main axis, and ξ(t) is the phase difference introduced by the birefringence of the optical fiber;

[0071] The ratio of the difference between the two light intensities is used to obtain the differential light intensity contrast:

[0072] The output signal can be obtained from the G value without the noise term by calculation.

[0073] Step 5: If the current signal-to-noise ratio is higher than the preset signal-to-noise ratio, the noise suppression effect is achieved, otherwise, the polarization switching rate is increased, and steps 2-5 are repeated; specifically including the following steps:

[0074] Step 5.1: preset a required signal-to-noise ratio SNR S , if SNR R is greater than or equal to SNR S , the required polarization-induced phase noise suppression effect is achieved;

[0075] Step 5.2: if SNR R is less than SNR S , the polarization switching rate is increased, and steps 2-5 are repeated until the required noise suppression effect is achieved.

[0076] When the polarization state of the light pulse is switched at a preset frequency, the four-way weak measurement in a period is regarded as performing the same weak interaction, and the influence of the fiber birefringence is regarded as the same influence. The switching frequency of the optical path switcher is the same as the polarization switching rate. The faster the polarization switching rate, the better the noise suppression effect.

[0077] Example 2

[0078] The embodiment provides a system for suppressing polarization-induced phase noise in a weak measurement system, comprising the following modules:

[0079] Module M1: build a quantum weak measurement optical system based on an optical fiber with a time division polarization switching function, so that the light source emits light pulses at a preset frequency, and a polarization switch modulates the polarization state of each incident light pulse at the same frequency, changes the pre-selection of the weak measurement system, and introduces an external signal to generate a time-varying phase parameter during the interaction;

[0080] Module M2: introduce a reference phase to make the system work at a preset sensitivity and dynamic range;

[0081] Module M3: synchronize the optical path switcher through an external clock to enable different pre-selections to correspond to respective post-selections;

[0082] Module M4: receive the light pulse through a balanced detector, and obtain the signal-to-noise ratio of the current output signal through calculation;

[0083] Module M5: if the current signal-to-noise ratio is higher than the preset signal-to-noise ratio, the noise suppression effect is achieved, otherwise, the polarization switching rate is increased, and the iteration of modules M2-M5 is repeated.

[0084] Example 3

[0085] Those skilled in the art can understand this embodiment as a more specific description of Embodiment 1 and Embodiment 2.

[0086] This embodiment provides a method for suppressing polarization-induced phase noise in a weak measurement system based on optical fiber, including:

[0087] Step 1: Construct a fiber-based quantum weak measurement optical system with time-division polarization switching function. The light source emits light pulses at a certain frequency. The polarization switcher modulates the polarization state of each incident light pulse at the same frequency (the light pulse emission frequency and the polarization switcher modulation frequency are always the same, referred to as the polarization switching rate). This is equivalent to changing the preselection of the weak measurement system and generating time-varying phase parameters by introducing external signals during the weak coupling process.

[0088] Step 2: Introduce a reference phase to make the system operate within a preset sensitivity and dynamic range;

[0089] Step 3: Use an external clock to synchronize and control the optical path switcher so that different pre-selections can correspond to their respective post-selections;

[0090] Step 4: Receive the light pulses using a balanced detector and calculate the signal-to-noise ratio of the current output signal;

[0091] Step 5: If the current signal-to-noise ratio is higher than the preset signal-to-noise ratio, the noise suppression effect is achieved; otherwise, increase the polarization switching rate and repeat steps 2, 3, and 4.

[0092] Step 1 includes:

[0093] Step 1.1: Modulate the light pulses output by the light source at a certain frequency into four pre-selection states |i1>, |i2>, |i3>, and |i4> respectively, with four light pulses constituting one cycle;

[0094] Step 1.2: The signal under test is encoded into a time-varying phase parameter during the interaction. The interaction process is represented as in, This is the Stokes polarization operator.

[0095] Step 2 includes: inserting a reference phase using a phase retarder after the interaction. Represented as

[0096] When the polarization state of an optical pulse switches at a certain frequency, the four weak measurements within one cycle can be regarded as performing the same weak interaction, and the influence of fiber birefringence can also be regarded as the same influence.

[0097] The step 3 comprises:

[0098] Step 3.1: synchronously control the polarization switch and the optical path switch with an external clock, so that the light pulses of different polarization states enter different post-selection optical paths;

[0099] Step 3.2: the post-selection states of the four post-selection optical paths correspond to the four pre-selection states respectively, denoted as |f1>, |f2>, |f3>, |f4>, and the light pulses of different pre-selection states are projected onto the respective post-selection states.

[0100] The switching frequency of the optical path switch is the same as the polarization switching rate.

[0101] The step 4 comprises: using light intensity as a detection index for weak measurement, and the light pulses of different polarization states enter the balanced detector in turn, and finally form time-division four-way weak measurement. The light intensity of the output light pulse is represented as: Where I0 is the initial light intensity, U(t) represents the unitary operator of the fiber system.

[0102] The value of the light intensity of the four-way time-division weak measurement output light pulse is detected by the balanced detector, and a correlation operation is performed:

[0103]

[0104]

[0105] Where θ(t) is the rotation angle of the fiber principal axis, and ξ(t) is the phase difference introduced by the fiber birefringence;

[0106] Then the differential light intensity contrast (abbreviated as G value) is obtained by using the ratio of the two light intensity differences:

[0107] From the expression of G value, it can be seen that the polarization-induced phase noise is completely eliminated.

[0108] In fact, no matter how fast the polarization switching rate is, it can only mean that the interference received in one period is very close, but not exactly the same, so the G value obtained is noise-containing. Through calculation, the signal-to-noise ratio SNR of the output signal can be obtained R .

[0109] The faster the polarization switching rate is, the better the noise suppression effect is.

[0110] The step 5 comprises:

[0111] Step 5.1: preset a required signal-to-noise ratio SNR S , if SNR R is greater than or equal to SNR SIf the SNR is greater than the preset SNR, it indicates that the scheme achieves the required effect of suppressing polarization-induced phase noise.

[0112] Step 5.2: If the SNR is less than the preset SNR, increase the polarization switching rate, and repeat steps 2, 3, 4, and 5 until the required noise suppression effect is achieved. R Step 5.2: If the SNR is less than the preset SNR, increase the polarization switching rate, and repeat steps 2, 3, 4, and 5 until the required noise suppression effect is achieved. S Step 5.2: If the SNR is less than the preset SNR, increase the polarization switching rate, and repeat steps 2, 3, 4, and 5 until the required noise suppression effect is achieved.

[0113] Example 4

[0114] Those skilled in the art can understand this embodiment as a more specific description of Embodiment 1 and Embodiment 2.

[0115] The embodiment provides a system for suppressing polarization-induced phase noise in a fiber-based weak measurement system, comprising:

[0116] Module M1: build a fiber-based quantum weak measurement optical system with time-division polarization switching function, the light source emits light pulses at a certain frequency, and the polarization state of each incident light pulse is modulated by a polarization switch at the same frequency (the light pulse emission frequency and the polarization switch modulation frequency are always the same, referred to as the polarization switching rate), which is equivalent to changing the pre-selection of the weak measurement system, and introducing an external signal to generate a time-varying phase parameter during the interaction;

[0117] Module M2: introduce a reference phase to make the system work within a preset sensitivity and dynamic range;

[0118] Module M3: use an external clock to synchronize the control of the optical path switcher, so that different pre-selections can correspond to their own post-selections;

[0119] Module M4: use a balanced detector to receive the light pulse, and calculate the signal-to-noise ratio of the current output signal;

[0120] Module M5: if the current signal-to-noise ratio is higher than the preset signal-to-noise ratio, the noise suppression effect is achieved, otherwise increase the polarization switching rate and repeat modules M2, M3, M4, and M5.

[0121] The module M1 comprises:

[0122] Module M1.1: modulate the light pulses output by the light source at a certain frequency into four pre-selection states |i1>, |i2>, |i3>, and |i4>, and four light pulses form a period;

[0123] Module M1.2: the signal to be measured is encoded into a time-varying phase parameter during the interaction The interaction process is represented as wherein, is the Stokes polarization operator.

[0124] The module M2 includes: inserting reference phase with phase retarder after interaction is expressed as

[0125] When the polarization state of light pulse is switched at a certain frequency, four-way weak measurement in a cycle can be regarded as the same weak interaction, and the influence of fiber birefringence can also be regarded as the same influence.

[0126] The module M3 includes:

[0127] Module M3.1: synchronously control polarization switch and optical path switch with external clock, so that light pulses of different polarization states enter different post-selection optical paths;

[0128] Module M3.2: the post-selection states of four post-selection optical paths correspond to four pre-selection states respectively, expressed as |f1>, |f2>, |f3>, |f4>, and light pulses of different pre-selection states are projected onto the respective post-selection states.

[0129] The switching frequency of optical path switch is the same as the polarization switching rate.

[0130] The module M4 includes: weak measurement is carried out by using light intensity as detection index, light pulses of different polarization states enter balanced detector in turn, and finally time-division four-way weak measurement is formed. The light intensity of output light pulse is expressed as: Where I0 is the initial light intensity, represents the unitary operator of fiber action system.

[0131] The value of output light pulse light intensity of four-way time-division weak measurement is detected by using balanced detector, and correlation operation is carried out:

[0132]

[0133]

[0134] Where θ(t) is the rotation angle of fiber principal axis, and ξ(t) is the phase difference introduced by fiber birefringence;

[0135] The differential light intensity contrast is obtained by using the ratio of the two light intensity differences: From the expression of G value, it can be seen that the polarization-induced phase noise is completely eliminated.

[0136] In fact, no matter how fast the polarization switching rate is, it can only mean that the interference received in a cycle is very close, but not exactly the same, so the obtained G value contains noise. Through calculation, the signal-to-noise ratio SNR of output signal can be obtained R .

[0137] The faster the polarization switching rate, the better the noise suppression effect.

[0138] The M5 comprises:

[0139] Step M5.1: preset a required signal-to-noise ratio SNR S If SNR R is greater than or equal to SNR S , it indicates that the scheme achieves the required effect of suppressing polarization-induced phase noise.

[0140] Step M5.2: if SNR R is less than SNR S , increase the polarization switching rate, and repeat modules M2, M3, M4, and M5 until the required noise suppression effect is achieved.

[0141] Example 5

[0142] Those skilled in the art can understand this embodiment as a more specific description of embodiments 1-4.

[0143] Since weak measurement was discovered by Aharonov et al. in 1988, it has been applied to various fields and has achieved a large number of research results, among which the most famous is the ultra-high sensitivity measurement of the spin Hall effect. Although the application of weak measurement technology has made great progress, most of the current research is based on the design and implementation of a free-space platform. Due to cost, stability, portability and other reasons, it is difficult to apply to actual scenarios. With the development and maturity of fiber sensing technology, using fiber components instead of free-space components in the system is one of the methods to solve this problem. Although optical fibers have many advantages, such as resistance to electromagnetic interference, corrosion resistance, and high stability, their disadvantage of being susceptible to birefringence effects cannot be ignored. In fiber sensing, the presence of fiber birefringence can cause polarization-induced phase noise, which is particularly pronounced in long fibers. Especially in weak measurement where the polarization state of light is used as the system state, fiber birefringence becomes a key factor affecting measurement accuracy. The purpose of this embodiment is to provide a scheme for suppressing polarization-induced phase noise in a fiber-based weak measurement system.

[0144] As shown in Figure 2 , the scheme for suppressing polarization-induced phase noise in a fiber-based weak measurement system provided by the embodiment comprises: a light source 1, a polarization switch 2, an external clock 3, an interaction process 4, a reference phase 5, an optical path switch 6, a first post-selection process 7, a second post-selection process 8, a third post-selection process 9, a fourth post-selection process 10, a balanced detector 11, and a computer 12.

[0145] The light source 1 emits light pulses at a certain frequency, and each light pulse is modulated by the polarization switch 2 at the same frequency (polarization switching rate), then phase encoded by external signal interaction process 4, and phase adjusted by reference phase 5; Four light pulses are a cycle, and each light pulse is sent to the corresponding post-selection light path by the light path switch 6 according to the polarization switching rate; The first light pulse in a cycle passes through the first post-selection process 7, the second light pulse passes through the second post-selection process 8, the third light pulse passes through the third post-selection process 9, and the fourth light pulse passes through the fourth post-selection process 10; The last light pulse enters the balanced detector 11 for receiving and the computer 11 for data processing in turn; The external clock 3 is connected to the light source 1, the polarization switch 2, the light path switch 6 and the computer 12 for synchronous control. Including the following steps:

[0146] Step A: Build a quantum weak measurement optical system based on optical fiber with time division polarization switching function, the light source 1 emits light pulses at a certain frequency, and each incident light pulse is modulated by the polarization switch 2 at the same frequency (the frequency of light pulse emission and the modulation frequency of polarization switch are always the same, referred to as polarization switching rate), which is equivalent to changing the front of the weak measurement system, and introducing external signal to generate time-varying phase parameter in the interaction process 4;

[0147] Step B: Select the reference phase 5 to make the system work in the preset sensitivity and dynamic range;

[0148] Step C: Use the external clock 3 to synchronize the light path switch 6, so that different pre-selection can correspond to the corresponding post-selection;

[0149] Step D: Use the balanced detector 11 to receive the light pulse, and calculate the signal-to-noise ratio of the current output signal;

[0150] Step E: If the current signal-to-noise ratio is higher than the preset signal-to-noise ratio, the noise suppression effect is achieved, otherwise, increase the polarization switching rate and repeat steps B, C, D and E.

[0151] Among them, the step A includes the following steps:

[0152] Step A1: Pre-selection step: modulate the light pulses output by the light source at a certain frequency into four pre-selection states |i1>, |i2>, |i3>, |i4>, and four light pulses are a cycle;

[0153] Step A2: Interaction step: the signal to be measured is encoded into time-varying phase parameter in the interaction process The interaction process is represented as Wherein, is the Stokes polarization operator;

[0154] Wherein, the step B, after interaction, using phase retarder inserts reference phase Indicated as

[0155] In step A and step B, when the polarization state of light pulse is switched at a certain frequency, four-way weak measurement in a cycle can be regarded as the same weak interaction, and the influence of fiber birefringence can also be regarded as the same influence.

[0156] Wherein, the step C, comprising the following steps:

[0157] Step C1: using external clock to synchronously control polarization switcher and optical path switcher, so that light pulses of different polarization states enter different post-selection optical paths;

[0158] Step C2: post-selection step: the post-selection states of four post-selection optical paths correspond to four pre-selection states respectively, indicated as |f1>, |f2>, |f3>, |f4>, and light pulses of different pre-selection states are projected onto the respective post-selection states.

[0159] In step C, the switching frequency of optical path switcher is the same as the polarization switching rate.

[0160] Wherein, the step D, using light intensity as detection index to perform weak measurement, light pulses of different polarization states enter balanced detector in turn, and finally form time-division four-way weak measurement. The light intensity of output light pulse is indicated as: Wherein I0 is initial light intensity, Indicated as unitary operator of fiber action system.

[0161] Using balanced detector to detect the value of four-way time-division weak measurement output light pulse light intensity, and performing correlation operation:

[0162]

[0163]

[0164] Wherein θ(t) is the rotation angle of fiber main axis, and ξ(t) is the phase difference introduced by fiber birefringence;

[0165] Using the ratio of the two light intensity differences to obtain differential light intensity contrast:

[0166] From the expression of G value, it can be seen that the polarization-induced phase noise is completely eliminated.

[0167] In fact, the faster the polarization switching rate, the closer the interference received in one cycle, but not exactly the same, so the G value obtained is noisy. Through calculation, the signal-to-noise ratio SNR of the output signal can be obtained R .

[0168] In step D, the faster the polarization switching rate, the better the noise suppression effect.

[0169] The flowchart of step E is shown in Figure 3 , and includes the following steps:

[0170] Step E1: threshold setting step: according to the actual demand, a required signal-to-noise ratio threshold SNR S is preset. If SNR R is greater than or equal to SNR S , it means that the scheme has achieved the required effect of suppressing polarization-induced phase noise.

[0171] Step E2: if SNR R is less than SNR S , increase the polarization switching rate, and repeat steps B, C, D, and E until the required noise suppression effect is achieved.

[0172] The time-varying parameter real-time estimation system based on weak measurement technology provided by the embodiment comprises: module M1: building a quantum weak measurement optical system based on optical fiber with time division polarization switching function; the light source emits light pulses at a certain frequency, and the polarization state of each incident light pulse is modulated by a polarization switch at the same frequency (the light pulse emission frequency and the polarization switch modulation frequency are always the same, referred to as the polarization switching rate), which is equivalent to changing the pre-selection of the weak measurement system, and a time-varying phase parameter is generated by introducing an external signal in the interaction process; module M2: introducing a reference phase to make the system work at a preset sensitivity and dynamic range; module M3: using an external clock to synchronously control the optical path switcher, so that different pre- selections can correspond to respective post- selections; module M4: using a balanced detector to receive the light pulse, and calculating the signal-to-noise ratio of the current output signal; module M5: if the current signal-to-noise ratio is higher than the preset signal-to-noise ratio, the noise suppression effect is achieved, otherwise the polarization switching rate is increased and the modules M2, M3, M4 and M5 are repeated.

[0173] The module M1 comprises: module M1.1: modulating the light pulses output by the light source at a certain frequency into four pre-selection states |i1>, |i2>, |i3>, |i4>, and four light pulses form a cycle; module M1.2: the signal to be measured is encoded into a time-varying phase parameter in the interaction The interaction process is represented as , wherein The Stokes polarization operator;

[0174] The module M2 comprises: inserting reference phase by phase retarder after interaction The output light intensity is expressed as

[0175] When the polarization state of light pulse is switched at a certain frequency, four-way weak measurement in a cycle can be regarded as the same weak interaction, and the influence of fiber birefringence can also be regarded as the same influence.

[0176] The module M3 comprises: module M3.1: synchronously controlling polarization switch and optical path switch by external clock, so that light pulses of different polarization states enter different post-selection optical paths; module M3.2: the post-selection states of four post-selection optical paths correspond to four pre-selection states respectively, expressed as |f1>, |f2>, |f3>, |f4>, and light pulses of different pre-selection states are projected onto the respective post-selection states.

[0177] The switching frequency of the optical path switch is the same as the polarization switching rate.

[0178] The module M4 comprises: performing weak measurement by using light intensity as detection index, light pulses of different polarization states enter the balanced detector in turn, and finally form time-division four-way weak measurement. The output light intensity is expressed as Where I0 is the initial light intensity, The unitary operator of the fiber action system is expressed as U(t). The value of the output light intensity of four-way time-division weak measurement is detected by the balanced detector, and correlation operation is performed:

[0179]

[0180]

[0181] Where θ(t) is the rotation angle of the fiber main axis, and ξ(t) is the phase difference introduced by the fiber birefringence;

[0182] The differential light intensity contrast is obtained by using the ratio of the two light intensity differences:

[0183] From the expression of G value, it can be seen that the polarization-induced phase noise is completely eliminated. In fact, no matter how fast the polarization switching rate is, it can only mean that the interference received in a cycle is very close, but not exactly the same, so the obtained G value contains noise. Through calculation, the signal-to-noise ratio SNR of the output signal can be obtained R

[0184] The faster the polarization switching rate is, the better the noise suppression effect is.

[0185] The module M5 comprises: module M5.1: preset a required signal-to-noise ratio SNR S If SNR R is greater than or equal to SNR S , it indicates that the scheme achieves the required effect of suppressing polarization-induced phase noise; module M5.2: if SNR R is less than SNR S , the polarization switching rate is increased, and modules M2, M3, M4 and M5 are repeated until the required noise suppression effect is achieved.

[0186] The application can suppress the polarization-induced phase noise caused by the disturbance of the single-mode fiber, and realize high-precision measurement of time-varying parameters.

[0187] Those skilled in the art know that, in addition to implementing the system and each device, module and unit thereof provided by the application in the form of pure computer readable program code, the system and each device, module and unit thereof provided by the application can also be implemented in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers and embedded microcontrollers by logically programming the method steps to achieve the same functions. Therefore, the system and each device, module and unit thereof provided by the application can be considered as a hardware component, and the devices, modules and units included therein for achieving various functions can also be considered as structures within the hardware component; the devices, modules and units for achieving various functions can also be considered as both software modules for implementing methods and structures within the hardware component.

[0188] The specific embodiments of the application are described above. It should be understood that the application is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essential content of the application. In the case of no conflict, the embodiments of the application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A method for suppressing polarization-induced phase noise in a weak measurement system, characterized in that, The method comprises the following steps: Step 1: building a quantum weak measurement optical system based on optical fiber with time division polarization switching function, making the light source emit light pulses at a preset frequency, modulating the polarization state of each incident light pulse with a polarization switch at the same frequency, changing the pre-selection of the weak measurement system, and generating a time-varying phase parameter by introducing an external signal during the interaction process; Step 2: introducing a reference phase to make the system work within a preset sensitivity and dynamic range; Step 3: synchronously controlling the optical path switcher by an external clock to make different pre-selections correspond to respective post-selections; Step 4: receiving the light pulse by a balanced detector, and calculating the signal-to-noise ratio of the current output signal; Step 5: if the current signal-to-noise ratio is higher than a preset signal-to-noise ratio, the noise suppression effect is achieved, otherwise, the polarization switching rate is increased, and steps 2-5 are repeated.

2. The method of claim 1, wherein the polarization-induced phase noise is suppressed in the weak measurement system. The step 1 specifically comprises the following steps: Step 1.1: modulating the light pulses output by the light source at a preset frequency into four pre-selection states |i1>, |i2>, |i3>, |i4>, and four light pulses form a cycle; Step 1.2: The signal under test is encoded in the interaction as a time-varying phase parameter The interaction process is represented as where, is the Stokes polarization operator.

3. The method of claim 2, wherein the polarization-induced phase noise is suppressed in the weak measurement system. The step 2, after the interaction, inserts a reference phase with a phase retarder is represented as 4. The method of claim 3, wherein the polarization-induced phase noise is suppressed in the weak measurement system. When the polarization state of the light pulse is switched at a preset frequency, the four-way weak measurement in a cycle is regarded as a same weak interaction, and is regarded as a same influence affected by the birefringence of the optical fiber.

5. The method of claim 4, wherein the polarization-induced phase noise is suppressed in the weak measurement system. The step 3 specifically comprises the following steps: Step 3.1: synchronously controlling the polarization switcher and the optical path switcher by an external clock to make the light pulses with different polarization states enter different post-selection light paths; Step 3.2: the post-selection states of the four post-selection light paths correspond to the four pre-selection states respectively, and are represented as |f1>, |f2>, |f3>, |f4>, and the light pulses with different pre-selection states are projected onto respective post-selection states.

6. The method of claim 5, wherein the polarization-induced phase noise is suppressed in the weak measurement system. The switching frequency of the optical path switcher is the same as the polarization switching rate.

7. The method of claim 6, wherein the polarization-induced phase noise is suppressed in the weak measurement system. In the step 4, the light intensity is used as a detection index for weak measurement, the light pulses with different polarization states enter the balanced detector in turn, and finally time-division four-way weak measurement is formed; The light intensity of the output light pulse is represented as: where I0is the initial light intensity, U represents the unitary operator of the fiber action system; The balanced detector is used to detect the value of the light intensity of the four-way time-division weak measurement output light pulse, and relevant operations are performed: Where θ(t) is the rotation angle of the optical fiber main shaft, and ξ(t) is the phase difference introduced by the birefringence of the optical fiber; The differential light intensity contrast is obtained using the ratio of the two light intensities: The output signal can be obtained from the G value without noise terms through calculation.

8. The method of claim 7, wherein the polarization-induced phase noise is suppressed in the weak measurement system. The faster the polarization switching rate is, the better the noise suppression effect is.

9. The method of claim 8, wherein the polarization-induced phase noise is suppressed in the weak measurement system. The step 5 specifically comprises the following steps: Step 5.1: preset a required signal-to-noise ratio SNR S , if SNR R is greater than or equal to SNR S , the effect of suppressing polarization-induced phase noise is achieved. Step 5.2: If SNR R is less than SNR S , then increase the polarization switching rate and repeat steps 2-5 until the desired noise suppression effect is achieved.

10. A system for suppressing polarization-induced phase noise in a weak measurement system, characterized in that, The method comprises the following modules: Module M1: building a quantum weak measurement optical system based on optical fiber with time division polarization switching function, making the light source emit light pulses at a preset frequency, modulating the polarization state of each incident light pulse with a polarization switch at the same frequency, changing the pre-selection of the weak measurement system, and generating a time-varying phase parameter by introducing an external signal during the interaction process; Module M2: introducing a reference phase to make the system work within a preset sensitivity and dynamic range; Module M3: synchronously controlling the optical path switcher by an external clock to make different pre-selections correspond to respective post-selections; Module M4: receiving the light pulse by a balanced detector, and calculating the signal-to-noise ratio of the current output signal; Module M5: if the current signal-to-noise ratio is higher than a preset signal-to-noise ratio, the noise suppression effect is achieved, otherwise, the polarization switching rate is increased, and steps 2-5 are repeated. Module M5: if the current signal-to-noise ratio is higher than the preset signal-to-noise ratio, the noise suppression effect is achieved, otherwise, the polarization switching rate is increased, and the iteration of modules M2-M5 is repeated.

Images