A measuring device and method for the length difference of an interference ring arm

Abstract

The application discloses a kind of measuring device and method of interference ring arm length difference, which is based on the interference ring working principle between the result of the interference of optical pulse in interference ring and the modulation electric signal acting on phase modulator, proposes to control the relative delay between optical pulse and modulation electric signal, scan the waveform of modulation electric signal by two optical pulse components in interference ring respectively, and obtain the arm length difference of interference ring based on scanning result. Therefore, the measurement of the arm length difference of interference ring can be accurately realized with simple measurement structure and control process.

Description

Technical Field

[0001] This invention relates to the field of quantum secure communication, and in particular to a device and method for measuring the length difference of an interferometer ring arm. Background Technology

[0002] Quantum key distribution technology differs from cryptography, which relies on computational complexity. Based on the quantum mechanical principles of no cloning and uncertainty, it is resistant to threats to cryptography, such as quantum computing. Currently, quantum key distribution devices based on the decoy state BB84 protocol typically require high-speed, precise intensity modulation, while quantum key distribution devices using polarization coding schemes typically require high-speed, precise polarization state modulation.

[0003] For example, in Figure 1 In the intensity modulation scheme based on the interference ring shown, the intensity modulation result is related to the phase difference modulated by the phase modulator in the interference ring between two optical pulse components propagating in opposite directions along the interference ring. The precise modulation of this phase difference is directly related to the time difference between the arrival of the two optical pulse components at the phase modulator in the interference ring. Similarly, in Figure 2 In the polarization control scheme based on the interference ring shown, the polarization modulation result is also related to the phase difference modulated by the phase modulator in the interference ring between two optical pulse components that are transmitted in opposite directions along the interference ring. The precise modulation of this phase difference is also directly related to the time difference between the arrival of the two optical pulse components at the phase modulator.

[0004] Therefore, in intensity modulation and polarization control schemes based on interferometric rings, accurately determining the time difference between the arrival of two opposing optical pulse components in the interferometric ring at the phase modulator is crucial. Since the two optical pulse components travel at the same speed, the time difference between their arrival at the phase modulator in the interferometric ring is proportional to the path difference between the two ports of the interferometric ring's optical beam splitter and the inside of the phase modulator. Therefore, controlling this time difference can be converted into controlling the path difference or the fiber length difference, i.e., controlling the arm length difference.

[0005] However, since the phase modulator is encapsulated inside, it is difficult to directly measure the path length inside the phase modulator using conventional length measuring tools, that is, it is difficult to directly and accurately obtain this arm length difference.

[0006] Although existing technologies have proposed many solutions for measuring arm length differences in interferometers, such as Figure 3 and 4As shown, these schemes target fiber Michelson or Mach-Zehnder interferometers, and their measurement process relies on the fact that when a light pulse is input to such an interferometer, two light pulses with a specific time interval are output. These two light pulses interfere with another interferometer to produce three light pulses. However, in the scheme using an interferometer ring, the above measurement conditions do not exist, making it impossible to accurately obtain the arm length difference of the interferometer ring using existing arm length difference measurement methods. Summary of the Invention

[0007] To address the aforementioned problems in existing technologies, this invention discloses a device and method for measuring the arm length difference of an interferometer ring. Based on the interferometer ring's working principle—the interference of optical pulses within the interferometer ring and the modulation signal acting on a phase modulator—the invention proposes controlling the relative delay between the optical pulses and the modulation signal. Two optical pulse components are used to scan the waveform of the modulation signal within the interferometer ring, and the arm length difference of the interferometer ring is obtained based on the scanning results. Thus, the arm length difference of the interferometer ring can be accurately measured using a simple measurement structure and control process.

[0008] Specifically, the first aspect of the present invention relates to a method for measuring the length difference of an interferometer ring arm, which includes an optical pulse generation step, a modulation signal generation step, a scanning step, and a measurement step.

[0009] In the optical pulse generation step, an optical pulse is generated according to a first time sequence and then enters the interference loop;

[0010] In the modulation signal generation step, a modulation electrical signal is generated according to the first time sequence, and the phase modulator in the interference loop modulates the optical pulse based on the modulation electrical signal;

[0011] In the scanning step, at time T(i), the control delay unit introduces a relative delay amount DT(i) between the optical pulse and the modulation electrical signal, and uses a measuring instrument to measure the interference signal formed by the optical pulse in the interference loop under the delay amount DT(i) to obtain the measurement result R(i);

[0012] In the measurement step, the arm length difference L of the interference ring is obtained by using the correspondence between the measurement result R(i) and the delay amount DT(i), i = 1, ..., N, where N is a positive integer.

[0013] Furthermore, the time difference between two adjacent moments T(i) and T(i-1) is set to be greater than the sum of the response time of the delay unit and the response time of the measuring instrument.

[0014] Furthermore, the arm length difference L = T*C / n, T = |T2-T1|, C is the speed of light, n is the refractive index of the transmission medium of the interference ring, and T1 and T2 are the delay amounts introduced by the delay unit when the two light pulse components in the interference ring are aligned with the center position of the modulated electrical signal in time.

[0015] Optionally, in the measurement step, the correspondence is represented by a characteristic curve, where the first coordinate axis of the characteristic curve is the delay amount DT(i), and the second coordinate axis is the measurement result R(i).

[0016] Furthermore, the characteristic curve has a first peak and a second peak, the first peak having the largest second coordinate value P1_max, and the second peak having the largest second coordinate value P2_max;

[0017] In the measurement step, the first coordinate values ​​DT1_U and DT1_D of the points with second coordinate values ​​of K*P1_max on the rising and falling edges of the first peak are determined, as are the first coordinate values ​​DT2_U and DT2_D of the points with second coordinate values ​​of K*P2_max on the rising and falling edges of the second peak. T1 and T2 are calculated according to the formulas T1=(DT1_U+DT1_D) / 2 and T2=(DT2_U+DT2_D) / 2, where K is a preset coefficient.

[0018] Preferably, the coefficient K is set to 0.8.

[0019] Preferably, the optical pulse and the modulated electrical signal are periodic signals of the same origin.

[0020] Alternatively, the delay unit can be implemented using an electrical delay chip or an adjustable fiber optic delay line.

[0021] Optionally, for an interferometric loop used for intensity modulation, the measuring instrument is an optical power measuring instrument; for an interferometric loop used for polarization modulation, the measuring instrument is a polarization analysis instrument.

[0022] A second aspect of the present invention relates to a measuring device for the length difference of an interferometric ring arm, comprising a pulse light source, a driving circuit, a delay unit, a measuring instrument, and a control unit;

[0023] The pulsed light source is configured to generate light pulses according to a first time sequence and output them to the interference ring;

[0024] The driving circuit is configured to generate a modulated electrical signal according to the first time sequence and output it to the phase modulator in the interference loop.

[0025] The delay unit is configured to introduce a relative delay amount DT(i) between the optical pulse and the modulated electrical signal at time T(i);

[0026] The measuring instrument is configured to measure the interference signal formed by the light pulse in the interference loop to obtain the measurement result R(i), which corresponds to the delay amount DT(i).

[0027] The control unit is configured to determine the arm length difference L of the interference ring, i = 1, ..., N, where N is a positive integer, based on the correspondence between the measurement result R(i) and the delay amount DT(i).

[0028] Furthermore, the measuring device of the present invention may also include a clock source configured to provide a time synchronization signal to the pulse light source and the driving circuit.

[0029] Furthermore, the delay unit includes an electrical delay device disposed between the clock source and the pulsed light source and / or between the clock source and the driving circuit; and / or, the delay unit includes an adjustable fiber delay line disposed between the pulsed light source and the interference ring.

[0030] Optionally, the measuring instrument includes an optical power measuring instrument or a polarization analysis instrument.

[0031] Furthermore, the control unit is used to control the delay unit, and is configured such that the time interval between two consecutive changes in the delay amount DT(i) is greater than the sum of the response time of the delay unit and the response time of the measuring instrument.

[0032] Furthermore, the control unit is configured to calculate the arm length difference L according to the formula L=T*C / n, T=|T2-T1|, where C is the speed of light, n is the refractive index of the transmission medium of the interference ring, and T1 and T2 are the delay amounts introduced by the delay unit when the two light pulse components in the interference ring are aligned with the center position of the modulated electrical signal in time.

[0033] Furthermore, the control unit is further configured to:

[0034] Characteristic curves are generated using the delay amount DT(i) and the measurement result R(i) as the first and second coordinate axes, respectively. The maximum second coordinate value P1_max of the first peak and the maximum second coordinate value P2_max of the second peak of the characteristic curves are then obtained.

[0035] Determine the first coordinate values ​​DT1_U and DT1_D of the points with second coordinate values ​​of K*P1_max on the rising and falling edges of the first peak, and the first coordinate values ​​DT2_U and DT2_D of the points with second coordinate values ​​of K*P2_max on the rising and falling edges of the second peak. Calculate T1 and T2 according to the formulas T1=(DT1_U+DT1_D) / 2 and T2=(DT2_U+DT2_D) / 2, where K is a preset coefficient.

[0036] Preferably, the coefficient K = 0.8. Attached Figure Description

[0037] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0038] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 An intensity modulation scheme based on an interference ring in the prior art is illustrated schematically;

[0040] Figure 2 The diagram schematically illustrates a polarization control scheme based on an interference ring in the prior art;

[0041] Figure 3-4 The prior art methods for measuring arm length difference in interferometers are schematically illustrated.

[0042] Figure 5 An embodiment of the measuring device for the length difference of the interferometric ring arm according to the present invention is illustrated schematically;

[0043] Figure 6 The characteristic curves for measuring the length difference of interferometric ring arms according to the present invention are schematically shown.

[0044] Figure 7 Another embodiment of the measuring device for the interferometric ring arm length difference according to the present invention is illustrated schematically;

[0045] Figure 8 Another embodiment of the measuring device for the length difference of the interference ring arm according to the present invention is illustrated schematically. Detailed Implementation

[0046] In the following description, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are provided by way of example in order to fully convey the spirit of the invention to those skilled in the art. Therefore, the invention is not limited to the embodiments disclosed herein.

[0047] Figure 5 An embodiment of the measuring device for the length difference of the interferometric ring arm according to the present invention is shown.

[0048] like Figure 5 As shown, the object of measurement in the measuring device of the present invention is an interference loop, which has a beam splitter, an optical fiber connecting the two ports of the beam splitter to form a loop, and a phase modulator disposed on the optical fiber loop.

[0049] When an optical pulse is input from the input end of the interference loop and reaches the beam splitter, it will be split into two optical pulse components and output from the two ports of the beam splitter into the optical fiber loop, thus transmitting towards each other in the optical fiber loop.

[0050] Typically, two optical pulse components traveling in opposite directions in an optical fiber loop will pass through a phase modulator sequentially. By providing a modulation electrical signal to the phase modulator via its electrical interface, the amount of phase modulation on the passing optical pulse components can be controlled. In other words, the amount of phase modulation on an optical pulse component is related to the voltage of the modulation electrical signal acting on the phase modulator at the corresponding moment.

[0051] The two optical pulse components will eventually return to the beam splitter simultaneously and interfere to form an interference signal. The output interference signal is related to the phase difference generated by the phase modulator modulating the two optical pulse components.

[0052] Based on this object under test, the measuring device of the present invention may include a clock source, a pulse light source, a driving circuit, a delay unit, a measuring instrument, and a control unit.

[0053] A clock source is used to generate a time synchronization signal, for example, to achieve time synchronization between a pulsed light source and a driving circuit.

[0054] The pulsed light source is configured to generate optical pulses according to a first time sequence. This first time sequence can be a periodic sequence or have other preset temporal characteristics. For example, the pulsed light source can be a semiconductor laser or another type of laser.

[0055] exist Figure 5 In this implementation, a pulsed light source is connected to the input end of the interference ring so as to input light pulses into the interference ring, thereby allowing the measurement of the length difference of the interference ring arms.

[0056] In this invention, the driving circuit is used to generate a modulated electrical signal having the same time sequence as the optical pulse. Those skilled in the art will know that this modulated electrical signal has a rising edge portion and a falling edge portion.

[0057] The driving circuit is connected to the phase modulator electrical interface of the interference ring so as to input the modulation electrical signal into the phase modulator in the interference ring, thereby controlling the amount of phase modulation achieved by the phase modulator on the optical pulse.

[0058] The delay unit can be in the form of an electrical delay chip, used to provide an adjustable delay for the time synchronization signal output from the clock source, thereby allowing precise control over the relative delay (or its variation) between the optical pulse and the modulated electrical signal. In this invention, a control unit is configured to control the amount of delay provided by the delay unit.

[0059] exist Figure 5 In this implementation, a delay chip is placed between the clock source and the driving circuit to introduce a certain delay into the modulation signal, thereby precisely controlling the relative delay (or its variation) between the optical pulse and the modulation signal.

[0060] The measuring instrument is connected to the output of the interference ring to measure the interference signal and generate measurement results.

[0061] In this invention, if the interference ring is used to achieve intensity modulation, the intensity (power) information of the interference signal will be related to the phase difference achieved by the phase modulator in the interference ring on the optical pulse component. Therefore, the measuring instrument can be an optical power measuring instrument to obtain the intensity information of the interference signal as the measurement result, thereby characterizing the phase difference information achieved by the phase modulator on the optical pulse component. As an example, the optical power measuring instrument can be a photodiode or an optical power meter.

[0062] If an interferometer loop is used to achieve polarization modulation, the polarization information of the interference signal will be related to the phase difference achieved by the phase modulator in the interferometer loop on the optical pulse component. Therefore, a polarization analyzer can be used to obtain the polarization information of the interference signal as the measurement result, thereby characterizing the phase difference information achieved by the phase modulator on the optical pulse component. As an example, the polarization analyzer can be a polarization analyzer.

[0063] To better understand the measurement principle of this invention, the following will be combined with... Figure 5 The measuring device according to the present invention will be described in detail.

[0064] The method for measuring the length difference of the interference ring arm according to the present invention may include an optical pulse generation step, a modulation signal generation step, a scanning step, and a measurement step.

[0065] In the optical pulse generation step, the pulse source generates an optical pulse based on the time synchronization signal according to the first time sequence. As mentioned above, the optical pulse will enter the interference ring through the input end of the interference ring and be divided into two optical pulse components that are transmitted towards each other in the interference ring.

[0066] For example, a pulsed light source can generate light pulses with a period of 100 MHz and a full width at half maximum (FWHM) of no more than 100 ps.

[0067] In the modulation signal generation step, the driving circuit also generates a modulation electrical signal based on the time synchronization signal according to the first time sequence, which will act on the phase modulator of the interference ring through the phase modulator electrical interface of the interference ring.

[0068] For example, the modulated electrical signal generated by the driving circuit can be an electrical signal with a period of 100MHz that is from the same source as the optical pulse, with a rising edge of no more than 1ns and a falling edge of no more than 1ns, and its peak-to-peak voltage Vpp is 5V.

[0069] In the scanning step, the delay unit is controlled by the control unit to introduce a certain delay amount to the optical pulse and / or the modulation electrical signal, thereby changing the relative delay between the optical pulse and the modulation electrical signal, and the interference signal formed by the optical pulse in the interference loop under this delay amount is measured by the measuring instrument.

[0070] As mentioned earlier, the modulated electrical signal has a rising edge and a falling edge. When the optical pulse component passes through the phase modulator, the different positions of the modulated electrical signal (e.g., rising edge, falling edge, or part in between) act on the phase modulator, and the voltage used to drive the phase modulator will be different. Therefore, the phase modulation amount obtained by the optical pulse component will also be different, and the interference signal generated by the interference will also be different.

[0071] In other words, by introducing a delay into the optical pulse and / or the modulating electrical signal, the relative delay between the optical pulse and the modulating electrical signal can be changed, thus altering the temporal correspondence between the optical pulse passing through the phase modulator and the modulating electrical signal acting on the phase modulator. Since the modulating electrical signal has a certain waveform in the time domain, this change in temporal correspondence leads to different amounts of phase modulation achieved on the optical pulse components. This difference ultimately reflects as different interference signals generated by the interference loops, meaning that the measurement results obtained by the measuring instrument from measuring the interference signals will differ.

[0072] For example, by gradually increasing the delay introduced into the optical pulse or modulated electrical signal, the relative delay between the optical pulse and the modulated electrical signal can be increased, causing the optical pulse component to gradually change from being aligned with the falling edge of the modulated electrical signal to being aligned with the rising edge. Correspondingly, the measurement results obtained, corresponding to this change in timing alignment, will exhibit waveform characteristics similar to those of the modulated electrical signal. In this invention, this waveform characteristic will be used to obtain the timing alignment relationship between the optical pulse and the modulated electrical signal, thereby acquiring the arm length difference of the interference loop.

[0073] Specifically, by controlling the delay unit to introduce different delay amounts DT(i) into the optical pulse or modulated electrical signal at different times T(i), the relative delay ΔDT(i) between the optical pulse and the modulated electrical signal can be changed, and the waveform of the modulated electrical signal can be scanned in the time domain using the optical pulse.

[0074] For example, the delay unit can be controlled to send different delay amounts according to a preset time interval ΔT = T(i) - T(i-1). This time interval ΔT can be set to be greater than the sum of the response time of the delay unit and the response time of the measuring instrument.

[0075] As an example, the delay unit can be controlled to emit delay amounts DT(i) in increments of 0, 1, 2, ..., n at time intervals of ΔT = 200ms, with each increment being 10ps.

[0076] Simultaneously, the interference signal formed by the light pulse in the interference loop is measured using a measuring instrument to obtain the measurement result R(i) corresponding to the delay amount DT(i).

[0077] By using the scanning step, the optical pulse components entering the short arm and long arm from the beam splitter can be scanned across the entire waveform of the modulated electrical signal at their timing alignment positions with the modulated electrical signal, thereby obtaining the delay amounts T1 and T2 provided by the delay unit when the two optical pulse components are aligned with the center position of the modulated electrical signal, respectively.

[0078] At this point, those skilled in the art will understand that the arm length difference L of the interference ring will satisfy the formula L=|T2-T1|*C / n, where C is the speed of light and n is the refractive index of the transmission medium (e.g., optical fiber) of the interference ring.

[0079] In this invention, by acquiring the measurement results R(i) under multiple delay amounts DT(i) (i = 1, ..., N) in the scanning step, the correspondence between the measurement results R(i) and the delay amounts DT(i) can be established in the measurement step, and the aforementioned delay amounts T1 and T2 can be determined, thereby determining the arm length difference L.

[0080] For example, the control unit can generate a corresponding characteristic curve based on the delay amount DT(i) and the measurement result R(i) data, with the delay amount DT(i) as the horizontal axis and the measurement result R(i) as the vertical axis.

[0081] Figure 6 The characteristic curves for measuring the length difference of interferometric ring arms according to the present invention are schematically shown.

[0082] like Figure 6 As shown, the characteristic curve will have a first peak and a second peak, which are generated respectively during the process of the optical pulse component entering the phase modulator via the short arm changing its alignment with one of the rising and falling edges of the modulation signal to the other, and during the process of the optical pulse component entering the phase modulator via the long arm changing its alignment with one of the rising and falling edges of the modulation signal to the other.

[0083] Therefore, the peak value of the first peak (i.e., the maximum second coordinate value) P1_max and the peak value of the second peak (i.e., the maximum second coordinate value) P2_max can be read, and the x-coordinates corresponding to the points on the rising and falling edges of the first peak with an amplitude of K times the peak value (i.e., the second coordinate value is K*P1_max) can be determined, namely the delay amounts DT1_U and DT1_D, and the x-coordinates corresponding to the points on the rising and falling edges of the second peak with an amplitude of K times the peak value (i.e., the second coordinate value is K*P2_max) can be determined, namely the delay amounts DT2_U and DT2_D.

[0084] Finally, calculate parameter T1 according to the formula T1=(DT1_U+DT1_D) / 2, and calculate parameter T2 according to the formula T2=(DT2_U+DT2_D) / 2.

[0085] After obtaining parameters T1 and T2, the control unit can obtain the arm length difference L of the interference ring according to L=T*C / n, T=|T2-T1|.

[0086] In the preferred example, the coefficient K can be 0.8.

[0087] Figure 7 Another embodiment of the measuring device according to the present invention is shown. It is related to... Figure 5 The difference is that the delay chip is placed between the clock source and the pulse light source to introduce a certain delay into the light pulse, thereby precisely controlling the relative delay (or its variation) between the light pulse and the modulated electrical signal.

[0088] Figure 8 Another embodiment of the measuring device according to the invention is shown, which is related to... Figure 5 and 7The difference lies in that the delay unit is implemented using an adjustable fiber delay line. Therefore, in this embodiment, the adjustable fiber delay line is disposed between the pulse light source and the input end of the interference loop, for example, connected to the output end of the pulse light source, thereby providing a delay for the light pulse arriving at the interference loop, thereby precisely controlling the change in the relative delay between the light pulse and the modulated electrical signal.

[0089] In summary, the device and method for measuring the arm length difference of an interferometer ring according to the present invention, based on the interferometric ring working principle between the interference of light pulses in the interferometer ring and the modulation electrical signal acting on the phase modulator, proposes to control the relative delay between the light pulses and the modulation electrical signal, and to use two light pulse components to scan the waveform of the modulation electrical signal in the interferometer ring respectively, and obtain the arm length difference of the interferometer ring based on the scanning results. Therefore, the arm length difference of the interferometer ring can be accurately measured with a simple measurement structure and control process.

[0090] Although the present invention has been described above with reference to the accompanying drawings and specific embodiments, those skilled in the art will readily recognize that the above embodiments are merely exemplary and used to illustrate the principles of the present invention. They do not limit the scope of the present invention. Those skilled in the art can make various combinations, modifications and equivalent substitutions to the above embodiments without departing from the spirit and scope of the present invention.

Claims

1. A method for measuring the length difference of an interferometer ring arm, comprising a light pulse generation step, a modulation signal generation step, a scanning step, and a measurement step; In the optical pulse generation step, an optical pulse is generated according to a first time sequence and then enters the interference loop; In the modulation signal generation step, a modulation electrical signal is generated according to the first time sequence, and the phase modulator in the interference loop modulates the optical pulse based on the modulation electrical signal; In the scanning step, at time T(i), the control delay unit introduces a relative delay amount DT(i) between the optical pulse and the modulation electrical signal, and uses a measuring instrument to measure the interference signal formed by the optical pulse in the interference loop under the delay amount DT(i) to obtain the measurement result R(i); In the measurement step, the arm length difference L of the interference ring is obtained by using the correspondence between the measurement result R(i) and the delay amount DT(i), i=1,...,N, where N is a positive integer; The interference loop has a beam splitter, an optical fiber connecting the two ports of the beam splitter to form a loop, and a phase modulator disposed on the optical fiber loop.

2. The measurement method as described in claim 1, wherein, The time difference between two adjacent moments T(i) and T(i-1) is set to be greater than the sum of the response time of the delay unit and the response time of the measuring instrument.

3. The measurement method as described in claim 1, wherein, The arm length difference L = T*C / n, T = |T2-T1|, C is the speed of light, n is the refractive index of the transmission medium of the interference ring, and T1 and T2 are the delay amounts introduced by the delay unit when the two light pulse components in the interference ring are aligned with the center position of the modulated electrical signal in time.

4. The measurement method as described in claim 3, wherein, In the measurement step, the correspondence is represented by a characteristic curve, where the first axis of the characteristic curve is the delay amount DT(i), and the second axis is the measurement result R(i).

5. The measurement method as described in claim 4, wherein, The characteristic curve has a first peak and a second peak, the first peak has the largest second coordinate value P1_max, and the second peak has the largest second coordinate value P2_max. In the measurement step, the first coordinate values ​​DT1_U and DT1_D of the points with second coordinate values ​​of K*P1_max on the rising and falling edges of the first peak are determined, as are the first coordinate values ​​DT2_U and DT2_D of the points with second coordinate values ​​of K*P2_max on the rising and falling edges of the second peak. T1 and T2 are calculated according to the formulas T1=(DT1_U+DT1_D) / 2 and T2=(DT2_U+DT2_D) / 2, where K is a preset coefficient.

6. The measurement method as described in claim 5, wherein, Set the coefficient K to 0.

8.

7. The measurement method as described in claim 1, wherein, The optical pulses and modulated electrical signals are periodic signals of the same origin.

8. The measurement method as described in claim 1, wherein, The delay unit is implemented using an electrical delay chip or an adjustable fiber optic delay line.

9. The measurement method according to any one of claims 1-8, wherein, For the interferometer loop used for intensity modulation, the measuring instrument is an optical power measuring instrument; for the interferometer loop used for polarization modulation, the measuring instrument is a polarization analysis instrument.

10. A measuring device for the length difference of an interferometric ring arm, comprising a pulse light source, a driving circuit, a delay unit, a measuring instrument, and a control unit; The pulsed light source is configured to generate light pulses according to a first time sequence and output them to the interference ring; The driving circuit is configured to generate a modulated electrical signal according to the first time sequence and output it to the phase modulator in the interference loop. The delay unit is configured to introduce a relative delay amount DT(i) between the optical pulse and the modulated electrical signal at time T(i); The measuring instrument is configured to measure the interference signal formed by the light pulse in the interference loop to obtain the measurement result R(i), which corresponds to the delay amount DT(i). The control unit is configured to determine the arm length difference L of the interference loop, i=1,...,N, where N is a positive integer, based on the correspondence between the measurement result R(i) and the delay amount DT(i). The interference loop has a beam splitter, an optical fiber connecting the two ports of the beam splitter to form a loop, and a phase modulator disposed on the optical fiber loop.

11. The measuring device of claim 10, further comprising a clock source configured to provide a time synchronization signal to the pulse light source and the driving circuit.

12. The measuring device as claimed in claim 11, wherein, The delay unit includes an electrical delay device, which is disposed between the clock source and the pulse light source and / or between the clock source and the driving circuit; And / or, the delay unit includes an adjustable fiber delay line disposed between the pulsed light source and the interference ring.

13. The measuring device as claimed in claim 10, wherein, The measuring instruments include optical power measuring instruments or polarization analysis instruments.

14. The measuring device as claimed in claim 10, wherein, The control unit is used to control the delay unit and is configured such that the time interval between two consecutive changes to the delay amount DT(i) is greater than the sum of the response time of the delay unit and the response time of the measuring instrument.

15. The measuring device as claimed in claim 10, wherein, The control unit is configured to calculate the arm length difference L according to the formula L=T*C / n, where T=|T2-T1|, C is the speed of light, n is the refractive index of the transmission medium of the interference ring, and T1 and T2 are the delay amounts introduced by the delay unit when the two light pulse components in the interference ring are aligned with the center position of the modulated electrical signal in time.

16. The measuring device as claimed in claim 15, wherein, The control unit is further configured to: Characteristic curves are generated using the delay amount DT(i) and the measurement result R(i) as the first and second coordinate axes, respectively. The maximum second coordinate value P1_max of the first peak and the maximum second coordinate value P2_max of the second peak of the characteristic curves are then obtained. Determine the first coordinate values ​​DT1_U and DT1_D of the points with second coordinate values ​​of K*P1_max on the rising and falling edges of the first peak, and the first coordinate values ​​DT2_U and DT2_D of the points with second coordinate values ​​of K*P2_max on the rising and falling edges of the second peak. Calculate T1 and T2 according to the formulas T1=(DT1_U+DT1_D) / 2 and T2=(DT2_U+DT2_D) / 2, where K is a preset coefficient.

17. The measuring device as claimed in claim 16, wherein, The coefficient K = 0.8.

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