Phase-locked device, method and system based on unequal-arm interferometer

Abstract

This application discloses a phase-locked device, method, and system based on an unequal-arm interferometer. The unequal-arm interferometer is used to perform unequal-arm interference on an initial beam emitted from a light source to output an interference beam with a phase difference. The device includes a phase-locked unit and a frequency adjustment unit. The phase-locked unit is used to detect the light intensity of the interference beam to determine the phase-lock point and adjust the unequal-arm interferometer according to the light intensity change to balance the phase difference of the interference beam according to the phase-lock point. The frequency adjustment unit is used to adjust the frequency of the initial beam to change the phase difference of the interference beam. By setting a frequency adjuster before the initial beam enters the unequal-arm interferometer, the application achieves a translation of the interference curve by changing the frequency of the initial beam without changing the phase-locked light intensity. This allows the phase, which was originally near the extreme point, to be transformed into a position that is easy to lock, thereby achieving phase locking at any position and improving the adjustability of the interferometer while ensuring stability.

Description

Technical Field

[0001] This application belongs to the field of optical measurement technology, and in particular relates to a phase-locked device, method and system based on an unequal-arm interferometer. Background Technology

[0002] An unequal-arm interferometer is a precision measuring instrument based on the principle of optical interference. Its core feature is that the two interferometer arms are of unequal length. Optical signals are transmitted through two fiber optic arms of unequal length, called the reference arm and the measuring arm, respectively. When the optical signal propagates through these two arms, the difference in path length creates an optical path difference, which in turn produces interference at the point of convergence. By changing the optical path difference, the optical field can be controlled through interference, including achieving beam splitting with a controllable splitting ratio and measuring input photons under superposition basis vectors.

[0003] However, unequal-arm interferometers lack sufficient stability; environmental factors can randomly cause drift in the relative phase of the two optical signals. For example, temperature affects the refractive index of the optical fiber, and vibration causes changes in the fiber length, thus interfering with the interference results. Therefore, an active feedback system is needed to balance the disturbances.

[0004] Current active feedback systems typically incorporate a phase modulator into the interferometer and use the light intensity at one of the exit points as a reference phase-locked point to establish the feedback circuit. However, at the extreme points of light intensity—the points of maximum and minimum intensity—the phase does not exhibit sufficient slope change to achieve phase locking via active feedback. Therefore, achieving phase locking of arbitrary phases, especially at extreme points, is crucial for energy-time entanglement measurements in quantum optics. Summary of the Invention

[0005] This application provides a phase-locked device, method, and system based on an unequal-arm interferometer, aiming to solve the problem that existing unequal-arm interferometers cannot perform phase-locking at any phase.

[0006] In a first aspect, this application provides a phase-locked loop device based on an unequal-arm interferometer, wherein the unequal-arm interferometer is used to perform unequal-arm interference on an initial beam emitted by a light source to output an interference beam with a phase difference; the device includes:

[0007] A phase-locked unit is used to detect the light intensity of the interference beam to determine the phase-lock point, and to adjust the unequal-arm interferometer according to the light intensity change so as to balance the phase difference of the interference beam according to the phase-lock point;

[0008] A frequency adjustment unit is used to adjust the frequency of the initial beam to change the phase difference of the interference beam.

[0009] Furthermore, the frequency adjustment unit includes an acousto-optic modulator and an adjustable attenuator. The input end of the acousto-optic modulator is used to receive the initial light beam, and the adjustable attenuator is connected to the output end of the acousto-optic modulator.

[0010] Furthermore, the phase-locked unit includes a photodetector, a feedback circuit, and a phase adjuster. The input end of the photodetector is used to receive the interference beam. The feedback circuit is connected between the output end of the photodetector and the input end of the phase adjuster. The output end of the phase adjuster is connected to the unequal-arm interferometer.

[0011] Secondly, this application provides a phase-locked loop method based on an unequal-arm interferometer, the method comprising:

[0012] The initial beam is subjected to unequal-arm interference by an unequal-arm interferometer to output an interference beam with a phase difference;

[0013] The intensity of the interference beam is detected to determine the phase-locked point, and the unequal-arm interferometer is adjusted according to the intensity change to balance the phase difference of the interference beam according to the phase-locked point;

[0014] The frequency of the initial beam is adjusted to change the phase difference of the interference beam.

[0015] Thirdly, this application provides a measurement system based on an unequal-arm interferometer, the system including a light source, an unequal-arm interferometer, and a phase-locked device based on the unequal-arm interferometer as described above.

[0016] Compared with the prior art, this application sets a frequency adjuster before the initial beam enters the unequal arm interferometer. Without changing the intensity of the phase-locked beam, the frequency adjuster changes the frequency of the initial beam to achieve the translation of the interference curve. This allows the phase that was originally located near the extreme point to be transformed into a position that is easy to lock, thereby achieving phase locking at any position. This improves the adjustability of the interferometer while ensuring stability. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a block diagram of a phase-locked loop device based on an unequal-arm interferometer, provided for an embodiment of this application.

[0019] Figure 2 for Figure 1 A schematic diagram of one embodiment of the shown example;

[0020] Figure 3 for Figure 1 A schematic diagram of an experimental scenario in the illustrated embodiment;

[0021] Figure 4 for Figure 1 A schematic diagram showing the relationship between the intensity of the interference beam and the phase difference in the illustrated embodiment. Detailed Implementation

[0022] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] The directional terms used in this application, such as "up," "down," "front," "back," "left," and "right," are merely for reference in the accompanying drawings. Therefore, the directional terms used are for illustrative and interpretative purposes only, and not for limiting the scope of this application. Furthermore, in the accompanying drawings, structures that are similar or identical are indicated by the same reference numerals.

[0024] This application provides a phase-locked device based on an unequal-arm interferometer, which can be applied to time-path entanglement measurement in quantum optics. For example... Figure 1 As shown in the embodiments of this application, in the phase-locked device based on an unequal-arm interferometer, the unequal-arm interferometer is used to perform unequal-arm interference on an initial beam emitted by a light source to output an interference beam with a phase difference. The phase-locked device includes a phase-locking unit and a frequency adjustment unit. The phase-locking unit is used to detect the light intensity of the interference beam to determine the phase-locking point, and adjust the unequal-arm interferometer according to the light intensity change to balance the phase difference of the interference beam according to the phase-locking point. The frequency adjustment unit is used to adjust the frequency of the initial beam to change the phase difference of the interference beam.

[0025] As we know, an unequal-arm interferometer is mainly composed of a light source, a beam splitter, arms of unequal length, a receiver, and other auxiliary equipment. Its working principle is based on the phenomenon of light interference. By comparing the light signals in the reference light path formed by the unequal-length arms and the light path of the object under test, information about the object is obtained. Specifically, during the measurement process, an initial light beam is emitted from a continuous or pulsed laser. This initial light beam is split into two beams by the beam splitter. These two beams enter the arms of the unequal-arm interferometer and form two different light paths. One serves as the reference light path, with a fixed length. The other, as the measurement beam, passes through the object under test and has a different length than the reference light path, thus having different phases. The properties and shape of the object under test affect the light signals in this light path. Finally, the receiver receives the light signals from the two light paths and observes the interference beam formed after their interference. By analyzing the intensity of the interference beam, the interference result at the output of the interferometer can be obtained.

[0026] Understandably, due to the lack of sufficient stability in unequal-arm interferometers, environmental changes can randomly cause phase shifts in the relative phase of the two optical signals. For example, temperature affects the refractive index of the optical fiber, and vibration causes changes in the fiber length, thus interfering with the interference results. Therefore, an active feedback system is needed to balance the disturbances. A phase-locked unit is used to detect the intensity of the interference beam to determine the phase-lock point and adjust the unequal-arm interferometer according to the intensity change to balance the phase difference of the interference beam based on the phase-lock point. However, in the region near the intensity extremum, the intensity does not have sufficient slope change relative to the phase, making phase-locking impossible through an active feedback system. By setting a frequency adjustment unit before the initial beam is emitted and enters the unequal-arm interferometer, the frequency of the initial beam is adjusted, thereby changing the phase difference of the interference beam. Without changing the intensity of the phase-locked beam, the frequency adjuster is used to change the frequency of the initial beam to achieve a translation of the interference curve, so that the phase originally near the extremum can also be converted into an easily locked position, thus achieving phase locking at any position.

[0027] In one exemplary embodiment, the frequency adjustment unit includes an acousto-optic modulator and an adjustable attenuator, wherein the input of the acousto-optic modulator is used to receive the initial light beam, and the adjustable attenuator is connected to the output of the acousto-optic modulator.

[0028] For acousto-optic modulators, set the corresponding carrier frequency or operating frequency according to the required laser frequency range. For adjustable attenuators, set the attenuation amount to an appropriate initial value, which can be selected based on actual needs and the initial intensity of the laser signal. Adjust the laser carrier frequency or operating frequency using the control knobs, switches, or digital interface on the acousto-optic modulator to achieve the desired laser frequency. During adjustment, a spectrum analyzer or other testing equipment can be used to monitor laser frequency changes to ensure accuracy. Use an adjustable attenuator to adjust the laser signal attenuation as needed. Operate the adjustable attenuator using knobs, switches, or digital controls, following the instructions or markings according to the specific model and operating method. During attenuation adjustment, a signal analyzer or other testing equipment can be used to monitor the intensity and quality of the laser signal, and the attenuation amount can be adjusted based on the monitoring results to achieve the required laser power level.

[0029] In some embodiments, such as Figure 2 As shown, the phase-locked unit includes a photodetector, a feedback circuit, and a phase adjuster. The input end of the photodetector is used to receive the interference beam. The feedback circuit is connected between the output end of the photodetector and the input end of the phase adjuster. The output end of the phase adjuster is connected to the unequal-arm interferometer.

[0030] A photodetector is used to detect the intensity of the interference beam. By converting the optical signal of the interference beam into an electrical signal, the feedback circuit performs PID analysis on the electrical signal generated by the photodetector, converts and amplifies it as necessary, and obtains a high-voltage electrical signal, which is then sent to the phase adjuster. The phase adjuster receives the high-voltage signal from the feedback circuit in real time and changes the phase of the second arm relative to the first arm in the optical path by physically adjusting the unequal-arm interferometer. This balances the phase disturbances caused by the environment and completes real-time closed-loop optical phase locking.

[0031] When it is necessary to change the phase that needs to be locked, the frequency of the phase-locked laser incident is changed using a frequency modulator, which is equivalent to shifting the interference curve; for example... Figure 4 As shown, without changing the intensity of the phase-locked laser, the interference curve is shifted by changing the frequency of the phase-locked laser using a frequency modulator, moving it from the solid line to the dashed line. The phase, originally near the extreme point (the point where the normalized intensity is 0 or 1), can be transformed into a position that is easy to lock. Furthermore, since the slope of the phase-locked point remains unchanged, the PID parameters of the feedback circuit can be adjusted once and used continuously at any phase. Because the phase-locked point remains constant, the feedback circuit will drive the phase modulator to reach a new phase to achieve that phase-locked point, maintaining the phase balance of the interference beam.

[0032] In an experimental scenario, such as Figure 3As shown, two beams with different polarizations (probe beam H and phase-locked laser V) are used for phase locking and detection respectively. The two beams are transmitted independently in the interferometer and separated by a polarization beam splitter at the exit. The phase-lock point of the feedback circuit is set according to the intensity of the phase-locked laser, and the PID parameters are adjusted so that the feedback circuit can keep the light intensity at photodetector 2 constant. At this time, the phase difference between the two arms in the unequal-arm interferometer remains constant. If the phase-locking device functions normally, with the phase-lock point remaining constant, as the frequency shift of the frequency adjuster increases, the feedback circuit controls the phase adjuster to gradually change the phase in the interferometer. The phase difference sensed by the probe laser will gradually change, thus causing the light intensity value at photodetector 1 to gradually change. In the experiment, the arm length difference of the unequal-arm interferometer is about 15m, the free spectral range is about 13MHz, and the adjustment range of the frequency adjuster is 72MHz to 94MHz, which can completely cover one cycle.

[0033] This application also provides a phase-locked loop method based on an unequal-arm interferometer, the method comprising:

[0034] Step 1: Perform unequal-arm interference on the initial beam using an unequal-arm interferometer to output an interference beam with a phase difference;

[0035] Step 2: Detect the light intensity of the interference beam to determine the phase-locked point, and adjust the unequal-arm interferometer according to the light intensity change to balance the phase difference of the interference beam based on the phase-locked point;

[0036] Step 3: Adjust the frequency of the initial beam to change the phase difference of the interference beam.

[0037] In one embodiment, an unequal-arm interferometer is used to perform unequal-arm interference on an initial beam to output an interference beam with a phase difference; the intensity of the interference beam is detected by a phase-locked unit to determine the phase-lock point, and the unequal-arm interferometer is adjusted according to the intensity change to balance the phase difference of the interference beam according to the phase-lock point; the frequency of the initial beam is adjusted by setting a frequency adjuster to change the phase difference of the interference beam.

[0038] This application also provides a measurement system based on an unequal-arm interferometer, the system including a light source, an unequal-arm interferometer, and a phase-locked device based on the unequal-arm interferometer as described above.

[0039] Compared to related technologies, this application, by setting a frequency adjuster before the initial beam enters the unequal-arm interferometer, shifts the interference curve by changing the frequency of the initial beam without altering the phase-locked beam intensity. This allows the phase, originally near an extreme point, to be converted into an easily lockable position. This achieves phase locking at any position, further improving the measurement sensitivity of the system. Furthermore, since the phase-locked point slope remains unchanged, the PID parameters of the feedback circuit can be adjusted once and used continuously at any phase.

[0040] It is understood that this application has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of this application. Furthermore, based on the teachings of this application, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of this application. Therefore, this application is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of this application.

Claims

1. A phase-locked loop method based on an unequal-arm interferometer, characterized in that, The unequal-arm interferometer is used to perform unequal-arm interference on the initial beam emitted by the light source to output an interference beam with a phase difference; the method includes: The initial beam is subjected to unequal-arm interference by an unequal-arm interferometer to output an interference beam with a phase difference; The intensity of the interference beam is detected to determine the phase-locked point, and the unequal-arm interferometer is adjusted according to the intensity change to balance the phase difference of the interference beam according to the phase-locked point; Adjust the frequency of the initial beam to change the phase difference of the interference beam; The frequency adjustment unit includes an acousto-optic modulator and an adjustable attenuator. The input end of the acousto-optic modulator is used to receive the initial light beam, and the adjustable attenuator is connected to the output end of the acousto-optic modulator. The phase-locked unit includes a photodetector, a feedback circuit, and a phase adjuster. The input end of the photodetector is used to receive the interference beam. The feedback circuit is connected between the output end of the photodetector and the input end of the phase adjuster. The output end of the phase adjuster is connected to the unequal-arm interferometer.

2. A measurement system based on an unequal-arm interferometer, characterized in that, The system includes a light source, an unequal-arm interferometer, and the phase-locked loop method based on the unequal-arm interferometer as described in claim 1.

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