Optical feedback cavity enhancement technique transmission frequency lock stability evaluation method and system

Abstract

The application discloses an optical feedback cavity enhancement technology transmission frequency locking stability evaluation method and system, and belongs to the technical field of laser frequency stability evaluation. In view of the problem that the resolution of the spectrum is reduced in the current frequency stability evaluation, leading to low error estimation accuracy, an evaluation system for the stability of the optical feedback cavity enhancement technology transmission frequency locking is provided. The optical path subsystem comprises a laser controller, a temperature control base, a diode laser, a collimating lens, an isolator, a matching lens, a first plane mirror, a second plane mirror, a piezoelectric ceramic, a third plane mirror, a first focusing lens, a photodetector, a second focusing lens, a detector, a V-shaped three-mirror cavity, a frequency locking subsystem, a phase-locked amplifier, a PID controller and a high-voltage amplifier, and a stability evaluation subsystem, an adder, a function generator, a bias DC beam splitter, a power amplification module, a frequency mixing module and a collection card.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of laser frequency stability evaluation, and particularly relates to an optical feedback cavity enhanced technique transmission frequency locking stability evaluation method and system. BACKGROUND

[0002] In the fields of nonlinear frequency conversion, non-classical light field preparation, gas laser spectrum detection, etc., cavity enhancement technology is often used, that is, the laser is coupled into an external resonant cavity for resonance enhancement, passive amplification, and improvement of the cavity laser power. However, the application of cavity enhancement technology requires locking the laser frequency and the resonant frequency of the cavity. The optical feedback cavity enhancement technology uses optical feedback and PDH technology to lock the laser frequency to the resonant cavity mode frequency, thereby achieving the enhancement of the cavity laser power. The specific scheme is that the laser output by the semiconductor laser is incident into the resonant cavity, the resonant cavity feeds back the resonant laser to the semiconductor laser, and the PDH technology is used to lock the phase of the feedback light, so that the phase of the feedback light is the same as that of the laser output by the semiconductor laser. At this time, the laser frequency is locked to the frequency of the feedback light.

[0003] The PDH technology is a commonly used locking technology. In the locking process, the laser needs to be modulated first, and the error signal is generated by demodulating the reflected light or the transmitted light signal of the cavity, so as to control and lock the phase of the feedback light. After locking, the jitter of the error signal is often used to evaluate the stability of the locking. However, in the process of demodulation and locking using the transmitted light, there are certain limitations in evaluating the frequency stability by using the error signal demodulated by the transmitted light, because the power spectral density of the error signal will be affected by the Bessel function effect. Specifically, in the process of transmission frequency locking, due to the limitation of the cavity mode linewidth, the modulation frequency is generally not greater than 50 kHz. When the modulation frequency is low, the frequency interval between the sideband and the carrier is small, which will cause the sideband to overlap in the frequency spectrum. In the frequency stability evaluation and error detection, the overlapping sideband will make it difficult to distinguish between the carrier and the sideband, and it is difficult to accurately extract the frequency error signal. In this way, the resolution of the frequency spectrum will be reduced, resulting in inaccurate error estimation. Under low-frequency modulation, noise (especially low-frequency noise) can easily interfere with the sideband signal. In this case, due to the close distance between the sideband and the carrier, the influence of the noise signal is easily misinterpreted as the frequency error signal, thereby amplifying the error and causing the system to be unable to accurately estimate the stability of the laser frequency. SUMMARY

[0004] In view of the problem of low error estimation accuracy caused by the resolution of the frequency spectrum being reduced in the current frequency stability evaluation, the present application provides an optical feedback cavity enhanced technique transmission frequency locking stability evaluation method and system.

[0005] In order to achieve the above-mentioned purpose, the present application adopts the following technical scheme:

[0006] An evaluation system for optical feedback cavity enhancement technology to improve frequency locking stability, comprising: an optical path subsystem, a frequency locking subsystem and a stability evaluation subsystem;

[0007] The optical path subsystem comprises: a laser controller, a temperature control base, a diode laser, a collimating lens, an isolator, a matching lens, a first plane mirror, a second plane mirror, a piezoelectric ceramic PZT, a third plane mirror, a first focusing lens, a photodetector, a second focusing lens, a detector, a V-shaped three-mirror cavity; the frequency locking subsystem comprises: a phase-locked amplifier, a PID controller and a high-voltage amplifier; and the stability evaluation subsystem comprises: an adder, a function generator, a bias-tee, a power amplifier module, a mixing module and an acquisition card.

[0008] The semiconductor laser is mounted on the temperature control base, the function generator and the phase-locked amplifier respectively provide a modulation signal to the laser controller through the adder, and the laser controller modulates the output laser frequency; the laser passes through the collimating lens to form a parallel light beam, enters the matching lens after passing through the isolator for mode matching, is reflected by the first plane mirror to the second plane mirror, and is reflected by the second plane mirror into the V-shaped three-mirror cavity for resonance; the resonant laser transmitted by the front cavity mirror of the V-shaped three-mirror cavity is fed back to the semiconductor laser in the original path, the laser transmitted by the rear cavity mirror of the V-shaped three-mirror cavity enters the photodetector after being focused by the first focusing lens, the photodetector is connected to the phase-locked amplifier, the phase-locked amplifier is connected to the PID controller, the PID controller is connected to the high-voltage amplifier, and the high-voltage amplifier controls the piezoelectric ceramic PZT fixed on the second plane mirror; the directly reflected light of the V-shaped three-mirror cavity passes through the third mirror, is focused by the second focusing lens and then enters the detector, the detector is connected to the bias-tee, the bias-tee is connected to the power amplifier, the light passes through the power amplifier and then enters the mixing module, the other end of the mixing module is connected to the function generator to provide a demodulation signal, and the demodulated signal is collected by the acquisition card; the collected error signal is sent to a computer.

[0009] Further, the matching lens is used for frequency matching with the resonant cavity mode to ensure maximum efficient coupling of the laser into the resonant cavity.

[0010] Further, the laser controller is used for controlling and modulating the output laser frequency.

[0011] Further, the piezoelectric ceramic PZT is used for accurately adjusting the phase of the laser feedback to achieve precise locking of the laser frequency.

[0012] Further, the modulation signal provided by the function generator is in the order of MHZ, and the modulation signal provided by the phase-locked amplifier is in the order of khz.

[0013] Further, the diode laser is a semiconductor laser.

[0014] Further, the V-type three-mirror cavity is used for reducing the interference of direct reflected light and ensuring the accurate locking of the laser frequency and the cavity mode.

[0015] Further, the V-type three-mirror cavity has a fineness of 16000, the line width of the cavity film is 33khz, and the modulation and demodulation frequencies of 30khz are selected to perform the transmission frequency locking.

[0016] Further, two 30db attenuation filters are arranged on the detector.

[0017] Further, the isolator is used for reducing the feedback rate of the feedback light to 10 -4 -10 -5 orders of magnitude.

[0018] An evaluation method for the stability of the transmission frequency locking of an optical feedback cavity enhancement technology, the MHz order modulation signal output by a function generator and the kHz order modulation signal output by a phase-locked amplifier are superimposed through an adder and then input into a laser controller, and the laser frequency output by the laser controller is modulated;

[0019] The laser output by the diode laser installed on the temperature control base passes through a collimating lens to make the laser beam approximate to parallel light parallel to the optical platform, passes through an isolator to reduce the feedback rate, passes through a matching lens to match the laser frequency with the mode of the resonant cavity, sequentially passes through a first plane mirror and a second plane mirror, and then enters the V-type three-mirror cavity; at the transmission end of the resonant cavity, the transmission light of the V-type three-mirror cavity enters a photodetector through a first focusing lens, the photodetector inputs the transmission signal into a phase-locked amplifier, the phase-locked amplifier mixes the transmission signal and the kHz modulation signal to demodulate an error signal and input the error signal into a PID controller, the PID controller outputs to a high-voltage amplifier, and then the high-voltage amplifier controls the piezoelectric ceramic on the second plane mirror to adjust the phase of the feedback light in real time, so as to realize the locking of the laser frequency to the cavity mode frequency.

[0020] At the reflection end of the resonant cavity, the reflection light of the V-type three-mirror cavity passes through a third mirror, then passes through a second focusing lens and enters the detector, the signal of the detector is input into a DC bias beam splitter, then passes through a power amplifier and enters a mixing module, the other end of the mixing module is connected with a function generator, the function generator provides a high-frequency signal of MHz order for demodulation, and the demodulated error signal is collected through a collection card; the collected error signal is calculated through a MATLAB program to obtain a power spectrum density image of the error signal, so as to evaluate the stability of the transmission frequency locking.

[0021] The theoretical support used in the application is as follows:

[0022] In the process of transmission frequency locking, the selection of modulation frequency is restricted by the linewidth of the resonant cavity. Specifically, the frequency higher than the linewidth of the resonant cavity cannot pass through the resonant cavity. For a resonant cavity with high precision, the linewidth of the cavity film is usually in the order of kHz. Therefore, the modulation frequency should also be selected in the order of kHz. Under low-frequency modulation (e.g., lower than 50 kHz), since the modulation frequency is close to the linewidth of the resonant cavity, the interval between the sideband and the carrier becomes small, which makes it difficult to distinguish between the sideband and the carrier. The error signal obtained in this way not only reflects the phase noise of the carrier, but also contains the average phase noise of the sideband. Especially in the case of strong low-frequency noise, the mixing of the carrier and sideband phase noises makes it impossible to accurately estimate the frequency stability of the laser using the error signal. Therefore, we simultaneously modulate the laser frequency at a high frequency (in the order of MHz) and demodulate the error signal of the resonant cavity reflected light signal to evaluate the stability of the transmission locking. High-frequency modulation can ensure clear distinction between the carrier and the sideband, so that the error signal obtained can accurately reflect the phase noise of the carrier, and thus more accurately evaluate the stability of the system after locking.

[0023] Compared with the prior art, the present application has the following advantages:

[0024] 1. The present application realizes the locking of the laser frequency to the resonant cavity mode frequency based on optical feedback and feedback light phase control. Compared with the traditional direct locking of the laser and resonant cavity frequencies, the locking bandwidth required by the present application is lower, and the anti-interference performance is stronger.

[0025] 2. The present application provides a method for evaluating the stability of transmission locking by using the error signal obtained by high-frequency modulation and demodulation of the reflected light signal. This method can effectively improve the accuracy of frequency stability evaluation and avoid the problem of inaccurate error signal caused by the blurring of the Bessel function sideband due to the too low modulation frequency of transmission locking. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 A system for evaluating the stability of the transmission locking of the optical feedback cavity enhanced system.

[0027] Figure 2 A power spectral density image of the error signal of the transmission light locking stability obtained.

[0028] Reference: 1, temperature control base; 2, diode laser; 3, collimating lens; 4, isolator; 5, matching lens; 6, first plane mirror; 7, second plane mirror; 8, piezoelectric ceramic (PZT); 9, third plane mirror; 10, first focusing lens; 11, photodetector; 12, second focusing lens; 13, detector; 14, phase-locked amplifier; 15, PID controller; 16, high-voltage amplifier; 17, adder; 18, function generator; 19, laser controller; 20, bias-tee; 21, power amplifier module; 22, mixing module; 23, acquisition card; 24, V-type three-mirror cavity; 25, computer; DETAILED DESCRIPTION

[0029] In order to understand the present application, it will be described in detail. However, the present application has multiple implementations and is not limited to the specific examples listed herein. The presentation of these examples is intended to deepen the overall understanding of the disclosure of the present application.

[0030] An evaluation system for evaluating the frequency locking stability of an optical feedback cavity enhancement technology, comprising: an optical path subsystem, a frequency locking subsystem and a stability evaluation subsystem;

[0031] The optical path subsystem comprises: a laser controller 19, a temperature control base 1, a diode laser 2, a collimating lens 3, an isolator 4, a matching lens 5, a first plane mirror 6, a second plane mirror 7, a piezoelectric ceramic (PZT) 8, a third plane mirror 9, a first focusing lens 10, a photodetector 11, a second focusing lens 12, a detector 13, and a V-type three-mirror cavity 24; the frequency locking subsystem: a phase-locked amplifier 14, a PID controller 15 and a high-voltage amplifier 16; the stability evaluation subsystem: an adder 17, a function generator 18, a bias-tee 20, a power amplifier module 21, a mixing module 22 and an acquisition card 23;

[0032] The semiconductor laser 2 is installed on the temperature control base 1, the function generator 18 and the phase-locked amplifier 14 respectively give a modulation signal to the laser controller 19 through the adder 17, and the laser frequency of the output is modulated through the laser controller 19; the laser passes through the collimating lens 3 to form a parallel light beam, enters the matching lens 5 for mode matching after passing through the isolator 4, and then the laser is reflected to the second plane mirror 7 by the first plane mirror 6, and then the laser is reflected into the V-type three-mirror cavity 24 by the second plane mirror 7; the resonant laser transmitted by the front cavity mirror of the V-type three-mirror cavity 24 is fed back to the semiconductor laser 2 in the original way, and the laser transmitted by the rear cavity mirror of the V-type three-mirror cavity 24 enters the photodetector 11 after being focused by the first focusing lens 10, the photodetector 11 is connected with the phase-locked amplifier 14, the phase-locked amplifier 14 is connected with the PID controller 15, the PID controller 15 is connected with the high-voltage amplifier 16, and the high-voltage amplifier 16 controls the piezoelectric ceramic (PZT) 8 fixed on the second plane mirror 7; the directly reflected light of the V-type three-mirror cavity 24 passes through the third mirror 9, is focused by the second focusing lens 12 and then enters the detector 13, the detector 13 is connected with the DC bias beam splitter 20, the DC bias beam splitter 20 is connected with the power amplifier 21, and the power amplifier 21 enters the mixing module 22, the other end of the mixing module 22 is connected with the function generator 18 to provide a demodulation signal, and the demodulated signal is collected by the acquisition card 23; the collected error signal is sent into the computer 25.

[0033] Further, the matching lens 5 is used for frequency matching with the resonant cavity mode to ensure the maximum efficiency of the laser coupled into the resonant cavity.

[0034] Further, the laser controller 19 is used for controlling and modulating the output laser frequency.

[0035] Further, the isolator is used to reduce the feedback rate of the feedback light to 10 -4 -10 -5 orders of magnitude.

[0036] Further, the piezoelectric ceramic (PZT) 8 is used for accurately adjusting the phase of the laser feedback to realize the accurate locking of the laser frequency.

[0037] Further, the modulation signal provided by the function generator 18 is 1.5 MHZ; and the modulation model provided by the phase-locked amplifier 14 is 30 khz.

[0038] Further, the diode laser 2 is a semiconductor laser.

[0039] Further, the V-type three-mirror cavity 24 is used to reduce the interference of the directly reflected light and ensure the high matching degree of the laser frequency and the cavity mode.

[0040] Further, the V-type three-mirror cavity 24 has a fineness of 16000, and the line width of the cavity film is 33 kHz, and a modulation and demodulation frequency of 30 kHz is selected to perform the transmission frequency locking.

[0041] Further, two 30db attenuation filters are arranged on the detector 13.

[0042] An evaluation method for the stability of the transmission frequency locking of an optical feedback cavity enhancement technique, the MHz order modulation signal output by the function generator 18 and the kHz order modulation signal output by the phase-locked amplifier 14 are superimposed through the adder 17 and input to the laser controller 19, and the laser frequency output by the laser controller 19 is modulated;

[0043] The laser output by the diode laser 2 mounted on the temperature control base 1 passes through the collimating lens 3 to make the laser beam approximately parallel to the parallel light of the optical platform, passes through an isolator 4 to reduce the feedback rate, and then passes through a matching lens 5 to match the laser frequency with the mode of the resonant cavity, and then the laser sequentially passes through the first plane mirror 6 and the second plane mirror 7, and the piezoelectric ceramic 8 is attached to the side of the second plane mirror 7, and then the laser enters the V-type three-mirror cavity 24; at the transmission end of the resonant cavity, the transmission light of the V-type three-mirror cavity 24 enters the photodetector 11 through the first focusing lens 10, and the photodetector 11 inputs the transmission signal into the phase-locked amplifier 14, the phase-locked amplifier 14 mixes the transmission signal and the kHz modulation signal to demodulate the error signal and input it to the PID controller 15, the PID controller 15 outputs to the high-voltage amplifier 16, and then the high-voltage amplifier 16 controls the piezoelectric ceramic 8 on the second plane mirror 7 to adjust the phase of the feedback light in real time, thereby realizing the locking of the laser frequency to the cavity mode frequency;

[0044] At the reflection end of the resonant cavity, the reflected light of the V-type three-mirror cavity 24 passes through the third mirror 9, then passes through the second focusing lens 12 and enters the detector 13, the signal of the detector 13 is input to the DC bias beam splitter 20, then passes through the power amplifier 21 and enters the mixing module 22, the other end of the mixing module 22 is connected with the function generator 18, the function generator 18 provides a high-frequency signal of MHz order for demodulation, and the demodulated error signal is collected by the acquisition card 23; the collected error signal is calculated by the MATLAB program to obtain the power spectrum density image of the error signal, so as to evaluate the stability of the transmission frequency locking.

[0045] As shown in Figure 2 the power spectrum density image of the error signal demodulated by the reflected light, we can see that in the low frequency region of about 1000 Hz, the PDH technology for transmission light locking has a certain suppression effect on low frequency noise.

[0046] The details of the application not described herein are considered known to those skilled in the art. Although the foregoing description of the application has been described in some detail for the purposes of clarity and the understanding of the application, it should be appreciated that the application is not limited to the particular embodiments or examples described. It should be readily understood that various changes can be made therein without departing from the spirit and scope of the application defined by the appended claims and that equivalent materials can be substituted.

Claims

1. An optical feedback cavity enhancement technology transmission frequency locking stability evaluation system, characterized by: include: Optical path subsystem, frequency locking subsystem and stability evaluation subsystem; The optical path subsystem comprises: a laser controller (19), a temperature control base (1), a diode laser (2), a collimating lens (3), an isolator (4), a matching lens (5), a first plane reflector (6), a second plane reflector (7), a piezoelectric ceramic (8); a third plane reflector (9), a first focusing lens (10), a photodetector (11), a second focusing lens (12), a detector (13), and a V-shaped three-mirror cavity (24); the frequency locking subsystem comprises: a phase-locked amplifier (14), a PID controller (15), and a high-voltage amplifier (16); the stability evaluation subsystem comprises: an adder (17), a function generator (18), a biased DC beam splitter (20), a power amplifier module (21), a frequency mixing module (22), and an acquisition card (23); The diode laser (2) is mounted on a temperature-controlled base (1); a function generator (18) and a phase-locked amplifier (14) respectively send a modulation signal to a laser controller (19) through an adder (17); the laser controller (19) modulates the output laser frequency; the laser forms a parallel beam through a collimating lens (3), passes through an isolator (4), and enters a matching lens (5) for mode matching; the laser is then reflected by a first plane reflector (6) to a second plane reflector (7), and then reflected by the second plane reflector (7) into a V-shaped three-mirror cavity (24) for resonance; the resonant laser transmitted through the front cavity mirror of the V-shaped three-mirror cavity (24) is fed back to the semiconductor laser (2) along the original path; the laser transmitted through the rear cavity mirror of the V-shaped three-mirror cavity (24) is focused by a first focusing lens (10) and enters a photodetector (11); the photodetector (11) is connected to a phase-locked amplifier (14), the phase-locked amplifier (14) is connected to a PID controller (15), the PID controller (15) is connected to a high-voltage amplifier (16), and the high-voltage amplifier (16) controls the piezoelectric ceramic (8) fixed on the second plane reflector (7); the directly reflected light of the V-shaped three-mirror cavity (24) passes through the third reflector (9), is focused by the second focusing lens (12), and then enters the detector (13), the detector (13) is connected to a biased DC beam splitter (20), the biased DC beam splitter (20) is connected to a power amplifier (21), and enters a mixing module (22) after passing through the power amplifier (21), the other end of the mixing module (22) is connected to a function generator (18), and provides a demodulated signal, and the demodulated signal is collected by an acquisition card (23); the collected error signal is sent to a computer (25).

2. The optical feedback cavity enhancement technology transmission frequency locking stability evaluation system according to claim 1, characterized in that: The matching lens (5) is used to perform frequency matching with the resonant cavity mode to ensure maximum efficiency of laser coupling into the resonant cavity.

3. The optical feedback cavity enhancement technology transmission frequency locking stability evaluation system according to claim 1, characterized in that: The laser controller (19) is used to control and modulate the output laser frequency.

4. The optical feedback cavity enhancement technology transmission frequency locking stability evaluation system according to claim 1, characterized in that: The piezoelectric ceramic (8) is used to precisely adjust the phase of laser feedback to achieve precise locking of the laser frequency.

5. The optical feedback cavity enhancement technology transmission frequency locking stability evaluation system according to claim 1, characterized in that: The modulation signal provided by the function generator (18) is of the MHz order; the modulation signal provided by the lock-in amplifier (14) is of the kHz order.

6. The optical feedback cavity enhancement technology transmission frequency locking stability evaluation system according to claim 1, characterized in that: The diode laser (2) is a semiconductor laser.

7. The optical feedback cavity enhancement technology transmission frequency locking stability evaluation system according to claim 1, characterized in that: The V-shaped three-mirror cavity (24) is used to reduce the interference of directly reflected light and ensure the precise locking of the laser frequency and the cavity mode.

8. The optical feedback cavity enhancement technology transmission frequency locking stability evaluation system according to claim 1, characterized in that: The V-shaped three-mirror cavity (24) has a finesse of 16,000 and a line width of the cavity film of 33 kHz.

9. The optical feedback cavity enhancement technology transmission frequency locking stability evaluation system according to claim 1, characterized in that: The isolator (4) is used to reduce the feedback rate of the feedback light to 10 -4 -10 -5 Magnitude.

10. A method for evaluating transmission frequency locking stability of optical feedback cavity enhancement technology, characterized by: The MHz-level modulation signal output by the function generator (18) and the kHz-level modulation signal output by the phase-locked amplifier (14) are respectively superimposed through the adder (17) and input into the laser controller (19), and the output laser frequency is modulated by the laser controller (19); the laser output by the diode laser (2) mounted on the temperature-controlled base (1) passes through the collimating lens (3) so that the laser beam is approximately parallel to the optical platform, passes through an isolator (4) to reduce the feedback rate, and then passes through a matching lens (5) to match the laser frequency with the mode of the resonant cavity. The laser passes through the first plane reflector (6) and the second plane reflector (7) in turn, and a piezoelectric ceramic (8) is attached to one side of the second plane reflector (7). Then, the laser enters the V-type three-mirror cavity (24); at the transmission end of the resonant cavity, the transmitted light of the V-type three-mirror cavity (24) enters the photodetector (11) through the first focusing lens (10), and the photodetector (11) inputs the transmitted signal into the phase-locked amplifier (14), and the phase-locked amplifier (14) inputs the transmitted signal into the phase-locked amplifier (14). The signal is mixed with the kHz modulated signal, and the error signal is demodulated and input to the PID controller (15). The PID controller (15) outputs the error signal to the high-voltage amplifier (16). Then, the high-voltage amplifier (16) adjusts the phase of the feedback light in real time by controlling the piezoelectric ceramic (8) on the second plane reflector (7), thereby achieving the locking of the laser frequency to the cavity mode frequency. At the reflection end of the resonant cavity, the reflected light of the V-shaped three-mirror cavity (24) passes through the third reflector (9), passes through the second focusing lens (12), and then enters the detector (13). The signal of the detector (13) is input to the biased DC beam splitter (20), and then passes through the power amplifier (21) and enters the mixing module (22). The other end of the mixing module (22) is connected to the function generator (18). The function generator (18) provides MHz-level high-frequency signal demodulation. The demodulated error signal is collected by the acquisition card (23). The collected error signal is calculated by the MATLAB program to obtain the power spectrum density image of the error signal, thereby evaluating the stability of the transmission frequency locking.

Images