Method and system for evaluating transmission frequency locking stability of optical feedback cavity enhancement technology

Abstract

The invention discloses an optical feedback cavity enhancement technology transmission frequency locking stability assessment method and system, and belongs to the technical field of laser frequency stability assessment. In order to solve the problem of low error estimation accuracy caused by reduction of the resolution of a frequency spectrum in current frequency stability evaluation, the invention provides an evaluation system for transmission frequency locking stability of an optical feedback cavity enhancement technology and an optical path subsystem. Comprising 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 and piezoelectric ceramics. A third plane mirror, a first focusing lens, a photoelectric detector, a second focusing lens, a detector and a V-shaped three-mirror cavity; the frequency locking subsystem comprises a lock-in amplifier, a PID controller and a high-voltage amplifier; and the stability evaluation subsystem comprises an adder, a function generator, a bias direct current beam splitter, a power amplification module, a frequency mixing module and an acquisition card.

Description

Technical Field

[0001] The invention belongs to the technical field of laser frequency stability evaluation, and in particular relates to a method and system for evaluating transmission frequency locking stability of an optical feedback cavity enhancement technology. Background Art

[0002] Cavity enhancement technology is often used in the fields of nonlinear frequency conversion, nonclassical light field preparation, gas laser spectrum detection, etc., that is, coupling the laser to an external resonant cavity for resonance enhancement, achieving passive amplification, and increasing the laser power in the cavity. 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 a combination of optical feedback and PDH technology to lock the laser frequency to the cavity mode frequency of the resonant cavity, thereby achieving the enhancement of the laser power in the cavity. The specific scheme is that the laser output by the semiconductor laser is incident on the resonant cavity, and the resonant cavity feeds back the resonant laser into the semiconductor laser. The PDH technology is used to lock the phase of the feedback light so that it is the same as the phase of the laser emitted by the laser. At this time, the laser frequency is locked to the feedback light frequency.

[0003] PDH technology is a commonly used locking technology. During the locking process, the laser needs to be modulated first, and the error signal is generated by demodulating the reflected light or transmitted light signal of the cavity, so as to control and lock the phase of the feedback light. After locking, people often use the jitter of the error signal to evaluate the stability of the lock. However, in the process of demodulation and locking using transmitted light, there are certain limitations in using the error signal demodulated by the transmitted light to evaluate the frequency stability. This is because the power spectrum 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 more than 50khz. When the modulation frequency is low, the frequency interval between the sideband and the carrier is small, which will cause the sidebands in the spectrum to overlap. In frequency stability evaluation and error detection, overlapping sidebands 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 spectrum will decrease, resulting in inaccurate error estimation. Under low-frequency modulation, noise (especially low-frequency noise) is easy to interfere with the sideband signal. In this case, since the sideband is too close to the carrier, the impact of the noise signal can be easily misunderstood as a frequency error signal, thereby amplifying the error and causing the system to be unable to accurately estimate the stability of the laser frequency. Summary of the invention

[0004] In view of the problem that the resolution of the spectrum is reduced, resulting in low error estimation accuracy in the current frequency stability evaluation, the present invention provides a method and system for evaluating the transmission frequency locking stability using an optical feedback cavity enhancement technology.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

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

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

[0008] The semiconductor laser is installed on a temperature-controlled base, and the function generator and the phase-locked amplifier respectively give a modulation signal to the laser controller through an adder, and the laser controller modulates the output laser frequency; the laser forms a parallel beam through a collimating lens, passes through an isolator and enters a matching lens for mode matching, and then the laser is reflected to the second plane reflector through a first plane reflector, and then reflected by the second plane reflector into a V-shaped three-mirror cavity for resonance; the resonant laser transmitted through the front cavity mirror of the V-shaped three-mirror cavity is fed back to the semiconductor laser in the original path, and the laser transmitted through the rear cavity mirror of the V-shaped three-mirror cavity is focused by a first focusing lens and then enters a photoelectric The detector, 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, the high-voltage amplifier controls the piezoelectric ceramic PZT fixed on the second plane reflector; the direct reflected light of the V-shaped three-mirror cavity passes through the third reflector, is focused by the second focusing lens and then enters the detector, the detector is connected to the biased DC beam splitter, the biased DC beam splitter is connected to the power amplifier, and enters the mixing module after passing through the power amplifier, 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 the computer.

[0009] Furthermore, the matching lens is used to perform frequency matching with the resonant cavity mode to ensure maximum efficiency of laser coupling into the resonant cavity.

[0010] Furthermore, the laser controller is used to control and modulate the output laser frequency.

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

[0012] Furthermore, the modulation signal provided by the function generator is of the MHZ order; the modulation signal provided by the lock-in amplifier is of the khz order.

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

[0014] Furthermore, the V-shaped three-mirror cavity is used to reduce the interference of directly reflected light and ensure the precise locking of the laser frequency and the cavity mode.

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

[0016] Furthermore, the detector is provided with two 30db attenuation filters.

[0017] Furthermore, the isolator is used to reduce the feedback rate of the feedback light to 10 -4 -10 -5 Magnitude.

[0018] A method for evaluating the transmission frequency locking stability of an optical feedback cavity enhancement technology, wherein a MHz-level modulation signal output by a function generator and a kHz-level modulation signal output by a phase-locked amplifier are respectively superimposed through an adder and input into a laser controller, and the laser controller modulates the output laser frequency;

[0019] The laser output by the diode laser installed on the temperature-controlled base passes through a collimating lens so that the laser beam is approximately parallel light parallel to the optical platform, passes through an isolator to reduce the feedback rate, and then passes through a matching lens to match the laser frequency with the mode of the resonant cavity. The laser passes through the first plane reflector and the second plane reflector in turn, and a piezoelectric ceramic is attached to one side of the second plane reflector. Then the laser enters the V-shaped three-mirror cavity; at the transmission end of the resonant cavity, the transmitted light of the V-shaped three-mirror cavity enters the photodetector through the first focusing lens, and the photodetector inputs the transmission signal into the phase-locked amplifier. The phase-locked amplifier mixes the transmission signal and the kHz modulation signal, demodulates the error signal and inputs it to the PID controller, and the PID controller outputs it to the high-voltage amplifier. Then the high-voltage amplifier controls the piezoelectric ceramic on the second plane reflector to adjust the feedback light phase in real time, thereby realizing the locking of the laser frequency to the cavity mode frequency.

[0020] At the reflection end of the resonant cavity, the reflected light of the V-shaped three-mirror cavity passes through the third reflector, then passes through the second focusing lens and enters the detector. The signal of the detector is input to the biased DC beam splitter, and then passes through the power amplifier and enters the mixing module. The other end of the mixing module is connected to the function generator, which provides MHz-level high-frequency signal demodulation. The demodulated error signal is collected through the acquisition card; the collected error signal is calculated by the MATLAB program to obtain the power spectral density image of the error signal, so as to evaluate the stability of the transmission frequency locking.

[0021] The theoretical support utilized by the present invention is as follows:

[0022] When performing transmission frequency locking, the selection of modulation frequency will be restricted by the line width of the resonant cavity. Specifically, frequencies higher than the line width of the resonant cavity cannot pass through the resonant cavity. For high-fineness resonant cavities, the line width of the cavity membrane is usually in the kHz range. Therefore, the modulation frequency should also be selected in the kHz range. Under low-frequency modulation (such as less than 50kHz), since the modulation frequency is close to the line width of the resonant cavity, the interval between the sideband and the carrier becomes smaller, making 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 includes the average phase noise of the sideband. Especially in the case of strong low-frequency noise, the mixture of carrier and sideband phase noise makes it impossible to accurately estimate the frequency stability of the laser using the error signal. Therefore, we simultaneously perform high-frequency modulation (MHz range) on the laser frequency, and demodulate the resonant cavity reflected light signal to obtain the error signal, and use this error signal to evaluate the stability of transmission locking. High-frequency modulation can ensure a clear distinction between the carrier and the sideband, so that the obtained error signal 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 invention has the following advantages:

[0024] 1. The present invention realizes the locking of the laser frequency to the cavity mode frequency of the resonant cavity based on optical feedback and feedback light phase control. Compared with the traditional direct locking of the laser and the resonant cavity frequency, the present invention requires a lower locking bandwidth and has stronger anti-interference ability.

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

[0026] Figure 1 An example of a system for evaluating the transmission locking stability of an optical feedback cavity enhancement system.

[0027] Figure 2 The power spectral density image of the error signal obtained for the transmitted light locking stability.

[0028] Figure numerals: 1, temperature control base; 2, diode laser; 3, collimating lens; 4, isolator; 5, matching lens; 6, first plane reflector; 7, second plane reflector; 8, piezoelectric ceramic (PZT); 9, third plane reflector; 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, biased DC beam splitter (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 gain a deeper understanding of the present invention, we will provide a comprehensive and detailed description of the present invention. However, the present invention has multiple implementations and is not limited to the specific examples listed herein. The presentation of these examples is intended to deepen the comprehensive understanding of the disclosure of the present invention.

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

[0031] The optical path subsystem includes: 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, and a piezoelectric ceramic (PZT) 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 includes: a phase-locked amplifier 14, a PID controller 15, and a high-voltage amplifier 16; the stability evaluation subsystem includes: an adder 17, a function generator 18, a biased DC beam splitter (BIAS-TEE) 20, a power amplifier module 21, a mixing module 22, and an acquisition card 23;

[0032] The semiconductor laser 2 is mounted on the temperature control base 1, and 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 controller 19 modulates the output laser frequency; the laser forms a parallel light beam through the collimating lens 3, passes through the isolator 4 and enters the matching lens 5 for mode matching, and then the laser is reflected to the second plane reflector 7 through the first plane reflector 6, and then reflected by the second plane reflector 7 into the 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, and the laser transmitted through the rear cavity mirror of the V-shaped three-mirror cavity 24 is focused by the first focusing lens 10 and enters the photodetector 11, and the photodetector The detector 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 a piezoelectric ceramic (PZT) 8 fixed on a second plane reflector 7; the direct reflected light of the V-shaped three-mirror cavity 24 passes through a third reflector 9, is focused by a second focusing lens 12, and then enters a 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.

[0033] Furthermore, 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.

[0034] Furthermore, the laser controller 19 is used to control and modulate the output laser frequency.

[0035] Furthermore, the isolator is used to reduce the feedback rate of the feedback light to 10 -4 -10 -5 Magnitude.

[0036] Furthermore, the piezoelectric ceramic (PZT) 8 is used to precisely adjust the phase of the laser feedback to achieve precise locking of the laser frequency.

[0037] Furthermore, the modulation signal provided by the function generator 18 is 1.5 MHZ; the modulation signal provided by the lock-in amplifier 14 is 30 khz.

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

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

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

[0041] Furthermore, the detector 13 is provided with two 30db attenuation filters.

[0042] A method for evaluating the transmission frequency locking stability of an optical feedback cavity enhancement technology, wherein a MHz-level modulation signal output by a function generator 18 and a kHz-level modulation signal output by a phase-locked amplifier 14 are respectively superimposed by an adder 17 and then input into a laser controller 19, and the laser controller 19 modulates the output laser frequency;

[0043] The laser output by the diode laser 2 installed on the temperature control base 1 passes through the collimating lens 3 so that the laser beam is approximately parallel light 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 sequence. A piezoelectric ceramic 8 is attached to one side of the second plane reflector 7, and then the laser enters the V-shaped three-mirror cavity 24; at the transmission end of the resonant cavity, the transmitted light of the V-shaped 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, and the phase-locked amplifier 14 mixes the transmission signal and the kHz modulation signal, demodulates the error signal and inputs it to the PID controller 15, and the PID controller 15 outputs it to the high-voltage amplifier 16, and then the high-voltage amplifier 16 controls the piezoelectric ceramic 8 on the second plane reflector 7 to adjust the feedback light phase in real time to achieve 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-shaped three-mirror cavity 24 passes through the third reflector 9, then passes through the second focusing lens 12 and 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, and 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, so as to evaluate the stability of the transmission frequency locking.

[0045] like Figure 2 As shown in the figure, it is a power spectrum density image drawn using the error signal demodulated by reflected light. We can see that in the low-frequency region around 1000 Hz, the PDH technology using transmitted light locking has a certain inhibitory effect on low-frequency noise.

[0046] The contents not described in detail in the specification of the present invention belong to the prior art known to the professional and technical personnel in the field. Although the illustrative specific embodiments of the present invention are described above to facilitate the understanding of the present invention by the technical personnel in the field, it should be clear that the present invention is not limited to the scope of the specific embodiments. For the ordinary technical personnel in the field, as long as various changes are within the spirit and scope of the present invention defined and determined by the attached claims, these changes are obvious, and all inventions and creations using the concept of the present invention are protected.

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), and 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 mixing module (22), and an acquisition card (23); The semiconductor laser (2) is mounted on a temperature control 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 passes through a collimating lens (3) to form a parallel beam, passes through an isolator (4) and enters a matching lens (5) for mode matching; the laser then passes through a first plane reflector (6) to reflect to a second plane reflector (7), and then is reflected by the second plane reflector (7) to enter 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 then 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 a piezoelectric ceramic (8) fixed on a second plane reflector (7); the direct reflected light of the V-shaped three-mirror cavity (24) passes through a third reflector (9), is focused by a second focusing lens (12), and then enters a 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) to provide 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. According to claim 1, the optical feedback cavity enhancement technology transmission frequency locking stability evaluation system is characterized by: The matching lens (5) is used to perform frequency matching with the resonant cavity mode to ensure that the laser is coupled into the resonant cavity with maximum efficiency.

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

4. According to claim 1, the optical feedback cavity enhancement technology transmission frequency locking stability evaluation system is characterized by: The piezoelectric ceramic (8) is used to accurately adjust the phase of laser feedback to achieve accurate 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 accurate 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 fineness of 16000 and a line width 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 the transmission frequency locking stability of an optical feedback cavity enhancement technology, characterized in that: 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 an adder (17) and input into a laser controller (19), and the laser frequency output is modulated by the laser controller (19); the laser light output by the diode laser (2) installed on the temperature control base (1) passes through a 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 light passes through a first plane reflector (6) and a second plane reflector (7) in sequence, and a piezoelectric ceramic (8) is attached to one side of the second plane reflector (7), and then the laser light enters a V-shaped three-mirror cavity (24); at the transmission end of the resonant cavity, the transmitted light of the V-shaped three-mirror cavity (24) enters a photodetector (11) through a first focusing lens (10), and the photodetector (11) inputs the transmission signal into the phase-locked amplifier (14), and the phase-locked amplifier (14) transmits the transmission signal. The signal is mixed with a kHz modulation signal, and an error signal is demodulated and input to a PID controller (15). The PID controller (15) outputs the error signal to a 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 realizing 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 a biased DC beam splitter (20), and then passes through a power amplifier (21) and enters a mixing module (22). The other end of the mixing module (22) is connected to a function generator (18). The function generator (18) provides a high-frequency signal demodulation of the MHz level. The demodulated error signal is collected by an acquisition card (23). The collected error signal is calculated by a MATLAB program to obtain a power spectrum density image of the error signal, thereby evaluating the stability of the transmission frequency locking.

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