Frequency stabilization device based on combination of F-P cavity and reference cell

Abstract

According to the frequency stabilizing device based on the combination of the F-P cavity and the reference cell, a traditional F-P cavity is filled with atomic molecule gas, a feedback signal acts on the cavity length of the F-P cavity through the saturated absorption frequency stabilizing technology, the cavity length is locked on the atomic molecule energy level transition frequency, the interference of the cavity length caused by the environmental influence is overcome, and the stability of the frequency stabilizing device is improved. Meanwhile, the F-P cavity with the locked cavity length is applied to PDH frequency stabilization of a laser. The device is compact in structure, short-term frequency stability of PDH frequency stabilization and long-term frequency stability of saturated absorption frequency stabilization can be considered, and the environmental adaptability of frequency-stabilized laser is improved.

Description

Technical Field

[0001] The present application relates to the field of laser frequency stabilization, and in particular to a frequency stabilization device based on the combination of an FP cavity and a reference cell. Background Art

[0002] Frequency-stabilized lasers have broad application prospects in the fields of atomic manipulation, laser communication, lidar, precision spectroscopy, etc. The current mainstream laser frequency stabilization methods include the PDH (Proud-Drever-Hall) frequency stabilization method with the FP cavity as the reference source and the saturation absorption frequency stabilization method with the atomic and molecular energy level transition frequency as the reference source. The former can achieve better short-term frequency stability, but the FP cavity length is easily affected by environmental interference, resulting in the degradation of the long-term frequency stabilization effect, while the latter can achieve better long-term frequency stability. At present, the technical difficulties of PDH frequency stabilization are mainly concentrated on the stability of the FP cavity. Although a good frequency stabilization effect can be achieved in a laboratory environment, it is difficult to achieve portability and multi-environment application.

[0003] PDH frequency stabilization technology combines frequency modulation technology and optical heterodyne detection technology. The laser is modulated by an electro-optic modulator, and the photodetector detects the reflected signal after the laser is vertically incident on the FP cavity. The error signal is multiplied and demodulated with the demodulation signal of the same frequency, and fed back to the laser, and finally the laser frequency is locked at the resonant frequency of the FP cavity. The resonant frequency of the FP cavity is ν = pc / (2nL), where p is an arbitrary positive integer, c is the speed of light, n is the refractive index, and L is the length of the FP cavity. It is not difficult to see that the stability of the resonant frequency depends to a large extent on the stability of the cavity length. At present, the ultra-stable lasers obtained by the laboratory using PDH technology mostly use materials with a small thermal expansion coefficient as the cavity and support of the FP cavity. At the same time, the cavity is placed in a thermal insulation and seismic isolation environment to ensure the stability of the cavity length as much as possible.

[0004] In the application process of portable lasers, it is inevitable to deal with different environments, and the frequency stability is difficult to reach the laboratory level. At this time, the stability of the FP cavity length is particularly important. Saturated absorption frequency stabilization technology uses the atomic and molecular energy level transition frequency as the frequency reference source, and the error signal after modulation and demodulation is fed back to the laser to achieve frequency stability. Under normal conditions, the energy level transition frequency has excellent stability, which also makes the saturated absorption frequency stabilization have good long-term frequency stability.

[0005] Therefore, based on the respective disadvantages of the above two methods, the present application proposes a laser frequency stabilization device suitable for use in transportation and multi-environment application scenarios. Summary of the invention

[0006] The purpose of the present invention is to propose a frequency stabilization device based on the combination of an FP cavity and a reference cell in response to the needs of portable and multi-environment laser applications. The device combines the advantages of the two frequency stabilization methods and can be integrated, providing a solution for achieving laboratory level in the future when frequency-stabilized lasers are portable and applied in multiple environments.

[0007] The present invention discloses a frequency stabilization device based on the combination of an FP cavity and a reference cell and a working method thereof. The frequency stabilization device includes a laser, an electro-optic modulator, a signal generator, a mixer, a servo control system, a photodetector, thick glass, a polarization beam splitter, a quarter-wave plate, an FP cavity filled with atomic and molecular gas, and piezoelectric ceramics.

[0008] During operation, the laser generates laser light and fine-tunes the working point so that a large light signal is detected at the transmission of the FP cavity filled with atomic and molecular gas. The sawtooth signal generator is turned on to generate the same frequency to control the laser and piezoelectric ceramics respectively, so that the laser frequency and the FP cavity resonant frequency are always consistent. The laser frequency can also transmit the FP cavity while periodically traversing within a certain range. At this time, a saturated absorption spectrum line will be observed at the transmission of the FP cavity. Fine-tune the laser working point and the piezoelectric ceramic voltage so that the saturated absorption spectrum line has only one peak and is in the center of the screen. Turn on the piezoelectric ceramic modulation, and multiply and demodulate it with the transmission signal at the mixer, and the error signal obtained is fed back to the piezoelectric ceramic. Turn on the electro-optic modulator to modulate the laser, and multiply and demodulate it with the monitoring signal reflected by the quarter-wave plate and the beam splitter prism, and the error signal obtained is fed back to the laser. Turn off the sawtooth wave, and turn on two servo control systems at the same time, so that the cavity length is locked to the FP cavity with stable energy level transition spectrum and the laser frequency is locked to the stable frequency laser at the resonant frequency of the FP cavity.

[0009] The device has a compact structure and can take into account both the short-term frequency stability of PDH frequency stabilization and the long-term frequency stability of saturated absorption frequency stabilization, thereby improving the environmental adaptability of the frequency-stabilized laser and providing a new solution for the portability and multi-environmental application of the frequency-stabilized laser.

[0010] Compared with the existing frequency stabilization scheme, the beneficial effects of the present invention are:

[0011] (1) The atomic and molecular gases are filled into the FP cavity, and the structure can be integrated, which is conducive to the realization of a portable design; (2) The design combines the advantages of saturated absorption frequency stabilization and PDH frequency stabilization, and locks the cavity length of the FP cavity, which is susceptible to environmental interference, at a stable atomic and molecular energy level transition frequency, thereby ensuring the stability of the FP cavity; (3) Two sets of servo control systems are used, and the PDH frequency stabilization achieved by the FP cavity with a stable cavity length ensures the stability of the stabilized frequency laser, which can ensure that the laser has good performance in a variety of environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0013] Figure 1 A schematic diagram of a frequency stabilization device based on the combination of a FP cavity and a reference cell according to the present invention;

[0014] Figure 2 The present invention is a flow chart of a frequency stabilization method based on the combination of an FP cavity and a reference cell. DETAILED DESCRIPTION

[0015] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. It should be noted that, in the absence of conflict, the various features in the embodiments of the present application can be combined with each other, and the combined embodiments are still within the scope of protection of the present application.

[0016] In the description of the present application, it should be noted that, unless otherwise specified and limited, the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. indicate the orientation or position relationship based on the orientation or position relationship shown in the drawings, or the orientation or position relationship in which the product of the application is usually placed when in use. They are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second", "third", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0017] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0018] See attached Figure 1The present application proposes a frequency stabilization device based on the combination of FP cavity and reference cell, including 1. laser light source, 2. servo system 1, 3. signal generator 1, 4. electro-optic modulator, 5. signal generator 2, 6. phase shifter 1, 7. mixer 1, 8. photodetector 1, 9. signal generator 3, 10. phase shifter 2, 11. servo system 2, 12. mixer 2, 13. thick glass 1, 14. polarization beam splitter prism, 15. quarter wave plate, 16. FP cavity injected with atomic and molecular gas, 17. piezoelectric ceramics, 18. thick glass 2, 19. photodetector 2, 20. reflector.

[0019] After passing through the electro-optic modulator 4, the laser is divided into two beams by the high-transmittance and low-reflection thick glass 13, one beam of transmitted light and one beam of reflected light; the transmitted light is reflected by the reflector 20 and the thick glass 18 as pump light, and the reflected light is used as detection light. The detection light enters the FP cavity, and the reflected signal is detected by the photodetector (PD) 18 through the quarter-wave plate 15 and the beam splitting prism 14, and the transmitted signal is detected by the photodetector 2 19, which are respectively used as signal sources for PDH frequency stabilization and saturation absorption frequency stabilization. The signal generator 1 3 generates a sawtooth wave sweep signal with the same frequency to control the laser current and the piezoelectric ceramic PZT voltage. The signal generator 2 5 and the signal generator 3 9 have different modulation signal frequencies due to different frequency stabilization methods, and modulate and demodulate the laser and the piezoelectric ceramic PZT respectively. The error signals after demodulation and filtering are respectively fed back and controlled by the servo system 1 2 and the servo system 2 11 to the laser light source 1 and the piezoelectric ceramic PZT 17, so as to ensure the stability of the cavity length of the FP cavity 16 and realize PDH frequency stabilization.

[0020] See attached Figure 2 The flow chart of the frequency stabilization method of the frequency stabilization device based on the combination of the FP cavity and the reference cell proposed in this application comprises the following steps:

[0021] Step 1: Turn on the laser and fine-tune the laser operating point so that a large optical signal can be detected at the transmission of the FP cavity when the laser is in free operation, even if the laser is near the resonance frequency of the FP cavity;

[0022] Step 2: Load the sawtooth wave signal of the same frequency to the laser and the piezoelectric ceramic PZT, and fine-tune the sawtooth wave amplitude so that the laser can observe a relatively clear and complete saturation absorption spectrum at the transmission point of the FP cavity, that is, the output light emitted by the laser can always transmit the FP cavity;

[0023] Step 3: Fine-tune the laser operating point, the piezoelectric ceramic PZT control voltage and the sawtooth wave amplitude simultaneously, so that only one peak can be observed in the saturated absorption spectrum, and it is in the center of the observation screen;

[0024] Step 4: Generate a sinusoidal signal to modulate the piezoelectric ceramic PZT. At the same time, another identical signal is phase-shifted and connected to the mixer. It is multiplied and demodulated with the signal at the transmission point of the FP cavity to generate an error signal. The error signal acts on the piezoelectric ceramic PZT.

[0025] Step 5: Start the electro-optic modulator EOM to generate a sinusoidal signal with a frequency much higher than the line width of the FP cavity itself, and use the electro-optic modulator to modulate the laser; another identical demodulated signal is phase-shifted and multiplied with the FP strong reflected light photodetector signal to demodulate and observe the error signal, which acts on the laser;

[0026] Step six, turn off the sawtooth wave signal and start two servo control systems at the same time to control the FP cavity length stability and the laser PDH frequency stabilization at the same time.

[0027] Implementation

[0028] Combined with Figure 1 , Attachment Figure 2 , a DFB laser with a central wavelength of 780nm and a power of 30mW starts from the laser light source 1, passes through EOM4 and is divided into two beams by thick glass 13. The transmitted light is used as pump light, and the reflected light is used as detection light to be vertically incident into the FP cavity 16 of the rubidium atomic gas. Fine-tuning the laser working point can monitor the optical signal on the photodetector 2 19, and the laser frequency is near the resonant frequency at this time. Turn on the signal generator 13 to load the same frequency sawtooth wave to the laser light source 1 and the piezoelectric ceramic PZT17 to ensure that the laser frequency can also transmit the FP cavity when it periodically traverses, so that the saturated absorption spectrum can be observed on the photodetector 2 19. Fine-tune the working point of the laser light source 1 and the control voltage of the piezoelectric ceramic PZT17 so that a peak in the absorption spectrum is in the center of the observation, and fine-tune the sawtooth wave amplitude of the signal generator 3 so that there is only this peak in the center of the observation screen. The signal generator 3 9 is turned on to generate a 10kHz sinusoidal signal to modulate the piezoelectric ceramic PZT17 and the same signal is processed by the phase shifter 2 10 and then multiplied and demodulated by the signal of the photodetector 2 19 at the mixer 2 12, and the piezoelectric ceramic PZT17 is feedback controlled by the servo system 2 11.

[0029] Turn on the signal generator 25 to generate a 20MHz sinusoidal signal, use EOM4 to modulate the laser, the modulated laser is reflected back by the F-P16 cavity, monitored by the quarter-wave plate 15 and the polarization splitter prism 14, and is multiplied and demodulated at the mixer 7. The error signal generated is fed back to the laser light source 1 through the servo system 2 to achieve PDH frequency stabilization.

[0030] Although the present invention has been disclosed as above with preferred embodiments, the embodiments are not intended to limit the present invention. Any equivalent changes or modifications made without departing from the spirit and scope of the present invention also fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the content defined by the claims of the present application.

Claims

1. A frequency stabilization device based on the combination of FP cavity and reference cell, characterized in that: The device comprises a laser light source (1), a servo system (2), a signal generator (3), an electro-optic modulator (EOM) (4), a signal generator (5), a phase shifter (6), a mixer (7), a photodetector (8), a signal generator (9), a phase shifter (10), a servo system (11), a mixer (12), a thick glass (13), a polarization beam splitter (14), a quarter-wave plate (15), an FP cavity (16) injected with atomic and molecular gas, a piezoelectric ceramic PZT (17), a thick glass (18), a photodetector (19), and a reflector (20); the laser light emitted by the laser light source passes through the electro-optic modulator (4) and is then divided into two beams, a transmitted light beam and a reflected light beam, by the high-transmittance and low-reflection thick glass (13); the transmitted light is reflected by the reflector (20) and the thick glass (18) as pump light, and the reflected light is used as detection light; The detection light is incident on the FP cavity, the reflected signal is detected by the photodetector 1 (8) through the quarter wave plate (15) and the beam splitting prism (14), and the transmitted signal is detected by the photodetector 2 (19), which are respectively used as signal sources for PDH frequency stabilization and saturation absorption frequency stabilization; Signal generator one (3) generates a sawtooth wave sweeping signal with the same frequency to control the laser current and the piezoelectric ceramic PZT voltage; signal generator two (5) and signal generator three (9) have different modulation signal frequencies to modulate and demodulate the laser and the piezoelectric ceramic PZT respectively; the error signals after demodulation and filtering are respectively fed back through servo system one (2) and servo system two (11) to control the laser light source (1) and the piezoelectric ceramic PZT (17), thereby ensuring the stability of the cavity length of the FP cavity (16) and achieving PDH frequency stabilization.

2. A frequency stabilization device based on the combination of FP cavity and reference cell according to claim 1, characterized in that: The FP cavity is filled with atomic and molecular gas, and reflected light and transmitted light are used simultaneously for frequency stabilization, which are used for PDH frequency stabilization and saturation absorption frequency stabilization respectively. The transmitted light is fed back to the piezoelectric ceramic PZT to lock the FP cavity length at the atomic and molecular energy level transition frequency, ensuring the stability of the cavity length.

3. A frequency stabilization device based on the combination of FP cavity and reference cell according to claim 2, characterized in that: The modulation and demodulation feedback system for PDH frequency stabilization composed of servo system one (2), signal generator two (5), phase shifter one (6), mixer one (7), and photodetector one (8) is the same as the system for saturated absorption frequency stabilization composed of signal generator three (9), phase shifter two (10), servo system two (11), mixer two (12), and photodetector two (19).

4. A method for employing a frequency stabilizing device according to any one of claims 1 to 3, characterized in that: The following steps are included: Step 1: Turn on the laser and fine-tune the laser operating point so that a large optical signal can be detected at the transmission of the FP cavity when the laser is in free operation, even if the laser is near the resonance frequency of the FP cavity; Step 2: Load the sawtooth wave signal of the same frequency to the laser and the piezoelectric ceramic PZT, and fine-tune the sawtooth wave amplitude so that the laser can observe a relatively clear and complete saturation absorption spectrum at the transmission point of the FP cavity, that is, the output light emitted by the laser can always transmit the FP cavity; Step 3: Fine-tune the laser operating point, the piezoelectric ceramic PZT control voltage and the sawtooth wave amplitude simultaneously, so that only one peak can be observed in the saturated absorption spectrum, and it is in the center of the observation screen; Step 4: Generate a sinusoidal signal to modulate the piezoelectric ceramic PZT. At the same time, another identical signal is phase-shifted and connected to the mixer. It is multiplied and demodulated with the signal at the transmission point of the FP cavity to generate an error signal. The error signal acts on the piezoelectric ceramic PZT. Step 5: Start the electro-optic modulator EOM to generate a sinusoidal signal with a frequency much higher than the line width of the FP cavity itself, and use the electro-optic modulator to modulate the laser; another identical demodulated signal is phase-shifted and multiplied with the FP strong reflected light photodetector signal to demodulate and observe the error signal, which acts on the laser; Step six, turn off the sawtooth wave signal and start two servo control systems at the same time to control the FP cavity length stability and the laser PDH frequency stabilization at the same time.

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