486nm blue laser frequency stabilization device based on fabry-perot cavity

Abstract

The application provides a 486nm blue laser frequency stabilization device based on a Fabry-Perot cavity, which comprises a 972nm laser, an optical isolator, an optical fiber beam splitter, a frequency doubling crystal, a phase modulator, an optical fiber collimating head, a Fabry-Perot cavity, a modulation and demodulation module and a PID control module. After passing through the optical fiber beam splitter, the 972nm laser generates two paths, one of which enters the Fabry-Perot cavity after phase modulation, and the frequency is locked on the cavity, and after obtaining the error signal, the 972nm laser is feedback adjusted by the PID control module circuit to realize frequency stabilization. The other path passes through the frequency doubling crystal to output 486nm laser, that is, the 486nm blue light source with high stability is obtained by stabilizing the 972nm laser. The application has the advantages of simple and compact structure, good reliability of the optical path system, good stability of the output 486nm blue light, and can meet the needs of high-precision ocean laser radar detection and communication.

Description

Technical Field

[0001] This invention belongs to the field of laser frequency stabilization technology, specifically relating to a device for frequency stabilization of a 972nm laser based on a Fabry-Perot cavity, and subsequently frequency doubling to output a 486nm blue frequency-stabilized laser. Background Technology

[0002] 486nm blue light possesses strong deep-sea penetration capabilities and low transmission loss in deep ocean waters, making it effective for deep-sea exploration and information transmission, marine chlorophyll detection, and underwater target detection. It also holds significant application potential in both military and civilian fields, including resource surveys and the protection of maritime rights. In particular, the 486nm wavelength is well-matched to the Fraunhofer dark line of the sun, exhibiting low background light interference and thus enhancing radar detection capabilities during the day. Therefore, 486nm blue laser light is an important light source for underwater laser communication and detection.

[0003] PDH (Pound-Drever-Hall) frequency stabilization technology is a widely used active frequency stabilization technique. Optical Fabry-Perot cavities are primarily made of glass with ultra-low coefficient of thermal expansion and can serve as a stable frequency reference. The reflective FP Fabry-Perot cavity is unaffected by the FP Fabry-Perot cavity response time, allowing for timely measurement and handling of frequency drift.

[0004] Underwater laser detection and communication is a major research focus. When detecting ocean profile echo signals, the signals contain scattering from suspended particles and water molecules. Particle scattering is influenced by the type of particles. Blue light hyperspectral detection requires high-power output, narrow linewidth, and high frequency stability from the laser. To achieve accurate measurement of the optical parameters of underwater particles, breakthroughs in blue light hyperspectral resolution laser detection technology are urgently needed. Due to various factors such as the working environment, the laser center wavelength is prone to random drift, affecting detection accuracy. However, the 486nm blue light wavelength has the advantage of matching the Fraunhofer dark line of the sun and low background light interference, which can improve radar detection capabilities during the day. Therefore, research on the marine applications of the 486nm blue light band is gradually becoming a hot topic. Thus, there is an urgent need for 486nm blue lasers with frequency stabilization capabilities to meet the needs of marine detection and communication applications. By locking the 972nm laser onto the cavity based on a Fabry-Bohr cavity, the frequency of the 972nm laser is stabilized. By combining a frequency doubling crystal with a frequency stabilization device, a highly stable 486nm blue light can be output, thereby achieving the goal of outputting a seed light source with narrow linewidth and high stability, and better meeting the needs of relevant marine underwater applications. Summary of the Invention

[0005] The purpose of this invention is to address the problems in the prior art by proposing a 486nm blue laser frequency stabilization device based on a Fabry-Perot cavity, so as to obtain a highly stable 486nm laser output with a narrow linewidth, thereby meeting the needs of high-precision marine lidar detection and communication.

[0006] The basic idea of ​​this invention is:

[0007] By splitting the output of the 972nm laser, one path enters the Fabry-Perot cavity after phase modulation, locking its frequency on the cavity. After acquiring the error signal, the 972nm laser is stabilized by feedback adjustment through PID circuits, etc. The other path outputs 486nm laser through a frequency doubling crystal. In other words, a highly stable 486nm blue light source is obtained by stabilizing the 972nm laser.

[0008] The technical solution of the present invention is as follows:

[0009] It includes a 972nm laser, an optical isolator, an optical fiber beam splitter, a phase modulator, an optical fiber collimator, a Fabry-Perot cavity, a photodetector, a modulation and demodulation module, and a PID control module. The 972nm laser contains an SMA current tuning port for receiving the feedback adjustment signal output from the PID control module.

[0010] After passing through an optical isolator, the 972nm laser enters an optical fiber beam splitter. The optical fiber beam splitter splits the laser beam, with one beam passing through a frequency doubling crystal to output 486nm blue light, and the other beam passing through a phase modulator for phase modulation. The modulated laser is then output through an optical fiber collimator and enters a Fabry-Perot cavity. The Fabry-Perot cavity reflects the modulated light multiple times and outputs it to a photodetector through a rear cavity mirror.

[0011] The photodetector receives and processes the optical signal transmitted from the Fabry-Perot cavity rear mirror, converting it into an electrical signal and transmitting it to the modulation and demodulation module. The modulation and demodulation module outputs an radio frequency signal to the phase modulator for phase modulation of the 972nm laser. Simultaneously, the intrinsic reference signal of the radio frequency signal output by the modulation and demodulation module is mixed with the received electrical signal to obtain a frequency drift error signal, which is then transmitted to the PID control module. The PID control module processes the received frequency drift error signal and outputs a feedback adjustment signal to the 972nm laser through the SMA current tuning port, controlling the 972nm laser to perform current tuning of the laser frequency, thereby achieving a stable frequency output of the 972nm laser and ultimately realizing a stable frequency output of 486nm blue light.

[0012] Furthermore, the polarization extinction ratio of the fiber optic beam splitter is greater than 18dB.

[0013] Furthermore, the frequency doubling crystal (4) is an LBO crystal or a BIBO crystal.

[0014] Furthermore, the phase modulator is an optical fiber coupled lithium niobate electro-optic phase modulator with a modulation bandwidth of not less than 150MHz and an insertion loss of less than 3dB.

[0015] Furthermore, the Fabry-Perot cavity is made of glass with a low coefficient of expansion, placed inside an Invar shell, and then placed inside a constant temperature control device. The precision of the Fabry-Perot cavity is higher than 1000.

[0016] Furthermore, the photodetector is an indium gallium arsenide photodetector, and the bandwidth of the photodetector needs to be greater than the radio frequency signal bandwidth of the phase modulator.

[0017] Furthermore, the frequency of the radio frequency signal output by the modulation circuit of the modulation and demodulation module is adjustable.

[0018] Furthermore, the PID control module is a PID control circuit.

[0019] The present invention has the following beneficial effects:

[0020] This invention discloses a 486nm blue laser frequency stabilization device based on a Fabry-Perot cavity. A 972nm laser is split by an optical fiber beam splitter. One beam is output as a 486nm blue light source via a frequency doubling crystal, while the other beam passes through a phase modulator and then through an optical fiber collimator before entering the Fabry-Perot cavity. The 972nm laser frequency is stabilized on the Fabry-Perot cavity. A photodetector converts the optical signal into the required sideband error signal, which is then fed into a modulation and demodulation module. After mixing, the signal enters a PID control module. The PID circuit outputs a feedback signal to the SMA current tuning port of the 972nm laser. The PID control circuit continuously adjusts the output laser frequency based on the deviation between the feedback signal and the set value, thereby suppressing external interference and stabilizing the laser frequency. This achieves tuning compensation for the frequency drift of the 972nm laser stabilized on the reference cavity, ultimately stabilizing the frequency of the frequency-doubled 486nm laser and outputting a narrow-linewidth, high-stability blue light source.

[0021] This invention features a simple and stable structure. Both the beam splitting and modulation sections are made of optical fiber, and the various components can be connected via jumper heads or fiber optic fusion splices, making debugging easy. The output from the collimator enters the Fabry-Perot cavity, and the optical path requirements can be met with simple lens position adjustments. The structure is compact and easy to adjust.

[0022] By stabilizing the frequency of a 972nm laser and then using a frequency doubling crystal to double its frequency to output a 486nm blue light source, the laser exhibits high frequency stability and narrow linewidth. Its 486nm wavelength is better matched to the Fraunhofer dark line of the sun, resulting in lower background light interference. This technology is suitable for high-precision marine lidar detection and communication applications. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the 486nm blue laser frequency stabilization device based on a Fabry-Perot cavity according to the present invention.

[0024] Among them, 1 is a 972nm laser, 2 isolator, 3 is fiber beam splitter, 4 is frequency doubling crystal, 5 is phase modulator, 6 is fiber collimator, 7 is Fabry-Perot cavity, 8 is photodetector, 9 is modulation and demodulation module, and 10 is PID control module. Detailed Implementation

[0025] Specific embodiments of the present invention will be described in further detail with reference to the accompanying drawings.

[0026] Figure 1 A schematic diagram of an embodiment of the present invention is shown. This embodiment relates to a 486nm blue laser frequency stabilization device based on a Fabry-Perot cavity. The output front end of the fiber collimator is entirely a fiber optic path, containing a phase modulator and a frequency doubling crystal. It has the advantages of compact structure, simplicity and easy adjustment. The Fabry-Perot cavity is a spatial optical path. The signal output from the Fabry-Perot cavity is received by the modulation and demodulation module. After modulation and demodulation, the signal is mixed and processed before entering the PID control module to generate a feedback signal. The 972nm laser is tuned and its output frequency is controlled according to the error signal to maintain the stability of the laser's output laser frequency.

[0027] Example

[0028] This invention discloses a 486nm blue laser frequency stabilization device based on a Fabry-Perot cavity. Fabry-Perot cavity-based frequency stabilization utilizes an ultra-stable optical cavity as a frequency reference. Through electro-optic phase modulation and phase demodulation, an error signal is generated. This error signal is then controlled by adjusting the laser's operating current to achieve faster and more precise tuning control of the 972nm laser frequency, thereby realizing frequency stabilization. Specifically, this 486nm blue laser frequency stabilization device based on a Fabry-Perot cavity, as follows... Figure 1As shown, it includes: a 972nm laser 1, used to output a 972nm laser to be stabilized. After passing through an optical isolator 2 and an optical fiber beam splitter 3, it is split into two paths. One path enters a frequency doubling crystal 4 and outputs a 486nm laser. The other path enters a phase modulator 5, which modulates to form a sideband. It exits through an optical fiber collimator 6 and enters a Fabry-Perot cavity 7. After multi-beam resonance within the cavity, it is transmitted from the rear end of the cavity mirror and enters a photodetector 8 to be converted into an electrical signal.

[0029] The modulation and demodulation module 9 transmits an radio frequency signal to the phase modulator 5, causing the phase modulator 5 to perform phase modulation on the 972nm laser. At the same time, the modulation and demodulation module 9 processes the electrical signal and mixes it with the intrinsic reference signal of the radio frequency signal to obtain an error signal. The error signal is then output as a feedback signal by the PID control module 10 and fed back to the SMA current tuning port of the 972nm laser 1. By controlling the tuning of the 972nm laser 1, the output laser frequency of the 972nm laser 1 is stabilized, thereby locking the laser frequency to the Fabry-Perot cavity.

[0030] Specifically, in this embodiment, the 972nm laser is a DFB single-frequency narrow-linewidth laser. This DFB single-frequency narrow-linewidth laser can be a fiber laser or other types of lasers, with an output optical power greater than 1mW. The single-frequency narrow-linewidth laser has a built-in temperature monitoring device, such as a temperature sensor, to ensure stable operating temperature. Simultaneously, the output laser of this single-frequency narrow-linewidth laser is linearly polarized and has current tuning functionality, including an SMA current tuning port for receiving signals for current tuning during frequency stabilization. The laser frequency feedback adjustment signal generated by the PID control module can control the 972nm laser 1 to perform high-speed, small-range, fine calibration of the laser output frequency. Compared to most methods that use PZT piezoelectric ceramics to control the cavity length and adjust the laser frequency, in this embodiment, controlling the current of the 972nm laser 1 to perform high-speed, small-range, fine calibration of the laser output frequency results in a simpler optical path and circuit structure. It also provides more sensitive and precise sensing and adjustment of minute frequency changes, while avoiding the use of high-voltage electricity for driving, reducing the use of high-voltage power supplies, and making the overall structure more stable and energy-efficient.

[0031] The aforementioned fiber optic beam splitter 3 splits the 972nm laser output from the isolator 2 into two beams. One beam serves as a frequency-stabilized optical signal that enters the subsequent optical path for frequency stabilization, while the other beam serves as the output light from the 972nm laser 1 for use by the subsequent frequency-doubling crystal 4. In this embodiment, the fiber optic beam splitter 3 is preferably a polarization-maintaining fiber optic beam splitter with a polarization extinction ratio greater than 18dB. The splitting ratio of the fiber optic beam splitter can be selected according to the actual application requirements.

[0032] The aforementioned phase modulator 5 is used to perform phase modulation on the laser frequency, generating two sideband frequency signals with a certain frequency difference near the laser center frequency. In this embodiment, the phase modulator 5 is an optical fiber coupled lithium niobate electro-optic phase modulator. The modulation bandwidth of the optical fiber coupled lithium niobate electro-optic phase modulator is not less than 150MHz, the insertion loss is less than 3dB, and the input and output pigtails of the optical fiber coupled phase modulator are single-mode polarization-maintaining pigtails.

[0033] The laser output from the phase modulator 5 passes through the fiber collimator 6 and enters the spatial optical path. The fiber collimator 6 needs to ensure good collimation of the output beam. The spot size is selected according to the specific application. In this example, the output spot of the fiber collimator 6 is about 0.6 mm. It is collimated and incident into the Fabry-Perot cavity 7. After resonance, the output laser signal is transmitted through the rear cavity mirror and enters the photodetector 8. When monitoring the transmitted signal with an oscilloscope, if there is a multimode situation, a convex lens with a suitable focal length can be selected for mode matching to ensure that the signal is a single-mode pulse peak.

[0034] The Fabry-Perot cavity 7 selected above is made of low-expansion-coefficient glass. Its cavity mirror coating meets the relevant transmission and reflection characteristics of 972nm laser. It is encapsulated with Invar materials to ensure that its precision and wavelength selectivity are not affected by external temperature and vibration, forming a very stable reference cavity. During debugging, a piezoelectric scanning device is used to monitor and ensure that it is in single-longitudinal-mode operation. By driving the piezoelectric scanning device on the cavity to generate periodic sawtooth waves, the generation of single-longitudinal mode within a sawtooth wave scanning cycle can be monitored. When there is only one transmission peak signal in a sawtooth wave cycle, the laser operates in single-longitudinal mode in the cavity, avoiding the generation of multiple transmission peaks that affect the acquisition of transmission signals. Furthermore, by observing whether there is a difference between the corresponding positions of the transmission peak and the sawtooth wave signal at different times, it can be seen that the output frequency of the laser is randomly drifting or even exhibiting mode skipping. At the same time, it ensures the normal generation of the double-sideband of the modulation signal. This Fabry-Perot cavity can be encapsulated with constant temperature and vibration isolation, placed on a vibration damping platform, and temperature controlled by a temperature control box. Based on the design requirements, a Fabry-Perot cavity with a precision of approximately 1500 was selected, featuring a confocal cavity structure. To better meet application requirements, its size was also minimized to within 50mm to reduce the overall size of the equipment.

[0035] The 972nm laser 1, isolator 2, fiber beam splitter 3, frequency doubling crystal 4, phase modulator 5, and fiber collimator 6 are connected in sequence. Since isolator 2, fiber beam splitter 3, frequency doubling crystal 4, phase modulator 5, and fiber collimator 6 are all fiber optic devices, the connection between each fiber optic device is achieved through fiber optic fusion splicing or by connecting via patch cord flanges, ensuring the reliability of the connection between each fiber optic device and the stability of the polarization state.

[0036] The three components—photodetector 8, modulation / demodulation module 9, and PID control module 10—are interconnected. Photodetector 8 receives the optical signal emitted from the Fabry-Perot cavity via the rear cavity mirror and is connected to modulation / demodulation module 9. Modulation / demodulation module 9 outputs an RF signal to phase modulator 5 to modulate the laser in the optical path. Simultaneously, modulation / demodulation module 9 outputs an intrinsic reference signal for the RF signal and mixes the photoelectric signal received by photodetector 8 with the intrinsic reference signal output by modulation / demodulation module 9. PID control module 10 is connected to both modulation / demodulation module 9 and 972nm laser 1. After obtaining the frequency drift error signal, this error signal is transmitted to PID control module 10. PID control module 10 amplifies the amplitude and delays the phase of the error signal and feeds it back to 972nm laser 1, controlling 972nm laser 1 to perform current tuning of the laser frequency, thus achieving frequency stabilization.

[0037] The aforementioned photodetector 8 includes an indium gallium arsenide photodiode and a signal amplification circuit. The photodiode has a cathode grounded and covers a wavelength of 972nm. To address the issue of weak dark current generated by the photodiode due to weak light signal during use, a transimpedance gain amplification circuit is added to the photodiode. When using an oscilloscope to detect the transmission signal, an adjustable transimpedance gain of 10kV / A, 100kV / A, or 1000kV / A can be selected according to the transmission peak signal to better meet the requirements for acquiring the transmission signal.

[0038] The aforementioned modulation and demodulation module 9 includes a modulation circuit and a demodulation circuit. The modulation circuit is connected to the phase modulator 5 and outputs a radio frequency signal to the phase modulator 5, so that the phase modulator 5 modulates the laser in the optical path, and the frequency of the output radio frequency signal can be adjusted. The demodulation circuit is connected to the photodetector and the PID control module respectively. The demodulation circuit has a built-in analog mixing and demodulation function, which can mix and demodulate the electrical signal output by the photodetector 8 with the intrinsic reference signal output by the modulation and demodulation module 9 to obtain the frequency drift error signal of the 972nm laser 1. The intrinsic reference signal is phase-shifted by a phase shifter to cooperate with the mixer and loop filter to detect the error signal. Unwanted harmonics are filtered out by a low-pass filter to obtain a dispersive differential error signal. The output signal of the mixer is filtered by a low-pass filter, which can effectively suppress high-frequency signals in the mixing signal and only allow low-frequency signals to pass.

[0039] The aforementioned PID control module 10 is a PID control circuit used to amplify the amplitude and delay the phase of the error signal output from the modulation and demodulation module 9, feeding it back to the 972nm laser 1 to control the current tuning of the 972nm laser 1 and stabilize the frequency of the laser output from the 972nm laser 1. The main function of the PID control module in the system is to perform a series of proportional, derivative, and integral operations on the demodulated PDH error signal. The PID module used in this example is a series PID structure, which includes two stages of PI to meet signal processing under different conditions. The first stage is a low-frequency PIP plus a high-frequency D, which can further increase the low-frequency gain; the second stage is a regular PI. The first stage can be optionally turned off as needed, using only the second-stage PI for locking. Simultaneously, according to different feedback requirements, dual feedback outputs are provided: one output goes only through the first-stage PID to the high-speed feedback port; the other output goes through the PID and then through the PI to the low-speed feedback interface. By combining high-speed PIPD feedback with low-speed PI feedback, a larger low-speed locking range and higher locking bandwidth can be achieved. During operation, the center point of the output voltage is scanned and locked by setting appropriate output bias voltage and scan range intervals to obtain the correct reference signal. The modulation and demodulation phase and amplitude are set, and the error is zeroed to obtain the correct error signal. A correct error signal satisfies high signal-to-noise ratio, high slope, and no zero-point offset. Adjusting different demodulation phases can obtain a steeper, higher-slope error signal, and adjusting the modulation amplitude can increase the error signal amplitude. Simultaneously, the module's feedback output, including scanning signals, determines the correct feedback direction. Under certain fine PIP and PID gain adjustments (setting range 0-60000, representing gain 0-1), a certain P-component feedback is generated, widening the reference signal (transmitted signal). After selecting a suitable signal width, the primary PID parameters are set. Before simple locking, basic integral settings are required to complete the locking. The integral setting parameters are set to 330Hz, keeping the PIP setting shorted and disabled, and the derivative setting shorted and disabled. When signal locking begins, the locking flag value is compared with the reference signal (transmitted signal). During signal scanning, once a certain position is reached where the reference signal exceeds the lock flag value, scanning stops and locking is initiated. Finally, PID parameters are optimized. After locking is complete, further optimization of PIP settings, derivative settings, and error zeroing can achieve better signal feedback output adjustment and frequency stabilization.

[0040] When connecting the photodetector 8, the modulation and demodulation module 9, the PID control module 10 and the 972nm laser 1, the signal lines are connected by radio frequency lines and the power supply lines are connected by wires.

[0041] The aforementioned frequency doubling crystal 4, after being frequency stabilized, outputs a high-frequency stable 972nm laser from the 972nm laser 1. This laser beam passes through the fiber optic beam splitter 3, with one beam entering the frequency doubling crystal 4. After passing through the frequency doubling crystal, it emits 486nm blue light, thus exhibiting the advantages of narrow linewidth and high frequency stability. Frequency doubling crystals can primarily be LBO or BIBO crystals. LBO crystals are slightly deliquescent, possess good physicochemical properties, good optical homogeneity, low internal envelope, high damage threshold, moderate nonlinear optical coefficient, small walk-off angle, and large allowable angle. They offer advantages such as a high damage threshold, wide transmission band and allowable angle, and small walk-off angle, making them widely used in engineering applications. Compared to LBO crystals, BIBO crystals are less prone to deliquescence, have a higher laser damage threshold, and exhibit more stable physicochemical properties. Furthermore, the effective nonlinear coefficient of BIBO crystals is approximately three times that of LBO crystals, resulting in significantly higher frequency doubling conversion efficiency, which is far superior to LBO crystals under the same size conditions. This makes BIBO crystals more suitable for applications in high-power laser systems. However, due to the more complex manufacturing process and the relatively immature research on BIBO crystals, their price is relatively higher, and the beam quality for frequency doubling output is also inferior to that of LBO crystals. Therefore, different frequency doubling crystals can be selected based on specific application requirements and the specific laser source output.

[0042] Using the above technical solution, the 486nm blue laser frequency stabilization device based on a Fabry-Perot cavity has interconnected fiber optic lines, a spatial Fabry-Perot cavity optical path, and electrical signal lines. The 972nm laser is current-tuned according to the feedback signal from the electrical signal lines to suppress external interference and stabilize the laser output frequency. The fiber optic lines are connected to the laser and have an isolator, a fiber beam splitter, a phase modulator, and a fiber collimator connected in sequence. The fiber beam splitter and phase modulator are both single-mode polarization-maintaining fiber coupling devices. The laser output passes through the isolator and then enters the fiber beam splitter. After passing through the fiber beam splitter, the laser is split into two beams. One beam is output for frequency doubling to output 486nm blue light, and the other beam enters the phase modulator. This beam is then phase-modulated and enters the fiber collimator. The optical signal enters the Fabry-Perot cavity in the spatial optical path. After multiple reflections within the Fabry-Perot cavity, it is transmitted through the rear cavity mirror and output. A photodetector in the electrical signal circuit receives this output optical signal, which is converted into an electrical signal and mixed with the intrinsic reference signal output from the modulation and demodulation module in the demodulation circuit section to obtain an error signal. The error signal is processed by the PID control module and outputs a feedback adjustment signal to the laser to compensate for low and high frequencies. The PID control circuit continuously controls the laser current tuning based on the deviation between the feedback information and the set value, thereby suppressing external interference and stabilizing the laser frequency. The frequency-stabilized 972nm laser is then doubled by the frequency doubling section to output a narrow-linewidth, highly stable 486nm blue light, which can meet the needs of various marine and underwater exploration and communication applications. The optical path of this device combines fiber optic and spatial optical paths, which is a mature technology and simpler to build and debug, requiring only collimation of the Fabry-Perot cavity. In addition, the optical path system has good reliability, and the use of a small-volume Fabry-Perot cavity further reduces the size and weight of the optical path, which plays an important role in the miniaturization of the laser. For the circuit section, the designed circuit simultaneously provides modulation signals to the phase modulator and demodulates the photoelectric signals acquired by the photodetector. Furthermore, in practical use, the PID control module is integrated with the modulation / demodulation module, further compressing the circuit size. Signal processing is controlled through a unified computer application interface. The overall frequency stabilization device has been significantly optimized in size, and the power supply port is simple and portable, avoiding the use of high-voltage devices. It boasts advantages in both small size and energy efficiency, offering significant advantages for applications with high-frequency, narrow-linewidth 486nm solid-state lasers. Meanwhile, effectively suppressing solar background light noise interference is crucial for achieving efficient and stable operation around the clock in both marine lidar systems and underwater laser communication systems. Research shows that within the blue light transmission window spectrum of seawater, there exists a relatively distinct dark line in the solar radiation spectrum, namely the Fraunhofer dark line (H-β line), with a center wavelength of 486.13nm.Clearly, as long as the center wavelength of the laser emission source falls on the dark line of the sun, and both the laser spectral linewidth and the photodetector (PD) filter bandwidth are smaller than the H-β linewidth (approximately 0.1 nm), the impact of solar background noise on the receiving system can be significantly reduced, and the signal-to-noise ratio of the photodetector can be significantly improved. Analysis of the optimal wavelength for marine lidar detection of global ocean optical parameters from the perspectives of seawater detection depth and signal-to-noise ratio also shows that the 486 nm blue light wavelength has significant advantages in effectively improving global ocean detection depth and echo signal-to-noise ratio, making it the best choice for marine lidar source wavelength. Therefore, the ever-expanding field of laser applications in oceanography is constantly increasing the demand for blue-green all-solid-state lasers with high repetition rate, high average power, and low repetition rate, large pulse energy output. With the application of hyperspectral detection technology in ocean detection, the demand for single-frequency, high-energy 486 nm blue lasers with frequency stabilization / frequency locking functions will become increasingly urgent. Existing technologies can achieve narrow linewidth, high-energy blue laser pulse output, but they suffer from drawbacks such as easy center wavelength drift. This device effectively fills the current gap in the availability of a suitable 486nm frequency-stabilized blue light source. It is suitable for seed sources required by narrow-linewidth, high-energy blue lasers and can well meet the needs of high-precision marine lidar detection and communication. It is of great significance for research on marine exploration and underwater communication.

Claims

1. A 486 nm blue laser frequency stabilization device based on a Fabry-Perot cavity, characterized in that, It comprises: 972nm laser (1), optical isolator (2), optical fiber beam splitter (3), frequency doubling crystal (4), phase modulator (5), optical fiber collimating head (6), Fabry-Perot cavity (7), photodetector (8), modem module (9), PID control module (10), the 972nm laser (1) contains SMA current tuning port for receiving feedback adjustment signal output by PID control module (10); The 972nm laser (1) emits the light to be stabilized, which successively passes through the optical isolator (2) and the optical fiber beam splitter (3), one way of laser passes through the frequency doubling crystal (4) to output 486nm blue light, and the other way of laser passes through the phase modulator (5) for phase modulation and then collimates into the Fabry-Perot cavity (7) through the optical fiber collimating head (6), and transmits into the photodetector (8) from the rear cavity mirror of the Fabry-Perot cavity (7) after intracavity multi-beam resonance, and transmits to the modem module (9) after the photodetector (8) converts the optical signal into an electrical signal, the modem module outputs the radio frequency signal to the phase modulator (5) for phase modulation of the 972nm laser, and the modem module mixes the intrinsic reference signal outputting the radio frequency signal with the received electrical signal to obtain the frequency drift error signal and then transmits it to the PID control module (10); the PID control module (10) amplifies the amplitude and delays the phase of the received frequency drift error signal and then outputs the feedback adjustment signal to the 972nm laser (1) through the SMA current tuning port, controls the 972nm laser (1) to current tune the frequency of the laser, obtains the 972nm laser frequency stabilization output, and further realizes the 486nm blue light frequency stabilization output.

2. The 486 nm blue laser frequency stabilization apparatus based on a Fabry-Perot cavity according to claim 1, wherein, The polarization extinction ratio of the optical fiber beam splitter (3) is greater than 18dB.

3. The 486 nm blue laser frequency stabilization apparatus based on a Fabry-Perot cavity according to claim 1, characterized in that, The frequency doubling crystal (4) is LBO crystal or BIBO crystal.

4. The 486 nm blue laser frequency stabilization apparatus based on a Fabry-Perot cavity according to claim 1, wherein, The phase modulator (5) is a fiber-coupled lithium niobate electro-optic phase modulator, whose modulation bandwidth is not less than 150MHz and the insertion loss is less than 3dB.

5. The 486 nm blue laser frequency stabilization apparatus based on a Fabry-Perot cavity according to claim 1, wherein, The Fabry-Perot cavity (7) is a low-expansion coefficient glass material with a fineness higher than 1000.

6. The 486 nm blue laser frequency stabilization apparatus based on a Fabry-Perot cavity according to claim 1, wherein: The photodetector (8) is an indium gallium arsenide photodetector, and the bandwidth of the photodetector is greater than the radio frequency signal bandwidth of the phase modulator (5).

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