Narrow linewidth light source based on dual suppression of broadband intensity noise and frequency noise

Abstract

The present invention provides a narrow linewidth light source based on dual suppression of broadband intensity noise and frequency noise, including: an optical signal output module for outputting signal light; a first intensity noise suppression module, including a first optical processing unit and a first electrical processing unit connected to each other, suppressing the intensity noise inherent in the relaxation oscillation of the laser; a second intensity noise suppression module, including a second optical processing unit and a second electrical processing unit connected to each other, suppressing the medium and low frequency intensity noise of the laser; a third intensity noise suppression module, receiving the second signal light and performing amplification processing in a gain saturation state, suppressing the medium and high frequency intensity noise of the laser; a phase noise suppression module, including a third optical processing unit and a third electrical processing unit connected to each other, suppressing the phase noise of the laser. The beneficial effect of the present invention is to achieve broadband noise suppression and phase suppression, so that the intensity noise of the entire frequency band of the narrow linewidth laser is reduced by 40dB, ensuring the stability and reliability of the laser output power.

Description

Technical Field

[0001] The invention belongs to the technical field of optical fiber laser production, and in particular relates to a narrow line width light source based on dual suppression of wide frequency band intensity noise and frequency noise. Background Art

[0002] In the prior art, a technical solution combining high saturation power low noise PD with photoelectric feedback is loaded on the driver of SOA to obtain wide-band ultra-low intensity noise suppression. However, a polarization controller is required to control the polarization of SOA to obtain SOA gain saturation effect. The size is large and it is not easy to integrate into the module. The unstable polarization state control leads to unstable suppression effect and unstable laser output power. The font optical feedback suppresses intensity noise and adopts delayed optical fiber, which needs to be thermally insulated and seismically isolated. It is easily affected by ambient temperature and vibration, and has poor long-term reliability and stability. In addition, the first-level optical feedback cannot achieve wide-band intensity noise suppression. An unbalanced interferometer is used as a discriminator to suppress phase noise. The unbalanced interferometer adopts 50-200m, and the diameter of the optical fiber interferometer is at least 52mm, and the thickness is 8-11mm. The whole needs to be thermally insulated, and the size after packaging is at least 124*94*40mm. The entire unbalanced interferometer is large in size and also needs to be thermally insulated. Compared with the passive discriminator structure size: 5.5*50mm, the size is more than 22 times larger, and the interferometer structure is easily affected by ambient temperature and vibration, and has poor long-term reliability and stability. Summary of the invention

[0003] In view of the above problems, the present invention provides a narrow linewidth light source based on dual suppression of broadband intensity noise and frequency noise to solve the above or other former problems existing in the prior art.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is: a narrow linewidth light source based on dual suppression of broadband intensity noise and frequency noise, comprising:

[0005] An optical signal output module, used for outputting signal light;

[0006] A first intensity noise suppression module includes a first optical processing unit and a first electrical processing unit connected to each other, wherein the first optical processing unit receives the signal light and divides the signal light into two beams, wherein one beam is output as the first signal light and the other beam enters the first electrical processing unit, and a suppression electrical signal is generated by phase adjustment, and the suppression electrical signal acts on the optical signal output module to suppress the inherent intensity noise of the relaxation oscillation of the laser;

[0007] A second intensity noise suppression module includes a second optical processing unit and a second electrical processing unit connected to each other, wherein the second optical processing unit receives a first signal light, the first signal light is divided into two beams, one beam of light is output as a second signal light, and the other beam of light enters the second electrical processing unit, and a feedback signal is obtained through PID feedback processing to suppress the medium and low frequency intensity noise of the laser;

[0008] A third intensity noise suppression module receives the second signal light and performs amplification processing in a gain saturation state to suppress the medium and high frequency intensity noise of the laser;

[0009] The phase noise suppression module includes a third optical processing unit and a third electrical processing unit connected to each other. The third optical processing unit receives the signal light output by the third intensity noise suppression module and divides the signal light into reference light and signal light. The light enters the third electrical processing unit for frequency mixing to generate an error signal. The error signal is processed by a feedback loop and acts on the optical signal output module to suppress the phase noise of the laser.

[0010] Furthermore, the optical signal output module includes a first pump source, a first wavelength division multiplexer and a fiber Bragg grating connected in sequence. The light output by the first pump source enters the fiber Bragg grating through the first wavelength division multiplexer, and the signal light generated by the fiber Bragg grating is output through the first wavelength division multiplexer.

[0011] Furthermore, the first optical processing unit includes a first isolator and a first spectrometer connected to each other. The first isolator filters the received signal light, and the first spectrometer splits the filtered signal light to output a first signal light. Another light signal enters the first electrical processing unit, and the first electrical processing unit converts and phase-adjusts the light signal.

[0012] Furthermore, the first electrical processing unit includes a first photodetector, a ROS circuit and a first pump driving circuit connected in sequence, the first pump driving circuit is connected to the first pump source, the first photodetector converts a beam of light after beam splitting processing into an electrical signal, the ROS circuit performs phase adjustment processing on the electrical signal, and the first pump driving circuit drives the first pump source to operate according to the electrical signal after the phase adjustment processing.

[0013] Furthermore, the second optical processing unit includes a second pump source, a second wavelength division multiplexer, a second isolator and a second optical splitter connected in sequence. An erbium-doped optical fiber is connected between the second wavelength division multiplexer and the second isolator. Under the action of the laser output by the second pump source, the erbium-doped optical fiber amplifies the signal light entering the erbium-doped optical fiber through the second wavelength division multiplexer. The amplified signal light enters the second optical splitter through the second isolator for beam splitting processing. One beam of light enters the third intensity noise suppression module, and the other beam of light enters the second electrical processing unit.

[0014] Furthermore, the second electrical processing unit includes a second photodetector, a first PID control circuit and a second pump driving circuit connected in sequence. The second photodetector receives a beam of signal light output by the second spectrometer and converts it into an electrical signal. The electrical signal is processed by the first PID control circuit to generate a feedback signal. The second pump driving circuit drives the second pump source to operate according to the feedback signal.

[0015] Furthermore, the third intensity noise suppression module includes a connected optical amplifier and a third spectrometer. The optical amplifier performs nonlinear amplification processing on the second signal light under a gain saturation state. The third spectrometer splits the processed signal light, one beam serves as the output light of the laser, and the other beam enters the phase noise suppression module.

[0016] Furthermore, the third optical processing unit includes a fourth optical splitter, a narrowband filter and an electrically adjustable attenuator. The fourth optical splitter is connected to the narrowband filter and the electrically adjustable attenuator respectively. The narrowband filter filters a beam of optical signals separated by the fourth optical splitter. The electrically adjustable attenuator performs power control on another beam of optical signals separated by the fourth optical splitter. The narrowband filter and the electrically adjustable attenuator are both connected to the third electrical processing unit. The third electrical processing unit processes the optical signal processed by the narrowband filter and the electrically adjustable attenuator.

[0017] Furthermore, the third electrical processing unit includes a balanced detector, an operational amplifier, a low-pass filter, a second PID control circuit and a high-voltage operational amplifier circuit which are connected in sequence. The balanced detector is respectively connected to the narrowband filter and the electrically adjustable attenuator. The balanced detector performs mixing processing on the optical signal processed by the narrowband filter and the electrically adjustable attenuator, and demodulates a frequency drift error signal. After the frequency drift error signal is amplified by the operational amplifier, it is demodulated by the low-pass filter to obtain an error signal in the low-frequency band. The second PID control circuit amplifies the amplitude of the error signal in the low-frequency band, and the high-voltage operational amplifier circuit is feedback-controlled to act on the fiber Bragg grating to suppress phase noise.

[0018] Furthermore, the third electrical processing unit includes a PI control circuit, a low-pass filter, a second PID control circuit and a high-voltage operational amplifier circuit which are connected in sequence. The PI control circuit is respectively connected to the narrowband filter and the electrically adjustable attenuator. The PI control circuit processes the optical signal processed by the narrowband filter and the electrically adjustable attenuator to generate an error signal. After the error signal is filtered and amplified by the low-pass filter and the second PID control circuit, the high-voltage operational amplifier circuit is feedback-controlled to act on the fiber Bragg grating to suppress phase noise.

[0019] Due to the adoption of the above technical scheme, the intensity noise suppression of the narrow linewidth light source adopts a technology combining two-stage photoelectric feedback and optical amplifier. The first stage adopts photoelectric feedback to identify the inherent intensity noise of relaxation oscillation in the laser and suppresses it by phase adjustment. The second stage adopts PID feedback circuit to suppress medium and low frequency intensity noise. The third stage adopts the saturation gain effect of the optical amplifier to suppress medium and high frequency band intensity noise, which can achieve wide-band intensity noise suppression. Compared with the existing one-stage photoelectric feedback to achieve broadband intensity noise suppression and the use of optical feedback to use delayed optical fiber, both of which require thermal insulation and seismic isolation and are easily affected by ambient temperature and vibration, the two-stage photoelectric feedback has better long-term reliability and stability, and achieves wide-band noise suppression, so that the intensity noise of the entire frequency band of the narrow linewidth laser is reduced by 40dB, ensuring the stability and reliability of the laser output power.

[0020] The size of the athermal packaged narrowband filter is the same as that of the optical device, which has a size advantage over the fiber interferometer structure and is easy to be packaged in constant temperature and vibration isolation. After packaging, the size is smaller than that of the interferometer structure. The interferometer structure is easily disturbed by ambient temperature and vibration, and has poor long-term reliability and stability. The athermal packaged narrowband filter is not easily disturbed by the external environment and has good long-term reliability and stability.

[0021] The fiber Bragg grating with piezoelectric ceramics is set up to compare the difference between the signal light from the narrowband filter and the reference light to form an error signal, and the optical frequency jitter signal of the laser is converted into a power jitter signal. The error signal drives the piezoelectric ceramics to tune the wavelength through the feedback loop high-voltage operational amplifier circuit, thereby suppressing the laser phase noise and stabilizing the frequency of the laser output laser. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic structural diagram of a narrow line width light source according to an embodiment of the present invention;

[0023] Figure 2 It is a schematic structural diagram of a narrow linewidth light source according to another embodiment of the present invention.

[0024] In the figure:

[0025] 1. first pump source, 2. first wavelength division multiplexer, 3. fiber Bragg grating, 4. first isolator, 5. first optical splitter, 6. second wavelength division multiplexer, 7. erbium-doped optical fiber, 8. second isolator, 9. second optical splitter, 10. optical amplifier, 11. third optical splitter, 12. fourth optical splitter, 13. narrowband filter, 14. electrically adjustable attenuator, 15. balanced detector, 16. operational amplifier, 17. first photodetector, 18. ROS circuit, 19. first pump driving circuit, 20. second photodetector, 21. first PID control circuit, 22. second pump driving circuit, 23. second pump source, 24. low-pass filter, 25. second PID control circuit, 26. high-voltage operational amplifier circuit, 27. third photodetector, 28. fourth photodetector, 29. PI adjustment circuit DETAILED DESCRIPTION

[0026] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0027] Figure 1 A structural schematic diagram of an embodiment of the present invention is shown. This embodiment relates to a narrow linewidth light source based on dual suppression of wide-band intensity noise and frequency noise. A two-stage photoelectric feedback structure is adopted and combined with the nonlinear amplification effect under the saturation gain of the optical amplifier to suppress the intensity noise of different frequency bands in the narrow linewidth laser. A narrow broadband filter is used to convert the optical frequency jitter into optical power jitter due to the insertion loss of the optical frequency to suppress the phase noise, thereby ensuring the output power stability and reliability of the narrow linewidth laser.

[0028] A narrow linewidth light source based on dual suppression of broadband intensity noise and frequency noise, such as Figure 1 As shown, including,

[0029] An optical signal output module, used for outputting signal light;

[0030] A first intensity noise suppression module includes a first optical processing unit and a first electrical processing unit connected to each other, wherein the first optical processing unit receives the signal light and divides the signal light into two beams, one of which is output as the first signal light, and the other enters the first electrical processing unit and generates a suppression electrical signal after phase adjustment processing, and the suppression electrical signal acts on the optical signal output module to suppress the intensity noise of the output laser;

[0031] A second intensity noise suppression module includes a second optical processing unit and a second electrical processing unit connected to each other, the second optical processing unit receives a first signal light, the first signal light is divided into two beams, one beam of light is output as a second signal light, and the other beam of light enters the second electrical processing unit, the second electrical processing unit processes the beam of light, the optical signal is converted into an electrical signal, a feedback signal is obtained after the electrical signal is processed, and acts on a pump source to suppress the intensity noise of the output laser;

[0032] A third intensity noise suppression module receives the second signal light, amplifies the second signal light, suppresses the intensity noise of the output laser, and the amplified signal light is divided into two beams, which are used as the output light signal and the third signal light respectively;

[0033] The phase noise suppression module includes a third optical processing unit and a third electrical processing unit connected to each other. The third optical processing unit receives a third signal light and processes the third signal light to generate an error signal. The error signal is processed by the third electrical processing unit and acts on the optical signal output module to suppress the phase noise of the output laser.

[0034] The optical signal output module outputs a signal light of a required wavelength, and the signal light is processed by the first intensity noise suppression module to output an electrical signal, and the output electrical signal is fed back to act on the pump source of the optical signal output module to adjust the intensity noise inherent frequency of the output laser of the optical signal output module; the first optical signal output by the first intensity noise suppression module enters the second intensity noise suppression module, and the second intensity noise suppression module processes the first optical signal, and the obtained feedback electrical signal acts on the pump source in the second intensity noise suppression module to suppress the medium and low frequency intensity noise of the output laser; the second optical signal output from the second intensity noise suppression module enters the third intensity noise suppression module, and the third intensity noise suppression module amplifies the second optical signal to suppress the medium and high frequency intensity noise of the output laser, and a beam of light output by the third intensity noise suppression module is used as the output light of the narrow line width light source, and another beam of light output by the third intensity noise suppression module enters the phase noise suppression module, and the phase noise suppression module processes the optical signal, and the generated error signal is fed back to act on the fiber Bragg grating 3 of the optical signal output module to suppress the phase noise of the output laser. The first intensity noise suppression module, the second intensity noise suppression module, the third intensity noise suppression module and the phase noise suppression module are set up, and two-stage photoelectric feedback is used to the pump laser driving circuit, which is combined with the nonlinear amplification effect of the optical amplifier 10 in the gain saturation state to suppress the intensity noise of different frequency bands, and utilize the insertion loss formed by the narrow bandwidth filter of the heat-free package on the optical frequency to convert the optical frequency jitter into optical power jitter, perform phase noise suppression, achieve long-term reliability and stability suppression, and ensure the stability and reliability of the laser output power.

[0035] Specifically, Figure 1 As shown, the above-mentioned optical signal output module includes a first pump source 1, a first wavelength division multiplexer 2 and a fiber Bragg grating 3 which are connected in sequence. The light output by the first pump source 1 enters the fiber Bragg grating 3 through the first wavelength division multiplexer 2. The signal light generated by the fiber Bragg grating 3 is output through the first wavelength division multiplexer 2. The fiber Bragg grating 3 performs frequency selection on the incoming laser to obtain a laser with a desired wavelength. The laser with the desired wavelength is output through the first wavelength division multiplexer 2 and enters the first intensity noise suppression module.

[0036] The first pump source 1 is a 980nm pump laser, which is used to provide 980nm light to enter the fiber grating 3, so as to realize the amplification of the 1550nm signal light. The 980nm light of the first pump source 1 will enter the fiber grating 3 through one end of the first wavelength division multiplexer 2. The fiber grating 3 constitutes a resonant cavity, selects the frequency of the radiated laser, and the 980nm light in the fiber grating 3 realizes the amplification of the 1550nm light, realizes the single longitudinal mode operation, and obtains the laser output of the required wavelength. The other end connects the 1550nm signal light generated in the fiber grating 3 to the first isolator 4 of the first intensity noise suppression module.

[0037] The above-mentioned fiber grating 3 has piezoelectric ceramics, which can realize the tunability of the laser frequency.

[0038] In the above-mentioned first intensity noise suppression module, the first optical processing unit includes a first isolator 4 and a first optical splitter 5 connected to each other, the first isolator 4 filters the received signal light, the first optical splitter 5 performs beam splitting on the filtered signal light, one beam of light is output as the first signal light, enters the second intensity noise suppression module, and the other beam of light signal enters the first electrical processing unit. Specifically, the first isolator 4 filters out the 980nm pump light, and allows the 1550nm signal forward transmission light to pass through while isolating the light transmitted in the direction, thereby preventing the reflected light from affecting the stability of the system, the 1550nm signal light output by the first isolator 4 is divided into two beams by the first optical splitter 5, one beam of light enters the second intensity noise suppression module as the 1550nm optical signal, and the other beam of light enters the first electrical processing unit, the first electrical processing unit converts and phase-adjusts the beam of light signal to generate a relaxation oscillation suppression electrical signal, the relaxation oscillation suppression electrical signal acts on the first pump source 1 of the optical signal output module, and suppresses the inherent intensity noise of the relaxation oscillation of the laser output by the optical signal output module.

[0039] The first electrical processing unit includes a first photodetector 17, a ROS circuit 18 and a first pump driving circuit 19 which are connected in sequence. The first pump driving circuit 19 is connected to the optical signal output module. The first photodetector 17 converts a beam of light after the splitting process into an electrical signal. The ROS circuit 18 performs phase adjustment on the electrical signal. The first pump driving circuit 19 drives the optical signal output module to operate according to the electrical signal after the phase adjustment process, so as to suppress the inherent frequency part of the intensity noise of the output laser. Specifically, the first photodetector 17 receives one of the beams of light split by the first beam splitter 5, and the beam of light is converted into a photoelectric signal in the first photodetector 17. The first photodetector 17 detects the size of the signal light output by the fiber Bragg grating 3 and converts it into an electrical signal, which carries the signal light intensity information; the ROS circuit 18 receives the electrical signal output by the first photodetector 17, and the electrical signal is converted by a transimpedance amplifier and then amplified by the amplifier. The phase adjustment circuit performs phase adjustment on the amplified electrical signal to generate a relaxation oscillation suppression voltage signal, and the relaxation oscillation suppression voltage signal is transmitted to the first pump driving circuit 19, and the first pump driving circuit 19 drives the first pump source 1. The relaxation oscillation suppression voltage signal feedback suppresses the first pump driving circuit 19, and then feedback controls the current driving circuit unit inside the first pump source 1, adjusts the pump current of the first pump source 1, and suppresses the intensity noise of the inherent relaxation oscillation output by the laser.

[0040] The first optical splitter 5 is a fiber optical splitter. The splitting ratio of the first optical splitter 5 is determined according to the actual light output from the fiber grating 3 , and at least -15 dBm is required to enter the first pump source 1 .

[0041] The above-mentioned ROS circuit 18 and the first pump driving circuit 19 are both known circuit structures and are selected according to actual needs. The ROS circuit 18 suppresses light feedback to the first pump driving circuit 19 by adjusting the phase of the relaxation oscillation noise existing in the fiber grating 3 to form a relaxation oscillation suppression electrical signal phase adjustment.

[0042] In the above-mentioned second intensity noise suppression module, the second optical processing unit includes a second pump source 23, a second wavelength division multiplexer 6, a second isolator 8 and a second optical splitter 9 which are connected in sequence. An erbium-doped optical fiber 7 is connected between the second wavelength division multiplexer 6 and the second isolator 8. The laser output by the second pump source 23 enters the erbium-doped optical fiber 7 through the second wavelength division multiplexer 6, so that the erbium-doped optical fiber 7 works, and the first signal light entering the erbium-doped optical fiber 7 through the second wavelength division multiplexer 6 is amplified. The amplified signal light enters the second optical splitter 9 through the second isolator 8 for beam splitting processing. One beam of light is output as an optical signal, that is, the second signal light is output and enters the third intensity noise suppression module. The other beam of light enters the second electrical processing unit. The second electrical processing unit converts the optical signal and performs PID feedback processing to generate a feedback signal. The feedback signal acts on the second pump source 23 to suppress the low-frequency intensity noise in the output laser.

[0043] The second pump source 23 is a 980nm pump laser, which is used to provide 980nm light. The 980nm light enters the erbium-doped optical fiber 7 through one end of the second wavelength division multiplexer 6. Under the 980nm pumping action of the second pump source 23, the erbium-doped optical fiber 7 undergoes a working energy level transition, directly amplifies the first signal light (1550nm signal light), and realizes secondary amplification of the 1550nm signal light. The other end of the second wavelength division multiplexer 6 connects the 1550nm signal light generated in the erbium-doped optical fiber 7 to the second isolator 8. The isolator 8 filters out the 980nm pump light of the second pump source 23, and allows the 1550nm signal light transmitted in the forward direction to pass through while isolating the light transmitted in the forward direction, thereby preventing the reflected light from affecting the stability of the system. The second optical splitter 9 divides the 1550nm signal light transmitted by the second isolator 8 into two beams, one of which is output as the second signal light (1550nm optical signal), which enters the third intensity noise suppression module, and the other enters the second electrical processing unit to suppress the intensity noise in the medium and low frequency bands.

[0044] The second electrical processing unit includes a second photodetector 20, a first PID control circuit 21 and a second pump drive circuit 22 connected in sequence. The second photodetector 20 receives a beam of signal light output by the second beam splitter 9 and converts it into an electrical signal. The electrical signal is processed by the first PID control circuit 21 to generate a feedback signal. The second pump drive circuit 22 drives the second pump source 23 according to the feedback signal to suppress the intensity noise in the medium and low frequency bands of the output laser. The second photodetector 20 detects the size of a beam of signal light output by the second beam splitter 9 and converts the beam of signal light into an electrical signal carrying the signal light intensity information. The electrical signal output by the second photodetector 20 enters the first PID control circuit 21. The electrical signal amplified by the transimpedance amplifier is used as an error signal, and the feedback signal is obtained by combining the proportional integral differential (PID) module, and then the feedback signal is loaded on the second pump drive circuit 22. The second pump drive circuit 22 pumps the second pump source 23, thereby suppressing the intensity noise in the medium and low frequency bands of the output laser.

[0045] The second optical splitter 9 is a fiber optical splitter. The splitting ratio of the second optical splitter 9 is determined according to the actual light output, and at least -15 dBm is required to enter the second pump source 23 .

[0046] The proportional-integral-derivative (PID) module obtains a feedback signal and feeds back the feedback signal to the second pump driving circuit 22 .

[0047] The third intensity noise suppression module includes an optical amplifier 10 and a third optical splitter 11 connected to each other. The optical amplifier 10 receives the second signal light output by the second optical splitter 9 and amplifies the second signal light. The third optical splitter 11 splits the amplified optical signal. One optical signal is output as the output light of the laser, and the other enters the phase noise suppression module to suppress the phase noise. The second signal light uses the nonlinear amplification effect of the gain saturation state of the optical amplifier 10 to suppress the high-frequency intensity noise in the output laser. The third optical splitter 11 divides the signal light processed by the optical amplifier 10 into two beams, one of which is output as a 1550nm optical signal (as the output laser of the laser), and the other enters the phase noise suppression module to suppress the laser phase noise.

[0048] In the above-mentioned phase noise suppression module, the third optical processing circuit includes a fourth optical splitter 12, a narrowband filter 13 and an electrically adjustable attenuator 14. Another optical signal (1550nm signal light) separated by the third optical splitter 11 is split by the fourth optical splitter 12 into two beams of light. The fourth optical splitter 12 is connected to the narrowband filter 13 and the electrically adjustable attenuator 14 respectively. The narrowband filter 13 performs filtering processing on one optical signal separated by the fourth optical splitter 12. The electrically adjustable attenuator 14 performs power control on the other optical signal separated by the fourth optical splitter 12. The narrowband filter 13 and the electrically adjustable attenuator 14 are both connected to the third electrical processing unit. The third electrical processing unit performs phase noise suppression processing on the optical signal processed by the narrowband filter 13 and the electrically adjustable attenuator 14. The fourth spectrometer 12 divides the 1550nm signal light output laser into two beams, one of which enters the electrically adjustable attenuator 14 and is used as reference light after processing, and the other enters the narrowband filter 13 and is used as signal light after processing. The narrowband filter 13 adopts athermal packaging, and the high and low temperature drift of 0-50℃ is ≤1pm, and the bandwidth requirement of 3dB is ≤16MHz. Constant temperature vibration isolation packaging is required, and a thermoelectric cooler is required for constant temperature control. The attenuated power range of the electrically adjustable attenuator 14 is 0-20dB.

[0049] The third optical splitter 11 is a fiber optic splitter, which is used to split the 1550nm signal light output laser into two beams, one of which is output as a 1550nm optical signal, and the other enters the balanced detector loop to suppress the laser phase noise. The splitting ratio of the third optical splitter 11 is determined according to the actual light output, and at least -15dBm is required to enter the second pump source 23.

[0050] The fourth optical splitter 12 is a fiber optical splitter, and the splitting ratio of the fourth optical splitter 12 is 50 / 50, that is, the signal light entering the fourth split light beam 12 is equally split.

[0051] The narrowband filter 13 and the electrically adjustable attenuator 14 are both commercially available products and can be selected according to actual needs.

[0052] The third electrical processing unit includes a balanced detector 15, an operational amplifier 16, a low-pass filter 24, a second PID control circuit 25 and a high-voltage operational amplifier circuit 26 which are connected in sequence. The balanced detector 15 is connected to the narrowband filter 13 and the electrically adjustable attenuator 14 respectively. The optical signal processed by the narrowband filter 13 and the electrically adjustable attenuator 14 is mixed by the balanced detector 15 to generate a frequency drift error signal. The frequency drift error signal is amplified by the operational amplifier 16 and enters the low-pass filter 24 to demodulate the error signal in the low frequency band. The second PID control circuit 25 amplifies the amplitude of the error signal in the low frequency band to obtain a feedback signal. The feedback signal acts on the fiber grating 3 through the high-voltage operational amplifier circuit 26 to tune the frequency of the output laser and suppress phase noise.

[0053] The port bandwidth of the above-mentioned balanced detector 15 is 15kHz, and the output voltage noise is 10mVpp. It can mix the photoelectric signal output by the narrowband filter 13 with the reference signal output by the electrically adjustable attenuator 14 to demodulate the frequency drift error signal of the laser. The balanced detector 15 needs to use a low-noise photoelectric detector, and the corresponding photoelectric conversion curve must ensure uniformity within 0.02A / W.

[0054] The operational amplifier 16 has low noise and a bandwidth of 10 MHz, and proportionally amplifies the frequency drift error signal.

[0055] The bandwidth of the low-pass filter 24 is 15 kHz, and the error signal in the low frequency band is demodulated.

[0056] The second PID control circuit 25 amplifies the amplitude of the output error electrical signal and feedback controls the high-voltage operational amplifier circuit 26 to suppress the laser output phase noise.

[0057] The high-voltage operational amplifier circuit 26 drives the piezoelectric ceramic of the fiber grating 3 to tune the frequency of the laser, stabilize the frequency of the laser output, and suppress the phase noise of the laser.

[0058] Or, if Figure 2As shown, the third electrical processing unit includes a PI control circuit, a low-pass filter 24, a second PID control circuit 25 and a high-voltage operational amplifier circuit 26 connected in sequence. The PI control circuit is respectively connected to the narrowband filter 13 and the electrically adjustable attenuator 14. The PI control circuit adjusts the optical signal processed by the narrowband filter 13 and the electrically adjustable attenuator 14, and demodulates the frequency drift error signal. After the frequency drift error signal is amplified by the PI control circuit, an error signal in the low frequency band is demodulated. The second PID control circuit 25 amplifies the amplitude of the error signal in the low frequency band to obtain a feedback signal. The feedback signal acts on the fiber grating 3 through the high-voltage operational amplifier circuit 26 to tune the frequency of the output laser and suppress phase noise.

[0059] The above-mentioned PI control circuit includes a third photodetector 27, a fourth photodetector 28 and a PI adjustment circuit 29. The third photodetector 27 is connected to the narrowband filter 13 to receive the signal light output by the narrowband filter 13. The fourth photodetector 28 is connected to the electrically adjustable attenuator 14 to receive the reference light output by the electrically adjustable attenuator 14. The third photodetector 27 and the fourth photodetector 28 are both connected to the PI adjustment circuit 29. The PI adjustment circuit 29 is connected to the low-pass filter 24. The electrical signal output by the third photodetector 27 and the electrical signal output by the fourth photodetector 28 enter the PI adjustment circuit 29 for amplification and then enter the low-pass filter 24.

[0060] The third photodetector 27 and the fourth photodetector 28 are both commercially available products and can be selected according to actual needs.

[0061] The above-mentioned PI adjustment circuit 29 is a known circuit and is selected according to actual needs.

[0062] The process of intensity noise suppression and frequency noise suppression by the narrow linewidth light source based on dual suppression of broadband intensity noise and frequency noise is as follows:

[0063] The light outputted by the fiber Bragg grating 3 is split by the first optical splitter 5, and a certain proportion (the proportion is selected according to actual needs) of the light enters the first photodetector 17. The first photodetector 17 converts the optical signal into an electrical signal. The electrical signal adjusts the phase of the relaxation oscillation noise existing in the fiber Bragg grating 3 through the ROS circuit 18 to form a relaxation oscillation suppression electrical signal. The relaxation oscillation suppression electrical signal is fed back to the first pump driving circuit 19 for suppression. The first pump driving circuit 19 drives the first pump source 1, adjusts the pump current of the first pump source 1, and suppresses the part of the inherent frequency of the intensity noise. After the output laser of the narrow linewidth laser is amplified by the erbium-doped fiber 7, it passes through the second optical splitter 9 and a certain proportion (the proportion is selected according to actual needs) of the light enters the second photodetector 20. The second photodetector 20 converts the optical signal into an electrical signal, and uses it as an error signal to obtain a feedback signal in combination with the first PID control circuit 21. The feedback signal is loaded into the second pump driving circuit 22 to drive the second pump source 23, thereby suppressing the low-frequency intensity noise in the output laser. Next, the output laser of the narrow linewidth laser passes through the optical amplifier 10 , and the nonlinear amplification effect of the optical amplifier 10 in the gain saturation state is used to suppress the medium and high frequency intensity noise.

[0064] The output end of the narrow linewidth laser is split by the fourth beam splitter 12, and the output laser is divided into two paths. One path is injected into the athermal packaged narrowband filter 13, and this path is used as the signal light. The narrowband filter 13 has a very narrow bandwidth, and the wavelength of the laser is controlled in the middle position of one side of the narrowband filter 13. When the laser frequency drifts, the output light insertion loss value will change, and the optical frequency jitter is converted into optical power jitter. At the same time, the other path of light is attenuated and adjusted to the same as the output light of the athermal packaged narrowband filter 13 by the electrically adjustable attenuator 14, and is used as the reference light. After the reference light and the signal light enter the balanced detector 15, two error signals with a certain power difference are generated.

[0065] The error signal is amplified by an operational amplifier 16, and the high-frequency noise part of the amplified error signal is filtered out by a low-pass filter 24, and then processed by a second PID control circuit 25 to obtain a feedback signal. The feedback signal is fed back to the high-voltage operational amplifier circuit 26 of the fiber grating 3 of the narrow linewidth laser, and then the piezoelectric ceramic of the fiber grating 3 is driven to tune the wavelength, thereby achieving laser phase noise suppression.

[0066] In the narrow linewidth light source based on dual suppression of broadband intensity noise and frequency noise, a first pump source 1, a first wavelength division multiplexer 2, a fiber grating 3, a first isolator 4, a first optical splitter 5, a second wavelength division multiplexer 6, an erbium-doped fiber 7, a second isolator 8, a second optical splitter 9, an optical amplifier 10, a third optical splitter 11, a fourth optical splitter 12, a narrowband filter 13 and an electrically adjustable attenuator 14 constitute an optical path structure, and the optical path structure is composed of an optical fiber coupling device, an optical fiber optical splitter, an optical fiber isolator, a photodetector, an optical amplifier, an electrically adjustable attenuator and an athermal packaged narrowband filter. The circuit structure comprises two-stage photoelectric feedback (relaxation oscillation suppression circuit, PID feedback circuit), a balanced detector circuit, a low-pass filter circuit, a PID feedback circuit and a high-voltage amplifier circuit, and performs three-stage intensity noise suppression to achieve suppression of intensity noise in different frequency bands and frequency noise suppression.

[0067] Due to the adoption of the above technical scheme, the intensity noise suppression of the narrow linewidth light source adopts a technology combining two-stage photoelectric feedback and optical amplifier. The first stage adopts photoelectric feedback to identify the inherent intensity noise of relaxation oscillation in the laser and suppresses it by phase adjustment. The second stage adopts PID feedback circuit to suppress medium and low frequency intensity noise. The third stage adopts the saturation gain effect of the optical amplifier to suppress medium and high frequency band intensity noise, which can achieve wide-band intensity noise suppression. Compared with the existing one-stage photoelectric feedback to achieve broadband intensity noise suppression and the use of optical feedback to use delayed optical fiber, both of which require thermal insulation and seismic isolation and are easily affected by ambient temperature and vibration, the two-stage photoelectric feedback has better long-term reliability and stability, and achieves wide-band noise suppression, so that the intensity noise of the entire frequency band of the narrow linewidth laser is reduced by 40dB, ensuring the laser Output power stability and reliability; The size of the athermal packaged narrowband filter is the same as that of the optical device, which has a size advantage over the fiber interferometer structure and is easy to perform constant temperature vibration isolation packaging. After packaging, the size is smaller than that of the interferometer structure, and the interferometer structure is easily disturbed by ambient temperature and vibration, and has poor long-term reliability and stability. The athermal packaged narrowband filter is not easily disturbed by the external environment and has good long-term reliability and stability; The fiber grating with piezoelectric ceramics is set to compare the difference between the signal light from the narrowband filter and the reference light to form an error signal, and the optical frequency jitter signal of the laser is converted into a power jitter signal. The error signal drives the piezoelectric ceramics for wavelength tuning through the feedback loop high-voltage operational amplifier circuit, thereby suppressing the laser phase noise and stabilizing the frequency of the laser output.

[0068] The embodiments of the present invention are described in detail above, but the contents described are only preferred embodiments of the present invention and cannot be considered to limit the scope of implementation of the present invention. All equivalent changes and improvements made according to the scope of application of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A narrow linewidth light source based on dual suppression of broadband intensity noise and frequency noise, characterized in that: include, An optical signal output module, used for outputting signal light; A first intensity noise suppression module, comprising a first optical processing unit and a first electrical processing unit connected to each other, wherein the first optical processing unit receives the signal light, divides the signal light into two beams, one beam of light is output as the first signal light, and the other beam of light enters the first electrical processing unit, generates a suppression electrical signal through phase adjustment, and the suppression electrical signal acts on the optical signal output module to suppress the intensity noise inherent in the relaxation oscillation of the laser; A second intensity noise suppression module includes a second optical processing unit and a second electrical processing unit connected to each other, wherein the second optical processing unit receives the first signal light, the first signal light is divided into two beams, one beam of light is output as the second signal light, and the other beam of light enters the second electrical processing unit, and a feedback signal is obtained through PID feedback processing to suppress the medium and low frequency intensity noise of the laser; A third intensity noise suppression module receives the second signal light and performs amplification processing in a gain saturation state to suppress the medium and high frequency intensity noise of the laser; A phase noise suppression module comprises a third optical processing unit and a third electrical processing unit connected to each other, wherein the third optical processing unit receives the signal light output by the third intensity noise suppression module, and separates the signal light into reference light and signal light, and enters the third electrical processing unit to perform frequency mixing processing to generate an error signal, and the error signal is processed by a feedback loop and acts on the optical signal output module to suppress the phase noise of the laser; The optical signal output module comprises a first pump source, a first wavelength division multiplexer and a fiber Bragg grating connected in sequence, the light output by the first pump source enters the fiber Bragg grating through the first wavelength division multiplexer, and the signal light generated by the fiber Bragg grating is output through the first wavelength division multiplexer; The third optical processing unit includes a fourth optical splitter, a narrowband filter and an electrically adjustable attenuator, the fourth optical splitter is connected to the narrowband filter and the electrically adjustable attenuator respectively, the narrowband filter performs filtering processing on a beam of optical signal separated by the fourth optical splitter, the electrically adjustable attenuator performs power control on another beam of optical signal separated by the fourth optical splitter, the narrowband filter and the electrically adjustable attenuator are both connected to the third electrical processing unit, and the third electrical processing unit processes the optical signal processed by the narrowband filter and the electrically adjustable attenuator; The third electrical processing unit comprises a balanced detector, an operational amplifier, a low-pass filter, a second PID control circuit and a high-voltage operational amplifier circuit connected in sequence, the balanced detector is connected to the narrow-band filter and the electrically adjustable attenuator respectively, the balanced detector performs frequency mixing processing on the optical signal processed by the narrow-band filter and the electrically adjustable attenuator, and demodulates a frequency drift error signal, the frequency drift error signal is amplified by the operational amplifier, and then demodulated by the low-pass filter to obtain an error signal in a low frequency band, the second PID control circuit amplifies the amplitude of the error signal in the low frequency band, and feedback controls the high-voltage operational amplifier circuit to act on the fiber Bragg grating to suppress phase noise; or, The third electrical processing unit includes a PI control circuit, a low-pass filter, a second PID control circuit and a high-voltage operational amplifier circuit which are connected in sequence. The PI control circuit is connected to the narrowband filter and the electrically adjustable attenuator respectively. The PI control circuit processes the optical signal processed by the narrowband filter and the electrically adjustable attenuator to generate an error signal. After the error signal is filtered and amplified by the low-pass filter and the second PID control circuit, the high-voltage operational amplifier circuit is feedback-controlled to act on the fiber Bragg grating to suppress phase noise.

2. The narrow linewidth light source based on dual suppression of broadband intensity noise and frequency noise according to claim 1, characterized in that: The first optical processing unit includes a first isolator and a first spectrometer connected to each other. The first isolator filters the received signal light, and the first spectrometer splits the filtered signal light to output the first signal light. Another light signal enters the first electrical processing unit, and the first electrical processing unit converts and phase-adjusts the light signal.

3. The narrow linewidth light source based on dual suppression of broadband intensity noise and frequency noise according to claim 2, characterized in that: The first electrical processing unit includes a first photodetector, a ROS circuit and a first pump driving circuit connected in sequence, the first pump driving circuit is connected to the first pump source, the first photodetector converts a beam of light after beam splitting processing into an electrical signal, the ROS circuit performs phase adjustment processing on the electrical signal, and the first pump driving circuit drives the first pump source to operate according to the electrical signal after the phase adjustment processing.

4. The narrow linewidth light source based on dual suppression of broadband intensity noise and frequency noise according to any one of claims 1 to 3, characterized in that: The second optical processing unit includes a second pump source, a second wavelength division multiplexer, a second isolator and a second optical splitter connected in sequence. An erbium-doped optical fiber is connected between the second wavelength division multiplexer and the second isolator. Under the action of the laser output by the second pump source, the erbium-doped optical fiber amplifies the signal light entering the erbium-doped optical fiber through the second wavelength division multiplexer. The amplified signal light enters the second optical splitter through the second isolator for beam splitting processing. One beam of light enters the third intensity noise suppression module, and the other beam of light enters the second electrical processing unit.

5. The narrow linewidth light source based on dual suppression of broadband intensity noise and frequency noise according to claim 4, characterized in that: The second electrical processing unit includes a second photodetector, a first PID control circuit and a second pump driving circuit connected in sequence. The second photodetector receives a beam of signal light output by the second spectrometer and converts it into an electrical signal. The electrical signal is processed by the first PID control circuit to generate the feedback signal. The second pump driving circuit drives the second pump source to operate according to the feedback signal.

6. The narrow linewidth light source based on dual suppression of broadband intensity noise and frequency noise according to claim 5, characterized in that: The third intensity noise suppression module includes an optical amplifier and a third spectrometer connected to each other. The optical amplifier performs nonlinear amplification processing on the second signal light under a gain saturation state. The third spectrometer splits the processed signal light, one beam serves as the output light of the laser, and the other beam enters the phase noise suppression module.

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