Intensity noise suppression system and method of single-frequency amplification fiber laser

Abstract

The invention discloses an intensity noise suppression system and method for a single-frequency amplification fiber laser. The system comprises a pumping source, an oscillator, an amplifier and an output end cap which are sequentially arranged along a light path, the oscillator comprises a high-reflectivity fiber bragg grating, a gain fiber and a low-reflectivity fiber bragg grating which are sequentially arranged along a light path; the system further comprises a first tunable band-pass filter and a second tunable band-pass filter which are arranged behind the pumping source and the gain optical fiber respectively. Through the cooperative adjustment of the two band-pass filters, the pumping energy entering the oscillator and the emission spectrum range of the gain fiber are accurately controlled, and the occurrence probability of the relaxation oscillation phenomenon is reduced. Stable laser oscillation is output through the low-reflection fiber bragg grating and then is efficiently coupled to the amplifier through the mode field adapter, and stable output of single-frequency amplification laser and intensity noise suppression of the single-frequency amplification fiber laser are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fiber lasers, and more specifically, relates to an intensity noise suppression system and method for a single-frequency amplified optical fiber laser. Background Art

[0002] Since the invention of the laser, noise has been a central topic in the field of laser physics and engineering. The laser noise characteristics are of great significance to the application of lasers in precision measurement, optical communication, sensing and other fields. It determines the ultimate performance of these systems. A single-frequency amplified fiber laser is a device that can produce lasers with a single frequency (i.e., monochromaticity). With the increasing application of single-frequency lasers in precision measurement, coherent communication, lidar and optical sensing, people have gradually begun to pay attention to their noise performance. In high-sensitivity optical measurements, the laser source is required to have extremely low intensity noise to obtain a high signal-to-noise ratio; in coherent precision measurements, the laser frequency noise directly determines the detection sensitivity.

[0003] The sources of intensity noise vary according to different frequency bands, and can be mainly divided into three categories: low frequency, medium frequency, and high frequency. Technical noise in the low frequency band is mainly caused by external interference, power fluctuations of the pump source, etc. Relaxation oscillation in the medium frequency band is the main reason for the fluctuation of the output power of single longitudinal mode lasers, and is also the main source of intensity noise. It originates from the laser oscillation caused by the nonlinear interaction between the inversion particles in the gain medium and the photons in the laser cavity, which is manifested as the change of light intensity with damped oscillation over time in certain frequency bands, and the RIN enhancement in a relatively narrow frequency interval around this frequency, that is, the relaxation oscillation peak commonly seen in the RIN spectrum, which is generally between tens of kHz and several MHz. Quantum noise in the high frequency band is also called shot noise. At a frequency higher than the relaxation oscillation frequency, the intensity noise of the fiber laser gradually decreases and tends to the quantum noise limit. It originates from the light quantum fluctuations generated in the process of laser energy quantization (during photoelectric detection), and produces background white noise in the entire spectrum.

[0004] The main technical measures for intensity noise suppression are divided into passive suppression technology and active suppression technology. Passive suppression technology uses measures such as package isolation and precise temperature control to solve the technical noise problem in the low-frequency band. Active suppression technology suppresses the mid-frequency noise caused by relaxation oscillation, which accounts for the majority of the intensity noise, by adding new modulation devices to the original system or designing a new optical path structure. It is the focus and difficulty of intensity noise suppression for single longitudinal mode lasers. Common active suppression technologies are:

[0005] (1) Intensity noise suppression based on photoelectric feedback. The principle is to use a photodetector to detect the laser to be stabilized and convert it into an electrical signal. Then the photoelectric feedback circuit performs amplitude and phase control on the electrical signal. The processed signal can be used to feedback control the driving current of the pump laser or adjust the output laser intensity modulator [such as acousto-optic modulator (AOM), electro-optic modulator (EOM), liquid crystal noise attenuator, etc.], thereby suppressing the intensity noise.

[0006] (2) Intensity noise suppression based on a mode cleaner. The device generally outputs the laser through a mode cleaner and then through a beam splitter to a photodetector (PD). The signal from the photodetector is passed through a servo system to adjust the laser power, thereby achieving intensity noise suppression.

[0007] (3) Intensity noise suppression based on injection locking. Injection locking refers to the injection of an external optical signal into a laser. When the wavelength of the injected light and the wavelength of the injected laser are within the locking range, the free oscillation mode of the injected laser is suppressed, and its output frequency is locked to the frequency of the external injected laser. The intensity noise suppression method based on injection locking does not require the introduction of additional control and detection systems, making the overall structure relatively simple and easy to build and operate. However, the premise of this method is the existence of a laser with excellent intensity noise performance, and its center frequency is close to that of the single longitudinal mode fiber laser to be optimized. This premise makes the application of this method relatively difficult and its application range becomes narrower.

[0008] (4) Based on the intensity noise suppression of the optical amplifier, the gain self-modulation method uses the gain saturation effect of the semiconductor optical amplifier or the optical fiber amplifier to make the passing laser gain self-modulate, which can reduce the power fluctuation and thus achieve the purpose of noise suppression.

[0009] However, the above schemes involve multiple components and steps when achieving laser noise suppression. These components and steps require precise control and coordination, making the design and operation of the entire system more complicated. For example, the intensity noise suppression technology based on photoelectric feedback requires multiple parts such as photodetectors, feedback circuits, pump lasers or output laser intensity modulators to work together, which increases the complexity of the system; and the various components involved are not all in the form of optical fibers, and may include some non-optical photodetectors, electronic circuits, modulators, etc., which will introduce additional connection points and potential loss sources during use, affecting the overall performance of the laser. Summary of the invention

[0010] In view of the above defects or improvement needs of the prior art, the present invention provides a system and method for suppressing the intensity noise of a single-frequency amplified fiber laser. Based on the dual-bandpass filtering technology, a tunable filter is placed at the pump source position and the gain position in the single-frequency amplified laser structure. By controlling the filtering bandwidth of the two bandpass filters, the dynamic change of the gain in the single-frequency laser amplification process is managed, thereby optimizing the intensity noise of the output single-frequency laser. When the bandwidth of the two filters is adjusted to a specific combination ratio, the laser will achieve the best noise suppression level. The present invention has a simple structure and adopts an all-fiber structure, which is convenient for integration and miniaturization; the suppression method is flexible in operation and can be applied to the intensity noise suppression of single-frequency amplified fiber lasers, and can also be used for single-frequency oscillators.

[0011] In order to achieve the above-mentioned object, one aspect of the present invention provides an intensity noise suppression system for a single-frequency amplified fiber laser, comprising a pump source, an oscillator, an amplifier and an output end cap arranged in sequence along an optical path; wherein,

[0012] The oscillator comprises a high-reflection fiber Bragg grating, a gain fiber and a low-reflection fiber Bragg grating arranged in sequence along an optical path;

[0013] The system also includes a first tunable bandpass filter for adjusting the pump energy entering the oscillator and suppressing the intensity noise caused by the pump disturbance and a second tunable bandpass filter for adjusting the emission spectrum range of the gain fiber and optimizing the gain characteristics of the gain fiber, thereby reducing the intracavity loss and reducing the intensity noise;

[0014] Through the coordinated adjustment of the first tunable bandpass filter and the second tunable bandpass filter, the output of the pump source and the emission characteristics of the gain fiber are precisely controlled, thereby achieving effective suppression of intensity noise and improving the stability and reliability of the laser; the stable laser oscillation formed in the resonant cavity is output through the low-reflection fiber Bragg grating, and then efficiently coupled to the amplifier through the mode field adapter, and finally the output of stable single-frequency amplified laser is achieved through the output end cap.

[0015] Furthermore, the first tunable bandpass filter is arranged between the pump source and the high-reflection fiber Bragg grating.

[0016] Furthermore, the second tunable bandpass filter is arranged between the gain fiber and the low-reflection fiber Bragg grating.

[0017] Furthermore, the amplifier comprises a beam combiner, an amplifier-stage gain optical fiber and a cladding light filter which are sequentially arranged at intervals along the optical path; the laser output by the low-reflection fiber Bragg grating passes through a mode field adapter and is efficiently coupled to the amplifier.

[0018] Furthermore, the amplifier also includes a first amplification stage pump source and a second amplification stage pump source for providing necessary energy for optical signal amplification; the laser coupled to the amplifier is provided with energy by the first amplification stage pump source and the second amplification stage pump source, and after being combined by a beam combiner, they act together on the amplification stage gain optical fiber; the excess cladding light in the optical signal amplification process is filtered out by a cladding light filter and then output through an output end cap.

[0019] Furthermore, it also includes a third tunable bandpass filter for adjusting the spectrum and energy stability of the pump light after the beam combiner, and suppressing the disturbance of the pump and the intensity noise caused by the pump disturbance.

[0020] Furthermore, the third tunable bandpass filter is arranged between the beam combiner and the amplifier stage gain optical fiber.

[0021] A second aspect of the present invention provides a method for suppressing intensity noise of a single-frequency amplified fiber laser, which is implemented by using the intensity noise suppression system of the single-frequency amplified fiber laser, and comprises the following steps:

[0022] S1: Arrange the pump source, oscillator, mode field adapter, amplifier, and output end cap in sequence along the optical path; arrange the first tunable bandpass filter between the pump source and the high-reflection fiber Bragg grating of the oscillator, arrange the second tunable bandpass filter between the gain fiber of the oscillator and the low-reflection fiber Bragg grating, arrange the third tunable bandpass filter between the combiner of the amplifier and the gain fiber of the amplifier stage, and start the pump source;

[0023] S2: adjusting the filtering bandwidth of the first tunable bandpass filter as needed to control the spectral output energy of the pump source, thereby accurately controlling the pump energy entering the oscillator and reducing the intensity noise caused by pump disturbance;

[0024] S3: By adjusting the filtering bandwidth of the second tunable bandpass filter, the emission range of the gain fiber emission spectrum is controlled, the gain characteristics of the gain fiber are optimized, the intracavity loss is reduced and the spontaneous radiation noise is improved, and then a stable laser oscillation is formed in the resonant cavity;

[0025] S4: After the stable laser oscillation is output by the low-reflection fiber Bragg grating, it is efficiently coupled to the amplifier through the mode field adapter; the energy is provided by the first amplification stage pump source and the second amplification stage pump source, and after the beam is combined by the combiner, it is adjusted by the third tunable bandpass filter and acts on the amplification stage gain fiber together; further suppressing the pump disturbance and reducing the intensity noise caused by the pump disturbance;

[0026] S5: After filtering out the excess cladding light in the optical signal amplification process through the cladding light filter, a high-stability, high-coherence single-frequency laser is output through the output end cap to achieve intensity noise suppression of the single-frequency amplified fiber laser.

[0027] The third aspect of the present invention provides a single-frequency amplified fiber laser based on an all-fiber structure, which is implemented by applying the intensity noise suppression method of the single-frequency amplified fiber laser.

[0028] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:

[0029] (1) The intensity noise suppression system and method of the single-frequency amplified fiber laser of the present invention comprises three tunable bandpass filters, which are respectively located after the pump source, after the gain fiber, and between the beam combiner and the gain fiber of the amplifier stage; the main function of these three filters is to adjust the width and energy of the spectrum to optimize the performance of the laser; the first tunable bandpass filter is located after the pump source, and the output spectrum width and energy of the pump source can be changed by adjusting its filter bandwidth and central wavelength; in this way, the pump energy entering the oscillator can be accurately controlled, and the intensity noise caused by pump disturbances (such as fluctuations in pump light intensity, wavelength changes, etc.) can be reduced. The second tunable bandpass filter is located after the gain fiber 4. By adjusting its filtering bandwidth, the emission spectrum range of the gain fiber 4 can be further adjusted, so that the gain characteristics of the gain fiber can be optimized, the single-frequency stability and output power stability of the laser can be improved, thereby reducing the intracavity loss and reducing the intensity noise; the third tunable bandpass filter is located between the beam combiner and the gain fiber of the amplifier stage. The spectrum and energy stability of the pump light after the beam combiner is adjusted by the third tunable bandpass filter, further suppressing the pump disturbance, reducing the intensity noise caused by the pump disturbance, thereby improving the output stability and performance of the amplifier. The intensity noise suppression system of the single-frequency amplified fiber laser of the present invention achieves effective suppression of the intensity noise by accurately controlling the output of the pump source and the emission characteristics of the gain fiber, thereby improving the stability and reliability of the laser.

[0030] (2) The intensity noise suppression method of the single-frequency amplified fiber laser of the present invention comprises the following steps: adding a tunable filter after the pump source; tuning the filter bandwidth of the filter to control the spectral output energy of the pump source under different filter bandwidths, stabilizing the pump wavelength and power, and thereby improving the disturbance of the pump source; adding a tunable filter in the oscillator cavity, tuning the filter bandwidth of the filter, and controlling the emission range of the gain fiber emission spectrum under different filter bandwidths after the gain fiber emits the spectrum line, thereby reducing the cavity loss and improving the spontaneous radiation noise; the pump source disturbance and the cavity loss are the main causes of the relaxation oscillation phenomenon; rationally controlling the filter bandwidths of the two bandpass filters to manage the intensity noise in the single-frequency laser amplification process; the present invention precisely controls the pump energy entering the oscillator and the emission spectrum range of the gain fiber through the coordinated adjustment of the first tunable bandpass filter and the second tunable bandpass filter, thereby reducing the probability of the relaxation oscillation phenomenon.

[0031] (3) The intensity noise suppression system and method of the single-frequency amplified fiber laser of the present invention adopts an all-fiber structure, which can provide better optical signal transmission performance, higher stability and lower loss, and is also easy to integrate and maintain. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a schematic structural diagram of an intensity noise suppression system for a single-frequency amplified fiber laser according to an embodiment of the present invention;

[0033] Figure 2 A schematic flow chart of a method for suppressing intensity noise of a single-frequency amplified fiber laser according to an embodiment of the present invention;

[0034] Figure 3 It is a schematic diagram of a filter controlling the output stability of a pump source under different filter bandwidths in a method for suppressing intensity noise of a single-frequency amplified fiber laser according to an embodiment of the present invention;

[0035] Figure 4 It is a cross-sectional schematic diagram of a filter controlling the emission of a gain fiber under different filter bandwidths in a method for suppressing intensity noise of a single-frequency amplified fiber laser according to an embodiment of the present invention.

[0036] In all the drawings, the same reference numerals represent the same technical features, specifically: 1-pump source, 2-first tunable bandpass filter, 3-high-reflection fiber Bragg grating, 4-gain fiber, 5-second tunable bandpass filter, 6-low-reflection fiber Bragg grating, 7-mode field adapter, 8-first amplifier stage pump source, 9-second amplifier stage pump source, 10-combiner, 11-third tunable bandpass filter, 12-amplifier stage gain fiber, 13-cladding light filter, 14-output end cap. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0038] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, when an element is referred to as being "fixed to", "disposed on" or "provided on" another element, it may be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it may be directly connected to the other element or indirectly connected to the other element; the terms "installed", "connected", "connected" and "provided with" should be understood in a broad sense, for example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the internal connection of the two elements or the interaction relationship between the two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0039] In addition, the terms "first", "second", etc. are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0040] The existing technology involves multiple components and steps when achieving laser noise suppression. These components and steps require precise control and coordination, making the design and operation of the entire system more complicated. Moreover, the various components involved are not all in the form of optical fibers. They may include some non-optical photodetectors, electronic circuits, modulators, etc., which will introduce additional connection points and potential loss sources during use, affecting the overall performance of the laser. The all-fiber structure refers to all components in the system, including gain media, filters, modulators, etc., which are built based on optical fiber technology. The advantage of the all-fiber structure is that it can provide better optical signal transmission performance, higher stability and lower loss, and it is also easy to integrate and maintain. Other studies have found that the dynamic changes in particle number inversion and the determination of optical gain absorption play an important role in the suppression level of intensity noise.

[0041] Example 1

[0042] Based on the above reasons, if Figure 1As shown, the present invention provides an intensity noise suppression system for a single-frequency amplified fiber laser, which can be applied to the noise suppression of a single-frequency amplified fiber laser, and the suppression system is an all-fiber structure, which is simple in structure, easy to integrate, and flexible in suppression mode operation; the system comprises a pump source 1, an oscillator, a mode field adapter 7, an amplifier, and an output end cap 14 arranged in sequence along an optical path; the oscillator comprises a high-reflection fiber Bragg grating 3, a gain fiber 4, and a low-reflection fiber Bragg grating 6 arranged in sequence along the optical path; a first tunable bandpass filter 2 is arranged between the pump source 1 and the high-reflection fiber Bragg grating 3; a second tunable bandpass filter 5 is arranged between the gain fiber 4 and the low-reflection fiber Bragg grating 6; through the first tunable bandpass filter 2 and the second The coordinated adjustment of the two tunable bandpass filters 5 ensures that the number of lower energy level particles that transition upward through the gain fiber 4 and the number of upper energy level particles emitted by the pump source 1 remain in a balanced state during the optical oscillation process, so that the pump light 1 is converted into laser light in the gain fiber 4, and then reflects back and forth in the resonant cavity to form a stable laser oscillation; after the stable laser oscillation is output through the low-reflection fiber Bragg grating 6, it is efficiently coupled to the amplifier through the mode field adapter 7; finally, a stable single-frequency amplified laser is output through the output end cap 14; the present invention accurately controls the output of the pump source and the emission characteristics of the gain fiber through the first tunable bandpass filter and the second tunable bandpass filter, thereby achieving effective suppression of intensity noise and improving the stability and reliability of the laser.

[0043] Furthermore, the pump source 1 is used to provide pump energy for the oscillator of the laser; the stability of the pump source directly affects the output stability and intensity noise level of the laser; therefore, selecting a high-performance, low-noise pump source is the basis for reducing intensity noise. The first tunable bandpass filter 2 is used to change the width and output energy of the output spectrum of the pump source 1, adjust the pump energy entering the oscillator and suppress the intensity noise caused by the pump disturbance; the high-reflection fiber Bragg grating 3 and the low-reflection fiber Bragg grating 6 together constitute the two cavity mirrors of the oscillator; their main function is to form a stable optical resonant cavity and provide the necessary feedback mechanism for laser oscillation; among them, the high-reflection fiber Bragg grating 3 has a high reflectivity, and as the main cavity mirror, it is mainly used to reflect laser light to form a stable optical resonant cavity. The selection of its reflectivity and central wavelength has an important influence on the output wavelength and stability of the laser; the low-reflection fiber Bragg grating 6 has a low reflectivity, and as the secondary cavity mirror, it is mainly used to output laser light. The selection of its reflectivity and central wavelength can adjust the output power and stability of the laser; the gain fiber 4 is the core component of the laser, which absorbs the energy of the pump light to make the particles transition, thereby generating Gain; The performance of the gain fiber 4 directly affects the output power, spectral characteristics and intensity noise level of the laser; The second tunable bandpass filter 5 is located after the gain fiber 4. By adjusting its filtering bandwidth, the emission spectrum range of the gain fiber 4 can be further adjusted, which can optimize the gain characteristics of the gain fiber, improve the single-frequency stability and output power stability of the laser, and thus reduce the intensity noise; The working process of the oscillator is similar to a "dam", with water inflow and water outflow processes at the same time. Compared with the lower energy level, the number of particles in the water inflow transitions to the upper energy level, and compared with the upper energy level, the unstable particles in the water outflow release photons to transition to the lower energy level. The first tunable bandpass filter 2 and the second tunable bandpass filter 5 can be compared to the width of the waterway used to control the inflow and outflow of water. By reasonably adjusting the width of the waterway for inflow and outflow of water, the two can achieve an optimal combination, so that the dam does not overflow or dry up, further causing the oscillator to work "quietly" and further suppressing the intensity noise.

[0044] Furthermore, the mode field adapter 7 is used to connect the oscillator to the amplifier, and its main function is to achieve mode field adaptation and conversion, ensuring that the laser output from the oscillator can be efficiently coupled to the amplifier, preparing for subsequent optical signal amplification; when the pump source 1 provides light energy to the oscillator, the pump light will undergo particle transitions in the gain fiber 4, and the number of transitions and the wavelength depend on the emission spectrum range of the gain fiber 4; by adjusting the filtering bandwidth of the second tunable bandpass filter 5, the emission spectrum range of the gain fiber 4 is further adjusted; the pump light 1 is converted into laser light in the gain fiber 4, and then reflected back and forth in the resonant cavity to form a stable laser oscillation; the stable laser oscillation is output through the low-reflection fiber Bragg grating 6, and then efficiently coupled to the amplifier through the mode field adapter 7; the laser signal transmitted from the oscillator is enhanced by the amplifier, and finally the amplified stable single-frequency laser light is safely and effectively transmitted to an external system or device through the output end cap 14. The present invention coordinates the first tunable bandpass filter 2 and the second tunable bandpass filter 5 so that the number of lower-level particles that transition upward through the gain fiber 4 and the number of upper-level particles emitted by the pump source 1 maintain a balanced state during the optical oscillation process. This balanced state helps to reduce the fluctuation of particle number reversal, thereby reducing the probability of relaxation oscillation and achieving intensity noise suppression.

[0045] The rate equation characterizes the change in the energy of the entire energy level system by describing the change of the inversion particle and the photon density in the cavity over time. In this process, pump absorption, inversion particle number density, intracavity photon number density, and intracavity loss are not fixed values. During long-term operation, the values ​​of these items will fluctuate around a fixed value, causing the laser output power to fluctuate and bring intensity noise. Intensity noise can be regarded as a small disturbance in the steady state. Pump disturbances (such as fluctuations in pump light intensity, wavelength changes, etc.) and intracavity losses are the main causes of relaxation oscillations. Relaxation oscillations are caused by the instability of particle number inversion. This instability can cause rapid fluctuations in laser output power and generate intensity noise. Therefore, this instability can be reduced by precisely controlling the pump energy and spectral characteristics. That is, by suppressing relaxation oscillations, intensity noise can be effectively reduced and the output stability and performance of the laser can be improved.

[0046] Example 2

[0047] The amplifier of the intensity noise suppression system of a single-frequency amplified fiber laser provided by the present invention comprises a beam combiner 10, an amplifier-stage gain fiber 12 and a cladding light filter 13 which are arranged in sequence along an optical path; the laser output by the low-reflection fiber Bragg grating 6 passes through a mode field adapter 7 and is efficiently coupled to the amplifier; the amplifier also comprises a first amplifier-stage pump source 8 and a second amplifier-stage pump source 9; the laser coupled to the amplifier is provided with energy by the first amplifier-stage pump source 8 and the second amplifier-stage pump source 9, and is combined by the beam combiner 10 and acts on the amplifier-stage gain fiber 12 together; the redundant cladding light in the optical signal amplification process is filtered out by the cladding light filter 13 and then output through the output end cap 14.

[0048] Furthermore, the first amplification stage pump source 8 and the second amplification stage pump source 9 are used to provide necessary energy for optical signal amplification; their performance and stability directly affect the working state of the amplifier and the characteristics of the output laser; by providing stable pump energy to the amplifier, it can be ensured that the optical signal maintains a low intensity noise level during the amplification process; the beam combiner 10 is used to combine the pump light of the first amplification stage pump source 8 and the second amplification stage pump source 9, so that the two pump lights can act together on the gain fiber 12 in the amplifier to improve the amplification efficiency and stability of the optical signal; the gain fiber 12 of the amplifier stage provides gain for optical amplification, and its performance directly affects the gain efficiency of the amplifier and the spectrum of the output laser. Characteristics; Through reasonable design and selection of gain optical fiber, the amplification effect of optical signal can be effectively improved while maintaining a low intensity noise level; the cladding light filter 13 is used to filter out excess cladding light in the amplification process to ensure that the beam quality of the amplified light is improved; the presence of cladding light may have an adverse effect on the performance of the amplifier and the output beam quality, so by filtering out the cladding light, the output stability and beam quality of the amplifier can be improved; the output end cap 14 serves as the output end of the amplifier, and its main function is to output the amplified laser to the outside; the design and manufacture of the optical output end cap need to take into account factors such as beam quality, output stability and loss to ensure that the final output performance of the amplifier meets application requirements.

[0049] Example 3

[0050] The intensity noise suppression system of a single-frequency amplified fiber laser provided by the present invention is different from that of Example 2 only in that a third tunable bandpass filter 11 is provided between the beam combiner 10 and the amplifier stage gain fiber 12; the third tunable bandpass filter 11 is used for further stabilizing and selecting the wavelength of the laser at the amplifier stage; when the oscillator generates laser light with low intensity noise, when it passes through the amplifier, the spectrum and energy stability of the pump light after the beam combiner 10 are managed by controlling the filtering bandwidth of the third tunable bandpass filter 11, thereby further suppressing the disturbance of the pump and further suppressing the intensity noise caused by the pump disturbance. Specifically, the low-intensity noise laser output by the oscillator is efficiently coupled to the amplifier after passing through the mode field adapter 7; the first amplifier stage pump source 8 and the second amplifier stage pump source 9 provide energy for the amplification stage of the laser; the multiple light beams are combined into one light beam by the beam combiner 10; the spectrum and energy stability of the pump light after the beam combination by the beam combiner 10 are adjusted by the third tunable bandpass filter 11, and the pump disturbance is further suppressed, and the intensity noise caused by the pump disturbance is reduced, thereby improving the output stability and performance of the amplifier; the gain is provided for light amplification by the amplifier stage gain fiber 12; the excess cladding light in the beam amplification process is filtered out by the cladding light filter 13 to ensure the high beam quality of the amplified light; finally, the amplified laser is output to the outside through the output end cap 14; the pump source 1, the oscillator, the amplifier, the first tunable bandpass filter 2, the second tunable bandpass filter 5, the third tunable bandpass filter 11 and the output end cap 14 work together to form a complete single-frequency fiber laser system, which can produce a single-frequency laser output with high stability and high coherence.

[0051] like Figure 2-Figure 4 As shown, the second aspect of the present invention provides a method for suppressing intensity noise of a single-frequency amplified fiber laser, which is implemented by the intensity noise suppression system of the single-frequency amplified fiber laser, and includes the following steps:

[0052] S1: Arrange the pump source 1, oscillator, amplifier, and output end cap 14 in sequence along the optical path; arrange the first tunable bandpass filter 2 between the pump source 1 and the high-reflection fiber Bragg grating 3 of the oscillator, arrange the second tunable bandpass filter 5 between the gain fiber 4 of the oscillator and the low-reflection fiber Bragg grating 6, arrange the third tunable bandpass filter 11 between the combiner 10 of the amplifier and the gain fiber 12 of the amplifier stage, and start the pump source 1;

[0053] S2: adjusting the filtering bandwidth of the first tunable bandpass filter 2 as needed to control the spectral output energy of the pump source 1, thereby accurately controlling the pump energy entering the oscillator and reducing the intensity noise caused by pump disturbances (such as pump light intensity fluctuations, wavelength changes, etc.);

[0054] Specifically, the filtering bandwidth of the first tunable bandpass filter 2 is adjusted as needed, and the spectral output energy of the pump source 1 is controlled under different filtering bandwidths, thereby achieving precise control of the wavelength and power of the pump light output by the pump source 1, and reducing the intensity noise caused by pump disturbances (such as pump light intensity fluctuations, wavelength changes, etc.);

[0055] S3: By adjusting the filtering bandwidth of the second tunable bandpass filter 5, the emission range of the emission spectrum of the gain fiber 4 is controlled, the gain characteristics of the gain fiber are optimized, the intracavity loss is reduced and the spontaneous radiation noise is improved, and then a stable laser oscillation is formed in the resonant cavity;

[0056] S4: After the stable laser oscillation is output by the low-reflection fiber Bragg grating 6, it is efficiently coupled to the amplifier through the mode field adapter 7; the first amplifier stage pump source 8 and the second amplifier stage pump source 9 provide energy, and the beam combiner 10 combines the beams and then adjusts them through the third tunable bandpass filter 11, and then acts on the amplifier stage gain fiber 12 together, so as to further suppress the pump disturbance and reduce the intensity noise caused by the pump disturbance, thereby improving the output stability and performance of the amplifier;

[0057] S5: After filtering out the excess cladding light in the optical signal amplification process through the cladding light filter 13, a single-frequency laser with high stability and high coherence is output through the output end cap 14, thereby achieving intensity noise suppression of the single-frequency amplified fiber laser.

[0058] Furthermore, in step S3, the pump light adjusted by the first tunable bandpass filter 2 undergoes particle transition in the gain fiber 4 after passing through the high-reflection fiber Bragg grating 3; by adjusting the filtering bandwidth of the second tunable bandpass filter 5, the emission range of the emission spectrum of the gain fiber 4 is controlled under different filtering bandwidths; so that the number of lower-level particles that transition upward through the gain fiber 4 and the number of upper-level particles emitted by the pump source 1 are kept balanced during the optical oscillation process, the occurrence of relaxation oscillation phenomenon is reduced, and the intensity noise is suppressed at the same time; the pump light 1 is converted into laser in the gain fiber 4 and then reflected back and forth in the resonant cavity to form a stable laser oscillation; the present invention achieves the reduction of laser pump disturbance and the improvement of intracavity loss through the coordinated adjustment of the first tunable bandpass filter 2 and the second tunable bandpass filter 5, thereby achieving efficient suppression of spontaneous radiation noise.

[0059] Furthermore, in step S4, the spectrum and energy stability of the pump light after being combined by the combiner 10 are adjusted by the third tunable bandpass filter 11, so as to further suppress the pump disturbance and reduce the intensity noise caused by the pump disturbance, thereby improving the output stability and performance of the amplifier; the gain fiber 12 is used to provide gain for the optical amplification, and the cladding light filter 13 filters out the excess cladding light in the process of light beam amplification, so as to ensure the high beam quality of the amplified light; finally, the amplified, high-stability, high-coherence single-frequency laser is output to the outside through the output end cap 14.

[0060] The third aspect of the present invention provides a single-frequency amplified fiber laser based on an all-fiber structure, which is implemented by applying the intensity noise suppression method of the single-frequency amplified fiber laser.

[0061] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An intensity noise suppression system for a single-frequency amplified fiber laser, characterized in that: It comprises a pump source (1), an oscillator, an amplifier and an output end cap (14) which are arranged in sequence along an optical path; wherein: The oscillator comprises a high-reflection fiber Bragg grating (3), a gain fiber (4) and a low-reflection fiber Bragg grating (6) which are arranged in sequence along an optical path; The system also includes a first tunable bandpass filter (2) for adjusting the pump energy entering the oscillator and suppressing the intensity noise caused by the pump disturbance, and a second tunable bandpass filter (5) for adjusting the emission spectrum range of the gain fiber (4) to optimize the gain characteristics of the gain fiber, thereby reducing the intracavity loss and reducing the intensity noise; Through the coordinated adjustment of the first tunable bandpass filter (2) and the second tunable bandpass filter (5), the output of the pump source (1) and the emission characteristics of the gain optical fiber (4) are precisely controlled, thereby achieving effective suppression of intensity noise and improving the stability and reliability of the laser; the stable laser oscillation formed in the resonant cavity is output through the low-reflection fiber Bragg grating (6), and then efficiently coupled to the amplifier through the mode field adapter (7), and finally the output of stable single-frequency amplified laser is achieved through the output end cap (14).

2. The intensity noise suppression system of a single-frequency amplified fiber laser according to claim 1, characterized in that: The first tunable bandpass filter (2) is arranged between the pump source (1) and the high-reflection fiber Bragg grating (3).

3. The intensity noise suppression system of a single-frequency amplified fiber laser according to claim 1, characterized in that: The second tunable bandpass filter (5) is arranged between the gain optical fiber (4) and the low-reflection fiber Bragg grating (6).

4. An intensity noise suppression system for a single-frequency amplified fiber laser according to any one of claims 1 to 3, characterized in that: The amplifier comprises a beam combiner (10), an amplifier-stage gain optical fiber (12) and a cladding light filter (13) which are sequentially arranged at intervals along an optical path; the laser output by the low-reflection fiber Bragg grating (6) passes through a mode field adapter (7) and is efficiently coupled to the amplifier.

5. The method for suppressing intensity noise of a single-frequency amplified fiber laser according to claim 4, characterized in that: The amplifier further comprises a first amplification stage pump source (8) and a second amplification stage pump source (9) for providing necessary energy for optical signal amplification; the laser coupled to the amplifier is provided with energy by the first amplification stage pump source (8) and the second amplification stage pump source (9), and after being combined by a beam combiner (10), the lasers act together on the amplification stage gain optical fiber (12); and the excess cladding light in the optical signal amplification process is filtered out by a cladding light filter (13) and then output through an output end cap (14).

6. The intensity noise suppression system of a single-frequency amplified fiber laser according to claim 5, characterized in that: It also includes a third tunable bandpass filter (11) for adjusting the spectrum and energy stability of the pump light after the beam combiner (10) and suppressing the disturbance of the pump and the intensity noise caused by the pump disturbance.

7. The intensity noise suppression system of a single-frequency amplified fiber laser according to claim 5, characterized in that: The third tunable bandpass filter (11) is arranged between the beam combiner (10) and the amplifier-stage gain optical fiber (12).

8. A method for suppressing intensity noise of a single-frequency amplified fiber laser, characterized in that: The intensity noise suppression system of the single-frequency amplified fiber laser according to any one of claims 1 to 7 is implemented, comprising the following steps: S1: a pump source (1), an oscillator, a mode field adapter (7), an amplifier, and an output end cap (14) are sequentially arranged along an optical path; a first tunable bandpass filter (2) is arranged between the pump source (1) and a high-reflection fiber Bragg grating (3) of the oscillator, a second tunable bandpass filter (5) is arranged between a gain fiber (4) of the oscillator and a low-reflection fiber Bragg grating (6), and a third tunable bandpass filter (11) is arranged between a beam combiner (10) of the amplifier and an amplifier-stage gain fiber (12), and the pump source (1) is started; S2: adjusting the filtering bandwidth of the first tunable bandpass filter (2) as required to control the spectral output energy of the pump source (1), thereby accurately controlling the pump energy entering the oscillator and reducing the intensity noise caused by pump disturbance; S3: By adjusting the filtering bandwidth of the second tunable bandpass filter (5), the emission range of the emission spectrum of the gain fiber (4) is controlled, the gain characteristics of the gain fiber are optimized, the intracavity loss is reduced and the spontaneous radiation noise is improved, and thus stable laser oscillation is formed in the resonant cavity; S4: After the stable laser oscillation is output by the low-reflection fiber Bragg grating (6), it is efficiently coupled to the amplifier through the mode field adapter (7); the energy is provided by the first amplifier stage pump source (8) and the second amplifier stage pump source (9), and after the beam is combined by the beam combiner (10), it is adjusted by the third tunable bandpass filter (11) and acts on the amplifier stage gain fiber (12); the pump disturbance is further suppressed and the intensity noise caused by the pump disturbance is reduced; S5: After filtering out excess cladding light in the optical signal amplification process through a cladding light filter (13), a single-frequency laser with high stability and high coherence is output through an output end cap (14), thereby achieving intensity noise suppression of the single-frequency amplified optical fiber laser.

9. A single-frequency amplified fiber laser based on an all-fiber structure, characterized in that: This is achieved by using the intensity noise suppression method of a single-frequency amplified fiber laser as described in claim 8.

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