1018nm mode-locked laser with tunable wavelength

Abstract

The invention discloses a wavelength-tunable 1018nm mode-locked laser, which comprises a pumping source, a wavelength division multiplexer, a gain optical fiber, a delay optical fiber, a nonreciprocal phase shifter, a first coupler, a fiber grating, a temperature control module and an isolator, and is characterized in that the pumping source is connected with the reflection end of the wavelength division multiplexer, and the common end of the wavelength division multiplexer is connected with the gain optical fiber; the signal end of the wavelength division multiplexer is connected with the first coupler, the gain optical fiber, the delay optical fiber, the nonreciprocal phase shifter and the first coupler are connected in sequence, the wavelength division multiplexer, the gain optical fiber, the delay optical fiber, the nonreciprocal phase shifter and the first coupler form an annular loop, the first coupler is connected with the fiber bragg grating and the isolator, and the fiber bragg grating is connected with the isolator. The temperature control module is used for controlling the temperature of the fiber grating. According to the 1018nm mode-locked laser, the full-polarization-maintaining optical fiber and the polarization-maintaining optical device are used, so that the 1018nm mode-locked laser has excellent long-term working stability and output characteristic reproduction capability, and meanwhile, the full-optical-fiber structure has the advantages of miniaturization, integration and easiness in maintenance.

Description

A wavelength-tunable 1018nm mode-locked laser Technical Field

[0001] This invention relates to the field of fiber laser technology, specifically to a wavelength-tunable 1018nm mode-locked laser. Background Technology

[0002] Compared with solid-state lasers, mode-locked fiber lasers are important light sources in applications such as ultra-precision manufacturing, optical communication, optical frequency combs, and quantum sensing due to their advantages such as low pulse noise, good beam quality, and high stability.

[0003] The operating wavelengths of common passively mode-locked lasers are typically concentrated at 1030 nm, 1064 nm, or 1550 nm, depending on the rare-earth ion doping in the fiber. Exploration of 1018 nm passively mode-locked fiber lasers remains to be studied. This is because the emission intensity of ytterbium-doped fiber at 1018 nm is much lower than at 1030 nm, leading to significant spontaneous emission amplification (ASE) noise at 1030 nm, meaning that obtaining a high signal-to-noise ratio 1018 nm laser presents a challenge. However, the 1018 nm laser is the fundamental frequency of the 509 nm laser used in the preparation of cesium Rydberg states, thus holding significant application value in cesium Rydberg state excitation. Furthermore, passively mode-locked ultrafast lasers offer significant advantages over traditional modulated ns pulses in Rydberg excitation, including higher peak power, higher time resolution, and higher repetition rate.

[0004] For passively mode-locked fiber lasers, saturable absorbers play a crucial role in self-initiation and stable mode-locking operation. Material-based saturable absorbers, such as semiconductor saturable absorber mirrors (SESAMs) and carbon nanotubes (CNTs), have been used to generate mode-locked pulses in the 1 μm band due to their ease of coupling into fiber systems. However, the long-term operational stability of these fiber lasers is challenged by the inherent properties of the materials. Artificially constructed saturable absorbers, such as nonlinear polarization rotation (NPRs), offer a mature solution due to their simple structure, requiring only a combination of polarization devices, and are also commonly used to generate mode-locked pulses in the 1 μm band. However, achieving precise polarization control and maintaining a fully polarization-maintaining (PM) fiber structure for long-term stability and performance repeatability in NPR-based passive mode-locking is quite challenging. Nonlinear optical ring mirrors (NOLMs) can also generate 1 μm mode-locked pulses, but NOLM mode-locking requires sufficient nonlinear phase shift to accumulate between backpropagating light to initiate mode-locking, which necessitates longer cavity lengths or additional amplifiers, thus complicating laser design. In recent years, nonlinear amplifying ring mirrors (NALMs) have attracted considerable attention by optimizing the self-starting characteristics of non-reciprocal phase shifters within fiber rings. NALM-based fiber lasers can achieve fully polarization-maintaining fiber structures, possess excellent self-starting mode-locking mechanisms, and do not have short lifetime limitations, making them ideal saturable absorbers.

[0005] To precisely match the excitation wavelength of Rydberg state atoms, the center wavelength of the laser typically needs to be stable over a long period and possess a certain degree of tunability. Some researchers have achieved wavelength tuning through grating diffraction selection (Optics Communications 559 (2024) 130398), but the laser constructed using this method has a spatial structure, and its long-term stability remains to be verified. Temperature-tuned fiber gratings are an effective method; temperature-induced micro-variations in the fiber grating period can achieve precise center wavelength tuning, and long-term temperature control can ensure the long-term stability of the grating's reflected wavelength. Summary of the Invention

[0006] The purpose of this invention is to provide a wavelength-tunable 1018nm mode-locked laser to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a wavelength-tunable 1018nm mode-locked laser, comprising a pump source, a wavelength division multiplexer, a gain fiber, a delay fiber, a non-reciprocal phase shifter, a first coupler, a fiber grating, a temperature control module, and an isolator. The pump source is connected to the reflecting end of the wavelength division multiplexer, the common end of the wavelength division multiplexer is connected to the gain fiber, and the signal end of the wavelength division multiplexer is connected to the first coupler. The gain fiber, the delay fiber, the non-reciprocal phase shifter, and the first coupler are connected sequentially. The wavelength division multiplexer, the gain fiber, the delay fiber, the non-reciprocal phase shifter, and the first coupler form a loop. The first coupler is connected to the fiber grating and the isolator respectively. The temperature control module is used to control the temperature of the fiber grating.

[0008] Furthermore, the pump source is a butterfly-packaged semiconductor laser with a working center wavelength of 974nm or 976nm, coupled by a single-mode fiber, and has a maximum output power greater than 200mW; the gain fiber is a single-clad or double-clad polarization-maintaining ytterbium-doped silica fiber operating in core-pump mode, with an absorption coefficient for pump light greater than 25dB / m; the delay fiber is a PM980 fiber, used to increase the nonlinear phase shift difference accumulated in the bidirectional transmission light within the resonant cavity to optimize self-starting performance and adjust the repetition frequency of the output pulse.

[0009] Furthermore, the non-reciprocal phase shifter consists of two Faraday rotators and a quarter-wave plate, or it consists of a polarization beam splitter and combiner, a Faraday rotator, an eighth-wave plate, and a mirror. The bidirectional transmitted light in the resonant cavity generates an additional π / 2 phase through the non-reciprocal phase shifter to optimize the mode-locked self-starting performance.

[0010] Furthermore, the first coupler is a 2×2 coupler with a splitting ratio of not 50:50; the fiber grating is a narrow-bandwidth fiber Bragg grating or a wide-bandwidth chirped fiber Bragg grating with a dispersion parameter of less than 1 ps / nm, the fiber grating is inscribed on PM980 fiber, and the reflectivity of the fiber grating to signal light is greater than 25%; the isolator has an isolation of greater than 20 dB and is used to cut off the output path optical coupling back to the resonant cavity.

[0011] The present invention also provides a wavelength-tunable 1018nm mode-locked laser, comprising a pump source, a wavelength division multiplexer, a gain fiber, a delay fiber, a non-reciprocal phase shifter, a first coupler, a fiber grating, a temperature control module, and a second coupler. The pump source is connected to the reflection end of the wavelength division multiplexer, the common end of the wavelength division multiplexer is connected to the gain fiber, and the signal end of the wavelength division multiplexer is connected to the first coupler. The gain fiber, the second coupler, the delay fiber, the non-reciprocal phase shifter, and the first coupler are sequentially connected to form a loop. The first coupler is connected to the fiber grating, and the temperature control module is used to control the temperature of the fiber grating.

[0012] Furthermore, the pump source is a butterfly-packaged semiconductor laser with a working center wavelength of 974nm or 976nm, coupled by a single-mode fiber, and has a maximum output power greater than 200mW; the gain fiber is a single-clad or double-clad polarization-maintaining ytterbium-doped silica fiber operating in core-pump mode, with an absorption coefficient for pump light greater than 25dB / m; the delay fiber is a PM980 fiber, used to increase the nonlinear phase shift difference accumulated in the bidirectional transmission light within the resonant cavity to optimize self-starting performance and adjust the repetition frequency of the output pulse.

[0013] Furthermore, the non-reciprocal phase shifter consists of two Faraday rotators and a quarter-wave plate, or it consists of a polarization beam splitter and combiner, a Faraday rotator, an eighth-wave plate, and a mirror. The bidirectional transmitted light in the resonant cavity generates an additional π / 2 phase through the non-reciprocal phase shifter to optimize the mode-locked self-starting performance.

[0014] Furthermore, the first coupler is a 2×2 coupler with a splitting ratio of not 50:50; the fiber grating is a narrow-bandwidth fiber Bragg grating or a wide-bandwidth chirped fiber Bragg grating with a dispersion parameter of less than 1 ps / nm, the fiber grating is inscribed on PM980 fiber, and the reflectivity of the fiber grating to signal light is greater than 25%; the isolator has an isolation of greater than 20 dB and is used to cut off the output path optical coupling back to the resonant cavity.

[0015] Furthermore, it also includes an isolator, to which the second coupler is connected.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1) The 1018nm mode-locked laser realized by the present invention uses all polarization-maintaining fiber and polarization-maintaining optical devices, which has excellent long-term working stability and output characteristic reproducibility. At the same time, the all-fiber structure has the advantages of miniaturization, integration and easy maintenance.

[0017] 2) The 1018nm mode-locked laser implemented in this invention combines a nonlinear amplifying ring mirror and a fiber grating-based spectral filtering technique, giving it a high spectral signal-to-noise ratio and easy self-starting characteristics.

[0018] 3) The 1018nm mode-locked laser implemented in this invention achieves a stable mode-locked output with a repetition frequency of 1MHz-100MHz by changing the length of the PM980 fiber in the resonant cavity without affecting the stable mode-locked output. Furthermore, continuous tuning of the pulse width of 100fs-100ps can be achieved through dispersion management.

[0019] 4) The 1018nm mode-locked laser implemented in this invention can achieve long-term stability of the laser output wavelength through the temperature control module, and can achieve wavelength tuning of more than 300GHz through temperature tuning. Attached Figure Description

[0020] Figure 1 is a schematic diagram of a wavelength-tunable 1018nm mode-locked laser structure according to Embodiment 1 of the present invention; Figure 2(a) shows the pulse sequence of the output laser of a wavelength-tunable 1018nm mode-locked laser according to Embodiment 1, in which the pulse sequence shows that the mode-locked laser outputs stably; Figure 2(b) shows the output spectrum of the laser, with a 20dB bandwidth of 0.498nm; Figure 3 is a schematic diagram of a wavelength-tunable 1018nm mode-locked laser structure according to Embodiment 2 of the present invention; Figure 4(a) shows the repetition frequency radio frequency spectrum of the output laser of a wavelength-tunable 1018nm mode-locked laser according to Embodiment 2, with a repetition frequency of 25.71MHz; Figure 4(b) shows the pulse autocorrelation trajectory of the laser, with a measured and fitted pulse width of 12.92ps; Figure 4(c) shows the output spectrum of the laser, with a 20dB bandwidth of 0.908nm; Figure 4(d) shows that the signal-to-noise ratio of the output spectrum of the laser exceeds 45dB. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1: Referring to Figure 1, a wavelength-tunable 1018nm mode-locked laser includes a pump source 1, a wavelength division multiplexer 2, a gain fiber 3, a delay fiber 4, a non-reciprocal phase shifter 5, a first coupler 6, a fiber grating 7, a temperature control module 8, and an isolator 9. The pump source 1 is connected to the reflecting end of the wavelength division multiplexer 2, the common end of the wavelength division multiplexer 2 is connected to the gain fiber 3, and the signal end of the wavelength division multiplexer 2 is connected to the first coupler 6. The gain fiber 3, the delay fiber 4, the non-reciprocal phase shifter 5, and the coupler 6 are connected in sequence. The wavelength division multiplexer 2, the gain fiber 3, the delay fiber 4, the non-reciprocal phase shifter 5, and the first coupler 6 form a loop. The first coupler 6 is connected to the fiber grating 7 and the isolator 9 respectively. The temperature control module 8 is used to control the temperature of the fiber grating 7.

[0023] The laser in this embodiment consists of a nonlinear amplifying ring (NALM) and a linear arm connected to a narrowband fiber Bragg grating (fiber grating 7). They are connected by a 2×2 polarization-maintaining fiber coupler (first coupler 6) with a splitting ratio of 30:70 at 1018 nm. The NALM ring includes a 976 / 1018 nm polarization-maintaining wavelength division multiplexer (wavelength division multiplexer 2) and ytterbium-doped fiber (gain fiber 3) as the gain medium. A 2m polarization-maintaining PM980 fiber (delay fiber 4) is used to induce a nonlinear phase shift difference between clockwise and counterclockwise propagation to enhance the self-starting capability of mode-locked operation. The non-reciprocal phase shifter 5 consists of a polarization beam splitter and combiner, a Faraday rotator, and an eighth-waveplate, providing a linear phase bias of -π / 2. A 0.4m gain fiber 3 is connected to pump source 1 via a wavelength division multiplexer 2 with an operating wavelength of 976 / 1018 nm. Pump source 1 pumps the core of the gain fiber. An isolator 9 with an operating wavelength of 1018 nm is connected to the output of a 2×2 polarization-maintaining fiber coupler. The remaining portion of the fiber cavity consists of polarization-maintaining PM980 fiber. The total cavity length is approximately 3.5m, and the net cavity dispersion at 1018 nm is 0.805 ps². The temperature control module 8 maintains the fiber grating at a constant temperature of 25°C.

[0024] The laser cavity is entirely composed of polarization-maintaining fibers and fiber optic assemblies, which helps to improve the long-term stability of the output pulse.

[0025] Pump source 1 is a single-mode 976nm laser diode, model LC96Z600-76, a 14-pin butterfly-packaged single-mode pumped laser tube, coupled by single-mode fiber, with a maximum output power greater than 200mW.

[0026] The wavelength division multiplexer 2 includes a reflector, a common terminal, and a signal terminal. The reflector is connected to the pump source 1, the common terminal is connected to the gain fiber 3, and the signal terminal is connected to the first coupler 6.

[0027] Gain fiber 3 is a double-clad ytterbium-doped fiber with a core diameter of 5 μm and a cladding diameter of 130 μm. The cladding pump absorption at 975 nm is 1.80 dB / m, and the core absorption coefficient for pump light is greater than 25 dB / m.

[0028] The delay fiber 4 is a PM980 fiber, used to increase the nonlinear phase shift difference accumulated by the bidirectional transmission light in the resonant cavity to optimize the self-starting performance and adjust the repetition frequency of the output pulse. The pulse repetition frequency can be adjusted from MHz to hundreds of MHz by adjusting the length of the delay fiber.

[0029] One end of the first coupler 6 is connected to the fiber optic grating 7, which is defined as the incident end. The high splitting ratio port of the incident end is connected to the signal end of the wavelength division multiplexer 2, and the low splitting ratio port is connected to the non-reciprocal phase shifter 5.

[0030] The narrowband fiber Bragg grating (fiber grating 7) has a reflectivity of 99.7%, a center wavelength of approximately 1018 nm, a bandwidth of 0.25 nm, and a dispersion parameter of less than 1 ps / nm. Fiber grating 7 is inscribed on PM980 fiber, and its reflectivity to signal light is greater than 25%.

[0031] The temperature control module 8 consists of fiber optic grating encapsulated mechanical components, a thermoelectric cooler (TEC), a thermistor, and an operational amplifier-based analog PID temperature control circuit; it can achieve precise tuning of the fiber optic grating 7 temperature from 10℃ to 60℃ (corresponding to an adjustable center wavelength range greater than 300GHz), and long-term temperature stability is better than 0.005℃.

[0032] Isolator 9 has an isolation level greater than 20dB and is used to cut off the output path optical coupling back to the resonant cavity.

[0033] The average power of the mode-locked laser output is 1.92mW (single pulse energy is about 0.3nJ), and the center wavelength is 1017.7nm.

[0034] The fiber optic devices of the 1018nm mode-locked lasers based on nonlinear amplifying rings mentioned above are all made of polarization-maintaining fiber and are limited to slow-axis operation.

[0035] This embodiment achieves repetition frequency tuning of the resonant cavity by coupling a portion of the spatial optical path within the resonant cavity with a displacement stage or by configuring piezoelectric ceramic or other telescopic devices on the resonant cavity fiber. This embodiment also adds a coupler after the gain fiber within the resonant cavity to output laser light, enabling loss control and achieving higher output pulse energy. Furthermore, this embodiment achieves stable mode-locked pulse output by configuring the fiber grating of the linear arm as a fiber mirror and configuring an optical bandpass filter within the resonant cavity. Finally, this embodiment combines the coupler, wavelength division multiplexer, and phase shifter into a single composite device through device design, achieving a repetition frequency greater than 100MHz.

[0036] Example 2: Referring to Figure 3, a wavelength-tunable 1018nm mode-locked laser includes a pump source 1, a wavelength division multiplexer 2, a gain fiber 3, a second coupler 10, a delay fiber 4, a non-reciprocal phase shifter 5, a first coupler 6, a fiber grating 7, a temperature control module 8, and an isolator 9. The pump source 1 is connected to the reflection end of the wavelength division multiplexer 2, the common end of the wavelength division multiplexer 2 is connected to the gain fiber 3, and the signal end of the wavelength division multiplexer 2 is connected to the first coupler 6. The gain fiber 3, the second coupler 10, the delay fiber 4, the non-reciprocal phase shifter 5, and the first coupler 6 are connected sequentially. The wavelength division multiplexer 2, the gain fiber 3, the second coupler 10, the delay fiber 4, the non-reciprocal phase shifter 5, and the first coupler 6 form a loop. The second coupler 10 is connected to the isolator 9, and the first coupler 6 is connected to the fiber grating 7. The temperature control module 8 is used to control the temperature of the fiber grating 7.

[0037] The laser in this embodiment consists of a nonlinear amplifying ring (NALM) and a linear arm connected to a narrowband fiber Bragg grating (fiber grating 7). They are connected via a 2×2 polarization-maintaining fiber coupler (first coupler 6) with a splitting ratio of 30:70 at 1018 nm. The NALM ring includes a 976 / 1018 nm polarization-maintaining wavelength division multiplexer (wavelength division multiplexer 2) and ytterbium-doped fiber (gain fiber 3) as the gain medium. A 5m polarization-maintaining PM980 fiber (delay fiber 4) is used to induce a nonlinear phase shift difference between clockwise and counterclockwise propagation to enhance the self-starting capability of mode-locked operation. The non-reciprocal phase shifter 5 consists of a polarization beam splitter and combiner, a Faraday rotator, and an eighth-waveplate, providing a linear phase bias of -π / 2. A 0.4m gain fiber 3 is connected to a pump source 1 via a wavelength division multiplexer 2 with a working wavelength of 976 / 1018 nm. The pump source 1 pumps the core of the gain fiber. The gain fiber 3 is then connected to a 2×2 polarization-maintaining fiber coupler (second coupler 10) with a splitting ratio of 30:70 at 1018 nm. An isolator (isolator 9) with a working wavelength of 1018 nm is connected to the output of the 2×2 polarization-maintaining fiber coupler (second coupler 10). The remaining portion of the fiber cavity consists of polarization-maintaining PM980 fiber. The total cavity length is approximately 8m, and the net cavity dispersion at 1018 nm is 0.16 ps². The temperature control module 8 maintains the fiber grating 7 at a constant temperature of 25°C.

[0038] The laser cavity is entirely composed of polarization-maintaining fibers and fiber optic assemblies, which helps to improve the long-term stability of the output pulse.

[0039] Pump source 1 is a single-mode 976nm laser diode, model LC96Z600-76, a 14-pin butterfly-packaged single-mode pumped laser tube, coupled by single-mode fiber, with a maximum output power greater than 200mW.

[0040] The wavelength division multiplexer 2 includes a reflector, a common terminal, and a signal terminal. The reflector is connected to the pump source 1, the common terminal is connected to the gain fiber 3, and the signal terminal is connected to the first coupler 6.

[0041] Gain fiber 3 is a double-clad ytterbium-doped fiber with a core diameter of 5 μm and a cladding diameter of 130 μm. The cladding pump absorption at 975 nm is 1.80 dB / m, and the core absorption coefficient for pump light is greater than 25 dB / m.

[0042] The delay fiber 4 is a PM980 fiber, used to increase the nonlinear phase shift difference accumulated by the bidirectional transmission light in the resonant cavity to optimize the self-starting performance and adjust the repetition frequency of the output pulse. The pulse repetition frequency can be adjusted from MHz to hundreds of MHz by adjusting the length of the delay fiber.

[0043] One end of the first coupler 6 is connected to the fiber optic grating 7, which is defined as the incident end. The high splitting ratio port of the incident end is connected to the signal end of the wavelength division multiplexer 2, and the low splitting ratio port is connected to the non-reciprocal phase shifter 5.

[0044] The narrowband fiber Bragg grating (fiber grating 7) has a reflectivity of 99.7%, a center wavelength of approximately 1018 nm, a bandwidth of 0.25 nm, and a dispersion parameter of less than 1 ps / nm. Fiber grating 7 is inscribed on PM980 fiber, and its reflectivity to signal light is greater than 25%.

[0045] The temperature control module 8 consists of fiber optic grating encapsulated mechanical components, a thermoelectric cooler (TEC), a thermistor, and an operational amplifier-based analog PID temperature control circuit; it can achieve precise tuning of the fiber optic grating 7 temperature from 10℃ to 60℃ (corresponding to an adjustable center wavelength range greater than 300GHz), and long-term temperature stability is better than 0.005℃.

[0046] Isolator 9 has an isolation level greater than 20dB and is used to cut off the output path optical coupling back to the resonant cavity.

[0047] The stable mode-locked laser output has an average power of 56.06mW (single pulse energy of approximately 2.2nJ), a repetition frequency of 25.7MHz, a center wavelength of 1017.7nm, a spectral signal-to-noise ratio greater than 45dB, and a pulse width of 12.92ps.

[0048] The fiber optic devices of the 1018nm mode-locked lasers based on nonlinear amplifying rings mentioned above are all made of polarization-maintaining fiber and are limited to slow-axis operation.

[0049] This embodiment achieves repetition frequency tuning of the resonant cavity by coupling a portion of the spatial optical path within the resonant cavity with a displacement stage or by configuring piezoelectric ceramic or other telescopic devices on the resonant cavity fiber. This embodiment also adds a coupler after the gain fiber within the resonant cavity to output laser light, enabling loss control and achieving higher output pulse energy. Furthermore, this embodiment achieves stable mode-locked pulse output by configuring the fiber grating of the linear arm as a fiber mirror and configuring an optical bandpass filter within the resonant cavity. Finally, this embodiment combines the coupler, wavelength division multiplexer, and phase shifter into a single composite device through device design, achieving a repetition frequency greater than 100MHz.

[0050] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A wavelength-tunable 1018nm mode-locked laser, characterized in that, The system includes a pump source (1), a wavelength division multiplexer (2), a gain fiber (3), a delay fiber (4), a non-reciprocal phase shifter (5), a first coupler (6), a fiber grating (7), a temperature control module (8), and an isolator (9). The pump source (1) is connected to the reflection end of the wavelength division multiplexer (2), the common end of the wavelength division multiplexer (2) is connected to the gain fiber (3), and the signal end of the wavelength division multiplexer (2) is connected to the first coupler (6). The gain fiber (3), the delay fiber (4), the non-reciprocal phase shifter (5), and the first coupler (6) are connected in sequence. The wavelength division multiplexer (2), the gain fiber (3), the delay fiber (4), the non-reciprocal phase shifter (5), and the first coupler (6) form a loop. The first coupler (6) is connected to the fiber grating (7) and the isolator (9) respectively. The temperature control module (8) is used to control the temperature of the fiber grating (7).

2. The wavelength-tunable 1018nm mode-locked laser according to claim 1, characterized in that, The pump source (1) is a butterfly-packaged semiconductor laser with a working center wavelength of 974nm or 976nm. It is coupled and output by a single-mode fiber and has a maximum output power of more than 200mW. The gain fiber (3) is a single-clad or double-clad polarization-maintaining ytterbium-doped silica fiber operating in core-pump mode, with an absorption coefficient of more than 25dB / m for the pump light. The delay fiber (4) is a PM980 fiber, used to increase the nonlinear phase shift difference accumulated by the bidirectional transmission light in the resonant cavity to optimize the self-starting performance and adjust the repetition frequency of the output pulse.

3. A wavelength-tunable 1018nm mode-locked laser according to claim 1, characterized in that, The non-reciprocal phase shifter (5) consists of two Faraday rotators and a quarter-wave plate, or a polarization beam splitter and combiner, a Faraday rotator, an eighth-wave plate, and a mirror. The bidirectional transmitted light in the resonant cavity generates an additional π / 2 phase through the non-reciprocal phase shifter (5) to optimize the mode-locked self-starting performance.

4. A wavelength-tunable 1018nm mode-locked laser according to claim 1, characterized in that, The first coupler (6) is a 2×2 coupler with a splitting ratio of not 50:50; the fiber grating (7) is a narrow bandwidth fiber Bragg grating or a wide bandwidth chirped fiber Bragg grating with a dispersion parameter of less than 1ps / nm. The fiber grating (7) is inscribed on a PM980 fiber and has a reflectivity of more than 25% for the signal light; the isolator (9) has an isolation of more than 20dB and is used to cut off the output path optical coupling back to the resonant cavity.

5. A wavelength-tunable 1018nm mode-locked laser, characterized in that, The system includes a pump source (1), a wavelength division multiplexer (2), a gain fiber (3), a delay fiber (4), a non-reciprocal phase shifter (5), a first coupler (6), a fiber grating (7), a temperature control module (8), and a second coupler (10). The pump source (1) is connected to the reflection end of the wavelength division multiplexer (2), the common end of the wavelength division multiplexer (2) is connected to the gain fiber (3), and the signal end of the wavelength division multiplexer (2) is connected to the first coupler (6). The gain fiber (3), the second coupler (10), the delay fiber (4), the non-reciprocal phase shifter (5), and the first coupler (6) are connected in sequence. The wavelength division multiplexer (2), the gain fiber (3), the second coupler (10), the delay fiber (4), the non-reciprocal phase shifter (5), and the first coupler (6) form a loop. The first coupler (6) is connected to the fiber grating (7), and the temperature control module (8) is used to control the temperature of the fiber grating (7).

6. A wavelength-tunable 1018nm mode-locked laser according to claim 5, characterized in that, The pump source (1) is a butterfly-packaged semiconductor laser with a working center wavelength of 974nm or 976nm. It is coupled and output by a single-mode fiber and has a maximum output power of more than 200mW. The gain fiber (3) is a single-clad or double-clad polarization-maintaining ytterbium-doped silica fiber operating in core-pump mode, with an absorption coefficient of more than 25dB / m for the pump light. The delay fiber (4) is a PM980 fiber, used to increase the nonlinear phase shift difference accumulated by the bidirectional transmission light in the resonant cavity to optimize the self-starting performance and adjust the repetition frequency of the output pulse.

7. A wavelength-tunable 1018nm mode-locked laser according to claim 5, characterized in that, The non-reciprocal phase shifter (5) consists of two Faraday rotators and a quarter-wave plate, or a polarization beam splitter and combiner, a Faraday rotator, an eighth-wave plate, and a mirror. The bidirectional transmitted light in the resonant cavity generates an additional π / 2 phase through the non-reciprocal phase shifter (5) to optimize the mode-locked self-starting performance.

8. A wavelength-tunable 1018nm mode-locked laser according to claim 5, characterized in that, The first coupler (6) is a 2×2 coupler with a splitting ratio of not 50:50; the fiber grating (7) is a narrow bandwidth fiber Bragg grating or a wide bandwidth chirped fiber Bragg grating with a dispersion parameter of less than 1ps / nm. The fiber grating (7) is inscribed on a PM980 fiber and has a reflectivity of more than 25% for the signal light; the isolator (9) has an isolation of more than 20dB and is used to cut off the output path optical coupling back to the resonant cavity.

9. A wavelength-tunable 1018nm mode-locked laser according to claim 5, characterized in that, It also includes an isolator (9), to which the second coupler (10) is connected.

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