Mamyshev fiber laser based on nonlinear gain

Abstract

The present application discloses a Mamyshev fiber laser based on nonlinear gain, comprising: a Mamyshev oscillator having a first arm and a second arm; the first arm comprises a first beam combiner and a first highly nonlinear optical fiber, the second arm comprises a second beam combiner and a second highly nonlinear optical fiber; and two pump light generating modules, the pump light generating module comprises a fiber random laser and an amplifier with a tunable wavelength range, and the fiber random laser and the amplifier are connected in series. The Mamyshev fiber laser based on nonlinear gain proposed in the present application uses the nonlinear optical fiber as the gain of the Mamyshev oscillator, and a wavelength tunable pump light source module is provided, thereby modulating the pump light and the wavelength and power, and combining the nonlinear optical fiber to use the stimulated Raman effect as the gain, thereby exciting Stokes light with a wide tunable range, and then obtaining a high-power and high-energy ultrafast laser pulse output with a wide wavelength tunable range.

Description

Technical Field

[0001] The present application relates to the technical field of ultrafast optics and nonlinear optics, and to a Mamyshev fiber laser based on nonlinear gain. Background Art

[0002] Ultrafast pulse lasers have the characteristics of ultra-short output pulse duration, high repetition frequency, and high peak power. They are cutting-edge tools in the fields of modern medical diagnosis, nonlinear optics, and atomic quantum coherent control. Among various types of laser formats, fiber lasers show great advantages due to their compact structure, no need for collimation, good environmental adaptability, and low cost. At present, the methods for obtaining ultrafast lasers mainly include active mode locking and passive mode locking technologies. Active mode-locked fiber lasers require the introduction of a modulator, which may reduce their environmental stability. Usually, the output pulse duration of active mode-locked fiber lasers is in the picosecond range, which cannot meet people's demand for ultrafast pulse lasers. Passive mode locking is considered to be the easiest technology to generate pulses. Its principle is to use the nonlinear effect in the fiber or the absorption characteristics of the saturable absorber (SAs) itself to achieve the mode locking function. Mode-locked fiber lasers based on nonlinear effects require precise control of the coupling ratio at the output end of the fiber, and excessive nonlinear effects will cause pulse splitting, making it difficult to obtain high pulse energy; SAs based on various two-dimensional materials have a low damage threshold, which limits the generation of high-energy pulses.

[0003] In recent years, the Mamyshev oscillator (MO) has attracted widespread attention due to its high pulse energy and ultrashort pulse duration. Its principle is to achieve pulse broadening and spectral filtering compensation through self-phase modulation effect and then achieve self-amplitude modulation effect, which is the same as the effect of SA. In addition, MO can withstand nonlinear phase shifts of more than 60π and will not cause pulse splitting due to excessive nonlinear effects, so that MO can output pulses with higher peak power. Therefore, MO is considered to be a laser resonant cavity that can withstand high nonlinear effects and output high pulse energy. At present, Mamyshev oscillators have been deeply studied in the technical aspects of high peak power, high pulse energy and high repetition rate, and have achieved a series of results. In 2018, the MO successfully constructed using single-mode large-mode-field photonic crystal fiber had an output pulse peak power of up to 13 MW; the pulse energy of >200 nJ in single-mode fiber and >1 µJ in photonic crystal fiber far exceeded that of other saturable absorber fiber lasers; in 2019, a high-repetition-rate harmonic mode locking of 90 GHz was achieved by using dispersion-compensating fiber with large group velocity dispersion to construct the MO and appropriately adjusting the filter and intracavity gain.

[0004] However, most of the current research and experimental verification of MO is concentrated in the 1 μm and 1.5 μm bands, and the MO output laser wavelength is relatively fixed and the tunable range is narrow, resulting in the output laser failing to meet the needs of some special band light sources in practical applications. In addition, MO fiber lasers mostly use rare earth ion-doped optical fibers as gain media, which are limited by the emission bandwidth of the doped ions, resulting in a limited operating wavelength range of the laser, that is, its wavelength tunability is relatively limited.

[0005] In contrast, the Raman fiber laser in the related technology uses the stimulated Raman scattering effect in the passive fiber (nonlinear fiber) to provide gain. Stimulated Raman scattering is a nonlinear effect caused by the scattering between the medium molecules in the fiber and the light wave, which can produce Stokes light of different wavelengths. In theory, Raman fiber lasers can produce lasers working at any wavelength, with the advantages of small quantum loss, no photon darkening, low background noise, and flexible wavelength. Its application is very wide, including optical communication, communication sensing and multiphoton imaging. So far, continuous wave high-power Raman fiber lasers and amplifiers based on stimulated Raman scattering have been demonstrated in several special laser emission regions, such as 1.1-1.3 μm, 1.4-1.5 μm and 1.6-1.7 μm, which cannot be achieved by traditional lasers based on rare earth ion doping. Thanks to the advantages of flexible and easy wavelength control and cascade operation, Raman fiber lasers show great advantages in wavelength tunability. In the near-infrared band, ultra-wideband tunable Raman lasers with output powers in the watt range and operating wavelengths of 1-1.9 μm have been achieved.

[0006] At present, there are also lasers in the prior art that use the nonlinear effects of passive optical fibers for Mamyshev oscillators. For example, Chinese invention patent application CN 114696189 A, published on July 1, 2022, discloses a self-starting Mamyshev fiber oscillator device based on spectral modulation, in which a passive optical fiber is added after the gain optical fiber of the Mamyshev oscillator as a gain medium. Thus, after the laser pulse is amplified by the gain optical fiber, it enters the passive optical fiber to broaden the laser pulse spectrum and modulate the spectral intensity distribution, so that a working band with a stronger energy distribution can be obtained to match the filtering band of the spectral filter in the oscillator, thereby reducing the mode-locking threshold of the oscillator, which is beneficial to the self-consistency of the oscillator cycle and thus realizing self-starting operation.

[0007] However, although the lasers of the prior art can broaden the laser pulses through passive optical fibers to obtain a stronger energy working band that matches the spectral filter, the active optical fiber in the cavity will still limit the wavelength tuning range of the laser pulse and cannot meet the demand for pulsed lasers of specific wavelengths. If the pump power is directly increased, on the one hand, it will increase the load on the optical devices in the system and even cause damage to the devices, especially the load on the gain fiber and the filter. On the other hand, the gain fiber in the cavity will further amplify the pulse energy, resulting in excessive pulse energy, thereby accumulating excessive nonlinear effects and causing pulse splitting, which is not conducive to the stable operation of the MO. These factors limit the further increase in the power of the laser system, making it difficult to obtain high-power, high-pulse-energy femtosecond ultrashort pulses. Summary of the invention

[0008] The present application provides a Mamyshev fiber laser based on nonlinear gain, which aims to solve the problems raised in the background technology and is conducive to obtaining high-power and high-energy ultrafast laser pulse output with a wide wavelength tunable range.

[0009] In one embodiment, a nonlinear gain-based Mamyshev fiber laser is provided, comprising:

[0010] A Mamyshev oscillator having a first arm 1 and a second arm 2; the first arm 1 comprises a first beam combiner 201 and a first highly nonlinear optical fiber 301, the second arm 2 comprises a second beam combiner 202 and a second highly nonlinear optical fiber 302; and two pump light generating modules 101, the pump light generating modules 101 comprising an optical fiber random laser and an amplifier with a tunable wavelength range, the optical fiber random laser and the amplifier being connected in series;

[0011] Among them, the output end of one of the pump light generating modules 101 and the output end of the second arm 2 are simultaneously connected to the input end of the first combiner 201, and the first highly nonlinear optical fiber 301 is connected to the output end of the first combiner 201; the output end of another pump light generating module 101 and the first arm 1 are simultaneously connected to the input end of the second combiner 202, and the second highly nonlinear optical fiber 302 is connected to the output end of the second combiner 202, so that the first arm 1 and the second arm 2 are connected to form a ring cavity structure.

[0012] In an optional solution, the fiber random laser includes a first laser diode 102, a fiber ring mirror assembly 103, a third beam combiner 104, a first gain fiber 105 and a first transmission fiber 106;

[0013] Among them, the output ends of the first laser diode 102 and the fiber ring mirror assembly 103 are commonly connected to the input end of the third combiner 104, the output end of the third combiner 104 is connected to one end of the first gain fiber 105, and the other end of the first gain fiber 105 is connected to the first transmission fiber 106.

[0014] In an optional solution, the fiber ring mirror assembly 103 includes:

[0015] A coupler 1031, a second transmission optical fiber 1032 and a first bandpass filter 1033;

[0016] The incident end and the output end of the second transmission optical fiber 1032 are simultaneously connected to the input end of the coupler 1031, a first bandpass filter 1033 is arranged on the second transmission optical fiber 1032, and the coupler 1031 and the first laser diode 102 are respectively connected to the third combiner 104.

[0017] In an optional solution, the amplifier includes a second laser diode 108, a fourth beam combiner 109, a second gain fiber 110, and a first isolator 107;

[0018] Among them, the output end of the first transmission optical fiber 106 is connected to the input end of the first isolator 107, the output end of the first isolator 107 and the output end of the second laser diode 108 are commonly connected to the input end of the fourth combiner 109, one end of the second gain optical fiber 110 is connected to the output end of the fourth combiner 109, and the other end of the second gain optical fiber 110 serves as the output end of the pump light generating module 101.

[0019] In an optional solution, the first gain fiber 105 is a single-mode gain fiber, the second gain fiber 110 is a multi-mode gain fiber, and the first transmission fiber 106 and the second transmission fiber 1032 are single-mode fibers.

[0020] In an optional solution, the first arm 1 further includes:

[0021] A second isolator 401, a first output coupler 501, a first polarization controller 601 and a second bandpass filter 701 connected in series in sequence;

[0022] The input end of the second isolator 401 is connected to the output end of the first highly nonlinear optical fiber 301 , and the output end of the second bandpass filter 701 is connected to the input end of the second combiner 202 .

[0023] In an optional solution, the second arm 2 further includes:

[0024] A third isolator 402, a second output coupler 502, a second polarization controller 602 and a third bandpass filter 702 connected in series in sequence;

[0025] The input end of the third isolator 402 is connected to the output end of the second highly nonlinear optical fiber 302 , and the output end of the second bandpass filter 701 is connected to the input end of the first combiner 201 .

[0026] In an optional solution, the first bandpass filter 1033, the second bandpass filter 701 and the third bandpass filter 702 are filters with adjustable passbands.

[0027] In an optional solution, the first polarization controller 601 and the second polarization controller 602 are half-wave plates, quarter-wave plates or spatial polarization plates.

[0028] In an optional solution, the first output coupler 501 and the second output coupler 502 are output coupling mirrors or polarization beam splitters.

[0029] Beneficial effects of this application:

[0030] The nonlinear gain-based Mamyshev fiber laser proposed in the present application uses the nonlinear fiber as the gain of the Mamyshev oscillator and is provided with a wavelength-tunable pump light source module, thereby stimulating Stokes light with a wide tunable range by modulating the pump light, wavelength and power, and combining the nonlinear fiber with the stimulated Raman effect as gain, thereby obtaining a high-power and high-energy ultrafast laser pulse output with a wide wavelength tunable range. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0032] Figure 1 is a schematic diagram of the laser principle in one embodiment of the present application;

[0033] Figure 2 is a schematic diagram of a pump light generating module in an embodiment of the present application;

[0034] Reference numerals in the figures:

[0035] 1. First arm; 2. Second arm;

[0036] 101, pump light generating module; 102, first laser diode; 103, fiber ring mirror assembly; 1031, coupler; 1032, second transmission fiber; 1033, first bandpass filter; 104, third combiner; 105, first gain fiber; 106, first transmission fiber; 107, first isolator; 108, second laser diode; 109, fourth combiner; 110, second gain fiber;

[0037] 201, first beam combiner; 202, second beam combiner; 301, first highly nonlinear optical fiber; 302, second highly nonlinear optical fiber; 401, second isolator; 402, third isolator; 501, first output coupler; 502, second output coupler; 601, first polarization controller; 602, second polarization controller; 701, second bandpass filter; 702, third bandpass filter. DETAILED DESCRIPTION

[0038] The specific implementation methods of the present application are further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present application, but are not intended to limit the scope of the present application. Similarly, the following examples are only some embodiments of the present application rather than all embodiments, and all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of this application.

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

[0040] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection, an electrical connection, or communication with each other; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0041] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0042] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0043] At present, the application of passive mode-locking technology to Raman fiber lasers with flexible output wavelengths to generate ultrashort pulses in a wavelength range that traditional rare-earth-doped fiber lasers cannot obtain is one of the hot topics in the current research on Raman fiber lasers. Raman fiber lasers based on two-dimensional materials have achieved mode-locked pulse output working in the near-infrared band. However, the working wavelength of the laser needs to consider the characteristics of SAs, and the output pulse width is limited to the nanosecond level. Using nonlinear polarization rotation technology, Raman mode-locked lasers with a single pulse energy of 1.1 μJ and no pulse splitting, and a corresponding single pulse duration of 500 ns, have been achieved. For ultrafast pulses with a pulse duration of femtoseconds and high pulse energy, there is still a lot of room for improvement in Raman fiber lasers. Therefore, in order to obtain a fiber laser with a narrow pulse width, high energy and flexible and tunable working wavelength, applying stimulated Raman scattering to MO is an innovative idea that can optimize laser performance.

[0044] However, although the lasers in the prior art can broaden the laser pulses by utilizing the nonlinear effects of passive optical fibers to obtain a stronger energy working band that matches the spectral filter, it can only meet the needs of maintaining self-starting operation of the laser and it is difficult to obtain high-power, high-pulse energy femtosecond ultrashort pulses.

[0045] Based on this, the present application proposes the following embodiments after research and innovation.

[0046] In some embodiments, see Figure 1 and Figure 2 , provides a Mamyshev fiber laser based on nonlinear gain, comprising:

[0047] A Mamyshev oscillator having a first arm 1 and a second arm 2; the first arm 1 includes a first beam combiner 201 and a first highly nonlinear optical fiber 301, and the second arm 2 includes a second beam combiner 202 and a second highly nonlinear optical fiber 302; and two pump light generating modules 101, the pump light generating module 101 includes an optical fiber random laser and an amplifier with a tunable wavelength range, and the optical fiber random laser and the amplifier are connected in series;

[0048] Among them, the output end of one pump light generating module 101 and the output end of the second arm 2 are simultaneously connected to the input end of the first combiner 201, and the first highly nonlinear optical fiber 301 is connected to the output end of the first combiner 201; the output end of another pump light generating module 101 and the first arm 1 are simultaneously connected to the input end of the second combiner 202, and the second highly nonlinear optical fiber 302 is connected to the output end of the second combiner 202.

[0049] In this example, the first arm 1 and the second arm 2 are connected to form a ring cavity structure, forming the main structure of the laser with a Mamyshev oscillator as the laser resonant cavity. Among them, the pump light generating module 101 is a fiber random laser and an amplifier with a tunable wavelength range. Among them, the fiber random laser can be a semi-open fiber random laser with good tunability, simple structure, flexible wavelength, high power, low noise and other advantages, and it is simple to build and relatively low cost. It can directly generate a wavelength tunable laser output, and then after amplification by an amplifier, it can generate a pump light output that meets the requirements of power and wavelength.

[0050] In addition, the first high nonlinear optical fiber 301 and the second high nonlinear optical fiber 302 both use optical fibers with stimulated Raman scattering effect as gain media. The first high nonlinear optical fiber 301 and the second high nonlinear optical fiber 302 can receive the tuned pump light output by the pump light generating module 101, and then use Raman gain excitation to form Stokes light with a wide tunable range, which will ensure the coordination of the laser pulse and can quickly generate laser pulses that meet the needs. In this way, under the dominance of the locking mechanism of the Mamyshev oscillator, the self-starting locking is achieved by adjusting the adjustment devices in the first arm 1 and the second arm 2, and finally an ultrafast laser pulse output with narrow pulse width, high power and high energy is obtained.

[0051] In the resonant cavity of the MO of the present application, only the first high nonlinear fiber 301 and the second high nonlinear fiber 302 are used as gain fibers, and no other gain medium is used. In the process of generating Stokes light by using Raman gain, the generation of each level of Stokes light requires the pump power to reach a certain value, and a higher pump light power is required. Therefore, before performing Raman gain, a semi-open fiber random laser is first used for modulation, which can generate laser pulses with finer wavelength tuning and wider wavelength coordination range, and then enter the resonant cavity of the MO with only Raman gain, which will undoubtedly be beneficial to improving the quality of laser pulses and the stability of the Mamyshev oscillator.

[0052] The specific advantages of this application are as follows:

[0053] 1) In this application, a pump light with adjustable wavelength is first generated by a fiber random laser, and then amplified by an amplifier and input into the MO resonant cavity. Different wavelengths , the wavelength of the excited Stokes light is also different, so more wavelength outputs can be obtained, the interval between each order of wavelengths can be reduced, and more precise wavelength tuning can be achieved.

[0054] 2) Without increasing the pump light power, the present application can first adjust the wavelength of the pump laser to make the wavelength of the laser input into the MO resonant cavity longer, which is more conducive to the subsequent generation of long-wavelength Stokes light.

[0055] 3) There is only Raman gain in the MO cavity, and no other gain medium. Under the requirement of large pump power, it can avoid the problem of over-amplification of pulse energy similar to active gain fiber, slow down the phenomenon of pulse splitting, and maintain stable operation in the MO cavity.

[0056] In short, in this embodiment, two pump light generating modules 101 can be used to modulate and generate pump light seed sources with power and wavelength that meet the requirements, and then cooperate with the excitation effect of the highly nonlinear optical fiber in the oscillator of the MO, that is, nonlinear gain, so that narrow pulse width, high power, and high energy ultrafast laser pulse output with a wide wavelength tunable range can be obtained. This will be beneficial to the potential development needs of optical communications, remote sensing, laser micromachining and other fields, and is also of great significance for subsequent scientific research.

[0057] In this embodiment, the first high nonlinear optical fiber 301 and the second high nonlinear optical fiber 302 are made of quartz optical fiber, which can be generally applied to pump light sources of various wavelengths and is expected to achieve a wide wavelength tunable range from 1 μm to 1.9 μm.

[0058] In some embodiments, see Figure 2 , the fiber random laser includes a first laser diode 102, a fiber ring mirror assembly 103, a third beam combiner 104, a first gain fiber 105 and a first transmission fiber 106;

[0059] The output ends of the first laser diode 102 and the fiber ring mirror assembly 103 are commonly connected to the input end of the third combiner 104 . The output end of the third combiner 104 is connected to one end of the first gain fiber 105 . The other end of the first gain fiber 105 is connected to the first transmission fiber 106 .

[0060] Among them, the first gain fiber 105 provides gain for the laser resonant cavity, the first transmission fiber 106 has randomly distributed Rayleigh scattering, providing wide spectrum feedback, and the fiber ring mirror assembly 103 provides high reflectivity for specific wavelengths, so that only lasers of specific wavelengths can oscillate in the cavity and finally output, meeting the light source requirements for exciting Raman scattering in the MO on the back side.

[0061] In some embodiments, see Figure 2 , the fiber ring mirror assembly 103 comprises:

[0062] A coupler 1031, a second transmission optical fiber 1032 and a first bandpass filter 1033;

[0063] Among them, the incident end and the output end of the second transmission optical fiber 1032 are simultaneously connected to the input end of the coupler 1031, the first bandpass filter 1033 is arranged on the second transmission optical fiber 1032, and the coupler 1031 and the first laser diode 102 are respectively connected to the third combiner 104 through optical fibers.

[0064] The fiber ring mirror is composed of the coupler 1031, the second transmission optical fiber 1032 and the first bandpass filter 1033, forming a fiber loop, which is equivalent to a high-reflectivity mirror, thereby improving the utilization rate of the gain optical fiber. In addition, the first bandpass filter 1033 is provided in the fiber ring mirror assembly 103, so that the reflection of the bandpass wavelength can be realized, forming a mirror with high reflectivity for a specific wavelength, thereby realizing the output of a laser of a specific wavelength.

[0065] The specific process is that the laser input by the first laser diode 102 first enters the first gain fiber 105 to stimulate the spontaneous amplification radiation therein, and the wide-spectrum spontaneous amplification radiation returns to the fiber ring mirror assembly 103 through the third combiner 104, and finally passes through the adjustable first bandpass filter 1033, and is selected to return with a narrower wavelength, thereby achieving wavelength tuning.

[0066] In some embodiments, the second transmission optical fiber 1032 may be fused at two output ends to form a ring loop.

[0067] In some embodiments, see Figure 2, the amplifier includes a second laser diode 108, a fourth beam combiner 109 and a second gain fiber 110; and a first isolator 107;

[0068] The output end of the first transmission optical fiber 106 is connected to the input end of the first isolator 107, the output end of the first isolator 107 and the output end of the second laser diode 108 are commonly connected to the input end of the fourth combiner 109, one end of the second gain optical fiber 110 is connected to the output end of the fourth combiner 109, and the other end of the second gain optical fiber 110 serves as the output end of the pump light generating module 101.

[0069] The first isolator 107 ensures unidirectional operation of the laser to prevent any potential feedback from the subsequent parts and ensure that the fiber random laser seed source is always stable. The second gain fiber 110 can amplify the laser output by the front-end fiber random laser, and finally form a high-power pump light source to input the MO resonant cavity, which is more conducive to the subsequent excitation of Raman medium and the generation of Stokes light.

[0070] In some embodiments, see Figure 1 and Figure 2 The first transmission optical fiber 106 and the second transmission optical fiber 1032 are single-mode optical fibers, and the first gain optical fiber 105 and the second gain optical fiber 110 can be multi-mode gain optical fibers, which can provide greater gain and output power.

[0071] In some embodiments, see Figure 1 , the first arm 1 also includes:

[0072] A second isolator 401, a first output coupler 501, a first polarization controller 601 and a second bandpass filter 701 connected in series in sequence;

[0073] The input end of the second isolator 401 is connected to the output end of the first highly nonlinear optical fiber 301 , and the output end of the second bandpass filter 701 is connected to the input end of the second combiner 202 .

[0074] In some embodiments, see Figure 1 , the second arm 2 also includes:

[0075] A third isolator 402, a second output coupler 502, a second polarization controller 602 and a third bandpass filter 702 connected in series in sequence;

[0076] The input end of the third isolator 402 is connected to the output end of the second high nonlinear optical fiber 302 , and the output end of the second bandpass filter 701 is connected to the input end of the first combiner 201 .

[0077] In some embodiments, the first bandpass filter 1033 , the second bandpass filter 701 , and the third bandpass filter 702 are all filters with adjustable passbands.

[0078] In some implementations, the first bandpass filter 1033 , the second bandpass filter 701 , and the third bandpass filter 702 may be formed by connecting a grating and a collimator, respectively.

[0079] In some embodiments, the first polarization controller 601 and the second polarization controller 602 may be half-wave plates, quarter-wave plates, or spatial polarizers.

[0080] In some embodiments, the first output coupler 501 and the second output coupler 502 may be output coupling mirrors or polarization beam splitters.

[0081] In some embodiments, the first arm 1 and the second arm 2 are connected to form a ring cavity structure, wherein the second isolator 401 and the third isolator 402 ensure unidirectional operation of the laser, and the mode-locking start of the entire ring-shaped MO cavity is realized based on NPE. The change of the polarization state inside the oscillator is achieved by adjusting the first polarization controller 601 and the second polarization controller 602, and the laser output is obtained through the output coupler.

[0082] After the MO oscillator of the present application obtains the initial pulse, the self-phase modulation effect in the optical fiber will cause the pulse to be broadened. The broadened pulse is filtered by the first bandpass filter 1033 and the second bandpass filter 701 through the central wavelength deviating from the central wavelength of the initial pulse, that is, the offset filtering mechanism, and the low-intensity pulse is filtered out, only the high-intensity pulse is retained, and the two arms connected in series strengthen this effect that can be equivalent to a saturable absorber, and finally a high-intensity pulse is obtained.

[0083] The above are only some embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application. Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations of the present invention. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. Mamyshev fiber laser based on nonlinear gain, characterized in that: include: A Mamyshev oscillator having a first arm and a second arm; the first arm comprises a first beam combiner, a first highly nonlinear optical fiber and a second bandpass filter, and the second arm comprises a second beam combiner, a second highly nonlinear optical fiber and a third bandpass filter; the gain medium in the first arm comprises only a medium having a stimulated Raman scattering effect in the first highly nonlinear optical fiber, and the gain medium in the second arm comprises only a medium having a stimulated Raman scattering effect in the second highly nonlinear optical fiber, without other active gain media; and Two pump light generating modules, the pump light generating modules comprising a fiber random laser with a tunable wavelength range and an amplifier; the fiber random laser comprising a first laser diode, a fiber ring mirror assembly, a first gain fiber and a first transmission fiber, the fiber ring mirror assembly comprising a coupler, a second transmission fiber and a first bandpass filter, the incident end and the output end of the second transmission fiber are simultaneously connected to the input end of the coupler, and the first bandpass filter is arranged on the second transmission fiber; The output ends of the first laser diode and the coupler are respectively connected to one end of the first gain fiber, and the other end of the first gain fiber is connected to the first transmission fiber; The amplifier includes a second laser diode and a second gain fiber; the other end of the first transmission fiber relative to the first gain fiber and the second laser diode are respectively connected to the second gain fiber, and the other end of the second gain fiber serves as the output end of the pump light generating module; Among them, the output ends of the second gain fiber and the third bandpass filter of one of the pump light generating modules are simultaneously connected to the input end of the first beam combiner, and the first highly nonlinear fiber is connected to the output end of the first beam combiner; the output ends of the second gain fiber and the second bandpass filter of another of the pump light generating modules are simultaneously connected to the input end of the second beam combiner, and the second highly nonlinear fiber is connected to the output end of the second beam combiner, so that the first arm and the second arm are connected to form a ring cavity structure.

2. The Mamyshev fiber laser based on nonlinear gain according to claim 1, characterized in that: The fiber random laser includes a third beam combiner; The output ends of the first laser diode and the fiber ring mirror assembly are commonly connected to the input end of the third beam combiner, and the output end of the third beam combiner is connected to one end of the first gain fiber.

3. The Mamyshev fiber laser based on nonlinear gain according to claim 2, characterized in that: The coupler and the first laser diode are connected to the input end of the third beam combiner respectively.

4. The Mamyshev fiber laser based on nonlinear gain according to claim 3, characterized in that: The amplifier includes a fourth combiner and a first isolator; Among them, the output end of the first transmission optical fiber is connected to the input end of the first isolator, the output end of the first isolator and the output end of the second laser diode are commonly connected to the input end of the fourth combiner, and one end of the second gain optical fiber is connected to the output end of the fourth combiner.

5. The Mamyshev fiber laser based on nonlinear gain according to claim 4, characterized in that: The first gain fiber is a single-mode gain fiber, the second gain fiber is a multi-mode gain fiber, and the first transmission fiber and the second transmission fiber are single-mode fibers.

6. The Mamyshev fiber laser based on nonlinear gain according to claim 1, characterized in that: The first arm further comprises: A second isolator, a first output coupler, and a first polarization controller connected in series in sequence; The input end of the second isolator is connected to the output end of the first highly nonlinear optical fiber, and the output end of the second bandpass filter is connected to the input end of the second combiner.

7. The Mamyshev fiber laser based on nonlinear gain according to claim 6, characterized in that: The second arm further comprises: A third isolator, a second output coupler, and a second polarization controller connected in series in sequence; The input end of the third isolator is connected to the output end of the second highly nonlinear optical fiber, and the output end of the second bandpass filter is connected to the input end of the first combiner.

8. The Mamyshev fiber laser based on nonlinear gain according to claim 7, characterized in that: The first band-pass filter, the second band-pass filter and the third band-pass filter are all adjustable band-pass filters.

9. The Mamyshev fiber laser based on nonlinear gain according to claim 7, characterized in that: The first polarization controller and the second polarization controller are half-wave plates, quarter-wave plates or spatial polarizers.

10. The Mamyshev fiber laser based on nonlinear gain according to claim 7, characterized in that: The first output coupler and the second output coupler are output coupling mirrors or polarization beam splitters.

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