CN111834871A - Energy-adjustable pulse cluster fiber laser and regulation and control method - Google Patents
Energy-adjustable pulse cluster fiber laser and regulation and control method Download PDFInfo
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Abstract
The invention discloses an energy-adjustable pulse cluster optical fiber laser and a regulation and control method, wherein the laser comprises: a main resonant cavity and an auxiliary cavity; the main resonant cavity is used for generating fundamental frequency mode locking pulses; the main resonant cavity includes: the device comprises a pumping light source, a wavelength division multiplexer, a gain optical fiber, an optical fiber circulator, a material saturable absorber, a polarization controller and a first optical fiber coupler; the auxiliary cavity is used for modulating the fundamental frequency mode locking pulse; the accessory chamber includes: the X-type optical fiber coupler with adjustable splitting ratio, an optical fiber delay line and a second optical fiber coupler. The method comprises the steps of rotating the angle of a handle of a polarization controller and the extrusion intensity of the handle to generate fundamental frequency mode locking pulses, adjusting the light splitting ratio of an X-type optical fiber coupler to realize amplitude modulation of a fundamental frequency mode locking pulse sequence, heating an optical fiber delay line to realize width modulation of the pulse time profile of the mode locking pulse sequence, and realizing a pulse cluster with dynamically adjustable laser output energy. The invention is mainly used in the technical field of lasers.
Description
Technical Field
The invention relates to the technical field of lasers, in particular to an energy-adjustable pulse cluster fiber laser and a regulation and control method.
Background
Mode-locked lasers have been the light source of choice in the fields of laser physics, industrial applications, precision measurements, and biomedical imaging. Compared with an active mode-locked laser, the passive mode-locked fiber laser generates ultrashort pulses, and has the remarkable advantages of high peak power, good beam quality and the like, and is paid much attention. In general, a passive mode-locked fiber laser uses a single-mode fiber as a substrate, and the generated mode-locked pulse energy is limited within a nano-focus range due to the waveguide structure of the fiber and the constraint of the optical wave energy quantization effect. However, the conventional laser processing industry requires that the laser pulse energy be above the microjoule level during the processing time. Therefore, the pulse optical fiber laser with micro-focus energy level is an industry key technology and a leading-edge subject in the current laser technical field. To generate a high-energy pulse with a micro-focus level, a mode-locked laser pulse is usually amplified or multi-stage amplified outside a laser resonant cavity by technical schemes such as Chirped Pulse Amplification (CPA), Main Oscillation Power Amplification (MOPA), pulse optical parametric oscillation amplification (MOPO), main oscillation power re-amplification (MOPRA) and the like, so that the application requirement of industrial laser processing can be met. For example, laser pulses with an energy of 36.7 μ J can be obtained in a 2 μm band by a three-stage MOPA amplification technique [ Ref.1. P.Wan, et al.high pulse energy 2 μm femtosecond Fiber laser Express,2013,21(2): 1798-. However, the amplification schemes such as CPA, MOPA, MOPO and MOPRA not only increase the working cost of the laser system, but also additionally introduce higher nonlinear effect in the process of pulse energy amplification, so that the extra-cavity amplification technical schemes often need to adopt additional processing means to deal with the problem of residual high nonlinear effect. These energy amplification schemes outside the laser cavity add undoubtedly to the complexity, instability and cost of the laser system.
Mamyshev oscillators [ ref 3.p.sidorenko, et al.self-fed, multi-megawatt, Mamyshev oscillator. opt.lett.,2018,43(11):2672-2675 ] are one solution that can directly generate large energy light pulses in a laser. However, the mode-locking self-starting threshold of the Mamyshev oscillator is very high, and when the distance between the bandpass center wavelengths of two filters of the Mamyshev oscillator is larger than 4nm, self-starting mode locking cannot be generated generally. If the Mamyshev oscillator is easy to generate the self-starting mode-locking laser pulse, the self-starting mode-locking pulse can be obtained by means of external injection of a seed pulse or intensity modulation of pumping power. The high self-start threshold limits the wide application of Mamyshev lasers.
The existing fiber laser has the technical problems of low mode locking pulse energy and poor pulse energy controllability. Seeking to directly obtain micro-focus-level high-energy laser pulses from a fiber laser is an industry common requirement in the current laser application field and is also an important development direction of the current high-power laser pulses.
Disclosure of Invention
The present invention is directed to an energy-tunable pulse-burst fiber laser and a method for adjusting and controlling the same, which solve one or more of the problems of the prior art and provide at least one of the advantages of the present invention.
The solution of the invention for solving the technical problem is as follows: in one aspect, an energy tunable pulse cluster fiber laser includes: a main resonant cavity and an auxiliary cavity;
the main resonant cavity is used for generating fundamental frequency mode locking pulses; the main resonant cavity includes: the device comprises a pumping light source, a wavelength division multiplexer, a gain optical fiber, an optical fiber circulator, a material saturable absorber, a polarization controller and a first optical fiber coupler; the output end of the pumping light source is connected with a first input end of a wavelength division multiplexer through a single mode fiber, the output end of the wavelength division multiplexer is connected with one end of a gain fiber through the single mode fiber, the other end of the gain fiber is connected with a first end of a fiber circulator through the single mode fiber, a third end of the fiber circulator is connected with one end of a material saturated absorber through the single mode fiber, the other end of the material saturated absorber is connected with one end of a polarization controller through the single mode fiber, the other end of the polarization controller is connected with the input end of a first fiber coupler through the single mode fiber, a first output end of the first fiber coupler is connected with a second input end of the wavelength division multiplexer through the single mode fiber, and a second output end of the first fiber coupler is used for outputting laser;
the auxiliary cavity is used for modulating the fundamental frequency mode locking pulse; the accessory chamber includes: the first input end of the splitting ratio adjustable X-type optical fiber coupler is connected with the second end of the optical fiber loop device through a single-mode optical fiber, and the second input end of the splitting ratio adjustable X-type optical fiber coupler is connected with one end of the optical fiber delay line through a single-mode optical fiber; the first output end of the X-type optical fiber coupler with the adjustable splitting ratio is connected with the second output end of the X-type optical fiber coupler through a single-mode optical fiber to form a closed loop, the other end of the optical fiber delay line is connected with the first input end of the second optical fiber coupler through a single-mode optical fiber, and the first output end and the second output end of the second optical fiber coupler are connected through a single-mode optical fiber to form a closed loop.
Furthermore, the laser also comprises a heater, the optical fiber delay line is placed on a heating surface of the heater, and the heater is used for heating the optical fiber delay line.
Further, the material of the material saturable absorber includes: any one of graphene, carbon nanotubes, black phosphorus, molybdenum disulfide, a semiconductor saturated absorption mirror or alcohol.
Further, the first optical fiber coupler is a Y-shaped optical fiber coupler, and the fixed splitting ratio of the first optical fiber coupler ranges from 99:1 to 60: 40.
Furthermore, the splitting ratio of the X-type optical fiber coupler with the adjustable splitting ratio can be dynamically adjusted within the range of 99:1 to 50:50, the formed physical function is equivalent to that of a cavity mirror of an auxiliary cavity, and the reflectivity of the cavity mirror is dynamically adjustable within the range of 4% -100%.
Further, the fixed splitting ratio of the second optical fiber coupler is 50:50, the formed physical function is equivalent to that of another cavity mirror of the auxiliary cavity, and the reflectivity of the cavity mirror is 100%.
Furthermore, the auxiliary cavity forms a dynamic adjustable filter on the physical effect, and amplitude modulation and pulse profile modulation are carried out on the generated fundamental frequency mode-locked pulse sequence.
On the other hand, a method for regulating and controlling an energy-adjustable pulse cluster fiber laser is provided, which is applied to the energy-adjustable pulse cluster fiber laser according to any one of the above technical solutions, and includes:
step 2, adjusting the splitting ratio of the X-type optical fiber coupler with the adjustable splitting ratio in the auxiliary cavity, and dynamically modulating the amplitude of a fundamental frequency mode locking pulse sequence generated by the main resonant cavity, wherein the modulation depth dynamically changes from 0% to 100%, so that a pulse cluster with dynamically adjustable laser energy is obtained;
and 3, heating the optical fiber delay line in the auxiliary cavity, changing the cavity length of the auxiliary cavity, and realizing modulation of the pulse time profile of the mode-locked pulse sequence, wherein the width range of the pulse time profile can be dynamically changed between 1ns and 900ns, so that a laser pulse cluster with dynamically changed energy is obtained.
The invention has the beneficial effects that: on one hand, the laser is provided, the equivalent Fabry-Perot filtering effect formed by the auxiliary cavity can be used for easily changing the filtering effect intensity of the auxiliary cavity by simply adjusting the splitting ratio of the optical fiber coupler, so that different amplitude modulation can be carried out on a mode locking pulse sequence in the main resonant cavity, and a laser pulse cluster with dynamically adjustable energy is generated; by adjusting the cavity length of the auxiliary cavity, the width modulation of different pulse profiles is carried out on the mode locking pulse sequence in the main resonant cavity, and a high-energy laser pulse cluster can be obtained directly from a laser more easily.
In yet another aspect, a method of tuning the laser is provided to more easily obtain high energy laser pulse clusters directly from the laser.
The problems that the traditional fiber laser is low in output pulse energy and high-energy pulses in the Mamyshev oscillator are difficult to self-start are solved.
Drawings
In order to more clearly illustrate the technical solution in the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly described below. It is clear that the described figures are only some embodiments of the invention, not all embodiments, and that a person skilled in the art can also derive other designs and figures from them without inventive effort.
FIG. 1 is a schematic diagram of a laser configuration;
fig. 2 is a schematic diagram of the modulation principle of mode-locked pulses.
Detailed Description
The conception, the specific structure, and the technical effects produced by the present invention will be clearly and completely described below in conjunction with the embodiments and the accompanying drawings to fully understand the objects, the features, and the effects of the present invention. It is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments, and those skilled in the art can obtain other embodiments without inventive effort based on the embodiments of the present invention, and all embodiments are within the protection scope of the present invention. In addition, all the coupling/connection relationships mentioned herein do not mean that the components are directly connected, but mean that a better coupling structure can be formed by adding or reducing coupling accessories according to specific implementation conditions. All technical characteristics in the invention can be interactively combined on the premise of not conflicting with each other.
In this embodiment, the mechanism of generating the mode-locking pulse of the main cavity is as follows: the pumping light source 100 pumps the gain fiber 300 through the wavelength division multiplexer 200 to generate a laser signal. The laser signal is subjected to the combined action of dispersion and nonlinear, gain and loss, and saturated absorption and gain filtering, so that the laser light wave periodically undergoes the spectrum broadening caused by the nonlinear effect and the saturated absorption effect and the spectrum filtering caused by the gain filtering effect. When steady state is reached, a transient local distribution of laser energy, i.e. mode-locked pulses, occurs within a short periodic time slot. When the time interval of the mode-locking pulse is equal to the time when the optical wave runs in the laser for one circle, the mode-locking pulse works in the fundamental frequency state. The mode-locked pulse working in the negative group velocity dispersion region is restricted in the nano-focus level due to the energy quantization effect. The sequence of mode-locking pulses in the main cavity is shown schematically in figure 2.
The working mechanism of the auxiliary cavity 110 for modulating the mode locking pulse sequence of the main resonant cavity to generate the pulsating high-energy laser cluster is as follows: when the mode-locked pulse enters the auxiliary cavity 110, the auxiliary cavity 110 acts as a Fabry-perot filter to modulate the mode-locked pulse, thereby causing a pulsing phenomenon in the pulse train. Once the pulsation phenomenon occurs, the energy accumulated in the laser is not uniformly distributed in a ground state mode locking pulse sequence any more, but explosive energy release occurs at a certain specific laser operation circle number, so that strong energy laser pulse cluster output reaching the micro-focus level can be generated. The specific adjustment mode can be adjusted by the X-type optical fiber coupler 800 with adjustable splitting ratio. The modulation effect of the laser pulse clusters is shown schematically in fig. 2.
The accessory chamber 110 has two important modulation functions:
1. and adjusting the modulation depth. The splitting ratio of the X-type fiber coupler 800 with the adjustable splitting ratio in the auxiliary cavity 110 is dynamically adjusted, so that pulse cluster outputs with different modulation depths can be obtained. When the filtering modulation depth reaches 100%, the energy of the output laser pulse cluster is maximum.
2. And adjusting the pulse time profile. By heating the fiber delay line 900 in the auxiliary cavity 110, the pulse time profile presented changes, the number of mode-locked pulses contained in the pulse profile changes, and the laser pulse cluster energy changes.
In the auxiliary cavity 110, the connection mode of the X-type optical fiber coupler 800 with the adjustable splitting ratio and the second optical fiber coupler 920 constitutes two equivalent cavity mirrors of the auxiliary cavity 110. Wherein, the adjustable X type fiber coupler 800 of splitting ratio is equivalent to the adjustable chamber mirror of reflectivity, and the adjustable scope of reflectivity: 4% -100%; the second fiber coupler 920 is equivalent to a cavity mirror with a reflectivity of 100%. The incident light wave is input from the incident port of the second fiber coupler 920, and then all incident energy is reversely output from the incident port; the incident light wave is input from the incident port of the X-type optical fiber coupler with the adjustable splitting ratio, and only the light wave with partial energy is reversely output from the incident port. The mathematical relation between the splitting ratio rho and the equivalent cavity mirror reflectivity r is as follows:
to this end, the auxiliary cavity 110 forms a Fabry-Perot cavity structure.
The splitting ratio of the X-type fiber coupler 800 with the adjustable splitting ratio is adjusted, which is equivalent to adjusting the reflectivity of the cavity mirror of the auxiliary cavity 110, so that the filtering effect intensity of the auxiliary cavity 110 changes along with the change of the equivalent reflectivity of the cavity mirror, that is, the auxiliary cavity 110 has a dynamic filtering effect, and can perform amplitude modulation on the mode locking pulse in the main resonant cavity, and the amplitude modulation depth range can be from 0% to 100%, so that the laser output energy can be dynamically adjustable.
When the fiber delay line 900 is heated, it is possible to create an additional optical path (phase) for the light wave traveling through it. When the optical fiber delay line 900 is temperature modulated, the parameters of the optical fiber delay line 900 will change, resulting in the additional optical path (phase) of the light wave transmitted therein. In particular, the effect of temperature-induced fiber longitudinal strain causes the length L of the fiber delay line 900 to vary by Δ L; the transverse poisson effect of the optical fiber caused by the temperature enables the core diameter 2a of the optical fiber delay line 900 to have the variation of delta a, and further the propagation constant beta has the variation of delta beta; the refractive index n of the core of the optical fiber delay line 900 has a variable quantity of delta n due to the elasto-optic effect and the thermo-optic effect. It can be seen that the temperature induced changes in the parameters of the fiber delay line 900 will cause the additional phase Δ φ of the light wave transmitted therein to be:
to this end, the fiber delay line 900 is heated by the heater 910 to change the chamber length of the auxiliary chamber 110. The equivalent Fabry-Perot filtering effect formed by the auxiliary cavity 110 performs additional optical path modulation on the light wave transmitted therein along with the temperature change, the additional optical path modulation appears to perform time modulation on the mode-locked pulse in time, a pulsation phenomenon is generated, and the range of the pulse time width profile of the modulation function is in the order of several to hundreds of ns, so that the laser outputs laser pulse clusters with different energies.
The general working principle of the laser can be summarized as follows: when the laser light wave runs in the main resonant cavity, the laser light wave is subjected to the combined action of dispersion and nonlinearity, gain and loss, saturated absorption and gain filtering, so that the laser light wave periodically undergoes the spectrum broadening caused by the nonlinearity effect and the saturated absorption effect and the spectrum filtering caused by the gain filtering effect. When a steady state is reached, irregular background continuous light is effectively suppressed, and transient local distribution of laser energy, namely mode-locked pulses, appears in periodic short time slots. When the time interval of the pulse is equal to the time of one circle of the light wave running in the laser, the mode-locking pulse works in the fundamental frequency state. The fundamental mode-locked pulses exhibit a uniform sequence arrangement in the time domain. The fundamental mode-locked pulse in the main resonant cavity can be induced by the material saturable absorber 500, and can also be induced by the similar saturable absorption effect, such as the nonlinear polarization rotation technology (NPR), the nonlinear loop mirror technology (NOLM), the nonlinear amplification loop mirror technology (NALM), and the like. Because of the constraint of the fiber waveguide structure and the quantization of the light wave energy, the mode-locking pulse energy of the fiber laser working in the negative group velocity dispersion region is generally limited to the nano-focus level. When the mode-locked pulses enter the auxiliary cavity 110, the auxiliary cavity 110 is equivalent to a Fabry-Perot filter, and the intensity of the mode-locked pulse sequence can be modulated, so that the uniform ground-state mode-locked pulse sequence has a pulsation phenomenon similar to the distribution of a trigonometric cord function. Once the pulsation phenomenon occurs, the energy accumulated in the laser is not uniformly distributed in a ground state mode locking pulse sequence any more, but explosive energy release occurs at a certain specific laser operation circle number, so that strong energy laser pulse cluster output reaching the micro-focus level is generated. If the splitting ratio of the X-ray fiber coupler 800 is adjusted dynamically in the auxiliary cavity 110, which is equivalent to dynamically adjusting the filtering strength of the Fabry-perot filter, the pulse packet outputs with different modulation depths can be obtained dynamically. When the modulation depth of the fundamental frequency mode-locking pulse reaches 100%, the energy of the corresponding laser pulse cluster is maximum. At the same time, heating of fiber delay line 900, i.e., changing the cavity length of auxiliary cavity 110, causes the period of the equivalent filter function in auxiliary cavity 110 to change. Therefore, after the auxiliary cavity 110 performs time modulation on the mode-locked pulse sequence generated by the main resonant cavity, the time profile of the pulse phenomenon is changed, that is, the time width of one pulse profile is changed, and the number of mode-locked pulses contained in the pulse profile is changed along with the change of the cavity length. The higher the temperature, the larger the width of the pulse time profile, the larger the number of mode-locked pulses contained in the pulse profile, and the larger the laser cluster energy generated corresponding to one pulse.
The laser has the following distinct characteristics and effects:
1. the equivalent Fabry-Perot filtering effect formed by the auxiliary cavity 110 can easily change the filtering effect intensity of the auxiliary cavity 110 by simply adjusting the splitting ratio of the X-type fiber coupler 800, so as to perform different amplitude modulation on the mode-locked pulse sequence in the main resonant cavity and generate a laser pulse cluster with dynamically adjustable energy. The invention can more easily and directly obtain high-energy laser clusters from the laser, and solves the problems of low output pulse energy of the traditional fiber laser and difficult self-starting of high-energy pulses in the Mamyshev oscillator.
2. The filter function period of the auxiliary cavity 110 may be achieved by heating the fiber delay line 900 in the auxiliary cavity 110. The change in the period of the filter function of the auxiliary cavity 110 causes the auxiliary cavity 110 to modulate the main cavity mode-locked pulse train to produce a change in the pulse profile, thereby changing the energy of the laser cluster produced by one pulse.
3. Although the main resonant cavity and the auxiliary cavity 110 are combined to form the fiber laser with the composite structure, compared with some fiber lasers with the composite structure, the fiber laser with the composite structure is characterized in that the physical functions of the two cavities are relatively independent, and if they are respectively subjected to independent structural redesign and improvement, the functions will not affect each other.
At the connection position of the main resonant cavity and the auxiliary cavity 110, a first end of the optical fiber circulator 400 is connected with the gain optical fiber 300, a second end of the optical fiber circulator 400 is connected with the input end of the X-type optical fiber coupler 800 with the adjustable splitting ratio in the auxiliary cavity 110, and a third end of the optical fiber circulator 400 is connected with the material saturable absorber 500. The function is as follows: the mode locking pulse generated by the main resonant cavity is transmitted from the first end of the optical fiber circulator 400 to the second end thereof and enters the auxiliary cavity 110, and then the auxiliary cavity 110 performs filtering modulation on the mode locking pulse to generate a pulsation phenomenon, and a laser pulse cluster is output. The laser pulse clusters are reflected by the auxiliary cavity 110 and transmitted from the second end of the fiber circulator 400 to the third end thereof, thereby returning to the main cavity.
The material of the material saturable absorber 500 includes: any one of graphene, carbon nanotubes, black phosphorus, molybdenum disulfide, a semiconductor saturated absorption mirror or alcohol. The material saturable absorber 500 is a substance having a saturable absorption effect or a technology similar to the saturable absorption effect. The NPR, NOLM, NALM and other physical technical schemes can realize the optical saturated absorption effect.
In some preferred embodiments, the laser further comprises a heater 910, the optical fiber delay line 900 is disposed on a heating surface of the heater 910, and the heater 910 is used for heating the optical fiber delay line 900.
In some preferred embodiments, the first fiber coupler 700 is a Y-type fiber coupler with a splitting ratio in the range of 99:1 to 60:40 as the output of the entire laser. In practical application, different splitting ratio ports can be selected as the output of the laser according to requirements.
In some preferred embodiments, the splitting ratio of the X-type fiber coupler 800 with adjustable splitting ratio can be dynamically adjusted within a range of 99:1 to 50:50, and the formed physical function is equivalent to a cavity mirror of an auxiliary cavity, and the reflectivity of the cavity mirror is dynamically adjustable within a range of 4% -100%. The fixed splitting ratio of the second optical fiber coupler is 50:50, the formed physical function is equivalent to that of another cavity mirror of the auxiliary cavity, and the reflectivity of the cavity mirror is 100%.
In some preferred embodiments, the single mode fiber is a SMF-28e fiber. The gain fiber 300 includes:nd doped3+Gain fiber and Yb-doped fiber3+Gain optical fiber and doped Pr3+Gain optical fiber and Er-doped fiber3+Gain fiber or Tm-doped3+A gain fiber.
On the other hand, the present embodiment also provides a method for regulating and controlling an energy-tunable pulse cluster fiber laser, where the method is based on the energy-tunable pulse cluster fiber laser of any of the above embodiments, and the specific regulating and controlling method includes:
step 2, adjusting the splitting ratio of the X-type optical fiber coupler 800 with the adjustable splitting ratio in the auxiliary cavity, and dynamically modulating the amplitude of a fundamental frequency mode locking pulse sequence generated by the main resonant cavity, so as to obtain a laser cluster with dynamically changed modulation depth, wherein the modulation depth of the pulse cluster is 0% -100%, so as to obtain a pulse cluster with dynamically adjustable laser energy;
and 3, heating the optical fiber delay line 900 in the auxiliary cavity, changing the cavity length of the auxiliary cavity, realizing modulation of the pulse time profile of the mode-locked pulse sequence, limiting the width range of the pulse time profile to be between 1ns and 900ns, and obtaining the laser pulse cluster with dynamically changed energy.
Through the regulation, the laser output obtains a laser pulse cluster with dynamically changed energy.
While the preferred embodiments of the present invention have been illustrated and described, it will be understood by those skilled in the art that the present invention is not limited to the details of the embodiments shown and described, but is capable of numerous equivalents and substitutions without departing from the spirit of the invention and its scope is defined by the claims appended hereto.
Claims (8)
1. An energy tunable pulse cluster fiber laser, comprising: a main resonant cavity and an auxiliary cavity;
the main resonant cavity is used for generating fundamental frequency mode locking pulses; the main resonant cavity includes: the device comprises a pumping light source, a wavelength division multiplexer, a gain optical fiber, an optical fiber circulator, a material saturable absorber, a polarization controller and a first optical fiber coupler; the output end of the pumping light source is connected with a first input end of a wavelength division multiplexer through a single mode fiber, the output end of the wavelength division multiplexer is connected with one end of a gain fiber through the single mode fiber, the other end of the gain fiber is connected with a first end of a fiber circulator through the single mode fiber, a third end of the fiber circulator is connected with one end of a material saturated absorber through the single mode fiber, the other end of the material saturated absorber is connected with one end of a polarization controller through the single mode fiber, the other end of the polarization controller is connected with the input end of a first fiber coupler through the single mode fiber, a first output end of the first fiber coupler is connected with a second input end of the wavelength division multiplexer through the single mode fiber, and a second output end of the first fiber coupler is used for outputting laser;
the auxiliary cavity is used for modulating the fundamental frequency mode locking pulse; the accessory chamber includes: the first input end of the splitting ratio adjustable X-type optical fiber coupler is connected with the second end of the optical fiber loop device through a single-mode optical fiber, and the second input end of the splitting ratio adjustable X-type optical fiber coupler is connected with one end of the optical fiber delay line through a single-mode optical fiber; the first output end of the X-type optical fiber coupler with the adjustable splitting ratio is connected with the second output end of the X-type optical fiber coupler through a single-mode optical fiber to form a closed loop, the other end of the optical fiber delay line is connected with the first input end of the second optical fiber coupler through the single-mode optical fiber, and the first output end and the second output end of the second optical fiber coupler are connected through the single-mode optical fiber to form the closed loop.
2. The energy tunable pulse cluster fiber laser of claim 1, further comprising a heater, wherein the fiber delay line is disposed on a heating surface of the heater, and wherein the heater is configured to heat the fiber delay line.
3. The energy-tunable pulse cluster fiber laser of claim 1, wherein the material of the saturable absorber of the material comprises: any one of graphene, carbon nanotubes, black phosphorus, molybdenum disulfide, a semiconductor saturated absorption mirror or alcohol.
4. The energy-tunable pulse cluster fiber laser of claim 1, wherein the first fiber coupler is a Y-fiber coupler and the fixed splitting ratio of the first fiber coupler is in a range of 99:1 to 60: 40.
5. The energy-tunable pulse cluster fiber laser of claim 1, wherein the splitting ratio of the splitting ratio-tunable X-type fiber coupler can be dynamically tuned within a range of 99:1 to 50:50, and the physical function formed is equivalent to a cavity mirror of an auxiliary cavity, and the reflectivity of the cavity mirror is dynamically tunable within a range of 4% -100%.
6. The energy-tunable pulse cluster fiber laser of claim 5, wherein the fixed splitting ratio of the second fiber coupler is 50:50, and the formed physical function is equivalent to another cavity mirror of the auxiliary cavity, and the reflectivity of the cavity mirror is 100%.
7. The fiber laser of claim 1, wherein the auxiliary cavity forms a physically dynamically tunable filter that amplitude modulates and pulse profile modulates the generated fundamental mode-locked pulse train.
8. A method for regulating and controlling an energy-adjustable pulse cluster optical fiber laser is characterized by comprising the following steps: the method is applied to the energy-adjustable pulse cluster optical fiber laser of any one of claims 1 to 7, and comprises the following steps:
step 1, rotating the handle angle of a polarization controller and the extrusion strength of a handle, adjusting pumping power, and generating self-starting fundamental frequency mode locking pulses by a main resonant cavity based on a material saturated absorber;
step 2, adjusting the splitting ratio of the X-type optical fiber coupler with the adjustable splitting ratio in the auxiliary cavity, and dynamically modulating the amplitude of a fundamental frequency mode locking pulse sequence generated by the main resonant cavity, wherein the modulation depth dynamically changes from 0% to 100%, so that a pulse cluster with dynamically adjustable laser energy is obtained;
and 3, heating the optical fiber delay line in the auxiliary cavity, changing the cavity length of the auxiliary cavity, and realizing modulation of the pulse time profile of the mode-locked pulse sequence, wherein the width range of the pulse time profile can be dynamically changed between 1ns and 900ns, so that a laser pulse cluster with dynamically changed energy is obtained.
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