Fiber laser structure and laser generation method

Abstract

An optical fiber laser structure comprises a resonant cavity structure and a pumping source, and the pumping source is connected with the resonant cavity structure in a matched mode through a wavelength division multiplexing-collimator. The resonant cavity structure comprises a saturable absorber mirror, two lenses / lens groups, a gain fiber, a dispersion compensator and a laser output coupling mirror; the gain optical fiber is of a waveguide structure and is used for generating amplified spontaneous emission (ASE) light, transmitting laser and amplifying laser; the saturable absorption mirror is used for screening out signal laser from the noise; the dispersion compensator is used for performing dispersion compensation on the optical signal; the laser output coupling mirror is used for transmitting and reflecting optical signals, the transmitted optical signals are used as output laser, and the reflected optical signals continue to enter the resonant cavity structure. According to the invention, the pumping source enters the resonant cavity structure through the wavelength division multiplexing-collimator and can generate and output GHz femtosecond laser which is high in quality, high in stability and easy to integrate.

Description

Technical Field

[0001] The present invention relates to the field of lasers, and in particular to a fiber laser structure and a laser generating method. Background Art

[0002] As a key light source technology, femtosecond pulse laser technology has been rapidly developed for more than 40 years and has been widely used in key fields such as cutting-edge scientific research, industrial laser precision processing, defense equipment confrontation, and medical and health care. These fields are directly related to national development, scientific and technological progress, and people's living needs. The application of femtosecond laser technology has significantly improved my country's scientific and technological innovation capabilities and played an irreplaceable role in enhancing international competitiveness.

[0003] Recently, high-repetition-rate GHz femtosecond lasers have played a key role in many cutting-edge scientific fields. For example, the introduction of ablation cooling technology has opened up new application prospects for the development of GHz repetition-rate, high-power femtosecond pulses. Experiments have shown that GHz repetition-rate femtosecond lasers not only have the high quality of traditional femtosecond laser processing, but also have processing efficiency comparable to nanosecond lasers. This ablation cooling technology based on GHz femtosecond lasers can fill the shortcoming of low throughput of femtosecond laser processing in industrial applications, and has great research significance for the processing of hard / brittle materials.

[0004] In order to achieve high-efficiency and high-precision "ablation cooling" laser processing, it is first necessary to obtain high-repetition-rate GHz femtosecond laser output. Some manufacturers use extracavity repetition-rate multiplication to obtain GHz pulses. In fact, the conventional seed source with a repetition rate of tens of MHz or hundreds of MHz is split outside the cavity, and a time delay is made along the way, and then the beam is combined to increase the repetition rate. Therefore, it is necessary to accurately control the splitting power ratio and the size of the time delay, otherwise serious power modulation and noise will occur in the subsequent amplification. This method is a helpless move, and the system is relatively complicated.

[0005] Relatively speaking, it is more reliable to generate GHz femtosecond laser directly from the fundamental frequency mode-locked resonant cavity. The structure of high repetition rate GHz mode-locked fiber laser can be divided into linear cavity and ring cavity. Compared with the ring cavity structure, the optical path structure of the linear cavity is simpler and easier to integrate. High repetition rate linear cavity fiber laser usually adopts passive mode locking, which can easily achieve fundamental frequency continuous wave mode locking above 3 GHz. The current maximum repetition rate of linear cavity laser is 19 GHz.

[0006] The common semiconductor saturable absorber (SESAM) mode-locked GHz fiber laser structure usually uses a phosphate glass gain fiber with a very high doping concentration, so the required gain fiber length is extremely short (several cm or even <1 cm) to obtain sufficient gain. In order to further shorten the cavity length, the SESAM is usually directly attached to one end of the gain fiber, and a two-color film is coated on the other end (pump wavelength anti-reflection, mode-locked laser wavelength high reflection); to increase stability, the fiber is encapsulated in a ceramic ferrule, so the pump can be directly connected to the gain fiber through the flange and injected into the gain fiber. This linear cavity fiber laser has an unparalleled high repetition rate advantage, but its output power is extremely low, usually below 0.1 mW, which brings great difficulties to the subsequent amplification system. In addition, this cavity type has no spatial part and lacks dispersion compensation elements (usually it is necessary to provide negative dispersion several times that of the gain fiber), so the output pulse width is difficult to reach the femtosecond level (usually >3 ps).

[0007] Therefore, it is necessary to improve the existing linear cavity fiber lasers to improve the quality, stability and magnitude of the laser. Summary of the invention

[0008] The purpose of the present invention is to overcome the defects of the prior art and to propose a fiber laser structure and a laser generating method.

[0009] The present invention is implemented by the following technical solutions: a fiber laser structure, including a resonant cavity structure and a pump source, wherein the pump source is connected to the resonant cavity structure through a wavelength division multiplexing-collimator; The resonant cavity structure includes a saturable absorber mirror, a first lens / lens group, a gain fiber, a second lens / lens group, a dispersion compensator and a laser output coupling mirror; The pump source is transmitted to the wavelength division multiplexing-collimator through a passive optical fiber, and the wavelength division multiplexing-collimator is connected to the gain optical fiber and enters the resonant cavity structure, wherein: The gain optical fiber is a waveguide structure, used to generate amplified spontaneous emission light ASE, transmission laser and amplification laser; The first lens / lens group is used to converge the optical signal output by the gain optical fiber onto the saturable absorber mirror; The saturable absorption mirror is used to filter out high-intensity signal laser from noise, thereby forming a pulse and reflecting the pulse laser; The second lens / lens group is used to collimate or converge the optical signal output by the gain optical fiber to the laser output coupling mirror; The dispersion compensator is used to perform dispersion compensation on the optical signal; The laser output coupling mirror is used to transmit and reflect light signals. The transmitted light signal is used as output laser, and the reflected light signal continues to enter the resonant cavity structure.

[0010] Preferably, the gain optical fiber comprises a left optical fiber end face and a right optical fiber end face; The wavelength division multiplexing-collimator (9) is connected to the left optical fiber end face (3); Or the wavelength division multiplexing-collimator (9) is connected to the right optical fiber end face (5); Alternatively, the left optical fiber end face (3) and the right optical fiber end face (5) of the wavelength division multiplexing-collimator (9) are connected simultaneously.

[0011] Preferably, the wavelength division multiplexing-collimator comprises an optical fiber ferrule, a third lens / lens group and a dichroic filter, wherein: The optical fiber ferrule is used to fix the passive optical fiber and the gain optical fiber; The third lens / lens group is used to collimate the pump light output by the passive optical fiber and the laser output by the gain optical fiber; The dichroic filter is used to reflect the pump light collimated by the third lens / lens group and couple it into the gain optical fiber, while transmitting the laser light collimated by the third lens / lens group into the free space.

[0012] Preferably, when the wavelength division multiplexing-collimator is connected to the right optical fiber end face, The original pump light of the pump source is transmitted to the wavelength division multiplexing-collimator through the passive optical fiber, then reflected by the dichroic filter, and transmitted to the gain optical fiber, so that the gain optical fiber achieves population inversion and obtains amplified spontaneous emission light ASE; The ASE generated by the gain fiber is transmitted to the left and converged to the saturable absorber through the left fiber end face and the first lens / lens group; the noise is filtered out at the saturable absorber to select the signal laser and form a pulsed laser; The pulsed laser after filtering out noise is transmitted to the right through the saturable absorber mirror, and is focused to the fiber end face by the first lens / lens group again, and then coupled into the gain fiber. At this time, the gain fiber amplifies the pulsed laser and suppresses the noise at the same time, thereby obtaining an amplified pulsed laser. The amplified pulsed laser is collimated to free space by the third lens / lens group and the dichroic filter, and then transmitted to the right to the dispersion compensator, where dispersion compensation is performed, the pulse width is narrowed, and then transmitted to the laser output coupling mirror; The pulsed laser is reflected and transmitted simultaneously on the front surface of the laser output coupling mirror, of which a small part is transmitted as the output laser; the remaining part is reflected and continues to transmit to the left in the cavity, and then passes through the dispersion compensator and the wavelength division multiplexing-collimator in succession; The reflected pulse is further dispersion compensated in the dispersion compensator, and then coupled to the gain fiber through the wavelength division multiplexing-collimator, amplified again in the gain fiber, and continues to be transmitted to the left, completing a laser transmission cycle.

[0013] Preferably, when the wavelength division multiplexing-collimator is connected to the left optical fiber end face, The original pump light of the pump source is transmitted to the wavelength division multiplexing-collimator through the passive optical fiber, then reflected by the dichroic filter, and transmitted to the gain optical fiber, where the population inversion is achieved to obtain amplified spontaneous emission light ASE; The ASE generated by the gain fiber is also transmitted to the left, passes through the third lens / lens group and the dichroic filter, and is collimated and transmitted to the first lens / lens group and converged to the saturable absorber mirror; at the saturable absorber mirror, the noise is filtered out and the signal laser is selected to form a pulsed laser; The pulsed laser with improved signal-to-noise ratio is reflected by the saturable absorber mirror and transmitted to the right, and then transmitted to the gain fiber through the first lens / lens group and the wavelength division multiplexing-collimator. At this time, the gain fiber amplifies the pulsed laser signal and suppresses the noise to obtain an amplified laser signal. The amplified laser signal is collimated to the free space or converged to the front surface of the laser output coupling mirror through the right fiber end face and the second lens / lens group. The specific method is determined by the distance from the right fiber end face to the second lens / lens group. Transmitted to the right to the dispersion compensator, where dispersion compensation is performed, the pulse width becomes narrower, and then transmitted to the laser output coupling mirror; The pulsed laser is reflected and transmitted simultaneously on the front surface of the laser output coupling mirror, with a small portion of the light being transmitted as the output laser; the remaining portion is reflected and continues to be transmitted to the left in the cavity, then passes through the dispersion compensator, the second lens / lens group and the right optical fiber end face, and is transmitted to the left to the gain fiber. The laser pulse signal is amplified again in the gain fiber and continues to be transmitted to the left, completing a laser transmission cycle.

[0014] Preferably, it further comprises two first wavelength division multiplexing-collimators, a second wavelength division multiplexing-collimator, a first pump source and a second pump source; When the first WDM-collimator is connected to the left fiber end face, and the second WDM-collimator is connected to the right fiber end face at the same time, The first pump source and the second pump source both generate original pump light, which is transmitted to the first wavelength division multiplexing-collimator and the second wavelength division multiplexing-collimator via the first passive optical fiber and the second passive optical fiber respectively; Then, the light is reflected by the dichroic filters of the first wavelength division multiplexing-collimator and the second wavelength division multiplexing-collimator, and transmitted to the gain fiber together, thereby achieving population inversion in the gain fiber and obtaining amplified spontaneous emission light ASE. The ASE generated by the gain fiber is transmitted to the left, passes through the lens of the first wavelength division multiplexing-collimator and the dichroic filter, is collimated and transmitted to the first lens / lens group, and then is focused to the saturable absorber mirror through the first lens / lens group; The saturable absorber mirror is located at the focal plane of the focused beam and provides a pulse forming mechanism - filtering out the high-intensity signal laser from the noise to generate a pulsed laser. The pulsed laser reflected by the saturable absorber is transmitted to the right, and is transmitted to the gain fiber again through the first lens / lens group and the first wavelength division multiplexing-collimator. At this time, the gain fiber amplifies the signal laser and suppresses the noise to obtain an amplified pulsed laser. The amplified pulse laser is collimated to free space through the lens and dichroic filter of the second wavelength division multiplexing-collimator, and then continues to transmit to the right from the free space; The pulse output from the second wavelength division multiplexing-collimator is dispersion compensated by the dispersion compensator, the pulse width becomes narrower, and then it is transmitted to the laser output coupling mirror; the laser is reflected and transmitted simultaneously on the front surface of the laser output coupling mirror, a small part of which is transmitted as the output laser; the remaining part is reflected by the laser output coupling mirror, continues to be transmitted to the left in the cavity, and then passes through the dispersion compensator and the second wavelength division multiplexing-collimator in succession; the pulse continues to be dispersion compensated in the dispersion compensator, and then is efficiently coupled to the gain fiber through the second wavelength division multiplexing-collimator, the pulse is amplified again in the gain fiber, and continues to be transmitted to the left, completing a laser transmission cycle.

[0015] The present invention provides a laser generation method, which uses the above-mentioned wavelength division multiplexing-collimator and the fiber laser structure connected to the right fiber end face, and the method comprises the following steps: Step S1: generating original pump light: the pump source generates original pump light and transmits it to the wavelength division multiplexing-collimator via a passive optical fiber; Step S2: Spontaneous emission light generation: the original pump light is reflected by the dichroic filter and transmitted to the gain fiber, so that the gain fiber achieves population inversion and obtains amplified spontaneous emission light ASE; Step S3: Pulsed laser generation: ASE generated by the gain fiber is transmitted to the left through the left fiber end face and the first lens / lens group and converged to the saturable absorber mirror; noise is filtered out at the saturable absorber mirror to select high-intensity signal laser to form a pulsed laser; Step S4: Pulse laser amplification: The pulse laser with improved signal-to-noise ratio is transmitted to the right through the saturable absorber mirror, and is focused to the left fiber end face by the first lens / lens group again, and then coupled into the gain fiber. At this time, the gain fiber amplifies the pulse laser and suppresses the noise to obtain an amplified pulse laser. Step S5: Pulse laser output: the amplified pulse laser is collimated to free space through the third lens / lens group and the dichroic filter, and is continuously transmitted to the right from the free space to the dispersion compensator; Dispersion compensation is performed in the dispersion compensator, the pulse width becomes narrower, and then it is transmitted to the laser output coupling mirror; The pulsed laser is reflected and transmitted simultaneously on the front surface of the laser output coupling mirror, of which a small part is transmitted as the output laser; the remaining part is reflected and continues to transmit to the left in the cavity, and then passes through the dispersion compensator and the wavelength division multiplexing-collimator in succession; The reflected pulse is further dispersion compensated in the dispersion compensator, and then coupled to the gain fiber through the wavelength division multiplexing-collimator, amplified again in the gain fiber, and continues to be transmitted to the left, completing a laser transmission cycle.

[0016] The present invention provides a second laser generation method, which uses a fiber laser structure in which a wavelength division multiplexing-collimator is connected to a left fiber end face, and the method comprises the following steps: Step S1: generating original pump light: the original pump light of the pump source is transmitted to the wavelength division multiplexing-collimator via the passive optical fiber; Step S2: Spontaneous emission light generation: the original pump light is reflected by the dichroic filter and transmitted to the gain fiber, so that the gain fiber achieves population inversion and obtains amplified spontaneous emission light ASE; Step S3: Pulse laser generation: ASE generated by the gain fiber is also transmitted to the left, passes through the third lens / lens group and the dichroic filter, and is collimated and transmitted to the first lens / lens group and converged to the saturable absorber mirror; at the saturable absorber mirror, noise is filtered out to select high-intensity signal laser to generate pulse laser; Step S3: Pulse laser amplification: The pulse laser is reflected by the saturable absorber mirror and transmitted to the right, and then transmitted to the gain fiber through the first lens / lens group and the wavelength division multiplexing-collimator. At this time, the gain fiber amplifies the pulse laser signal and suppresses the noise to obtain an amplified laser signal. Step S4: Pulse laser output: the amplified laser signal is collimated to the free space or converged to the front surface of the laser output coupling mirror through the right optical fiber end face and the second lens / lens group; Transmitted to the right to the dispersion compensator, where dispersion compensation is performed, the pulse width becomes narrower, and then transmitted to the laser output coupling mirror; The pulsed laser is reflected and transmitted simultaneously on the front surface of the laser output coupling mirror, with a small portion of the light being transmitted as the output laser; the remaining portion is reflected and continues to be transmitted to the left in the cavity, then passes through the dispersion compensator, the second lens / lens group and the right optical fiber end face, and is transmitted to the left to the gain fiber. The laser pulse signal is amplified again in the gain fiber and continues to be transmitted to the left, completing a laser transmission cycle.

[0017] The present invention also provides a third laser generation method, which uses a fiber laser structure in which a wavelength division multiplexing-collimator is simultaneously connected to a left fiber end face and a right-left fiber end face, and the method comprises the following steps: Step S1: generating original pump light: the first pump source and the second pump source both generate original pump light, which are transmitted to the first wavelength division multiplexing-collimator and the second wavelength division multiplexing-collimator via the first passive optical fiber and the second passive optical fiber respectively; Step S2: spontaneous emission light is generated: it is reflected by the dichroic filter of the first wavelength division multiplexing-collimator and the second wavelength division multiplexing-collimator, and transmitted to the gain fiber together, so that the gain fiber achieves population inversion and obtains amplified spontaneous emission light ASE; Step S3: Pulsed laser generation: ASE generated by the gain fiber is transmitted to the left, passes through the lens of the first wavelength division multiplexing-collimator and the dichroic filter, is collimated and transmitted to the first lens / lens group, and then is focused to the saturable absorber mirror through the first lens / lens group; The saturable absorber mirror is located at the focal plane of the focused beam and provides a pulse forming mechanism - filtering out the high-intensity signal laser from the noise to generate a pulsed laser. Step S4: Pulse laser amplification: The pulse laser is reflected by the saturable absorber and transmitted to the right, and then transmitted to the gain fiber through the first lens / lens group and the first wavelength division multiplexing-collimator. At this time, the gain fiber amplifies the signal laser and suppresses the noise to obtain an amplified pulse laser. Step S5: Pulse laser output: the amplified pulse laser passes through the lens of the second wavelength division multiplexing-collimator and the dichroic filter, is collimated to the free space, and continues to transmit to the right; The pulse output from the second wavelength division multiplexing-collimator is dispersion compensated by the dispersion compensator, the pulse width becomes narrower, and then it is transmitted to the laser output coupling mirror; the laser is reflected and transmitted simultaneously on the front surface of the laser output coupling mirror, a small part of which is transmitted as the output laser; the remaining part is reflected by the laser output coupling mirror, continues to be transmitted to the left in the cavity, and then passes through the dispersion compensator and the second wavelength division multiplexing-collimator in succession; the pulse continues to be dispersion compensated in the dispersion compensator, and then is efficiently coupled to the gain fiber through the second wavelength division multiplexing-collimator, the pulse is amplified again in the gain fiber, and continues to be transmitted to the left, completing a laser transmission cycle.

[0018] The beneficial effects of the present invention are: In the present invention, the original pump light of the pump source enters into the resonant cavity structure through a wavelength division multiplexing-collimator. The resonant cavity structure is provided with a saturable absorption mirror, multiple groups of lenses / lens groups, a gain fiber, a dispersion compensator and a laser output coupling mirror. With the cooperation of these devices, the laser signal is continuously screened and amplified to generate and output high-quality, high-stability and easy-to-integrate GHz femtosecond laser. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the resonant cavity structure of the present invention; Figure 2This is a schematic diagram of the structure of Embodiment 1 of the present invention; Figure 3 It is a schematic diagram of the structure of the wavelength division multiplexing-collimator of the present invention; Figure 4 This is a schematic diagram of the structure of Embodiment 2 of the present invention; Figure 5 This is a schematic diagram of the structure of Embodiment 3 of the present invention; Figure 6 The schematic diagrams of the three situations of the image formation of a divergent point light source through a single convex lens; Figure 7 This is a schematic diagram of the image formation of a divergent point light source through two convex lenses; Figure 8 Three ways to set up a saturable absorber for a resonant cavity structure; Fig. 9 This is the graph of the variation of w0' / w0 with s / f; Fig.10 is the graph of the variation of ZR' with s / f; Fig.11 is the graph showing the variation of (s+s') / f with s / f; Fig.12 This is a schematic diagram of the structure of Example 6; Fig.13 The results of the structural working experiment of Example 6 are shown in FIG. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments, but the scope of protection claimed in the present invention is not limited to the following specific embodiments.

[0021] The following is a detailed description of a fiber laser structure of this scheme.

[0022] A fiber laser structure includes a resonant cavity structure and a pump source 10, wherein the pump source 10 is connected to the resonant cavity structure via a wavelength division multiplexing-collimator 9; like Figure 1 The resonant cavity comprises a saturable absorber mirror 1, a first lens / lens group 2, a gain fiber 4, a second lens / lens group 6, a dispersion compensator 7 and a laser output coupling mirror 8; The pump source 10 is transmitted to the wavelength division multiplexing-collimator 9 through the passive optical fiber 11, and the wavelength division multiplexing-collimator 9 is connected to the gain optical fiber 4 and enters the resonant cavity structure, wherein: The pump source 10 is a laser diode, which is used to generate original pump light and activate the inversion particles of the gain fiber 4 through the original pump light.

[0023] The gain fiber 4 is a waveguide structure, used to generate amplified spontaneous emission light ASE, transmission laser and amplification laser, and has a length of less than 10 cm; The first lens / lens group 2 is used to converge the optical signal output by the gain optical fiber 4 onto the saturable absorber mirror 1; The saturable absorber mirror 1 is used to filter out the signal laser from the noise, thereby forming a pulse and reflecting the pulsed laser. The saturable absorber mirror 1 has a high absorption rate for low-intensity lasers and a low absorption rate for high-intensity lasers, thereby filtering out the signal from the noise and providing the laser with an ultrafast pulse formation mechanism to assist in laser mode locking.

[0024] The second lens / lens group 6 is used to collimate or converge the optical signal output by the gain optical fiber 4 to the laser output coupling mirror 8; The dispersion compensator 7 is used to perform dispersion compensation on the optical signal and to provide negative group delay dispersion to the laser.

[0025] The laser output coupling mirror 8 is used to transmit and reflect light signals. The transmitted light signal is used as output laser, and the reflected light signal continues to enter the resonant cavity structure.

[0026] Specifically, the gain optical fiber 4 includes a left optical fiber end face 3 and a right optical fiber end face 5; The wavelength division multiplexing-collimator 9 is connected to the left optical fiber end face 3; Or the wavelength division multiplexing-collimator 9 is connected to the right optical fiber end face 5; Alternatively, the left optical fiber end face 3 and the right optical fiber end face 5 of the wavelength division multiplexing-collimator 9 are connected simultaneously.

[0027] The wavelength division multiplexing-collimator 9 includes an optical fiber ferrule 12, a third lens / lens group 13 and a dichroic filter 14, wherein: The optical fiber ferrule 12 is used to fix the passive optical fiber 11 and the gain optical fiber 4; The third lens / lens group 13 is used to collimate the pump light output by the passive optical fiber 11 and the laser output by the gain optical fiber 4; The dichroic filter 14 is used to reflect the pump light collimated by the third lens / lens group 13 and couple it into the gain fiber 4, while transmitting the laser light collimated by the third lens / lens group 13 into the free space.

[0028] The first lens / lens group 2 and the second lens / lens group 6 may be single lenses or double lenses, wherein the principle of light beam transformation by a single lens is as follows: In 1983, Sidney Self developed a formula for calculating the transformation of a Gaussian beam through a thin lens: in and are the distances from the incident beam waist and the exit beam waist to the lens, is the focal length of the lens, is the Rayleigh distance of the incident beam, i.e., the distance from the beam waist radius to The distance traveled by times the beam waist radius is also called the "collimation" distance.

[0029] in, is the incident beam waist radius, is the wavelength of light.

[0030] It can be obtained from the following formula The expression is: The magnification (reduction) factor of the output beam waist radius is: In the formula, is the output beam waist radius, expressed as: The Rayleigh distance for the output light is: by Figure 1 The left side of the gain fiber is used as an example for explanation: when the first lens / lens group 2 is a single convex lens, the single lens can focus the divergent light beam output from the left fiber end face 3 onto the saturable absorber mirror 1.

[0031] According to the imaging principle of convex lenses, there are roughly three situations when a divergent point light source is transmitted through a single convex lens. It can be classified according to the different positions of the incident point light source on the optical axis of the lens, such as Figure 6 shown.

[0032] Depend on Figure 6 The following conclusions can be drawn: When the incident point light source is within one focal length (F position): the outgoing light diverges and has no beam waist (as shown by the gray arrow); when the incident point light source is at F, the output light is collimated (as shown by the black arrow).

[0033] When the incident point light source is between F and 2F: the outgoing light converges outside twice the focal length (2F); the closer the point light source is to F, the farther the image point is from 2F, and the larger the outgoing beam waist radius; in particular: when s=2f, s'=2f; When the incident point light source is outside the 2F position: the outgoing light converges between F and 2F; and the farther the point light source is from the 2F position, the closer the image point is to the F position, and the smaller the outgoing beam waist radius is.

[0034] The purpose of the lens / lens group, whether it is a single lens or a double lens, is to focus the light beam diverged from one device into another device. By selecting a suitable lens / lens group, the light spot at the exit position and the light spot at the focus position and the divergence angle can be matched. In particular, when coupling from the end face of one optical fiber to the end face of another optical fiber, by selecting a suitable lens / lens group, the mode fields of the two can be matched.

[0035] The principle of dual-lens imaging is as follows: like Figure 7 As shown in the figure, the double lens system includes two convex lenses, which transmit the point light source diverging from D1 to the right and focus it at D2. The two lenses are denoted as F1 and F2, and their functions are to collimate the divergent light and focus the collimated light respectively. Collimation and focusing are inverse processes, which can be described by the following formula: in and are the beam waist diameters of the collimated beam, is the wavelength, and are the focal lengths of the collimating lens and the focusing lens, respectively. and are the waist diameters of the incident light and the outgoing light, respectively. In particular, when the focal planes of F1 and F2 are both the fiber end faces, and are the mode field diameters of the two optical fibers respectively.

[0036] When the conditions are met: When , the coupling efficiency is highest, and the appropriate lens focal length is selected based on this condition.

[0037] exist Figure 1 In the described resonant cavity structure, the divergent light beam emitted from the left optical fiber end face 3 needs to be focused onto the saturable absorber mirror 1 and the efficiency of reflection back to the optical fiber end face is very high, so that the resonant cavity can be mode-locked.

[0038] There are three ways to achieve this, as follows: like Figure 8 As shown in the figure, the double lens system: the divergent light output from the left fiber end face 3 is first collimated by lens f1, then focused to the saturable absorber mirror 1 by lens f2, then reflected by the saturable absorber mirror 1, and coupled back to the left fiber end face 3 through two lenses. This method of using two lenses to collimate first and then focus is called a double lens system.

[0039] Lensless system: The divergent light output from the left fiber end face 3 is directly reflected back by the saturable absorber mirror 1 and coupled into the left fiber end face 3. It is worth noting that since the return light is also divergent, the distance between the saturable absorber mirror 1 and the left fiber end face 3 must be very close (less than the Rayleigh distance of the fiber output light beam) or even close to each other in order to obtain a higher coupling efficiency.

[0040] Single lens system: The divergent light output from the left optical fiber end face 3 is directly focused by a single lens onto the saturable absorber mirror 1 and then reflected back to the left optical fiber end face 3.

[0041] use Figure 8 The saturable absorber setting method (c) has the following four advantages: Relative to Figure 8 In the setting of (b), since the return light is convergent, theoretically the mode field diameter focused on the left optical fiber end face 3 can be equal to the mode field diameter emitted from the left optical fiber end face 3, so it has a higher coupling efficiency.

[0042] Relative to Figure 8 (a) The spot size focused on the saturable absorber mirror 1 can be adjusted continuously. Figure 8 (c) The distance s between the left fiber end face 3 and the lens is as follows: Fig. 9 shown.

[0043] Even if a single lens with different focal lengths is used, the same focused spot size and Rayleigh distance can be achieved. Fig. 9 As shown in the figure: no matter how large the focal length is, when s / f>1.1, the directions of w0' / w0 are almost the same. Fig.10 As shown: No matter how large the focal length is, when s / f>1.1, Z R The advantage of a larger Rayleigh distance for the focused spot is that a slight axial translation (caused by the environment) will not have a significant effect on the coupling efficiency.

[0044] The distance s+s' between the saturable absorber 1 and the left optical fiber end face 3 can be adjusted to be very small, and the smaller the focal length f of the lens, the smaller s+s'. Fig.11 As shown in the figure, for lenses with different focal lengths, when s / f>1.1, the trends of (s+s') / f are almost the same, so the smaller f is, the smaller s+s' is. Shorter s+s' can shorten the length of the resonant cavity, which is crucial for the design of high repetition rate mode-locked lasers.

[0045] Example 1: WDM-collimator on the right side of gain fiber like Figure 2 As shown, the wavelength division multiplexing-collimator is placed at the right end of the gain optical fiber 4 , that is, the wavelength division multiplexing-collimator 9 is connected to the right optical fiber end face 5 .

[0046] At this point, the entire structure works as follows: The original pump light generated by the pump source 10 is transmitted to the wavelength division multiplexing-collimator 9 via the passive optical fiber 11, and then reflected by the dichroic filter 14 and transmitted to the gain optical fiber 4, so that the gain optical fiber 4 achieves population inversion and obtains amplified spontaneous emission light ASE; The ASE generated by the gain fiber 4 is transmitted to the left through the left fiber end face and the first lens / lens group 2 and converged to the saturable absorber 1; at the saturable absorber 1, the spontaneous radiation light is filtered to remove noise and select the signal laser to form a pulsed laser; The pulsed laser after filtering out noise is transmitted to the right through the saturable absorber 1, and is focused to the fiber end face 3 by the first lens / lens group 2 again, and then coupled into the gain fiber 4. At this time, the gain fiber 4 amplifies the pulsed laser and suppresses the noise at the same time, thereby obtaining an amplified pulsed laser. The amplified pulsed laser is collimated to the free space through the third lens / lens group 13 and the dichroic filter 14, and then continues to transmit to the right from the free space to the dispersion compensator 7 (the principle is as follows Figure 6 (a) shows that dispersion compensation is performed in the dispersion compensator 7, the pulse width becomes narrower, and then it is transmitted to the laser output coupling mirror 8; The pulsed laser is reflected and transmitted at the front surface of the laser output coupling mirror 8, a small part of which is transmitted as the output laser. The remaining part is reflected and continues to transmit to the left in the cavity, and then passes through the dispersion compensator 7 and the wavelength division multiplexing-collimator 9; The reflected pulse is further dispersion compensated in the dispersion compensator 7, and then coupled to the gain fiber 4 via the wavelength division multiplexing-collimator 9, where it is amplified again and continues to be transmitted to the left, completing a laser transmission cycle.

[0047] The above process is a complete cycle of the laser transmission process. The intracavity laser operates periodically in the laser composed of all the above devices, forming a pulsed laser, which is amplified and finally forms a stable continuous wave mode-locked pulse laser output, that is, a high-quality, high-efficiency, high-magnitude femtosecond laser. The output parameters of the mode-locked pulse are jointly determined by the parameter combination of each device in the cavity.

[0048] Corresponding to the structure of Example 1, the steps of a laser generation method using a fiber laser structure in which a wavelength division multiplexing-collimator is connected to the right fiber end face are as follows: Step S1: generating original pump light: the pump source generates original pump light and transmits it to the wavelength division multiplexing-collimator via a passive optical fiber; Step S2: Spontaneous emission light generation: the original pump light is reflected by the dichroic filter and transmitted to the gain fiber, so that the gain fiber achieves population inversion and obtains amplified spontaneous emission light (ASE); Step S3: Pulsed laser generation: ASE generated by the gain fiber is transmitted to the left through the left fiber end face and the first lens / lens group and converged to the saturable absorber mirror; noise is filtered out at the saturable absorber mirror to select high-intensity signal laser to form a pulsed laser; Step S4: Pulse laser amplification: The pulse laser with improved signal-to-noise ratio is transmitted to the right through the saturable absorber mirror, and is focused to the fiber end face by the first lens / lens group again, and then coupled into the gain fiber. At this time, the gain fiber amplifies the pulse laser and suppresses the noise to obtain an amplified pulse laser. Step S5 Pulse laser output: The amplified pulse laser is collimated to free space through the third lens / lens group and the dichroic filter, and then continues to transmit to the right to the dispersion compensator (the principle is as follows Figure 6 (a)); Dispersion compensation is performed in the dispersion compensator, the pulse width becomes narrower, and then it is transmitted to the laser output coupling mirror; The pulsed laser is reflected and transmitted simultaneously on the front surface of the laser output coupling mirror, of which a small part is transmitted as the output laser; the remaining part is reflected and continues to transmit to the left in the cavity, and then passes through the dispersion compensator and the wavelength division multiplexing-collimator in succession; The reflected pulse is further dispersion compensated in the dispersion compensator, and then coupled to the gain fiber through the wavelength division multiplexing-collimator, amplified again in the gain fiber, and continues to be transmitted to the left, completing a laser transmission cycle.

[0049] Example 2: WDM-collimator on the left side of gain fiber like Figure 4 As shown, in this embodiment, the wavelength division multiplexing-collimator 9 is connected to the left optical fiber end face 3.

[0050] At this point, the entire structure works as follows: The original pump light of the pump source 10 is transmitted to the wavelength division multiplexing-collimator 9 via the passive optical fiber 11, and then reflected by the dichroic filter 14 and transmitted to the gain optical fiber 4, so that the gain optical fiber 4 achieves population inversion and obtains amplified spontaneous emission light ASE; The ASE generated by the gain fiber 4 is also transmitted to the left, passes through the third lens / lens group 13 and the dichroic filter 14, and is collimated and transmitted to the first lens / lens group 2 to converge to the saturable absorber mirror 1; at the saturable absorber mirror 1, the noise is filtered out and the signal laser is selected to form a pulsed laser.

[0051] The generated pulsed laser is reflected by the saturable absorber mirror 1 and transmitted to the right, and then transmitted to the gain fiber 4 through the first lens / lens group 2 and the wavelength division multiplexing-collimator 9. At this time, the gain fiber 4 amplifies the pulsed laser signal and suppresses the noise at the same time. The amplified laser signal is transmitted to the free space through the right fiber end face 5 and the second lens / lens group 6, and continues to be transmitted to the right.

[0052] It is worth noting that the laser output from the right fiber end face 5 is divergent. There are two possibilities for the output laser after passing through the second lens / lens group 6: one is to collimate to free space (the principle is as follows Figure 6 (a)); the second is to converge to the front surface of the laser output coupling mirror 8 (the principle is as follows Figure 6 (b) or (c)), depending on the distance from the right fiber end face 5 to the second lens / lens group 6. The dispersion compensator 7 between the second lens / lens group 6 and the laser output coupling mirror 8 provides dispersion compensation to narrow the pulse width.

[0053] The pulsed laser is reflected and transmitted simultaneously on the front surface of the laser output coupling mirror 8, a small part of which is transmitted as the output laser; the remaining part is reflected and continues to be transmitted to the left in the cavity, and then passes through the dispersion compensator 7, the second lens / lens group 6 and the right fiber end face 5. In the two cases described above (whether collimated or converged), the process of transmitting to the left through the right fiber end face 5 to the gain fiber 4 can achieve high-efficiency coupling. The laser pulse signal is amplified again in the gain fiber 4 and continues to be transmitted to the left.

[0054] The above process is a complete cycle of the laser transmission process. The intracavity laser operates periodically in the laser composed of all the above devices, forming a pulsed laser, which is amplified and finally forms a stable continuous wave mode-locked pulse laser output. The output parameters of the mode-locked pulse are jointly determined by the parameter combination of each device in the cavity.

[0055] Corresponding to the structure of Example 2, the steps of a laser generation method using a fiber laser structure in which a wavelength division multiplexing-collimator is connected to the left fiber end face are as follows: Step S1: generating original pump light: the original pump light of the pump source is transmitted to the wavelength division multiplexing-collimator via the passive optical fiber; Step S2: Spontaneous emission light generation: the original pump light is reflected by the dichroic filter and transmitted to the gain fiber, so that the gain fiber achieves population inversion and obtains amplified spontaneous emission light ASE; Step S3: Pulse laser generation: ASE generated by the gain fiber is also transmitted to the left, passes through the third lens / lens group and the dichroic filter, and is collimated and transmitted to the first lens / lens group and converged to the saturable absorber mirror; at the saturable absorber mirror, noise is filtered out to select high-intensity signal laser to generate pulse laser; Step S3: Pulse laser amplification: The pulse laser is reflected by the saturable absorber mirror and transmitted to the right, and then transmitted to the gain fiber through the first lens / lens group and the wavelength division multiplexing-collimator. At this time, the gain fiber amplifies the pulse laser signal and suppresses the noise to obtain an amplified laser signal. Step S4: Pulsed laser output: The amplified laser signal is collimated to free space or converged to the front surface of the laser output coupling mirror via the right optical fiber end face and the second lens / lens group, depending on the distance from the right optical fiber end face (5) to the second lens / lens group (6).

[0056] Transmitted to the right to the dispersion compensator, where dispersion compensation is performed, the pulse width becomes narrower, and then transmitted to the laser output coupling mirror; The pulsed laser is reflected and transmitted simultaneously on the front surface of the laser output coupling mirror 8, with a small portion of the light being transmitted as the output laser; the remaining portion is reflected and continues to be transmitted to the left in the cavity, then passes through the dispersion compensator, the second lens / lens group and the right optical fiber end face, and is transmitted to the left to the gain optical fiber. The laser pulse signal is amplified again in the gain optical fiber and continues to be transmitted to the left, completing a laser transmission cycle.

[0057] Example 3: Dual wavelength division multiplexing-collimator like Figure 5 As shown, in this embodiment, two sequentially connected pump sources and wavelength division multiplexing-collimators are provided, and the two wavelength division multiplexing-collimators are respectively connected to the left fiber end face 3 and the right fiber end face 5 of the gain fiber.

[0058] Two pump sources, named as: a first pump source 10 and a second pump source 10'; Two passive optical fibers, named a first passive optical fiber 11 and a second passive optical fiber 11 ′; Two wavelength division multiplexing-collimators, named as a first wavelength division multiplexing-collimator 9 and a second wavelength division multiplexing-collimator 9'; At this point, the entire structure works as follows: The first pump source 10 and the second pump source 10' both generate original pump light, which is transmitted to the first wavelength division multiplexing-collimator 9 and the second wavelength division multiplexing-collimator 9' through the first passive optical fiber 11 and the second passive optical fiber 11' respectively; Then, the light is reflected by the dichroic filters 14 of the first wavelength division multiplexing-collimator 9 and the second wavelength division multiplexing-collimator 9' and transmitted to the gain fiber 4 together, thereby achieving population inversion in the gain fiber 4 and obtaining amplified spontaneous emission light ASE.

[0059] The ASE generated by the gain fiber 4 is transmitted to the left, passes through the lens of the first wavelength division multiplexing-collimator 9 and the dichroic filter 14, is collimated and transmitted to the first lens / lens group 2, and then is focused to the saturable absorber mirror 1 through the first lens / lens group 2; The saturable absorption mirror 1 is located at the focal plane of the focused light beam and provides a pulse forming mechanism - filtering out high-intensity signal laser from noise, thereby generating a pulse laser; The pulse laser reflected by the saturable absorber mirror 1 is transmitted to the right, and is transmitted to the gain fiber 4 again through the first lens / lens group 2 and the first wavelength division multiplexing-collimator 9. At this time, the gain fiber 4 amplifies the signal laser and suppresses the noise to obtain an amplified pulse laser. The amplified pulse laser passes through the lens of the second wavelength division multiplexing-collimator 9' and the dichroic filter 14, is collimated into free space, and continues to transmit to the right; The pulse output from the second wavelength division multiplexing-collimator 9' undergoes dispersion compensation through the dispersion compensator 7, and the pulse width becomes narrower, and then is transmitted to the laser output coupling mirror 8; the laser light is simultaneously reflected and transmitted on the front surface of the laser output coupling mirror 8, and a small part of the light is transmitted as the output laser; the remaining part is reflected by the laser output coupling mirror 8, and continues to be transmitted to the left in the cavity, and then passes through the dispersion compensator 7 and the second wavelength division multiplexing-collimator 9' in sequence; The pulse continues to be dispersion compensated in the dispersion compensator 7, and then is efficiently coupled to the gain fiber 4 through the second wavelength division multiplexing-collimator 9'. The pulse is amplified again in the gain fiber 4 and continues to be transmitted to the left, completing a laser transmission cycle.

[0060] The above process is a complete cycle of the laser transmission process. The intracavity laser operates periodically in the laser composed of all the above devices, forming a pulsed laser, which is amplified and finally forms a stable continuous wave mode-locked pulse laser output. The output parameters of the mode-locked pulse are jointly determined by the parameter combination of each device in the cavity.

[0061] Corresponding to the structure of Example 3, the steps of a laser generation method using a fiber laser structure in which a wavelength division multiplexing-collimator is simultaneously connected to the left fiber end face and the right and left fiber end faces are as follows: Step S1: generating original pump light: the first pump source and the second pump source both generate original pump light, which are transmitted to the first wavelength division multiplexing-collimator and the second wavelength division multiplexing-collimator via the first passive optical fiber and the second passive optical fiber respectively; Step S2: spontaneous emission light is generated: it is reflected by the dichroic filter of the first wavelength division multiplexing-collimator and the second wavelength division multiplexing-collimator, and transmitted to the gain fiber together, so that the gain fiber achieves population inversion and obtains amplified spontaneous emission light ASE; Step S3: Pulsed laser generation: ASE generated by the gain fiber is transmitted to the left, passes through the lens of the first wavelength division multiplexing-collimator and the dichroic filter, is collimated and transmitted to the first lens / lens group, and then is focused to the saturable absorber mirror through the first lens / lens group; The saturable absorber mirror is located at the focal plane of the focused beam and provides a pulse forming mechanism - filtering out the high-intensity signal laser from the noise to generate a pulsed laser. Step S4: Pulse laser amplification: The pulse laser is reflected by the saturable absorber and transmitted to the right, and then transmitted to the gain fiber through the first lens / lens group and the first wavelength division multiplexing-collimator. At this time, the gain fiber amplifies the signal laser and suppresses the noise to obtain an amplified pulse laser. Step S5: Pulse laser output: the amplified pulse laser passes through the lens of the second wavelength division multiplexing-collimator and the dichroic filter, is collimated to the free space, and continues to transmit to the right; The pulse output from the second wavelength division multiplexing-collimator is dispersion compensated by the dispersion compensator, the pulse width becomes narrower, and then it is transmitted to the laser output coupling mirror; the laser is reflected and transmitted simultaneously on the front surface of the laser output coupling mirror, a small part of which is transmitted as the output laser; the remaining part is reflected by the laser output coupling mirror, continues to be transmitted to the left in the cavity, and then passes through the dispersion compensator and the second wavelength division multiplexing-collimator in succession; the pulse continues to be dispersion compensated in the dispersion compensator, and then is efficiently coupled to the gain fiber through the second wavelength division multiplexing-collimator, the pulse is amplified again in the gain fiber, and continues to be transmitted to the left, completing a laser transmission cycle.

[0062] like Fig.12 As shown, it includes multiple devices 19-27, and the specific names and parameters of the multiple devices are as follows: Device 19: Semiconductor saturable absorber mirror (SESAM); parameters: modulation depth 18%, saturation flux 100 μJ / cm 2 , relaxation time 9ps.

[0063] Device 20: convex lens; parameters: focal length 6 mm.

[0064] Device 21: Beveled end face; parameter: bevel angle is 8°.

[0065] Device 22: Yb-doped optical fiber; parameters: optical fiber length ~4.5cm, absorption coefficient 2400dB / m@976nm, mode field diameter 5μm@1060nm.

[0066] Device 23: Passive optical fiber; model: HI1060, length>20cm.

[0067] Device 24: laser diode; wavelength 976nm, maximum output power 900mW.

[0068] Device 25: wavelength division multiplexing-collimator; parameters: reflection wavelength 970-980nm, transmission wavelength 1010-1100nm, collimation distance 110mm.

[0069] Device 26: grating; parameters: 1000 lines / mm, incident angle 28-33°.

[0070] Device 26': Same as device 26; two gratings are placed in parallel, and the vertical distance between the grating pairs is 1 mm.

[0071] Device 27: coupling output mirror; parameters: wavelength 1000-1100nm, transmittance ≤5%, reflectivity ≥95%.

[0072] The working process of this embodiment includes a coupling process and an adjustment and locking process: Coupling process: Press Fig.12 Install the components so that the distance between component 20 and component 21 is between 1.1-1.4 times the focal length. Adjust the output power of component 24 to below 50mW. Place component 19 on the focal plane on the image side, and adjust the θ-φ direction of component 19 to make the reflected light return to component 21, and adjust it to the maximum optical power output by component 25. Make the light output by component 25 incident on component 26 at a range of 28°-33°, and make components 26 and 26' parallel, and adjust the vertical distance to about 1mm. Adjust component 27 so that the reflected light returns to component 25, and adjust the output power to the maximum to complete the coupling process.

[0073] Adjust the mode-locking process: adjust the pump source power to above 600 mW, observe the pulse sequence from device 27 with an oscilloscope, and observe the mode-locking spectrum with a spectrometer.

[0074] The experimental results obtained by using this embodiment are as follows: like Fig.13 As shown, the output result is measured from the output port of device 27. Among them, Fig.13 (a) is the output spectrum at different powers. The color changes from gray to black, which represents the process of gradually increasing pump power. The inset shows the output spectrum width at different powers. Fig.13 (b) shows the autocorrelation curve of the direct output (black solid line) and the autocorrelation curve after dechirping with a grating outside the cavity (gray solid line) when the pump power is 900mW. The dashed lines of different colors represent the Gaussian fitting curves of the two. The direct output autocorrelation pulse width is 128fs, and the corresponding Gaussian electric field strength half-width is 90.5fs; the autocorrelation pulse width after dechirping is 116fs, and the corresponding Gaussian electric field strength half-width is 82fs. Fig.13 (c) shows the measured pulse train with a pulse interval of approximately 925 ps. Fig.13 (d) shows the measured RF spectrum, the corresponding repetition frequency is about 1.08 GHz, and the measured resolution bandwidth is 1 kHz; the inset shows the RF spectrum with a frequency range of 26.5 GHz and a resolution bandwidth of 10 kHz.

[0075] According to the disclosure and teaching of the above description, those skilled in the art to which the present invention belongs may also make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and changes to the invention should also fall within the scope of protection of the claims of the present invention. In addition, although some specific terms are used in this specification, these terms are only for the convenience of description and do not constitute any limitation to the invention.

Claims

1. A fiber laser structure, characterized in that: It comprises a resonant cavity structure and a pump source (10), wherein the pump source (10) is connected to the resonant cavity structure via a wavelength division multiplexing-collimator (9); The resonant cavity structure comprises a saturable absorber mirror (1), a first lens / lens group (2), a gain optical fiber (4), a second lens / lens group (6), a dispersion compensator (7) and a laser output coupling mirror (8); The pump source (10) is transmitted to the wavelength division multiplexing-collimator (9) through the passive optical fiber (11), and the wavelength division multiplexing-collimator (9) is connected to the gain optical fiber (4) and enters the interior of the resonant cavity structure, wherein: The gain optical fiber (4) is a waveguide structure, used to generate amplified spontaneous emission light ASE, transmission laser and amplification laser; The first lens / lens group (2) is used to converge the optical signal output by the gain optical fiber (4) onto the saturable absorber mirror (1); The saturable absorption mirror (1) is used to filter out high-intensity signal laser from noise, thereby forming a pulse and reflecting the pulse laser; The second lens / lens group (6) is used to collimate or converge the optical signal output by the gain optical fiber (4) to the laser output coupling mirror (8); The dispersion compensator (7) is used to perform dispersion compensation on the optical signal; The laser output coupling mirror (8) is used to transmit and reflect light signals; the transmitted light signal is used as output laser light, and the reflected light signal enters the resonant cavity structure and continues to oscillate.

2. A fiber laser structure as claimed in claim 1, characterized in that: The gain optical fiber (4) comprises a left optical fiber end face (3) and a right optical fiber end face (5); The wavelength division multiplexing-collimator (9) is connected to the left optical fiber end face (3); Or the wavelength division multiplexing-collimator (9) is connected to the right optical fiber end face (5); Alternatively, the left optical fiber end face (3) and the right optical fiber end face (5) of the wavelength division multiplexing-collimator (9) are connected simultaneously.

3. A fiber laser structure as claimed in claim 2, characterized in that: The wavelength division multiplexing-collimator (9) comprises an optical fiber insert (12), a third lens / lens group (13) and a dichroic filter (14), wherein: The optical fiber insert (12) is used to fix the passive optical fiber (11) and the gain optical fiber (4); The third lens / lens group (13) is used to collimate the pump light output by the passive optical fiber (11) and the laser light output by the gain optical fiber (4); The dichroic filter (14) is used to reflect the pump light collimated by the third lens / lens group (13) and couple it into the gain optical fiber (4), while transmitting the laser light collimated by the third lens / lens group (13) into free space.

4. A fiber laser structure as claimed in claim 3, characterized in that: When the wavelength division multiplexing-collimator (9) is connected to the right optical fiber end face (5), The original pump light of the pump source (10) is transmitted to the wavelength division multiplexing-collimator (9) via the passive optical fiber (11), then reflected by the dichroic filter (14) and transmitted to the gain optical fiber (4), thereby achieving population inversion in the gain optical fiber (4) and obtaining amplified spontaneous emission light ASE; The ASE generated by the gain optical fiber (4) is transmitted to the left through the left optical fiber end face (3) and the first lens / lens group (2) and converged to the saturable absorption mirror (1); at the saturable absorption mirror (1), noise is filtered out and high-intensity signal laser is selected to form a pulsed laser; The pulsed laser with improved signal-to-noise ratio is transmitted to the right through the saturable absorber mirror (1), and is focused to the left optical fiber end face (3) through the first lens / lens group (2) again, and then coupled into the gain optical fiber (4). At this time, the gain optical fiber (4) amplifies the pulsed laser and suppresses the noise, thereby obtaining an amplified pulsed laser. The amplified pulsed laser light is collimated into free space via a third lens / lens group (13) and a dichroic filter (14), and then continues to be transmitted to the right to a dispersion compensator (7); Dispersion compensation is performed in the dispersion compensator (7), the pulse width is narrowed, and then the pulse is transmitted to the laser output coupling mirror (8); The pulsed laser is reflected and transmitted simultaneously on the front surface of the laser output coupling mirror (8), wherein a small portion of the light is transmitted and serves as the output laser; the remaining portion is reflected and continues to be transmitted to the left in the cavity, and then passes through the dispersion compensator (7) and the wavelength division multiplexing-collimator (9) in sequence; The reflected pulse is further dispersion compensated in the dispersion compensator (7), then coupled to the gain fiber (4) via the wavelength division multiplexing-collimator (9), amplified again in the gain fiber (4), and continues to be transmitted to the left, completing a laser transmission cycle.

5. A fiber laser structure as claimed in claim 3, characterized in that: When the wavelength division multiplexing-collimator (9) is connected to the left optical fiber end face (3), The original pump light of the pump source (10) is transmitted to the wavelength division multiplexing-collimator (9) via the passive optical fiber (11), then reflected by the dichroic filter (14) and transmitted to the gain optical fiber (4), thereby achieving population inversion in the gain optical fiber (4) and obtaining amplified spontaneous emission light ASE; The ASE generated by the gain optical fiber (4) is also transmitted to the left, passes through the third lens / lens group (13) and the dichroic filter (14), and is collimated and transmitted to the first lens / lens group (2) and converged to the saturable absorption mirror (1); at the saturable absorption mirror (1), noise is filtered out and high-intensity signal laser is selected to form a pulsed laser; The pulsed laser with improved signal-to-noise ratio is reflected by the saturable absorber mirror (1) and transmitted to the right, and then transmitted to the gain optical fiber (4) through the first lens / lens group (2) and the wavelength division multiplexing-collimator (9). At this time, the gain optical fiber (4) amplifies the pulsed laser signal and suppresses the noise, thereby obtaining an amplified laser signal. The amplified laser signal is collimated to free space or converged to the front surface of the laser output coupling mirror 8 via the right optical fiber end face (5) and the second lens / lens group (6), depending on the distance from the right optical fiber end face (5) to the second lens / lens group (6); Transmitted to the right to the dispersion compensator (7), where dispersion compensation is performed and the pulse width is narrowed, and then transmitted to the laser output coupling mirror (8); The pulsed laser is reflected and transmitted simultaneously on the front surface of the laser output coupling mirror (8), wherein a small portion of the light is transmitted as the output laser; the remaining portion is reflected and continues to be transmitted to the left in the cavity, then passes through the dispersion compensator (7), the second lens / lens group (6) and the right optical fiber end face (5), and is transmitted to the left to the gain optical fiber (4). The laser pulse signal is amplified again in the gain optical fiber (4) and continues to be transmitted to the left, completing a laser transmission cycle.

6. A fiber laser structure as claimed in claim 3, characterized in that: It comprises two first wavelength division multiplexing-collimators (9), a second wavelength division multiplexing-collimator (9'), a first pump source (10) and a second pump source (10'); When the first wavelength division multiplexing-collimator (9) is connected to the left optical fiber end face (3), and the second wavelength division multiplexing-collimator (9') is connected to the right optical fiber end face (5) at the same time, The first pump source (10) and the second pump source (10') both generate original pump light, which is transmitted to the first wavelength division multiplexing-collimator (9) and the second wavelength division multiplexing-collimator (9') via the first passive optical fiber (11) and the second passive optical fiber (11'), respectively; Then, the light is reflected by the dichroic filters (14) of the first wavelength division multiplexing-collimator (9) and the second wavelength division multiplexing-collimator (9'), and transmitted to the gain optical fiber (4) together, thereby achieving population inversion in the gain optical fiber (4) and obtaining amplified spontaneous emission light ASE; The ASE generated by the gain optical fiber (4) is transmitted to the left, passes through the lens of the first wavelength division multiplexing-collimator (9) and the dichroic filter (14), is collimated and transmitted to the first lens / lens group (2), and then is focused to the saturable absorber mirror (1) through the first lens / lens group (2); The saturable absorber mirror (1) is located at the focal plane of the focused beam and provides a pulse forming mechanism - filtering out high-intensity signal laser from noise, thereby generating pulsed laser. The pulsed laser reflected by the saturable absorber mirror (1) is transmitted to the right, and is transmitted to the gain optical fiber (4) again through the first lens / lens group (2) and the first wavelength division multiplexing-collimator (9). At this time, the gain optical fiber (4) amplifies the signal laser and suppresses the noise, thereby obtaining an amplified pulsed laser. The amplified pulse laser is collimated to free space through the lens of the second wavelength division multiplexing-collimator (9') and the dichroic filter (14), and continues to be transmitted to the right; The pulse output from the second wavelength division multiplexing-collimator (9') is dispersion compensated by the dispersion compensator (7), the pulse width is narrowed, and then it is transmitted to the laser output coupling mirror (8); the laser light is reflected and transmitted at the front surface of the laser output coupling mirror (8), a small part of which is transmitted as the output laser light; the remaining part is reflected by the laser output coupling mirror (8), continues to be transmitted to the left in the cavity, and then passes through the dispersion compensator (7) and the second wavelength division multiplexing-collimator (9') in sequence; wherein the pulse continues to be dispersion compensated in the dispersion compensator (7), and then is efficiently coupled to the gain optical fiber (4) through the second wavelength division multiplexing-collimator (9'), the pulse is amplified again in the gain optical fiber (4), and continues to be transmitted to the left, completing a laser transmission cycle.

7. A laser generation method, using the fiber laser structure as claimed in claim 4, characterized in that: The method comprises the following steps: Step S1: generating original pump light: the pump source (10) generates original pump light and transmits it to the wavelength division multiplexing-collimator (9) via the passive optical fiber (11); Step S2: spontaneous emission light generation: the original pump light is reflected by the dichroic filter (14) and transmitted to the gain optical fiber (4), thereby achieving population inversion in the gain optical fiber (4) and obtaining amplified spontaneous emission light ASE; Step S3: generating pulsed laser light: the ASE generated by the gain optical fiber (4) is transmitted to the left through the left optical fiber end face (3) and the first lens / lens group (2) and converged to the saturable absorber mirror (1); at the saturable absorber mirror (1), noise is filtered out to select high-intensity signal laser light, thereby forming a pulsed laser light; Step S4: Pulse laser amplification: the pulse laser with improved signal-to-noise ratio is transmitted to the right through the saturable absorber mirror (1), and is focused to the left optical fiber end face (3) by the first lens / lens group (2) again, and then coupled into the gain optical fiber (4). At this time, the gain optical fiber (4) amplifies the pulse laser and suppresses the noise, thereby obtaining an amplified pulse laser. Step S5: pulse laser output: the amplified pulse laser is collimated to free space via the third lens / lens group (13) and the dichroic filter (14), and then continues to be transmitted to the right to the dispersion compensator (7); Dispersion compensation is performed in the dispersion compensator (7), the pulse width is narrowed, and then the pulse is transmitted to the laser output coupling mirror (8); The pulsed laser is reflected and transmitted simultaneously on the front surface of the laser output coupling mirror (8), wherein a small portion of the light is transmitted and serves as the output laser; the remaining portion is reflected and continues to be transmitted to the left in the cavity, and then passes through the dispersion compensator (7) and the wavelength division multiplexing-collimator (9) in sequence; The reflected pulse is further dispersion compensated in the dispersion compensator (7), then coupled to the gain fiber (4) via the wavelength division multiplexing-collimator (9), amplified again in the gain fiber (4), and continues to be transmitted to the left, completing a laser transmission cycle.

8. A laser generation method, using the fiber laser structure as claimed in claim 5, characterized in that: The method comprises the following steps: Step S1: generating original pump light: the original pump light from the pump source (10) is transmitted to the wavelength division multiplexing-collimator (9) via the passive optical fiber (11); Step S2: spontaneous emission light generation: the original pump light is reflected by the dichroic filter (14) and transmitted to the gain optical fiber (4), thereby achieving population inversion in the gain optical fiber (4) and obtaining amplified spontaneous emission light ASE; Step S3: Pulsed laser generation: The ASE generated by the gain optical fiber (4) is also transmitted to the left, passes through the third lens / lens group (13) and the dichroic filter (14), is collimated and transmitted to the first lens / lens group (2), and converges to the saturable absorber (1); at the saturable absorber (1), noise is filtered out to select high-intensity signal laser, thereby generating pulsed laser; Step S3: Pulse laser amplification: The pulse laser is reflected by the saturable absorber mirror (1) and transmitted to the right, and then transmitted to the gain fiber (4) through the first lens / lens group (2) and the wavelength division multiplexing-collimator (9). At this time, the gain fiber (4) amplifies the pulse laser signal and suppresses the noise to obtain an amplified laser signal. Step S4: pulsed laser output: the amplified laser signal is collimated to the free space or converged to the front surface of the laser output coupling mirror (8) via the right optical fiber end face (5) and the second lens / lens group (6); Transmitted to the right to the dispersion compensator (7), where dispersion compensation is performed and the pulse width is narrowed, and then transmitted to the laser output coupling mirror (8); The pulsed laser is reflected and transmitted simultaneously on the front surface of the laser output coupling mirror (8), wherein a small portion of the light is transmitted as the output laser; the remaining portion is reflected and continues to be transmitted to the left in the cavity, then passes through the dispersion compensator (7), the second lens / lens group (6) and the right optical fiber end face (5), and is transmitted to the left to the gain optical fiber (4). The laser pulse signal is amplified again in the gain optical fiber (4) and continues to be transmitted to the left, completing a laser transmission cycle.

9. A laser generation method, using the fiber laser structure as claimed in claim 6, characterized in that: The method comprises the following steps: Step S1: generating original pump light: the first pump source (10) and the second pump source (10') both generate original pump light, which is transmitted to the first wavelength division multiplexing-collimator (9) and the second wavelength division multiplexing-collimator (9') via the first passive optical fiber (11) and the second passive optical fiber (11'), respectively; Step S2: spontaneous emission light is generated: it is reflected by the dichroic filters (14) of the first wavelength division multiplexing-collimator (9) and the second wavelength division multiplexing-collimator (9'), and transmitted to the gain optical fiber (4) together, so that the gain optical fiber (4) achieves population inversion and obtains amplified spontaneous emission light ASE; Step S3: Pulsed laser generation: ASE generated by the gain fiber is transmitted to the left, passes through the lens of the first wavelength division multiplexing-collimator (9) and the dichroic filter (14), is collimated and transmitted to the first lens / lens group (2), and then is focused to the saturable absorber mirror (1) through the first lens / lens group (2); The saturable absorber mirror (1) is located at the focal plane of the focused beam and provides a pulse forming mechanism - filtering out high-intensity signal laser from noise, thereby generating pulsed laser. Step S4: Pulse laser amplification: The pulse laser is reflected by the saturable absorber mirror (1) and transmitted to the right, and then transmitted to the gain fiber (4) through the first lens / lens group (2) and the first wavelength division multiplexing-collimator (9). At this time, the gain fiber (4) amplifies the signal laser and suppresses the noise, thereby obtaining an amplified pulse laser. Step S5: pulse laser output: the amplified pulse laser passes through the lens of the second wavelength division multiplexing-collimator (9') and the dichroic filter (14), is collimated to the free space, and continues to be transmitted to the right; The pulse output from the second wavelength division multiplexing-collimator (9') is dispersion compensated by the dispersion compensator (7), the pulse width is narrowed, and then it is transmitted to the laser output coupling mirror (8); the laser light is reflected and transmitted at the front surface of the laser output coupling mirror (8), a small part of which is transmitted as the output laser light; the remaining part is reflected by the laser output coupling mirror (8), continues to be transmitted to the left in the cavity, and then passes through the dispersion compensator (7) and the second wavelength division multiplexing-collimator (9') in sequence; wherein the pulse continues to be dispersion compensated in the dispersion compensator (7), and then is efficiently coupled to the gain optical fiber (4) through the second wavelength division multiplexing-collimator (9'), the pulse is amplified again in the gain optical fiber (4), and continues to be transmitted to the left, completing a laser transmission cycle.

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