Fiber laser structure based on multi-lens coupling and laser generation method

Abstract

An optical fiber laser structure based on multi-lens coupling comprises a resonant cavity structure and a pumping source, and the pumping source is in optical signal connection with the resonant cavity structure through a lens combination. 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 achieving population inversion, obtaining amplified spontaneous emission (ASE) light and transmitting or 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. The pumping source enters the resonant cavity structure through the lens combination and can generate and output GHz femtosecond laser which is high in quality, high in stability, high in magnitude 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 based on multi-lens coupling 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 propose a fiber laser structure based on multi-lens coupling and a laser generation method.

[0009] The present invention is achieved through the following technical solutions: A fiber laser structure based on multi-lens coupling includes a resonant cavity structure and a pump source, wherein the pump source is connected to the resonant cavity structure through a lens combination structure; 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 lens combination structure includes a dichroic mirror and at least one lens / lens group; The original pump light of the pump source is coupled into any end of the gain optical fiber through a lens combination structure; 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 the optical signal, the transmitted optical signal is used as the output laser, and the reflected optical signal continues to enter the resonant cavity structure; The dichroic mirror is used to transmit pump light and reflect laser signals, and the lens is used to collimate or focus laser signals.

[0010] Preferably, the lens assembly is arranged on the left side of the gain optical fiber; The dichroic mirror is provided with a fifth lens / lens group in the direction of the right optical fiber end face leading to the passive optical fiber; the dichroic mirror is provided with a fourth lens / lens group in the direction leading to the saturable absorber mirror; The original pump light generated by the pump source is transmitted to the right fiber end face and the fifth lens / lens group through the passive optical fiber, and then transmitted to the left fiber end face through the dichroic mirror; the original pump light is coupled into the gain fiber, so that the gain fiber achieves population inversion and obtains amplified spontaneous emission light ASE; The spontaneous emission light ASE generated by the gain fiber is transmitted to the left, passes through the left fiber end face, and then is reflected on the inner surface of the dichroic mirror and transmitted to the fourth lens / lens group and the saturable absorber mirror. The dichroic mirror and the fourth lens / lens group are used to converge the optical signal output from the left fiber end face to the saturable absorber mirror through the dichroic mirror; The saturable absorber mirror is located at the focal plane of the focused beam and provides a pulse forming mechanism - filtering out high-intensity signal laser from noise to form a pulsed laser; The laser reflected by the saturable absorber is transmitted downward, and is focused to the left fiber end face by the fourth lens / lens group and the dichroic mirror again, and then coupled into the gain fiber. At this time, the gain fiber amplifies the signal laser and suppresses the noise to obtain an amplified pulse laser. The amplified pulsed laser 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 method used is determined by the distance from the right fiber end face to the second lens / lens group. Continue to transmit to the right, transmitted to the dispersion compensator, where dispersion compensation is performed, the pulse width becomes narrower, and then transmitted to the laser output coupling mirror; It is transmitted to the front surface of the laser output coupling mirror, where reflection and transmission occur simultaneously. A small portion of the light is transmitted as the output laser; the remaining portion is reflected by the laser output coupling mirror and continues to be transmitted to the left in the cavity, and then passes through the second lens / lens group of the dispersion compensator and the right optical fiber end face to be coupled to the gain fiber, where it is amplified again and continues to be transmitted to the left, completing a laser transmission cycle.

[0011] Preferably, the lens assembly is arranged on the left side of the gain optical fiber; The dichroic mirror is provided with a fifth lens / lens group in the direction of the right fiber end face leading to the passive fiber, and the dichroic mirror is provided with a third lens / lens group in the direction of the left fiber end face leading to the gain fiber; The original pump light generated by the pump source is transmitted to the right fiber end face and the fifth lens / lens group through the passive optical fiber, and converges to a point M between the dichroic mirror and the fifth lens / lens group through the fifth lens / lens group; The pump light diverged from point M is transmitted to the right, transmitted through the dichroic mirror, transmitted to the third lens / lens group and focused to the left fiber end face, coupled into the gain fiber, so that the gain fiber achieves population inversion and obtains amplified spontaneous emission light ASE; The spontaneous emission light ASE generated by the gain fiber is transmitted to the left, passes through the left fiber end face and the third lens / lens group, and then reflects on the inner surface of the dichroic mirror and focuses to the saturable absorber mirror. The saturable absorber mirror is located on the focal plane of the focused beam and provides a pulse formation mechanism - filtering out high-intensity signal laser from noise, thereby forming a pulse laser; The pulsed laser reflected by the saturable absorber is transmitted downward, and is focused to the left fiber end face by the dichroic mirror and the third lens / lens group again, and is coupled into the gain fiber. At this time, the gain fiber amplifies the pulsed laser and suppresses the noise, thereby obtaining an amplified pulsed laser. The amplified pulsed laser 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 method used is determined by the distance from the right fiber end face to the second lens / lens group. Continue to transmit to the right, transmitted to the dispersion compensator, where dispersion compensation is performed, the pulse width becomes narrower, and then transmitted to the laser output coupling mirror; It is transmitted to the front surface of the laser output coupling mirror, where reflection and transmission occur simultaneously. A small portion of the light is transmitted as the output laser; the remaining portion is reflected by the laser output coupling mirror and continues to be transmitted to the left in the cavity, and then passes through the second lens / lens group of the dispersion compensator and the right optical fiber end face to be coupled to the gain fiber, where it is amplified again and continues to be transmitted to the left, completing a laser transmission cycle.

[0012] Preferably, the lens assembly is arranged on the left side of the gain optical fiber; A third lens / lens group is arranged in the direction of the left fiber end face of the dichroic mirror leading to the gain fiber; The original pump light generated by the pump source is transmitted to the right fiber end face through the passive optical fiber, then transmitted through the dichroic mirror, transmitted to the third lens / lens group and focused to the left fiber end face and coupled into the gain fiber, 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 left fiber end face and the third lens / lens group, and then reflects on the inner surface of the dichroic mirror and focuses on the saturable absorber mirror. The saturable absorber mirror is located on the focal plane of the focused beam and provides a pulse formation mechanism - filtering the signal laser from the noise to form a pulse laser. The pulsed laser is transmitted downward, and is focused to the left optical fiber end face through the dichroic mirror and the third lens / lens group again, and is coupled into the gain optical fiber, where the pulsed laser is amplified and noise is suppressed to obtain an amplified pulsed laser; The amplified pulsed laser 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 method used is determined by the distance from the right fiber end face to the second lens / lens group. Continue to transmit to the right, transmitted to the dispersion compensator, where dispersion compensation is performed, the pulse width becomes narrower, and then transmitted to the laser output coupling mirror; It is transmitted to the front surface of the laser output coupling mirror, where reflection and transmission occur simultaneously. A small portion of the light is transmitted as the output laser; the remaining portion is reflected by the laser output coupling mirror and continues to be transmitted to the left in the cavity, and then passes through the second lens / lens group of the dispersion compensator and the right optical fiber end face to be coupled to the gain fiber, where it is amplified again and continues to be transmitted to the left, completing a laser transmission cycle.

[0013] Preferably, the lens assembly is arranged on the left side of the gain optical fiber; The dichroic mirror is provided with a fifth lens / lens group in the direction of the right fiber end face leading to the passive fiber, the dichroic mirror is provided with a third lens / lens group in the direction of the left fiber end face leading to the gain fiber, and the dichroic mirror is provided with a fourth lens / lens group in the direction leading to the saturable absorber mirror; The original pump light emitted by the pump source is transmitted through the passive optical fiber to the right optical fiber end face connected to the passive optical fiber and the fifth lens / lens group, and is collimated and transmitted to the dichroic mirror through the fifth lens / lens group; The original pump light is transmitted through the dichroic mirror, collimated and transmitted to the third lens / lens group and focused to the left fiber end face of the gain fiber, thereby coupling into the gain fiber, 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 left fiber end face and the third lens / lens group, and then is reflected on the inner surface of the dichroic mirror and transmitted to the fourth lens / lens group and the saturable absorber mirror; Among them, the dichroic mirror separates the pump light and the spontaneous radiation light, and the saturable absorption mirror is located on the focal plane of the focused beam, providing a pulse forming mechanism - filtering the signal laser from the noise to form a pulsed laser; The laser reflected by the saturable absorber is transmitted downward, and is focused to the left fiber end face by the fourth lens / lens group, the dichroic mirror and the third lens / lens group again, thereby coupling into the gain fiber, where the signal laser is amplified and the noise is suppressed to obtain an amplified pulse laser. The laser reflected by the saturable absorber is transmitted downward, and is focused to the left fiber end face by the saturable absorber, the dichroic mirror and the third lens / lens group again, thereby coupling into the gain fiber, where the signal laser is amplified and the noise is suppressed to obtain an amplified pulse laser. The amplified pulsed laser 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 method used is determined by the distance from the right fiber end face to the second lens / lens group. Continue to transmit to the right, transmitted to the dispersion compensator, where dispersion compensation is performed, the pulse width becomes narrower, and then transmitted to the laser output coupling mirror; It is transmitted to the front surface of the laser output coupling mirror, where reflection and transmission occur simultaneously. A small portion of the light is transmitted as the output laser; the remaining portion is reflected by the laser output coupling mirror and continues to be transmitted to the left in the cavity, and then passes through the second lens / lens group of the dispersion compensator and the right optical fiber end face to be coupled to the gain fiber, where it is amplified again and continues to be transmitted to the left, completing a laser transmission cycle.

[0014] Preferably, the lens assembly is arranged on the right side of the gain optical fiber; The dichroic mirror is provided with a fifth lens / lens group in the direction of the right optical fiber end face leading to the passive optical fiber, and a fourth lens / lens group in the direction of the dichroic mirror leading to the dispersion compensator; The original pump light generated by the pump source is transmitted to the right fiber end face and the fifth lens / lens group through the passive optical fiber, and then transmitted to the right fiber end face of the gain fiber through the dichroic mirror and coupled into the gain fiber, so that the gain fiber achieves population inversion and obtains amplified spontaneous emission light ASE; The ASE generated by the gain fiber is transmitted to the left, passes through the left fiber end face and the first lens / lens group, and then is transmitted to the saturable absorber mirror. The saturable absorber mirror is located on the focal plane of the focused beam and provides a pulse forming mechanism - filtering the signal laser from the noise to form a pulse laser. The pulse laser reflected by the saturable absorber is transmitted to the right, and is focused to the left fiber end face by the first lens / lens group again and coupled into the gain fiber. The signal laser is amplified at the gain fiber, and the noise is suppressed at the same time, to obtain an amplified pulse laser. The amplified pulsed laser is transmitted to the right, passes through the right fiber end face of the gain fiber, and then is reflected on the inner surface of the dichroic mirror and transmitted to the fourth lens / lens group and the dispersion compensator. Dispersion compensation is performed at the dispersion compensator, the pulse width is narrowed, 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, with a small portion of the light being transmitted as the output laser; the remaining portion is reflected by the output coupling mirror and continues to be transmitted downward in the cavity, and is again focused to the right fiber end face of the gain fiber through the fourth lens / lens group and the dichroic mirror and coupled to the gain fiber. The pulse is amplified again in the gain fiber and continues to be transmitted to the left, completing a laser transmission cycle.

[0015] Preferably, the lens assembly is arranged on the right side of the gain optical fiber; The dichroic mirror is provided with a fifth lens / lens group in the direction of the right fiber end face leading to the passive fiber, and the dichroic mirror is provided with a third lens / lens group in the direction of the right fiber end face leading to the gain fiber; The original pump light generated by the pump source is transmitted to the right fiber end face and the fifth lens / lens group through the passive optical fiber. The original pump light output from the right fiber end face of the passive optical fiber is divergent and converges at point N between the dichroic mirror and the fifth lens / lens group through the fifth lens / lens group. The original pump light diverged from point N is transmitted to the left, transmitted through the dichroic mirror, transmitted to the third lens / lens group and focused to the right fiber end face and coupled into the gain fiber, so that the gain fiber achieves population inversion and obtains amplified spontaneous emission light ASE; The ASE generated by the gain fiber is transmitted to the left, passes through the left fiber end face and the first lens / lens group, and then is transmitted to the saturable absorber mirror. The saturable absorber mirror is located on the focal plane of the focused beam and provides a pulse forming mechanism - filtering the signal laser from the noise to form a pulse laser. The formed pulse laser is transmitted to the right, and is focused to the left optical fiber end face by the first lens / lens group again and coupled into the gain optical fiber, where the signal laser is amplified and the noise is suppressed to obtain an amplified pulse laser; The amplified pulsed laser is transmitted to the right through the right optical fiber end face and the third lens / lens group, and then reflected on the inner surface of the dichroic mirror and transmitted to the dispersion compensator, where it is dispersion compensated and then transmitted to the output laser output coupling mirror; The pulsed laser is reflected and transmitted simultaneously on the front surface of the output coupling mirror, with a small portion of the light being transmitted as the output laser; the remaining portion is reflected by the output coupling mirror, continues to be transmitted downward in the cavity, and is again focused to the right fiber end face by the dichroic mirror and the third lens / lens group, where the pulse continues to be dispersion compensated in the dispersion compensator and is then coupled to the gain fiber through the right fiber end face, where the pulse is amplified again and continues to be transmitted to the left, completing a laser transmission cycle.

[0016] Preferably, the lens assembly is arranged on the right side of the gain optical fiber; A third lens / lens group is arranged in the direction of the right fiber end face of the dichroic mirror leading to the gain fiber; The original pump light generated by the pump source is transmitted to the right fiber end face of the passive fiber through the passive fiber, then transmitted through the dichroic mirror, transmitted to the third lens / lens group and focused to the right fiber end face of the gain fiber and coupled into the gain fiber, achieving population inversion in the gain fiber to obtain amplified spontaneous emission light ASE; The ASE generated by the gain fiber is transmitted to the left, passes through the left fiber end face and the first lens / lens group, and then is transmitted to the saturable absorber mirror. The saturable absorber mirror is located on the focal plane of the focused beam and provides a pulse forming mechanism - filtering the signal laser from the noise to form a pulse laser. The pulsed laser reflected by the saturable absorber is transmitted to the right, and is focused to the left fiber end face by the first lens / lens group again, thereby being efficiently coupled into the gain fiber. At this time, the gain fiber amplifies the signal laser and suppresses the noise, thereby obtaining an amplified pulsed laser. The amplified pulsed laser is transmitted to the right, passes through the right fiber end face of the gain fiber and the third lens / lens group, is dispersion compensated in the dispersion compensator, and then transmitted to the output laser output coupling mirror; The pulsed laser is reflected and transmitted simultaneously on the front surface of the laser output coupling mirror, and a small portion of the light is transmitted as the output laser. The remaining part is reflected by the laser output coupling mirror and continues to be transmitted downward in the cavity. It is focused to the right fiber end face of the gain fiber again through the dichroic mirror and the third lens / lens group. The pulse continues to be dispersion compensated in the dispersion compensator and coupled to the gain fiber. It is amplified again in the gain fiber and continues to be transmitted to the left, completing a pulse laser transmission process.

[0017] Preferably, the lens assembly is arranged on the right side of the gain optical fiber; The dichroic mirror is provided with a fifth lens / lens group in the direction of the right fiber end face leading to the passive fiber, a third lens / lens group in the direction of the right fiber end face leading to the gain fiber, and a fourth lens / lens group in the direction of the dichroic mirror leading to the dispersion compensator; The original pump light generated by the pump source is transmitted to the right optical fiber end face and the fifth lens / lens group through the passive optical fiber, and is collimated by the fifth lens / lens group and transmitted to the dichroic mirror; The original pump light is transmitted through the dichroic mirror, collimated and transmitted to the third lens / lens group and focused to the right fiber end face of the gain fiber and coupled into the gain fiber to achieve population inversion in the gain fiber, thereby obtaining amplified spontaneous emission light ASE; The spontaneous emission light ASE generated by the gain fiber is transmitted to the left, passes through the left fiber end face and the first lens / lens group, and then is transmitted to the saturable absorber mirror. The saturable absorber mirror is located on the focal plane of the focused light beam and provides a pulse forming mechanism - filtering the signal laser from the noise to form a pulse laser. The pulse laser is transmitted to the right, and is focused to the left fiber end face by the first lens / lens group again and coupled into the gain fiber. The signal laser is amplified at the gain fiber, and the noise is suppressed at the same time, to obtain an amplified pulse laser. The amplified laser is transmitted to the right, passing through the right fiber end face of the gain fiber and the third lens / lens group, and then reflected on the inner surface of the dichroic mirror and transmitted to the fourth lens / lens group and the dispersion compensator. The dispersion compensator provides dispersion compensation, narrows the pulse width, and then transmits to the output laser output coupling mirror; The laser is reflected and transmitted simultaneously on the front surface of the laser output coupling mirror, wherein a small part of the light is transmitted as the output laser; the remaining part is reflected by the laser output coupling mirror, continues to be transmitted downward in the cavity, and again passes through the fourth lens / lens group, the dichroic mirror and the third lens / lens group to be focused to the right fiber end face of the gain fiber, wherein the pulse continues to be dispersion compensated in the dispersion compensator, and then is coupled to the gain fiber through the right fiber end face, where the pulse is amplified again and continues to be transmitted to the left, completing a transmission cycle of a pulsed laser.

[0018] A laser generating method, using the above lens combination arranged on the right side of the gain optical fiber; The dichroic mirror is provided with a fifth lens / lens group in the direction of the right fiber end face leading to the passive fiber, a third lens / lens group in the direction of the right fiber end face leading to the gain fiber, and a fourth lens / lens group in the direction of the dichroic mirror leading to the dispersion compensator. The method comprises the following steps: Step S1: generating original pump light: a pump source generates original pump light; Step S2: Spontaneous radiation light generation: the original pump light is transmitted to the right optical fiber end face and the fifth lens / lens group through the passive optical fiber, and is collimated by the fifth lens / lens group and transmitted to the dichroic mirror; The original pump light is transmitted through the dichroic mirror, collimated and transmitted to the third lens / lens group and focused to the right fiber end face of the gain fiber and coupled into the gain fiber to achieve population inversion in the gain fiber, thereby obtaining amplified spontaneous emission light ASE; Step S3: Pulse laser generation: The spontaneous emission light ASE generated by the gain fiber is transmitted to the left, passes through the left fiber end face and the first lens / lens group, and then is transmitted to the saturable absorber mirror. The saturable absorber mirror is located on the focal plane of the focused light beam and provides a pulse formation mechanism - filtering the signal laser from the noise, thereby forming a pulse laser; Step S4: Pulse laser amplification: The pulse laser is transmitted to the right, and is focused to the left optical fiber end face by the first lens / lens group again and coupled into the gain optical fiber. The signal laser is amplified at the gain optical fiber, and the noise is suppressed at the same time, to obtain an amplified pulse laser. Step S5: Laser output: The amplified laser is transmitted to the right, passes through the right fiber end face of the gain fiber and the third lens / lens group, and then reflects on the inner surface of the dichroic mirror and is transmitted to the fourth lens / lens group and the dispersion compensator. The dispersion compensator provides dispersion compensation, narrows the pulse width, and then is transmitted to the output laser output coupling mirror; The laser is reflected and transmitted simultaneously on the front surface of the laser output coupling mirror, wherein a small part of the light is transmitted as the output laser; the remaining part is reflected by the laser output coupling mirror, continues to be transmitted downward in the cavity, and again passes through the fourth lens / lens group, the dichroic mirror and the third lens / lens group to be focused to the right fiber end face of the gain fiber, wherein the pulse continues to be dispersion compensated in the dispersion compensator, and then is coupled to the gain fiber through the right fiber end face, where the pulse is amplified again and continues to be transmitted to the left, completing a transmission cycle of a pulsed laser.

[0019] 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 the lens assembly. The resonant cavity structure is provided with a saturable absorption mirror, multiple groups of lenses / lens groups, gain optical fiber, dispersion compensator and 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

[0020] Figure 1 This is a schematic diagram of the structure of the present invention when implementing a situation 1-4; Figure 2 This is a schematic diagram of the structure of situation 1-1 in one implementation of the present invention; Figure 3 This is a schematic diagram of the structure of situation 1-2 in one implementation of the present invention; Figure 4 This is a schematic diagram of the structure of situation 1-2 in one implementation of the present invention; Figure 5 This is a schematic diagram of the structure of the present invention when implementing situation 1-3; Figure 6 This is a schematic diagram of the structure of Case 2-4 in Embodiment 2 of the present invention; Figure 7 This is a schematic diagram of the structure of the second embodiment of the present invention when the situation 2-1; Figure 8 This is a schematic diagram of the structure of the second embodiment of the present invention when the situation 2-2; Fig. 9 This is a structural schematic diagram of situation 2-2 in the second implementation of the present invention; Fig.10 This is a schematic diagram of the structure of the second embodiment of the present invention when the situation 2-3; Fig.11 The schematic diagrams of the three situations of the image formation of a divergent point light source through a single convex lens; Fig.12 This is a schematic diagram of the image formation of a divergent point light source through two convex lenses; Fig.13 Three ways to set up a saturable absorber for a resonant cavity structure; Fig.14 This is the graph of the variation of w0' / w0 with s / f; Fig.15 is the graph of the variation of ZR' with s / f; Fig.16 This is a graph showing the variation of (s+s') / f with s / f. DETAILED DESCRIPTION

[0021] 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.

[0022] The following is a detailed description of a fiber laser structure based on multi-lens coupling in this scheme.

[0023] A fiber laser structure based on multi-lens coupling includes a resonant cavity structure and a pump source, wherein the pump source is connected to the resonant cavity structure through an optical signal via a lens combination structure; The resonant cavity structure includes 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 lens combination structure includes a dichroic mirror 16 and at least one lens / lens group; The original pump light of the pump source is coupled into any end of the gain optical fiber through a lens combination structure; 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 the optical signal. The transmitted optical signal is used as the output laser, and the reflected optical signal continues to enter the resonant cavity structure. The dichroic mirror 16 is used to transmit pump light and reflect laser signals, and the lens is used to converge laser signals. The dichroic mirror 16 is tilted, and its reflection angle is between 15-75 degrees. The reflection angle of the dichroic mirror 16 used in this embodiment is 45 degrees.

[0024] Specifically, the pump source 10 is connected to the dichroic mirror 16 through the right fiber end face 5 of the passive optical fiber 11, and the dichroic mirror 16 can be arbitrarily provided with a lens in any one of the three directions: the direction leading to the right fiber end face 5 of the passive optical fiber 11, the direction leading to the left fiber end face 3 of the gain optical fiber 4, and the direction leading to the saturable absorber mirror 1.

[0025] Embodiment 1: Lens assembly on the left side of gain fiber 4 In this embodiment, the pump source is connected to the left optical signal of the gain fiber through a lens combination; Specifically, let: the dichroic mirror 16 is provided with a fifth lens / lens group 18 in the direction of the right fiber end face 5 leading to the passive optical fiber 11, the dichroic mirror 16 is provided with a third lens / lens group 15 in the direction of the left fiber end face 3 leading to the gain optical fiber 4, and the dichroic mirror 16 is provided with a fourth lens / lens group 17 in the direction of the saturable absorber mirror 1.

[0026] According to the arrangement of the third lens / lens group 15, the fourth lens / lens group 17 and the fifth lens / lens group 18, the three-sided lens / lens group can be divided into four cases.

[0027] The following describes the four situations in detail: Case 1-1: The third lens / lens group 15 is missing, and the fourth lens / lens group 17 and the fifth lens / lens group 18 are present at the same time like Figure 2 As shown, at this point, the working process of the entire structure is as follows: The original pump light generated by the pump source 10 is transmitted to the right fiber end face 5 and the fifth lens / lens group 18 through the passive optical fiber 11, and then transmitted to the left fiber end face 3 through the dichroic mirror 16. The function of the fifth lens / lens group 18 is to make the mode field and divergence angle of the pump light at the left fiber end faces 3 and 5 match as much as possible, so as to achieve efficient pump coupling. The principle is as follows: Fig.11 (b) or (c) or Fig.12 The pump is efficiently coupled into the gain fiber 4, so that the gain fiber 4 achieves population inversion and obtains amplified spontaneous emission light ASE.

[0028] The ASE generated by the gain fiber 4 is transmitted to the left, passes through the left fiber end face 3, and then reflects on the inner surface of the dichroic mirror 16 and is transmitted to the fourth lens / lens group 17 and the saturable absorber mirror 1. Among them, due to the difference between the transmission wavelength and the reflection wavelength, the dichroic mirror 16 separates the pump and laser. At the same time, the function of the fourth lens / lens group 17 is to make the optical signal output from the left fiber end face 3 converge to the saturable absorber mirror 1 through the dichroic mirror 16. The principle is as follows: Fig.11 (b) or (c) or Fig.12 shown.

[0029] The saturable absorber mirror 1 is located at the focal plane of the focused beam and provides a pulse forming mechanism - filtering the signal laser from the noise to form a pulse.

[0030] The laser reflected by the saturable absorber 1 is transmitted downward, and is focused to the left fiber end face 3 by the fourth lens / lens group 17 and the dichroic mirror 16 again, so as to be efficiently coupled into the gain fiber 4. At this time, the gain fiber 4 amplifies the signal laser and suppresses the noise. The amplified laser is transmitted to the free space through the right fiber end faces 5 and 6, and continues to transmit to the right. It is worth noting that the laser output from the right fiber end face 5 is divergent, and there are two possibilities for the output laser after passing through the second lens / lens group 6: one is to collimate to the free space (such as Fig.11 (a)); the second is to converge to the front surface of the laser output coupling mirror 8 (as shown Fig.11 (b) or (c) in FIG. 1 ), 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.

[0031] The laser is transmitted to the right to the front surface of the laser output coupling mirror 8, and reflection and transmission occur at the same time. 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, 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 pulse is amplified again in the gain fiber 4 and continues to be transmitted to the left.

[0032] 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.

[0033] The steps of a laser generation method using the above embodiment structure (the lens combination is on the left side of the gain fiber 4, the third lens / lens group 15 is absent, and the fourth lens / lens group 17 and the fifth lens / lens group 18 exist at the same time) are as follows: Step S1: generating original pump light: the pump source 10 generates original pump light; Step S2: Spontaneous emission light generation: the original pump light is transmitted to the right fiber end face 5 and the fifth lens / lens group 18 via the passive optical fiber 11, and then transmitted to the left fiber end face 3 via the dichroic mirror 16; the original pump light is coupled into the gain optical fiber 4, so that the gain optical fiber 4 achieves population inversion, and amplified spontaneous emission light ASE is obtained; Step S3: Pulse laser generation: ASE generated by the gain fiber 4 is transmitted to the left, passes through the left fiber end face 3, and then is reflected on the inner surface of the dichroic mirror 16 and transmitted to the fourth lens / lens group 17 and the saturable absorber mirror 1. The dichroic mirror 16 and the fourth lens / lens group 17 are used to converge the optical signal output from the left fiber end face 3 to the saturable absorber mirror 1 through the dichroic mirror 16; The saturable absorption mirror 1 is located on the focal plane of the focused light beam and provides a pulse forming mechanism - filtering out high-intensity signal laser from noise to form a pulse laser; Step S4: Pulse laser amplification: The laser reflected by the saturable absorber mirror 1 is transmitted downward, and is focused to the left fiber end face 3 by the fourth lens / lens group 17 and the dichroic mirror 16 again, and then coupled into the gain fiber 4. At this time, the gain fiber 4 amplifies the signal laser and suppresses the noise to obtain an amplified pulse laser; Step S5: laser output: the amplified pulse laser 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; Continue to transmit to the right, transmitted to the dispersion compensator 7, dispersion compensation is performed in the dispersion compensator 7, the pulse width becomes narrower, and then transmitted to the laser output coupling mirror 8; It is transmitted to the front surface of the laser output coupling mirror 8, where reflection and transmission occur simultaneously. A small portion of the light is transmitted as the output laser; the remaining portion is reflected by the laser output coupling mirror 8, continues to be transmitted to the left in the cavity, and then passes through the second lens / lens group 6 of the dispersion compensator 7 and the right optical fiber end face 5 to be coupled to the gain optical fiber 4, is amplified again in the gain optical fiber 4, and continues to be transmitted to the left, completing a laser transmission cycle.

[0034] Case 1-2: The fourth lens / lens group 17 is missing, and the third lens / lens group 15 and 18 are present at the same time like Figure 3 and Figure 4 shown.

[0035] At this point, the entire structure works as follows: The original pump light generated by the pump source 10 is transmitted to the right fiber end face 5 and the fifth lens / lens group 18 through the passive optical fiber 11. It is worth noting that the pump light output from the right fiber end face 5 is divergent, and converges at a point between the dichroic mirror 16 and the fifth lens / lens group 18 (assuming this point is point M) through the fifth lens / lens group 18. The principle is as follows: Fig.11 (b) or (c) or Fig.12 .

[0036] The pump light diverging from point M is transmitted to the right, transmitted through the dichroic mirror 16, transmitted to the third lens / lens group 15 and focused to the left fiber end face 3, thereby efficiently coupling into the gain fiber 4, so that the gain fiber 4 achieves population inversion and obtains amplified spontaneous emission light ASE. The spontaneous emission light ASE generated by the gain fiber 4 is transmitted to the left, passes through the left fiber end face 3 and the third lens / lens group 15, and then reflects on the inner surface of the dichroic mirror 16 and is focused to the saturable absorber 1. The principle is as follows: Fig.11 (b) or (c) or Fig.12 The saturable absorber mirror 1 is located at the focal plane of the focused beam and provides a pulse forming mechanism - filtering the signal laser from the noise to form a pulse.

[0037] Among them, due to the difference between the transmission wavelength and the reflection wavelength, the dichroic mirror 16 separates the pump and the laser. It is worth noting that the role of the third lens / lens group 15 in this structure is not only to converge the laser emitted from the left fiber end face 3 to the saturable absorber mirror 1, but also to combine with the fifth lens / lens group 18 to make the mode field and divergence angle of the pump light at the left fiber end face 3 and the right fiber end face 5 match as much as possible, thereby achieving efficient pump coupling. The laser reflected by the saturable absorber mirror 1 is transmitted downward, and is focused to the left fiber end face 3 through the dichroic mirror 16 and the third lens / lens group 15 again, so as to be efficiently coupled into the gain fiber 4. At this time, the gain fiber 4 amplifies the signal laser and suppresses the noise. The amplified laser is transmitted to the free space through the right fiber end faces 5 and 6, and continues to transmit to the right. It is worth noting that the laser output from the right fiber end face 5 is divergent, and there are two possibilities for the output laser after passing through the second lens / lens group 6: one is to collimate to the free space (such as Fig.11 (a)); the second is to converge to the front surface of the laser output coupling mirror 8 (as shown Fig.11 (b) or (c) in FIG. 1 ), depending on the distance from the right optical fiber end face 5 to the second lens / lens group 6.

[0038] The dispersion compensator 7 between the second lens / lens group 6 and the laser output coupling mirror 8 is used to provide dispersion compensation to narrow the pulse width. The laser is transmitted to the right to the front surface of the laser output coupling mirror 8, and reflection and transmission occur at the same time, of which 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, the second lens / lens group 6 and the right fiber end face 5 in sequence.

[0039] In the above two cases (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 pulse is amplified again in the gain fiber 4 and continues to be transmitted to the left.

[0040] 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.

[0041] The steps of a laser generation method using the above embodiment structure (the lens combination is on the left side of the gain fiber 4, the fourth lens / lens group 17 is absent, and the third lens / lens group 15 and 18 exist at the same time) are as follows: Step S1: generating original pump light: the pump source 10 generates original pump light; Step S2: Spontaneous radiation light generation: the original pump light is transmitted to the right fiber end face 5 and the fifth lens / lens group 18 via the passive optical fiber 11, and converges to a point M between the dichroic mirror 16 and the fifth lens / lens group 18 via the fifth lens / lens group 18; The pump light diverging from point M is transmitted to the right, transmitted through the dichroic mirror 16, transmitted to the third lens / lens group 15 and focused to the left fiber end face 3, coupled into the gain fiber 4, so that the gain fiber 4 achieves population inversion, and obtains amplified spontaneous emission light ASE; Step S3: Pulse laser generation: The ASE generated by the gain fiber 4 is transmitted to the left, passes through the left fiber end face 3 and the third lens / lens group 15, and then reflects on the inner surface of the dichroic mirror 16 and focuses on the saturable absorber mirror 1. The saturable absorber mirror 1 is located on the focal plane of the focused light beam and provides a pulse formation mechanism - filtering out high-intensity signal laser from noise, thereby forming a pulse laser; Step S4: Pulse laser amplification: The pulse laser reflected by the saturable absorber mirror 1 is transmitted downward, and is focused to the left fiber end face 3 by the dichroic mirror 16 and the third lens / lens group 15 again, and is coupled into the gain fiber 4. At this time, the gain fiber 4 amplifies the pulse laser and suppresses the noise to obtain an amplified pulse laser. Step S5: laser output: the amplified pulse laser 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; Continue to transmit to the right, transmitted to the dispersion compensator 7, dispersion compensation is performed in the dispersion compensator 7, the pulse width becomes narrower, and then transmitted to the laser output coupling mirror 8; It is transmitted to the front surface of the laser output coupling mirror 8, where reflection and transmission occur simultaneously. A small portion of the light is transmitted as the output laser; the remaining portion is reflected by the laser output coupling mirror 8, continues to be transmitted to the left in the cavity, and then passes through the second lens / lens group 6 of the dispersion compensator 7 and the right optical fiber end face 5 to be coupled to the gain optical fiber 4, is amplified again in the gain optical fiber 4, and continues to be transmitted to the left, completing a laser transmission cycle.

[0042] Case 1-3: The fourth lens / lens group 17, 18 is missing, and the third lens / lens group 15 is present like Figure 5 shown.

[0043] At this point, the entire structure works as follows: The original pump light generated by the pump source 10 is transmitted to the right fiber end face 5 via the passive optical fiber 11, and then transmitted through the dichroic mirror 16, transmitted to the third lens / lens group 15 and focused to the left fiber end face 3, thereby being efficiently coupled into the gain fiber 4, so that the gain fiber 4 achieves a population inversion and obtains amplified spontaneous emission light ASE.

[0044] The spontaneous emission light ASE generated by the gain fiber 4 is transmitted to the left, passes through the left fiber end face 3 and the third lens / lens group 15, and then reflects on the inner surface of the dichroic mirror 16 and is focused to the saturable absorber mirror 1. The saturable absorber mirror 1 is located on the focal plane of the focused light beam and provides a pulse formation mechanism - filtering the signal laser from the noise to form a pulse.

[0045] It is worth noting that the function of the third lens / lens group 15 in this structure is not only to converge the laser emitted from the left fiber end face 3 to the saturable absorber 1, but also to make the mode field and divergence angle of the pump light at the left fiber end face 3 and the right fiber end face 5 match as much as possible, so as to achieve efficient pump coupling. The principle is as follows: Fig.11 (b) or (c) or Fig.12 shown.

[0046] The laser reflected by the saturable absorber mirror 1 is transmitted downward, and is focused to the left fiber end face 3 by the dichroic mirror 16 and the third lens / lens group 15 again, thereby being efficiently coupled into the gain fiber 4. At this time, the gain fiber 4 amplifies the signal laser and suppresses the noise at the same time.

[0047] The amplified laser is transmitted to the free space through the right fiber end faces 5 and 6, and continues to transmit to the right. It is worth noting that the laser output from the right fiber end face 5 is divergent, and there are two possibilities for the output laser after passing through the second lens / lens group 6: one is to collimate to the free space (such as Fig.11 (a)); the second is to converge to the front surface of the laser output coupling mirror 8 (as shown Fig.11 (b) or (c) in FIG. 1 ), 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.

[0048] The laser is transmitted to the right to the front surface of the laser output coupling mirror 8, and reflection and transmission occur at the same time. 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, 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 pulse is amplified again in the gain fiber 4 and continues to be transmitted to the left.

[0049] 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.

[0050] The steps of a laser generation method using the above embodiment structure (the lens combination is on the left side of the gain fiber 4, the fourth lens / lens group 17, 18 is absent, and the third lens / lens group 15 exists) are as follows: Step S1: generating original pump light: the pump source 10 generates original pump light; Step S2: Spontaneous emission light generation: the original pump light is transmitted to the right fiber end face 5 through the passive optical fiber 11, then transmitted through the dichroic mirror 16, transmitted to the third lens / lens group 15 and focused to the left fiber end face 3 to be coupled into the gain fiber 4, so that the gain fiber 4 achieves population inversion and obtains amplified spontaneous emission light ASE; Step S3: Pulse laser generation: The ASE generated by the gain fiber 4 is transmitted to the left, passes through the left fiber end face 3 and the third lens / lens group 15, and then reflects on the inner surface of the dichroic mirror 16, and is focused to the saturable absorber mirror 1. The saturable absorber mirror 1 is located on the focal plane of the focused light beam, providing a pulse formation mechanism - filtering the signal laser from the noise, thereby forming a pulse laser; Step S4: Pulse laser amplification: The pulse laser is transmitted downward, and is focused to the left fiber end face 3 through the dichroic mirror 16 and the third lens / lens group 15 again, and is coupled into the gain fiber 4, where the pulse laser is amplified and noise is suppressed to obtain an amplified pulse laser; Step S5: laser output: the amplified pulse laser 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; Continue to transmit to the right, transmitted to the dispersion compensator 7, dispersion compensation is performed in the dispersion compensator 7, the pulse width becomes narrower, and then transmitted to the laser output coupling mirror 8; It is transmitted to the front surface of the laser output coupling mirror 8, where reflection and transmission occur simultaneously. A small portion of the light is transmitted as the output laser; the remaining portion is reflected by the laser output coupling mirror 8, continues to be transmitted to the left in the cavity, and then passes through the second lens / lens group 6 of the dispersion compensator 7 and the right optical fiber end face 5 to be coupled to the gain optical fiber 4, is amplified again in the gain optical fiber 4, and continues to be transmitted to the left, completing a laser transmission cycle.

[0051] Case 1-4: The third lens / lens group 15, 17, 18 exist at the same time like Figure 1 shown.

[0052] At this point, the entire structure works as follows: The original pump light emitted by the pump source 10 is transmitted through the passive optical fiber 11 to the right optical fiber end face 5 connected to the passive optical fiber 11 and the fifth lens / lens group 18, and is collimated and transmitted to the dichroic mirror 16 through the fifth lens / lens group 18; The original pump light is transmitted through the dichroic mirror 16, collimated and transmitted to the third lens / lens group 15 and focused to the left fiber end face 3 of the gain fiber 4, thereby coupling into the gain fiber 4 to achieve population inversion in the gain fiber 4, and obtaining amplified spontaneous emission light ASE; The ASE spontaneous radiation light generated by the gain fiber 4 is transmitted to the left, passes through the left fiber end face 3 and the third lens / lens group 15, and then is reflected on the inner surface of the dichroic mirror 16 and transmitted to the fourth lens / lens group 17 and the saturable absorber mirror 1; Among them, due to the difference between the transmission wavelength and the reflection wavelength, the dichroic mirror 16 separates the pump light and the spontaneous radiation light, and the saturable absorption mirror 1 is located on the focal plane of the focused light beam, providing a pulse forming mechanism - filtering the signal laser from the noise, thereby forming a pulse laser; The laser reflected by the saturable absorber mirror 1 is transmitted downward, and is focused to the left fiber end face 3 by the fourth lens / lens group 17, the dichroic mirror 16 and the third lens / lens group 15 again, so as to be coupled into the gain fiber 4, where the signal laser is amplified and the noise is suppressed to obtain an amplified pulse laser; The amplified pulse laser is transmitted to the free space through the right optical fiber end face 5 and the second lens / lens group 6 or continues to be transmitted to the right to the dispersion compensator 7; If it is transmitted to the dispersion compensator 7, dispersion compensation is performed in the dispersion compensator 7, the pulse width becomes narrower, and then it is transmitted to the front surface of the laser output coupling mirror 8, where reflection and transmission occur simultaneously, wherein a small part of the light is transmitted as the output laser; the remaining part is reflected by the laser output coupling mirror 8, continues to be transmitted to the left in the cavity, and then is transmitted to the gain fiber 4 through the dispersion compensator 7, the second lens / lens group 6 and the right optical fiber end face 5 to be amplified again, and continues to be transmitted to the left.

[0053] 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.

[0054] The steps of a laser generation method using the above embodiment structure (the lens combination is on the left side of the gain fiber 4, and the third lens / lens group 15, 17, 18 exist at the same time) are as follows: Step S1: generating original pump light: the pump source 10 generates original pump light; Step S2: Spontaneous radiation light generation: the original pump light is transmitted through the passive optical fiber 11 to the right optical fiber end face 5 connected to the passive optical fiber 11 and the fifth lens / lens group 18, and is collimated and transmitted to the dichroic mirror 16 through the fifth lens / lens group 18; The original pump light is transmitted through the dichroic mirror 16, collimated and transmitted to the third lens / lens group 15 and focused to the left fiber end face 3 of the gain fiber 4, thereby coupling into the gain fiber 4 to achieve population inversion in the gain fiber 4, and obtaining amplified spontaneous emission light ASE; Step S3: Pulsed laser generation: ASE generated by the gain fiber 4 is transmitted to the left, passes through the left fiber end face 3 and the third lens / lens group 15, and then is reflected on the inner surface of the dichroic mirror 16 and transmitted to the fourth lens / lens group 17 and the saturable absorber mirror 1; Among them, the dichroic mirror 16 separates the pump light and the spontaneous radiation light, and the saturable absorption mirror 1 is located on the focal plane of the focused light beam, providing a pulse forming mechanism - filtering the signal laser from the noise, thereby forming a pulse laser; Step S4: Pulse laser amplification: The laser reflected by the saturable absorber mirror 1 is transmitted downward, and is focused to the left fiber end face 3 by the fourth lens / lens group 17, the dichroic mirror 16 and the third lens / lens group 15 again, so as to be coupled into the gain fiber 4, where the signal laser is amplified and the noise is suppressed to obtain an amplified pulse laser; Step S5: laser output: the amplified pulse laser 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; Continue to transmit to the right, transmitted to the dispersion compensator 7, dispersion compensation is performed in the dispersion compensator 7, the pulse width becomes narrower, and then transmitted to the laser output coupling mirror 8; It is transmitted to the front surface of the laser output coupling mirror 8, where reflection and transmission occur simultaneously. A small portion of the light is transmitted as the output laser; the remaining portion is reflected by the laser output coupling mirror 8, continues to be transmitted to the left in the cavity, and then passes through the second lens / lens group 6 of the dispersion compensator 7 and the right optical fiber end face 5 to be coupled to the gain optical fiber 4, is amplified again in the gain optical fiber 4, and continues to be transmitted to the left, completing a laser transmission cycle.

[0055] Embodiment 2: The lens assembly is on the right side of the gain fiber 4 like Figure 6 As shown, the difference between this embodiment and embodiment 1 is that the lens assembly is arranged on the right side of the gain fiber 4, and the pump source 10 passes through the lens assembly and the right fiber end face 5 of the gain fiber 4 and enters the gain fiber 4.

[0056] The four situations of lens combination are the same as those in Example 1, except that they all pass through the right optical fiber end face 5 and enter the gain optical fiber 4 .

[0057] Specifically, the pump source 10 is connected to the dichroic mirror 16 via the right fiber end face 5' of the passive optical fiber 11, and the dichroic mirror 16 can be provided with a lens in any one of the three directions: the direction leading to the right fiber end face 5' of the passive optical fiber 11, the direction leading to the right fiber end face 5 of the gain optical fiber 4, and the direction leading to the dispersion compensator 7.

[0058] Specifically, let: the dichroic mirror 16 is provided with a fifth lens / lens group 18 in the direction of the right fiber end face 5' leading to the passive optical fiber 11, the dichroic mirror 16 is provided with a third lens / lens group 15 in the direction of the right fiber end face 5 leading to the gain optical fiber 4, and the dichroic mirror 16 is provided with a fourth lens / lens group 17 in the direction of the dispersion compensator 7.

[0059] This embodiment is also divided into four situations, and the four situations are described in detail below: Case 2-1: The third lens / lens group 15 is missing, and the fourth lens / lens group 17 and the fifth lens / lens group 18 are present at the same time like Figure 7 As shown, the original pump light generated by the pump source 10 is transmitted to the right fiber end face 5' and the fifth lens / lens group 18 through the passive optical fiber 11, and then transmitted to the right fiber end face 5 of the gain optical fiber 4 through the dichroic mirror 16. Among them, the function of the fifth lens / lens group 18 is to make the mode field and divergence angle of the pump light at the right fiber end face 5' and the right fiber end face 5 of the gain optical fiber 4 when the passive optical fiber 11 is transmitted to match as much as possible, so as to achieve efficient pump coupling. The principle is as follows: Fig.11 (b) or (c) or Fig.12 shown.

[0060] The pump light is efficiently coupled into the gain fiber 4, so that the gain fiber 4 achieves population inversion and obtains amplified spontaneous emission light ASE. The spontaneous emission light generated by the gain fiber 4 is transmitted to the left, passes through the left fiber end face 3 and the first lens / lens group 2, and then is transmitted to the saturable absorber 1. It is worth noting that the laser transmitted from the left fiber end face 3 to the free space is divergent, and is focused to the saturable absorber 1 by the first lens / lens group 2. The principle is as follows: Fig.11 (b) or (c) or Fig.12 shown.

[0061] The saturable absorber mirror 1 is located on the focal plane of the focused beam, providing a pulse formation mechanism - filtering the signal laser from the noise to form a pulse. The laser reflected by the saturable absorber mirror 1 is transmitted to the right, and is focused to the left fiber end face 3 by the first lens / lens group 2 again, thereby being efficiently coupled into the gain fiber 4. At this time, the gain fiber 4 amplifies the signal laser and suppresses the noise.

[0062] The amplified laser is transmitted to the right, passes through the right fiber end face 5 of the gain fiber 4, and then reflects on the inner surface of the dichroic mirror 16 and is transmitted to the fourth lens / lens group 17, the dispersion compensator 7 and the output coupling mirror 8. The dispersion compensator 7 between the fourth lens / lens group 17 and the output coupling mirror 8 provides dispersion compensation, narrows the pulse width, and then transmits to the output coupling mirror 8.

[0063] The laser is reflected and transmitted at the front surface of the output coupling mirror 8 at the same time, and a small part of the light is transmitted as the output laser; the remaining part is reflected by the output coupling mirror 8, continues to be transmitted downward in the cavity, and is focused to the right fiber end face 5 of the gain fiber 4 again through the fourth lens / lens group 17 and the dichroic mirror 16. Among them, the pulse continues to be dispersion compensated in the dispersion compensator 7, and then is efficiently coupled to the gain fiber 4 through the right fiber end face 5 of the gain fiber 4, and the pulse is amplified again in the gain fiber 4 and continues to be transmitted to the left.

[0064] 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.

[0065] The steps of a laser generation method using the above embodiment structure (the lens combination is on the right side of the gain fiber 4, the third lens / lens group 15 is absent, and the fourth lens / lens group 17 and the fifth lens / lens group 18 exist at the same time) are as follows: Step S1: generating original pump light: the pump source 10 generates original pump light; Step S2: Spontaneous emission light generation: the original pump light is transmitted to the right fiber end face 5' and the fifth lens / lens group 18 through the passive optical fiber 11, and then transmitted to the right fiber end face 5 of the gain optical fiber 4 through the dichroic mirror 16 and coupled into the gain optical fiber 4, so that the gain optical fiber 4 achieves population inversion and obtains amplified spontaneous emission light ASE; Step S3: Pulse laser generation: The ASE generated by the gain fiber 4 is transmitted to the left, passes through the left fiber end face 3 and the first lens / lens group 2, and then is transmitted to the saturable absorber 1. The saturable absorber 1 is located on the focal plane of the focused light beam and provides a pulse forming mechanism - filtering the signal laser from the noise, thereby forming a pulse laser. Step S4: Pulse laser amplification: The pulse laser reflected by the saturable absorber mirror 1 is transmitted to the right, and is focused to the left fiber end face 3 by the first lens / lens group 2 again and coupled into the gain fiber 4, where the signal laser is amplified and the noise is suppressed to obtain an amplified pulse laser; Step S5: laser output: the amplified pulsed laser is transmitted to the right, passes through the right fiber end face 5 of the gain fiber 4, and then is reflected on the inner surface of the dichroic mirror 16 and transmitted to the fourth lens / lens group 17 and the dispersion compensator 7. Dispersion compensation is performed at the dispersion compensator 7, the pulse width is narrowed, and then transmitted to the laser output coupling mirror (8); The 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 by the output coupling mirror 8, continues to be transmitted downward in the cavity, and is again focused to the right fiber end face 5 of the gain fiber 4 through the fourth lens / lens group 17 and the dichroic mirror 16 and coupled to the gain fiber 4. The pulse is amplified again in the gain fiber 4 and continues to be transmitted to the left, completing a laser transmission cycle.

[0066] Case 2-2: The fourth lens / lens group 17 is missing, and the third lens / lens group 15 and 18 are present at the same time like Figure 8 and Fig. 9 As shown, the original pump light generated by the pump source 10 is transmitted to the right fiber end face 5' of the passive fiber 11 and the fifth lens / lens group 18 through the passive fiber 11. It is worth noting that the pump light output from the right fiber end face 5' of the passive fiber 11 is divergent, and converges at a point between the dichroic mirror 16 and the fifth lens / lens group 18 (assuming this point is point N) through the fifth lens / lens group 18. The principle is as follows: Fig.11 (b) or (c) or Fig.12 .

[0067] The pump light diverged from point N is transmitted to the left, transmitted through the dichroic mirror 16, transmitted to the third lens / lens group 15 and focused to the device 5, thereby efficiently coupling into the gain fiber 4, so that the gain fiber 4 achieves population inversion and obtains amplified spontaneous emission light ASE. The spontaneous emission light ASE generated by the gain fiber 4 is transmitted to the left, passes through the left fiber end face 3 and the first lens / lens group 2, and then is transmitted to the saturable absorber 1. It is worth noting that the laser transmitted from the left fiber end face 3 to the free space is divergent, and is focused to the saturable absorber 1 through the first lens / lens group 2. The principle is as follows: Fig.11 (b) or (c) or Fig.12 shown.

[0068] The saturable absorber mirror 1 is located on the focal plane of the focused beam, providing a pulse formation mechanism - filtering the signal laser from the noise to form a pulse. The laser reflected by the saturable absorber mirror 1 is transmitted to the right, and is focused to the left fiber end face 3 by the first lens / lens group 2 again, so as to be efficiently coupled into the gain fiber 4. At this time, the gain fiber 4 amplifies the signal laser and suppresses the noise. The amplified laser is transmitted to the right, passes through the device 5 and the third lens / lens group 15, and then is reflected on the inner surface of the dichroic mirror 16 and transmitted to the dispersion compensator 7 and the output coupling mirror 8.

[0069] It is worth noting that the function of the third lens / lens group 15 is not only to collimate or focus the laser light emitted from the device 5 to the output coupling mirror 8, but also to combine with the fifth lens / lens group 18 to match the mode field and divergence angle of the pump light at the device 5 and the device 5' as much as possible, so as to achieve efficient pump coupling. The function of the dispersion compensator 7 between the dichroic mirror 16 and the output coupling mirror 8 is to provide dispersion compensation, narrow the pulse width, and then transmit it to the output coupling mirror 8. The laser is reflected and transmitted at the front surface of the output coupling mirror 8 at the same time, of which a small part of the light is transmitted as the output laser; the remaining part is reflected by the output coupling mirror 8, continues to be transmitted downward in the cavity, and is focused to the device 5 again through the dichroic mirror 16 and the third lens / lens group 15. Among them, the pulse continues to obtain dispersion compensation in the dispersion compensator 7, and then is efficiently coupled to the gain fiber 4 through the device 5. The pulse is amplified again in the gain fiber 4 and continues to be transmitted to the left.

[0070] 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.

[0071] The steps of a laser generation method using the above embodiment structure (the lens combination is on the right side of the gain fiber 4, the fourth lens / lens group 17 is absent, and the third lens / lens group 15 and 18 exist at the same time) are as follows: Step S1: generating original pump light: the pump source 10 generates original pump light; Step S2: Spontaneous radiation light generation: the original pump light is transmitted to the right fiber end face 5' and the fifth lens / lens group 18 through the passive optical fiber 11. The original pump light output from the right fiber end face 5' of the passive optical fiber 11 is divergent and converges to the N point between the dichroic mirror 16 and the fifth lens / lens group 18 through the fifth lens / lens group 18. The original pump light diverging from point N is transmitted to the left, transmitted through the dichroic mirror 16, transmitted to the third lens / lens group 15 and focused to the right fiber end face 5, thereby coupling into the gain fiber 4, so that the gain fiber 4 achieves population inversion and obtains amplified spontaneous emission light ASE; Step S3: Pulse laser generation: The ASE generated by the gain fiber 4 is transmitted to the left, passes through the left fiber end face 3 and the first lens / lens group 2, and then is transmitted to the saturable absorber 1. The saturable absorber 1 is located on the focal plane of the focused light beam and provides a pulse forming mechanism - filtering the signal laser from the noise, thereby forming a pulse laser. Step S4: Pulse laser amplification: The pulse laser reflected by the saturable absorber mirror 1 is transmitted to the right, and is focused to the left fiber end face 3 by the first lens / lens group 2 again, and is coupled into the gain fiber 4, where the signal laser is amplified and the noise is suppressed to obtain an amplified pulse laser; Step S5: laser output: the amplified pulsed laser is transmitted to the right through the right optical fiber end face 5 and the third lens / lens group 15, and then reflected on the inner surface of the dichroic mirror 16 and transmitted to the dispersion compensator 7, where dispersion compensation is performed and then transmitted to the output laser output coupling mirror 8; The pulsed laser is reflected and transmitted simultaneously on the front surface of the output coupling mirror 8, wherein a small portion of the light is transmitted as the output laser; the remaining portion is reflected by the output coupling mirror 8, continues to be transmitted downward in the cavity, and is again focused to the right fiber end face 5 through the dichroic mirror 16 and the third lens / lens group 15, wherein the pulse continues to be dispersion compensated in the dispersion compensator 7, and then is coupled to the gain fiber 4 through the right fiber end face 5, where the pulse is amplified again and continues to be transmitted to the left, completing a laser transmission cycle.

[0072] Case 2-3: The fourth lens / lens group 17 and 18 are both missing, and the third lens / lens group 15 exists like Fig.10 As shown, the original pump light generated by the pump source 10 is transmitted to the right fiber end face 5' of the passive optical fiber 11 through the passive optical fiber 11, and then transmitted through the dichroic mirror 16, transmitted to the third lens / lens group 15 and focused to the right fiber end face 5 of the gain optical fiber 4, thereby efficiently coupling into the gain optical fiber 4, so that the gain optical fiber 4 achieves a population inversion and obtains amplified spontaneous emission light ASE.

[0073] The spontaneous emission light ASE generated by the gain fiber 4 is transmitted to the left, passes through the left fiber end face 3 and the first lens / lens group 2, and then is transmitted to the saturable absorber 1. It is worth noting that the laser transmitted from the left fiber end face 3 to the free space is divergent, and is focused to the saturable absorber 1 by the first lens / lens group 2. The principle is as follows: Fig.11 (b) or (c) or Fig.12shown.

[0074] The saturable absorber mirror 1 is located on the focal plane of the focused beam, providing a pulse formation mechanism - filtering the signal laser from the noise to form a pulse. The laser reflected by the saturable absorber mirror 1 is transmitted to the right, and is focused to the left fiber end face 3 by the first lens / lens group 2 again, thereby being efficiently coupled into the gain fiber 4. At this time, the gain fiber 4 amplifies the signal laser and suppresses the noise.

[0075] The amplified laser is transmitted to the right, passing through the right fiber end face 5 of the gain fiber 4 and the third lens / lens group 15, and then reflected on the inner surface of the dichroic mirror 16 and transmitted to the dispersion compensator 7 and the output coupling mirror 8. Among them, due to the difference between the transmission wavelength and the reflection wavelength, the dichroic mirror 16 separates the pump and the laser. It is worth noting that the role of the third lens / lens group 15 in this structure is not only to converge the laser emitted from the right fiber end face 5 of the gain fiber 4 to the output coupling mirror 8, but also to make the mode field and divergence angle of the pump light at the right fiber end face 5' of the passive fiber 11 and the right fiber end face 5 of the gain fiber 4 as much as possible, so as to achieve efficient pump coupling.

[0076] The function of the dispersion compensator 7 between the dichroic mirror 16 and the output coupling mirror 8 is to provide dispersion compensation, narrow the pulse width, and then transmit it to the output coupling mirror 8. The laser is reflected and transmitted at the same time on the front surface of the output coupling mirror 8, of which a small part of the light is transmitted as the output laser; the remaining part is reflected by the output coupling mirror 8, continues to be transmitted downward in the cavity, and is focused to the right fiber end face 5 of the gain fiber 4 again through the dichroic mirror 16 and the third lens / lens group 15. Among them, the pulse continues to obtain dispersion compensation in the dispersion compensator 7, and then is efficiently coupled to the gain fiber 4 through the right fiber end face 5 of the gain fiber 4, and the pulse is amplified again in the gain fiber 4 and continues to be transmitted to the left.

[0077] 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.

[0078] The steps of a laser generation method using the above embodiment structure (the fourth lens / lens group 17 and 18 are both absent, and the third lens / lens group 15 exists) are as follows: Step S1: generating original pump light: the pump source 10 generates original pump light; Step S2: Spontaneous emission light generation: the original pump light is transmitted to the right fiber end face 5' of the passive fiber 11 through the passive fiber 11, and then transmitted through the dichroic mirror 16, transmitted to the third lens / lens group 15 and focused to the right fiber end face 5 of the gain fiber 4 and coupled into the gain fiber 4, and the population inversion is achieved in the gain fiber 4 to obtain amplified spontaneous emission light ASE; Step S3: Pulse laser generation: The ASE generated by the gain fiber 4 is transmitted to the left, passes through the left fiber end face 3 and the first lens / lens group 2, and then is transmitted to the saturable absorber 1. The saturable absorber 1 is located on the focal plane of the focused light beam and provides a pulse forming mechanism - filtering the signal laser from the noise, thereby forming a pulse laser. Step S4: Pulse laser amplification: The pulse laser reflected by the saturable absorber mirror 1 is transmitted to the right, and is focused to the left fiber end face 3 by the first lens / lens group 2 again, so as to be efficiently coupled into the gain fiber 4. At this time, the gain fiber 4 amplifies the signal laser and suppresses the noise, thereby obtaining an amplified pulse laser. Step S5: laser output: the amplified pulsed laser is transmitted to the right, passes through the right fiber end face 5 of the gain fiber 4 and the third lens / lens group 15, is dispersion compensated in the dispersion compensator 7, and then transmitted to the output laser output coupling mirror 8; The pulse laser is reflected and transmitted simultaneously on the front surface of the laser output coupling mirror 8, and a small portion of the light is transmitted as the output laser; The remaining part is reflected by the laser output coupling mirror 8, continues to be transmitted downward in the cavity, and is focused to the right fiber end face 5 of the gain fiber 4 again through the dichroic mirror 16 and the third lens / lens group 15. The pulse continues to be dispersion compensated in the dispersion compensator 7 and is coupled to the gain fiber 4, where it is amplified again and continues to be transmitted to the left, completing a pulse laser transmission process.

[0079] Case 2-4: The third lens / lens group 15, 17, 18 exist at the same time like Figure 6 As shown, the original pump light generated by the pump source 10 is transmitted to the right fiber end face 5' of the passive fiber 11 and the fifth lens / lens group 18 through the passive fiber 11. It is worth noting that the pump light output from the right fiber end face 5 of the gain fiber 4 is divergent, and is collimated and transmitted to the dichroic mirror 16 through the fifth lens / lens group 18. The principle is as follows: Fig.11 (a).

[0080] The pump light is transmitted through the dichroic mirror 16, collimated and transmitted to the third lens / lens group 15 and focused to the right fiber end face 5 of the gain fiber 4, thereby efficiently coupling into the gain fiber 4, so that the gain fiber 4 achieves population inversion and obtains amplified spontaneous emission light ASE. The spontaneous emission light ASE generated by the gain fiber 4 is transmitted to the left, passes through the left fiber end face 3 and the first lens / lens group 2, and then is transmitted to the saturable absorber 1. It is worth noting that the laser transmitted from the left fiber end face 3 to the free space is divergent, and is focused to the saturable absorber 1 through the first lens / lens group 2. The principle is as follows: Fig.11 (b) or (c) or Fig.12 shown.

[0081] The saturable absorber mirror 1 is located on the focal plane of the focused beam, providing a pulse formation mechanism - filtering the signal laser from the noise to form a pulse. The laser reflected by the saturable absorber mirror 1 is transmitted to the right, and is focused to the left fiber end face 3 by the first lens / lens group 2 again, thereby being efficiently coupled into the gain fiber 4. At this time, the gain fiber 4 amplifies the signal laser and suppresses the noise.

[0082] The amplified laser is transmitted to the right, passing through the right fiber end face 5 of the gain fiber 4 and the third lens / lens group 15, and then reflected on the inner surface of the dichroic mirror 16 and transmitted to the fourth lens / lens group 17, the dispersion compensator 7 and the output coupling mirror 8. Among them, due to the difference between the transmission wavelength and the reflection wavelength, the dichroic mirror 16 separates the pump and the laser. It is worth noting that the laser transmitted from the right fiber end face 5 of the gain fiber 4 to the free space is divergent, and is collimated and transmitted to the surface of the dichroic mirror 16 through the third lens / lens group 15, and then reflected to the fourth lens / lens group 17 and focused to the output coupling mirror 8. The principle is as follows: Fig.11 (a) shown.

[0083] The function of the dispersion compensator 7 between the fourth lens / lens group 17 and the output coupling mirror 8 is to provide dispersion compensation, narrow the pulse width, and then transmit it to the output coupling mirror 8. The laser is reflected and transmitted at the same time on the front surface of the output coupling mirror 8, of which a small part of the light is transmitted as the output laser; the remaining part is reflected by the output coupling mirror 8, continues to be transmitted downward in the cavity, and is focused to the right fiber end face 5 of the gain fiber 4 again through the fourth lens / lens group 17, the dichroic mirror 16 and the third lens / lens group 15. Among them, the pulse continues to obtain dispersion compensation in the dispersion compensator 7, and then is efficiently coupled to the gain fiber 4 through the device 5, and the pulse is amplified again in the gain fiber 4 and continues to be transmitted to the left.

[0084] 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.

[0085] The multi-lens coupled fiber laser structure of Cases 2-4 of this embodiment is used to form a laser generation method, which includes the following steps: Step S1: generating original pump light: the pump source 10 generates original pump light; Step S2: Spontaneous radiation light generation: the original pump light is transmitted to the right optical fiber end face 5' and the fifth lens / lens group 18 through the passive optical fiber 11, and is collimated and transmitted to the dichroic mirror 16 through the fifth lens / lens group 18; The original pump light is transmitted through the dichroic mirror 16, collimated and transmitted to the third lens / lens group 15 and focused to the right fiber end face 5 of the gain fiber 4 and coupled into the gain fiber 4 so that the gain fiber 4 achieves population inversion and obtains amplified spontaneous emission light ASE; Step S3: Pulse laser generation: The spontaneous emission light ASE generated by the gain fiber 4 is transmitted to the left, passes through the left fiber end face 3 and the first lens / lens group 2, and then is transmitted to the saturable absorber 1. The saturable absorber 1 is located on the focal plane of the focused light beam and provides a pulse forming mechanism - filtering the signal laser from the noise, thereby forming a pulse laser; Step S4: Pulse laser amplification: The pulse laser is transmitted to the right, and is focused to the left fiber end face 3 by the first lens / lens group 2 again, and is coupled into the gain fiber 4, where the signal laser is amplified and the noise is suppressed to obtain an amplified pulse laser; Step S5: Laser output: The amplified laser is transmitted to the right, passes through the right fiber end face 5 of the gain fiber 4 and the third lens / lens group 15, and then reflects on the inner surface of the dichroic mirror 16 and is transmitted to the fourth lens / lens group 17 and the dispersion compensator 7. The dispersion compensator 7 provides dispersion compensation, narrows the pulse width, and then transmits to the output laser output coupling mirror 8; The laser is reflected and transmitted at the front surface of the laser output coupling mirror 8 at the same time, wherein a small part of the light is transmitted as the output laser; the remaining part is reflected by the laser output coupling mirror 8, continues to be transmitted downward in the cavity, and is again focused to the right fiber end face 5 of the gain fiber 4 through the fourth lens / lens group 17, the dichroic mirror 16 and the third lens / lens group 15, wherein the pulse continues to be dispersion compensated in the dispersion compensator 7, and then is coupled to the gain fiber 4 through the right fiber end face 5, where the pulse is amplified again and continues to be transmitted to the left; Step S6: Laser generation: The reflected laser returns to the resonant cavity structure, and steps S1-S5 are repeated in the resonant cavity structure. After multiple reflections and amplifications, the photons in the resonant cavity structure gradually tend to be consistent, forming a stable continuous wave mode-locked pulse laser output, and obtaining high-quality, high-efficiency, and high-magnitude femtosecond laser.

[0086] Specifically, the first lens / lens group 2, the second lens / lens group 6, the third lens / lens group 15, the fourth lens / lens group 17, and the fifth lens / lens group 18 mentioned in all the above embodiments 1 and 2 can be single lenses or double lenses, wherein the principle of realizing 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.

[0087] in, is the incident beam waist radius, is the wavelength of light.

[0088] 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 6 Take an example to illustrate: 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 optical fiber end face 3 onto the saturable absorber mirror 1 .

[0089] 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 Fig.11 shown.

[0090] Depend on Fig.11 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).

[0091] 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.

[0092] 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.

[0093] The principle of dual-lens imaging is as follows: like Fig.12 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 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.

[0094] When the conditions are met: When , the coupling efficiency is highest, and the appropriate lens focal length is selected based on this condition.

[0095] 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.

[0096] There are three ways to achieve this, as follows: like Fig.13 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.

[0097] 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.

[0098] 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.

[0099] use Fig.13 The saturable absorber setting method (c) has the following four advantages: Relative to Fig.13 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.

[0100] Relative to Fig.13 In the setting of (a), the spot size focused on the saturable absorber 1 can be continuously adjusted. Fig.13 The distance s between the left fiber end face 3 and the lens in (c) is as follows: Fig.14 shown.

[0101] Even if a single lens with different focal lengths is used, the same focused spot size and Rayleigh distance can be achieved. Fig.14 As shown: No matter how large the focal length is, when s / f>1.1, w 0 ' / w 0 The directions of Fig.15 As shown: No matter how large the focal length is, when s / f>1.1, ZR 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.

[0102] 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.16 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.

[0103] 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 based on multi-lens coupling, characterized in that: It includes a resonant cavity structure and a pump source, wherein the pump source is connected to the resonant cavity structure through a lens combination structure; 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 lens combination structure comprises a dichroic mirror (16) and at least one lens / lens group; The original pump light of the pump source is coupled into any end of the gain optical fiber through a lens combination structure; 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, and the reflected light signal enters the resonant cavity structure and continues to oscillate; The dichroic mirror (16) is used for transmitting pump light and reflecting laser signals, and the lens is used for collimating or focusing laser signals.

2. A fiber laser structure based on multi-lens coupling as claimed in claim 1, characterized in that: The lens assembly is arranged on the left side of the gain optical fiber (4); The dichroic mirror (16) is provided with a fifth lens / lens group (18) in the direction of the right optical fiber end face (5) leading to the passive optical fiber (11); and the dichroic mirror (16) is provided with a fourth lens / lens group (17) in the direction of the saturable absorber mirror (1); The original pump light generated by the pump source (10) is transmitted to the right optical fiber end face (5) and the fifth lens / lens group (18) through the passive optical fiber (11), and then transmitted to the left optical fiber end face (3) through the dichroic mirror (16); the original pump light is coupled into the gain optical fiber (4), so that the gain optical fiber (4) achieves a population inversion, thereby obtaining amplified spontaneous emission light ASE; The ASE generated by the gain optical fiber (4) is transmitted to the left, passes through the left optical fiber end face (3), and then is reflected on the inner surface of the dichroic mirror (16) and transmitted to the fourth lens / lens group (17) and the saturable absorber mirror (1). The function of the fourth lens / lens group (17) is to converge the optical signal output from the left optical fiber end face (3) to the saturable absorber mirror (1) via the dichroic mirror (16); 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 to form a pulsed laser. The laser light reflected by the saturable absorber mirror (1) is transmitted downward, and is focused to the left optical fiber end face (3) by the fourth lens / lens group (17) and the dichroic mirror (16) and then coupled into the gain optical fiber (4). At this time, the gain optical fiber (4) amplifies the signal laser light and suppresses the noise, thereby obtaining an amplified pulse laser light. The amplified pulsed laser light 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); The light continues to be transmitted to the right and is transmitted to the dispersion compensator (7). The light undergoes dispersion compensation in the dispersion compensator (7), and the pulse width becomes narrower. The light is then transmitted to the laser output coupling mirror (8). The light is transmitted to the front surface of the laser output coupling mirror (8), where it is reflected and transmitted simultaneously. A small portion of the light is transmitted as the output laser. The remaining portion 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), the second lens / lens group (6) and the right optical fiber end face (5) to be coupled to the gain optical fiber (4), is amplified again in the gain optical fiber 4, and continues to be transmitted to the left, completing a laser transmission cycle.

3. The fiber laser structure based on multi-lens coupling as claimed in claim 1, characterized in that: The lens assembly is arranged on the left side of the gain optical fiber (4); The dichroic mirror (16) is provided with a fifth lens / lens group (18) in the direction of the right optical fiber end face (5) leading to the passive optical fiber (11), and the dichroic mirror (16) is provided with a third lens / lens group (15) in the direction of the left optical fiber end face (3) leading to the gain optical fiber (4); The original pump light generated by the pump source (10) is transmitted to the right optical fiber end face (5) and the fifth lens / lens group (18) via the passive optical fiber (11), and converges at a point M between the dichroic mirror (16) and the fifth lens / lens group (18) via the fifth lens / lens group (18); The pump light diverged from point M is transmitted to the right, transmitted through a dichroic mirror (16), transmitted to a third lens / lens group (15) and focused to a left optical fiber end face (3), thereby coupling into a gain optical fiber (4), causing the gain optical fiber (4) to achieve population inversion, and obtaining amplified spontaneous emission light ASE; The ASE generated by the gain fiber (4) is transmitted to the left, passes through the left fiber end face (3) and the third lens / lens group (15) in sequence, and then is reflected on the inner surface of the dichroic mirror (16) and focused to the saturable absorber mirror (1). The saturable absorber mirror (1) is located on the focal plane of the focused light beam and provides a pulse forming mechanism - filtering out high-intensity signal laser from noise, thereby forming a pulse laser. The pulsed laser reflected by the saturable absorber mirror (1) is transmitted downward, and is focused to the left optical fiber end face (3) by the dichroic mirror (16) and the third lens / lens group (15) again, and is 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 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); The light continues to be transmitted to the right and is transmitted to the dispersion compensator (7). The light undergoes dispersion compensation in the dispersion compensator (7), and the pulse width becomes narrower. The light is then transmitted to the laser output coupling mirror (8). The light is transmitted to the front surface of the laser output coupling mirror (8), where it is reflected and transmitted simultaneously. A small portion of the light is transmitted as the output laser. The remaining portion 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), the second lens / lens group (6) and the right optical fiber end face (5) to be coupled to the gain optical fiber (4), is amplified again in the gain optical fiber (4), and continues to be transmitted to the left, completing a laser transmission cycle.

4. The fiber laser structure based on multi-lens coupling as claimed in claim 1, characterized in that: The lens assembly is arranged on the left side of the gain optical fiber (4); A third lens / lens group (15) is arranged in the direction of the left optical fiber end face (3) of the dichroic mirror (16) leading to the gain optical fiber (4); The original pump light generated by the pump source (10) is transmitted to the right fiber end face (5) through the passive optical fiber (11), then transmitted through the dichroic mirror (16), transmitted to the third lens / lens group (15) and focused to the left fiber end face (3) and coupled into the gain fiber (4), thereby achieving a population inversion in the gain fiber (4) and obtaining amplified spontaneous emission light ASE; The ASE generated by the gain fiber (4) is transmitted to the left, passes through the left fiber end face (3) and the third lens / lens group (15) in sequence, and then reflects on the inner surface of the dichroic mirror (16) and is focused to the saturable absorber mirror (1). The saturable absorber mirror (1) is located on the focal plane of the focused light beam and provides a pulse forming mechanism - filtering the signal laser from the noise, thereby forming a pulse laser. The pulsed laser is transmitted downward, and is focused to the left optical fiber end face (3) through the dichroic mirror (16) and the third lens / lens group (15) again, and is coupled into the gain optical fiber (4), where the pulsed laser is amplified and noise is suppressed, thereby obtaining an amplified pulsed laser; The amplified pulsed laser 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); The light continues to be transmitted to the right and is transmitted to the dispersion compensator (7). The light undergoes dispersion compensation in the dispersion compensator (7), and the pulse width becomes narrower. The light is then transmitted to the laser output coupling mirror (8). The light is transmitted to the front surface of the laser output coupling mirror (8), where it is reflected and transmitted simultaneously. A small portion of the light is transmitted as the output laser. The remaining portion 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), the second lens / lens group (6) and the right optical fiber end face (5) to be coupled to the gain optical fiber (4), is amplified again in the gain optical fiber 4, and continues to be transmitted to the left, completing a laser transmission cycle.

5. The fiber laser structure based on multi-lens coupling as claimed in claim 1, characterized in that: The lens assembly is arranged on the left side of the gain optical fiber (4); The dichroic mirror (16) is provided with a fifth lens / lens group (18) in the direction of the right optical fiber end face (5) leading to the passive optical fiber (11), the dichroic mirror (16) is provided with a third lens / lens group (15) in the direction of the left optical fiber end face (3) leading to the gain optical fiber (4), and the dichroic mirror (16) is provided with a fourth lens / lens group (17) in the direction of the saturable absorber mirror (1); The original pump light emitted by the pump source (10) is transmitted via the passive optical fiber (11) to the right optical fiber end face (5) connected to the passive optical fiber (11) and the fifth lens / lens group (18), and is collimated and transmitted to the dichroic mirror (16) via the fifth lens / lens group (18); The original pump light is transmitted through the dichroic mirror (16), collimated and transmitted to the third lens / lens group (15) and focused to the left fiber end face (3) of the gain fiber (4), thereby coupling into the gain fiber (4), achieving population inversion in the gain 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 left optical fiber end face (3) and the third lens / lens group (15) in sequence, and then is reflected on the inner surface of the dichroic mirror (16) and transmitted to the fourth lens / lens group (17) and the saturable absorber (1). The function of the fourth lens / lens group (17) is to converge the optical signal output from the left optical fiber end face (3) to the saturable absorber (1) via the dichroic mirror (16); The saturable absorber mirror (1) is located at the focal plane of the focused beam and provides a pulse forming mechanism - filtering the signal laser from the noise to form a pulsed laser; The laser light reflected by the saturable absorber mirror (1) is transmitted downward, and is focused to the left optical fiber end face (3) again through the fourth lens / lens group (17), the dichroic mirror (16) and the third lens / lens group (15), thereby being coupled into the gain optical fiber (4), where the signal laser light is amplified and noise is suppressed, thereby obtaining an amplified pulse laser light; The amplified pulsed laser light 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); The light continues to be transmitted to the right and is transmitted to the dispersion compensator (7). The light undergoes dispersion compensation in the dispersion compensator (7), and the pulse width becomes narrower. The light is then transmitted to the laser output coupling mirror (8). The light is transmitted to the front surface of the laser output coupling mirror (8), where it is reflected and transmitted simultaneously. A small portion of the light is transmitted as the output laser. The remaining portion 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), the second lens / lens group (6) and the right optical fiber end face (5) to be coupled to the gain optical fiber (4), is amplified again in the gain optical fiber 4, and continues to be transmitted to the left, completing a laser transmission cycle.

6. The fiber laser structure based on multi-lens coupling as claimed in claim 1, characterized in that: The lens assembly is arranged on the right side of the gain optical fiber; The dichroic mirror (16) is provided with a fifth lens / lens group (18) in the direction of the right optical fiber end face (5') leading to the passive optical fiber (11), and a fourth lens / lens group (17) is provided in the direction of the dichroic mirror (16) leading to the dispersion compensator (7); The original pump light generated by the pump source (10) is transmitted to the right fiber end face (5') and the fifth lens / lens group (18) through the passive optical fiber (11), and then transmitted to the right fiber end face (5) of the gain optical fiber (4) through the dichroic mirror (16) and coupled into 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 fiber (4) is transmitted to the left, passes through the left fiber end face (3) and the first lens / lens group (2), and then is transmitted to the saturable absorber (1). The saturable absorber (1) is located on the focal plane of the focused light beam and provides a pulse forming mechanism - filtering the signal laser from the noise, thereby forming a pulse laser. The pulse laser reflected by the saturable absorber mirror (1) is transmitted to the right, and is focused to the left optical fiber end face (3) by the first lens / lens group (2) again, and is coupled into the gain optical fiber (4), where the signal laser is amplified and noise is suppressed, thereby obtaining an amplified pulse laser; The amplified pulsed laser is transmitted to the right, passes through the right fiber end face (5) of the gain fiber (4), and then is reflected on the inner surface of the dichroic mirror (16) and transmitted to the fourth lens / lens group (17) and the dispersion compensator (7). Dispersion compensation is performed at the dispersion compensator (7), the pulse width is narrowed, and then the laser 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), wherein a small portion of the light is transmitted as the output laser light; the remaining portion is reflected by the output coupling mirror (8), continues to be transmitted downward in the cavity, and is again focused to the right fiber end face (5) of the gain fiber (4) through the fourth lens / lens group (17) and the dichroic mirror (16) and coupled to the gain fiber (4). The pulse is amplified again in the gain fiber (4), and continues to be transmitted to the left, completing a laser transmission cycle.

7. The fiber laser structure based on multi-lens coupling as claimed in claim 1, characterized in that: The lens assembly is arranged on the right side of the gain optical fiber (4); The dichroic mirror (16) is provided with a fifth lens / lens group (18) in the direction of the right optical fiber end face (5') leading to the passive optical fiber (11), and the dichroic mirror (16) is provided with a third lens / lens group (15) in the direction of the right optical fiber end face (5) leading to the gain optical fiber (4); The pump source (10) generates original pump light which is transmitted to the right fiber end face (5') and the fifth lens / lens group (18) through the passive optical fiber (11); the original pump light output from the right fiber end face (5') of the passive optical fiber (11) is divergent and converges to point N between the dichroic mirror (16) and the fifth lens / lens group (18) through the fifth lens / lens group (18); The original pump light diverged from point N is transmitted to the left, transmitted through a dichroic mirror (16), transmitted to the third lens / lens group (15) and focused to the right optical fiber end face (5), thereby coupling into the gain optical fiber (4), causing the gain optical fiber (4) to achieve population inversion, and obtaining amplified spontaneous emission light ASE; The ASE generated by the gain fiber (4) is transmitted to the left, passes through the left fiber end face (3) and the first lens / lens group (2), and then is transmitted to the saturable absorber (1). The saturable absorber (1) is located on the focal plane of the focused light beam and provides a pulse forming mechanism - filtering the signal laser from the noise, thereby forming a pulse laser. The pulsed laser reflected by the saturable absorber mirror (1) is transmitted to the right, and is focused to the left optical fiber end face (3) by the first lens / lens group (2) again, and is coupled into the gain optical fiber (4), where the signal laser is amplified and noise is suppressed, thereby obtaining an amplified pulsed laser; The amplified pulsed laser is transmitted to the right through the right optical fiber end face (5) and the third lens / lens group (15), and then reflected on the inner surface of the dichroic mirror (16) and transmitted to the dispersion compensator (7), where dispersion compensation is performed and then transmitted to the output laser output coupling mirror (8); The pulsed laser is simultaneously reflected and transmitted on the front surface of the output coupling mirror (8), wherein a small portion of the light is transmitted as the output laser; the remaining portion is reflected by the output coupling mirror 8, continues to be transmitted downward in the cavity, and is again focused to the right optical fiber end face (5) through the dichroic mirror (16) and the third lens / lens group (15), wherein the pulse continues to be dispersion compensated in the dispersion compensator (7), and then is coupled to the gain optical fiber (4) through the right optical fiber end face (5), and the pulse is amplified again in the gain optical fiber (4), and continues to be transmitted to the left, completing a laser transmission cycle.

8. The fiber laser structure based on multi-lens coupling as claimed in claim 1, characterized in that: The lens assembly is arranged on the right side of the gain optical fiber; A third lens / lens group (15) is provided in the direction of the right optical fiber end face (5) of the dichroic mirror (16) leading to the gain optical fiber (4); The original pump light generated by the pump source (10) is transmitted to the right fiber end face (5') of the passive fiber (11) through the passive fiber (11), then transmitted through the dichroic mirror (16), transmitted to the third lens / lens group (15) and focused to the right fiber end face (5) of the gain fiber (4) and coupled into the gain fiber (4), so that the gain 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, passes through the left fiber end face (3) and the first lens / lens group (2), and then is transmitted to the saturable absorber (1). The saturable absorber (1) is located on the focal plane of the focused light beam and provides a pulse forming mechanism - filtering the signal laser from the noise, thereby forming a pulse laser. The pulsed laser reflected by the saturable absorber mirror (1) is transmitted to the right, and is focused to the left optical fiber end face (3) by the first lens / lens group (2) again, so as to be efficiently coupled into the gain optical fiber (4). At this time, the gain optical fiber (4) amplifies the signal laser and suppresses the noise, thereby obtaining an amplified pulsed laser. The amplified pulsed laser is transmitted to the right, passes through the right fiber end face (5) of the gain fiber (4) and the third lens / lens group (15), is dispersion compensated in the dispersion compensator (7), and then transmitted to the output 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 part is reflected by the laser output coupling mirror (8), continues to be transmitted downward in the cavity, and is focused again by the dichroic mirror (16) and the third lens / lens group (15) to the right fiber end face (5) of the gain fiber (4). The pulse continues to be dispersion compensated in the dispersion compensator (7) and coupled to the gain fiber (4). It is amplified again in the gain fiber (4) and continues to be transmitted to the left, completing a pulse laser transmission process.

9. The fiber laser structure based on multi-lens coupling according to claim 1, characterized in that: The lens assembly is arranged on the right side of the gain optical fiber (4); The dichroic mirror (16) is provided with a fifth lens / lens group (18) in the direction of the right optical fiber end face (5') leading to the passive optical fiber (11), the dichroic mirror (16) is provided with a third lens / lens group (15) in the direction of the right optical fiber end face (5) leading to the gain optical fiber (4), and the dichroic mirror (16) is provided with a fourth lens / lens group (17) in the direction of the dispersion compensator (7); The original pump light generated by the pump source (10) is transmitted to the right optical fiber end face (5') and the fifth lens / lens group (18) through the passive optical fiber (11), and is collimated and transmitted to the dichroic mirror (16) through the fifth lens / lens group (18); The original pump light is transmitted through the dichroic mirror (16), collimated and transmitted to the third lens / lens group (15) and focused to the right fiber end face (5) of the gain fiber (4), thereby coupling into the gain fiber (4), causing the gain fiber (4) to achieve population inversion, and obtaining amplified spontaneous emission light ASE; The spontaneous emission light ASE generated by the gain fiber (4) is transmitted to the left, passes through the left fiber end face (3) and the first lens / lens group (2), and then is transmitted to the saturable absorber (1). The saturable absorber (1) is located on the focal plane of the focused light beam and provides a pulse forming mechanism - filtering the signal laser from the noise, thereby forming a pulse laser. The pulse laser reflected by the saturable absorber mirror (1) is transmitted to the right, and is focused to the left optical fiber end face (3) by the first lens / lens group (2) again, and is coupled into the gain optical fiber (4), where the signal laser is amplified and noise is suppressed, thereby obtaining an amplified pulse laser; The amplified laser light is transmitted to the right, passes through the right fiber end face (5) of the gain fiber (4) and the third lens / lens group (15) in sequence, and then is reflected on the inner surface of the dichroic mirror (16) and transmitted to the fourth lens / lens group (17) and the dispersion compensator (7). The dispersion compensator (7) provides dispersion compensation, narrows the pulse width, and then transmits to the output laser output coupling mirror (8); The laser light is simultaneously reflected and transmitted on the front surface of the laser output coupling mirror (8), wherein a small portion of the light is transmitted as the output laser light; the remaining portion is reflected by the laser output coupling mirror (8), continues to be transmitted downward in the cavity, and is again focused to the right fiber end face (5) of the gain fiber (4) through the fourth lens / lens group (17), the dichroic mirror (16) and the third lens / lens group (15), wherein the pulse continues to be dispersion compensated in the dispersion compensator (7), and then is coupled to the gain fiber (4) through the right fiber end face (5), and the pulse is amplified again in the gain fiber (4), and continues to be transmitted to the left, completing a transmission cycle of a pulsed laser.

10. A laser generating method, characterized in that: The fiber laser structure according to claim 9 is applied, characterized in that the method comprises the following steps: Step S1: generating original pump light: a pump source (10) generates original pump light; Step S2: Spontaneous radiation light generation: the original pump light is transmitted to the right optical fiber end face (5') and the fifth lens / lens group (18) through the passive optical fiber (11), and is collimated and transmitted to the dichroic mirror (16) through the fifth lens / lens group (18); The original pump light is transmitted through the dichroic mirror (16), collimated and transmitted to the third lens / lens group (15), focused to the right fiber end face (5) of the gain fiber (4), and coupled into the gain fiber (4), thereby achieving a population inversion in the gain fiber (4) and obtaining amplified spontaneous emission light ASE; Step S3: Pulsed laser generation: the spontaneous emission light ASE generated by the gain fiber (4) is transmitted to the left, passes through the left fiber end face (3) and the first lens / lens group (2), and then is transmitted to the saturable absorber (1). The saturable absorber (1) is located on the focal plane of the focused light beam and provides a pulse forming mechanism - filtering the signal laser from the noise, thereby forming a pulsed laser; Step S4: Pulse laser amplification: The pulse laser reflected by the saturable absorber mirror (1) is transmitted to the right, and is focused to the left optical fiber end face (3) by the first lens / lens group (2) again, and is coupled into the gain optical fiber (4), where the signal laser is amplified and noise is suppressed, thereby obtaining an amplified pulse laser; Step S5: laser output: the amplified laser is transmitted to the right, passes through the right fiber end face (5) of the gain fiber (4) and the third lens / lens group (15), and then reflects on the inner surface of the dichroic mirror (16) and is transmitted to the fourth lens / lens group (17) and the dispersion compensator (7). The dispersion compensator (7) provides dispersion compensation, narrows the pulse width, and is then transmitted to the output laser output coupling mirror (8); The laser light is simultaneously reflected and transmitted on the front surface of the laser output coupling mirror (8), wherein a small portion of the light is transmitted as the output laser light; the remaining portion is reflected by the laser output coupling mirror (8), continues to be transmitted downward in the cavity, and is again focused to the right fiber end face (5) of the gain fiber (4) through the fourth lens / lens group (17), the dichroic mirror (16) and the third lens / lens group (15), wherein the pulse continues to be dispersion compensated in the dispersion compensator (7), and then is coupled to the gain fiber (4) through the right fiber end face (5), and the pulse is amplified again in the gain fiber (4), and continues to be transmitted to the left, completing a transmission cycle of a pulsed laser.

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