A fiber laser structure and a laser generation method

Abstract

A kind of optical fiber laser structure, including resonant cavity structure and pump source, the pump source is connected with the resonant cavity structure by wave division multiplexing-collimator cooperation;The resonant cavity structure can be saturated absorption mirror, 2 lens / lens group, gain optical fiber, dispersion compensator and laser output coupling mirror;The gain optical fiber is waveguide structure, for generating amplified spontaneous emission light ASE, transmission laser and amplification laser;Saturable absorption mirror is used to filter out signal laser from noise;The dispersion compensator is used for dispersion compensation to optical signal;Laser output coupling mirror is used for transmitting and reflecting optical signal, and the transmitted optical signal is used as output laser, and the reflected optical signal continues to enter the resonant cavity structure inside.In the present application, pump source enters into resonant cavity structure by wave division multiplexing-collimator can generate and output high quality, high stability, easy integration GHz femtosecond laser.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lasers, in particular to a fiber laser structure and a laser generation method. BACKGROUND

[0002] Femtosecond pulse laser technology, as a key light source technology, has been widely used in key fields such as frontier scientific research, industrial laser precision machining, national defense equipment confrontation, and medical and health care after more than 40 years of rapid development. These fields are directly related to the development of the country, scientific and technological progress, and the needs of the public life. The use of femtosecond laser technology has significantly improved the country's scientific and technological innovation ability, and has played an irreplaceable role in enhancing international competitiveness.

[0003] Recently, high-repetition-frequency GHz femtosecond lasers play a key role in many frontier scientific fields. For example, the proposal of ablation cooling technology opens up new application prospects for GHz repetition frequency and high-power femtosecond pulses. Experiments have shown that GHz repetition frequency femtosecond lasers not only have high quality of traditional femtosecond laser processing, but also have processing efficiency comparable to nanosecond lasers. This ablation cooling technology based on GHz femtosecond laser can fill the short board of low throughput of femtosecond laser processing in industrial applications, and has great research significance for hard / brittle material processing.

[0004] In order to realize high-efficiency and high-precision "ablation cooling" laser processing, the first thing is to obtain high-repetition-frequency GHz femtosecond laser output. Some manufacturers use off-cavity frequency multiplication to obtain GHz pulses. In fact, it is to divide the conventional seed source with a repetition frequency of tens of MHz or hundreds of MHz off-cavity, make one of them pass through a time delay, and then combine them to increase the repetition frequency. Therefore, the power ratio of the beam splitting and the size of the time delay need to be accurately controlled, otherwise serious power modulation and spurious frequency will occur in the subsequent amplification. This method is a last resort, and the system is relatively complex.

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

[0006] The common existing semiconductor saturable absorber (SESAM) mode-locked GHz fiber laser structure usually adopts a phosphate glass gain fiber with extremely high doping concentration, so that a length of the gain fiber as short as several centimeters or even less than 1 centimeter can obtain sufficient gain. In order to further shorten the cavity length, the SESAM is directly attached to one end of the gain fiber, and a dichroic film (transmission at the pump wavelength and high reflection at the mode-locked laser wavelength) is coated on the other end; in order to increase the stability, the fiber is packaged in a ceramic insert, so that 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 the output power is extremely low, usually below 0.1 mW, which brings great difficulty to the subsequent amplification system. In addition, the cavity type has no spatial part and lacks a dispersion compensation element (usually providing several times the negative dispersion 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 laser to improve the quality, stability and magnitude of the laser. SUMMARY

[0008] The purpose of the present application is to overcome the defects of the prior art and provide a fiber laser structure and a laser generation method.

[0009] The present application is realized by the following technical scheme: a fiber laser structure, comprising a resonant cavity structure and a pump source, the pump source being connected with the resonant cavity structure through a wavelength division multiplexing-collimator;

[0010] The resonant cavity structure comprises 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;

[0011] The pump source is transmitted to the wavelength division multiplexing-collimator through a passive optical fiber, and the wavelength division multiplexing-collimator is connected with the gain fiber to enter the inside of the resonant cavity structure, wherein:

[0012] The gain fiber is a waveguide structure for generating amplified spontaneous emission (ASE), transmitting laser and amplifying laser;

[0013] The first lens / lens group is used for converging the light signal output by the gain fiber onto the saturable absorber mirror;

[0014] The saturable absorber mirror is used for screening out high-intensity signal laser from noise to form a pulse and reflect the pulse laser;

[0015] The second lens / lens group is used for collimating or converging the light signal output by the gain fiber to the laser output coupling mirror;

[0016] The dispersion compensator is used for dispersion compensation of the optical signal.

[0017] The laser output coupling mirror is used for transmitting and reflecting 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.

[0018] Preferably, the gain fiber comprises a left fiber end face and a right fiber end face.

[0019] The wavelength division multiplexing-collimator (9) is connected with the left fiber end face (3).

[0020] Or the wavelength division multiplexing-collimator (9) is connected with the right fiber end face (5).

[0021] Or the wavelength division multiplexing-collimator (9) is connected with the left fiber end face (3) and the right fiber end face (5) simultaneously.

[0022] Preferably, the wavelength division multiplexing-collimator comprises a fiber ferrule, a third lens / lens group and a dichroic filter, wherein:

[0023] The fiber ferrule is used for fixing the passive fiber and the gain fiber.

[0024] The third lens / lens group is used for collimating the pump light output by the passive fiber and the laser output by the gain fiber.

[0025] The dichroic filter is used for reflecting the pump light collimated by the third lens / lens group and coupling it into the gain fiber, and transmitting the laser collimated by the third lens / lens group to the free space.

[0026] Preferably, when the wavelength division multiplexing-collimator is connected with the right fiber end face,

[0027] The original pump light of the pump source is transmitted to the wavelength division multiplexing-collimator through the passive fiber, then reflected at the dichroic filter and transmitted to the gain fiber, so that the gain fiber realizes population inversion and obtains amplified spontaneous emission light ASE;

[0028] The ASE generated by the gain fiber is transmitted to the left through the left fiber end face and the first lens / lens group to the saturable absorber mirror; the noise is filtered out at the saturable absorber mirror to obtain signal laser, forming pulsed laser;

[0029] The pulsed laser after filtering out the noise is transmitted to the right through the saturable absorber mirror, and then focused to the fiber end face through the first lens / lens group and coupled into the gain fiber; at this time, the gain fiber amplifies the pulsed laser and suppresses the noise, obtaining amplified pulsed laser;

[0030] The amplified pulsed laser is collimated to free space through the third lens / lens group and the dichroic filter, and continues to transmit to the right to the dispersion compensator, where the dispersion compensation is performed, the pulse width is narrowed, and then transmitted to the laser output coupling mirror;

[0031] The pulsed laser is reflected and transmitted at the same time at the front surface of the laser output coupling mirror, where a small part of the light is transmitted as output laser; the remaining part is reflected and continues to transmit to the left in the cavity, and then passes through the dispersion compensator and the wavelength division multiplexing-collimator in sequence;

[0032] The reflected pulse continues to be dispersion compensated in the dispersion compensator, and then coupled to the gain fiber through the wavelength division multiplexing-collimator, where it is amplified again and continues to transmit to the left, completing a laser transmission cycle.

[0033] Preferably, when the wavelength division multiplexing-collimator is connected with the left fiber end face,

[0034] The original pump light of the pump source is transmitted to the wavelength division multiplexing-collimator through the passive optical fiber, and then reflected at the dichroic filter and transmitted to the gain fiber, where the population inversion is realized and amplified spontaneous emission light ASE is obtained;

[0035] The ASE generated by the gain fiber also transmits to the left, collimates and transmits to the first lens / lens group through the third lens / lens group and the dichroic filter, and converges to the saturable absorption mirror; at the saturable absorption mirror, the noise is filtered out and the signal laser is screened out, forming the pulsed laser;

[0036] The pulsed laser with improved signal-to-noise ratio is reflected to the right through the saturable absorption mirror, and then transmitted to the gain fiber again through the first lens / lens group and the wavelength division multiplexing-collimator; at this time, the gain fiber amplifies the pulsed laser signal and suppresses the noise, obtaining the amplified laser signal;

[0037] The amplified laser signal collimates to free space or converges to the front surface of the laser output coupling mirror through the right fiber end face and the second lens / lens group, which is determined by the distance from the right fiber end face to the second lens / lens group;

[0038] Transmits to the right to the dispersion compensator, where the dispersion compensation is performed, the pulse width is narrowed, and then transmitted to the laser output coupling mirror;

[0039] The pulsed laser is reflected and transmitted at the same time at the front surface of the laser output coupling mirror, where a small part of the light is transmitted as output laser; the remaining part is reflected and continues to transmit to the left in the cavity, and then passes through the dispersion compensator, the second lens / lens group and the right fiber end face in sequence, and transmits to the left to the gain fiber, where the laser pulse signal is amplified again and continues to transmit to the left, completing a laser transmission cycle.

[0040] Preferably, it further comprises two first wavelength division multiplexing-collimators, a second wavelength division multiplexing-collimator, a first pump and a second pump source;

[0041] The first wavelength division multiplexing-collimator is connected with the left fiber end face, and the second wavelength division multiplexing-collimator is connected with the right fiber end face at the same time,

[0042] The first pump source and the second pump source both generate original pump light, which is transmitted to the first wavelength division multiplexing-collimator and the second wavelength division multiplexing-collimator through the first passive optical fiber and the second passive optical fiber respectively;

[0043] The original pump light is reflected by the dichroic filter of the first wavelength division multiplexing-collimator and the second wavelength division multiplexing-collimator, and is transmitted to the gain optical fiber together, so that the gain optical fiber realizes population inversion and obtains amplified spontaneous emission light (ASE);

[0044] The ASE generated by the gain optical fiber is transmitted to the left, passes through the lens and the dichroic filter of the first wavelength division multiplexing-collimator, is collimated and transmitted to the first lens / lens group, and is focused to the saturable absorber mirror through the first lens / lens group;

[0045] The saturable absorber mirror is located on the focal plane of the focused light beam, and provides a pulse forming mechanism to filter out high-intensity signal laser from noise, thereby generating pulsed laser;

[0046] The pulsed laser reflected by the saturable absorber mirror is transmitted to the right, and is transmitted to the gain optical fiber again through the first lens / lens group and the first wavelength division multiplexing-collimator, at this time the gain optical fiber amplifies the signal laser and suppresses the noise, and obtains amplified pulsed laser;

[0047] The amplified pulsed laser is collimated to free space through the lens and the dichroic filter of the second wavelength division multiplexing-collimator, and continues to be transmitted to the right from the free space;

[0048] The pulse output from the second wavelength division multiplexing-collimator is color dispersion compensated by the color dispersion compensator, the pulse width is narrowed, and then the pulse is transmitted to the laser output coupling mirror; the laser is reflected and transmitted at the same time on the front surface of the laser output coupling mirror, a small part of light is transmitted as output laser; the remaining part is reflected by the laser output coupling mirror, and continues to be transmitted to the left in the cavity, and then passes through the color dispersion compensator and the second wavelength division multiplexing-collimator in sequence; wherein, the pulse continues to be color dispersion compensated by the color dispersion compensator, and then is coupled to the gain optical fiber by the second wavelength division multiplexing-collimator, the pulse is amplified again in the gain optical fiber, and continues to be transmitted to the left, thereby completing a laser transmission cycle.

[0049] The application provides a laser generation method, which applies a fiber laser structure in which a wavelength division multiplexing-collimator is connected with a left fiber end face, and the method comprises the following steps:

[0050] Step S1: original pump light generation: the pump source generates original pump light which is transmitted to the wavelength division multiplexing-collimator through a passive optical fiber;

[0051] Step S2: spontaneous emission light generation: the original pump light is reflected at the dichroic filter and is transmitted to the gain optical fiber, so that the gain optical fiber realizes particle inversion and obtains amplified spontaneous emission light (ASE);

[0052] Step S3: pulse laser generation: the ASE generated by the gain optical fiber is transmitted to the left through the left fiber end face and the first lens / lens group and is focused on the saturable absorption mirror; noise is filtered out at the saturable absorption mirror to form high-intensity signal laser, and pulse laser is formed;

[0053] Step S4: pulse laser amplification: the pulse laser with improved signal-to-noise ratio is transmitted to the right through the saturable absorption mirror, is focused to the left fiber end face again through the first lens / lens group and is coupled into the gain optical fiber; at this time, the gain optical fiber amplifies the pulse laser and suppresses noise, and amplified pulse laser is obtained;

[0054] Step S5: pulse laser output: the amplified pulse laser is collimated to free space through the third lens / lens group and the dichroic filter and is continuously transmitted to the dispersion compensator from the free space;

[0055] The dispersion compensator performs dispersion compensation, the pulse width is narrowed, and then the pulse laser is transmitted to the laser output coupling mirror;

[0056] The pulse laser is reflected and transmitted at the front surface of the laser output coupling mirror, a small part of light is transmitted as output laser; the remaining part is reflected and continuously transmitted to the left in the cavity, and then passes through the dispersion compensator and the wavelength division multiplexing-collimator in sequence;

[0057] The reflected pulse is continuously compensated in the dispersion compensator, is coupled into the gain optical fiber through the wavelength division multiplexing-collimator, is amplified again in the gain optical fiber and continuously transmitted to the left, and a laser transmission cycle is completed.

[0058] The application provides a second laser generation method, which applies a fiber laser structure in which a wavelength division multiplexing-collimator is connected with a left fiber end face, and the method comprises the following steps:

[0059] Step S1: original pump light generation: the pump source generates original pump light which is transmitted to the wavelength division multiplexing-collimator through a passive optical fiber;

[0060] Step S2 spontaneous emission light generation: the original pump light is reflected on the dichroic filter and transmitted to the gain fiber, so that the gain fiber realizes population inversion, and amplified spontaneous emission light ASE is obtained;

[0061] Step S3 pulse laser generation: the ASE generated by the gain fiber is also transmitted to the left, passes through the third lens / lens group and the dichroic filter, is collimated and transmitted to the first lens / lens group, and is converged to the saturable absorber mirror; noise is filtered out at the saturable absorber mirror to obtain high-intensity signal laser, and pulse laser is generated;

[0062] Step S3 pulse laser amplification: the pulse laser is reflected to the right through the saturable absorber mirror, and is transmitted to the gain fiber again through the first lens / lens group and the wavelength division multiplexing-collimator; at this time, the gain fiber amplifies the pulse laser signal and suppresses noise, and an amplified laser signal is obtained;

[0063] Step S4 pulse laser output: the amplified laser signal is collimated to 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;

[0064] transmitted to the right to the dispersion compensator, the dispersion compensator is compensated, the pulse width is narrowed, and then transmitted to the laser output coupling mirror;

[0065] The pulse laser is reflected and transmitted on the front surface of the laser output coupling mirror at the same time, a small part of light is transmitted as output laser; the remaining part is reflected and continues to transmit to the left in the cavity, and then passes through the dispersion compensator, the second lens / lens group and the right fiber end face in sequence, and is transmitted to the left to the gain fiber, the laser pulse signal is amplified again in the gain fiber, and continues to transmit to the left, completing a laser transmission cycle.

[0066] The application also provides a third laser generation method, which applies a wavelength division multiplexing-collimator and a fiber laser structure in which the left fiber end face and the right fiber end face are connected at the same time, and the method comprises the following steps:

[0067] Step S1 original pump light generation: the first pump source and the second pump source both generate original pump light, which is transmitted to the first wavelength division multiplexing-collimator and the second wavelength division multiplexing-collimator through the first passive optical fiber and the second passive optical fiber respectively;

[0068] Step S2 spontaneous emission light generation: the original pump light is reflected on the dichroic filter of the first wavelength division multiplexing-collimator and the second wavelength division multiplexing-collimator, and is transmitted to the gain fiber together, so that the gain fiber realizes population inversion, and amplified spontaneous emission light ASE is obtained;

[0069] Step S3 pulse laser generation: the ASE generated by the gain fiber is transmitted to the left, collimated by the lens and dichroic filter of the first wavelength division multiplexer-collimator, transmitted to the first lens / lens group, and focused to the saturable absorber mirror by the first lens / lens group;

[0070] The saturable absorber mirror is located on the focal plane of the focused light beam, and provides a pulse formation mechanism to filter out high-intensity signal laser from noise, thereby generating pulse laser;

[0071] Step S4 pulse laser amplification: the pulse laser is reflected to the right by the saturable absorber mirror, and transmitted to the gain fiber again through the first lens / lens group and the first wavelength division multiplexer-collimator, at this time the gain fiber amplifies the signal laser and suppresses the noise, thereby obtaining amplified pulse laser;

[0072] Step S5 pulse laser output: the amplified pulse laser is collimated to the free space by the lens and dichroic filter of the second wavelength division multiplexer-collimator, and continues to be transmitted to the right;

[0073] The pulse output from the second wavelength division multiplexer-collimator is color dispersion compensated by the color dispersion compensator, the pulse width is narrowed, and then transmitted to the laser output coupling mirror; the laser is reflected and transmitted at the same time on the front surface of the laser output coupling mirror, a small part of light is transmitted as output laser; the remaining part is reflected by the laser output coupling mirror, continues to be transmitted to the left in the cavity, and then passes through the color dispersion compensator and the second wavelength division multiplexer-collimator in sequence; wherein, the pulse continues to be color dispersion compensated by the color dispersion compensator, and then coupled to the gain fiber by the second wavelength division multiplexer-collimator, the pulse is amplified again in the gain fiber, and continues to be transmitted to the left, thereby completing a laser transmission cycle.

[0074] The beneficial effects of the present application are:

[0075] In the present application, the original pump light of the pump source enters the resonant cavity structure through the wavelength division multiplexer-collimator, the resonant cavity structure is provided with a saturable absorber mirror, a plurality of lenses / lens groups, a gain fiber, a color dispersion compensator and a laser output coupling mirror, and the laser signal is continuously screened and amplified under the cooperation of these devices, thereby generating and outputting high-quality, high-stability and easily integrated GHz femtosecond laser. BRIEF DESCRIPTION OF DRAWINGS

[0076] Figure 1 It is a schematic diagram of the resonant cavity structure of the present application;

[0077] Figure 2 It is a structure schematic diagram of embodiment 1 of the present application;

[0078] Figure 3 It is a structure schematic diagram of the wavelength division multiplexer-collimator of the present application;

[0079] Figure 4 Structure diagram of embodiment 2 of the present application;

[0080] Figure 5 Structure diagram of embodiment 3 of the present application;

[0081] Figure 6 Principle diagram of three cases of imaging of divergent point light source through single convex lens;

[0082] Figure 7 Principle diagram of imaging of divergent point light source through two convex lenses;

[0083] Figure 8 Three ways of setting saturable absorber in resonant cavity structure;

[0084] Figure 9 Graph of variation of w0' / w0 with s / f;

[0085] Figure 10 Graph of variation of ZR' with s / f;

[0086] Figure 11 Graph of variation of (s+s') / f with s / f;

[0087] Figure 12 Structure diagram of embodiment 6;

[0088] Figure 13 Display diagram of experimental results of structure of embodiment 6. DETAILED DESCRIPTION

[0089] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with embodiments, but the scope of protection of the present application is not limited to the following specific embodiments.

[0090] The following specifically describes one optical fiber laser structure of the present scheme.

[0091] An optical fiber laser structure, comprising resonant cavity structure and pump source 10, the pump source 10 is connected with the resonant cavity structure through wavelength division multiplexing-collimator 9;

[0092] As Figure 1 described, the resonant cavity comprises saturable absorber mirror 1, first lens / lens group 2, gain optical fiber 4, second lens / lens group 6, dispersion compensator 7 and laser output coupling mirror 8;

[0093] The pump source 10 is transmitted to the wavelength division multiplexing-collimator 9 through passive optical fiber 11, the wavelength division multiplexing-collimator 9 is connected with the gain optical fiber 4 to enter the inside of the resonant cavity structure, wherein:

[0094] The pump source 10 is a laser diode, which is used to generate original pump light and activate the inverted particles of the gain fiber 4 by the original pump light.

[0095] The gain fiber 4 is a waveguide structure, which is used to generate amplified spontaneous emission light ASE, transmit laser and amplify laser, and the length is less than 10 cm;

[0096] The first lens / lens group 2 is used to converge the light signal output by the gain fiber 4 to the saturable absorber mirror 1;

[0097] The saturable absorber mirror 1 is used to filter out the signal laser from the noise, so as to form a pulse and reflect the pulse laser, and the saturable absorber mirror 1 has high absorption rate for low-intensity laser and low absorption rate for high-intensity laser, so as to filter out the signal from the noise, which is used to provide a mechanism for forming ultrafast pulses for the laser and assist the laser in mode locking.

[0098] The second lens / lens group 6 is used to collimate or converge the light signal output by the gain fiber 4 to the laser output coupling mirror 8;

[0099] The dispersion compensator 7 is used to compensate the dispersion of the light signal, which is used to provide negative group delay dispersion for the laser.

[0100] The laser output coupling mirror 8 is used to transmit and reflect the light signal, and the transmitted light signal is used as output laser, and the reflected light signal continues to enter the resonant cavity structure.

[0101] Specifically, the gain fiber 4 includes a left fiber end face 3 and a right fiber end face 5;

[0102] The wavelength division multiplexer-collimator 9 is connected with the left fiber end face 3;

[0103] Or the wavelength division multiplexer-collimator 9 is connected with the right fiber end face 5;

[0104] Or the wavelength division multiplexer-collimator 9 is connected with the left fiber end face 3 and the right fiber end face 5 at the same time.

[0105] The wavelength division multiplexer-collimator 9 includes a fiber stub 12, a third lens / lens group 13 and a dichroic filter 14, wherein:

[0106] The fiber stub 12 is used to fix the passive fiber 11 and the gain fiber 4;

[0107] The third lens / lens group 13 is used to collimate the pump light output by the passive fiber 11 and the laser output by the gain fiber 4;

[0108] The dichroic filter 14 is used to reflect the pump light collimated from the third lens / lens group 13 and couple it into the gain fiber 4, while simultaneously transmitting the laser collimated from the third lens / lens group 13 into free space.

[0109] The first lens / lens group 2 and the second lens / lens group 6 can be a single lens or a double lens. The principle of beam transformation achieved by a single lens is as follows:

[0110] In 1983, Sidney Self developed a formula for calculating the transformation of a Gaussian beam through a thin lens:

[0111]

[0112] in and These are the distances from the incident beam waist and the exit beam waist to the lens, respectively. The focal length of the lens. The Rayleigh distance of the incident beam, i.e., the distance from the beam waist radius to the incident beam. The distance traveled by twice the waist radius is also called the "collimation" distance.

[0113]

[0114] in, It is the waist radius of the incident beam. It is the wavelength of light.

[0115] From the following formula, we can obtain... The expression:

[0116]

[0117] The magnification (reduction) factor of the waist radius of the emitted beam is:

[0118]

[0119] In the formula, The expression for the output beam waist radius is:

[0120]

[0121] The Rayleigh distance for output light is:

[0122]

[0123] by Figure 1 Taking the left side of the gain fiber as an example: when the first lens / lens group 2 is a single convex lens, the single lens can focus the diverging beam output from the left fiber end face 3 onto the saturable absorber 1.

[0124] According to the imaging principle of convex lens, there are three cases when a divergent point source is transmitted through a single convex lens. They can be classified according to the different positions of the incident point source on the optical axis of the lens, as shown in Figure 6 .

[0125] The following conclusions can be drawn: Figure 6

[0126] When the incident point source is within one focal length (F position): the outgoing light is divergent, without beam waist (as shown by the gray arrow); when the incident point source is at F, the output light is collimated (as shown by the black arrow).

[0127] When the incident point source is between F and 2F: the outgoing light converges outside two focal lengths (2F); the closer the point source is to the F position, the farther the image point is from the 2F position, and the larger the outgoing beam waist radius is; in particular: s = 2f, s' = 2f;

[0128] When the incident point source is outside the 2F position: the outgoing light converges between F and 2F; and the farther the point 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.

[0129] The purpose of the lens / lens group, whether single lens or double lens, is to focus the light beam emitted by one device into another device. By selecting appropriate lenses / lens groups, the spot at the outgoing position and the spot at the focusing position are matched with the divergence angle. In particular, when coupling from the end face of one optical fiber to the end face of another optical fiber, by selecting appropriate lenses / lens groups, the mode fields of the two can be matched.

[0130] The imaging principle of double lens is as follows:

[0131] As shown in Figure 7 , the double lens system includes two convex lenses, which make the point source diverging from D1 transmit and focus to D2. The two lenses are denoted as F1 and F2, respectively, and their functions are to collimate the divergent light and focus the collimated light, respectively. Collimation and focusing are reciprocal processes, which can be described by the following formula:

[0132]

[0133]

[0134] wherein and are the beam waist diameters of the collimated light beam, is the wavelength, and are the focal lengths of the collimating lens and the focusing lens, respectively, and ​The waist diameters of the incident light and the exit light, respectively. In particular, when the focal planes of F1 and F2 are both the end faces of the optical fiber, and The mode field diameters of the two optical fibers, respectively.

[0135] When the condition:

[0136]

[0137] is met, the coupling efficiency is the highest, and the appropriate lens focal length size is selected according to this condition.

[0138] In the resonant cavity structure described in Figure 1 , it is necessary to focus the divergent light beam emitted by the left optical fiber end face 3 to the saturable absorber mirror 1, and make the reflection back to the optical fiber end face with high efficiency, so that the resonant cavity can realize mode locking.

[0139] There are three methods to achieve this, and the specific methods are as follows:

[0140] As shown in Figure 8 , the double-lens system: the divergent light output by the left optical fiber end face 3 is first collimated by the lens f1, and then focused to the saturable absorber mirror 1 by the lens f2, and then reflected by the saturable absorber mirror 1, and coupled back to the left optical fiber end face 3 through the two lenses. This way of using two lenses, collimating first and then focusing, is called a double-lens system.

[0141] The lensless system: the divergent light output by the left optical fiber end face 3 is directly reflected back by the saturable absorber mirror 1 and coupled into the left optical fiber end face 3. It is worth noting that since the back light is also divergent, the distance between the saturable absorber mirror 1 and the left optical fiber end face 3 must be very close (less than the Rayleigh distance of the optical fiber exit light beam) or even attached to obtain a higher coupling efficiency.

[0142] The single-lens system: the divergent light output by the left optical fiber end face 3 is directly focused to the saturable absorber mirror 1 by a single lens, and then reflected back to the left optical fiber end face 3.

[0143] The saturable absorber setting method of Figure 8 (c) has the following four advantages:

[0144] Compared with the setting method of Figure 8 (b), since the back light is convergent, the mode field diameter focused to the left optical fiber end face 3 can be equal to the mode field diameter of the left optical fiber end face 3, so it has a higher coupling efficiency.

[0145] Compared with the setting method of Figure 8 (a), the spot size focused to the saturable absorber mirror 1 can be continuously adjusted, and only the Figure 8(c) the distance s between the left fiber facet 3 and the lens, as shown in Figure 9

[0146] Even with different focal length lenses, the same focused spot size and Rayleigh range can be achieved. As shown in Figure 9 Figure 10 As shown in the figure, no matter how large the focal length is, when s / f>1.1, the trend of w0’ / w0 is almost the same. As shown in the figure, no matter how large the focal length is, when s / f>1.1, the trend of Z R ’ is almost the same. The advantage of a larger Rayleigh range for the focused spot is that a slight axial shift (caused by the environment) will not have a large impact on the coupling efficiency.

[0147] The distance s+s’ between the saturable absorber mirror 1 and the left fiber facet 3 can be adjusted to be very small, and the smaller the focal length f of the lens, the smaller the s+s’. As shown in the figure, for lenses with different focal lengths, when s / f>1.1, the trend of (s+s’) / f is almost the same, so the smaller the f, the smaller the s+s’. A shorter s+s’ can shorten the length of the resonant cavity, which is crucial for the design of high-repetition-rate mode-locked lasers. Figure 11

[0148] Embodiment 1: Wavelength division multiplexer-collimator on the right side of the gain fiber

[0149] As shown in the figure, the wavelength division multiplexer-collimator is placed at the right end of the gain fiber 4, i.e., the wavelength division multiplexer-collimator 9 is connected to the right fiber facet 5. Figure 2 At this time, the working process of the entire structure is as follows:

[0150] The original pump light generated by the pump source 10 is transmitted to the wavelength division multiplexer-collimator 9 through the passive fiber 11, and then reflected by the dichroic filter 14 and transmitted to the gain fiber 4, so that the gain fiber 4 achieves particle inversion and obtains amplified spontaneous emission light ASE;

[0151] The ASE generated by the gain fiber 4 is transmitted to the left through the left fiber facet and the first lens / lens group 2 and focused on the saturable absorber mirror 1; at the saturable absorber mirror 1, the spontaneous emission light is filtered to remove noise and the signal laser is screened out to form pulsed laser;

[0152] The pulsed laser after filtering out the noise is transmitted to the right through the saturable absorber mirror 1, and then focused to the fiber facet 3 through the first lens / lens group 2 and coupled into the gain fiber 4, at this time the gain fiber 4 amplifies the pulsed laser and suppresses the noise to obtain amplified pulsed laser;

[0153]

[0154] ​​​​The amplified pulse laser is collimated to free space by the third lens / lens group 13 and the dichroic filter 14, and continues to transmit to the dispersion compensator 7 from the free space (principle as Figure 6 (a) shown), and the pulse width is narrowed by the dispersion compensation in the dispersion compensator 7, and then transmitted to the laser output coupling mirror 8;

[0155] The pulse laser is reflected and transmitted at the same time on the front surface of the laser output coupling mirror 8, wherein a small part of light is transmitted as output laser. The remaining part is reflected and continues to transmit to the left in the cavity, and then passes through the dispersion compensator 7 and the wavelength division multiplexing-collimator 9 in sequence;

[0156] The reflected pulse continues to be dispersion compensated in the dispersion compensator 7, and then coupled into the gain fiber 4 through the wavelength division multiplexing-collimator 9, and amplified again in the gain fiber 4 to continue to transmit to the left, completing a laser transmission cycle.

[0157] The above process is a complete cycle of the laser transmission process. The cavity laser periodically operates in the laser formed by all the above devices to form pulse laser, obtain amplification, and finally form stable continuous wave mode-locked pulse laser output, that is, high-quality, high-efficiency, and high-magnitude femtosecond laser. The output parameters of the mode-locked pulse are determined by the combination of the parameters of each device in the cavity.

[0158] Corresponding to the structure of embodiment 1, a laser generation method using the structure of the fiber laser in which the wavelength division multiplexing-collimator is connected to the right fiber end face is as follows:

[0159] Step S1 original pump light generation: the original pump light generated by the pump source is transmitted to the wavelength division multiplexing-collimator through the passive fiber;

[0160] Step S2 spontaneous emission light generation: the original pump light is reflected in the dichroic filter and transmitted to the gain fiber, so that the gain fiber realizes particle inversion and obtains amplified spontaneous emission light (ASE);

[0161] Step S3 pulse laser generation: the ASE generated by the gain fiber transmits to the left through the left fiber end face and the first lens / lens group and converges to the saturable absorption mirror; the noise is filtered out in the saturable absorption mirror to form pulse laser with high intensity signal light;

[0162] Step S4 pulse laser amplification: the pulse laser with improved signal-to-noise ratio transmits to the right through the saturable absorption mirror, and is focused to the fiber end face through the first lens / lens group and then coupled into the gain fiber. At this time, the gain fiber amplifies the pulse laser and suppresses the noise to obtain amplified pulse laser;

[0163] Step S5 pulse laser output: the amplified pulse laser is collimated to free space by the third lens / lens group and dichroic filter, and continues to transmit to the right to the dispersion compensator (principle as Figure 6 (a) shown);

[0164] The dispersion compensation is performed in the dispersion compensator, the pulse width is narrowed, and then transmitted to the laser output coupling mirror.

[0165] The pulse laser is reflected and transmitted at the same time in front of the laser output coupling mirror, wherein a small part of light is transmitted as output laser; the remaining part is reflected and continues to transmit to the left in the cavity, and then passes through the dispersion compensator and the wavelength division multiplexing-collimator in turn.

[0166] Among them, the reflected pulse continues to be dispersion compensated in the dispersion compensator, and then coupled to the gain fiber through the wavelength division multiplexing-collimator, and is amplified again in the gain fiber to continue to transmit to the left, completing a laser transmission cycle.

[0167] Embodiment 2: wavelength division multiplexing-collimator on the left side of the gain fiber

[0168] As shown in Figure 4 , in this embodiment, the wavelength division multiplexing-collimator 9 is connected with the left fiber end face 3.

[0169] At this time, the working process of the whole structure is as follows:

[0170] The original pump light of the pump source 10 is transmitted to the wavelength division multiplexing-collimator 9 through the passive optical fiber 11, and then reflected in the dichroic filter 14 and transmitted to the gain fiber 4, so that the gain fiber 4 realizes particle inversion and obtains amplified spontaneous emission light ASE.

[0171] The ASE generated by the gain fiber 4 also transmits to the left, passes through the third lens / lens group 13 and the dichroic filter 14, and is collimated and transmitted to the first lens / lens group 2 to converge to the saturable absorption mirror 1; the noise is filtered out at the saturable absorption mirror 1 to form a pulse laser.

[0172] The generated pulse laser is reflected to the right through the saturable absorption mirror 1, and then transmitted to the gain fiber 4 again through the first lens / lens group 2 and the wavelength division multiplexing-collimator 9; at this time, the gain fiber 4 amplifies the pulse laser signal and suppresses the noise, and the amplified laser signal is transmitted to the free space through the right fiber end face 5 and the second lens / lens group 6, and continues to transmit to the right.

[0173] It is worth noting that the laser output from the right fiber end face 5 is divergent, and the output laser passing through the second lens / lens group 6 has two possibilities: one is collimated to free space (principle as Figure 6(a) shown); second, converging to the front surface of the laser output coupling mirror 8 (principle as shown in (b) or (c), depending on the distance from the right fiber end face 5 to the second lens / lens group 6. The dispersion compensator 7 between the second lens / lens group 6 and the laser output coupling mirror 8 functions to provide dispersion compensation, so as to narrow the pulse width. Figure 6

[0174] The pulse laser is simultaneously reflected and transmitted at the front surface of the laser output coupling mirror 8, wherein a small portion of light is transmitted as output laser; the remaining portion is reflected and continues to transmit leftward in the cavity, and then successively passes through the dispersion compensator 7, the second lens / lens group 6 and the right fiber end face 5. In the above two cases (whether collimation or convergence), the process of transmitting leftward from the right fiber end face 5 to the gain fiber 4 can achieve high-efficiency coupling. The laser pulse signal is amplified again in the gain fiber 4 and continues to transmit leftward.

[0175] The above process is a complete cycle of laser transmission. The cavity laser periodically operates in the laser formed by all the above-mentioned devices, forms a pulse laser, is amplified, and finally forms a stable continuous wave mode-locked pulse laser output. The output parameters of the mode-locked pulse are determined by the combination of the parameters of each device in the cavity.

[0176] Corresponding to the structure of Example 2, a laser generation method using a wavelength division multiplexing-collimator and a fiber laser structure connected with the left fiber end face is as follows:

[0177] Step S1 original pump light generation: the original pump light of the pump source is transmitted to the wavelength division multiplexing-collimator through the passive optical fiber;

[0178] Step S2 spontaneous emission light generation: the original pump light is reflected at the dichroic filter and transmitted to the gain fiber, so that the gain fiber realizes particle inversion and obtains amplified spontaneous emission light ASE;

[0179] Step S3 pulse laser generation: the ASE generated by the gain fiber also transmits leftward, passes through the third lens / lens group and the dichroic filter, collimates and transmits to the first lens / lens group to converge on the saturable absorption mirror; the noise is filtered out at the saturable absorption mirror to obtain high-intensity signal laser, and the pulse laser is generated;

[0180] Step S3 pulse laser amplification: the pulse laser is reflected rightward by the saturable absorption mirror, and then transmits to the gain fiber again through the first lens / lens group and the wavelength division multiplexing-collimator. At this time, the gain fiber amplifies the pulse laser signal and suppresses the noise to obtain an amplified laser signal;

[0181] ​Step S4 Pulse laser output: The amplified laser signal is aligned with the right fiber end face and the second lens / lens group until it reaches free space or converges to the front surface of the laser output coupling mirror, depending on the distance from the right fiber end face (5) to the second lens / lens group (6).

[0182] The pulse is transmitted to the right to the dispersion compensator, where dispersion compensation is performed, the pulse width narrows, and then the pulse is transmitted to the laser output coupling mirror.

[0183] The pulsed laser is simultaneously reflected and transmitted on the front surface of the laser output coupling mirror 8. A small portion of the light is transmitted and becomes the output laser; the remaining portion is reflected and continues to propagate to the left within the cavity. It then passes through the dispersion compensator, the second lens / lens group, and the right fiber end face, and is transmitted to the gain fiber to the left. The laser pulse signal is amplified again in the gain fiber and continues to propagate to the left, completing one laser transmission cycle.

[0184] Example 3: Dual Wavelength Division Multiplexing-Collimator

[0185] like Figure 5 As shown, in this embodiment, two pump sources and wavelength division multiplexing-collimators are connected in sequence. The two wavelength division multiplexing-collimators are respectively connected to the left fiber end face 3 and the right fiber end face 5 of the gain fiber.

[0186] Two pump sources are named: first pump source 10 and second pump source 10';

[0187] Two passive optical fibers are named the first passive optical fiber 11 and the second passive optical fiber 11'.

[0188] Two wavelength division multiplexing-collimators are named the first wavelength division multiplexing-collimator 9 and the second wavelength division multiplexing-collimator 9'.

[0189] At this point, the entire structure works as follows:

[0190] Both the first pump source 10 and the second pump source 10' generate raw pump light, which is transmitted to the first wavelength division multiplexing-collimator 9 and the second wavelength division multiplexing-collimator 9' via the first passive optical fiber 11 and the second passive optical fiber 11', respectively.

[0191] Subsequently, the dichroic filters 14 of the first wave division multiplexing-collimator 9 and the second wave division multiplexing-collimator 9' are reflected and transmitted together to the gain fiber 4, thereby enabling the gain fiber 4 to achieve population inversion and obtain amplified spontaneous emission light ASE.

[0192] The ASE generated by the gain fiber 4 is transmitted to the left, passes through the lens of the first wavelength division multiplexing-collimator 9 and the dichroic filter 14, and is collimated to the first lens / lens group 2, and then focused by the first lens / lens group 2 to the saturable absorber mirror 1.

[0193] The saturable absorber mirror 1 is located on the focal plane of the focused light beam, providing a pulse forming mechanism to filter out high-intensity signal laser from noise, thereby generating pulsed laser;

[0194] The pulsed laser reflected by the saturable absorber mirror 1 is transmitted to the right, and then transmitted to the gain fiber 4 again through the first lens / lens group 2 and the first wavelength division multiplexing-collimator 9, at this time the gain fiber 4 amplifies the signal laser while suppressing the noise, obtaining amplified pulsed laser;

[0195] The amplified pulsed laser is collimated to the free space through the lens of the second wavelength division multiplexing-collimator 9' and the dichroic filter 14, and continues to transmit to the right;

[0196] The pulse output from the second wavelength division multiplexing-collimator 9' is color dispersion compensated by the color dispersion compensator 7, the pulse width is narrowed, and then transmitted to the laser output coupling mirror 8; the laser is reflected and transmitted at the same time on the front surface of the laser output coupling mirror 8, a small part of the light is transmitted as output laser; the remaining part is reflected by the laser output coupling mirror 8, and continues to transmit to the left in the cavity, and then passes through the color dispersion compensator 7 and the second wavelength division multiplexing-collimator 9' in sequence;

[0197] Among them, the pulse continues to be color dispersion compensated by the color dispersion compensator 7, and then is coupled to the gain fiber 4 by the second wavelength division multiplexing-collimator 9' with high efficiency, the pulse is amplified again in the gain fiber 4, and continues to transmit to the left, completing a laser transmission cycle.

[0198] The above process is a complete cycle of the laser transmission process. The cavity laser operates periodically in the laser formed by all the above devices, forms pulsed laser, is amplified, and finally forms stable continuous wave mode-locked pulsed laser output. The output parameters of the mode-locked pulse are determined by the combination of the parameters of each device in the cavity.

[0199] Corresponding to the structure of Example 3, a laser generation method using a wavelength division multiplexing-collimator and a fiber laser structure in which the left fiber end face and the right and left fiber end faces are connected at the same time is as follows:

[0200] Step S1 original pump light generation: the first pump source and the second pump source both generate original pump light, which is transmitted to the first wavelength division multiplexing-collimator and the second wavelength division multiplexing-collimator through the first passive optical fiber and the second passive optical fiber respectively;

[0201] Step S2 spontaneous emission light generation: the reflected light on the dichroic filter of the first wavelength division multiplexing-collimator and the second wavelength division multiplexing-collimator is transmitted to the gain fiber together, so that the gain fiber realizes population inversion, and obtains amplified spontaneous emission light ASE;

[0202] Step S3 Pulse laser generation: The ASE generated by the gain fiber is transmitted to the left, passes through the lens and dichroic filter of the first wavelength division multiplexing-collimator, is collimated and transmitted to the first lens / lens group, and then focused by the first lens / lens group to the saturable absorber mirror;

[0203] The saturable absorber mirror is located on the focal plane of the focused beam, providing a pulse formation mechanism—filtering out high-intensity laser signals from noise to generate pulsed lasers;

[0204] Step S4 Pulse Laser Amplification: The pulse laser is reflected to the right by the saturable absorber mirror, and then transmitted to the gain fiber through the first lens / lens group and the first wavelength division multiplexing-collimator. At this time, the gain fiber amplifies the signal laser and suppresses the noise, resulting in an amplified pulse laser.

[0205] Step S5 Pulse Laser Output: The amplified pulse laser passes through the lens and dichroic filter of the second wavelength division multiplexing-collimator, is collimated to free space, and continues to propagate to the right;

[0206] The pulse output from the second wavelength division multiplexing-collimator undergoes dispersion compensation via a dispersion compensator, narrowing the pulse width, before being transmitted to the laser output coupling mirror. The laser light is simultaneously reflected and transmitted on the front surface of the laser output coupling mirror, with a small portion transmitted as the output laser. The remaining portion is reflected by the laser output coupling mirror and continues to propagate left within the cavity, passing through the dispersion compensator and the second wavelength division multiplexing-collimator. The pulse receives further dispersion compensation at the dispersion compensator and is then efficiently coupled to the gain fiber via the second wavelength division multiplexing-collimator. The pulse is amplified again in the gain fiber and continues to propagate left, completing one laser transmission cycle.

[0207] like Figure 12 As shown, this includes devices 19-27 and more. The specific names and parameters of these devices are as follows:

[0208] Device 19: Semiconductor saturable absorber mirror (SESAM); Parameters: Modulation depth 18%, saturation flux 100 μJ / cm 2 Relaxation time is 9 ps.

[0209] Device 20: Convex lens; Parameter: Focal length 6mm.

[0210] Device 21: Beveled end face; Parameter: Bevel angle is 8°.

[0211] Device 22: Yb-doped fiber; Parameters: Fiber length ~4.5cm, absorption coefficient 2400dB / m@976nm, mode field diameter 5μm@1060nm.

[0212] Device 23: Passive optical fiber; Model: HI1060, Length > 20cm.

[0213] Device 24: Laser diode; wavelength 976 nm, maximum output power 900 mW.

[0214] Device 25: Wavelength division multiplexer-collimator; parameters: reflective wavelength 970-980 nm, transmissive wavelength 1010-1100 nm, collimation distance 110 mm.

[0215] Device 26: Grating; parameters: 1000 lines / mm, incident angle 28-33°.

[0216] Device 26': Identical with device 26; two pieces of grating are placed in parallel, and the distance between the two grating pairs is 1 mm.

[0217] Device 27: Coupling output mirror; parameters: wavelength 1000-1100 nm, transmittance ≤5%, reflectance ≥95%.

[0218] The working process of the embodiment includes coupling process and mode-locking adjustment process:

[0219] Coupling process: according to the following steps Figure 12 After installing all the devices, the distance between device 20 and device 21 is between 1.1-1.4 times of focal length. The output power of device 24 is adjusted to be below 50 mW. Device 19 is placed on the focal plane of the image side, and the θ-φ direction of device 19 is adjusted so that the reflected light returns to device 21, and the adjustment is completed when the output light power of device 25 is maximum. The light output from device 25 is incident to device 26 at an angle of 28°-33°, and device 26 and 26' are placed in parallel with a vertical distance of about 1 mm. Device 27 is adjusted so that the reflected light returns to device 25, and the output power is adjusted to be maximum, and the coupling process is completed.

[0220] Mode-locking adjustment process: the pump power is adjusted to be above 600 mW, and pulse sequence is observed from device 27 by using an oscilloscope, and mode-locked spectrum is observed by using a spectrometer.

[0221] The experimental results obtained by using the working process of the embodiment are as follows:

[0222] As shown in Figure 13 , the output results are measured from the output port of device 27. Among them, Figure 13 (a) is the output spectrum under different powers, and the color gradually changes from gray to black, which represents the process of gradually increasing pump power, and the insert shows the output spectrum width under different powers. Figure 13(b) The autocorrelation curve of the directly output pulse (black solid line) and the dechirped pulse (gray solid line) are shown, the different color dashed lines represent the Gaussian fitting curves of the two pulses respectively; the directly output pulse width is 128 fs, and the corresponding Gaussian electric field intensity half width is 90.5 fs; the dechirped pulse width is 116 fs, and the corresponding Gaussian electric field intensity half width is 82 fs. Figure 13 (c) The measured pulse sequence is shown, and the pulse interval is about 925 ps. Figure 13 (d) The measured radio frequency spectrum is shown, and the corresponding repetition frequency is about 1.08 GHz, and the measured resolution bandwidth is 1 kHz; the inserted figure shows the radio frequency spectrum with a frequency range of 26.5 GHz, and the resolution bandwidth is 10 kHz.

[0223] According to the disclosure and teaching of the above description, those skilled in the art of the present application can also make changes and modifications to the above embodiments. Therefore, the present application is not limited to the specific embodiments disclosed and described above, and some modifications and changes of the application should fall within the protection scope of the claims of the present application. In addition, although some specific terms are used in the specification, these terms are only for convenience of explanation and do not constitute any limitation on the application.

Claims

1. A fiber laser structure, characterized by, The resonant cavity structure comprises a saturable absorber mirror (1), a first lens / lens group (2), a gain fiber (4), a second lens / lens group (6), a dispersion compensator (7) and a laser output coupling mirror (8). The resonant cavity structure comprises a saturable absorber mirror (1), a first lens / lens group (2), a gain fiber (4), a second lens / lens group (6), a dispersion compensator (7) and a laser output coupling mirror (8). The pump source (10) is transmitted to the wavelength division multiplexing-collimator (9) through the passive optical fiber (11), and the wavelength division multiplexing-collimator (9) is connected with the gain fiber (4) to enter the inside of the resonant cavity structure. The gain fiber (4) is a waveguide structure, which is used for generating amplified spontaneous emission light ASE, transmitting laser and amplifying laser. The first lens / lens group (2) is used for converging the light signal output by the gain fiber (4) on the saturable absorber mirror (1). The saturable absorber mirror (1) is used for filtering out high-intensity signal laser from noise to form a pulse and reflect the pulse laser. The second lens / lens group (6) is used for collimating or converging the light signal output by the gain fiber (4) to the laser output coupling mirror (8). The dispersion compensator (7) is used for dispersion compensation of the light signal. The laser output coupling mirror (8) is used for transmitting and reflecting the light signal, and the transmitted light signal is used as output laser, and the reflected light signal enters the resonant cavity structure to continue oscillation. The length of the gain fiber (4) is 4.5 cm, the absorption coefficient is 2400 dB / m@976 nm, and the mode field diameter is 5 μm@1060 nm. The dispersion compensator (7) adopts a pair of parallel grating pairs, the parallel grating pairs have a vertical distance of 1 mm, the grating parameters are 1000 lines / mm, and the incident angle is 2833°. The wavelength division multiplexing-collimator (9) comprises a fiber ferrule (12), a third lens / lens group (13) and a dichroic filter (14), wherein: The fiber ferrule (12) is used for fixing the passive optical fiber (11) and the gain fiber (4); The third lens / lens group (13) is used for collimating the pump light output by the passive optical fiber (11) and the laser output by the gain fiber (4); The dichroic filter (14) is used for reflecting and coupling the pump light collimated by the third lens / lens group (13) into the gain fiber (4), and transmitting the laser collimated by the third lens / lens group (13) to the free space; When the wavelength division multiplexing-collimator (9) is connected with the right fiber end face (5), The original pump light of the pump source (10) is transmitted to the wavelength division multiplexing-collimator (9) through the passive optical fiber (11), and then reflected at the dichroic filter (14) and transmitted to the gain fiber (4), so that the gain fiber (4) realizes population inversion and obtains amplified spontaneous emission light ASE; The ASE generated by the gain fiber (4) is transmitted to the left through the left fiber end face (3) and the first lens / lens group (2) to converge on the saturable absorber mirror (1); the saturable absorber mirror (1) filters out high-intensity signal laser from noise to form pulse laser; The pulse laser with improved signal-to-noise ratio is transmitted to the right through the saturable absorber mirror (1), focused to the left fiber end face (3) again through the first lens / lens group (2), and then coupled into the gain fiber (4), at this time, the gain fiber (4) amplifies the pulse laser and suppresses the noise, and the amplified pulse laser is obtained; The amplified pulse laser is collimated to the free space through the third lens / lens group (13) and the dichroic filter (14), and continues to be transmitted to the right to the dispersion compensator (7); The dispersion compensation is performed on the dispersion compensator (7), the pulse width is narrowed, and then transmitted to the laser output coupling mirror (8); The pulse laser is reflected and transmitted on the front surface of the laser output coupling mirror (8), a small part of light is transmitted as output laser, and the remaining part is reflected and continues to be transmitted to the left in the cavity, and then passes through the dispersion compensator (7) and the wavelength division multiplexing-collimator (9) in sequence; Among them, the reflected pulse continues to be dispersion compensated in the dispersion compensator (7), and then coupled into the gain fiber (4) through the wavelength division multiplexing-collimator (9), and amplified again in the gain fiber (4), and continues to be transmitted to the left, completing a laser transmission cycle.

2. A fiber laser structure, characterized by The resonant cavity structure and the pump source (10) are included, the pump source is connected with the resonant cavity structure through the wavelength division multiplexing-collimator; The resonant cavity structure includes the saturable absorber mirror (1), the first lens / lens group (2), the gain fiber (4), the second lens / lens group (6), the dispersion compensator (7) and the laser output coupling mirror (8); The pump source (10) is transmitted to the wavelength division multiplexing-collimator (9) through the passive optical fiber (11), the wavelength division multiplexing-collimator (9) is connected with the gain fiber (4) to enter the resonant cavity structure, wherein: The gain fiber (4) is a waveguide structure, used for generating amplified spontaneous emission light ASE, transmitting laser and amplifying laser; The first lens / lens group (2) is used for converging the light signal output by the gain fiber (4) on the saturable absorber mirror (1); The saturable absorber mirror (1) is used for screening high-intensity signal laser from noise, thereby forming a pulse and reflecting the pulse laser; The second lens / lens group (6) is used for collimating or converging the light signal output by the gain fiber (4) to the laser output coupling mirror (8); The dispersion compensator (7) is used for dispersion compensation of the light signal; The laser output coupling mirror (8) is used for transmitting and reflecting the light signal, the transmitted light signal is used as output laser, and the reflected light signal enters the resonant cavity structure to continue oscillation; The length of the gain fiber (4) is 4.5cm, the absorption coefficient is 2400dB / m@976nm, and the mode field diameter is 5μm@1060nm; The dispersion compensator (7) adopts a pair of parallel grating pairs, the parallel grating pairs have a vertical distance of 1mm, the grating parameters are 1000 lines / mm, and the incident angle is 2833°; The wavelength division multiplexing-collimator (9) includes the fiber ferrule (12), the third lens / lens group (13) and the dichroic filter (14), wherein: The optical fiber ferrule (12) is used for fixing the passive optical fiber (11) and the gain optical fiber (4); The third lens / lens group (13) is used for collimating the pump light output by the passive optical fiber (11) and the laser output by the gain optical fiber (4); The dichroic filter (14) is used for reflecting the pump light collimated by the third lens / lens group (13) and coupling into the gain optical fiber (4), and transmitting the laser collimated by the third lens / lens group (13) to free space; When the wavelength division multiplexing-collimator (9) is connected with the left optical fiber end face (3), The original pump light of the pump source (10) is transmitted to the wavelength division multiplexing-collimator (9) through the passive optical fiber (11), and then reflected at the dichroic filter (14) and transmitted to the gain optical fiber (4), so that the gain optical fiber (4) realizes population inversion and obtains amplified spontaneous emission light (ASE); The ASE generated by the gain optical fiber (4) is also transmitted to the left, and then collimated and transmitted to the first lens / lens group (2) through the third lens / lens group (13) and the dichroic filter (14) and converged to the saturable absorber mirror (1); the noise is filtered out at the saturable absorber mirror (1) to obtain high-intensity signal laser, forming pulsed laser; The pulsed laser with improved signal-to-noise ratio is reflected to the right through the saturable absorber mirror (1), and then transmitted to the gain optical fiber (4) through the first lens / lens group (2) and the wavelength division multiplexing-collimator (9) again, at this time the gain optical fiber (4) amplifies the pulsed laser signal and suppresses the noise to obtain amplified laser signal; The amplified laser signal is collimated to free space or converged to the front surface of the laser output coupling mirror (8) through the right optical fiber end face (5) and the second lens / lens group (6), depending on the distance between the right optical fiber end face (5) and the second lens / lens group (6); The signal is transmitted to the right to the dispersion compensator (7), and the dispersion compensator (7) performs dispersion compensation, narrows the pulse width, and then transmits to the laser output coupling mirror (8); The pulsed laser is reflected and transmitted at the front surface of the laser output coupling mirror (8), a small part of which is transmitted as output laser; the remaining part is reflected and continues to transmit to the left in the cavity, and then transmits to the left to the gain optical fiber (4) through the dispersion compensator (7), the second lens / lens group (6) and the right optical fiber end face (5) in sequence, and the laser pulse signal is amplified again in the gain optical fiber (4) to continue to transmit to the left, completing a laser transmission cycle.

3. A fiber laser structure, characterized by The resonant cavity structure and the pump source are connected through the wavelength division multiplexing-collimator; The resonant cavity structure includes a saturable absorber mirror (1), a first lens / lens group (2), a gain optical fiber (4), a second lens / lens group (6), a dispersion compensator (7) and a laser output coupling mirror (8); The pump source is transmitted to the wavelength division multiplexing-collimator through the passive optical fiber, and the wavelength division multiplexing-collimator is connected with the gain optical fiber (4) to enter the inside of the resonant cavity structure, wherein: The gain optical fiber (4) is a waveguide structure, which is used for generating amplified spontaneous emission light (ASE), transmitting laser and amplifying laser. The first lens / lens group (2) is used for converging the light signal output by the gain optical fiber (4) onto the saturable absorber mirror (1); The saturable absorber mirror (1) is used for filtering out high-intensity signal laser from noise, thereby forming a pulse and reflecting the pulse laser; The second lens / lens group (6) is used for collimating or converging the light signal output by the gain optical fiber (4) onto the laser output coupling mirror (8); The dispersion compensator (7) is used for dispersion compensation of the light signal; The laser output coupling mirror (8) is used for transmitting and reflecting the light signal, the transmitted light signal is used as output laser, and the reflected light signal enters the resonant cavity structure to continue oscillation; The fiber length of the gain optical fiber (4) is 4.5 cm, the absorption coefficient is 2400 dB / m@976 nm, and the mode field diameter is 5 μm@1060 nm; The dispersion compensator (7) adopts a pair of parallel gratings, the parallel grating pair has a vertical distance of 1 mm, and the grating parameters are 1000 lines / mm and an incident angle of 2833°; The wavelength division multiplexer-collimator includes a fiber stub (12), a third lens / lens group (13), and a dichroic filter (14), wherein: The fiber stub (12) is used for fixing the passive optical fiber and the gain optical fiber (4); The third lens / lens group (13) is used for collimating the pump light output by the passive optical fiber and the laser output by the gain optical fiber (4); The dichroic filter (14) is used for reflecting and coupling the pump light collimated by the third lens / lens group (13) into the gain optical fiber (4), and transmitting the laser collimated by the third lens / lens group (13) to free space; It also includes two first wavelength division multiplexer-collimators (9), a second wavelength division multiplexer-collimator (9'), a first pump source (10), and a second pump source (10'); The first wavelength division multiplexer-collimator (9) is connected with the left fiber end face (3), and the second wavelength division multiplexer-collimator (9') is connected with the right fiber end face (5) at the same time, The first pump source (10) and the second pump source (10') both generate original pump light, which is transmitted to the first wavelength division multiplexer-collimator (9) and the second wavelength division multiplexer-collimator (9') through the first passive optical fiber (11) and the second passive optical fiber (11') respectively; The reflection occurs on the dichroic filter (14) of the first wavelength division multiplexer-collimator (9) and the second wavelength division multiplexer-collimator (9'), and the two are jointly transmitted to the gain optical fiber (4), so that the gain optical fiber (4) realizes population inversion and obtains amplified spontaneous emission light ASE; The ASE generated by the gain optical fiber (4) is transmitted to the left, passes through the lens and the dichroic filter (14) of the first wavelength division multiplexer-collimator (9), is collimated and transmitted to the first lens / lens group (2), and then is focused by the first lens / lens group (2) 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 to filter out high-intensity signal laser from noise, thereby generating pulse laser; The pulse laser reflected by the saturable absorption mirror (1) transmits to the right, and then transmits to the gain optical fiber (4) through the first lens / lens group (2) and the first wavelength division multiplexing-collimator (9) again, at this time, the gain optical fiber (4) amplifies the signal laser and suppresses the noise, and the amplified pulse laser is obtained; The amplified pulse laser is collimated to the free space through the lens of the second wavelength division multiplexing-collimator (9') and the dichroic filter (14), and continues to transmit to the right; The pulse output from the second wavelength division multiplexing-collimator (9') is color dispersion compensated by the color dispersion compensator (7), the pulse width is narrowed, and then transmitted to the laser output coupling mirror (8); the laser is reflected and transmitted on the front surface of the laser output coupling mirror (8) at the same time, a small part of light is transmitted as output laser; the remaining part is reflected by the laser output coupling mirror (8) and continues to transmit to the left in the cavity, and then passes through the color dispersion compensator (7) and the second wavelength division multiplexing-collimator (9') in sequence; wherein, the pulse continues to be color dispersion compensated by the color dispersion compensator (7), and then is coupled to the gain optical fiber (4) by the second wavelength division multiplexing-collimator (9') efficiently, the pulse is amplified again in the gain optical fiber (4), and continues to transmit to the left, completing a laser transmission cycle.

4. A method of laser generation using the fiber laser structure according to claim 1, characterized in that, The method comprises the following steps: Step S1: original pump light generation: the pump source (10) generates original pump light which is transmitted to the wavelength division multiplexing-collimator (9) through the passive optical fiber (11); Step S2: spontaneous emission light generation: the original pump light is reflected by the dichroic filter (14) and transmitted to the gain optical fiber (4), so that the gain optical fiber (4) realizes population inversion and obtains amplified spontaneous emission light ASE; Step S3: pulse laser generation: the ASE generated by the gain optical fiber (4) transmits to the left through the left optical fiber end face (3) and the first lens / lens group (2) and converges on the saturable absorption mirror (1); the noise is filtered out in the saturable absorption mirror (1), and high-intensity signal laser is screened out to form pulse laser; Step S4: pulse laser amplification: the pulse laser with improved signal-to-noise ratio transmits to the right through the saturable absorption mirror (1), and is focused to the left optical fiber end face (3) through the first lens / lens group (2) and then coupled into the gain optical fiber (4) again, at this time, the gain optical fiber (4) amplifies the pulse laser and suppresses the noise, and the amplified pulse laser is obtained; Step S5: pulse laser output: the amplified pulse laser is collimated to the free space through the third lens / lens group (13) and the dichroic filter (14), and continues to transmit to the right to the color dispersion compensator (7); The color dispersion compensator (7) is color dispersion compensated, the pulse width is narrowed, and then transmitted to the laser output coupling mirror (8); The pulse laser is reflected and transmitted on the front surface of the laser output coupling mirror (8) at the same time, a small part of light is transmitted as output laser; the remaining part is reflected and continues to transmit to the left in the cavity, and then passes through the color dispersion compensator (7) and the wavelength division multiplexing-collimator (9) in sequence; Wherein, the reflected pulse continues to be dispersion compensated in the dispersion compensator (7), and then is coupled to the gain fiber (4) through the wavelength division multiplexer-collimator (9), is amplified again in the gain fiber (4), continues to keep leftward transmission, and completes a laser transmission cycle.

5. A method of laser generation, using the fiber laser structure according to claim 2, characterized in that, The method comprises the following steps: Step S1: original pump light generation: the original pump light of the pump source (10) is transmitted to the wavelength division multiplexer-collimator (9) through the passive optical fiber (11); Step S2: spontaneous emission light generation: the original pump light is reflected at the dichroic filter (14), is transmitted to the gain fiber (4), and thus the gain fiber (4) realizes population inversion, and obtains amplified spontaneous emission light ASE; Step S3: pulse laser generation: the ASE generated by the gain fiber (4) also transmits leftward, collimates and transmits to the first lens / lens group (2) through the third lens / lens group (13) and the dichroic filter (14), and converges to the saturable absorber mirror (1); noise is filtered out at the saturable absorber mirror (1), high-intensity signal laser is screened out, and pulse laser is generated; Step S3: pulse laser amplification: the pulse laser is reflected rightward through the saturable absorber mirror (1), transmits to the gain fiber (4) again through the first lens / lens group (2) and the wavelength division multiplexer-collimator (9), at this time, the gain fiber (4) amplifies the pulse laser signal, suppresses noise at the same time, and obtains amplified laser signal; Step S4: pulse laser output: the amplified laser signal collimates to free space or converges to the front surface of the laser output coupling mirror (8) through the right optical fiber end face (5) and the second lens / lens group (6); Transmits rightward to the dispersion compensator (7), is dispersion compensated in the dispersion compensator (7), the pulse width is narrowed, and then transmits to the laser output coupling mirror (8); The pulse laser is reflected and transmitted at the front surface of the laser output coupling mirror (8) at the same time, wherein a part of light is transmitted as output laser; the remaining part is reflected, continues to transmit leftward in the cavity, then transmits leftward to the gain fiber (4) through the dispersion compensator (7), the second lens / lens group (6) and the right optical fiber end face (5) in sequence, the laser pulse signal is amplified again in the gain fiber (4), continues to keep leftward transmission, and completes a laser transmission cycle.

6. A method of laser generation, using the fiber laser structure according to claim 3, characterized in that, The method comprises the following steps: Step S1: original pump light generation: the first pump source (10) and the second pump source (10') both generate original pump light, which is transmitted to the first wavelength division multiplexer-collimator (9) and the second wavelength division multiplexer-collimator (9') through the first passive optical fiber (11) and the second passive optical fiber (11') respectively; Step S2: spontaneous emission light generation: the original pump light is reflected at the dichroic filter (14) of the first wavelength division multiplexer-collimator (9) and the second wavelength division multiplexer-collimator (9'), and is transmitted to the gain fiber (4) together, so that the gain fiber (4) realizes population inversion, and obtains amplified spontaneous emission light ASE; Step S3: pulse laser generation: the ASE generated by the gain fiber (4) also transmits leftward, collimates and transmits to the first lens / lens group (2) through the third lens / lens group (13) and the dichroic filter (14), and converges to the saturable absorber mirror (1); noise is filtered out at the saturable absorber mirror (1), high-intensity signal laser is screened out, and pulse laser is generated; Step S3: pulse laser amplification: the pulse laser is reflected rightward through the saturable absorber mirror (1), transmits to the gain fiber (4) again through the first lens / lens group (2) and the wavelength division multiplexer-collimator (9), at this time, the gain fiber (4) amplifies the pulse laser signal, suppresses noise at the same time, and obtains amplified laser signal; Step S4: pulse laser output: the amplified laser signal collimates to free space or converges to the front surface of the laser output coupling mirror (8) through the right optical fiber end face (5) and the second lens / lens group (6); Transmits rightward to the dispersion compensator (7), is dispersion compensated in the dispersion compensator (7), the pulse width is narrowed, and then transmits to the laser output coupling mirror (8); The pulse laser is reflected and transmitted at the front surface of the laser output coupling mirror (8) at the same time, wherein a part of light is transmitted as output laser; the remaining part is reflected, continues to transmit leftward in the cavity, then transmits leftward to the gain fiber (4) through the dispersion compensator (7), the second lens / lens group (6) and the right optical fiber end face (5) in sequence, the laser pulse signal is amplified again in the gain fiber (4), continues to keep leftward transmission, and completes a laser transmission cycle. Step S3: Pulse laser generation: the ASE generated by the gain fiber is transmitted to the left, collimated by the lens and dichroic filter (14) of the first wavelength division multiplexer-collimator (9), and focused by the first lens / lens group (2) 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 to filter out high-intensity signal laser from noise, thereby generating pulse laser; Step S4: Pulse laser amplification: the pulse laser is reflected to the right by the saturable absorber mirror (1), and transmitted again to the gain fiber (4) through the first lens / lens group (2) and the first wavelength division multiplexer-collimator (9), at which time the gain fiber (4) amplifies the signal laser while suppressing noise, obtaining amplified pulse laser; Step S5: Pulse laser output: the amplified pulse laser is collimated by the lens and dichroic filter (14) of the second wavelength division multiplexer-collimator (9') to free space and continues to transmit to the right; The pulse output from the second wavelength division multiplexer-collimator (9') is color dispersion compensated by the color dispersion compensator (7), the pulse width is narrowed, and then transmitted to the laser output coupling mirror (8); the laser is reflected and transmitted at the same time on the front surface of the laser output coupling mirror (8), a small part of the light is transmitted as output laser; the remaining part is reflected by the laser output coupling mirror (8) and continues to transmit to the left in the cavity, then passes through the color dispersion compensator (7) and the second wavelength division multiplexer-collimator (9') in turn; among them, the pulse continues to be color dispersion compensated by the color dispersion compensator (7), and then is coupled to the gain fiber (4) by the second wavelength division multiplexer-collimator (9') with high efficiency, the pulse is amplified again in the gain fiber (4) and continues to transmit to the left, completing a laser transmission cycle.

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