CN119381878B - Optical fiber laser structure and laser generation method - Google Patents
Optical fiber laser structure and laser generation methodInfo
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- CN119381878B CN119381878B CN202411592719.9A CN202411592719A CN119381878B CN 119381878 B CN119381878 B CN 119381878B CN 202411592719 A CN202411592719 A CN 202411592719A CN 119381878 B CN119381878 B CN 119381878B
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/35—Non-linear optics
- G02F1/365—Non-linear optics in an optical waveguide structure
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
- H01S3/06—Construction or shape of active medium
- H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
- H01S3/067—Fibre lasers
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
- H01S3/08—Construction or shape of optical resonators or components thereof
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/09—Processes or apparatus for excitation, e.g. pumping
- H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
- H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
- H01S3/094049—Guiding of the pump light
- H01S3/094053—Fibre coupled pump, e.g. delivering pump light using a fibre or a fibre bundle
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
- H01S3/10007—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating in optical amplifiers
- H01S3/10023—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating in optical amplifiers by functional association of additional optical elements, e.g. filters, gratings, reflectors
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
- H01S3/11—Mode locking; Q-switching; Other giant-pulse techniques, e.g. cavity dumping
- H01S3/1106—Mode locking
- H01S3/1112—Passive mode locking
- H01S3/1115—Passive mode locking using intracavity saturable absorbers
- H01S3/1118—Semiconductor saturable absorbers, e.g. semiconductor saturable absorber mirrors [SESAMs]; Solid-state saturable absorbers, e.g. carbon nanotube [CNT] based
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- Materials Engineering (AREA)
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- Lasers (AREA)
Abstract
The optical fiber laser structure comprises a resonant cavity structure and a pump source, wherein the pump source is connected with the resonant cavity structure in a matched mode through a wavelength division multiplexing-collimator, the resonant cavity structure is provided with a saturable absorber mirror, 2 lenses/lens groups, a gain optical fiber, a dispersion compensator and a laser output coupling mirror, the gain optical fiber is of a waveguide structure and is used for generating Amplified Spontaneous Emission (ASE), transmitting laser and amplifying laser, the saturable absorber mirror is used for screening out signal laser from noise, the dispersion compensator is used for carrying out dispersion compensation on optical signals, the laser output coupling mirror is used for transmitting and reflecting the optical signals, the transmitted optical signals are used as output laser, and the reflected optical signals continue to enter the resonant cavity structure. The pump source enters the resonant cavity structure through the wavelength division multiplexing-collimator to generate and output high-quality, high-stability and easy-to-integrate GHz femtosecond laser.
Description
Technical Field
The invention relates to the field of lasers, in particular to a fiber laser structure and a laser generating method.
Background
The femtosecond pulse laser technology is used as a key light source technology, and is widely applied to key fields such as leading edge scientific research, industrial laser precision machining, national defense equipment countermeasure, medical health and the like through rapid development for over forty years. These areas are directly related to the development of countries, technological progress and the living needs of the masses. The application of the femtosecond laser technology remarkably improves the technological innovation capability of China and plays an irreplaceable role in enhancing the international competitiveness.
Recently, high repetition rate GHz femtosecond lasers play a key role in a number of leading-edge scientific fields. For example, the proposal of ablation cooling (ablation cooling) technology opens up a new application prospect for the development of GHz repetition frequency and high-power femtosecond pulse. Experiments prove that the femtosecond laser with the GHz repetition frequency not only has high quality of the traditional femtosecond laser processing, but also has the processing efficiency which can be compared with nanosecond laser. The ablation cooling technology based on GHz femtosecond laser can fill the short plate with low throughput in the industrial application of femtosecond laser processing, and has great research significance on the processing of hard/brittle materials.
In order to realize high-efficiency and high-precision 'ablation cooling' laser processing, the high-repetition-frequency GHz femtosecond laser output is firstly obtained. Some manufacturers acquire GHz pulses by adopting an extra-cavity repetition frequency multiplication mode, and actually beam-splitting a seed source with a conventional repetition frequency of tens of MHz or hundreds of MHz by the outside of the cavity, so that one path is delayed by time, and beam combination is performed to lift the repetition frequency. The size of the splitting power ratio and time delay needs to be precisely controlled, otherwise, serious power modulation and noise frequency can be generated in subsequent amplification. This approach is a non-trivial example and the system is more complex.
In contrast, it is more reliable to generate GHz femtosecond laser directly from the resonant cavity of fundamental mode locking. The structure of the high-repetition frequency GHz mode-locked fiber laser can be divided into a linear cavity and an annular cavity. Compared with the annular cavity structure, the optical path structure of the linear cavity is simpler and is easy to integrate. The high-repetition-frequency linear cavity fiber laser usually adopts passive mode locking, which can easily realize the mode locking of fundamental frequency continuous waves of more than 3 GHz, and the highest repetition frequency of the current linear cavity laser is 19 GHz.
The existing common semiconductor saturable absorber (SESAM) mode-locked GHz fiber laser structure generally adopts phosphate glass gain fiber with extremely high doping concentration, so that the required gain fiber has extremely short length (a few cm or even <1 cm) to obtain enough gain. In order to further shorten the cavity length, SESAM is usually directly attached to one end of the gain fiber, while another end is coated with a bicolor film (pump wavelength anti-reflection, mode locking laser wavelength high reflection), and in order to increase stability, the fiber is packaged in a ceramic ferrule, so that the pump can be directly connected with the gain fiber through a flange and injected into the gain fiber. The linear cavity fiber laser has the incomparable advantage of high repetition frequency, but the output power is extremely low and is usually below 0.1 mW, and the subsequent amplification system is more difficult. Furthermore, the cavity has no spatial portion, lacks a dispersion compensating element (typically providing a negative dispersion that is several times that of the gain fiber), and therefore the output pulse width is difficult to reach on the order of femtoseconds (typically >3 ps).
Therefore, improvements to the existing linear cavity fiber lasers are needed to improve the quality and stability of the laser.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a fiber laser structure and a laser generating method.
The optical fiber laser structure comprises a resonant cavity structure and a pump source, wherein the pump source is connected with the resonant cavity structure in a matched manner through a wavelength division multiplexing-collimator;
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;
The pump source is transmitted to a wavelength division multiplexing-collimator through a passive optical fiber, the wavelength division multiplexing-collimator is connected with the gain optical fiber and enters the inside of the resonant cavity structure, wherein:
the gain optical fiber is of a waveguide structure and is used for generating Amplified Spontaneous Emission (ASE), transmission laser and amplified laser;
The first lens/lens group is used for converging the optical signals output by the gain optical fiber onto the saturable absorber mirror;
The saturable absorber mirror is used for screening out high-intensity signal laser from noise so as to form pulses and reflect the pulse laser;
The second lens/lens group is used for collimating or converging the optical signals output by the gain optical fiber to the laser output coupling mirror;
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.
Preferably, the gain fiber comprises a left fiber end face and a right fiber end face;
the wavelength division multiplexing-collimator (9) is connected with the left optical fiber end face (3);
or the wavelength division multiplexing-collimator (9) is connected with the right optical fiber end face (5);
or the left optical fiber end face (3) and the right optical fiber end face (5) of the wavelength division multiplexing-collimator (9) are connected at the same time.
Preferably, the wavelength division multiplexing-collimator comprises an optical fiber ferrule, a third lens/lens group and a dichroic filter, wherein:
the optical fiber core insert is used for fixing a passive optical fiber and a gain optical fiber;
The third lens/lens group is used for collimating the pump light output by the passive optical fiber and the laser light output by the gain optical fiber;
the dichroic filter is used for reflecting and coupling the pump light collimated by the third lens/lens group into the gain fiber, and transmitting the laser collimated by the third lens/lens group into free space.
Preferably, when the wavelength division multiplexing-collimator is connected with the end face of the right optical fiber,
The original pump light of the pump source is transmitted to a wavelength division multiplexing-collimator through a passive optical fiber, reflected by a dichroic filter and transmitted to a gain optical fiber, so that the gain optical fiber realizes particle number inversion and amplified spontaneous emission light ASE is obtained;
ASE generated by the gain optical fiber is transmitted leftwards and converged to a saturable absorber mirror through the end face of the left optical fiber and the first lens/lens group;
The pulse laser after noise filtering is transmitted rightwards through a saturable absorber mirror, is focused to the end face of the optical fiber through a first lens/lens group again and is then coupled into a gain optical fiber, at the moment, the gain optical fiber amplifies the pulse laser, and simultaneously suppresses noise to obtain amplified pulse laser;
The amplified pulse laser is quasi-transmitted to the right to a dispersion compensator through a third lens/lens group and a dichroic filter until reaching a free space, the dispersion compensator performs dispersion compensation, the pulse width is narrowed, and then the pulse laser is transmitted to a laser output coupling mirror;
The pulse laser is reflected and transmitted at the front surface of the laser output coupling mirror, wherein a small part of the pulse laser is transmitted as output laser, and the rest part of the pulse laser 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;
The reflected pulse is further subjected to dispersion compensation in the dispersion compensator, is coupled to the gain fiber through the wavelength division multiplexing-collimator, is amplified again in the gain fiber, and is further subjected to left transmission, so that a laser transmission period is completed.
Preferably, when the wavelength division multiplexing-collimator is connected with the end face of the left optical fiber,
The original pump light of the pump source is transmitted to a wavelength division multiplexing-collimator through a passive optical fiber, reflected by a dichroic filter, transmitted to a gain optical fiber, and subjected to particle number inversion at the gain optical fiber to obtain amplified spontaneous emission light ASE;
The ASE generated by the gain fiber is transmitted leftwards, is collimated and transmitted to the first lens/lens group to be converged to the saturable absorber mirror through the third lens/lens group and the dichroic filter, and is filtered out noise at the saturable absorber mirror to screen out signal laser to form pulse laser;
the pulse laser with the improved signal-to-noise ratio is reflected by the saturable absorber mirror to be transmitted to the right, and is transmitted to the gain fiber through the first lens/lens group and the wavelength division multiplexing-collimator again, at the moment, the gain fiber amplifies the pulse laser signal and simultaneously suppresses noise to obtain an amplified laser signal;
The amplified laser signal is collimated to free space or converged to the front surface of the laser output coupling mirror by the right fiber end face and the second lens/lens group, in which way the laser signal is specifically determined by the distance from the right fiber end face to the second lens/lens group;
Right transmitted to the dispersion compensator, the dispersion compensator performs dispersion compensation, the pulse width is narrowed, and then transmitted to the laser output coupling mirror;
the pulse laser is reflected and transmitted simultaneously on the front surface of the laser output coupling mirror, a small part of the pulse laser is transmitted as output laser, the rest part of the pulse laser is reflected and continuously transmitted to the left in the cavity, then sequentially passes through the dispersion compensator, the second lens/lens group and the right optical fiber end face and is transmitted to the gain optical fiber to the left, the laser pulse signal is amplified again in the gain optical fiber and continuously transmitted to the left, and a laser transmission period is completed.
Preferably, the system further comprises two first wavelength division multiplexing-collimators, a second wavelength division multiplexing-collimator, a first pump and a second pump source;
The first wavelength division multiplexing-collimator is connected with the end face of the left optical fiber, and when the second wavelength division multiplexing-collimator is simultaneously connected with the end face of the right optical fiber,
The first pump source and the second pump source generate original pump light, and the original pump light 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;
then, the two-color filter sheets of the first wavelength division multiplexing-collimator and the second wavelength division multiplexing-collimator are reflected and transmitted to the gain optical fiber together, so that the gain optical fiber realizes the particle number inversion and amplified spontaneous emission ASE is obtained;
ASE generated by the gain fiber is transmitted leftwards, collimated and transmitted to a first lens/lens group through a lens of a first wavelength division multiplexing-collimator and a dichroic filter, and focused to a saturable absorber mirror through the first lens/lens group;
the saturable absorber mirror is positioned on the focal plane of the focused light beam, and a pulse forming mechanism is provided, namely high-intensity signal laser is screened out from noise, so that pulse laser is generated;
The pulse laser reflected by the saturable absorber mirror is transmitted to the right, and is transmitted to the gain fiber through the first lens/lens group and the first wavelength division multiplexing-collimator again, at the moment, the gain fiber amplifies the signal laser, and simultaneously suppresses noise to obtain amplified pulse laser;
the amplified pulse laser passes through a lens of a second wavelength division multiplexing-collimator and a dichroic filter, is collimated to a free space, and is continuously transmitted to the right from the free space;
The pulse output from the second wavelength division multiplexing-collimator is subjected to dispersion compensation through a dispersion compensator, the pulse width is narrowed, and then the pulse is transmitted to a laser output coupling mirror, laser is reflected and transmitted simultaneously on the front surface of the laser output coupling mirror, a small part of the laser is transmitted in a light transmission mode and is used as output laser, the rest of the laser is reflected through the laser output coupling mirror and is continuously transmitted to the left in a cavity, and then the laser passes through the dispersion compensator and the second wavelength division multiplexing-collimator in sequence, wherein the pulse is continuously subjected to dispersion compensation in the dispersion compensator, is then efficiently coupled to a gain fiber through the second wavelength division multiplexing-collimator, is amplified again in the gain fiber, is continuously kept to be transmitted to the left, and a laser transmission period is completed.
The invention provides a laser generating method, which applies the optical fiber laser structure that the wavelength division multiplexing-collimator is connected with the right optical fiber end face, and the method comprises the following steps:
s1, generating original pump light, namely transmitting the original pump light generated by the pump source to a wavelength division multiplexing-collimator through a passive optical fiber;
s2, generating spontaneous emission light, namely reflecting original pump light in a dichromatic filter and transmitting the original pump light to a gain optical fiber, so that the gain optical fiber realizes particle number inversion and amplified spontaneous emission light ASE is obtained;
Step S3, pulse laser is generated, namely ASE generated by the gain optical fiber is transmitted to the left and converged to a saturable absorber mirror through the end face of the left optical fiber and the first lens/lens group;
Step S4, amplifying the pulse laser, namely transmitting the pulse laser with the improved signal-to-noise ratio to the right through a saturable absorber mirror, focusing the pulse laser to the end face of the left optical fiber through a first lens/lens group again, and then coupling the pulse laser into a gain optical fiber, wherein the gain optical fiber amplifies the pulse laser and simultaneously suppresses noise to obtain amplified pulse laser;
S5, outputting pulse laser, namely enabling the amplified pulse laser to pass through a third lens/lens group and a dichroic filter to reach a free space, and continuously transmitting the amplified pulse laser to the right from the free space to a dispersion compensator;
performing dispersion compensation on the dispersion compensator, narrowing pulse width and transmitting to a laser output coupling mirror;
The pulse laser is reflected and transmitted at the front surface of the laser output coupling mirror, wherein a small part of the pulse laser is transmitted as output laser, and the rest part of the pulse laser 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;
The reflected pulse is further subjected to dispersion compensation in the dispersion compensator, is coupled to the gain fiber through the wavelength division multiplexing-collimator, is amplified again in the gain fiber, and is further subjected to left transmission, so that a laser transmission period is completed.
The invention provides a second laser generating method, which applies a fiber laser structure that a wavelength division multiplexing-collimator is connected with the end face of a left fiber, and comprises the following steps:
S1, original pump light of a pump source is generated, wherein the original pump light of the pump source is transmitted to a wavelength division multiplexing-collimator through a passive optical fiber;
s2, generating spontaneous emission light, namely reflecting original pump light in a dichromatic filter and transmitting the original pump light to a gain optical fiber, so that the gain optical fiber realizes particle number inversion and amplified spontaneous emission light ASE is obtained;
step S3, pulse laser is generated, wherein ASE generated by the gain optical fiber is transmitted leftwards as well, and is collimated and transmitted to the first lens/lens group to be converged to the saturable absorber mirror through the third lens/lens group and the dichroic filter, noise is filtered out at the saturable absorber mirror, and high-intensity signal laser is screened out to generate pulse laser;
Step S3, amplifying pulse laser, namely transmitting the pulse laser to the right through reflection of a saturable absorber mirror, transmitting the pulse laser to a gain optical fiber through a first lens/lens group and a wavelength division multiplexing-collimator again, amplifying a pulse laser signal by the gain optical fiber at the moment, and simultaneously suppressing noise to obtain an amplified laser signal;
s4, outputting pulse laser, namely collimating the amplified laser signal to a free space through the end face of the right optical fiber and a second lens/lens group or converging the amplified laser signal to the front surface of a laser output coupling mirror;
Right transmitted to the dispersion compensator, the dispersion compensator performs dispersion compensation, the pulse width is narrowed, and then transmitted to the laser output coupling mirror;
The pulse laser is reflected and transmitted simultaneously on the front surface of the laser output coupling mirror, a small part of the pulse laser is transmitted and is used as output laser, the rest part of the pulse laser is reflected and continuously transmitted to the left in the cavity, then sequentially passes through the dispersion compensator, the second lens/lens group and the right optical fiber end face and is transmitted to the gain optical fiber to the left, the laser pulse signal is amplified again in the gain optical fiber and continuously transmitted to the left, and a laser transmission period is completed.
The invention also provides a third laser generating method, which applies a fiber laser structure that the wavelength division multiplexing-collimator is connected with the left fiber end face and the right and left fiber end faces at the same time, and the method comprises the following steps:
s1, generating original pump light, namely generating the original pump light by a first pump source and a second pump source, and transmitting the original pump light to a first wavelength division multiplexing-collimator and a second wavelength division multiplexing-collimator through a first passive optical fiber and a second passive optical fiber respectively;
S2, generating spontaneous emission light, namely reflecting the two-color filter sheets of the first wavelength division multiplexing collimator and the second wavelength division multiplexing collimator, and transmitting the two-color filter sheets to a gain optical fiber together, so that the gain optical fiber realizes particle number inversion and amplified spontaneous emission light ASE is obtained;
Step S3, pulse laser is generated, wherein ASE generated by the gain optical fiber is transmitted leftwards, collimated and transmitted to a first lens/lens group through a lens of a first wavelength division multiplexing-collimator and a dichroic filter, and focused to a saturable absorber mirror through the first lens/lens group;
the saturable absorber mirror is positioned on the focal plane of the focused light beam, and a pulse forming mechanism is provided, namely high-intensity signal laser is screened out from noise, so that pulse laser is generated;
Step S4, amplifying pulse laser, namely transmitting the pulse laser to the right through reflection of a saturable absorber mirror, transmitting the pulse laser to a gain optical fiber through a first lens/lens group and a first wavelength division multiplexing-collimator again, amplifying signal laser by the gain optical fiber at the moment, and simultaneously suppressing noise to obtain amplified pulse laser;
s5, outputting pulse laser, namely collimating the amplified pulse laser to a free space through a lens of a second wavelength division multiplexing-collimator and a dichroic filter, and continuing to transmit to the right;
The pulse output from the second wavelength division multiplexing-collimator is subjected to dispersion compensation through a dispersion compensator, the pulse width is narrowed, and then the pulse is transmitted to a laser output coupling mirror, laser is reflected and transmitted simultaneously on the front surface of the laser output coupling mirror, a small part of the laser is transmitted in a light transmission mode and is used as output laser, the rest of the laser is reflected through the laser output coupling mirror and is continuously transmitted to the left in a cavity, and then the laser passes through the dispersion compensator and the second wavelength division multiplexing-collimator in sequence, wherein the pulse is continuously subjected to dispersion compensation in the dispersion compensator, is then efficiently coupled to a gain fiber through the second wavelength division multiplexing-collimator, is amplified again in the gain fiber, is continuously kept to be transmitted to the left, and a laser transmission period is completed.
The beneficial effects of the invention are as follows:
The original pump light of the pump source enters the resonant cavity structure through the wavelength division multiplexing-collimator, the resonant cavity structure is provided with the saturable absorber mirror, the multiple groups of lenses/lens groups, the gain optical fiber, the dispersion compensator and the laser output coupling mirror, and laser signals are continuously screened and amplified under the cooperation of the components, so that the GHz femtosecond laser with high quality, high stability and easy integration is generated and output.
Drawings
FIG. 1 is a schematic diagram of a resonant cavity structure of the present invention;
FIG. 2 is a schematic structural diagram of embodiment 1 of the present invention;
FIG. 3 is a schematic diagram of a wavelength division multiplexing-collimator according to the present invention;
FIG. 4 is a schematic structural diagram of embodiment 2 of the present invention;
FIG. 5 is a schematic structural diagram of embodiment 3 of the present invention;
FIG. 6 is a schematic diagram of three cases where a divergent point source is imaged by a single convex lens;
FIG. 7 is a schematic diagram of a divergent point source imaged by two convex lenses;
FIG. 8 illustrates three ways of arranging a saturable absorber in a resonant cavity structure;
FIG. 9 is a graph showing the variation of w0'/w0 with s/f;
FIG. 10 is a graph showing the variation of ZR' with s/f;
FIG. 11 is a graph showing the variation of (s+s')/f with s/f;
FIG. 12 is a schematic view of the structure of example 6;
FIG. 13 shows the results of the experimental work of the structure of example 6.
Detailed Description
The present invention will be further described in detail with reference to the following examples, for the purpose of making the objects, technical solutions and advantages of the present invention more apparent, but the scope of the present invention is not limited to the following specific examples.
A fiber laser structure according to this embodiment is described in detail below.
The optical fiber laser structure comprises a resonant cavity structure and a pump source 10, wherein the pump source 10 is connected with the resonant cavity structure in a matching way through a wavelength division multiplexing-collimator 9;
As shown in fig. 1, the resonant cavity comprises a saturable absorber mirror 1, a first lens/lens group 2, a gain fiber 4, a second lens/lens group 6, a dispersion compensator 7 and a laser output coupling mirror 8;
The pump source 10 is transmitted to the wavelength division multiplexing-collimator 9 through the passive optical fiber 11, the wavelength division multiplexing-collimator 9 is connected with the gain optical fiber 4 and enters the inside of the resonant cavity structure, wherein:
the pump source 10 is a laser diode for generating the original pump light and activating the inversion particles of the gain fiber 4 by the original pump light.
The gain optical fiber 4 is of a waveguide structure and is used for generating Amplified Spontaneous Emission (ASE), transmission laser and amplified laser, and the length of the gain optical fiber is less than 10 cm;
The first lens/lens group 2 is used for converging the optical signals output by the gain optical fiber 4 onto the saturable absorber mirror 1;
The saturable absorber mirror 1 is used for screening signal laser from noise so as to form pulses and reflect the pulse laser, the saturable absorber mirror 1 has high absorptivity to low-intensity laser and low absorptivity to high-intensity laser so as to screen the signal from the noise, and the saturable absorber mirror is used for providing an ultrafast pulse forming mechanism for a laser and assisting the laser to lock modes.
The second lens/lens group 6 is used for collimating or converging the optical signals output by the gain fiber 4 to the laser output coupling mirror 8;
the dispersion compensator 7 is used for performing dispersion compensation on the optical signal and is used for providing negative group delay dispersion for the laser.
The laser output coupling mirror 8 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.
Specifically, the gain fiber 4 includes a left fiber end face 3 and a right fiber end face 5;
the wavelength division multiplexing-collimator 9 is connected with the left optical fiber end face 3;
or the wavelength division multiplexing-collimator 9 is connected with the right optical fiber end face 5;
Or the left optical fiber end face 3 and the right optical fiber end face 5 of the wavelength division multiplexing-collimator 9 are connected at the same time.
The wavelength division multiplexing-collimator 9 comprises an optical fiber ferrule 12, a third lens/lens group 13 and a 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 light output by the gain optical fiber 4;
The dichroic filter 14 is configured to reflect and couple the pump light collimated by the third lens/lens group 13 into the gain fiber 4, and transmit the laser light collimated by the third lens/lens group 13 into free space.
Wherein the first lens/lens group 2 and the second lens/lens group 6 may be single lenses or double lenses, wherein the principle of the single lenses for realizing the beam transformation is as follows:
1983. over the years SIDNEY SELF developed a formula for calculating the transformation of a gaussian beam through a thin lens:
Wherein the method comprises the steps of AndThe distances of the incoming beam waist and the outgoing beam waist to the lens,For the focal length of the lens,For rayleigh distance of incident beam, i.e. beam from beam waist radius to increaseThe distance taken by the beam waist radius is also referred to as the "collimation" distance.
Wherein, the Is the waist radius of the incident beam,Is the wavelength of light.
From the following can be derivedIs represented by the expression:
The expansion (contraction) multiple of the radius of the emergent beam waist is as follows:
In the formula, For output beam waist radius, the expression is:
the rayleigh distance for output light is:
Taking the left side of the gain fiber of fig. 1 as an example, when the first lens/lens group 2 is a single convex lens, the single lens can focus the divergent light beam output from the end face 3 of the left fiber to the saturable absorber mirror 1.
According to the principle of convex lens imaging, there are three general cases in which a divergent point light source is transmitted through a single convex lens. The incident point light sources can be classified according to their positions on the optical axis of the lens as shown in fig. 6.
From fig. 6, the following can be concluded:
The incident point light source is within one focal length (F position), the emergent light diverges and has no beam waist (shown by gray arrow), and when the incident point light source is positioned at F, the output light is collimated (shown by black arrow).
When the incident point light source is between F and 2F, the emergent light is converged outside the double focal length (2F), the closer the point light source is to the F position, the farther the image point is from the 2F position, the larger the emergent light beam waist radius is, and when s=2f, s' =2f;
When the incident point light source is out of the 2F position, emergent light is converged between F and 2F, and the farther the point light source is away from the 2F position, the closer the image point is to the F position, and the smaller the emergent light beam waist radius is.
The lens/lens group, whether single or double lens, is intended to focus the beam emanating from one device into the other. By selecting a proper lens/lens group, the light spot at the emergent position is matched with the light spot at the focusing position and the divergence angle. In particular, when coupling from the end face of one fiber to the end face of another fiber, the mode fields can be matched by selecting the appropriate lens/lens group.
The principle of double-lens imaging is as follows:
as shown in fig. 7, the two lens system includes two convex lenses, so that the point light source diverged from D1 is transmitted rightward to be focused at D2. The two lenses, denoted F1 and F2, function to collimate the divergent light and focus the collimated light, respectively. Collimation and focusing are reciprocal processes, which can be described by the following equation:
Wherein the method comprises the steps of AndThe beam waist diameters of the collimated light beams respectively,As a function of the wavelength(s),AndThe focal lengths of the collimating lens and the focusing lens respectively,AndThe waist diameters of the incident light and the outgoing light, respectively. In particular, when the focal planes of F1 and F2 are both fiber end faces,AndThe mode field diameters of the two fibers, respectively.
When the condition is satisfied:
when the coupling efficiency is highest, a proper lens focal length is selected according to the condition.
In the resonator structure depicted in fig. 1, the diverging beam exiting the left fiber end face 3 needs to be focused onto the saturable absorber mirror 1, and the efficiency of reflection back to the fiber end face is high to achieve mode locking of the resonator.
Three methods can be implemented, the specific method is as follows:
As shown in fig. 8, in the dual-lens system, divergent light output by the left optical fiber end face 3 is collimated by the lens f1, focused by the lens f2 to the saturable absorber mirror 1, reflected by the saturable absorber mirror 1, and coupled back to the left optical fiber end face 3 by two lenses. This way of using two lenses, first collimation and then focusing, is called a two lens system.
The diverging light output by the left optical fiber end face 3 is directly reflected by the saturable absorber mirror 1 and is coupled into the left optical 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 made very close (smaller than the rayleigh distance of the fiber exit beam) or even close to achieve a high coupling efficiency.
Single lens system diverging light output from the left fiber end face 3 is focused directly onto the saturable absorber mirror 1 by a separate lens and then reflected back to the left fiber end face 3.
The following 4 advantages are obtained by using the saturable absorber arrangement of fig. 8 (c):
in comparison with the arrangement of fig. 8 (b), since the return light is concentrated, the mode field diameter focused on the left optical fiber end face 3 can be theoretically equal to the mode field diameter emitted from the left optical fiber end face 3, and thus the coupling efficiency is higher.
With respect to the arrangement of fig. 8 (a), the spot size focused on the saturable absorber mirror 1 can be continuously adjusted, and only the distance s between the left fiber end face 3 and the lens in fig. 8 (c) needs to be adjusted, as shown in fig. 9.
Even with a single lens of different focal length, the same focused spot size and rayleigh distance can be achieved. As shown in FIG. 9, the trend of w 0'/ w0 almost coincides when s/f >1.1, no matter how large focal distance is used. As shown in FIG. 10, the trend of Z R' almost coincides when s/f >1.1, no matter how large focal distance is used. The benefit of having a larger rayleigh range for the focused spot is that (due to the environment) slight axial translations do not have a significant effect on the coupling efficiency.
The distance s+s 'between the saturable absorber mirror 1 and the left fiber end face 3 can be adjusted to be small, and the smaller the lens focal length f is, the smaller s+s'. As shown in fig. 11, for lenses of different focal lengths, when s/f >1.1, the trend of (s+s ')/f almost coincides, so that the smaller f, the smaller s+s'. Shorter s + s' can shorten the length of the cavity and is critical to the design of high repetition rate mode-locked lasers.
Example 1 wavelength division multiplexing collimator on the right side of gain fiber
As shown in fig. 2, a wavelength division multiplexing collimator is disposed at the right end of the gain fiber 4, i.e., the wavelength division multiplexing collimator 9 is connected to the right fiber end face 5.
At this time, the whole structure works as follows:
the original pumping light generated by the pumping source 10 is transmitted to the wavelength division multiplexing-collimator 9 through the passive optical fiber 11, reflected by the dichroic filter 14 and transmitted to the gain optical fiber 4, so that the gain optical fiber 4 realizes the particle number inversion, and amplified spontaneous emission light ASE is obtained;
ASE generated by the gain fiber 4 is transmitted leftwards and converged to the saturable absorber mirror 1 through the left fiber end face and the first lens/lens group 2, and signal laser is filtered out by filtering noise from spontaneous emission light at the saturable absorber mirror 1 to form pulse laser;
The pulse laser after noise filtering is transmitted rightward through the saturable absorber mirror 1, is focused to the fiber end face 3 through the first lens/lens group 2 again and then is coupled into the gain fiber 4, and the gain fiber 4 amplifies the pulse laser and simultaneously suppresses noise to obtain amplified pulse laser;
the amplified pulse laser is collimated to free space by the third lens/lens group 13 and the dichroic filter 14, and is continuously transmitted to the dispersion compensator 7 rightward from the free space (the principle is shown in fig. 6 (a)), the dispersion compensator 7 performs dispersion compensation, the pulse width is narrowed, and then the pulse width is transmitted to the laser output coupling mirror 8;
The pulse laser light is reflected and transmitted simultaneously at the front surface of the laser output coupling mirror 8, with a small portion of the light being transmitted as output laser light. The rest part is reflected and continuously transmitted to the left in the cavity, and then passes through the dispersion compensator 7 and the wavelength division multiplexing-collimator 9 in sequence;
The reflected pulse is continuously subjected to dispersion compensation in the dispersion compensator 7, is coupled to the gain fiber 4 through the wavelength division multiplexing-collimator 9, is amplified again in the gain fiber 4, continuously remains to be transmitted leftwards, and completes a laser transmission period.
The above process is one complete cycle of the laser delivery process. The laser in the cavity is operated periodically in the laser formed by all the devices to form pulse laser, the pulse laser is amplified, and finally stable continuous wave mode locking pulse laser output is formed, so that the high-quality, high-efficiency and high-quality femtosecond laser is obtained. The output parameters of the mode locking pulse are determined by the parameter combination of all devices in the cavity.
Corresponding to the structure of example 1, a laser generating method of a fiber laser structure to which a wavelength division multiplexing-collimator is applied and which is connected to the right fiber end face is as follows:
s1, generating original pump light, namely transmitting the original pump light generated by the pump source to a wavelength division multiplexing-collimator through a passive optical fiber;
s2, generating spontaneous emission light, namely reflecting original pump light in a dichromatic filter and transmitting the original pump light to a gain optical fiber, so that the gain optical fiber realizes particle number inversion and amplified spontaneous emission light (ASE) is obtained;
Step S3, pulse laser is generated, namely ASE generated by the gain optical fiber is transmitted to the left and converged to a saturable absorber mirror through the end face of the left optical fiber and the first lens/lens group;
Step S4, amplifying the pulse laser, namely transmitting the pulse laser with the improved signal-to-noise ratio to the right through a saturable absorber mirror, focusing the pulse laser to the end face of the optical fiber through a first lens/lens group again, and then coupling the pulse laser into a gain optical fiber, wherein the gain optical fiber amplifies the pulse laser and simultaneously suppresses noise to obtain amplified pulse laser;
Step S5, outputting pulse laser, namely enabling the amplified pulse laser to pass through a third lens/lens group and a dichroic filter to reach free space, and continuously transmitting the amplified pulse laser to the right to a dispersion compensator (the principle is shown in fig. 6 (a));
performing dispersion compensation on the dispersion compensator, narrowing pulse width and transmitting to a laser output coupling mirror;
The pulse laser is reflected and transmitted at the front surface of the laser output coupling mirror, wherein a small part of the pulse laser is transmitted as output laser, and the rest part of the pulse laser 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;
The reflected pulse is further subjected to dispersion compensation in the dispersion compensator, is coupled to the gain fiber through the wavelength division multiplexing-collimator, is amplified again in the gain fiber, and is further subjected to left transmission, so that a laser transmission period is completed.
Example 2 wavelength division multiplexing collimator on the left side of the gain fiber
In this embodiment, as shown in fig. 4, the wavelength division multiplexing-collimator 9 is connected to the left optical fiber end face 3.
At this time, the whole structure works as follows:
The original pump light of the pump source 10 is transmitted to the wavelength division multiplexing-collimator 9 through the passive optical fiber 11, reflected by the dichroic filter 14 and transmitted to the gain optical fiber 4, so that the gain optical fiber 4 realizes the particle number inversion, and amplified spontaneous emission light ASE is obtained;
The ASE generated by the gain fiber 4 is transmitted to the left, is collimated and transmitted to the first lens/lens group 2 through the third lens/lens group 13 and the dichroic filter 14 and is converged to the saturable absorber mirror 1, and noise is filtered out at the saturable absorber mirror 1 to screen out signal laser, so as to form pulse laser.
The generated pulse laser is reflected by the saturable absorber mirror 1 to be transmitted rightward, and is transmitted to the gain fiber 4 again through the first lens/lens group 2 and the wavelength division multiplexing-collimator 9, at the moment, the gain fiber 4 amplifies the pulse laser signal, simultaneously suppresses 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 to continue to be transmitted rightward.
It is noted that the laser light output from the right fiber end face 5 is divergent, and that the output laser light passing through the second lens/lens group 6 is possible in two ways, one being collimated to free space (principle shown in fig. 6 (a)) and the other being converged to the front surface of the laser output coupling mirror 8 (principle shown in fig. 6 (b) or (c)), depending on the distance from the right fiber end face 5 to the second lens/lens group 6. The dispersion compensator 7 between the second lens/lens group 6 and the laser output coupling mirror 8 functions to provide dispersion compensation, narrowing the pulse width.
The pulse laser is reflected and transmitted simultaneously on the front surface of the laser output coupling mirror 8, wherein a small part of the pulse laser is transmitted as output laser, and the rest of the pulse laser is reflected and continuously 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 in sequence. Both of the foregoing cases (whether collimated or converged), the leftward transmission to the gain fiber 4 through the right fiber end face 5 can achieve efficient coupling. The laser pulse signal is amplified again in the gain fiber 4 and continues to be transmitted to the left.
The above process is one complete cycle of the laser delivery process. The laser in the cavity runs periodically in the laser formed by all the devices to form pulse laser, the pulse laser is amplified, and finally stable continuous wave mode locking pulse laser output is formed. The output parameters of the mode locking pulse are determined by the parameter combination of all devices in the cavity.
Corresponding to the structure of example 2, a laser generating method of a fiber laser structure to which a wavelength division multiplexing-collimator is applied and which is connected to the end face of the left fiber is as follows:
S1, original pump light of a pump source is generated, wherein the original pump light of the pump source is transmitted to a wavelength division multiplexing-collimator through a passive optical fiber;
s2, generating spontaneous emission light, namely reflecting original pump light in a dichromatic filter and transmitting the original pump light to a gain optical fiber, so that the gain optical fiber realizes particle number inversion and amplified spontaneous emission light ASE is obtained;
step S3, pulse laser is generated, wherein ASE generated by the gain optical fiber is transmitted leftwards as well, and is collimated and transmitted to the first lens/lens group to be converged to the saturable absorber mirror through the third lens/lens group and the dichroic filter, noise is filtered out at the saturable absorber mirror, and high-intensity signal laser is screened out to generate pulse laser;
Step S3, amplifying pulse laser, namely transmitting the pulse laser to the right through reflection of a saturable absorber mirror, transmitting the pulse laser to a gain optical fiber through a first lens/lens group and a wavelength division multiplexing-collimator again, amplifying a pulse laser signal by the gain optical fiber at the moment, and simultaneously suppressing noise to obtain an amplified laser signal;
Step S4, outputting the pulse laser, wherein the amplified laser signal is collimated to a free space through the right optical fiber end face and the second lens/lens group or converged to the front surface of the laser output coupling mirror, and the distance from the right optical fiber end face (5) to the second lens/lens group (6) depends on the laser output coupling mirror.
Right transmitted to the dispersion compensator, the dispersion compensator performs dispersion compensation, the pulse width is narrowed, and then transmitted to the laser output coupling mirror;
The pulse laser is reflected and transmitted simultaneously on the front surface of the laser output coupling mirror 8, a small part of the pulse laser is transmitted as output laser, the rest part of the pulse laser is reflected and continuously transmitted to the left in the cavity, then sequentially passes through the dispersion compensator, the second lens/lens group and the right optical fiber end face and is transmitted to the gain optical fiber to the left, the laser pulse signal is amplified again in the gain optical fiber and continuously transmitted to the left, and a laser transmission period is completed.
Example 3 Dual wavelength division multiplexing collimator
As shown in fig. 5, in this embodiment, two pump sources and wavelength division multiplexing collimators connected in sequence are provided, and the two wavelength division multiplexing collimators are connected to the left fiber end face 3 and the right fiber end face 5 of the gain fiber, respectively.
Two pump sources, named first pump source 10 and second pump source 10';
two passive optical fibers, named first passive optical fiber 11 and second passive optical fiber 11';
Two wavelength division multiplexing-collimators, named first wavelength division multiplexing-collimator 9 and second wavelength division multiplexing-collimator 9';
at this time, the whole structure works as follows:
The first pump source 10 and the second pump source 10' generate original pump light, and the original pump light is transmitted to the first wavelength division multiplexing collimator 9 and the second wavelength division multiplexing collimator 9' through the first passive optical fiber 11 and the second passive optical fiber 11', respectively;
Then, the two-color filters 14 of the first wavelength division multiplexing collimator 9 and the second wavelength division multiplexing collimator 9' reflect and transmit the two-color filters to the gain fiber 4 together, so that the gain fiber 4 realizes the population inversion and amplified spontaneous emission ASE is obtained.
ASE generated by the gain fiber 4 is transmitted leftwards, collimated and transmitted to the first lens/lens group 2 through the lens of the first wavelength division multiplexing-collimator 9 and the dichroic filter 14, and then focused to the saturable absorber mirror 1 through the first lens/lens group 2;
the saturable absorber mirror 1 is positioned on the focal plane of the focused light beam, and provides a pulse forming mechanism, namely, high-intensity signal laser is screened out from noise, so that pulse laser is generated;
The pulse laser reflected by the saturable absorber mirror 1 is transmitted to the right, and is transmitted to the gain optical fiber 4 again through the first lens/lens group 2 and the first wavelength division multiplexing-collimator 9, at the moment, the gain optical fiber 4 amplifies the signal laser, and simultaneously suppresses noise to obtain amplified pulse laser;
the amplified pulse laser is collimated to free space by a lens of a second wavelength division multiplexing-collimator 9' and a dichroic filter 14, and is continuously transmitted to the right;
The pulse output from the second wavelength division multiplexing-collimator 9' is subjected to dispersion compensation through 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, a small part of the light is transmitted and used as output laser, and the rest part of the light is reflected through the laser output coupling mirror 8 and continuously transmitted to the left in the cavity and then sequentially passes through the dispersion compensator 7 and the second wavelength division multiplexing-collimator 9;
wherein, the pulse continues to obtain dispersion compensation in the dispersion compensator 7, and is then efficiently coupled to the gain fiber 4 via the second wavelength division multiplexing-collimator 9', and the pulse is amplified again in the gain fiber 4, and continues to remain to transmit leftwards, thus completing a laser transmission period.
The above process is one complete cycle of the laser delivery process. The laser in the cavity runs periodically in the laser formed by all the devices to form pulse laser, the pulse laser is amplified, and finally stable continuous wave mode locking pulse laser output is formed. The output parameters of the mode locking pulse are determined by the parameter combination of all devices in the cavity.
Corresponding to the structure of example 3, a laser generating method of a fiber laser structure to which a wavelength division multiplexing-collimator is applied and which is simultaneously connected to the left fiber end face and the right and left fiber end faces is as follows:
s1, generating original pump light, namely generating the original pump light by a first pump source and a second pump source, and transmitting the original pump light to a first wavelength division multiplexing-collimator and a second wavelength division multiplexing-collimator through a first passive optical fiber and a second passive optical fiber respectively;
S2, generating spontaneous emission light, namely reflecting the two-color filter sheets of the first wavelength division multiplexing collimator and the second wavelength division multiplexing collimator, and transmitting the two-color filter sheets to a gain optical fiber together, so that the gain optical fiber realizes particle number inversion and amplified spontaneous emission light ASE is obtained;
Step S3, pulse laser is generated, wherein ASE generated by the gain optical fiber is transmitted leftwards, collimated and transmitted to a first lens/lens group through a lens of a first wavelength division multiplexing-collimator and a dichroic filter, and focused to a saturable absorber mirror through the first lens/lens group;
the saturable absorber mirror is positioned on the focal plane of the focused light beam, and a pulse forming mechanism is provided, namely high-intensity signal laser is screened out from noise, so that pulse laser is generated;
Step S4, amplifying pulse laser, namely transmitting the pulse laser to the right through reflection of a saturable absorber mirror, transmitting the pulse laser to a gain optical fiber through a first lens/lens group and a first wavelength division multiplexing-collimator again, amplifying signal laser by the gain optical fiber at the moment, and simultaneously suppressing noise to obtain amplified pulse laser;
s5, outputting pulse laser, namely collimating the amplified pulse laser to a free space through a lens of a second wavelength division multiplexing-collimator and a dichroic filter, and continuing to transmit to the right;
The pulse output from the second wavelength division multiplexing-collimator is subjected to dispersion compensation through a dispersion compensator, the pulse width is narrowed, and then the pulse is transmitted to a laser output coupling mirror, laser is reflected and transmitted simultaneously on the front surface of the laser output coupling mirror, a small part of the laser is transmitted in a light transmission mode and is used as output laser, the rest of the laser is reflected through the laser output coupling mirror and is continuously transmitted to the left in a cavity, and then the laser passes through the dispersion compensator and the second wavelength division multiplexing-collimator in sequence, wherein the pulse is continuously subjected to dispersion compensation in the dispersion compensator, is then efficiently coupled to a gain fiber through the second wavelength division multiplexing-collimator, is amplified again in the gain fiber, is continuously kept to be transmitted to the left, and a laser transmission period is completed.
As shown in fig. 12, the device 19-27 comprises a plurality of devices, and specific names and parameters of the plurality of devices are as follows:
device 19 semiconductor saturable absorber mirror (SESAM), parameters: modulation depth 18%, saturation flux 100. Mu.J/cm 2, relaxation time 9ps.
The device 20 is a convex lens, and the parameters are the focal length 6mm.
The device 21 comprises an oblique head end face and a parameter of 8 degrees.
The device 22 is an Yb-doped optical fiber, and the parameters are that the length of the optical fiber is 4.5cm, the absorption coefficient is 2400dB/m@976nm, and the mode field diameter is 5 μm@1060nm.
Device 23 is a passive fiber, model HI1060, length >20cm.
Device 24 is a laser diode, the wavelength is 976nm, and the maximum output power is 900mW.
The device 25 is a wavelength division multiplexing-collimator, and the parameters are that the reflection wavelength is 970-980nm, the transmission wavelength is 1010-1100nm, and the collimation distance is 110mm.
The device 26 is a grating, the parameters are 1000 lines/mm, and the incident angle is 28-33 degrees.
The device 26' is identical to the device 26, and two gratings are placed in parallel with a vertical distance of 1mm.
The device 27 is a coupling output mirror, the parameters are that the wavelength is 1000-1100nm, the transmittance is less than or equal to 5%, and the reflectivity is more than or equal to 95%.
The working process of the embodiment comprises a coupling process and a mode locking adjustment process:
The coupling procedure is to mount the devices according to fig. 12 such that the distance between device 20 and device 21 is between 1.1-1.4 focal lengths. The output power of the device 24 is regulated to below 50 mW. The device 19 is placed on the focal plane of the image side, and the θ - φ direction of the device 19 is adjusted to return the reflected light to the device 21, so as to adjust the light power output by the device 25 to the maximum. Light output from device 25 is incident on device 26 in the range of 28 ° -33 ° while devices 26 and 26' are made parallel and the vertical distance is adjusted to about 1 mm. The coupling process is completed by adjusting device 27 to return the reflected light to device 25 and adjusting the output power to a maximum.
And (3) adjusting the mode locking process, namely adjusting the power of the pump source to be more than 600mW, observing the pulse sequence from an oscilloscope for observation at the device 27, and observing the mode locking spectrum by a spectrometer.
The experimental results obtained by working in this example were:
As shown in fig. 13, the output results are measured from the output port of device 27. In fig. 13 (a), the output spectrum at different powers is shown, the color represented by the gray gradually becoming black is the process of increasing the pump power gradually, and the inset shows the output spectrum width at different powers. Fig. 13 (b) shows an autocorrelation curve (black solid line) directly output and an autocorrelation curve (gray solid line) after the grating pair is chirped outside the cavity when the pump power is 900mW, the dashed lines of different colors respectively represent gaussian fitting curves of the two, the direct output autocorrelation pulse width is 128fs, the half-width of the corresponding gaussian electric field intensity is 90.5fs, the autocorrelation pulse width after the chirp is 116fs, and the half-width of the corresponding gaussian electric field intensity is 82fs. Fig. 13 (c) shows a measured pulse sequence with a pulse interval of about 925ps. FIG. 13 (d) shows the measured radio spectrum with a corresponding repetition frequency of about 1.08GHz and a measured resolution bandwidth of 1kHz, and the inset shows the radio spectrum with a frequency range of 26.5GHz and a resolution bandwidth of 10kHz.
Variations and modifications to the above would be obvious to persons skilled in the art to which the invention pertains from the foregoing description and teachings. Therefore, the invention is not limited to the specific embodiments disclosed and described above, but some modifications and changes of the invention should be also included in the scope of the claims of the invention. In addition, although specific terms are used in the present specification, these terms are for convenience of description only and do not constitute any limitation on the invention.
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