CN220914739U

CN220914739U - High-power high-stability full polarization-maintaining nine-shaped mode-locking fiber laser

Info

Publication number: CN220914739U
Application number: CN202322391830.9U
Authority: CN
Inventors: 王金章; 陈鑫洲; 冯磊; 张慧
Original assignee: Shenzhen University
Current assignee: Shenzhen University
Priority date: 2023-09-01
Filing date: 2023-09-01
Publication date: 2024-05-07
Anticipated expiration: 2033-09-01

Abstract

The utility model relates to the technical field of optical display, in particular to a high-power high-stability full polarization-maintaining nine-shaped mode-locking fiber laser which consists of a pumping source and a laser oscillation cavity, wherein a reflecting mirror can be replaced by a Martin stretcher. A laser oscillation cavity taking a reflecting mirror as an end mirror and a pumping source form a polarization maintaining fiber laser output pulse based on NALM mode locking to be in a soliton state; and the NALM mode-locking polarization-maintaining fiber laser with Martinz stretcher to replace the reflector outputs pulse in dissipative soliton state. The combination of the NALM module with phase bias with the all PM fiber structure of the present utility model ensures reliable start-up of mode locking and high pulse stability. Compared with a polarization maintaining single-mode fiber laser oscillator with the same mode locking mode, the laser provided by the utility model has the advantages that the average power and the pulse energy are obviously improved, and the dissipation soliton and the large-mode-area fiber are combined to realize larger power output.

Description

High-power high-stability full polarization-maintaining nine-shaped mode-locking fiber laser

Technical Field

The utility model relates to the technical field of optical display, in particular to a high-power high-stability full polarization-maintaining nine-shaped mode-locking fiber laser.

Background

Mode locking technology is one of the most common methods for realizing ultrashort laser pulse output, and comprises active mode locking and passive mode locking. The active mode locking is realized by adding an artificial modulator in a cavity, and is often limited by the response time of the modulator, the output pulse width can only reach the magnitude of nanoseconds (ns) and picoseconds (ps), and ultra-short pulse is difficult to obtain; the passive mode locking uses the saturable absorber effect, the mode locking is realized by utilizing the self structure of the resonant cavity rather than external modulation, the response speed is high, and the output pulse width can generally realize the output of picosecond or even femtosecond level pulses. In addition, the passive locking mold has the advantages of relatively simple structure, low cost, good stability and the like, and is widely applied to various mode locking oscillators.

Passive mode locking mechanisms often employ a saturable absorber to achieve mode locking. Existing relatively mature passive mode locking mechanisms include true saturable absorber mode locking and artificial saturable absorber mode locking. Wherein, the recovery time of the real saturable absorber is between hundred femtoseconds and nanoseconds, which limits the generation of ultrashort pulse; the artificial saturable absorber only needs a few femtoseconds, belongs to a fast saturation absorber, and is easier to generate high-peak ultrashort pulse. Two common forms thereof are nonlinear polarization rotation evolution (NPE) mode locking techniques and nonlinear loop mirror (NALM) mode locking techniques.

The optical fiber laser based on the mode locking technology can easily obtain nanosecond and femtosecond pulse output, the common optical fiber laser uses a non-polarization maintaining optical fiber as an optical fiber component, and under the condition that the laser operates for a long time, the mode locking is unstable due to environmental influence so as to influence the output stability of the laser, and the optical fiber laser is also a tripolite for realizing commercialization of the mode locking optical fiber laser. The polarization maintaining optical fiber is insensitive to the external environment, the non-polarization maintaining optical fiber is replaced by the polarization maintaining optical fiber, the modulation instability caused by the weak birefringence effect of the non-polarization maintaining optical fiber can be avoided, the overall environmental stability of the laser cavity is further improved, and the polarization maintaining optical fiber is an essential element for realizing the commercialization of the optical fiber laser.

The mode locking technology of the real saturable absorber is a common method for realizing the mode locking of the polarization maintaining fiber laser, but the real saturable absorber can be subjected to performance degradation and other problems after long-time operation, and needs to be replaced periodically to maintain the performance of the laser, so that the problem of difficult later maintenance exists when the polarization maintaining fiber laser is constructed by the real saturable absorber only. The artificial saturable absorber mode locking technology can ensure long-term stability and avoid the problem of later maintenance. NPE technology is widely used in ultrafast fiber oscillators due to its high damage threshold, ultrafast recovery time, and flexibility in cavity design. However, its most successful implementation is in non-Polarization Maintaining (PM) fibers, which makes NPE sensitive to environmental changes. In contrast, NALM not only has similar advantages as NPE, but is also highly compatible with fully polarization maintaining fibers, resistant to environmental disturbances and provides long-term stability. However, NALM is often neglected due to its poor self-starting capability. By introducing a non-reciprocal phase bias, a reflective NALM device with greatly enhanced self-priming capability has been demonstrated. The 9-shaped fiber laser not only has an all-PM structure with high environmental stability, but also has excellent low-noise characteristics. The rapid development of ultrafast laser applications requires, in addition to high environmental stability and low noise characteristics of fiber oscillators, continuous improvements in their output performance, such as achievable pulse energy and output power. However, the characteristics of mode-locked pulses are fundamentally limited by nonlinear phase accumulation. Pulse energy in conventional soliton mode-locked fiber lasers is typically limited to 0.1nJ. One common method of increasing energy is to operate a fiber laser in large normal dispersion to produce chirped pulses, commonly referred to as dissipative solitons. It has been shown in theory that for a given mode field area, the energy limit of the dissipative solitons is two orders of magnitude higher than the energy limit of the solitons. However, even with dispersion management, the relatively large nonlinearity prevents further increases in pulse energy due to the small core size (< 10 μm) of conventional single mode fibers. Enlarging the core size with large mode area fibers is a promising approach to break this obstacle. It is important to note that suppressing the higher order modes in these large mode area fibers to initiate and maintain mode locking is critical. Several techniques have been developed so far to suppress higher order modes, including winding the fiber, designing a mode filter based on a single mode fiber, and manufacturing true single mode large mode area fiber, photonic crystal fiber, and linear coupled core fiber.

So far, most of the research on mode-locked large mode field fiber oscillators has focused on ytterbium-doped fibers operating in the 1 μm region. Although extensive research has been conducted on conventional erbium-doped ultrafast fiber oscillators operating around 1.55 μm, the development of erbium-doped large-mode-field fiber oscillators has fallen behind the same type of oscillators based on ytterbium-doped fibers. Erbium-doped large mode field fibers are typically co-doped with Yb ions to increase pump absorption and reduce up-conversion, and with large amounts of phosphorus to enhance pump transmission. However, phosphorus increases the core refractive index, making it challenging to manufacture erbium ytterbium co-doped large mode field fibers with low numerical aperture. Thus, er/Yb doped large mode field step index fibers typically contain some higher order modes, which are detrimental to mode locking. So far, even with high-order mode suppression, only a small amount of mode locking reports of Er/Yb doped high-order mode fibers are available. The highest pulse energy of the mode-locked Er/Yb doped large mode field fiber oscillator is reported to be 20nJ, but the corresponding pulse duration (20 ps) is relatively long. If a custom-made multi-filament erbium-ytterbium co-doped large-mode-field single-mode fiber is used as a gain medium, the fiber oscillator directly generates soliton pulses with the duration of 1.6ps and the energy of 9.1 nJ. However, these Er/Yb doped large mode field fiber oscillators are mode locked by materials and absorbers and are based on non-polarization maintaining large mode field fibers, which is detrimental to long term stability. Let alone the perturbation of the higher order modes may further deteriorate the mode locking stability. It is necessary to overcome these limitations and seek a solution that is widely adaptable in terms of technical scalability and large-scale reproducibility.

Disclosure of utility model

In order to solve the problems, the utility model provides a high-power high-stability full polarization-maintaining nine-word mode-locked fiber laser, wherein a cavity reflection end mirror is replaced by a Martin stretcher to change cavity dispersion into positive dispersion so as to realize the output of a dissipative soliton, and the dissipative soliton is combined with a large-mode-area fiber so as to realize larger power output, thereby solving the problem that pulse energy cannot be further improved due to the limitation of a soliton state.

In order to achieve the above object, the embodiment of the present utility model provides the following technical solutions:

In a first aspect, the present utility model provides a high-power high-stability all-polarization-maintaining nine-shaped mode-locked fiber laser, including:

A laser oscillation cavity;

the nonreciprocal phase bias device is positioned in the laser oscillation cavity and consists of a Faraday rotator and a quarter wave plate and is used for enhancing the mode locking self-starting capability;

a hole diaphragm inserted into the laser oscillation cavity to suppress the high-order mode by spatial filtering;

the Martin stretcher is positioned in the laser oscillation cavity, replaces a reflecting end mirror in the cavity and is used for realizing the normalization of the chromatic dispersion in the cavity so as to output dissipation solitons;

A large mode area gain fiber is used for realizing high-power laser output.

As a further aspect of the present utility model, the nonreciprocal phase bias device is composed of two faraday rotators, which are a first faraday rotator and a second faraday rotator, and a quarter wave plate, which is a first quarter wave plate disposed between the first faraday rotator and the second faraday rotator.

As a further aspect of the present utility model, the relative angle between the faraday rotator of the nonreciprocal phase bias and the quarter-wave plate is pi/2.

As a further scheme of the utility model, the diameter of the gain optical fiber is 15cm, and the gain optical fiber is subjected to bending coiling, so that the suppression of a high-order mode is realized.

As a further scheme of the utility model, the gain optical fiber is a double-cladding polarization-maintaining Er/Yb doped optical fiber with the length of 2.07 meters, the fiber core diameter is 25 mu m, and the numerical aperture is 0.09.

As a further scheme of the utility model, the high-power high-stability full polarization-maintaining nine-shaped mode-locking fiber laser is also provided with a first fiber connector and a second fiber connector, the gain fiber is connected between the first fiber connector and the second fiber connector, the first fiber connector is positioned at one side of the first collimating lens, and the second fiber connector is positioned at one side of the second collimating lens.

As a further scheme of the utility model, a first dichroic mirror is arranged between the first collimating lens and the laser oscillation cavity, the pumping source is arranged towards the first dichroic mirror, the laser oscillation cavity is positioned in the first polarization beam splitter, a second quarter wave plate, a second polarization beam splitter and a third half wave plate are arranged between the first polarization beam splitter and the hole type diaphragm, and an end mirror is arranged on the other side of the hole type diaphragm.

As a further scheme of the utility model, the nonreciprocal phase biaser is arranged at the bottom side of the first polarization beam splitter, and a first half-wave plate, a second dichroic mirror and a second collimating lens are sequentially arranged between the nonreciprocal phase biaser and the second optical fiber connector.

As a further scheme of the utility model, the end mirror is a first reflecting mirror, and the laser oscillation cavity and the pumping source which take the first reflecting mirror as the end mirror form a polarization maintaining fiber laser output pulse based on NALM mode locking to be in a soliton state.

As a further scheme of the utility model, the end mirror is a Martin stretcher, and the Martin stretcher is used for replacing the NALM mode-locking polarization-maintaining fiber laser output pulse of the first reflecting mirror to be in a dissipative soliton state.

As a further aspect of the present utility model, the martinez stretcher includes a D-mirror, a grating, a focusing lens, and a second mirror.

Compared with the prior art, the high-power high-stability full polarization-maintaining nine-shaped mode-locked fiber laser provided by the utility model has the following beneficial effects:

1. mode locking self-starting capability enhancement: the nonreciprocal phase bias device introduced in the utility model is composed of the Faraday rotator and the quarter wave plate, so that the mode locking self-starting capability of the laser oscillation cavity is effectively enhanced. This enables the laser to more reliably enter a stable mode-locked state from the self-starting state, reducing instabilities during the starting process.

2. Higher order mode suppression: the aperture diaphragm inserted into the laser oscillation cavity has a spatial filtering function, and can suppress the generation of a higher order mode. By utilizing the characteristics of the spot radius of different modes, the influence of the high-order mode on laser output is successfully reduced, and the mode purity and quality of the laser are improved.

3. Dissipative soliton output: the introduction of the Martin stretcher changes the intra-cavity dispersion into positive dispersion, thereby realizing the output of dissipative solitons. The existence of the dissipative soliton enables the laser pulse energy to be further improved, so that laser output with higher power is realized, and the laser output is not limited by the soliton state.

4. High power output: by using a large mode area gain fiber and sinuously winding it, the generation of higher order modes is effectively controlled. This enables the laser to output higher power laser light, meeting the needs of a range of applications, including ultra-fast optics, etc.

5. The application prospect is wide: the high-power high-stability full polarization-maintaining nine-shaped mode-locking fiber laser has excellent performance and is suitable for fields of ultrafast optics, laser processing, medical equipment, scientific research and the like. Its high stability, high pulse quality and high power output provide a reliable laser source for a variety of applications.

In conclusion, the high-power high-stability full polarization-maintaining nine-shaped mode-locked fiber laser provided by the utility model has the advantages of obvious beneficial effects and innovativeness in the laser field through the characteristics of enhancement of mode locking self-starting capability, suppression of a high-order mode, dissipation of soliton output, high-power output and the like.

These and other aspects of the utility model will be more readily apparent from the following description of the embodiments. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the utility model as claimed.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present utility model, the following description will briefly introduce the drawings that are needed in the embodiments or the description of the prior art, and it is obvious that the drawings in the following description are only some embodiments of the present utility model. In the drawings:

Fig. 1 is a block diagram of a high-power high-stability all-polarization-maintaining nine-shaped mode-locked fiber laser according to an embodiment of the utility model.

Fig. 2 is a schematic diagram of soliton output spectrum when pump power is 2.85W in a high-power high-stability full polarization-maintaining nine-word mode-locked fiber laser according to an embodiment of the present utility model.

Fig. 3 is a schematic diagram of intensity and delay time in a 2.85W pump soliton output corresponding to pulse width and beam quality in a high-power high-stability full polarization maintaining nine-mode-locked fiber laser according to an embodiment of the present utility model.

Fig. 4 is a schematic diagram of beam diameter and position in the pulse width and beam quality corresponding to the output of the 2.85W pump soliton in the high-power high-stability full polarization-maintaining nine-word mode-locked fiber laser according to the embodiment of the utility model.

Fig. 5 is a schematic diagram of a pulse width and beam quality M ² corresponding to a 2.85W pump soliton output in a high-power high-stability full polarization-maintaining nine-mode-locked fiber laser according to an embodiment of the present utility model.

Fig. 6 is a spectrum diagram of two kinds of intra-cavity dispersion when soliton output is dissipated in a high-power high-stability full polarization-maintaining nine-shaped mode-locked fiber laser according to an embodiment of the utility model.

Fig. 7 is a pulse width diagram of two kinds of intra-cavity dispersion when dissipating soliton output in a high-power high-stability full polarization-maintaining nine-word mode-locked fiber laser according to an embodiment of the present utility model.

Fig. 8 is a relative intensity noise diagram of soliton pulse and dissipative soliton pulse in a high-power high-stability full polarization maintaining nine-word mode-locked fiber laser according to an embodiment of the utility model.

Fig. 9 is a schematic diagram of average output power of soliton pulse under maximum pump power in a high-power high-stability full polarization-maintaining nine-word mode-locked fiber laser according to an embodiment of the present utility model.

Fig. 10 is a schematic diagram of average output power of dissipative soliton pulses at maximum pump power in a high-power high-stability all-polarization-maintaining nine-mode-locked fiber laser according to an embodiment of the utility model.

Fig. 11 is a pulse width diagram of two kinds of intra-cavity dispersion when dissipating soliton output in a high-power high-stability full polarization-maintaining nine-word mode-locked fiber laser according to an embodiment of the present utility model.

Fig. 12 is a schematic diagram of a movable part of a martinz stretcher in a high-power high-stability all-polarization-maintaining nine-word mode-locked fiber laser according to an embodiment of the present utility model.

FIG. 13 is a spectrum chart and a pulse autocorrelation chart of the output of the high-power high-stability full polarization-maintaining nine-shaped mode-locked fiber laser under different chromatic dispersions according to an embodiment of the utility model.

Fig. 14 is a movable front view of a first mirror in a high-power high-stability all-polarization-maintaining nine-mode-locked fiber laser according to an embodiment of the present utility model.

Fig. 15 is a movable side view of a first mirror in a high-power high-stability all-polarization-maintaining nine-mode-locked fiber laser according to an embodiment of the present utility model.

Reference numerals:

1-pump source, 2-first dichroic mirror, 3-first collimating lens, 4-first fiber connector, 5-gain fiber, 6-second fiber connector, 7-second collimating lens, 8-second dichroic mirror, 9-first half wave plate, 10-first Faraday rotator, 11-first quarter wave plate, 12-second Faraday rotator, 13-second half wave plate, 14-first polarizing beam splitter, 15-third half wave plate, 16-second polarizing beam splitter, 17-second quarter wave plate, 18-pass stop, 19-first mirror, 20-D mirror, 21-grating, 22-focusing lens, 23-second mirror, 24-Martin stretcher, 25-non-reciprocal phase bias, 26-laser oscillation cavity.

Detailed Description

The present utility model will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present utility model more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the utility model.

Since the highest pulse energy of the mode-locked Er/Yb doped large mode field fiber oscillator is 20nJ, the corresponding pulse duration (20 ps) is relatively long. If a custom-made multi-filament erbium-ytterbium co-doped large-mode-field single-mode fiber is used as a gain medium, the fiber oscillator directly generates soliton pulses with the duration of 1.6ps and the energy of 9.1 nJ. However, these Er/Yb doped large mode field fiber oscillators are mode locked by materials and absorbers and are based on non-polarization maintaining large mode field fibers, which is detrimental to long term stability. Let alone the perturbation of the higher order modes may further deteriorate the mode locking stability.

In view of this, the utility model provides a high-power high-stability full polarization-maintaining nine-word mode-locked fiber laser, in which the cavity reflection end mirror is replaced by the Martin stretcher 24 to change the cavity dispersion into positive dispersion to realize the output of dissipative soliton, and the dissipative soliton is combined with the large-mode-area fiber to realize larger power output, so that the problem that the pulse energy cannot be further improved due to the limitation of the soliton state can be solved.

In the utility model, firstly, the problem of poor mode locking self-starting capability common to NALM is solved. The present utility model improves the mode locking self-starting capability of the mode locking laser oscillation cavity 26 by introducing a non-reciprocal phase bias 25 consisting of two faraday rotators and one quarter-wave plate in the NALM loop.

Next, in order to solve the problem that the higher order modes introduced by using the large-mode-area gain fiber 5 affect the laser mode locking. In the utility model, a hole diaphragm 18 is inserted into a laser oscillation cavity 26 to carry out spatial filtering, and the high-order mode is restrained by utilizing the characteristic that the radius of a high-order mode light spot is different from that of a fundamental mode light spot. In addition, the large-mode area gain optical fiber is bent and coiled with the diameter of about 15cm, and the high-order mode is restrained by utilizing the characteristic that the bending loss radius of different modes is different.

Finally, the problem that the pulse energy cannot be further improved due to the limitation of the soliton state is solved. The utility model replaces the intracavity reflection end mirror with the Martin stretcher 24 to change the intracavity dispersion into positive dispersion to realize the output of dissipative soliton, and the dissipative soliton and the large-mode-area optical fiber are combined to realize larger power output.

In particular, embodiments of the present application are further described below with reference to the accompanying drawings.

As shown in fig. 1, an embodiment of the present utility model provides a high-power high-stability all-polarization-maintaining nine-shaped mode-locked fiber laser, including:

A laser oscillation cavity 26;

A nonreciprocal phase bias device 25, located in the laser oscillation cavity 26, composed of a Faraday rotator and a quarter wave plate, for enhancing the mode locking self-starting capability;

a hole diaphragm 18 inserted in the laser oscillation cavity 26 for suppressing the higher order mode by spatial filtering;

A Martin stretcher 24, located in the laser oscillation cavity 26, for replacing the intracavity reflecting end mirror to achieve normalization of intracavity dispersion, thereby outputting dissipative solitons;

a large mode area gain fiber 5 for achieving high power laser output.

Referring to fig. 1, in the present embodiment, the nonreciprocal phase bias device 25 is composed of two faraday rotators, which are a first faraday rotator 10 and a second faraday rotator 12, respectively, and a quarter-wave plate, which is a first quarter-wave plate 11 disposed between the first faraday rotator 10 and the second faraday rotator 12.

The nonreciprocal phase bias device 25 introduced in the utility model is composed of a Faraday rotator and a quarter wave plate, so that the mode locking self-starting capability of the laser oscillation cavity 26 is effectively enhanced. This enables the laser to more reliably enter a stable mode-locked state from the self-starting state, reducing instabilities during the starting process.

The non-reciprocal phase bias device 25 is introduced into the NALM loop of the high-power high-stability full polarization maintaining nine-shaped mode locking fiber laser, and is used for improving the mode locking self-starting capability of the mode locking laser oscillation cavity 26. The aperture stop 18 inserted into the laser oscillation chamber 26 has a spatial filter function, and can suppress the generation of higher order modes. By utilizing the characteristics of the spot radius of different modes, the influence of the high-order mode on laser output is successfully reduced, and the mode purity and quality of the laser are improved.

In this embodiment, the relative angle between the faraday rotator and the quarter wave plate of the non-reciprocal phase-bias 25 is pi/2, as described with reference to fig. 1. In this embodiment, the diameter of the gain fiber 5 is 15cm and the gain fiber is bent and coiled, so as to suppress the higher order mode.

In this embodiment, the gain fiber 5 is a 2.07 m long double-clad polarization maintaining Er/Yb doped fiber, the core diameter is 25 μm, and the numerical aperture is 0.09. By using a large-mode-area gain fiber 5 and bending it around, the generation of higher-order modes is effectively controlled. This enables the laser to output higher power laser light, meeting the needs of a range of applications, including ultra-fast optics, etc.

Referring to fig. 1, in this embodiment, the high-power high-stability full polarization-maintaining nine-shaped mode-locked fiber laser is further provided with a first fiber connector 4 and a second fiber connector 6, the gain fiber 5 is connected between the first fiber connector 4 and the second fiber connector 6, the first fiber connector 4 is located at one side of the first collimating lens 3, and the second fiber connector 6 is located at one side of the second collimating lens 7.

The first dichroic mirror 2 is disposed between the first collimating lens 3 and the laser oscillating cavity 26, the pump source 1 is disposed towards the first dichroic mirror 2, the laser oscillating cavity 26 is located in the first polarizing beam splitter 14, a second quarter wave plate 17, a second polarizing beam splitter 16 and a third half wave plate 15 are disposed between the first polarizing beam splitter 14 and the aperture diaphragm 18, and an end mirror is disposed at the other side of the aperture diaphragm 18.

In this embodiment, the Martin stretcher 24 includes a D-mirror 20, a grating 21, a focusing lens 22, and a second mirror 23.

In this embodiment, the end mirror is a first mirror 19, and the laser oscillation cavity 26 and the pump source 1 with the first mirror 19 as the end mirror form a polarization maintaining fiber laser output pulse based on NALM mode locking to be in a soliton state.

In this embodiment, the end mirror is a martinez stretcher 24, and the martinez stretcher 24 replaces the NALM mode-locked polarization-maintaining fiber laser output pulse of the first mirror 19 to be in a dissipative soliton state. The introduction of the Martin stretcher 24 causes the intra-cavity dispersion to become positive, thereby effecting the output of dissipative solitons. The existence of the dissipative soliton enables the laser pulse energy to be further improved, so that laser output with higher power is realized, and the laser output is not limited by the soliton state.

Referring to fig. 1, in this embodiment, the nonreciprocal phase bias device 25 is disposed at the bottom side of the first polarizing beam splitter 14, and a first half-wave plate 9, a second dichroic mirror 8, and a second collimating lens 7 are sequentially disposed between the nonreciprocal phase bias device 25 and the second optical fiber connector 6.

The type and length of the optical fibers within the laser cavity 26 are uniform regardless of the type of laser. The gain fiber 5 is a 2.07 meter long double-clad polarization maintaining Er/Yb doped fiber (Nufern, PLMA-EYDF-25P/300-HE) with a core diameter of 25 μm and a numerical aperture of 0.09. Two matched passive polarization maintaining large mode area fibers (Nufern PLMA-GDF-25/300, total length about 0.83 m) were spliced to both ends of the gain fiber while the remaining free ends were polished at an angle of 8 deg. to eliminate parasitic oscillations.

The utility model puts the whole gain fiber into a cooling water tank to prevent the fiber from being damaged due to overheating under high pump power. The Group Velocity Dispersion (GVD) of these LMA fibers is predicted to be-28.6 ps 2/km. A transmission grating 21 (LIGHTSMYTH, T-940C) based on 940 lines/mm, an achromatic lens with a focal length of 100mm and a folded Ma Dingna-z stretcher 24 of two gold mirrors can be replaced into the cavity for tuning the chromatic dispersion. A pi/2 nonreciprocal phase bias 25 consisting of two faraday rotators and a quarter-wave plate is inserted in the loop to enhance the self-priming mode locking capability.

The nonreciprocal phase bias device 25 is used for improving the mode locking self-starting capability of the laser oscillation cavity 26; the hole diaphragm 18 is inserted into the laser oscillation cavity 26 to suppress the high-order mode, and uses the characteristic that the radius of the high-order mode light spot is different from that of the fundamental mode light spot; the Martin stretcher 24 is used for realizing the normalization of the intra-cavity dispersion, so as to output dissipative solitons; the output pulse in the mode locking state has the characteristics of high power, high stability and high-order mode inhibition.

Referring to fig. 1, the overall optical path trend of the high-power high-stability full polarization-maintaining nine-shaped mode-locked fiber laser is as follows: 976nm pump light is led into the large-mode-area gain optical fiber 5 through the first dichroic mirror 2, generated 1.5um signal light bidirectionally propagates in the optical fiber and enters a space optical path, the first dichroic mirror 8 and the second dichroic mirror 8 can lead out residual pump light to prevent damage to devices, the bidirectionally transmitted signal light finally converges at the first polarizing beam splitter 14, propagates towards the second polarizing beam splitter 16 and is partially reflected to serve as an output end, and after passing through the first reflecting mirror 19 or the Martinz stretcher 24, part of the signal light returns to the second polarizing beam splitter 16 to serve as a detection end to be output, and then the signal light continuously propagates towards the first polarizing beam splitter 14 and is divided into two light beams to enter the optical fiber part to realize circulation. Wherein a second quarter wave plate 17 is used to adjust the output power ratio of the output and detection ends of the second polarizing beam splitter 16, all of which are used to couple light into the first polarizing beam splitter 14. The aperture stop 18 is used to suppress the higher order mode laser. The first faraday rotator 10, the first quarter wave plate 11, and the second faraday rotator 12 constitute a nonreciprocal phase bias 25.

The initiation of mode locking with a pulse repetition rate of 61.93MHz was obtained at a pump power of 2.85W. In this case, the average power of the output port and the diagnostic port were 67.4mW and 3.85mW, respectively, corresponding to pulse energies of 1.1nJ and 60pJ, respectively. The spectrum is shown in figure 2, the spectrum difference of the two ports is caused by the difference of nonlinear effect of light accumulation in the two directions of NALM, the central wavelength is 1566nm, the bandwidth of-10 dB is 30nm, and the monitoring end is 14nm. The presence of a Kelly sideband on the spectrum indicates that the oscillator outputs a soliton-like pulse. Based on the positions of these sidebands, the Group Delay Dispersion (GDD) of the cavity is estimated to be-0.083 ps2. Neglecting the small dispersion of free space optics, the average GVD of LMA fiber (total length 2.9 m) is-28.62 ps2/km.

Fig. 3 to 5 show the autocorrelation trace of the soliton pulse and the beam quality M ². The two port output pulse autocorrelation diagrams conform to hyperbolic secant, and the real pulse widths are 213.6fs and 409.1fs respectively. The average M ² value (1.45) of the output ports is greater than the value (1.25) of the detection ports. This is possible because the aperture stop 18 for higher order mode suppression acts only on the transmissive portion of the polarizing beam splitter, resulting in higher order modes contributing more to the output port than the detection port. Nevertheless, these M ² values indicate that the beam quality is relatively high.

Replacement of the reflecting end mirror with a Martin stretcher 24 results in a dispersion tunable dissipative soliton laser cavity. When the intracavity dispersion is tuned from 0.112ps ² to 0.704ps ², the oscillator can achieve reliable mode locking, with the repetition frequency increasing from 49.4MHz to 49.86MHz. Beyond this dispersion range, it is difficult to initiate or maintain stable mode-locking operation. The output spectrum and compressed pulse autocorrelation traces after optimizing the output power at a representative net GDD of 0.704ps ² and 0.112ps ² are shown in fig. 6 and 7. For a cavity with an intra-cavity dispersion of 0.704ps ²(0.112ps², assuming a gaussian distribution of pulses, the average output power is 690mW (540 mW), the corresponding pulse energy is 13.84nJ (10.93 nJ), the pulse duration is 2ps (1.32 ps), and the Fourier transform limit is approximately 1.53ps (0.99 ps).

Fig. 7 to 11 show the broadband spectrum of soliton pulse states and dissipative soliton pulse pulses, respectively, while the corresponding illustrations show the fundamental spectrum at a 100kHz span. No visible envelope modulation demonstrates that the laser is operating in a single pulse regime, while a high signal-to-noise ratio (85 dB) indicates high amplitude stability. To further test the stability of the laser, the relative intensity noise and phase noise Power Spectral Densities (PSDs) of the soliton pulses and the dissipative soliton pulses are shown in fig. 8 and 9, respectively. The integral RIN of the soliton pulse over the entire frequency range [1Hz,10MHz ] was 0.023%, with the dissipative soliton pulse being 0.035%. The invention also shows the noise of the pump laser in 8. Clearly, the relative intensity noise of the laser cavity inherits the fraction of the pump laser noise that has an offset frequency of < 4 kHz. By integrating the phase noise PSD in the interval [1kHz,10MHz ], the timing jitter in both cases was estimated to be 41fs. However, the integral value represents only an upper limit, since the phase noise measurement is limited by the system noise floor at a frequency >10kHz [ section C of fig. 8 ]. By using highly sensitive measurement techniques, lower values can be expected. Finally, examining long term stability, the present invention records the average output power of soliton pulses and dissipative soliton pulses over 3 hours at maximum pump power that allows stable mode-locking operation, respectively, as shown in fig. 10 and 11. The corresponding highest average powers are 71mW and 627mW respectively, and the root mean square power fluctuation is less than 0.3%, which shows that the fiber has good stability, and all the fiber benefits from the structural design of the full polarization-maintaining fiber.

In some embodiments, the movable part of the martinez stretcher 24 is shown in fig. 12, the focusing lens 22 and the second reflecting mirror 23 are placed on a small optical platform, the distance between the focusing lens 22 and the second reflecting mirror is the focal length of the focusing lens 22, the optical platform is attached with a track which can move back and forth in one direction, and the moving direction of the optical platform is consistent with the direction of the light path after diffraction of the grating 21, so that real-time intra-cavity dispersion change can be realized by changing the distance between the focusing lens 22 and the grating 21 through the optical platform, and different dispersed dissipative solitons are output.

Referring to fig. 13, the moving optical stage changes its distance from the grating 21 such that the intra-cavity dispersion changes from negative to positive, the spectral change being shown in fig. 13. When dispersion is negative, the laser operates in a soliton pulse state, and the laser is expressed as a wide spectrum diagram in a frequency domain and is provided with sidebands, and the corresponding pulses in a time domain are very narrow.

However, the long-term stability of mode locking in the soliton state at this time is poor, which means that the 4 negative dispersion values shown in fig. 13 are not optimal dispersion values for mode locking of soliton pulses. When the intra-cavity dispersion is gradually changed into positive dispersion, the laser operates in a dissipative soliton pulse state, the spectrum is obviously narrowed and the edges are steep, the dissipative soliton spectrum is more typical, and the pulse is gradually widened due to the fact that the positive chirp is increased due to the dispersion change.

In this embodiment, referring to fig. 14 and 15, a movable schematic view of the first mirror 19 is shown, and the first mirror 19 is mounted on a support with a movable joint, which is purchased from the company cable Lei Bo. When the laser is built, the Martin stretcher 24 is directly built behind the first reflecting mirror 19, when the soliton state needs to be switched, the first reflecting mirror 19 can be switched by being broken off, the Martin stretcher 24 does not need to be built again and the light path is coupled, and the use efficiency is greatly improved.

In some embodiments, the high-concentration rare earth element doped gain fiber with other large mode field area can be replaced in the technical scheme, so that ultra-short laser pulse output of different working wave bands is realized. For example, a large mode field polarization-preserving thulium-doped fiber (PM-LMA-TDF) or a large mode field polarization-preserving thulium-holmium co-doped fiber (PM-LMA-THDF) is used for realizing 2 mu m-band laser output; and (3) realizing 1 mu m-band laser output by using a large-mode-field polarization-maintaining ytterbium-doped fiber (PM-LMA-YDF).

In some embodiments, the phase shifter formed by the half-wave plate and the faraday rotator in the above scheme is the nonreciprocal phase bias device 25 for realizing mode locking and self-starting of the laser, and can be replaced by any commercial device or optical device for realizing mode locking and self-starting and nonreciprocal phase bias.

In the high-power high-stability full polarization-maintaining nine-shaped mode-locked fiber laser, the combination of the NALM module with phase bias and the full PM fiber structure ensures the reliable starting of mode locking and high pulse stability. This configuration is very beneficial to the design of a mode-locked large-mode-area fiber oscillator, and effectively solves the problem that the disturbance of a higher-order mode often causes poor self-starting performance. Compared with the previous report about the phase bias NALM mode-locked erbium-doped fiber laser, the laser provided by the utility model is obviously improved in the aspects of average power and pulse energy, and compared with the polarization-maintaining single-mode fiber laser oscillator in the same mode-locked mode, the output single-pulse energy is improved by 13 times, and the average output power is improved by 17 times. One potentially attractive application for such high power lasers is the use of frequency doubling to produce an output of approximately 800nm, which is the preferred wavelength for many current applications of ultra-fast optics.

The high-power high-stability full polarization-maintaining nine-shaped mode-locking fiber laser has excellent performance and is suitable for fields of ultrafast optics, laser processing, medical equipment, scientific research and the like. Its high stability, high pulse quality and high power output provide a reliable laser source for a variety of applications.

The reason why the high-power high-stability full polarization-maintaining nine-shaped mode-locking fiber laser is applied is that the laser pulse width breaks through from nanosecond magnitude to femtosecond magnitude from the appearance of the first solid laser to the development of the current fiber laser, and the output performance of the laser also develops towards a higher and better direction. Compared with a solid-state laser, the ultrafast fiber laser has the advantages of good beam quality, high heat management efficiency, flexible and compact structure, low maintenance cost and the like, so that the ultrafast fiber laser has important application in the fields of military, scientific research, industry, medical treatment and the like. Ultrashort pulses of different wave bands can be output by changing the doped ion types of the gain fiber in the laser oscillation cavity 26, and the working wave band of the fiber laser is covered from a visible light wave band to a middle-far infrared wave band so as to meet different requirements of different fields. For example, ytterbium-doped fiber lasers can produce 1.0 μm band lasers, and have important applications in industrial fields (e.g., dicing, welding, etc.); the erbium-doped fiber laser can generate 1.5 mu m-band laser, the band is a low-loss communication window of an optical communication band, the loss transmitted in the fiber is usually only 0.2dB/km, and the research on a 1.5 mu m-band stable light source plays an important role in fiber communication; meanwhile, light with a wavelength of 1.5 μm is positioned in a human eye safety band, and the band has large contrast with the background for a plurality of targets (such as vehicles, ships, cement buildings and the like), and has attractive application in the military fields of laser radar, target identification and the like. For another example, the thulium-doped or holmium-doped fiber laser can generate 2 μm-band ultrashort laser pulses in a molecular fingerprint region, the band covers molecular absorption spectrums of CO ₂,H₂ O, NO ₂ and the like, a high-sensitivity gas sensor can be formed, the gas sensor is used for realizing atmosphere remote sensing, and the 2 μm-band ultrashort laser pulses are also widely applied to medical industry (such as laser surgical knife, tissue excision and the like) because more than 75% of human tissue is composed of water; meanwhile, the ultra-short pulse with the wave band of 2 mu m is used as a seed source of the laser, and the laser wavelength can be easily expanded to a middle-far infrared wave band with the wave length of more than 10 mu m by utilizing the optical nonlinear conversion effect (such as the techniques of difference frequency, supercontinuum generation and the like). Along with the development of optical fiber preparation technology and related fields, the optical fiber laser with better performance is continuously excavated, the polarization maintaining optical fiber laser with high stability and easy mode locking improves the overall environmental stability of the laser in application, makes an important contribution to the development of the optical fiber laser, and promotes the development of the optical fiber laser.

The foregoing description of the preferred embodiments of the utility model is not intended to be limiting, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and principles of the utility model.

Claims

1. The utility model provides a high power high stability all polarization-preserving nine style of calligraphy mode-locked fiber laser which characterized in that includes:

A laser oscillation cavity (26);

A nonreciprocal phase bias device (25) positioned in the laser oscillation cavity (26) and composed of a Faraday rotator and a quarter wave plate for enhancing the mode locking self-starting capability;

A hole diaphragm (18) inserted into the laser oscillation cavity (26) for suppressing the higher order mode by spatial filtering;

a Martin stretcher (24) positioned in the laser oscillation cavity (26) to replace the intracavity reflection end mirror for realizing the normalization of intracavity dispersion so as to output dissipative solitons;

A large mode area gain fiber (5) for achieving high power laser output.

2. The high power high stability all polarization maintaining nine mode locked fiber laser of claim 1, wherein the non-reciprocal phase bias (25) is comprised of two faraday rotators, a first faraday rotator (10) and a second faraday rotator (12), respectively, and a quarter wave plate, a first quarter wave plate (11) disposed between the first faraday rotator (10) and the second faraday rotator (12).

3. The high power high stability all polarization maintaining nine mode locked fiber laser of claim 2, wherein the relative angle between the faraday rotator and the quarter wave plate of the non-reciprocal phase bias (25) is pi/2.

4. The high-power high-stability full polarization-maintaining nine-shaped mode-locking fiber laser according to claim 1, wherein the high-power high-stability full polarization-maintaining nine-shaped mode-locking fiber laser is further provided with a first fiber connector (4) and a second fiber connector (6), the gain fiber (5) is connected between the first fiber connector (4) and the second fiber connector (6), the first fiber connector (4) is located on one side of the first collimating lens (3), and the second fiber connector (6) is located on one side of the second collimating lens (7).

5. The high-power high-stability full polarization-maintaining nine-shaped mode-locked fiber laser according to claim 4, wherein a first dichroic mirror (2) is arranged between the first collimating lens (3) and the laser oscillation cavity (26), the pump source (1) is arranged towards the first dichroic mirror (2), the laser oscillation cavity (26) is positioned in the first polarization beam splitter (14), a second quarter wave plate (17), a second polarization beam splitter (16) and a third half wave plate (15) are arranged between the first polarization beam splitter (14) and the hole type diaphragm (18), and an end mirror is arranged on the other side of the hole type diaphragm (18).

6. The high-power high-stability full polarization-maintaining nine-shaped mode-locked fiber laser according to claim 5, wherein the nonreciprocal phase bias device (25) is arranged at the bottom side of the first polarization beam splitter (14), and a first half wave plate (9), a second dichroic mirror (8) and a second collimating lens (7) are sequentially arranged between the nonreciprocal phase bias device (25) and the second fiber connector (6).

7. The high-power high-stability full polarization-maintaining nine-shaped mode-locked fiber laser according to claim 6, wherein the end mirror is a first reflecting mirror (19), and the laser oscillation cavity (26) with the first reflecting mirror (19) as the end mirror and the pump source (1) form a polarization-maintaining fiber laser output pulse based on NALM mode locking to be in a soliton state.

8. The high power high stability all polarization maintaining nine mode-locked fiber laser of claim 7, wherein the end mirror is a martinez stretcher (24), and the NALM mode-locked polarization maintaining fiber laser output pulse of the first mirror (19) is dissipated as soliton state with the martinez stretcher (24) replacing the first mirror (19).

9. The high power high stability all polarization maintaining nine mode locked fiber laser of claim 8, wherein said martinez stretcher (24) comprises a D-mirror (20), a grating (21), a focusing lens (22) and a second mirror (23).

10. The high power high stability all polarization maintaining nine mode locked fiber laser of claim 9, wherein the focusing lens (22) and the second mirror (23) of the martinz stretcher (24) are placed on a moving optical platform, the distance between the focusing lens (22) and the second mirror (23) is the focal length of the focusing lens (22), the optical platform is attached with a track moving back and forth in one direction, and the moving direction of the optical platform is consistent with the direction of the optical path after diffraction of the grating (21).