CN102185242B - Totally positive dispersion cavity mode-locked all-fiber laser - Google Patents

Abstract

The invention discloses a totally positive dispersion cavity mode-locked all-fiber laser, which is an environmentally-stable and novel-structured totally optical mode-locked super-short laser pulse laser which works in a totally positive dispersion area, and uses rare earth-mixed optical fibers as a laser gain medium, a polarization beam splitter to split light, a band-pass long-period fiber grafting filter as a mode-locked laser centre wavelength selection and mode-locked laser spectrum filtering optical pulse compression element, and a semiconductor saturable absorber as a mode-locked element and the like to form an optical fiber laser structure with high repetition rate, high power, simple structure and high efficiency. The laser outputs picosecond and femtosecond optical pulse-width polarized laser with a wavelength of 1 mu m which, after being amplified by the high-power optical fiber amplifier, can be used for molecularly systemic pumping-detection ultrafast optical physical experiment or environment monitoring, microwave photonic or biophysical detection, double-wavelength pumping-detection ultrafast optical physical experiment, frequency-combining optical radiation generation, coherent anti-stokes Raman scattering microscopy, micromachining and the like.

Description

Fully positive dispersion cavity mode-locked all-fiber laser

technical field

The invention relates to a fiber laser, in particular to a passively mode-locked all-fiber laser with high pulse repetition rate ultrashort laser pulse output, which is suitable for generating stable ultrashort laser pulse output for biomedicine such as multiphoton imaging microscopy Applications, etc. and the use of direct difference frequency method to generate ultrashort pulse mid-infrared laser radiation for pumping and detection of molecular systems and other scientific experiments, environmental monitoring and microwave photonics and biophysical detection, etc., belong to the field of optical information technology.

Background technique

Today's scientific experiments such as pumping and detection of molecular systems, environmental monitoring, microwave photonics and biophysical detection require mid-infrared light sources with high average power ultrashort pulses. In recent years, with the development of solid-state laser media such as tunable Ti:sapphire laser technology, harmonic frequency conversion technology, and optical parametric oscillation and amplification technology, high repetition rate ultra-short optical pulses covering from the extreme ultraviolet of 200nm to the mid-infrared of 4μm have been realized. . The THz system can provide a wavelength of more than 20μm.

In recent years, the rapid development of high-power fiber ultrashort optical pulse laser technology has provided new opportunities and possibilities for the development of high-power and high repetition rate mid-infrared radiation sources based on dual-wavelength mixing based on fiber laser technology (HMPask, RJCarman, DC Hanna , ACTropper, CJMackechnie, PRBarber, and JMDawes, IEEE J.Sel.Top.QuantumElectron.1, 2(1995).) (F.Roser, J.Rothhard, B.Ortac, A.Liem, O.Schmidt, T. Schreiber, J. Limpert, and A. Tunnermann, Opt. Lett. 30, 2754 (2005).). Due to its unique waveguide structure, fiber lasers are simple, high-efficiency, strong, lightweight, integrated, high-reliability, and high-stability. The recent development of Nd ³⁺ , Pr ³⁺ , Yb ³⁺ , Er ³⁺ and Tm ³⁺ fiber lasers and amplifiers with broadband laser oscillation provides the possibility of generating dual-wavelength ultrashort pulse lasers with wavelengths greater than 1 μm. However, Nd ³⁺ , Yb ³⁺ , Er ³⁺ and Tm ³⁺ fibers (Tm ³⁺ >200nm, Er ³⁺ >80nm) especially Tm ³⁺ doped fibers also produce dual wavelengths due to their wide gain bandwidth. Potentially efficient medium for femtosecond laser pulse oscillations (HMPask, RJ Carman, DC Hanna, ACTropper, CJ Mackechnie, PR Barber, and JM Dawes, IEEE J. Sel. Top. Quantum Electron. 1, 2 (1995).).

The use of semiconductor saturable absorbers as mode-locking elements to achieve passive mode-locking in fiber lasers to generate ultrashort laser pulses has always been a highly valued research field (A.Isomaki et al, Optics Express, Vol14, No.20, 9238, 2006) (A. Chong et al, Opt. Lett., Vol.33, No.22, 2638, 2008), and a large number of research results have been published, and there are also some commercial products. However, the existing commercial mode-locked fiber lasers only output single-wavelength laser light, and there is no commercial dual-wavelength mode-locked fiber laser.

Recent reports on the Y _b ³⁺ fiber laser literature (FrankW.Wise et al, High energy femtosecond fiber lasers based on pulsepropagation at normal dispersion, Laser & Photonics.Rev.2, No.1-2) in the full positive dispersion region , 58-73, 2008) made a big step forward in the ultrashort pulse fiber laser technology with large output energy, stable structure and practical application. Although the mode-locked fiber laser outputs picosecond laser pulses with a large number of positive linear chirps due to the total positive dispersion cavity, femtosecond laser pulses with large energy transformation limit can be obtained after compression by extracavity dispersion. Of course, due to This kind of laser adopts the mechanism of spectral filtering and optical pulse compression, so that the spectral bandwidth of the laser output is limited to a certain extent. However, because the structure of this laser is simplified and can realize all-fiber and output picosecond-level high-energy mode-locked optical pulses, it is subject to academic research. world's attention.

In a fully positive dispersion cavity mode-locked Yb-doped fiber laser, there have been some reports in the literature on the influence of spectral filtering on the formation of mode-locked laser pulses and the stability of the mode-locked fiber laser (BGBale et al, Spectral filtering for mode locking in the normal dispersive regime, OptLett., Vol.33, No, 9, 2008, 941; A. Chong et al, Properties of normal dispersion femtosecond fiber lasers, JOSA(B), Vol.25, No.2, 2008, 140). In the fully positive dispersion mode-locked fiber laser cavity, filtering plays a compression effect on the self-phase-modulated pulse-broadened optical pulse, and at the same time exerts an effect on the self-amplitude modulation in the cavity, which plays a very critical role in the stability of the mode-locked laser. It can be considered that proper spectral filtering is the key technology for the self-oscillation and stable mode-locking of fully positive dispersion mode-locked fiber lasers. It has been reported in public literature, such as the spectrum formed by interference filters with a bandwidth of 4 to 12nm or birefringent quartz plates of different thicknesses in the Yb3+-doped fiber laser of the nonlinear polarization rotation mechanism of the ring cavity by Cornell University in the United States in 2006 and 2007. The filter has achieved stable mode-locked oscillation (A.Chong et al, All Normal dispersion femtosecond fiber laser, OpticsExpress, Vol.14, No.21, 2006, 10095; A.Chong et al., All Normal dispersion femtosecond fiber laser with pulses energy above 20nJ, Optics letters, Vol.32, No.16, 2007, 2408; K.Kieu et al., Sub-100fs pulses at watt-level powers from a dissipative-soliton fiber laser, Opt Lett., Vol.34 , No.5, 2009, 539), in 2007-2008, the US Naval Laboratory and the Hanloway laser of the University of Hanloway in Germany also used a Y _b ³⁺ doped fiber laser with a fully positive dispersion ring cavity similar to the mode-locking mechanism to achieve Mode-locked oscillation (among them, the Naval Laboratory uses the full positive dispersion ring cavity to place the interference filter, while the German laser Hanloway uses a specially designed optical fiber wavelength division multiplexer (WDM) as the intracavity spectral filter to realize the pulse Principles of compression and initiation of intracavity semiconductor saturable absorbers (Janet W.Lou et al., Experimental measurements of soliton pulse characteristics from an all normal dispersion Yb-doped fiberlaser, Optics Express, Vol.15, No.8, 2007, 4960 ; O.Prochnow et al., All fibersimilariton laser at 1μm without dispersion compensation, Optics Express, Vol.15, No.11, 2007, 6889; Michael Schultz et al, All fiber Ytterbiumfemtosecond laser without dispersion compensation, Optics Express, Vo 16, No. 24, 2008, 19562)). The mode-locked laser with full polarization-maintaining doped Y _b ³⁺ fiber is used for the environment-stable positive dispersion. In 2008, Cornell University in the United States used the mode-locking mechanism of semiconductor saturable absorbers to adopt it in the linear cavity polarization-maintaining Y _b ³⁺ fiber laser. The spectral filter made of 12nm birefringent quartz plate realizes stable mode-locked oscillation (A. Chong et al., Environment stable all normal-dispersion femtosecond fiber laser, Optics letters, Vol.33, No.10, 2008, 1071) . In 2006, the Laser Engineering Institute of Osaka University in Japan adopted a fully polarization-maintaining fiber ring cavity Yb-doped fiber laser without intracavity dispersion compensation to achieve tuned mode-locked laser output (K.Sumimura et al, Environmentally-stablemode-locked Yb fiber laser composed of all polarization maintaining fiber with a broad tuning range, OSA/CLEO 2006, CThJ4.pdf). In recent years, mode-locked lasers using polarization-maintaining _Yb3 ^+-doped fibers, such as Germany and Denmark, generally use intracavity dispersion compensation such as diffraction grating pairs or photonic crystal fibers, or use reflective chirped fiber gratings (CFBG) as output Couplers and dispersion compensators (T.Schreiber et al, Microj oule levelall-polarization-maintaining femtosecond fiber source, Optics letters, Vol.31, No.5, 2006, 574; CKNielsen et al., Self-starting self-similar allpolarization maintaining Yb-doped fiber laser, Optics Express, Vol.13, No.23, 2005, 9346; B.Ortac et al, Experimental and numerical study of pulses dynamics in positive net cavity dispersion mode-locked Yb-doped fiber lasers, Optics Express , Vol.15, No.23, 2007, 15595; Dmitry et al., Monolithic all PM femtosecond Yb-fiber laser stabilized with a narrow-bandfiber Bragg grating and pulses-compressed in a hollow core photonic crystalfiber, Optics Express, Vol. 16, No. 18, 2008, 14004). However, in the above-mentioned currently reported mode-locked Yb-doped fiber lasers working in the total positive dispersion region, non-fiberized interference filters or reflective chirped fiber Bragg gratings (CFBG) are used in the cavity as cavity surface mirrors or The output mirror, these components or affect the full fiber optic cavity, or affect the design of the laser cavity.

In recent years, the progress of long period bandpass fiber grating (Long Period Grating, LPG) filter research (Radan Slavík et al., Long-Period Fiber-Grating-Based Filter for Generation of Picosecond and Subpicosecond Transform-Limited Flat-TopPulses, IEEE PHOTONICS TECHNOLOGY LETTERS, VOL.20, NO.10, 2008, 806; D.Nodop et.al., Long period gratings written in Large modephotonic crystal fiber, Appl.Physics.B, 92, 2008, 509-512) makes It is possible to design an all-fiber mode-locked laser working in a fully positive dispersion cavity using a long-period band-pass fiber grating filter as a mode-locked laser pulse compression and laser wavelength filter tuning element, but as far as the author knows, there is no public literature reports.

The Chinese invention patent with the publication number CN101202408A "Polarization-Maintaining Fiber Bragg Grating Tunable Dual-Wavelength Fiber Laser" uses two spectral reflection peaks of two different polarization states of the polarization-maintaining fiber Bragg grating to change the polarization maintaining by changing the pressure or temperature. The reflection peak position of the fiber grating realizes dual-wavelength linear polarization-tuned laser output. The disadvantages are: 1. The spectral interval of the two different reflection peaks (with different polarization states) caused by the inherent large birefringence of the polarization maintaining fiber is relatively small and the adjustment range is small; 2. Due to the narrow bandwidth Polarization-maintaining fiber gratings are used as the reflective surface of the laser cavity, so it is difficult to achieve passive mode-locking to generate ultrashort laser pulses; 3. This cavity structure is suitable for narrow-linewidth tunable dual-wavelength fiber lasers. The Chinese invention patent "a multi-wavelength output fiber laser" with the publication number CN1194453C uses AWG (arrayed waveguide grating) as an intracavity optical filter to realize multi-wavelength laser output.

In the Chinese invention patent "polarized dual-wavelength fiber ultrashort pulse laser" with the publication number CN101510663A, it is proposed to use the two optical axis directions (fast axis and slow axis) of the polarization-maintaining fiber as two wavelengths of laser light by means of polarization splitting. polarization direction. However, in this technology, two parallel diffraction grating pairs or reflective chirp fiber gratings (CFBG) are used in the laser cavity as two A wavelength dispersion compensation device to output dual-wavelength mode-locked laser pulses with a femtosecond pulse width.

After literature search, the following technologies involve mode-locked fiber lasers, such as Jian Liu, UltrshortStable Mode-locked Fiber Laser At One Micron By Using PolarizationMaintaining(PM) Fiber and Photonic Bandgap Fiber(PBF), US Patent, US2008/0151945 A1, Hong Lin, Wavelength Tunable, Polarization Stable Mode-locked Fiber Laser, World International Property Organization, PCT/US00/19170, 2001 and O.Okhotnikov et al, A Mode-Locked Fiber Laser, World International Property Organization, PCT/FI2006/050184, 2006 wait. The above-mentioned technology adopts the concept of working in the negative dispersion region, and there are solid diffraction grating pairs or photonic bandgap fiber gratings in the cavity for dispersion compensation, etc., which also affects the full-fiber laser cavity and affects the long-term stability of the mode-locked fiber laser. Sex, or the cost of the laser is very expensive to affect its scope of use.

Contents of the invention

In order to overcome the deficiencies in the prior art, the object of the present invention is to provide a mode-locked all-fiber laser that works in the full positive dispersion region, has no dispersion compensating elements, realizes all-fiber, is practical, and outputs high-energy laser pulses.

In order to achieve the above object, the technical scheme adopted in the present invention is:

A fully positive dispersion cavity mode-locked all-fiber laser, which is an all-fiber ultrashort pulse linear cavity laser operating in a fully positive dispersion region, and the linear cavity laser includes a first laser cavity end face and a semiconductor that can be used for mode locking Saturable absorber, fiber laser gain medium, band-pass long-period fiber grating, output coupler and the end face of the second laser cavity; the band-pass long-period fiber grating has a central wavelength of 1.0-1.1 μm and a bandwidth of 4 ~12nm band-pass long-period fiber grating, or two band-pass long-period fiber gratings with a central wavelength of 1.0-1.1μm and a bandwidth of 4-12nm, and the central wavelengths of each band-pass long-period fiber grating are different ; The fiber laser gain medium is a polarization-maintaining rare-earth-doped gain fiber.

This fully positive dispersion cavity mode-locked all-fiber linear cavity laser has the following three specific structures:

The structure of the first linear cavity laser is:

A semiconductor saturable absorber is attached to an optical fiber end face of a wavelength division multiplexer to generate mode-locked optical pulses;

A pump source provides pump light for the wavelength division multiplexer as input pump light;

A wavelength division multiplexer is connected to the polarization-maintaining rare-earth fiber for inputting the pump laser of the pump source into the polarization-maintaining rare-earth fiber to generate laser gain;

One end of a band-pass long-period polarization-maintaining fiber grating is connected to the other end of the polarization-maintaining gain fiber;

One end of a fiber coupler with only a single polarization axis oscillating output is connected to the other end of a band-pass long-period fiber grating;

A total reflection cavity mirror is connected to the other end of the output coupler.

The structure of the second linear cavity laser is:

A partial reflectivity coupling mirror is connected to the signal input fiber of the polarization maintaining 980/1064 wavelength division multiplexer;

The 976nm fiber-coupled pump laser is connected to the pump laser input fiber of the polarization-maintaining 980/1064 wavelength division multiplexer to input the pump laser into the laser cavity;

One end of a polarization-maintaining _Yb ³⁺ doped gain fiber is connected to the other end of the polarization-maintaining 980/1064 wavelength division multiplexer, which is the common end of the input of the signal laser and the pump laser;

The other end of the polarization-maintaining _Yb3 ⁺ -doped gain fiber is connected to a polarizing beam splitter beam-combining one-end polarization-maintaining fiber, and the polarization beam splitter separates two lasers with different polarization directions and wavelengths;

One end of the two polarization-maintaining fiber-coupled attenuators is respectively connected to the two polarization direction coupling fibers of the polarization beam splitter, and the two attenuators respectively adjust the net gain balance of the two wavelength lasers in the laser cavity;

The other end of the polarization-maintaining fiber-coupled attenuator is respectively connected to one end of two band-pass long-period polarization-maintaining fiber gratings with different central wavelengths and a bandwidth of 4 to 12nm. The function of the band-pass long-period polarization-maintaining fiber grating is dual The selection of the central wavelength of the wavelength laser and the compression of optical pulses by two wavelengths mode-locked laser spectrum filtering;

The two semiconductor saturable absorbers are respectively connected with the other ends of the two bandpass long-period polarization-maintaining fiber gratings through coupling optical systems or directly through optical glue. The semiconductor saturable absorbers act as mode-locking elements and laser cavity reflections element.

The structure of the third linear cavity laser is:

A coupling mirror with partial reflectivity is connected with a polarizing beam splitter and a one-end polarization-maintaining fiber;

The signal input fibers of the two polarization-maintaining fiber 980/1064 wavelength division multiplexers are respectively connected to the two polarization direction coupling fibers of the polarization beam splitter;

Two fiber-coupled 976nm pump lasers are respectively connected to the pump laser input fibers of two polarization-maintaining 980/1064 wavelength division multiplexers, and the pump laser is input into the laser cavity;

One end of two polarization-maintaining doped _Yb ³⁺ gain fibers of different lengths is respectively connected to the other end of two polarization-maintaining 980/1064 wavelength division multiplexers. This end is the common end of the signal laser and the pump laser. Y _b ³⁺ gain fiber produces laser gain under the action of pump laser;

The other ends of two different lengths of polarization-maintaining Y _b ³⁺ gain fibers are respectively connected to one end of two band-pass long-period polarization-maintaining fiber gratings with different center wavelengths and bandwidths from 4 to 12 nm. The role of the polarizing fiber grating is to select the central wavelength of the dual-wavelength laser and to compress the spectral filtering optical pulse of the two-wavelength mode-locked laser;

The two semiconductor saturable absorbers are respectively connected with the other ends of the band-pass long-period polarization-maintaining fiber gratings with different central wavelengths through the coupling optical system or directly through optical glue. The semiconductor saturable absorbers act as mode-locking elements and a Laser cavity reflective element.

A fully positive dispersion cavity mode-locked all-fiber laser, which is an ultrashort pulse non-polarization-maintaining fiber ring cavity laser operating in a total positive dispersion region, the ring cavity laser includes a fiber-coupled isolator, fiber polarization Controller, 976nm or 915nm pump laser with fiber-coupled output, 976/1060nm or 915/1064nm wavelength division multiplexer, ordinary single-mode Y _b ³⁺ fiber laser gain medium, a section of single-mode fiber, a single-mode ribbon A pass-through long-period fiber grating and a fiber-coupled polarization beam splitter; the single-mode band-pass long-period fiber grating has a central wavelength of 1.0 to 1.1 μm and a bandwidth of 4 to 12 nm; the structure of the laser is:

A fiber polarization controller is connected with a fiber-coupled isolator, the isolator ensures that the fiber ring cavity forms laser oscillation in one direction, and the fiber polarization controller adjusts and controls the laser polarization in the cavity;

The signal input end of a 980/1060 wavelength division multiplexer is connected with the optical fiber polarization controller;

The fiber-coupled pump laser is connected to the pump laser input end of the 980/1060 wavelength division multiplexer to couple the pump laser into the fiber ring laser cavity;

One end of the single-mode doped fiber gain medium is connected to the signal laser/pump laser hybrid end of the 980/1060 wavelength division multiplexer, and the gain medium generates signal laser gain under the pump laser;

One end of a common single-mode fiber is connected to the other end of the doped fiber gain medium;

One end of the single-mode bandpass long-period fiber grating is connected to the other end of a common single-mode fiber;

One end of another fiber polarization controller is connected to the other end of a bandpass long-period fiber grating, and the fiber polarization controller adjusts and controls the laser polarization in the cavity;

The input fiber end of a fiber-coupled polarization beam splitter is connected to the other end of the fiber polarization controller;

The input end of the fiber-coupled isolator is optically connected with an output end of the fiber-coupled polarization beam splitter to form a unidirectional ring fiber laser cavity, and the other output end fiber of the fiber-coupled polarization beam splitter is used as the mode-locked ring cavity laser output port.

A fully positive dispersion cavity mode-locked all-fiber laser, which is an ultrashort-pulse fully polarization-maintaining fiber ring cavity laser operating in the total positive dispersion region, and the ring cavity laser includes a fiber end surface pasted with a semiconductor saturable absorbing Polarization-maintaining fiber circulator, polarization-maintaining fiber isolator, polarization-maintaining fiber laser gain medium, band-pass type long-period polarization-maintaining fiber grating filter and output coupler; described band-pass type long-period fiber grating filter, The center wavelength is 1.0-1.1 μm, and the bandwidth is 4-12nm; the fiber laser gain medium uses a section of polarization-maintaining rare-earth-doped gain fiber as the gain medium; the structure of the laser is:

A pump source provides pump light for the wavelength division multiplexer as input pump light;

A wavelength division multiplexer is connected to the polarization-maintaining rare-earth fiber for inputting the pump laser of the pump source into the polarization-maintaining rare-earth fiber to generate laser gain;

One end of a band-pass long-period polarization-maintaining fiber grating is connected to the other end of the polarization-maintaining gain fiber. The function of the band-pass long-period polarization-maintaining fiber grating is to select the central wavelength of the mode-locked laser pulse and to compress the mode-locked spectrum pulse to realize Stable operation of mode-locked lasers;

One end of a fiber coupler with only a single polarization axis oscillating output is connected to the other end of a band-pass long-period fiber grating, and the mode-locked laser pulse is output from the fiber coupler;

The first end optical fiber of a polarization maintaining optical fiber circulator is connected with the other end of the optical fiber coupler;

The second-end fiber of a polarization-maintaining fiber looper is connected to a semiconductor saturable absorber through an optical lens or directly with optical glue. The nonlinear effect of the semiconductor saturable absorber on the laser produces a mode-locking effect in the ring cavity laser. Ultrashort laser pulses;

The third-end optical fiber of a polarization-maintaining fiber circulator is connected to a polarization-maintaining fiber-coupled isolator, and the isolator makes the fiber ring cavity laser unidirectionally generate laser oscillation;

The optical fiber at the output end of the isolator is connected with the optical fiber at the other end of the wavelength division multiplexer to form a complete, unidirectional oscillating ring laser cavity.

The polarization-maintaining rare-earth-doped gain fiber described in the technical solution of the present invention is an ordinary single-mode or single-mode polarization-maintaining rare-earth fiber, or a rare-earth-doped large-core single-mode polarization-maintaining fiber with double-layer pumping, or a rare-earth-doped A polarization-maintaining large core-diameter single-mode photonic crystal fiber; the rare earth doped is Nd ³⁺ , Yb ³⁺ doped.

Compared with the prior art, the present invention has the following obvious advantages:

1. The single-mode bandpass long-period fiber grating is used in the ring cavity mode-locked fiber laser. The whole laser works in the total positive dispersion region. There is no free space dispersion compensation device or photonic crystal dispersion compensation fiber in the cavity, realizing the integration of all optical fibers The optimized structure means that the laser cavity is more stable and practical, and can output greater laser pulse energy.

2. The band-pass long-period polarization-maintaining fiber grating is used in the linear cavity mode-locked polarization-maintaining fiber laser. The whole laser works in the total positive dispersion region. The laser design is simplified and all-fiber integration is realized, which also means that the laser cavity The body is more stable and practical, the environment is truly stabilized, and it can output greater laser pulse energy.

3. In the linear cavity mode-locked dual-wavelength fiber laser, a band-pass long-period polarization-maintaining fiber grating is used, and the entire two laser wavelength mode-locked lasers work in the full positive dispersion region. The laser design is more simplified and all-fiber integration is realized. , which also means that the laser cavity is more stable and practical, the environment is truly stabilized, and it can output greater dual-wavelength laser pulse energy.

Description of drawings

Fig. 1 is a schematic diagram of the structural composition of the all positive dispersion cavity mode-locked all-fiber laser provided in embodiment 1;

2 is a schematic diagram of the structure and composition of the fully positive dispersion cavity mode-locked all-fiber laser provided in Embodiment 2;

3 is a schematic diagram of the structure and composition of the all positive dispersion cavity mode-locked all-fiber laser provided in embodiment 3;

Fig. 4 is a schematic diagram of the structure and composition of the all positive dispersion cavity mode-locked all-fiber laser provided in embodiment 4;

Fig. 5 is a schematic diagram of the structure and composition of the all positive dispersion cavity mode-locked all-fiber laser provided in Embodiment 5.

In the figure: 0 (01, 02), semiconductor saturable absorber element for mode locking; 1 (101, 102), band-pass long-period polarization-maintaining fiber grating; 10, ordinary single-mode band-pass long-period fiber grating ; 2, polarization-maintaining fiber-coupled polarization beam splitter; 3 (301, 302), polarization-maintaining doped Y _b ³⁺ gain fiber; 30, ordinary single-mode doped Y _b ³⁺ gain fiber; 4 (401, 402), maintaining Polarized fiber 976/1064 wavelength division multiplexer; 40, single-mode fiber 976/1064 wavelength division multiplexer; 5 (51, 52), 976nm pump laser (source); 6, partial reflection output mirror; 8 (15 ), single-mode fiber polarization controller; 9, fiber-coupled polarization beam splitter; 12, total reflection mirror; 13, single-polarization polarization-maintaining fiber output coupler with a certain output ratio; 14, single-mode fiber-coupled isolator; 17, Polarization maintaining fiber looper; 18. Polarization maintaining fiber coupling isolator.

Detailed ways

The present invention will be further described below in conjunction with accompanying drawing and embodiment:

Example 1:

This embodiment provides a structure of a mode-locked fully polarization-maintaining Yb ³⁺ fiber-doped linear cavity laser working in the fully positive dispersion region and having a stable environment. A section of polarization-maintaining rare-earth-doped gain fiber is used as the gain medium. The band-pass polarization-maintaining long-period fiber grating filter with central wavelength and bandwidth is used as a component for central wavelength selection and spectral filtering pulse compression of mode-locked lasers, and realizes stable mode-locked oscillation of all-fiber ultrashort pulse lasers.

Referring to accompanying drawing 1, it is the schematic diagram of the cavity structure that adopts linear cavity mode-locking full polarization maintaining fiber laser in this embodiment; Components for center wavelength tuning and spectral filtering of pulse compression in mode lasers. The pump laser is coupled into the polarization-maintaining doped rare-earth fiber through a wavelength division multiplexer (WDM) to generate gain, and a band-pass long-period fiber grating filter with an appropriate central wavelength and bandwidth is used in the laser cavity as the choice of the central wavelength of the laser and The component for spectral filtering and pulse compression, the polarization-maintaining fiber output coupler outputs part of the mode-locked laser power and ensures only one optical axis direction of laser oscillation, the total reflection mirror is used as the first cavity end face of the laser cavity, and one is coupled through the optical system or directly bonded The semiconductor saturable absorber on the end face of the fiber is used as the second reflective cavity surface of the laser and the mode-locking component, the nonlinear effect of the semiconductor saturable absorber on the laser and the gain fiber, the appropriate central wavelength (1.0-1.1μm) and bandwidth (4-12nm) band-pass polarization-maintaining long-period fiber grating spectral filtering optical pulse compression, and generates stable mode-locked ultrashort pulse laser in the entire positive dispersion laser cavity. As can be seen from Figure 1, the specific connection relationship is: the pump laser 5 is coupled into the polarization-maintaining rare-earth fiber 3 through a wavelength division multiplexer (WDM) 4 to generate gain; the laser cavity uses a central wavelength of 1.1 μm, A band-pass long-period fiber grating filter 1 with a bandwidth of 6nm is used as a component for selecting the center wavelength of the laser and compressing optical pulses for spectral filtering; a polarization-maintaining fiber output coupler 13 and a band-pass long-period fiber grating filter with an appropriate bandwidth 1 connection, the polarization-maintaining fiber output coupler 13 outputs part of the mode-locked laser power and ensures only the laser oscillation in the direction of the slow axis; the total reflection mirror 12 is used as the first reflection end face of the laser cavity; one is coupled through an optical system or directly glued to the end face of the fiber The semiconductor saturable absorber 0 on the fiber laser is used as the second reflective cavity surface and the mode-locking component of the fiber laser. The nonlinear effect of the semiconductor saturable absorber 0 on the laser is related to the gain fiber 3. Band-pass polarization-maintaining long period with appropriate bandwidth The optical pulse compression 1 of the fiber grating filter generates a stable mode-locked ultrashort pulse laser in the entire positive dispersion laser cavity, which is output through the polarization-maintaining fiber output coupler 13 . All optical fiber devices in the all-fiber laser cavity are polarization-maintaining devices to ensure stable laser polarization in the cavity and stable mode-locked work in the environment.

Example 2:

This embodiment provides a structure of a mode-locked dual-wavelength fully polarization-maintaining Yb3+ fiber-doped linear cavity laser working in a fully positive dispersion region and operating in a stable environment. A section of polarization-maintaining rare-earth-doped gain fiber is used as the gain medium, and two band-pass polarization-maintaining long-period fiber grating filters with appropriate center wavelength (center wavelength 1.0-1.1μm adjustable) and bandwidth of 4-12nm are applied in the cavity The device is used as an element for selective tuning of the central wavelength of the dual-wavelength mode-locked fiber laser and spectral filtering optical pulse compression. The semiconductor saturable absorber is used to realize the stable mode-locked oscillation of the dual-wavelength all-fiber ultrashort pulse laser.

Figure 2 is a schematic diagram of the cavity structure of a dual-wavelength all-fiber linear cavity laser that adopts semiconductor saturable absorber mode-locking and works in the total positive dispersion region of this embodiment; The band-pass long-period fiber grating filter is used as a component for central wavelength selection and spectral filtering pulse compression of mode-locked lasers. The pump laser is coupled into the polarization-maintaining rare-earth fiber through a wavelength division multiplexer (WDM) to generate gain, the polarization beam splitter is used as a dual-wavelength laser splitting device, and two bandpass long-period polarization-maintaining fiber gratings with different center wavelengths are used as A dual-wavelength ultra-short-pulse fiber laser operating in the positive dispersion region with a dual-wavelength laser selection element in the laser cavity and a mode-locked spectral filter optical pulse compression element, and a semiconductor saturable absorber as a mode-locked element. Referring to accompanying drawing 2, the specific connection relation of this fiber laser structure is: a coupling mirror 6 of partial reflectivity is connected with the laser signal input fiber of polarization maintaining 980/1064 wavelength division multiplexer 4, and the function of coupling mirror 6 is output lock Mode laser pulses and the second reflective end face of the entire laser; a polarization-maintaining fiber wavelength division multiplexer (WDM) 4 is connected to the pump laser 5, and the pump laser 5 is coupled into the fiber through the wavelength division multiplexer (WDM) 4 In the laser cavity; one end of a section of polarization-maintaining doped Y _b ³⁺ gain fiber 3 is connected with the other end (signal laser and pump laser common end) of polarization-maintaining 980/1064 wavelength division multiplexer 4 to generate laser gain; The other end of the polarization-doped Y _b ³⁺ gain fiber 3 is connected to the polarizing beam splitter 2 beam-combining one-end polarization-maintaining fiber. separate; one end of two polarization-maintaining fiber-coupled attenuators 11,12 is respectively connected with two polarization direction coupling fibers of the polarization beam splitter 2, and the function of the attenuators 11,12 is to change the two wavelength arms of the dual-wavelength fiber laser loss to balance the net gain of the two wavelength lasers; the other end of the attenuator 11 and 12 coupled with the polarization-maintaining fiber is respectively connected to two different center wavelengths (one center wavelength is 1.02 μm, the other is 1.09 μm), and the bandwidth is 10nm One end of the band-pass long-period polarization-maintaining fiber grating 101, 102 is connected, and the role of the band-pass type long-period polarization-maintaining fiber grating 101, 102 is to select the central wavelength of the dual-wavelength laser and to compress the optical pulse of the two-wavelength mode-locked laser ; The two semiconductor saturable absorbers 01, 02 are respectively connected with the other ends of the two band-pass long-period polarization-maintaining fiber gratings 101, 102 through a coupling optical system or directly through optical glue, and the semiconductor saturable absorbers 01, 02 A cavity reflective element that acts as the mode-locking element and laser cavity. The polarization beam splitter 2 separates the two wavelengths of laser light in a polarized manner to control them separately (such as mode-locking, etc.), and the realization of the two-wavelength laser mode-locking is to use two semiconductor saturable absorbers 01, 02. Two bandpass long-period polarization-maintaining fiber gratings with different central wavelengths 101 and 102 select two different mode-locked central wavelengths and realize mode-locked spectral filtering optical pulse compression in the total positive dispersion laser cavity to achieve stable dual Wavelength mode-locked ultrashort pulse laser pulse output.

Example 3:

This embodiment provides a structure of a mode-locked dual-wavelength fully polarization-maintaining Y _b ³⁺ doped linear cavity fiber laser working in full positive dispersion and stable environment. Two polarization-maintaining rare-earth-doped gain fibers with different lengths are used as the gain medium, and two band-pass long-period polarization-maintaining fiber grating filters with an appropriate center wavelength (1.0-1.1μm) and a bandwidth of 4-12nm are applied in the cavity As an element for selective tuning of the central wavelength of a dual-wavelength mode-locked fiber laser and spectral filtering optical pulse compression, a semiconductor saturable absorber is used to realize the mode-locked oscillation of a dual-wavelength fully positive dispersion cavity all-fiber ultrashort pulse laser.

Figure 3 is a schematic diagram of the cavity structure of a dual-wavelength all-fiber linear cavity laser that uses a semiconductor saturable absorber to achieve mode locking and works in the total positive dispersion region in this embodiment; two appropriate center wavelengths (1.0～ 1.1μm) and bandwidth (4-12nm) band-pass long-period fiber grating filter is used as an element for selective tuning of the center wavelength of the mode-locked laser and optical pulse compression for spectral filtering. Referring to accompanying drawing 3, its concrete structure is: the coupling mirror 6 of a partial reflectivity is connected with polarization beam splitter 2 beam-combining one-word end polarization-maintaining optical fibers, and the function of coupling mirror 6 is the mode-locked laser output port and the first laser The reflective surface of the cavity; the signal laser input fibers of the two polarization-maintaining optical fibers 980/1064 wavelength division multiplexers 401, 402 are respectively connected to the two polarization direction coupling fibers of the polarization beam splitter 2, and the function of the polarization beam splitter 2 is The lasers of two wavelengths are separated spatially by polarization; two fiber-coupled 976nm pump lasers 51, 52 are respectively coupled into the fiber laser cavity through wavelength division multiplexers (WDM) 401, 402; the two sections are different One end of the polarization-maintaining doped Y _b ³⁺ gain fiber 301 of length, 302 is respectively connected with the other end (signal laser and pump laser common end) of two polarization-maintaining 980/1064 wavelength division multiplexers 4, and the pump laser is in Laser gain is generated in the gain fiber; the other ends of the two polarization-maintaining Y _b ³⁺ gain fibers 301 and 302 are respectively connected to two different center wavelengths (the wavelength can be selected as 1.02 and 1.08 μm) and the bandwidth is 12nm. One end of the long-period polarization-maintaining fiber gratings 101, 102 is connected, and the functions of the band-pass type long-period polarization-maintaining fiber gratings 101, 102 are the central wavelength selection of the dual-wavelength laser and the spectral filtering optical pulse compression of the two-wavelength mode-locked laser; The semiconductor saturable absorbers 01 and 02 are respectively connected to the other end fibers of the two bandpass long-period polarization-maintaining fiber gratings 101 and 102 through a coupling optical system or directly through optical glue, and the semiconductor saturable absorbers 01 and 02 act as laser locks Mode elements and cavity reflective elements of laser cavities. The polarization beam splitter 2 separates the two wavelengths of laser light in a polarized manner to control them separately (such as mode-locking, etc.), and the realization of the two-wavelength laser mode-locking is to use two semiconductor saturable absorbers 01, 02. Two band-pass long-period polarization-maintaining fiber gratings 101 and 102 with different central wavelengths and 12nm bandwidth select two different mode-locked central wavelengths and realize mode-locked spectral filtering pulse compression in the total positive dispersion laser cavity to form a stable Dual-wavelength mode-locked ultrashort pulse output.

Example 4:

This embodiment provides a structure of a mode-locked Y _b ³⁺ fiber laser working in a fully positive dispersion ring cavity. A section of single-mode rare earth-doped gain fiber is used as the gain medium, and an appropriate central wavelength (1.0-1.1 μm) and bandwidth (4-12nm) band-pass long-period fiber grating filter is used as a component for mode-locked laser center wavelength selection and spectral filtering optical pulse compression to realize stable mode-locked oscillation of all-fiber ultrashort pulse laser.

Referring to accompanying drawing 4, it is the all-fiber laser cavity structure schematic diagram that this embodiment adopts ring cavity nonlinear polarization rotation mode-locking; Utilized the band-pass type long-period fiber grating filter of appropriate center wavelength and bandwidth in the cavity as mode-locking Components for laser center wavelength selection and spectral filtering for optical pulse compression. The pump laser is coupled into a single-mode rare earth doped fiber through a wavelength division multiplexer (WDM) to generate gain, and a band-pass type long-period band-pass fiber grating filter with an appropriate bandwidth is used in the cavity of the ring cavity laser as the center wavelength of the laser. Components for selection and spectral filtering of optical pulse compression, a fiber-coupled isolator to ensure unidirectional oscillation of the fiber laser, two fiber polarization controllers to adjust the polarization direction of the laser in the fiber laser cavity, and a polarization beam splitter as the output of the mode-locked laser Coupler, gain fiber, band-pass long-period fiber grating filter, isolator, two fiber polarization controllers, and polarization beam splitter. The nonlinear polarization rotation saturable absorber of the laser generates stable mode-locked pulses. It can be seen from Fig. 4 that the specific connection relationship is: the pump laser 5 is coupled into the single-mode rare-earth doped optical fiber 30 through a wavelength division multiplexer (WDM) 40 to generate gain, and a bandpass with a suitable center wavelength of 1.02 μm and a bandwidth of 12 nm Type long-period fiber grating filter 10 is connected with single-mode doped rare-earth fiber 30 through a section of single-mode fiber 16, band-pass type long-period fiber grating filter 10 is used as the selection of laser center wavelength and the element of spectral filtering light pulse compression, one The fiber polarization controller 8 is connected with the long-period bandpass fiber grating filter 10. The function of the fiber polarization controller 8 is to adjust the polarization state of the laser in the cavity and generate a saturable absorber with other devices to generate a mode-locked laser pulse. A fiber coupling The polarization beam splitter 9 is connected with the fiber polarization controller 8 and forms a laser output port with a variable output ratio. A fiber-coupled isolator 14 is connected with the fiber-coupled polarization beam splitter 9. The function of the isolator 14 is to ensure that the ring The cavity fiber laser oscillates in one direction, and another fiber polarization controller 15 is connected to the isolator 14. The function of the fiber polarization controller 15 is to adjust the polarization state of the laser in the ring cavity and form passive mode-locking with other devices to generate ultrashort laser pulses. Saturable absorber, optical fiber polarization controller 15, wavelength division multiplexer (WDM) 40, single-mode rare earth doped optical fiber 30, a section of single-mode optical fiber 16, band-pass long-period fiber grating filter with appropriate central wavelength and bandwidth 10, fiber polarization controller 8, fiber-coupled polarization beam splitter 9, isolator 14 constitute a laser that utilizes nonlinear polarization rotation mode-locked ring cavity, and bandpass type long-period fiber grating filter 10 produces intracavity wavelength selection and Spectral filtering and optical pulse compression, two fiber polarization controllers 8 and 15, gain fiber 30, bandpass long-period fiber grating filter 10, and fiber-coupled polarization beam splitter 9 produce nonlinear polarization rotation saturable absorbers Mode locking.

Example 5:

This embodiment provides a structure of a mode-locked Y _b ³⁺ fully polarization-maintaining fiber ring cavity laser working in the fully positive dispersion region, using a section of polarization-maintaining rare-earth-doped gain fiber as the gain medium, and using a semiconductor saturable absorber to achieve locking In the cavity, a band-pass type long-period polarization-maintaining fiber grating filter with an appropriate central wavelength (1.0-1.1μm) and bandwidth (4-12nm) is used as a mode-locked laser for selective tuning of the central wavelength and spectral filtering for optical pulse compression. Components to achieve stable mode-locked oscillation of all-fiber ultrashort pulse lasers.

Referring to accompanying drawing 5, it is a kind of full polarization-maintaining fiber laser annular cavity structure schematic diagram that adopts semiconductor saturable absorber mode-locking described in the present embodiment; Utilized appropriate bandwidth (4～12nm) and central wavelength ( 1.0-1.1μm) band-pass long-period polarization-maintaining fiber grating filter is used as a component for selective tuning of the center wavelength of the mode-locked laser and spectral filtering optical pulse compression. The pump laser is coupled into the doped rare-earth fiber through a wavelength division multiplexer (WDM) to generate gain, and a band-pass long-period fiber grating filter with an appropriate bandwidth is used in the cavity of the ring cavity laser as the choice of the center wavelength of the laser and the spectrum A component for filtering optical pulse compression, a polarization-maintaining fiber-coupled isolator to ensure unidirectional ring oscillation of the fiber laser, a polarization-maintaining fiber coupler as a mode-locked laser output coupler, gain fiber, band-pass long-period fiber grating filter, The laser ring cavity composed of isolator, fiber coupler and semiconductor saturable absorber generates stable mode-locked laser pulses. Its specific connection relationship can be seen from Figure 5: the pump laser 5 is coupled into the polarization-maintaining doped rare-earth fiber 3 through a wavelength division multiplexer (WDM) 4 to generate gain; One end of the periodic polarization-maintaining fiber grating filter 1 is connected to the other end of the doped polarization-maintaining rare earth fiber 3, and the band-pass long-period fiber grating filter 1 is used as a component for selecting the center wavelength of the mode-locked fiber laser and compressing the optical pulse of the spectral filter One end fiber of a polarization fiber coupler 13 is connected with the other end fiber of the bandpass type long-period polarization maintaining fiber grating filter 1, and the effect of the polarization fiber coupler 13 is to output intracavity mode-locked laser light; a polarization maintaining fiber circulator The input fiber end of 17 is connected with the other end optical fiber of polarization fiber coupler 13, and a semiconductor saturable absorber O is coupled through an optical lens or directly glued on the second end optical fiber of polarization-maintaining optical fiber circulator 17 with optical glue, and the semiconductor can Saturable absorber 0 forms stable mode-locked laser pulses to the nonlinear effect of laser; the output fiber end of polarization-maintaining fiber circulator 17 is connected with the input end of polarization-maintaining fiber-optic isolator 18, and the effect of polarization-maintaining fiber-optic isolator 18 is to make The fiber ring cavity laser works in one direction; the output fiber of the polarization-maintaining fiber isolator 18 is connected to the signal input fiber of the wavelength division multiplexer (WDM) 4 to form a complete ring laser cavity; the semiconductor saturable absorber 0 pair The nonlinear effect of the laser and the gain fiber 3. Band-pass long-period polarization-maintaining fiber grating filter with appropriate bandwidth 1. Optical pulse compression, so as to generate stable mode-locked ultrashort pulse laser in the entire positive dispersion laser cavity, through polarization-maintaining Fiber output coupler 13 output.

Claims (1)

1. A fully positive dispersion cavity mode-locked all-fiber laser, said laser is a kind of ultrashort pulse fully polarization-maintaining fiber ring cavity laser working in a total positive dispersion region, characterized in that: said ring cavity laser It includes a polarization-maintaining fiber looper with a semiconductor saturable absorber attached to the fiber end, a polarization fiber isolator, a wavelength division multiplexer, a polarization-maintaining fiber laser gain medium, a band-pass long-period fiber grating filter, and a polarized fiber output Coupler; the central wavelength of the bandpass long-period fiber grating filter is 1.0-1.1 μm, and the bandwidth is 4-12nm; the polarization-maintaining fiber laser gain medium uses a section of polarization-maintaining rare-earth-doped gain fiber as the gain medium; The structure of the ring cavity laser is: a pumping source [5] provides pumping light for the wavelength division multiplexer [4] as input pumping light; the wavelength division multiplexer [4] and The polarization-maintaining fiber laser gain medium [3] is connected to input the pump light into the polarization-maintaining fiber laser gain medium [3] to generate laser gain; the band-pass long-period polarization-maintaining fiber grating filter One end of the device [1] is connected to the other end of the polarization-maintaining fiber laser gain medium [3], and the selection and locking of the center wavelength of the mode-locked laser pulse by the band-pass type long-period polarization-maintaining fiber grating filter [1] mode spectrum pulse compression to achieve stable mode-locking work; the polarization fiber output coupler is a fiber coupler with only a single polarization axis oscillation output, one end of which is connected to the other end of the band-pass long-period fiber grating filter [1] One end is connected, and the mode-locked laser pulse is output from the fiber coupler; the first end fiber of the polarization-maintaining fiber circulator [17] is connected to the other end of the fiber coupler [13]; the polarization-maintaining fiber The second-end optical fiber of the circulator [17] is connected to the semiconductor saturable absorber through an optical lens or directly with optical glue, and the nonlinear effect of the semiconductor saturable absorber on the laser produces mode locking in the ring cavity laser effect; the third end optical fiber of the polarization maintaining fiber looper [17] is connected to the polarization fiber isolator, and the polarization fiber isolator makes the ring cavity laser unidirectionally generate laser oscillation; the polarization fiber isolation The optical fiber at the output end of the device is connected to the optical fiber at the other end of the wavelength division multiplexer [4] to form a complete, unidirectional ring laser cavity.

Images