CN114498267A - Multi-wavelength high-repetition-frequency output tapered optical fiber, manufacturing method thereof and mode-locked laser - Google Patents
Multi-wavelength high-repetition-frequency output tapered optical fiber, manufacturing method thereof and mode-locked laser Download PDFInfo
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- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
- H01S3/06—Construction or shape of active medium
- H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
- H01S3/067—Fibre lasers
- H01S3/06708—Constructional details of the fibre, e.g. compositions, cross-section, shape or tapering
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
- H01S3/08—Construction or shape of optical resonators or components thereof
- H01S3/08086—Multiple-wavelength emission
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Abstract
The invention discloses a tapered optical fiber with multi-wavelength high repetition frequency output, a manufacturing method thereof and a mode-locked laser, wherein the length of the tapered optical fiber is less than 10cm, the middle part of the optical fiber is processed into a coaxial double-tapered region, and the coaxial double-tapered region has geometric parameters for realizing the mutual coupling of a core mode and a cladding mode. The gain intensity can be regulated and controlled by preparing the low-intensity high-loss coaxial tapered optical fiber to construct a laser resonant cavity of a fiber core mode and a cladding mode coupling mode, so that a spectrum filtering effect is realized, the effect can play a role in gain guiding in the pulse forming process, and finally the regulation and control of mode locking spectrum are realized. The laser characteristic of the mode locking spectrum is accurately controlled through the structural parameters of the tapered optical fiber, multiple wavelengths are finally output in GHz high repetition frequency laser, the number and the period of the multiple wavelengths can be accurately tuned, the laser maintains full optical fiber, the process is simple, and the large-scale production or application is facilitated.
Description
Technical Field
The application relates to the field of lasers, in particular to a multi-wavelength high-repetition-frequency output tapered optical fiber, a manufacturing method thereof and a mode-locked laser output by multi-wavelength high-repetition-frequency laser.
Background
The GHz high repetition frequency ultrafast laser with the multi-wavelength output spectral characteristic has important application in the fields of high-speed optical communication, microwave photonics, arbitrary waveform generation and the like. The multi-wavelength laser can provide required light sources for a plurality of channels simultaneously, so that the design of an optical transmitting end is more compact and economical, and the multi-wavelength laser has important application in a dense wavelength division multiplexing system. The currently reported GHz repetition frequency ultrafast fiber lasers are all single-wavelength output, and the reasons are as follows: GHz basic repetition frequency is required to be obtained according to a mode locking principle, the cavity length of a laser resonant cavity is required to be shortened to the centimeter magnitude, and a spectral filter is introduced into the resonant cavity in the conventional method for obtaining multi-wavelength output, so that the conventional method is difficult to implement due to the ultra-short resonant cavity length.
It would be possible to solve this problem if the characteristics of this type of laser could be exploited by introducing a mechanism with intensity modulation inside the cavity. Based on previous reports, such light sources are sensitive to system parameter anomalies, such as pulse doubling can be achieved by introducing a low finesse filter in the resonator [ Optics Express,25,24400(2017) ]; soliton molecular dynamics [ Optics Express,26,10842(2018) ], can be realized by introducing a tiny coupling angle into a laser resonant cavity; the weak nonlinear gain dynamics in the cavity can achieve the characteristic square wave packet operation [ Optics Express,25,20125(2017) ]. Therefore, if such a tapered structure can be developed directly on a high-concentration silica gain fiber, intensity modulation can be achieved within the cavity using its structural parameters, taking into account the modulated transmittance characteristics of the coaxial tapered fiber. Then the thermal insulation characteristic, modulation frequency and modulation intensity of the fiber core mode and the cladding mode are changed through a coupling mechanism of the fiber core mode and the cladding mode to realize the regulation and control of spectrum filtering, the effect plays a role in gain guide in the pulse forming process, and the regulation and control of mode-locked spectrum can be realized.
The low-loss high-strength tapered optical fiber has a mature production method in the prior art, and chinese patent CN112748495A discloses a device and a method for preparing a low-loss high-strength tapered optical fiber, so that the low-loss high-strength tapered optical fiber can be produced and integrated in a large scale, which provides a possibility for realizing the production of multi-wavelength high-repetition-frequency optical fibers.
Disclosure of Invention
Based on the background, the invention provides a method for realizing multi-wavelength in high repetition frequency ultrafast fiber laser, aiming to construct a novel coupling mode laser resonant cavity by preparing a coaxial tapered fiber with low intensity and high loss, accurately controlling the laser characteristic of a mode-locked spectrum through the structural parameters of the tapered fiber, and finally realizing multi-wavelength output in GHz high repetition frequency laser.
In a first aspect, embodiments of the present application provide a tapered optical fiber with multiple wavelength and high repetition frequency output, where the length of the optical fiber is less than 10cm, a coaxial biconical region is disposed in a middle portion of the optical fiber, and the coaxial biconical region has geometric parameters for coupling a core mode and a cladding mode. The optical fiber is controlled within the length range of less than 10cm to prepare an ultra-short resonant cavity, high repetition frequency laser with basic repetition frequency exceeding GHz can be further obtained on the basis of the ultra-short resonant cavity, and the coaxial double-cone region with the geometric parameters capable of realizing mutual coupling of a fiber core mode and a cladding mode can regulate and control gain intensity so as to realize a spectrum filtering effect, and the effect can play a role in gain guide in the pulse forming process, and finally realize regulation and control on a mode locking spectrum so as to obtain multi-wavelength mode locking output.
In some embodiments, the eigen-equation for the core mode and cladding mode coupling to each other is:
for beta<k0n2
For beta>k0n2
Wherein Jm，Ym，ImAnd KmIs Bessel and the modified Bessel equation, β is the mode transmission constant, k0Is the wave vector in vacuum, n2Is the cladding refractive index. By constructing the laser resonant cavity with a novel coupling mode, the precise regulation and control of the quantity and the interval of the output wavelengths of the mode-locked spectrum can be realized.
In some embodiments, the geometric parameters include a cone waist diameter of 10-50 μm, a cone length of less than 40mm, and a cone ramp angle, the total length of less than 10 cm. By changing the geometric parameters of the coaxial biconical region, the number and the wavelength interval of the output wavelengths can be regulated.
In some embodiments, the tapered optical fiber is formed by drawing a high concentration rare earth ion doped optical fiber. The high-concentration rare earth ion doped optical fiber has a better gain curve, can be compatible with a Wavelength Division Multiplexing (WDM) system, and has high pumping efficiency and stable working performance.
In a second aspect, embodiments of the present application further provide a method for fabricating a multi-wavelength high repetition frequency output tapered optical fiber, the tapered optical fiber having a central portion processed to form a concentric biconic region having geometric parameters for coupling core and cladding modes, the processing steps including:
s1, establishing a theoretical model of ultrafast laser through a nonlinear Schrodinger equation and a dynamic rate equation according to the multi-wavelength index to be realized, obtaining a mode-locked spectrum through a numerical calculation pulse evolution mechanism of a distributed Fourier method, and searching system parameters including modulation frequency, modulation intensity and the like of the coaxial biconical optical fiber;
s2: according to the adopted material and structural parameters of the high-gain optical fiber, structural parameter intervals such as core cladding radius and relative refractive index difference are brought into an eigenequation of mutual coupling of the core fiber model and the cladding layer model, a propagation constant of a fundamental mode and a high-order mode is solved by utilizing a bisection method and combining a single-mode condition, a thermal insulation condition curve is obtained, and geometric parameters for preparing the tapered optical fiber are searched;
s3: according to the relation between the tapering parameter of the molten state tapering method and the geometric structure of the tapered optical fiber, the stretching parameter is calculated by combining the size of the designed quasi-rectangular nozzle,
the calculation formula of the stretching parameters is as follows: r isw(x)＝r0exp[-x/2L0]，
Wherein r iswIs the radius of the cone waist obtained, r0Is the initial fiber radius, L0Is the waist length and x is the stretch length.
S4: the method comprises the steps of peeling off a coating layer of a gain optical fiber to be pulled, fixing two ends of the gain optical fiber to be pulled on a tapered platform respectively, heating and preheating to soften the optical fiber to be pulled through flame generated by a displaceable rectangular-like nozzle, and reversely drawing the optical fiber while melting under the moving flame through a stepping motor to form a coaxial biconical region with the geometric parameters.
By the manufacturing method, the geometric parameters required by the coaxial biconical region capable of realizing coupling of the fiber core mold and the cladding mold are calculated, preheating softening and molten state stretching are carried out through the rectangular-like nozzle, and the required coaxial biconical region of the tapered optical fiber is stretched, so that the coaxial biconical region meets the output condition of multi-wavelength high repetition frequency, has the characteristics of low loss and high strength, and is convenient for large-scale production and integration.
In a third aspect, an embodiment of the present application further provides an ultrafast fiber mode-locked laser for achieving multi-wavelength high repetition frequency output, where the laser includes an ultrashort laser resonant cavity, a wavelength division multiplexer, a pump source, and an optical isolator, where the ultrashort laser resonant cavity is provided with the tapered fiber as described above, the pump source is connected to a pump end of the wavelength division multiplexer, the optical isolator is connected to a signal end of the wavelength division multiplexer, and a common end of the wavelength division multiplexer is connected to the ultrashort laser resonant cavity; the wavelength division multiplexer is used for coupling the pump light into the ultrashort laser resonant cavity and outputting the generated laser pulse outwards through the isolator. The optical fiber is controlled within the length range of less than 10cm by using the tapered optical fiber, so that an ultra-short resonant cavity is prepared, a laser is prepared on the basis of the ultra-short resonant cavity, high repetition frequency laser with basic repetition frequency exceeding GHz can be obtained, a coaxial double-cone region with geometric parameters capable of realizing mutual coupling of a fiber core mode and a cladding mode can be provided, the gain intensity can be regulated and controlled, so that the spectrum filtering effect is realized, the effect can play a role of gain guidance in the pulse forming process, and finally the regulation and control of a mode locking spectrum are realized, so that the mode locking output of multiple wavelengths is obtained.
In some embodiments, the ultrashort laser resonator further includes a ferrule respectively fixedly connected to two ends of the tapered fiber and having an inner diameter matching the inner diameter of the tapered fiber, one end of the ferrule is connected to a fiber coating cavity mirror with a dielectric film, the other end of the ferrule is connected to a semiconductor saturable absorber mirror, and the fiber coating mirror is connected to the ferrule through a ceramic sleeve having an inner diameter matching the inner diameter of the ferrule.
The ultrashort laser resonant cavity with the structure can overcome the difficulty of regulating and controlling dispersion in the centimeter-level resonant cavity, and realize high repetition frequency laser output with adjustable pulse width.
In some embodiments, the laser modulates the number and spacing of wavelengths output by varying the geometric parameters of the tapered fiber that achieve core and cladding mode coupling.
In some embodiments, the pump source is a single mode semiconductor laser. The emission wavelength of which is matched with the pump absorption wavelength of the rare earth ions.
In some embodiments, the fiber coating cavity mirror is a polarization maintaining fiber based dispersion cavity mirror, the fiber pigtail of the pump source is a polarization maintaining fiber, and the wavelength division multiplexer is a polarization maintaining wavelength division multiplexer. By using the structure, the environmental stability can be improved, the reliability is increased, and the all-fiber laser with the polarization maintaining structure is further realized.
The embodiment of the application discloses multi-wavelength high-repetition-frequency output tapered optical fiber and a manufacturing method thereof and a laser, wherein a laser resonant cavity of a novel coupling mode is constructed by preparing a low-intensity high-loss coaxial tapered optical fiber, the laser characteristic of a mode locking spectrum is accurately controlled through the structural parameters of the tapered optical fiber, and finally, a plurality of wavelengths are output in GHz high-repetition-frequency laser, the multi-wavelength quantity and the period can be accurately tuned, the laser maintains full-fiber, the process is simple, and the large-scale production or application is facilitated.
Drawings
The accompanying drawings are included to provide a further understanding of the embodiments and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments and together with the description serve to explain the principles of the invention. Other embodiments and many of the intended advantages of embodiments will be readily appreciated as they become better understood by reference to the following detailed description. The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts.
FIG. 1 is a schematic diagram illustrating an overall structure of an ultrafast fiber mode-locked laser capable of realizing multi-wavelength high repetition frequency output according to an embodiment of the present invention;
FIG. 2 is a flow chart illustrating a method of making a multi-wavelength high repetition frequency output tapered optical fiber according to an embodiment of the present invention;
FIG. 3 shows a spectrum diagram of a dual wavelength output of an ultrafast fiber mode-locked laser test implementing multiple wavelength high repetition frequency output, in accordance with embodiments of the present invention;
FIG. 4 is a diagram illustrating the time domain waveform of a dual wavelength mode-locked laser for testing an ultrafast fiber mode-locked laser with multi-wavelength high repetition frequency output according to an embodiment of the present invention;
FIG. 5 shows a radio frequency spectrum diagram of a dual wavelength mode-locked laser for testing an ultrafast fiber mode-locked laser with multiple wavelength high repetition frequency output, according to an embodiment of the present invention;
FIG. 6 shows a spectrum of three-wavelength laser output for an ultrafast fiber mode-locked laser test with multiple-wavelength high repetition frequency output, according to an embodiment of the present invention;
fig. 7 shows a time domain waveform diagram of three-wavelength mode-locked laser for testing an ultrafast fiber mode-locked laser with multi-wavelength high repetition frequency output according to an embodiment of the present invention.
Detailed Description
The present application will be described in further detail with reference to the following drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not to be construed as limiting the invention. It should be noted that, for convenience of description, only the portions related to the related invention are shown in the drawings. It should be noted that the dimensions and sizes of the elements in the figures are not to scale and the sizes of some of the elements may be highlighted for clarity of illustration.
It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. The present application will be described in detail below with reference to the embodiments with reference to the attached drawings.
In the embodiment of the present application, a multi-wavelength high repetition frequency output tapered optical fiber is provided, as shown in fig. 1, a length of the tapered optical fiber 1 of the present disclosure is less than 10cm, a coaxial biconical region is disposed in a middle portion of the optical fiber 1, and the coaxial biconical region has geometric parameters for realizing mutual coupling between a core mode and a cladding mode. The tapered optical fiber 1 is obtained by melting and tapering a high-concentration rare earth ion-doped optical fiber, and has the characteristics of low loss and high strength.
The optical fiber is controlled within the length range of less than 10cm to prepare an ultra-short resonant cavity, high repetition frequency laser with basic repetition frequency exceeding GHz can be further obtained on the basis of the ultra-short resonant cavity, and the coaxial double-cone region with the geometric parameters capable of realizing mutual coupling of a fiber core mode and a cladding mode can regulate and control gain intensity so as to realize a spectrum filtering effect, and the effect can play a role in gain guide in the pulse forming process, and finally realize regulation and control on a mode locking spectrum so as to obtain multi-wavelength mode locking output.
In a specific embodiment of the present application, the eigen equation for the mutual coupling of the core mode and the cladding mode is:
for beta<k0n2
For beta>k0n2
Wherein Jm，Ym，ImAnd KmIs Bessel and the modified Bessel equation, β is the mode transmission constant, k0Is the wave vector in vacuum, n2Is the cladding refractive index.
By calculating a mode coupling eigenequation, an adiabatic condition curve of multi-wavelength high repetition frequency output can be obtained, and further, a proper geometric parameter of the coaxial biconical region is obtained.
In a specific embodiment of the present application, the geometric parameters include a cone waist diameter of 10-50 μm, a cone region length of less than 40mm, and a cone region gradual change angle, and the total length is less than 10 cm. By changing the geometric parameters of the coaxial biconical region, the number and the wavelength interval of the output wavelengths can be regulated.
In one specific embodiment of the present application, the tapered fiber is drawn from a commercial high concentration erbium doped silica fiber (Liekki). The erbium-doped fiber has a better gain curve and stable working performance.
The present application further provides a method for manufacturing a multi-wavelength high repetition frequency output tapered optical fiber, in which the central portion of the tapered optical fiber is processed to have a coaxial biconic region with geometric parameters for coupling the core mode and the cladding mode, as shown in fig. 2, and the processing steps include:
s1, establishing a theoretical model of ultrafast laser through a nonlinear Schrodinger equation and a dynamic rate equation according to the multi-wavelength index to be realized, obtaining a mode-locked spectrum through a numerical calculation pulse evolution mechanism of a distributed Fourier method, and searching system parameters including modulation frequency, modulation intensity and the like of the coaxial biconical optical fiber;
s2: according to the adopted material and structural parameters of the high-gain optical fiber, structural parameter intervals such as core cladding radius and relative refractive index difference are brought into an eigenequation of mutual coupling of the core fiber model and the cladding layer model, a propagation constant of a fundamental mode and a high-order mode is solved by utilizing a bisection method and combining a single-mode condition, a thermal insulation condition curve is obtained, and geometric parameters for preparing the tapered optical fiber are searched;
s3: according to the relation between the tapering parameter of the molten state tapering method and the geometric structure of the tapered optical fiber, the stretching parameter is calculated by combining the size of the designed quasi-rectangular nozzle,
the calculation formula of the stretching parameters is as follows: r isw(x)＝r0exp[-x/2L0]，
Wherein r iswIs the radius of the cone waist obtained, r0Is the initial radius of the optical fiber,L0is the waist length and x is the stretch length.
S4: and peeling off a coating layer of the optical fiber to be drawn, fixing two ends of the optical fiber to be drawn on a tapering platform respectively, heating and preheating the optical fiber to be drawn by flame generated by a displaceable quasi-rectangular nozzle to soften the optical fiber, and reversely drawing the optical fiber while melting the optical fiber under the moving flame by a stepping motor to form a coaxial biconical region with the geometric parameters.
Two ends of a commercial high-concentration erbium-doped fiber are respectively fixed into a ferrule with the inner diameter of 125 mu m, then the end surface is subjected to mirror polishing treatment, and the total length is less than 10 cm. The optical fiber was stripped of a 2.5cm long coating and both ends were fixed to a V-groove on a tapered platform with a magnet. Obtaining a tapering parameter value through theoretical calculation, installing a designed quasi-rectangular nozzle to a flame outlet of a hydrogen generator, preheating a gain optical fiber to be tapered for 1-2 minutes, and preparing the biconical gain optical fiber by using a fused tapering method.
The core insert can be a nano zirconia core insert.
One specific example of the tapering parameters may be: the edge interval of the left and right tapered platforms is 3.8cm, the stretching length is 6mm, the stretching speed is 0.15mm/s, the air flow is 300ml/min, and the width of the rectangular-like nozzle is about 3 mm.
The optical fiber drawing apparatus and method refer to the published Chinese patent CN112748495A "an apparatus and method for manufacturing a low-loss high-strength tapered optical fiber". Obtaining a thermal insulation condition curve by calculating an eigen equation of mutual coupling of a fiber core mold and a cladding mold, thereby obtaining the geometric parameters of the gain optical fiber, further calculating drawing parameters to obtain the technological parameters such as drawing length, speed and the like required in the drawing step, and then putting the optical fiber to be drawn into the drawing device according to the device and the drawing method shown in CN112748495A to draw out a coaxial biconical region with preset geometric parameters.
As shown in fig. 1, the present application further provides an ultrafast fiber mode-locked laser for achieving multi-wavelength high repetition frequency output, so as to obtain multi-wavelength high repetition frequency laser output.
The first embodiment is as follows:
the laser comprises an ultrashort laser resonant cavity, a wavelength division multiplexer 8, a pump source 9 and an optical isolator 10, wherein the ultrashort laser resonant cavity is provided with the tapered optical fiber 1 as claimed in any one of claims 1 to 4, the pump source 9 is connected with a pump end of the wavelength division multiplexer 8, the optical isolator 10 is connected with a signal end of the wavelength division multiplexer 8, and a common end of the wavelength division multiplexer 8 is connected with the ultrashort laser resonant cavity; the wavelength division multiplexer 8 is used for coupling pump light into the ultrashort laser resonant cavity and outputting the generated laser pulse outwards through the isolator 10.
The cavity is pumped with a single mode semiconductor laser with a wavelength of 974nm, and the pump source 9 is output using a single mode optical fiber with a maximum power of 900 mW. And the tail fiber of the pumping source is welded with the pumping end of the 980nm/1550nm wavelength division multiplexer 8. And the common end of the wavelength division multiplexer 8 is welded with the tail fiber of the film coating cavity mirror of the ultrashort laser resonant cavity. The multi-wavelength laser generated under pump excitation is output extracavity from the signal terminal of the wavelength division multiplexer 8 through the isolator 10. By utilizing the coupling mechanism of the fiber core mode and the cladding mode, the tapered optical fiber can regulate and control the gain intensity so as to realize the spectrum filtering effect and further play a role in gain guide in the pulse forming process.
The results of the multi-wavelength output obtained by the experiment are as follows:
when the pump power reaches 326mW, stable dual-wavelength mode-locked output is obtained. The measured spectrum is shown in FIG. 3, and the spectral lines are smooth, and the peak positions of the two wavelengths are 1561.7nm and 1562.5 nm. The time-domain mode-locked waveform diagram of the test is shown in fig. 4, the pulse interval is 0.98ns, and the corresponding repetition frequency is 1.016 GHz. Fig. 5 is a graph of the measured radio frequency spectrum under the state, from which it can be seen that the signal-to-noise ratio is 77dB, the dc mode-locked state is verified, and the mode-locked operation is stable.
When the pumping power is 620mW, the coaxial tapered optical fiber is further finely adjusted, and stable three-wavelength mode-locked output can be obtained. The spectrogram of the tested three-wavelength mode locking is shown in FIG. 6, and the spectral lines are smooth, and the peak positions of the three wavelengths are 1559.7nm, 1560.6nm and 1562.7nm respectively. The time domain waveform of the test is shown in fig. 7, the pulse interval is 0.984ns, and the corresponding repetition frequency is 1.016 GHz.
The embodiment verifies that the method realizes multi-wavelength output in GHz high repetition frequency ultrafast laser, and the output index proves that the mode locking operation is stable. The novel laser resonant cavity which takes full optical fiber into consideration has higher stability and practicability, is light and small, and ensures that the method is easy to popularize and realizes large-scale production and integration.
Further referring to fig. 1, in an embodiment of the present application, the ultrashort laser resonator further includes ferrules 2 and 3 respectively fixedly connected to two ends of the tapered fiber 1 and having inner diameters matching with each other, one end of the ferrule 2 is connected to a fiber coating cavity mirror 5 having a dielectric film 4, one end of the ferrule 3 is connected to a semiconductor saturable absorber mirror 7, and the fiber coating mirror 5 is connected to the ferrule 2 through a ceramic sleeve 6 having a matching inner diameter.
The ultrashort laser resonant cavity with the structure can overcome the difficulty of regulating and controlling dispersion in the centimeter-level resonant cavity, and realize high repetition frequency laser output with adjustable pulse width.
One end of the tapered optical fiber 1 is connected with an optical fiber coating cavity mirror 5 through a ceramic sleeve 6 with the inner diameter of 2.5mm, so that the low-loss light can pass through the tapered optical fiber. The dielectric film 4 is prepared by a plasma sputtering method, has a dichroic spectroscopic function, and has a pump light transmittance of 95% at a wavelength of 974nm and a laser reflectance of 99% at a wavelength of 1560nm or thereabouts. The other end of the tapered optical fiber is connected with a semiconductor saturable absorption mirror 7, the modulation depth of the semiconductor saturable absorption mirror 7 is 3 percent, the unsaturated absorption is 7 percent, and the saturation flux is 40 mu J/cm210ps recovery time and 450 μm thickness (Batop). The semiconductor saturable absorber mirror 7 can also be fixed by adhering it to the end face of the ferrule with epoxy resin.
In one embodiment of the present application, the laser modulates the number of wavelengths and wavelength spacing of the output by changing the geometric parameters of the tapered fiber that achieve core and cladding mode coupling.
In one embodiment of the present application, the pump source 11 is a single-mode semiconductor laser.
Example two:
in another embodiment of the present application, in order to further improve environmental stability, increase reliability, and further realize an all-fiber laser with a polarization-maintaining structure, the laser is configured as another embodiment, that is, the fiber coating cavity mirror 5 adopts a dispersion cavity mirror based on a polarization-maintaining fiber, the fiber pigtail of the pumping source 9 also adopts a polarization-maintaining fiber, and the wavelength division multiplexer 8 adopts a polarization-maintaining wavelength division multiplexer. By adopting the structure, the breakthrough experiment index is obtained, the environmental stability of the laser can be further improved, and the use of the laser under extreme conditions is expanded.
Specifically, in the preparation part of the dispersion cavity mirror 5, a commercial corning company PM1550 polarization-maintaining single-mode fiber is used for replacing a corning SM28e optical fiber, so that the dispersion cavity mirror based on the polarization-maintaining optical fiber is realized.
In the resonant cavity construction part, a polarization-maintaining dispersion cavity mirror 5 is connected with a coaxial conical optical fiber through a ceramic sleeve with the inner diameter of 2.5mm, so that low-loss light can pass through.
In the all-fiber laser part, a single-mode fiber pigtail of a semiconductor laser pumping source 9 with the wavelength of 974nm is changed into a PM980 polarization-maintaining fiber of Nufern company, and a wavelength division multiplexer 8 is changed into a polarization-maintaining wavelength division multiplexer using a PM1550 fiber.
The embodiment of the application discloses a multi-wavelength high-repetition-frequency output tapered optical fiber, a manufacturing method thereof and a laser, wherein a laser resonant cavity of a fiber core mode and a cladding mode coupling mode is constructed by preparing a low-intensity high-loss coaxial tapered optical fiber, the laser characteristic of a mode locking spectrum is accurately controlled through the structural parameters of the tapered optical fiber, and finally, the output of multiple wavelengths is realized in GHz high-repetition-frequency laser, the number and the period of the multiple wavelengths can be accurately tuned, the laser maintains full-fiber, the process is simple, and the large-scale production or application is facilitated.
While the present invention has been described with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.
In the description of the present application, it is to be understood that the terms "upper", "lower", "inner", "outer", and the like, indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, are only for convenience in describing the present application and simplifying the description, and do not indicate or imply that the referred devices or elements must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present application. The word 'comprising' does not exclude the presence of elements or steps not listed in a claim. The word 'a' or 'an' preceding an element does not exclude the presence of a plurality of such elements. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims shall not be construed as limiting the scope.
Claims (10)
1. The tapered optical fiber with multi-wavelength high repetition frequency output is characterized in that the length of the optical fiber is less than 10cm, a coaxial biconical region is arranged in the middle of the optical fiber, and the coaxial biconical region has geometric parameters for realizing mutual coupling of a core mode and a cladding mode.
2. The multi-wavelength high repetition frequency output tapered optical fiber according to claim 1, wherein the eigen equation for the mutual coupling of the core mode and the cladding mode is:
for beta<k0n2
For beta>k0n2
Wherein Jm，Ym，ImAnd KmIs Bessel and improved Bessel squareEquation, β is the modal transmission constant, k0Is the wave vector in vacuum, n2Is the cladding refractive index.
3. The multi-wavelength high repetition frequency output tapered optical fiber according to claim 2, wherein the geometrical parameters include a waist diameter of 10-50 μm, a taper section length of less than 40mm, and a taper section taper angle of less than 10cm in total length.
4. The tapered multi-wavelength high repetition frequency output optical fiber according to claim 3, wherein said tapered optical fiber is formed by drawing a highly doped rare earth ion optical fiber.
5. A method of making a tapered optical fiber with multiple wavelength high repetition frequency output, wherein the middle portion of the tapered optical fiber is processed into a coaxial biconic region as claimed in any of claims 1-4 having geometric parameters for core mode and cladding mode coupling, said processing steps comprising:
s1, establishing a theoretical model of ultrafast laser through a nonlinear Schrodinger equation and a dynamic rate equation according to the multi-wavelength index to be realized, obtaining a mode-locked spectrum through a numerical calculation pulse evolution mechanism of a distributed Fourier method, and searching system parameters including modulation frequency, modulation intensity and the like of the coaxial biconical optical fiber;
s2: according to the adopted material and structural parameters of the high-gain optical fiber, structural parameter intervals such as core cladding radius, relative refractive index difference and the like are brought into an eigenequation of mutual coupling of the fiber core model and the cladding model, a propagation constant of a fundamental mode and a high-order mode is solved by utilizing a bisection method and combining a single-mode condition, a thermal insulation condition curve is obtained, and the geometric parameters for preparing the tapered optical fiber are searched;
s3: according to the relation between the tapering parameter of the molten state tapering method and the geometric structure of the tapered optical fiber, the stretching parameter is calculated by combining the size of the designed quasi-rectangular nozzle,
the calculation formula of the stretching parameters is as follows: r isw(x)＝r0exp[-x/2L0]，
Wherein r iswIs the radius of the cone waist obtained, r0Is the initial fiber radius, L0Is the waist length and x is the stretch length.
S4: and peeling off a coating layer of the optical fiber to be drawn, fixing two ends of the optical fiber to be drawn on a tapering platform respectively, heating and preheating the optical fiber to be drawn by flame generated by a displaceable quasi-rectangular nozzle to soften the optical fiber, and reversely drawing the optical fiber while melting the optical fiber under the moving flame by a stepping motor to form a coaxial biconical region with the geometric parameters.
6. An ultrafast fiber mode-locked laser for realizing multi-wavelength high repetition frequency output, wherein the laser comprises an ultrashort laser resonant cavity, a wavelength division multiplexer, a pump source and an optical isolator, the ultrashort laser resonant cavity is provided with the tapered fiber according to any one of claims 1-4, the pump source is connected with the pump end of the wavelength division multiplexer, the optical isolator is connected with the signal end of the wavelength division multiplexer, and the common end of the wavelength division multiplexer is connected with the ultrashort laser resonant cavity; the wavelength division multiplexer is used for coupling the pump light into the ultrashort laser resonant cavity and outputting the generated laser pulse outwards through the isolator.
7. The ultrafast fiber mode-locked laser of claim 6, wherein the ultrashort laser resonator further comprises a ferrule having an inner diameter matching with the inner diameter of the tapered fiber, the ferrule is fixedly connected to both ends of the tapered fiber, one end of the ferrule is connected to a fiber coating cavity mirror having a dielectric film, the other end of the ferrule is connected to a semiconductor saturable absorber mirror, and the fiber coating mirror is connected to the ferrule through a ceramic sleeve having an inner diameter matching with the ferrule.
8. The ultrafast fiber mode-locked laser capable of achieving multi-wavelength high repetition frequency output according to claim 7, wherein the laser is capable of adjusting the number and the wavelength interval of the output by changing the geometrical parameters of the tapered fiber, which realize the mutual coupling of the core mode and the cladding mode.
9. The ultrafast fiber-locked laser capable of achieving multi-wavelength high repetition frequency output according to claim 8, wherein the pump source is a single-mode semiconductor laser.
10. The ultrafast fiber mode-locked laser capable of achieving multi-wavelength high repetition frequency output according to claim 6, wherein the fiber coating cavity mirror is a dispersion cavity mirror based on a polarization maintaining fiber, the fiber pigtail of the pumping source is a polarization maintaining fiber, and the wavelength division multiplexer is a polarization maintaining wavelength division multiplexer.
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