CN110858698B - Intermediate infrared femtosecond fiber laser light source system - Google Patents
Intermediate infrared femtosecond fiber laser light source system Download PDFInfo
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Abstract
The invention discloses a mid-infrared femtosecond fiber laser light source system. Wherein, this system includes: a passively mode-locked fiber oscillation cavity configured as a dispersion management cavity for outputting a high-order soliton pulse having a positive chirp; the polarization mode dispersion controller is connected with the passive mode-locking optical fiber oscillation cavity through an optical fiber and is used for applying polarization mode dispersion to the high-order soliton pulse for carrying out dispersion modulation and outputting the dispersion-modulated high-order soliton pulse; the optical fiber amplifier is connected with the polarization mode dispersion controller through an optical fiber and is used for carrying out amplification operation and compression operation on the dispersion-modulated high-order soliton pulse so as to realize the conversion from the dispersion-modulated high-order soliton pulse to the Raman soliton pulse; the tellurium-based soft glass fiber is connected with the fiber amplifier through the fiber and used for translating the Raman soliton pulse to a middle infrared band to obtain a tunable femtosecond Raman soliton pulse of the middle infrared band. The invention solves the technical problem of low conversion efficiency of the Raman solitons.
Description
Technical Field
The invention relates to the field of lasers, in particular to a middle infrared femtosecond fiber laser light source system.
Background
The tunable high-energy mid-infrared femtosecond pulse has important application value in numerous fields of biomedical treatment, biological imaging, mid-infrared nonlinearity, optical precision measurement, special gas detection, material precision processing and the like. At present, high-energy mid-infrared femtosecond pulses are mainly generated by soft glass optical fibers of optical parametric oscillation (OPO/OPA), mid-infrared crystals (Fe: Znse and Cr: Znse) with specific wavelengths or erbium/thulium ions. The method has the advantages of complex obtaining way, huge system, difficult operation and higher cost, is not suitable for large-scale popularization in a plurality of fields, and limits the application of the mid-infrared femtosecond pulse in a plurality of fields. In recent years, with the development of nonlinear fiber optics, research on obtaining a laser light source and a mid-infrared super-continuum light source by utilizing the nonlinear characteristics of optical fibers has become a hot point of research. The soliton self-frequency shift effect is utilized, not only can a high-average-power femtosecond pulse laser source be obtained, but also the femtosecond laser pulse output with tunable broadband can be realized without a wavelength tuning device. The soliton self-frequency shift refers to the phenomenon that when high-peak-power ultrashort pulses are transmitted in a negative dispersion waveguide, the ultrashort pulses enter a nonlinear medium and undergo red shift under the action of Raman scattering. The raman soliton self-frequency shift is more and more concerned by people because the raman soliton self-frequency shift can obtain high-quality femtosecond pulses with tunable spectrums. By using the mode of Raman soliton self-frequency shift, ultrashort pulses in a spectral range which cannot be covered by a conventional gain fiber can be obtained.
At present, Raman solitons are widely researched, but the full fiber degree of the currently reported Raman soliton system is not high; the purity of the Raman soliton spectrum is not high, the self-frequency shift of single Raman soliton laser cannot be kept, and the Raman soliton spectrum is mostly in a super-continuous spectrum form; the conversion efficiency of the Raman solitons is low, and the pumping conversion efficiency is lower than 50%. The broadband tunable mid-infrared Raman solitons with high energy, high efficiency and high purity obtained in the optical fibers have high application significance.
In summary, no effective solution has been proposed for the problem of low conversion efficiency of the raman soliton.
Disclosure of Invention
The embodiment of the invention provides a mid-infrared femtosecond fiber laser light source system, which at least solves the technical problem of low conversion efficiency of Raman solitons.
According to an aspect of an embodiment of the present invention, there is provided a mid-infrared femtosecond fiber laser light source system including: a passively mode-locked fiber oscillation cavity (110) configured as a dispersion management cavity for outputting high-order soliton pulses with positive chirp; the polarization mode dispersion controller (120) is connected with the passive mode-locking optical fiber oscillation cavity (110) through an optical fiber and is used for applying polarization mode dispersion to the high-order soliton pulse for carrying out dispersion modulation and outputting the dispersion-modulated high-order soliton pulse, wherein the value of the polarization mode dispersion applied to the high-order soliton pulse is determined according to the feedback of the energy of the Raman soliton pulse output by the optical fiber amplifier (130), so that the energy conversion efficiency of converting the high-order soliton pulse into the Raman soliton pulse reaches the maximum value; the optical fiber amplifier (130) is connected with the polarization mode dispersion controller (120) through an optical fiber and is used for carrying out amplification operation and compression operation on the dispersion-modulated high-order soliton pulse so as to realize the conversion from the dispersion-modulated high-order soliton pulse to the Raman soliton pulse; the tellurium-based soft glass fiber (140) is connected with the fiber amplifier (130) through the fiber and used for translating the Raman soliton pulse to a middle infrared band to obtain the tunable femtosecond Raman soliton pulse of the middle infrared band.
Furthermore, the dispersion management cavity comprises two kinds of dispersion optical fibers, a mode locking device and a polarization control device, the net dispersion of the dispersion management cavity is positive dispersion, and the net dispersion of the cavity is positive and close to zero.
Further, the two dispersion fibers are respectively second-order beta2>0 positive dispersion thulium-doped gain fiber and second-order dispersion beta'2<0, the lengths of the two dispersion optical fibers are respectively the length L of the positive dispersion thulium-doped gain optical fiber1And length L of negative dispersion passive transmission fiber2The dispersion of the dispersion management cavity satisfies the following condition: 0<β2* L1+β’2* L2≈0。
Further, the mode locking device is a semiconductor saturable absorber with wide spectral bandwidth, graphene, black scale or topological insulator material.
Further, the polarization control device is used for adjusting the polarization quantity in the dispersion management cavity, so that the dispersion management cavity outputs soliton pulses with the order number larger than 10, the width larger than 15nm and the central wavelength between 1900nm and 2000 nm.
Further, the optical fiber used in the polarization mode dispersion controller (120) satisfies at least two conditions as follows: the used optical fiber length is less than a first walk-off length (LW 1), wherein the first walk-off length (LW 1) is the walk-off length of the dispersion-modulated high-order soliton pulse in the used optical fiber; and the used optical fiber is negative dispersion at the wavelength of the dispersion modulated high-order soliton pulse, so as to pre-compress the dispersion modulated high-order soliton pulse until the width of the dispersion modulated high-order soliton pulse is less than 500fs, so that the first walk-off length (LW 1) is close to the first dispersion length of the pulse, wherein the first dispersion Length (LD) is the dispersion length of the dispersion modulated high-order soliton pulse in the used optical fiber.
Further, the gain fiber used in the fiber amplifier (130) adopts thulium-doped or thulium-holmium-doped fiber, the zero dispersion point of the gain fiber is near 1900nm, the second walk-off length (LW 2) is increased, and the dispersion-modulated high-order soliton pulse is made to work in the negative dispersion area of the gain fiber, so as to compress and amplify the dispersion-modulated high-order soliton pulse; the second walk-off length (LW 2) is the walk-off length of the dispersion modulated high order soliton pulse in the gain fiber, and is increased so that the compressed dispersion modulated high order soliton pulse is converted to a raman soliton pulse over a longer walk-off distance.
Furthermore, the tellurium-based soft glass fiber (140) is a tellurate or telluride fiber, the zero dispersion point of the tellurium-based soft glass fiber (140) is adjusted by adjusting the fiber core diameter value of the tellurium-based soft glass fiber (140) to be smaller than the wavelength of the Raman soliton pulse generated in the fiber amplifier (130), so that the Raman soliton pulse is converted to the intermediate infrared band efficiently to obtain the intermediate infrared femtosecond Raman soliton pulse, a soliton compression effect exists in the transmission process of the intermediate infrared femtosecond Raman soliton pulse, and the width of the intermediate infrared femtosecond Raman soliton pulse generated in the tellurium-based soft glass fiber is smaller than that of the Raman soliton pulse output from the fiber amplifier (130).
Further, the conversion efficiency of the high-order soliton pulse into the raman soliton pulse is adjusted by adjusting the value of the polarization mode dispersion applied to the high-order soliton pulse in the polarization mode dispersion controller (120); the wavelength of the intermediate infrared femtosecond Raman soliton pulse is adjusted by adjusting the amplification factor of the optical fiber amplifier (130), and the adjustment range of the wavelength of the intermediate infrared femtosecond Raman soliton pulse is 2000nm to 3000 nm.
Furthermore, the mid-infrared femtosecond Raman soliton pulse generated by the tellurium-based soft glass fiber (140) is a high-purity pulse, does not contain multi-stage Raman solitons and does not contain supercontinuum components.
In the embodiment of the invention, the laser oscillation cavity is reasonably designed, the module of the polarization mode dispersion controller (120) is added, the polarization dispersion management is carried out on the high-order soliton pulse, the conversion efficiency of the Raman soliton in the post-stage amplifier is controlled, the energy of the Raman soliton pulse output by the optical fiber amplifier (130) is detected, the energy value is fed back to the polarization mode dispersion controller (120) in a closed loop mode, and the value of the polarization mode dispersion applied to the high-order soliton pulse is determined, so that the maximization of the energy conversion efficiency from the high-order soliton pulse to the Raman soliton pulse is realized, and the technical problem of lower conversion efficiency of the Raman soliton is solved.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the invention without limiting the invention. In the drawings:
FIG. 1 is a schematic block diagram of an alternative mid-infrared femtosecond fiber laser light source system according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of an alternative mid-infrared femtosecond fiber laser light source system according to an embodiment of the invention;
FIG. 3 is a schematic diagram of an alternative mid-infrared femtosecond fiber laser light source system according to an embodiment of the invention;
fig. 4 is a schematic diagram of spectral components of a generated mid-infrared raman soliton according to an embodiment of the present invention.
Detailed Description
In order to make the technical solutions of the present invention better understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
According to the embodiment of the invention, the embodiment of the intermediate infrared femtosecond fiber laser light source system is provided. As shown in fig. 1, the system includes:
a passively mode-locked fiber oscillation cavity 110 configured as a dispersion management cavity for outputting a high-order soliton pulse having positive chirp;
a polarization mode dispersion controller 120 connected to the passive mode-locked fiber oscillation cavity 110 through a fiber, for applying polarization mode dispersion to the high order soliton pulse for dispersion modulation, and outputting the dispersion-modulated high order soliton pulse, wherein a value of the polarization mode dispersion applied to the high order soliton pulse is determined according to feedback of energy of the raman soliton pulse output from the fiber amplifier 130, so that an energy conversion efficiency of converting the high order soliton pulse into the raman soliton pulse reaches a maximum value;
the optical fiber amplifier 130 is connected to the polarization mode dispersion controller 120 through an optical fiber, and is configured to perform an amplification operation and a compression operation on the dispersion-modulated high-order soliton pulse, so as to realize conversion from the dispersion-modulated high-order soliton pulse to a raman soliton pulse; the tellurium-based soft glass fiber 140 is connected with the fiber amplifier 130 through a fiber and is used for translating the Raman soliton pulse to a middle infrared band to obtain a tunable femtosecond Raman soliton pulse of the middle infrared band.
In summary, the laser oscillation cavity is designed reasonably, the module of the polarization mode dispersion controller (120) is added, the polarization dispersion management is carried out on the high-order soliton pulse, the conversion efficiency of the raman soliton in the post-stage amplifier is controlled, the energy of the raman soliton pulse output by the optical fiber amplifier (130) is detected, the energy value is fed back to the polarization mode dispersion controller (120) in a closed loop mode, the value of the polarization mode dispersion applied to the high-order soliton pulse is determined, the maximization of the energy conversion efficiency from the high-order soliton pulse to the raman soliton pulse is achieved, and the technical problem that the conversion efficiency of the raman soliton is low is solved.
In the embodiment of the invention, the dispersion management cavity comprises two kinds of dispersion optical fibers, a mode locking device and a polarization control device, the net dispersion of the dispersion management cavity is positive dispersion, and the net dispersion of the cavity is positive and close to zero. The specific structure of the dispersion management cavity can be seen in fig. 2 or fig. 3.
In the embodiment of the invention, the two dispersion fibers are respectively second-order beta2>0 positive dispersion thulium-doped gain fiber and second-order dispersion beta'2<0, the lengths of the two dispersion optical fibers are respectively the length L of the positive dispersion thulium-doped gain optical fiber1And negative dispersion passive transmission optical fibreLength L2The dispersion of the dispersion management cavity satisfies the following condition: 0<β2* L1+β’2* L2≈0。
In the embodiment of the invention, the mode locking device is a semiconductor saturable absorber with wide spectral bandwidth, graphene, black scale or topological insulator material.
In the embodiment of the invention, the polarization control device is used for adjusting the polarization quantity in the dispersion management cavity, so that the dispersion management cavity outputs soliton pulses with the order number larger than 10, the width larger than 15nm and the central wavelength between 1900nm and 2000 nm.
In an embodiment of the present invention, the optical fiber used in the polarization mode dispersion controller (120) satisfies at least two conditions as follows: the length of the used optical fiber is less than the first walk-off length (LW1) Wherein the first walk-off length (L)W1) The walk-off length of the dispersion-modulated high-order soliton pulse in the used optical fiber; and the optical fiber used is negative dispersion at the wavelength of the dispersion modulated high-order soliton pulse, so as to pre-compress the dispersion modulated high-order soliton pulse until the width of the dispersion modulated high-order soliton pulse is less than 500fs, so that the first walk-off Length (LW) is made1) A first dispersion length near the pulse, wherein the first dispersion length (L)D) Is the dispersion length of the dispersion-modulated high-order soliton pulse in the fiber used.
In the embodiment of the invention, the gain fiber used in the fiber amplifier (130) adopts thulium-doped or thulium-holmium-doped fiber, and the zero dispersion point of the gain fiber is close to 1900nm and is used for increasing the second walk-off Length (LW)2) And is used for making the dispersion-modulated high-order soliton pulse work in the negative dispersion area of the gain fiber so as to compress and amplify the dispersion-modulated high-order soliton pulse; second walk-off Length (LW)2) For the walk-off length of the dispersion-modulated high-order soliton pulse in the gain fiber, the second walk-off length is increased, so that the compressed dispersion-modulated high-order soliton pulse is converted into the Raman soliton pulse at a longer walk-off distance.
In the embodiment of the invention, the tellurium-based soft glass fiber (140) is a tellurate or telluride fiber, the zero dispersion point of the tellurium-based soft glass fiber (140) is adjusted by adjusting the diameter value of the fiber core of the tellurium-based soft glass fiber (140) to be smaller than the wavelength of a Raman soliton pulse generated in the fiber amplifier (130), so that the Raman soliton pulse is converted to a middle infrared band efficiently to obtain a middle infrared femtosecond Raman soliton pulse, a soliton compression effect exists in the transmission process of the middle infrared femtosecond Raman soliton pulse, and the width of the middle infrared femtosecond Raman soliton pulse generated in the tellurium-based soft glass fiber is smaller than that of the Raman soliton pulse output in the fiber amplifier (130).
In particular, such fibers have the advantages of: the zero dispersion point is positioned near 2000nm, so that the pumping light and the Raman solitons can not walk away in a longer transmission distance, and the energy of the pumping light (namely high-order soliton pulse) can be transferred to the Raman solitons; the tellurate or telluride optical fiber has a high nonlinear coefficient which is about 10 times that of the quartz optical fiber, so that Raman solitons can be obtained in a short optical fiber, and the system is simple and reliable.
In the embodiment of the invention, the conversion efficiency of the high-order soliton pulse to the Raman soliton pulse is adjusted by adjusting the value of the polarization mode dispersion applied to the high-order soliton pulse in the polarization mode dispersion controller (120); the wavelength of the intermediate infrared femtosecond Raman soliton pulse is adjusted by adjusting the amplification factor of the optical fiber amplifier (130), and the adjustment range of the wavelength of the intermediate infrared femtosecond Raman soliton pulse is 2000nm to 3000 nm.
In the embodiment of the invention, the mid-infrared femtosecond Raman soliton pulse generated by the tellurium-based soft glass fiber (140) is a high-purity pulse, does not contain multi-stage Raman solitons and does not contain a supercontinuum component.
Embodiments of the present invention provide a system for generating high-energy, high-efficiency, high-purity tunable femtosecond raman solitons. The system adopts a dispersion management cavity or an ultra-short optical fiber cavity, obtains high-order positive dispersion Raman solitons in a laser cavity in a passive mode locking mode, controls the efficiency and wavelength translation amount of generating the Raman solitons through a polarization mode dispersion controller, and finally obtains intermediate infrared Raman solitons in intermediate infrared tellurium-based optical fibers with negative dispersion, wherein the Raman soliton pulse energy is more than 100nJ, the pulse conversion efficiency is more than 80%, the Raman solitons are expressed as single soliton pulse and do not contain multi-stage Raman solitons or any super-continuous spectrum components.
In the embodiment, the tellurate or telluride optical fiber is used as a nonlinear medium to extend the Raman soliton to the mid-infrared spectrum band, and the optical fiber has the advantages that: the zero dispersion point is positioned near 2000nm, so that the pumping light and the Raman solitons can not walk away in a longer transmission distance, and the energy of the pumping light can be transferred to the Raman solitons; the tellurate or telluride optical fiber has a high nonlinear coefficient which is about 10 times that of the quartz optical fiber, so that Raman solitons can be obtained in a short optical fiber, and the system is simple and reliable.
Fig. 2 is a schematic structural diagram of an alternative mid-infrared femtosecond fiber laser light source system according to an embodiment of the present invention.
As shown in fig. 2, one embodiment of the present invention is a dispersion managed oscillation cavity employing a ring cavity, which contains a thulium doped gain fiber 210 employing a positive dispersion fiber, a compensation fiber 220 having negative dispersion, a polarization controller 230, and a passive mode locking device 240. The cavity length of the dispersion management oscillation cavity is controlled within 3 meters, the length of the positive dispersion optical fiber and the length of the negative dispersion optical fiber are required not to exceed 1.5 meters, and the dispersion value of the positive dispersion optical fiber is 0.09 ps2Perm, the dispersion value of the negative dispersion fiber is-0.064 ps2M, net dispersion of the oscillation cavity is close to 0.02ps2. A polarization control device 230 within the cavity is used to adjust the amount of polarization in the dispersion managed oscillation cavity. The passive mode-locking device 240 is a transmission-type device, such as a projected semiconductor saturable absorber mirror (SESAM), a projected graphite two-dimensional material, or a projected topological insulator material, and requires a working bandwidth of the passive mode-locking device to be greater than 30 nm. The spectral width of high-order solitons output by the oscillation cavity is larger than 15nm, the soliton order is larger than 10, and the soliton center wavelength is between 1900nm and 2000 nm.
As shown in fig. 2, the high-order solitons are output from the dispersion management oscillation cavity and then subjected to dispersion mode control by the polarization mode dispersion controller 250, which is at a high levelThe wavelength of the first order soliton is negative dispersion, the first order soliton has precompression effect, the self-phase modulation and cross-phase modulation of the optical fiber of the polarization mode dispersion controller act together, and the high order soliton passes through a walk-off length LwThe post Raman soliton pulse light is established, and the length of the optical fiber of the polarization mode dispersion controller is larger than the walk-off length LwAnd less than 1.5 times the walk-off length Lw。
As shown in fig. 2, after passing through the polarization mode dispersion controller 250, the high-order solitons enter the optical fiber amplifier 260 for energy enhancement, the gain optical fiber adopted by the optical fiber amplifier 260 is a thulium-doped or thulium-holmium-doped optical fiber, and the gain optical fiber is negative dispersion at the wavelength of the high-order solitons to further compress the solitons, so that the high-order solitons continue to perform energy transfer to the raman solitons.
As shown in fig. 2, the polarization mode dispersion controller monitors the raman soliton energy in the optical fiber amplifier 260 through the raman soliton energy monitoring feedback system 280, and controls the conversion efficiency from the high-order solitons to the raman solitons by adjusting the value of the polarization mode dispersion, so that the conversion efficiency is finally higher than 90%.
Wherein the energy monitoring feedback system 280 comprises: the optical fiber amplifier 130 comprises a spectroscope, a first energy meter, a second energy meter, a control unit and a feedback transmission unit, wherein the spectroscope is used for separating the dispersion-modulated high-order soliton pulse in the optical fiber amplifier 130 from the Raman soliton pulse obtained through conversion and transmitting the separated dispersion-modulated high-order soliton pulse to the first energy meter and the Raman soliton pulse to the second energy meter respectively, the first energy meter is used for detecting the energy of the dispersion-modulated high-order soliton pulse, the second energy meter is used for detecting the energy of the Raman soliton pulse, and the control unit is used for receiving the outputs of the first energy meter and the second energy meter, calculating and storing the ratio of the outputs of the second energy meter and the first energy meter.
Further, the polarization mode dispersion controller 120 increases the value of the polarization mode dispersion from the initial value according to a predetermined step length, at this time, the energy monitoring feedback system 280 records and stores the ratio of the outputs of the second energy meter and the first energy meter, and feeds back the value of the polarization mode dispersion corresponding to the maximum value of the ratio of the outputs of the second energy meter and the first energy meter to the polarization mode dispersion controller 120, so that the polarization mode dispersion controller 120 performs dispersion modulation according to the value of the polarization mode dispersion corresponding to the maximum value.
In one arrangement, the control unit in the energy monitoring feedback system 280 determines a trend of a change in the ratio output by the second energy meter and the first energy meter, and sends a positive feedback signal to the polarization mode dispersion controller 120 through the feedback transmission unit when detecting that the ratio is large, and sends a negative feedback signal to the polarization mode dispersion controller 120 through the feedback transmission unit when detecting that the ratio is small. The value of the polarization mode dispersion in the polarization mode dispersion controller 120 is determined according to the received feedback signal, and when the received feedback signal is positive feedback, the value of the polarization mode dispersion is increased, and when the received feedback signal is negative feedback, the value of the polarization mode dispersion is decreased until the value of the polarization mode dispersion reaches the theoretical maximum value infinitely and dynamically.
In another scheme, the polarization mode dispersion controller 120 also includes a control unit, the polarization mode dispersion controller 120 and the energy monitoring feedback system 280 are provided with the same initial value of polarization mode dispersion, the control unit in the polarization mode dispersion controller 120 increases the value of polarization mode dispersion according to a first step length from the initial value, at this time, the energy monitoring feedback system 280 records and stores the ratio of the outputs of the second energy meter and the first energy meter, and records the change times of the ratio of the outputs of the second energy meter and the first energy meter, so as to determine the step times of the value of polarization mode dispersion in the polarization mode dispersion controller 120; meanwhile, when it is determined that the ratio of the outputs of the second energy meter and the first energy meter reaches the first maximum value, the energy monitoring feedback system 280 determines the number of steps corresponding to the first maximum value, and feeds the number of steps back to the control unit in the polarization mode dispersion controller 120 through the feedback transmission unit, after receiving the feedback value, the control unit in the polarization mode dispersion controller 120 increases or decreases the value of the polarization mode dispersion according to the second step length, where the second step length is half of the first step length, and increases and decreases the value of the polarization mode dispersion according to the second step length, respectively, to determine the adjustment direction, after determining the adjustment direction, continues to adjust the value of the polarization mode dispersion according to the foregoing method, after obtaining the second maximum value, continues to decrease the step length, and performs iterative adjustment in a loop. It has been found experimentally that three adjustments can already be made substantially close to the true maximum.
As shown in fig. 2, the system further translates the raman soliton generated by the fiber amplifier 260 to the mid-infrared band by using the tellurium-based soft glass fiber 270, which includes a tellurate fiber mainly made of TeO2 or a telluride fiber mainly made of Te, and the zero dispersion point of the tellurate fiber is about 1900nm, so as to ensure that the raman soliton propagates in the tellurate fiber in a negative dispersion form, and the nonlinear coefficient of the tellurate is 10 times that of the quartz glass fiber, so as to ensure that the short tellurium-based fiber generates the high-efficiency mid-infrared raman soliton. A Raman soliton wavelength monitoring feedback system is adopted between the optical fiber amplifier 260 and the tellurium-based soft glass optical fiber 270 to monitor the translation wavelength of mid-infrared femtosecond Raman solitons generated in the tellurium-based soft glass optical fiber, the central wavelength of the mid-infrared Raman solitons generated in the tellurium-based soft glass optical fiber 270 is adjusted by adjusting the amplification factor of the optical fiber amplifier 260, and finally the femtosecond mid-infrared Raman solitons are obtained in the tellurium-based soft glass optical fiber 270, and the conversion efficiency of the generated Raman solitons reaches 90%. The generated mid-infrared Raman solions are high-purity pulses, do not contain multi-stage Raman solions, do not contain supercontinuum components, and the spectrum of the pulses is shown in FIG. 4.
FIG. 3 is a schematic structural diagram of another alternative mid-infrared femtosecond fiber laser light source system according to the embodiment of the invention.
As shown in fig. 3, the oscillation cavity is passively mode-locked by a linear cavity, and the passive mode-locking device (310) is a reflective device, such as a reflective semiconductor saturable absorber mirror (SESAM), a reflective graphite two-dimensional material, a reflective topological insulator material, or a reflective black scale material. The devices in the cavity are arranged linearly and comprise a passive mode locking device (310), a negative dispersion optical fiber (320), a positive dispersion optical fiber (330) and a polarization controller (340), the oscillation cavity adopts a broadband Fiber Bragg Grating (FBG) to output pulses, the bandwidth of the optical fiber is more than 20nm, the length of the oscillation cavity is controlled within 2 meters, and the length of the positive dispersion optical fiber and the length of the negative dispersion optical fiber are requiredThe degree is not more than 1.5 m, and the dispersion value of the positive dispersion fiber is 0.09 ps2Perm, the dispersion value of the negative dispersion fiber is-0.064 ps2M, net dispersion of the oscillation cavity is close to 0.02ps2. An intra-cavity polarization control device (340) is used to adjust the amount of polarization in the dispersion-managed cavity. The spectral width of high-order solitons output by the oscillation cavity is larger than 15nm, the soliton order is larger than 10, and the soliton center wavelength is between 1900nm and 2000 nm.
It is understood that the polarization mode dispersion controller, the raman soliton energy monitoring feedback, the fiber amplifier, the raman soliton wavelength monitoring feedback, and the tellurium-based soft glass fiber in the embodiment shown in fig. 3 may be configured in the same manner as in the embodiments shown in fig. 1 and 2.
In some examples, the system may be constructed using polarization maintaining fiber
In some examples, the positive dispersion fiber in the oscillator may be replaced with other fibers in addition to the gain fiber, and other positive dispersion fibers may be introduced to dispersion manage the cavity.
The above-mentioned serial numbers of the embodiments of the present invention are merely for description and do not represent the merits of the embodiments.
In the above embodiments of the present invention, the descriptions of the respective embodiments have respective emphasis, and for parts that are not described in detail in a certain embodiment, reference may be made to related descriptions of other embodiments.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (10)
1. A mid-infrared femtosecond fiber laser light source system is characterized by comprising:
a passively mode-locked fiber oscillation cavity (110) configured as a dispersion management cavity for outputting high-order soliton pulses with positive chirp;
a polarization mode dispersion controller (120) connected to the passively mode-locked fiber oscillation cavity (110) through an optical fiber, for applying polarization mode dispersion to the high order soliton pulse for dispersion modulation, and outputting the dispersion-modulated high order soliton pulse, wherein a value of the polarization mode dispersion applied to the high order soliton pulse is determined according to feedback of energy of the raman soliton pulse output from the fiber amplifier (130), so that an energy conversion efficiency of converting the high order soliton pulse into the raman soliton pulse reaches a maximum value;
the optical fiber amplifier (130) is connected with the polarization mode dispersion controller (120) through an optical fiber and is used for carrying out amplification operation and compression operation on the dispersion-modulated high-order soliton pulse so as to realize the conversion from the dispersion-modulated high-order soliton pulse to a Raman soliton pulse;
the tellurium-based soft glass optical fiber (140) is connected with the optical fiber amplifier (130) through an optical fiber and is used for translating the Raman soliton pulse to a middle infrared band to obtain a tunable femtosecond Raman soliton pulse of the middle infrared band;
the optical fiber used in the polarization mode dispersion controller (120) satisfies at least two conditions:
the length of the optical fiber used is less than the first walk-off length (L)W1) Wherein the first walk-off length (L)W1) Is the walk-off length of the dispersion-modulated high-order soliton pulse in the used optical fiber; and
the optical fiber used is negatively dispersive at the wavelength of the dispersion modulated high order soliton pulse.
2. The system of claim 1, wherein the dispersion management cavity comprises two types of dispersive optical fibers, a mode locking device, and a polarization control device, wherein the dispersion management cavity has a net dispersion with a positive dispersion, and a positive and near zero net dispersion.
3. The system of claim 2, wherein the two dispersive fibers are each second-order β2>0 positive dispersion thulium-doped gain fiber and second-order dispersion beta'2<0, the lengths of the two dispersion optical fibers are respectively the length L of the positive dispersion thulium-doped gain optical fiber1And negative dispersion passive transmissionLength L of optical fiber2The dispersion of the dispersion management cavity satisfies the following condition: 0<β2*L1+β’2*L2≈0。
4. The system of claim 2, wherein the mode-locking device is a semiconductor saturable absorber, graphene, black scale, or topological insulator material with a broad spectral bandwidth.
5. The system of claim 2, wherein the polarization control device is configured to adjust the amount of polarization in the dispersion management cavity such that the dispersion management cavity outputs soliton pulses having an order greater than 10, a width greater than 15nm, and a center wavelength between 1900nm and 2000 nm.
6. The system according to claim 1, wherein the optical fiber used by the polarization mode dispersion controller (120) is used to pre-compress the dispersion modulated high order soliton pulses until the width of the dispersion modulated high order soliton pulses is less than 500fs, such that the first walk-off length (L) is less than 500fsW1) A first dispersion length near the pulse, wherein the first dispersion length (L)D) Is the dispersion length of the dispersion-modulated high-order soliton pulse in the fiber used.
7. The system according to claim 1, wherein the gain fiber used in the fiber amplifier (130) is a thulium-doped or thulium-holmium-doped fiber, the zero dispersion point of the gain fiber being near 1900nm for increasing the second walk-off length (L)W2) And is used for making the dispersion-modulated high-order soliton pulse work in the negative dispersion region of the gain fiber so as to compress and amplify the dispersion-modulated high-order soliton pulse;
the second walk-off length (L)W2) For the walk-off length of the dispersion modulated high order soliton pulse in the gain fiber, increasing the second walk-off length such that the dispersion modulated high order solitons are compressedThe pulse is converted into the Raman soliton pulse at a longer travel distance.
8. The system of claim 1, wherein the tellurium-based soft glass fiber (140) is a tellurate or telluride fiber, and the zero dispersion point of the tellurium-based soft glass fiber (140) is adjusted by adjusting the core diameter value of the tellurium-based soft glass fiber (140) to be smaller than the wavelength of the raman soliton pulse generated in the fiber amplifier (130) so as to efficiently convert the raman soliton pulse to the mid-infrared band to obtain a mid-infrared femtosecond raman soliton pulse, wherein a soliton compression effect exists during the transmission of the mid-infrared femtosecond raman soliton pulse, and the width of the mid-infrared femtosecond raman soliton pulse generated in the tellurium-based soft glass fiber is smaller than the raman soliton pulse output from the fiber amplifier (130).
9. The system according to any one of claims 1-8,
adjusting the conversion efficiency of the high order soliton pulse into a Raman soliton pulse by adjusting the value of the polarization mode dispersion applied to the high order soliton pulse in a polarization mode dispersion controller (120);
the wavelength of the mid-infrared femtosecond Raman soliton pulse is adjusted by adjusting the amplification factor of the optical fiber amplifier (130), and the adjustment range of the wavelength of the mid-infrared femtosecond Raman soliton pulse is 2000nm to 3000 nm.
10. The system according to any one of claims 1-8, wherein the mid-infrared femtosecond Raman soliton pulse generated by the tellurium-based soft glass fiber (140) is a high-purity pulse which does not contain multi-stage Raman solitons and does not contain supercontinuum components.
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| US6885683B1 (en) * | 2000-05-23 | 2005-04-26 | Imra America, Inc. | Modular, high energy, widely-tunable ultrafast fiber source |
| CN101499608B (en) * | 2009-03-06 | 2010-07-07 | 北京交通大学 | Optically parametric oscillator |
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| CN101076748A (en) * | 2004-11-22 | 2007-11-21 | Imra美国公司 | Examinant |
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