CN109560453B - Passive Q-switched mode-locked ring laser based on SBS and Fabry-Perot interferometer - Google Patents
Passive Q-switched mode-locked ring laser based on SBS and Fabry-Perot interferometer Download PDFInfo
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- 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
- H01S3/30—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range using scattering effects, e.g. stimulated Brillouin or Raman effects
- H01S3/302—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range using scattering effects, e.g. stimulated Brillouin or Raman effects in an optical fibre
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
- H01S3/06—Construction or shape of active medium
- H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
- H01S3/067—Fibre lasers
- H01S3/06791—Fibre ring lasers
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- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
- H01S3/11—Mode locking; Q-switching; Other giant-pulse techniques, e.g. cavity dumping
- H01S3/1106—Mode locking
- H01S3/1112—Passive mode locking
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Abstract
The invention discloses a passive Q-switched mode-locked ring laser based on SBS and Fabry-Perot interferometer, comprising: the optical fiber coupling device comprises a pumping source, a gain optical fiber, an optical fiber wavelength division multiplexer, a passive optical fiber, an optical fiber circulator and a Fabry-Perot interferometer, wherein the Fabry-Perot interferometer is composed of two optical fiber end faces with a small distance, the common optical fiber jumper end face and the common optical fiber jumper end face can be accurately aligned through an optical fiber flange plate and leave the distance, and the common optical fiber end face can be accurately aligned through other optical alignment tools and leave the distance. The pump source and the gain fiber are determined according to actual wavelength requirements. The central operating wavelength of the optical fiber circulator corresponds to the gain wavelength of the gain optical fiber. The two multiplexing wavelengths of the fiber wavelength division multiplexer are the pump wavelength and the gain wavelength of the gain fiber, respectively. The invention can inhibit the instability of the amplitude, the repetition frequency and the spectrum of the pulse emitted by the Brillouin passive Q-switched laser.
Description
Technical Field
The invention belongs to the technical field of fiber laser, and particularly relates to a passive Q-switched mode-locked ring laser based on multistage stimulated Brillouin scattering and Fabry-Perot interferometers.
Background
As one of important nonlinear effects in an optical fiber, Stimulated Brillouin Scattering (SBS) has a small excitation threshold, nonlinear back light Scattering, and has been widely used, such as optical fiber sensing and pulse width compression based on brillouin back Scattering, slow light control based on group refractive index change caused by stimulated brillouin Scattering, phase conjugation and beam quality optimization using stimulated brillouin Scattering in a multimode optical fiber, and a passive Q-switching effect and a modulation instability effect using stimulated brillouin Scattering. As one of pulse generation means that can realize full-fiber, the passive Q-switched effect and the relaxation oscillation effect of stimulated brillouin scattering SBS have been hot topics of ultrafast optical research. In 1997, researchers realized the self-starting Q-switch based on brillouin scattering in rare-earth ion doped fiber lasers for the first time, the feedback at two ends adopted in the experiment was a fiber loop resonator and a mirror, and as a typical narrow linewidth feedback device, the experimental scheme using the fiber loop resonator has been used up to now. Subsequently, researchers discovered a phenomenon in which mode-locked pulses were emitted based on the SBS modulation instability effect. Because the passive Q-switching and mode-locked laser based on SBS can be built near any wavelength with gain, SBS effect threshold can be reduced along with the increase of the length of the optical fiber, and additional optical devices are not needed, and the building is simple and convenient, so that the passive Q-switching and mode-locked laser is always an important research content in the laser field.
However, the passive Q-switched laser of SBS has the characteristic of unstable output pulse because of the dynamic mechanism of SBS. The instability of the SBS-based passively Q-switched output pulses arises from random thermal noise and random rayleigh scattering present within the laser. The thermal noise plays a role in initiating the brillouin scattering in the course of the brillouin scattering. While the feedback effect due to rayleigh scattering constitutes the cavity of the brillouin laser. The optical fiber ring resonator adopted in the previous experiment is generally narrow in line width, easy to excite stimulated Brillouin scattering, free of feedback effect on multi-stage Stokes light, and plays the most critical role in the unstable Q-switching process of random thermal noise and random Rayleigh scattering. In fact, the passive Q-switching effect of the brillouin Q-switched laser is caused by the combined action of nonlinear brillouin backscattering and linear rayleigh scattering, and the amplitude and repetition frequency of the Q-switched pulse fluctuate within the range of 20% to 40% due to the randomness of both the thermal noise and the backsrayleigh scattering causing spontaneous brillouin scattering. This causes instability and uncontrollable SBS passively Q-switched, which, although capable of producing occasional pulses with a very large peak-to-average power ratio, has significant drawbacks.
Firstly, the accidentally generated ultra-intense pulses with uncontrollable amplitudes can cause damage to the optical fibers and to the optical devices; second, the Q-switched pulse is usually accompanied by parasitic pulses and has a multimodal structure; finally, the amplitude and repetition frequency of the Q-switched output pulses are quite unstable. Therefore, the application of SBS-based passive Q-switching is greatly limited. To reduce the effects of thermal noise and other noise, researchers have suggested experiments in low temperature environments or other isolated systems, for example, the repetition rate of pulses can be stabilized by actively modulating the pulses with an acousto-optic modulator in the cavity, or the repetition rate of Q-switched pulses can be stabilized by modulating the gain of the pump pulses, but this approach does not help to stabilize the amplitude, and in neither approach, the stability of the spectrum is not mentioned. All the measures are effective, but all the measures complicate the system, weaken the advantage of economic, convenient and full-fiber of the Brillouin passive Q-switched laser, and do not fundamentally solve the problems.
Disclosure of Invention
Aiming at the defects or improvement requirements of the prior art, the invention provides a fully-fiber passive Q-switched mode-locked ring laser based on multi-stage stimulated Brillouin scattering and Fabry-Perot interferometer, so that the technical problems that the output of the conventional passive Q-switched laser based on stimulated Brillouin scattering is unstable, optical devices are damaged and the conventional passive Q-switched laser based on stimulated Brillouin scattering is difficult to use are solved.
In order to achieve the above object, the present invention provides a passively Q-switched mode-locked ring laser based on SBS and fabry-perot interferometers, comprising: the optical fiber laser device comprises a pumping laser unit, a Fabry-Perot interferometer, a passive optical fiber and an optical fiber circulator;
the first end of the pump laser unit is connected with the first end of the optical fiber circulator, the third end of the optical fiber circulator is connected with the second end of the pump laser unit, and the second end of the optical fiber circulator is connected with the Fabry-Perot interferometer;
the pump laser unit is used for realizing the introduction of pump energy and realizing the amplification and conversion of stimulated radiation of the pump energy into laser energy;
the optical fiber circulator is used for realizing the isolation of pumping laser and clockwise running laser and connecting the Fabry-Perot interferometer together to form an annular resonant cavity, wherein the laser generated in the annular resonant cavity runs in the direction set by the optical fiber circulator (5);
the passive optical fiber is positioned between the second end of the optical fiber circulator and the Fabry-Perot interferometer and is used for accumulating the Brillouin effect;
the Fabry-Perot interferometer is used for respectively modulating the multistage Stokes light generated by stimulated Brillouin scattering by utilizing the nano-level wavelength loss modulation effect of the Fabry-Perot interferometer to obtain stable Q-switched pulses or mode-locked pulses, and then outputting the Q-switched pulses or the mode-locked pulses from the end of the Fabry-Perot interferometer.
Preferably, the fabry-perot interferometer is comprised of a first fiber-optic endface and a second fiber-optic endface, and the first fiber-optic endface is aligned with the second fiber-optic endface with a predetermined spacing therebetween.
Preferably, the first optical fiber end face is a common optical fiber end face, and the second optical fiber end face is a common optical fiber end face or an optical fiber end face subjected to surface reflection enhancement processing.
Preferably, the pump laser unit includes: a pumping source, a fiber wavelength division multiplexer and a gain fiber;
the pumping source is connected with the short wavelength end of the optical fiber wavelength division multiplexer, two long wavelength ends of the optical fiber wavelength division multiplexer are respectively connected with the first end of the optical fiber circulator and the first end of the gain optical fiber, the second end of the gain optical fiber is connected with the third end of the optical fiber circulator, the second end of the optical fiber circulator is connected with the first end of the passive optical fiber, and the second end of the passive optical fiber is connected with the end face of the first optical fiber;
the pumping source is used for guiding pumping energy, the optical fiber wavelength division multiplexer is used for coupling the pumping energy into the annular resonant cavity and converting the pumping energy into laser energy through the gain optical fiber, and the gain optical fiber is used for realizing population inversion.
Preferably, the predetermined spacing between the first fiber end face and the second fiber end face is between 5 μm and 1000 μm.
Preferably, the 3dB transmission bandwidth of the optical fiber circulator is between 5nm and 20nm at the central wavelength, and the isolation is greater than 50 dB.
Preferably, the fiber optical circulator is a three-port optical circulator, the laser light generated in the ring resonator can only pass through the first port to the second port and the second port to the third port, and the pump laser light can not pass through any port.
Preferably, the rare earth ions doped in the gain fiber are one or more of ytterbium ions, erbium ions and thulium ions.
Preferably, the passive optical fiber is undoped with a gain medium.
In general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:
(1) conventional passive Q-switched SBS lasers achieve Q-switched operation by nonlinear brillouin scattering, and usually use a method of using a fiber ring resonator to cause in-loop optical resonance enhancement to cause stimulated brillouin scattering, but have been short of specific feedback for multi-stage stokes light, so spontaneous brillouin scattering and random distributed rayleigh scattering generated by random thermal noise play an important role in the start-up process of Q-switched pulses. The emitted pulses are therefore random, unstable and impractical. According to the invention, one optical fiber end face 7 and one optical fiber end face 6 are butted, and a gap is left, so that a Fabry-Perot interferometer in a cavity is generated, the interferometer can regulate and control the loss of wavelength in a nanometer order, and can also have a feedback effect on the Stokes light of a specific order after the basic condition of Q modulation of SBS is met, so that the Stokes light of different orders play different roles in the Q modulation process, and especially the feedback on the Stokes light of the specific order enables the Stokes light to play a role of stabilizing pulse. Therefore, the influence of thermal noise and random Rayleigh scattering on the output pulse is weakened, and the Q-switch pulse and the mode-locked pulse based on SBS with stable pulse amplitude, repetition frequency and spectrum are output.
(2) Compared with the conventional passive Q-switched mode-locked ring laser, the passive Q-switched mode-locked ring laser has the advantages of being capable of running under multiple wavelengths, high in damage threshold, easy to integrate all-fiber, low in cost, high in output power, few in devices and simple in light path. At present, the conventional Q-switched laser generation modes mainly comprise passive Q-switched modes such as a saturable absorber, a nonlinear annular mirror and nonlinear polarization rotation, and active Q-switched modes such as electro-optic Q-switched, acousto-optic Q-switched and turning mirror Q-switched modes, wherein the active Q-switched modes can operate under multiple wavelengths, but the cost is high, the system is complex and the integration is difficult. The saturable absorber Q-switching can only work in a specific wavelength range because of the specific wavelength absorption of the saturable absorber, and the damage threshold of the general saturable absorber is far lower than the damage threshold of the optical fiber, so that the potential of the optical fiber capable of emitting power is inhibited, and the saturable absorber Q-switching can only work as a seed light generator under low power. The modes of the nonlinear ring mirror, the nonlinear polarization rotation and the like need special device support, and the cost is high. The operation mechanism of the passive Q-switched mode-locked ring laser based on SBS of the invention is nonlinear stimulated Brillouin scattering effect, so that the passive Q-switched mode-locked ring laser can be generated under any medium and wavelength with Brillouin gain theoretically without the limitation of wavelength. Secondly, the structure of the passive Q-switched mode-locked ring laser based on the invention has low cost, and only two optical fiber end faces need to be butted, such as an optical fiber jumper end face and the like. The method is simple to operate and easy to realize, and the cost of pulse generation is further reduced. Secondly, based on the structure of the invention, full optical fiber packaging can be easily realized, and the structure is easy to be integrated with other systems, such as a multi-stage amplification system, a sensing system and the like. Furthermore, because the invention has simple structure and uses less optical devices, the stability and damage threshold of the whole system are greatly increased, and the system can operate under extremely high power. Finally, the laser structure can realize the output of Q-switched and mode-locked pulses, the output pulse width range is from microsecond to nanosecond, and the laser structure has wide practical application.
(3) The optical fiber end face 6 of the present invention adopts a common optical fiber end face, because once the optical fiber end face 6 has a high reflectivity, the optical fiber end face 6 forms a resonant cavity through the optical fiber circulator 5, which causes the continuous oscillation of the optical fiber, the population of the inversion particles cannot be gathered, and the stimulated brillouin scattering cannot form pulse output even if excited. Secondly, the optical fiber end face 7 may be a common optical fiber end face or an end face subjected to reflection enhancement processing, and if the reflection enhancement processing is performed, the reflectivity of the optical fiber end face 7 after the reflection enhancement processing is within a range from 5% to 40%, because too low reflectivity causes too low reflection of the fabry-perot cavity, the feedback of stokes light is weak and is submerged in thermal noise and random rayleigh scattering, oscillation cannot be formed, and random output of Q-switched pulses is caused. If the reflectivity is too high, the reflectivity of the Fabry-Perot cavity is too high, so that the signal light can only accumulate the inversion particle number in a very small distance range between the end faces of the two optical fibers, and the signal light is very easy to start oscillation under most conditions, and the accumulation of the inversion particle number cannot be formed, so that the laser is difficult to work in a pulse operation state.
(4) Because the bandwidth limiting devices in the cavity are fewer, the wide bandwidth output can be realized, and even the super-continuum spectrum can be generated.
(5) The invention realizes the stable and controllable output based on SBS passive Q-switched, promotes the research and the wide application of the SBS passive Q-switched laser, provides a feasible scheme for the passive Q-switched mode locking of full optical fiber and provides a feasible idea for manufacturing the pulse laser with low cost.
Drawings
Fig. 1 is a schematic structural diagram of a passively Q-switched mode-locked ring laser based on multiple stages of stimulated brillouin scattering and fabry-perot interferometers according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a structure for generating a Fabry-Perot interferometer according to an embodiment of the present invention, wherein jumper alignment is adopted;
fig. 3 is a Q-switched pulse sequence emitted by a passive Q-switched mode-locked ring laser based on multi-stage stimulated brillouin scattering and fabry-perot interferometer under 600mW of pump light according to an embodiment of the present invention;
fig. 4 is a radio frequency diagram of a Q-switched pulse sequence emitted by a passively Q-switched mode-locked ring laser based on multi-stage stimulated brillouin scattering and fabry-perot interferometer according to an embodiment of the present invention under 600mW of pump light;
fig. 5 is a mode-locked pulse sequence emitted by a passively Q-switched mode-locked ring laser based on multi-stage stimulated brillouin scattering and fabry-perot interferometer according to an embodiment of the present invention;
fig. 6 is a radio frequency diagram of a mode-locked pulse sequence emitted by a passively Q-switched mode-locked ring laser based on multiple stages of stimulated brillouin scattering and fabry-perot interferometers according to an embodiment of the present invention;
the same reference numbers will be used throughout the drawings to refer to the same or like elements or structures, wherein: 1-pumping source, 2-wavelength division multiplexer, 3-gain optical fiber, 4-passive optical fiber, 5-optical fiber optical circulator, 6-first optical fiber end face, 7-second optical fiber end face, 8-first fusion point, 9-second fusion point, 10-third fusion point, 11-fourth fusion point, 12-fifth fusion point, 13-sixth fusion point, 14-optical fiber flange plate, 15-first optical fiber jumper end face, 16-second optical fiber jumper end face, 17-first optical fiber jumper and 18-second optical fiber jumper.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The terms first, second, third and the like in the description and in the claims of the present invention are used for distinguishing between different objects and not for describing a particular order.
The invention provides a passive Q-switched mode-locked ring laser based on SBS and Fabry-Perot interferometer, which is used for breaking through the limitation that the traditional passive Q-switched and mode-locked based on SBS can not be practically applied due to the huge randomness and instability of the passive Q-switched and mode-locked laser. The basic idea is as follows: in the existing scheme, although the optical fiber ring resonator can generate an extremely narrow line width, the effect of noise is amplified, so that the instability of Q modulation of the Brillouin laser is caused. In the invention, an optical fiber end face 7 and an optical fiber end face 6 are butted and a gap is left, thus a Fabry-Perot interferometer in a cavity is generated, the interferometer can regulate and control the loss of the wavelength in a nanometer order, and can also have a feedback effect on Stokes light of a specific level after the basic condition of Q modulation of SBS is met, thus weakening the influence of thermal noise and random Rayleigh scattering on output pulse, and realizing the output of Q switching pulse and mode locking pulse based on SBS with stable pulse amplitude, repetition frequency and spectrum.
Fig. 1 is a schematic structural diagram of a fully-fiber passive Q-switched mode-locked ring laser based on multi-stage stimulated brillouin scattering and fabry-perot interferometer according to an embodiment of the present invention, where a pump laser unit includes a pump source 1, an optical fiber wavelength division multiplexer 2, and a gain fiber 3; the laser also comprises a passive optical fiber 4, an optical fiber circulator 5, a Fabry-Perot interferometer formed by a first optical fiber end face 6 and a second optical fiber end face 7, and a first fusion point 8, a second fusion point 9, a third fusion point 10, a fourth fusion point 11 and a fifth fusion point 12 which are generated by connecting all parts, as well as a sixth fusion point 13.
The pumping source 1 is connected with the short wavelength end of the optical fiber wavelength division multiplexer 2 through a first fusion point 8, two long wavelength ends of the optical fiber wavelength division multiplexer 2 are respectively connected with the first end of the gain optical fiber 3 and the first port of the optical fiber circulator 5 through a third fusion point 10 and a sixth fusion point 13, the first optical fiber end face 6 and the second optical fiber end face 7 can be aligned through an optical fiber flange or other optical alignment tools and are provided with a gap to form a Fabry-Perot interferometer, and the second optical fiber end face 7 serves as a main output end. The second end of the gain fiber 3 is connected with the third port of the optical fiber circulator 5 through a fifth fusion point 12, the first end of the passive fiber 4 is connected with the second port of the optical fiber circulator 5 through a fourth fusion point 11, and the second end of the passive fiber 4 is connected with the Fabry-Perot interferometer through a second fusion point 9. The laser can work in a Q-switching state and a mode locking state, and can stably emit pulses in nanosecond to microsecond magnitude.
In the embodiment of the present invention, the rare earth ions doped in the gain fiber 3 are one or more of ytterbium ions, erbium ions, and thulium ions. The wavelength emitted by the pumping source is 915nm or 976nm when the rare earth ions are ytterbium ions, the wavelength emitted by the pumping source is 980nm or 1480nm when the rare earth ions are erbium ions, and the wavelength emitted by the pumping source is 793nm or 980nm when the rare earth ions are thulium ions.
In the embodiment of the present invention, the optical fiber circulator 5 is a three-port optical circulator, and the laser path is from the first port to the second port and from the second port to the third port. The central wavelength is 1550nm and the bandwidth is +/-10 nm.
In an embodiment of the invention, the spacing between the first fiber end face 6 and the second fiber end face 7 is between 5 μm and 1000 μm. The first fiber end face 6 is a normal fiber end face, and the second fiber end face 7 may be a normal fiber end face or a fiber end face subjected to surface reflection enhancement treatment. After the second optical fiber end face 7 is subjected to surface reflection enhancement treatment, the 3dB bandwidth of the reflection enhancement is not less than 0.5nm, and the reflectivity is between 5% and 40%.
The ordinary fiber end face in the embodiment of the present invention refers to an end face obtained by cutting an optical fiber with a cleaver alone without any treatment.
In the embodiment of the present invention, the pump source 1 may be a conventional fiber-coupled semiconductor laser, or may be a solid laser. The laser is coupled and output by the optical fiber, and the diameter of the fiber core of the output optical fiber is consistent with that of the gain optical fiber 3, the passive optical fiber 4, the optical fiber circulator 5, the optical fiber wavelength division multiplexer 2 and the fiber core of the end face of the optical fiber so as to realize the minimum fusion loss. The laser is a single wavelength laser, the central emission wavelength of which is located in the absorption spectrum of the rare earth ions doped in the gain fiber 3, and the continuous pumping can generate the inverse particle number.
The optical fiber wavelength division multiplexer 2, which is a conventional optical fiber wavelength division multiplexer, functions to couple the pumping wavelength into the resonant cavity, and to connect the resonant cavity, and converts the pumping wavelength into laser energy through the gain fiber 3. The short wavelength end coupling wavelength is the pumping wavelength, and the two long wavelength end coupling wavelengths are the emission wavelengths of the gain fiber.
The gain fiber 3, which is a conventional rare earth ion doped fiber, is composed of a doped core, a silica cladding and a coating layer. The absorption wavelength of the doped rare earth ions corresponds to the pumping wavelength, and the emission wavelength corresponds to the operating wavelength of the optical fiber circulator 5.
A passive optical fiber 4, which may be a conventional quartz fiber or a photonic crystal fiber. Consists of a fiber core, a cladding and a coating layer.
The optical fiber optical circulator 5 is a three-port optical circulator, laser from the first port can be emitted from the second port without obstruction, laser from the second port can be emitted from the third port without obstruction, and other ports cannot pass. The center wavelength corresponds to the gain wavelength of the gain fiber 3, i.e. the center transit wavelength is located at the peak of the emission spectrum of the gain fiber, and the pump laser light cannot pass therethrough.
In the embodiment of the present invention, the positions of the first port and the third port of the optical fiber circulator 5 may be switched, so that the laser generated in the ring resonator may operate in either the counterclockwise direction or the clockwise direction.
The second optical fiber end face 7 and the first optical fiber end face 6 may be single-mode optical fibers or multimode optical fibers of the same specification, or both may be optical fiber jumpers, and the fiber cores of the two optical fiber jumpers have the same size. The second fiber end face 7 and the first fiber end face 6 can generate different feedbacks to stokes light generated by cascade after forming a fabry perot interferometer.
The following provides a specific embodiment corresponding to the structural schematic diagram of the present invention:
for the passive Q-switched mode-locked fiber laser based on SBS and fabry-perot interferometers shown in fig. 1, the pump source 1 is a 980nm semiconductor laser. The wavelength division multiplexer 2 is a 1 x 2 type three-port optical fiber coupler, the corresponding wavelength of a port is 980nm, the corresponding wavelength of a port two and a port three is 1550nm, and the bandwidth of the three ports is +/-10 nm. The gain fiber 3 is an erbium-doped fiber with a length of 9 m, and the passive fiber 4 is a standard single-mode fiber with a length of 20 m. The optical fiber circulator 5 is a three-port optical circulator, the laser path is from the first port to the second port and from the second port to the third port, the central wavelength is 1550nm, and the bandwidth is +/-10 nm. The first optical fiber end face 6 and the second optical fiber end face 7 are both standard single-mode jumpers.
Fig. 2 shows one of the structures for producing the fabry-perot interferometer, which is formed by butting optical fiber jumpers by optical fiber flanges, wherein the second optical fiber jumper end surface 16 of the second optical fiber jumper 18 is aligned with the first optical fiber jumper end surface 15 of the first optical fiber jumper 17 by the optical fiber flange 14, and the distance between the two jumper end surfaces is about 17.4 μm, so that a fabry-perot cavity having a wavelength modulation effect on nm level is formed. The Fabry-Perot cavity has weak feedback on the first multiple stokes lights generated by laser cascade connection, and generates more obvious feedback on the later multiple stokes lights generated in sequence.
Fig. 3 shows a Q-switched pulse sequence emitted by a fully-fibered passive Q-switched mode-locked ring laser based on multi-stage stimulated brillouin scattering and fabry-perot interferometer under 600mW of pump light according to an embodiment of the present invention.
Fig. 4 is a radio frequency diagram of a Q-switched pulse sequence emitted by a fully-fibered passive Q-switched mode-locked ring laser based on multi-stage stimulated brillouin scattering and fabry-perot interferometer under 600mW of pump light according to an embodiment of the present invention.
Fig. 5 shows a mode-locked pulse sequence emitted by a fully-fibered passively Q-switched mode-locked ring laser based on multiple stages of stimulated brillouin scattering and fabry-perot interferometers after adjusting the spacing between the fabry-perot interferometers according to an embodiment of the present invention.
Fig. 6 is a radio frequency diagram of a mode-locked pulse sequence emitted by a fully-fibered passively Q-switched mode-locked ring laser based on multiple stages of stimulated brillouin scattering and fabry-perot interferometers after adjusting the spacing between the fabry-perot interferometers according to an embodiment of the present invention.
Under the common superposition action among the wavelength modulation spectrum of the Fabry-Perot cavity, the gain spectrum of the gain fiber and the transmission spectrum of the fiber optic circulator and the line width narrowing action of random Rayleigh scattering, only the laser with narrow line width can oscillate in the cavity at first, and because a large number of reversal particle numbers are gathered in the cavity by the small feedback and the random Rayleigh distributed feedback of the Fabry-Perot cavity, the resonant cavity enters a low Q value state, the narrow line width laser causes the cascade stimulated Brillouin scattering in the cavity to emit the cascade Stokes light, the initial multiple stages of Stokes light are not modulated by the Fabry-Perot cavity, the low Q value resonant cavity is formed only by the weak Rayleigh distributed feedback in the cavity, after the multiple stages of Stokes light are excited, because the feedback in the cavity is obvious, the resonant cavity is a high Q value resonant cavity for the multiple stages of Stokes light, the energy accumulated in the cavity is emitted out of the resonant cavity in a very short time to form stable Q-switched pulses. The output pulse amplitude and the repetition frequency of the conventional SBS-based passive Q-switched laser fluctuate greatly within the range of 20% to 40%, which severely limits the practical application of the SBS-based passive Q-switched laser, but through the structure of the embodiment of the invention, the instability of the output pulse repetition frequency is greatly reduced under the pumping power of 600mW, as shown in FIG. 4, the signal-to-noise ratio is up to 67.37dB, which is the highest signal-to-noise ratio achieved by the existing SBS-based passive Q-switched laser, and the stability of the laser is fully proved. After the distance between Fabry-Perot cavities formed by two jumper end faces is slowly adjusted, the laser emits a stable mode-locked pulse sequence, the repetition frequency is 3.6MHz as shown in figure 6, the time corresponds to the time for one-pass cavity length of light circulation, the signal-to-noise ratio is up to 51dB, the emission pulse width is in nanosecond order, and the capability of the laser for generating stable narrow pulse width pulses is proved.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (7)
1. A passively Q-switched mode-locked ring laser based on SBS and fabry-perot interferometers, comprising: the device comprises a pumping laser unit, a Fabry-Perot interferometer, a passive optical fiber (4) and an optical fiber circulator (5);
the first end of the pump laser unit is connected with the first end of the optical fiber circulator (5), the third end of the optical fiber circulator (5) is connected with the second end of the pump laser unit, and the second end of the optical fiber circulator (5) is connected with the Fabry-Perot interferometer;
the pump laser unit is used for realizing the introduction of pump energy and realizing the amplification and conversion of stimulated radiation of the pump energy into laser energy;
the optical fiber circulator (5) is used for realizing the isolation of pumping laser and clockwise running laser and connecting the Fabry-Perot interferometer together to form an annular resonant cavity, wherein the laser generated in the annular resonant cavity runs in the direction set by the optical fiber circulator (5);
the passive optical fiber (4) is positioned between the second end of the optical fiber circulator (5) and the Fabry-Perot interferometer and is used for accumulating Brillouin effect;
the Fabry-Perot interferometer is composed of a first optical fiber end face (6) and a second optical fiber end face (7), the first optical fiber end face (6) is aligned to the second optical fiber end face (7) with a preset distance left between the first optical fiber end face and the second optical fiber end face, and is used for respectively modulating multi-stage Stokes light generated by stimulated Brillouin scattering by utilizing the nano-level wavelength loss modulation effect of the multi-stage Stokes light to obtain stable Q-switching pulses or mode-locking pulses, and then outputting the Q-switching pulses or the mode-locking pulses from the Fabry-Perot interferometer end.
2. The laser according to claim 1, wherein the first fiber end face (6) is a normal fiber end face and the second fiber end face (7) is a normal fiber end face or a fiber end face subjected to a surface reflection enhancement treatment.
3. The laser of claim 1, wherein the pump laser unit comprises: a pumping source (1), an optical fiber wavelength division multiplexer (2) and a gain optical fiber (3);
the pumping source (1) is connected with a short wavelength end of the optical fiber wavelength division multiplexer (2), two long wavelength ends of the optical fiber wavelength division multiplexer (2) are respectively connected with a first end of the optical fiber circulator (5) and a first end of the gain optical fiber (3), a second end of the gain optical fiber (3) is connected with a third end of the optical fiber circulator (5), a second end of the optical fiber circulator (5) is connected with a first end of the passive optical fiber (4), and a second end of the passive optical fiber (4) is connected with the first optical fiber end face (6);
the pumping source (1) is used for guiding pumping energy, the optical fiber wavelength division multiplexer (2) is used for coupling the pumping energy into the ring-shaped resonant cavity and converting the pumping energy into laser energy through the gain fiber (3), and the gain fiber (3) is used for realizing population inversion.
4. The laser according to claim 1, characterized in that the preset spacing between the first fiber end face (6) and the second fiber end face (7) is between 5 μm and 1000 μm.
5. A laser according to claim 1, characterized in that the fiber optical circulator (5) is a three-port optical circulator, the laser light generated in the ring resonator can only pass from the first port to the second port and from the second port to the third port, while the pump laser light cannot pass at either port.
6. A laser according to claim 3, characterized in that the rare earth ions doped by the gain fiber (3) are one or more of ytterbium ions, erbium ions and thulium ions.
7. A laser according to claim 1, characterized in that the passive fiber (4) is undoped with a gain medium.
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