CN112310794B - Higher harmonic mode-locked laser based on optical fiber coupler - Google Patents

Higher harmonic mode-locked laser based on optical fiber coupler Download PDF

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CN112310794B
CN112310794B CN202011164443.6A CN202011164443A CN112310794B CN 112310794 B CN112310794 B CN 112310794B CN 202011164443 A CN202011164443 A CN 202011164443A CN 112310794 B CN112310794 B CN 112310794B
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coupler
laser
optical fiber
interference ring
fiber
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CN112310794A (en
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周勇
王文洲
陈国梁
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Hefei Max Ray Photoelectric Technology Co ltd
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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
    • H01S3/10—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
    • 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
    • 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
    • H01S3/10—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
    • H01S3/1121—Harmonically mode locking lasers, e.g. modulation frequency equals multiple integers or a fraction of the resonator roundtrip time

Abstract

The invention discloses a higher harmonic mode-locked laser based on an optical fiber coupler, wherein pumping light generated by a pumping source enters a gain optical fiber through a wavelength division multiplexer, laser gain is provided, random noise pulse is generated, the random noise pulse is narrowed through a pulse narrowing mechanism, then is filtered through an isolator and an interference ring in sequence, and finally is output through a third coupler part, the rest part is amplified continuously through the wavelength division multiplexer and the gain optical fiber and continuously participates in intracavity operation, the interference ring comprises a first coupler and a second coupler, and the first coupler and the second coupler construct an interference ring by welding a single end and a large proportion end. When the laser is amplified, compressed and filtered in the cavity, stable pulse operation is generated, and when the longitudinal mode interval of the interference ring is integral multiple of the longitudinal mode interval of the laser, the repetition frequency of the output optical pulse is equal to the positive integral multiple of the longitudinal mode interval of the interference ring due to the standing wave effect of the laser.

Description

Higher harmonic mode-locked laser based on optical fiber coupler
Technical Field
The invention belongs to the technical field of lasers, and particularly relates to a high repetition frequency pulse fiber laser based on high-order harmonic mode locking.
Background
At present, technologies for generating pulse laser in a fiber laser mainly include gain switching, Q-switching, mode locking and the like, wherein only the mode-locked fiber laser can generate ultrafast optical pulses with pulse widths of picoseconds or femtoseconds. The generated optical pulse repetition frequency is based on the principle of mode-locked pulse generation
Figure GDA0003306610980000011
Where c is the speed of light, n is the refractive index of the fiber material, and L is the laser cavity length. Because the length of the laser cavity is limited by the lengths of the tail fiber and the gain fiber of the device in the process of building the laser, the shortest length can only achieve the meter magnitude, and the highest repetition frequency of the corresponding optical pulse can only reach dozens of MHz. In order to realize the output of the mode locking optical pulse with high repetition frequency, a method of exciting higher harmonic mode locking in a laser cavity is generally adopted, and the traditional method is to add an F-P interference etalon in the cavity. In order to improve the defects, the invention provides an interference ring structure built based on two optical fiber couplers, which is used for replacing the traditional F-The structure of the P interference etalon has the advantages of low manufacturing cost and tunable longitudinal mode interval. The generated high repetition frequency mode-locked optical pulse can be applied to the fields of optical communication, laser processing, frequency comb generation, high-power terahertz sources and the like.
Disclosure of Invention
The invention aims to provide a short-cavity interference ring structure based on an optical fiber coupler, which is used for replacing an F-P interference etalon in a traditional higher harmonic mode-locked optical fiber laser, reduces the manufacturing cost and simultaneously easily realizes the adjustment of the output longitudinal mode interval, thereby realizing the high repetition frequency mode-locked optical pulse output based on higher harmonic mode locking in the optical fiber laser.
In order to solve the technical problems, the invention is realized by the following technical scheme:
according to the higher harmonic mode-locked laser based on the optical fiber coupler, pumping light generated by a pumping source enters a gain optical fiber through a wavelength division multiplexer, laser gain is provided, random noise pulses are generated, the random noise pulses are narrowed through a pulse narrowing mechanism, then are filtered through an isolator and an interference ring in sequence, and are output through a third coupler part, and the rest part continues to pass through the wavelength division multiplexer and the gain optical fiber, is amplified and continues to participate in intracavity operation. The isolator ensures the unidirectional operation of the laser in the cavity, and when the laser in the cavity is subjected to amplification, compression and filtering repeatedly, stable pulse operation is generated. When the longitudinal mode interval of the interference ring is integral multiple of the longitudinal mode interval of the laser, the output optical pulse repetition frequency is equal to positive integral multiple of the longitudinal mode interval of the interference ring due to the standing wave effect of the laser, so that the higher harmonic mode-locked pulse output with high repetition frequency is realized. Because the interference ring only has two optical fiber devices, the length of the interference ring can be well limited to about 10 cm, and therefore mode-locking optical pulses with GHz or even higher repetition frequency can be easily generated.
The interference ring comprises a first coupler and a second coupler, the first coupler and the second coupler are used for constructing the interference ring by welding a single end and a large-proportion end, and the length of an optical fiber between the single ends of the two couplers is L1Optical fiber between two couplers with large-proportion endLength L2From which the length of the interference ring is obtained as L1+L2The transmittance is calculated by the formula:
Figure GDA0003306610980000021
Figure GDA0003306610980000022
Figure GDA0003306610980000031
wherein K1、K2The power coupling ratio of the coupler is beta, the propagation constant of the running laser is beta, the interference ring transmission spectrum obtained by drawing a formula is a series of discrete narrow-band transmission peaks, and the longitudinal mode interval of the transmission peaks is
Figure GDA0003306610980000032
Corresponding frequency interval
Figure GDA0003306610980000033
Where c is the speed of light, n is the refractive index of the fiber, and λ is the center wavelength of the laser. The repetition frequency of the mode-locked pulse output by the laser is positive integral multiple of the frequency interval delta f.
Further, the longitudinal mode interval can be changed by adjusting the length of the interference ring, and the longitudinal mode width can be changed by changing the power coupling ratio of the coupler.
Further, the pulse narrowing mechanism is based on two-dimensional saturable absorption materials including semiconductor saturable absorption mirrors, topological insulators, graphene, carbon nanotubes, transition metal oxides and transition metal sulfides.
Further, the pulse narrowing mechanism may also be a nonlinear transmission mechanism based on nonlinear polarization rotation or nonlinear fiber loop mirror.
Furthermore, the gain fiber is a rare earth ion doped fiber or a nonlinear gain fiber.
The invention has the following beneficial effects:
1. the pulse repetition frequency output by the laser is not limited by the cavity length of the laser, so that the laser can be built by utilizing longer gain optical fibers, and the mode locking pulse with higher power can be directly output.
2. The structure can realize the tuning of the longitudinal mode interval of the laser by changing the length of the interference ring, thereby realizing the high-order harmonic wave of the laser and simultaneously adjusting the output mode-locked pulse repetition frequency in a long cavity state.
3. The light pulse output by the structure has larger longitudinal mode interval and large chirp quantity, and is easy to realize the chirp amplification outside the cavity.
4. The optical fiber interference ring is used for replacing the traditional F-P interference etalon, the manufacturing cost is low, the difficulty is greatly reduced, and the longitudinal mode interval of the laser, namely the output pulse repetition frequency, is tunable.
Of course, it is not necessary for any product in which the invention is practiced to achieve all of the above-described advantages at the same time.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
FIG. 1: the structure of the laser is schematically shown.
FIG. 2: the invention relates to an interference ring structure and a transmission spectrum.
Detailed Description
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.
In the description of the present invention, it is to be understood that the terms "opening," "upper," "lower," "thickness," "top," "middle," "length," "inner," "peripheral," and the like are used in an orientation or positional relationship that is merely for convenience in describing and simplifying the description, and do not indicate or imply that the referenced component or element must have a particular orientation, be constructed and operated in a particular orientation, and thus should not be considered as limiting the present invention.
As shown in fig. 1-2: higher harmonic mode-locked laser based on optical fiber coupler
The fiber laser is constructed by fusion splicing of optical fibers according to the structure of fig. 1, and the operation process of the laser is as follows. Pumping light generated by a pumping source enters a gain optical fiber through a wavelength division multiplexer, laser gain is provided, random noise pulses are generated, the random noise pulses are narrowed through a pulse narrowing mechanism, then are filtered through an isolator and an interference ring in sequence, and finally are output through a third coupler part, and the rest part is amplified through the wavelength division multiplexer and the gain optical fiber and continuously participates in intracavity operation. The isolator ensures the unidirectional operation of the laser in the cavity, and when the laser in the cavity is subjected to amplification, compression and filtering repeatedly, stable pulse operation is generated. When the longitudinal mode interval of the interference ring is integral multiple of the longitudinal mode interval of the laser, the output optical pulse repetition frequency is equal to positive integral multiple of the longitudinal mode interval of the interference ring due to the standing wave effect of the laser, so that the higher harmonic mode-locked pulse output with high repetition frequency is realized. Because the interference ring only has two optical fiber devices, the length of the interference ring can be well limited to about 10 cm, and therefore mode-locking optical pulses with GHz or even higher repetition frequency can be easily generated.
The interference ring comprises a first coupler and a second coupler, the first coupler and the second coupler are used for constructing the interference ring by welding a single end and a large-proportion end, and the length of an optical fiber between the single ends of the two couplers is L1The length of the optical fiber between the large-proportion ends of the two couplers is L2From which the length of the interference ring is obtained as L1+L2Therein is passed throughThe formula for calculating the excess is as follows:
Figure GDA0003306610980000051
Figure GDA0003306610980000052
Figure GDA0003306610980000053
wherein K1、K2The coupler power coupling proportion is, beta is the propagation constant of the running laser, the longitudinal mode interval can be changed by adjusting the length of the interference ring, and the longitudinal mode width can be changed by changing the coupler power coupling proportion;
the interference ring transmission spectrum can be plotted as a series of discrete narrow-band transmission peaks according to the formula, as shown in fig. 2: the distance between the longitudinal modes of the transmission peak is
Figure GDA0003306610980000061
Corresponding frequency interval
Figure GDA0003306610980000062
Where c is the speed of light, n is the refractive index of the fiber, and λ is the center wavelength of the laser. The repetition frequency of the mode-locked pulse output by the laser is positive integral multiple of the frequency interval delta f.
The pulse narrowing mechanism is based on two-dimensional saturable absorption materials including semiconductor saturable absorption mirrors, topological insulators, graphene, carbon nanotubes, transition metal oxides and transition metal sulfides.
The pulse width mechanism can also be a nonlinear transmission mechanism based on nonlinear polarization rotation and nonlinear fiber loop mirror.
The gain fiber is a rare earth ion doped fiber or a nonlinear gain fiber.
In the description herein, references to the description of "one embodiment," "an example," "a specific example" or the like are intended to mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
The preferred embodiments of the invention disclosed above are intended to be illustrative only. The preferred embodiments are not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims (5)

1. High order harmonic mode-locked laser based on optical fiber coupler, its characterized in that:
pumping light generated by a pumping source enters a gain optical fiber through a wavelength division multiplexer, laser gain is provided, random noise pulses are generated, the random noise pulses are narrowed through a pulse narrowing mechanism, then are filtered through an isolator and an interference ring in sequence, and are output through a third coupler part, and the rest part is amplified through the wavelength division multiplexer and the gain optical fiber and continuously participates in intracavity operation;
the interference ring comprises a first coupler and a second coupler, the first coupler and the second coupler are used for constructing the interference ring by welding a single end and a large-proportion end, and the length of an optical fiber between the single ends of the two couplers is L1The length of the optical fiber between the large-proportion ends of the two couplers is L2From which the length of the interference ring is obtained as L1+L2The transmittance is calculated by the formula:
Figure FDA0003306610970000011
Figure FDA0003306610970000012
Figure FDA0003306610970000013
wherein K1、K2The power coupling ratio of the coupler is beta, the propagation constant of the running laser is beta, the interference ring transmission spectrum obtained by drawing a formula is a series of discrete narrow-band transmission peaks, and the longitudinal mode interval of the transmission peaks is
Figure FDA0003306610970000014
Corresponding frequency interval
Figure FDA0003306610970000015
Wherein c is the speed of light, n is the refractive index of the optical fiber, lambda is the central wavelength of the laser, and the repetition frequency of the mode-locking pulse output by the laser is a positive integer multiple of the frequency interval delta f.
2. The fiber coupler based higher harmonic mode-locked laser of claim 1, wherein: the longitudinal mode interval can be changed by adjusting the length of the interference ring, and the longitudinal mode width can be changed by changing the power coupling ratio of the coupler.
3. The fiber coupler based higher harmonic mode-locked laser according to claim 1 or 2, wherein: the pulse narrowing mechanism is based on two-dimensional saturable absorption materials including semiconductor saturable absorption mirrors, topological insulators, graphene, carbon nanotubes, transition metal oxides and transition metal sulfides.
4. The fiber coupler based higher harmonic mode-locked laser according to claim 1 or 2, wherein: the pulse width mechanism is a nonlinear transmission mechanism based on nonlinear polarization rotation or nonlinear fiber loop mirror.
5. The fiber coupler based higher harmonic mode-locked laser according to claim 1 or 2, wherein: the gain fiber is a rare earth ion doped fiber or a nonlinear gain fiber.
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