CN110244403B - Photonic crystal chirp Bragg optical fiber grating pulse stretcher - Google Patents
Photonic crystal chirp Bragg optical fiber grating pulse stretcher Download PDFInfo
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- CN110244403B CN110244403B CN201910412630.2A CN201910412630A CN110244403B CN 110244403 B CN110244403 B CN 110244403B CN 201910412630 A CN201910412630 A CN 201910412630A CN 110244403 B CN110244403 B CN 110244403B
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- 239000004038 photonic crystal Substances 0.000 title claims abstract description 35
- 239000013307 optical fiber Substances 0.000 title description 10
- 239000000835 fiber Substances 0.000 claims abstract description 56
- 239000006185 dispersion Substances 0.000 claims abstract description 20
- 239000000463 material Substances 0.000 claims abstract description 8
- 238000005253 cladding Methods 0.000 claims abstract description 5
- 230000001795 light effect Effects 0.000 claims abstract description 3
- 238000009826 distribution Methods 0.000 claims description 3
- 230000000694 effects Effects 0.000 claims description 3
- 230000005540 biological transmission Effects 0.000 claims description 2
- 230000003287 optical effect Effects 0.000 claims description 2
- 238000012886 linear function Methods 0.000 claims 1
- 230000003321 amplification Effects 0.000 abstract description 8
- 238000005530 etching Methods 0.000 abstract description 8
- 238000003199 nucleic acid amplification method Methods 0.000 abstract description 8
- 230000010354 integration Effects 0.000 abstract description 2
- 238000004519 manufacturing process Methods 0.000 abstract description 2
- 230000007613 environmental effect Effects 0.000 abstract 1
- 238000005516 engineering process Methods 0.000 description 6
- 230000009286 beneficial effect Effects 0.000 description 3
- 238000005457 optimization Methods 0.000 description 3
- 230000006835 compression Effects 0.000 description 2
- 238000007906 compression Methods 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 230000009022 nonlinear effect Effects 0.000 description 2
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- CUGMJFZCCDSABL-UHFFFAOYSA-N arsenic(3+);trisulfide Chemical compound [S-2].[S-2].[S-2].[As+3].[As+3] CUGMJFZCCDSABL-UHFFFAOYSA-N 0.000 description 1
- VTYDSHHBXXPBBQ-UHFFFAOYSA-N boron germanium Chemical compound [B].[Ge] VTYDSHHBXXPBBQ-UHFFFAOYSA-N 0.000 description 1
- 230000008878 coupling Effects 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
- 238000005859 coupling reaction Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000005315 distribution function Methods 0.000 description 1
- 238000004806 packaging method and process Methods 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
- G02B6/02076—Refractive index modulation gratings, e.g. Bragg gratings
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
- G02B6/02076—Refractive index modulation gratings, e.g. Bragg gratings
- G02B6/0208—Refractive index modulation gratings, e.g. Bragg gratings characterised by their structure, wavelength response
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- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
Abstract
The invention relates to the field of fiber ultrafast laser and slow light, in particular to a slow light photonic crystal chirped Bragg fiber grating stretcher. The fiber core is selected to be made of photosensitive materials, and the cladding is the band-gap photonic crystal fiber with periodically distributed air holes surrounding the fiber core. The chirped Bragg grating structure with variable periods is etched at the fiber core, the slow light effect is realized through the high group refractive index of the photonic band gap edge, the group delay of the chirped Bragg grating to different wavelengths is greatly increased, and the provided dispersion is also improved by one order of magnitude compared with the conventional chirped Bragg fiber grating. The invention can obtain larger pulse broadening factor when being applied to a chirped pulse amplification system, further improve the single pulse energy and the peak power upper limit which can be amplified and output by the fiber ultrafast laser, simultaneously has shorter grating etching length, has better environmental stability, and reduces the manufacturing difficulty and the later integration difficulty.
Description
Technical Field
The invention relates to the field of ultrafast laser technology and slow light technology, in particular to a giant dispersion amount photonic crystal chirped Bragg fiber grating stretcher.
Background
In the field of fiber ultrafast laser, the chirped pulse amplification technology is an effective technical approach for improving single pulse energy and peak power. The stretcher is one of core devices of the technology, and aims to stretch the time domain of ultrashort laser pulses, reduce peak power, provide precondition for subsequent amplification and compression, enable the peak power to be always lower than damage thresholds of devices such as optical fibers and the like in the pulse amplification process, and weaken nonlinear effect in the transmission process. Therefore, under the condition of the core diameter of the gain optical fiber at present, in order to obtain the amplified output of the fiber femtosecond laser with higher energy, it is important to increase the dispersion amount of the stretcher and obtain a wider pulse width.
At present, there are three main types of stretcher used in the chirped pulse amplification system, which are dispersion fiber, spatial grating and chirped bragg fiber grating. The dispersion fiber needs a long working length when providing large dispersion, and the serious nonlinear effect is introduced, so that the subsequent compression is not facilitated. When the grating is widened, not only is space element introduced to be not beneficial to full optical fiber, but also more loss is caused by grating diffraction efficiency and space coupling.
Compared with the former two kinds of stretchers, the chirped Bragg fiber grating has short length while ensuring full optical fiber, so that the chirped Bragg fiber grating has small additional loss, is hardly influenced by the nonlinearity of the optical fiber, and is widely used. However, when providing a larger dispersion, the etching length of the grating needs to be increased, and when the etching length is increased to about meter order, the manufacturing challenge and cost of the grating become key constraints of the broadening method. And secondly, the fiber grating needs to be prevented from being bent, so that the linear length of meter scale counteracts the advantages of compact volume and easy integrated packaging of the fiber laser. Therefore, it is difficult to achieve large dispersion under the prior art conditions by increasing the grating length to improve the grating dispersion capability.
Disclosure of Invention
The invention provides a chirp Bragg grating broadening device based on photonic crystal fiber, which aims to solve the technical problem of how to greatly improve the dispersion amount provided by a stretcher.
The invention realizes the purpose through the following technical scheme:
a widening device based on a photonic crystal chirped Bragg fiber grating adopts a band-gap photonic crystal fiber, the structure is a multi-cladding structure with periodically arranged air holes, a fiber core is a solid core and etches a Bragg grating with variable period, and the grating period is monotonically and linearly increased or decreased along the axial direction of the fiber.
For further optimization, the optical fiber background material adopts sulfide (n is 2.8) or semiconductor material (n is 3.4) with high refractive index, the refractive index of the optical fiber material is expressed as n, and the core adopts germanium-doped material.
As further optimization, the air holes can be in a circular shape, a square shape, a regular hexagon, a regular octagon or a regular dodecagon shape, and the air holes are in a regular hexagon, a regular octagon or a regular dodecagon shape multi-cladding structure in a regular triangle arrangement mode. The distance between any two nearest adjacent air holes is A, the diameter of the circumscribed circle of the air holes is represented by d, the ratio of the distance A of the air holes to the diameter d of the circumscribed circle of the air holes is increased, and the pulse within the working wavelength range of the laser can be transmitted in an infinite single mode.
As a further optimization, the etchingInitial grating constant of etched grating is lambda0The distribution of the grating constant along the z-axis of the fiber satisfies the function Λ (z) ═ Λ0+ξ1z+ξ2z2，ξ1And xi2Primary and secondary term coefficients, respectively.
The invention has the beneficial effects that:
the photonic crystal chirped Bragg fiber grating combines a slow light technology with a chirped fiber grating, and can greatly increase the dispersion of the grating under the condition of the same grating structure, thereby obtaining a larger broadening factor, greatly increasing the pulse width after broadening, reducing the subsequent amplification difficulty, and being expected to finally obtain ultrafast laser output with larger energy. The chirped pulse amplification technology can be expanded to the field of picosecond pulse amplification, and the output energy of picosecond pulses is greatly improved.
The photonic crystal chirped Bragg fiber grating has shorter fiber grating size, is beneficial to final system integration and thermal control, and can obtain better beam quality and better system stability.
The photonic crystal chirped Bragg fiber grating overcomes the defect that the bandwidth of the conventional photonic crystal Bragg grating is small, greatly improves the bandwidth of the photonic crystal fiber grating, and can meet the requirements of ultrafast laser broadening pulses with various wavelengths and wide spectrums.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly describes the embodiments or drawings used in the prior art. The drawings in the following description are only some of the embodiments of the present invention, and it is obvious to those skilled in the art that other drawings can be obtained based on the drawings without creative efforts.
FIG. 1 is a cross-sectional view of a photonic crystal chirped Bragg fiber grating according to an embodiment of the present invention;
FIG. 2 is a side cross-sectional view of a photonic crystal chirped Bragg fiber grating core according to an embodiment of the present invention;
FIG. 3 is a diagram illustrating the time delay and dispersion of a photonic crystal chirped Bragg fiber grating according to an embodiment of the present invention;
the photonic crystal fiber comprises a photonic crystal fiber core 1, an air hole 2, an air hole 3 and a grating etching area.
Detailed Description
The embodiments of the present invention will be described in further detail with reference to the drawings and examples. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.
FIG. 1 and FIG. 2 are a cross-sectional view and a side sectional view, respectively, of an optical fiber of the present invention. As shown in fig. 1, reference numeral 1 denotes a core region of a photonic crystal fiber, the cladding of which is formed of a plurality of (e.g., 4 to 8) air holes at regular hexagonal, regular octagonal, or regular dodecagonal lattice nodes, the air holes are not limited to circular, the diameter of the air holes in this embodiment is d, the distance between adjacent air holes is a, and d/a ranges from 0.2 to 0.4. The fiber core is made of a boron-germanium co-doped material, as shown in fig. 2, 3 represents a grating etching area, an ultraviolet light source is used for etching a bragg grating with a variable period in the fiber core area of the photonic crystal fiber, and the grating constant and the axial z satisfy the relationship: Λ (z) ═ Λ0+ξ1z+ξ2z2Wherein Λ0Is the grating constant of the upper end boundary of the grating, where Λ (z) is the grating constant variation function. Bragg resonance wavelength lambdaB2n Λ (z), it can be seen that bragg gratings with different periods can reflect different wavelengths, so that different wavelengths of pulses reflected by gratings in a fiber core generate optical path difference, and the dispersion effect is greatly increased by combining the slow light effect of the band-gap photonic crystal fiber. Regulating coefficient xi1And make xi2When the value is 0, a bragg grating having a linearly varying period can be obtained, and the linear chirp amount can be provided. Micro-increase or micro-decrease xi2Or adding a higher order term for z may further optimize the amount of higher order dispersion of the device.
The embodiment of the invention comprises the following steps: the central wavelength of an incident pulse is set to be 1030nm, the bandwidth is set to be 20nm, the pulse width is set to be 30ps, the photonic crystal substrate material is arsenic sulfide, and the refractive index at the central wavelength is set to be 2.47. Reference numeral 2 is an air hole which is arranged in a regular hexagon four-clad structure as shown in figure 1, which is convenient to show, and the grating period unit is divided intoThe length is set to nm, the unit length in the z direction is set to m, and the grating etching period distribution function is set as: 206nm +70nm/m × z, i.e. the initial grating period Λ (z) ═ z0206nm, coefficient xi1＝70nm/m，ξ2＝0nm/m2And the etching length is 100mm, the time delay and dispersion of the pulse of this embodiment are as shown in FIG. 3, the maximum wavelength of the pulse is close to 15ns relative to the shortest wavelength, and the dispersion near the center wavelength reaches 400ps2The photonic crystal chirped Bragg fiber grating has extremely strong dispersion effect, and the pulse width of the pulse can be widened to more than 15ns through the photonic crystal chirped Bragg fiber grating stretcher.
Claims (3)
1. A slow light photonic crystal chirped Bragg fiber grating is characterized in that the resonant structure of a photonic crystal fiber changes the dispersion characteristic of a medium, and a strong dispersion effect is generated at the edge of a photonic band gap, so that the group refractive index of the photonic crystal fiber is larger than the material refractive index of the photonic crystal fiber, the slow light effect is effectively realized, and the transmission speed of light pulses in the photonic crystal fiber is lower than 1/2 of the vacuum light speed; the variable-period Bragg grating is etched in the photosensitive fiber core of the photonic crystal fiber, the grating constant distribution is approximately linear function along the axial distribution of the fiber, and the dispersion amount provided by the stretcher can be greatly improved.
2. The slow-light photonic crystal chirped bragg fiber grating according to claim 1, wherein a cladding of the photonic crystal fiber is formed by a plurality of layers of air holes, and the ratio of the diameter of a circumscribed circle to the distance between adjacent air holes ranges from 0.2 to 0.4; all wavelength components of the optical pulse can be transmitted in an infinite single mode in the photonic crystal fiber.
3. The slow light photonic crystal chirped bragg fiber grating of claim 1, wherein the bragg grating is etched in the photonic crystal core, the etched region is rectangular or elliptical, and the axial distance of the grating along the fiber is a higher order function with respect to the axial distance.
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Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101290376A (en) * | 2008-06-06 | 2008-10-22 | 吉林大学 | Sampling polarization maintaining fiber bragg grating |
| WO2013109987A2 (en) * | 2012-01-20 | 2013-07-25 | The Board Of Trustees Of The Leland Stanford Junior University | System and method for measuring perturbations using a slow-light fiber bragg grating sensor |
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| WO2002101429A2 (en) * | 2001-06-08 | 2002-12-19 | Crystal Fibre A/S | Photonic bandgap fibre, and use thereof |
| CN1232843C (en) * | 2004-03-18 | 2005-12-21 | 上海交通大学 | Wide band-gap air counducting photon band-gap optical fiber |
| CN101907744B (en) * | 2010-07-12 | 2012-06-06 | 西北工业大学 | Filter for realizing bandwidth tuning based on optical fiber grating self-chirping effect |
| CN106338788B (en) * | 2016-09-29 | 2019-04-05 | 深圳大学 | A method of preparing Bragg grating on photonic crystal fiber |
| CN108061980A (en) * | 2017-12-18 | 2018-05-22 | 中国科学院西安光学精密机械研究所 | Chirped fiber grating dispersion amount adjustment method, device and the system comprising the device |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101290376A (en) * | 2008-06-06 | 2008-10-22 | 吉林大学 | Sampling polarization maintaining fiber bragg grating |
| WO2013109987A2 (en) * | 2012-01-20 | 2013-07-25 | The Board Of Trustees Of The Leland Stanford Junior University | System and method for measuring perturbations using a slow-light fiber bragg grating sensor |
Non-Patent Citations (1)
| Title |
|---|
| Numerical modeling of transverse mode;Mali Gong, Yanyang Yuan, Chen Li, Ping Yan, Haitao Zhang, Suying;《OPTICS EXPRESS》;20070305;全文 * |
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