CN111427116B - Multi-wavelength optical fiber mode switching method and system based on few-mode phase shift grating - Google Patents
Multi-wavelength optical fiber mode switching method and system based on few-mode phase shift grating Download PDFInfo
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- CN111427116B CN111427116B CN202010360462.XA CN202010360462A CN111427116B CN 111427116 B CN111427116 B CN 111427116B CN 202010360462 A CN202010360462 A CN 202010360462A CN 111427116 B CN111427116 B CN 111427116B
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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
- G02B6/02071—Mechanically induced gratings, e.g. having microbends
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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
- G02B6/02195—Refractive index modulation gratings, e.g. Bragg gratings characterised by means for tuning the grating
- G02B6/022—Refractive index modulation gratings, e.g. Bragg gratings characterised by means for tuning the grating using mechanical stress, e.g. tuning by compression or elongation, special geometrical shapes such as "dog-bone" or taper
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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
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/14—Mode converters
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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
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/27—Optical coupling means with polarisation selective and adjusting means
Abstract
The invention discloses a multi-wavelength optical fiber mode switching method and a system based on a few-mode phase shift grating, wherein the system comprises the following steps: few-mode optical fibers, a torsion device and a polarization controller; n high-order guided-mode long-period fiber gratings are arranged on the few-mode fiber, N is more than or equal to 2, and the N high-order guided-mode long-period fiber gratings are cascaded to form a phase-shift long-period fiber grating; the number of the torsion devices is 2, one torsion device is fixed, and the other torsion device can twist; two ends of the few-mode optical fiber are respectively fixed on 2 torsion devices, and the phase-shift long-period optical fiber grating is positioned between the 2 torsion devices; one end of the few-mode optical fiber is connected with the input end of the polarization controller. The invention uses the adjustable torsion device to rotate the inscribed phase-shift long-period fiber grating, changes the refractive index modulation of the phase-shift grating, and changes the resonance coupling condition of the mode, thereby realizing the switching between target modes under a plurality of wavelengths.
Description
Technical Field
The invention relates to the technical field of optical fiber communication, in particular to a multi-wavelength optical fiber mode switching method and system based on a few-mode phase shift grating.
Background
The space mode optical switching is a core technology of a future space division multiplexing optical network compatible with wavelength division multiplexing, the technology realizes the flow guiding between communication data and signals through two or more optical signal switching carrying different modes, and is a key for realizing the expansion of the future space division multiplexing communication network, and the orbital angular momentum OAM mode optical switching is one of the prior preferred schemes for realizing the space mode switching.
The OAM mode is used as a new wavelength-independent adjustable dimension of light, has infinite topology load, and OAM modes of different topology loads are mutually orthogonal, so that the OAM mode can be used as an independent space exchange base in a reconfigurable optical network of mode division multiplexing, and the capacity and the expansibility of the optical network are improved. However, how to implement dynamic operation and control of the OAM mode at different wavelengths and to be compatible with existing fiber systems becomes a technical difficulty.
The existing OAM exchange method is mostly based on devices such as a spatial phase plate and a spatial light modulator, the manufacturing cost of the devices is high, and when the OAM exchange method is combined with the existing optical fiber system, the OAM light beam is coupled into the optical fiber in a spatial light coupling mode, so that the coupling loss is high, and the OAM exchange method is difficult to integrate.
Disclosure of Invention
The invention aims to overcome the defects in the prior art, and provides a multi-wavelength optical fiber mode switching method and system based on a few-mode phase shift grating for an all-optical fiber, which have the advantages of simple structure and low cost.
The aim of the invention is achieved by the following technical scheme:
a multi-wavelength fiber mode switching system based on a few-mode phase shift grating, comprising: few-mode optical fibers, a torsion device and a polarization controller; n high-order guided-mode long-period fiber gratings are arranged on the few-mode fiber, N is more than or equal to 2, and the N high-order guided-mode long-period fiber gratings are cascaded to form a phase-shift long-period fiber grating; the number of the torsion devices is 2, one torsion device is fixed, and the other torsion device can twist; two ends of the few-mode optical fiber are respectively fixed on 2 torsion devices, and the phase-shift long-period optical fiber grating is positioned between the 2 torsion devices; one end of the few-mode optical fiber is connected with the polarization controller.
Preferably, the periods of the N high-order guided-mode long-period fiber gratings are the same, the interval between the high-order guided-mode long-period fiber gratings is half of the period, and the interval length is the magnitude of the phase shift.
Preferably, the twisting devices are each provided with a clamp for fixing the few-mode optical fiber.
Preferably, the core mode of the phase-shifted long period fiber grating is a conducting mode.
Preferably, the few-mode optical fiber is one of a four-mode optical fiber, a six-mode optical fiber, a seven-mode optical fiber, a nine-mode optical fiber and a twelve-mode optical fiber.
The switching method of the multi-wavelength optical fiber mode switching system based on the few-mode phase shift grating comprises the following steps:
s1, inputting laser into at least a mode fiber, and coupling the laser to a target mode through a grating mode coupling effect of a phase-shift long-period fiber grating;
s2, acquiring a mode field diagram of a target mode and an interference diagram of a corresponding mode;
s3, twisting the twisting device at the output end to twist the phase-shift long-period fiber grating, and changing the refractive index change of the phase-shift long-period fiber grating;
s4, acquiring a mode field diagram of the output mode after torsion and an interference diagram of a corresponding mode;
s5, comparing the mode field diagram of the target mode with the mode field diagram of the output mode after torsion, and comparing the interference diagram of the mode corresponding to the mode field diagram of the target mode with the interference diagram of the mode field diagram corresponding to the output mode after torsion to realize the switching of the optical fiber modes.
Preferably, n=2, the wavelength of light input into the few-mode optical fiber is 1537nm, the optical mode input into the few-mode optical fiber is OAM l=0, the grating output mode is OAM l=0 when the input end is not twisted, and the output optical mode after twisting is OAM l=2 when the input end is twisted by 240 degrees.
Preferably, n=2, the wavelength of light input into the few-mode optical fiber is 1537nm, the optical mode input into the few-mode optical fiber is OAM l=2, the grating output mode is still OAM l=2 when not twisted, and if the twist device at the input end is twisted 240 degrees, the twisted optical mode is OAM l=0.
Preferably, n=2, the wavelength of light input into the few-mode optical fiber is 1558nm, the optical mode input into the few-mode optical fiber is OAM l=0, and under the condition that no torsion exists, OAM l=0 realizes the output of OAM l=2 through the coupling effect of the grating, if the torsion device at the input end is twisted by 240 degrees, the output optical mode after torsion is OAM l=0.
Preferably, n=2, the wavelength of light input into the few-mode optical fiber is 1558nm, the optical mode input into the few-mode optical fiber is OAM l=2, and under the condition that no torsion exists, OAM l=2 realizes the output of OAM l=0 through the coupling effect of the grating, and if the torsion device at the input end is twisted by 240 degrees, the optical mode after torsion is OAM l=2.
Compared with the prior art, the invention has the following advantages:
the invention rotates the inscribed grating by using a set of adjustable torsion device, and aims to change the refractive index modulation of the phase shift grating, so that the resonance coupling condition of the mode is changed, and the coupling from the fundamental mode to the optical fiber high-order guided mode is realized at the same time under a plurality of wavelengths, and vice versa. The method has the advantages of simple process, low cost and low price, and can obtain good economic benefit.
Compared with a space mode conversion device, the phase-shift long-period fiber grating used in the method is an optical fiber type passive device, has strong compatibility with an optical fiber communication system, high system integration level and low cost, and is simple to manufacture. Compared with a long-period fiber grating device, the method can realize the coupling between modes under a plurality of wavelengths, and is more beneficial to realizing the dynamic switching of the modes by adjusting the coupling resonance condition. The small-mode phase-shift long-period fiber grating can be used as a grating-based mode switcher in a mode division multiplexing system.
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 specification, illustrate embodiments of the invention and together with the description serve to explain the invention. In the drawings:
fig. 1 is a schematic structural diagram of a multi-wavelength optical fiber mode switching system based on a few-mode phase shift grating according to the present embodiment.
Fig. 2 is a schematic structural diagram of a detection system of the multi-wavelength optical fiber mode switching system according to the present embodiment.
Fig. 3 (a) is a mode field diagram of the output mode when the input laser wavelength is 1537nm, the input laser mode OAM l=0, and the phase-shifted long-period fiber grating is not twisted in this embodiment.
Fig. 3 (b) is an interference diagram of the mode corresponding to the mode field diagram of the output mode when the phase-shifted long-period fiber grating is not twisted, with the input laser wavelength of 1537nm, the input laser mode OAM l=0 in this embodiment.
Fig. 3 (c) is a mode field diagram of an output mode when the input laser wavelength of the present embodiment is 1537nm, the input laser mode OAM l=0, and the phase-shifted long-period fiber grating is twisted 240 degrees.
Fig. 3 (d) is an interference diagram of the mode corresponding to the mode field diagram of the output mode when the input laser wavelength is 1537nm, the input laser mode OAM l=0, and the phase-shifted long-period fiber grating is twisted by 240 degrees in this embodiment.
Fig. 4 (a) is a mode field diagram of the output mode when the input laser wavelength is 1537nm, the input laser mode OAM l=2, and the phase-shifted long-period fiber grating is not twisted in this embodiment.
Fig. 4 (b) is an interference diagram of the mode corresponding to the mode field diagram of the output mode when the phase-shifted long-period fiber grating is not twisted, with the input laser wavelength of 1537nm, the input laser mode OAM l=2.
Fig. 4 (c) is a mode field diagram of an output mode when the input laser wavelength of the present embodiment is 1537nm, the input laser mode OAM l=2, and the phase-shifted long-period fiber grating is twisted by 240 degrees.
Fig. 4 (d) is an interference diagram of the mode corresponding to the mode field diagram of the output mode when the input laser wavelength is 1537nm, the input laser mode OAM l=2, and the phase-shifted long period fiber grating is twisted 240 degrees in this embodiment.
Fig. 5 (a) is a mode field diagram of an output mode when the input laser wavelength is 1558nm, the input laser optical mode OAM l=0, and the phase-shifted long-period fiber grating is not twisted in this embodiment.
Fig. 5 (b) is an interference diagram of the mode corresponding to the mode field diagram of the output mode when the phase-shifted long-period fiber grating is not twisted, in which the input laser wavelength is 1558nm, the input laser mode OAM l=0 in the present embodiment.
Fig. 5 (c) is a mode field diagram of an output mode when the input laser wavelength of the present embodiment is 1558nm, the input optical mode OAM l=0, and the phase-shifted long-period fiber grating is twisted by 240 degrees.
Fig. 5 (d) is an interference diagram of the mode corresponding to the mode field diagram of the output mode when the input laser wavelength is 1558nm, the input optical mode OAM l=0, and the phase-shifted long-period fiber grating is twisted by 240 degrees in this embodiment.
Fig. 6 (a) is a mode field diagram of an output mode when the input laser wavelength is 1558nm, the input optical mode OAM l=2, and the phase-shifted long-period fiber grating is not twisted in this embodiment.
Fig. 6 (b) is an interference diagram of the mode corresponding to the mode field diagram of the output mode when the phase-shifted long-period fiber grating is not twisted, in which the input laser wavelength is 1558nm and the input optical mode OAM l=2 in the present embodiment.
Fig. 6 (c) is a mode field diagram of an output mode when the input laser wavelength of the present embodiment is 1558nm, the input optical mode OAM l=2, and the phase-shifted long-period fiber grating is twisted by 240 degrees.
Fig. 6 (d) is an interference diagram of the mode corresponding to the mode field diagram of the output mode when the input laser wavelength is 1558nm, the input optical mode OAM l=2, and the phase-shifted long-period fiber grating is twisted by 240 degrees in this embodiment.
Detailed Description
The invention is further described below with reference to the drawings and examples.
Referring to fig. 1, a multi-wavelength fiber mode switching system 114 based on a few-mode phase shift grating, comprising: a few-mode fiber 101, torsion devices 102, 103, and polarization controller 104; the few-mode optical fiber 101 is provided with N high-order guided-mode long-period optical fiber gratings, N is more than or equal to 2, and the N high-order guided-mode long-period optical fiber gratings are cascaded to form a phase-shift long-period optical fiber grating 105; the number of the torsion devices is 2, one torsion device 103 is fixed, and the other torsion device 102 can twist; two ends of the few-mode optical fiber 101 are respectively fixed on the 2 torsion devices 102 and 103, and the phase-shift long-period optical fiber grating 105 is positioned between the 2 torsion devices 102 and 103; one end of the few-mode fiber 101 is connected to the input of the polarization controller 104.
Wherein the refractive index modulation of the phase-shifted long period fiber grating 105 is a strong modulation. The phase-shifted long period fiber grating 105 can achieve coupling of a fundamental mode to a higher order guided mode of the fiber and vice versa at multiple wavelengths. The method for manufacturing the phase-shift long-period fiber grating 105 comprises the following steps: by setting the cycle size, the cycle number and the machining power of the high-frequency carbon dioxide laser, single-sided repeated high-temperature ablation is carried out on the few-mode optical fiber 101, so that the fiber core and the cladding structure of the few-mode optical fiber 101 are obviously changed, and the few-mode phase-shift long-period fiber grating 105 with the refractive index emphasized and asymmetrically distributed is obtained. The phase-shifted long-period fiber grating 105 is a grating with a strong refractive index modulation, and is distinguished from the phase-shifted long-period fiber grating 105 formed in a single-mode fiber. A phase shifted long period fiber grating 105 is formed in the few-mode fiber 101 to achieve coupling between guided modes. Therefore, the phase-shift long-period fiber bragg grating has reasonable design, small insertion loss, simple structure and low cost, and can realize the switching of OAM modes under a plurality of wavelengths. The multi-wavelength optical fiber mode switching device can be compatible with a coarse wavelength division multiplexing system, fully utilizes the space modes and wavelengths of a plurality of different modes, and has important practical application in future space division multiplexing communication network expansion schemes.
Wherein the polarization controller 104 is located behind one of the twisting devices 103 for the purpose of changing the relative phase difference of the grating output modes; both twisting devices 102, 103 are provided with fiber clamps, so that the phase-shifted long-period fiber grating 105 can rotate together with the twisting device 102, and the purpose of the twisting devices is to change the refractive index distribution of the phase-shifted long-period fiber grating 105, so that the resonant coupling condition of the optical mode is changed, and thus two mode switching is realized under multiple wavelengths at the same time. In this embodiment, OAM l=0 may be coupled to OAM l=2 through the phase-shifted long-period fiber grating 105, and OAM l=2 may be coupled back to OAM l=0 through the grating. By twisting the phase-shifted long-period fiber grating 105 by the twisting device 102, the coupling resonance condition of the grating can be adjusted, and further dynamic switching between OAM l=2 and OAM l=0 is realized. The dynamic switching refers to changing the refractive index of the phase-shifted long-period fiber grating 105 by the torsion device 102 under the condition of fixed wavelength, and adjusting the coupling resonance condition so that the resonant mode of the wavelength is changed, thereby realizing mode switching.
It should be noted that, the multi-wavelength optical fiber mode switching system 114 of the present embodiment can implement switching between any two modes (OAM l=0, 1,2, 3) through reasonable grating parameter setting.
In this embodiment, the core mode of the phase-shifted long period fiber grating 105 is a conducting mode.
In this embodiment, n=2, and the periods of the 2 higher-order guided-mode long-period fiber gratings are the same, and the interval between the higher-order guided-mode long-period fiber gratings is half of the period, and the interval length is the magnitude of the phase shift. As shown in fig. 1, the grating period of the high-order guided-mode long-period fiber grating period is Λ, and the interval between the high-order guided-mode long-period fiber gratings is L PS 。
In the present embodiment, the twisting devices 102 and 103 are each provided with a jig 106 for fixing the few-mode optical fiber 101.
In this embodiment, the few-mode fiber 101 is a four-mode fiber.
The switching method of the multi-wavelength optical fiber mode switching system based on the few-mode phase shift grating comprises the following steps:
s1, inputting laser into at least a mode optical fiber 101, and coupling the laser to a target mode through a grating mode coupling effect of a phase-shift long-period optical fiber grating 105;
s2, acquiring a mode field diagram of a target mode and an interference diagram of a corresponding mode;
s3, twisting the twisting device 102 at the output end to twist the phase-shift long-period fiber grating 105, and changing the refractive index change of the phase-shift long-period fiber grating 105;
s4, acquiring a mode field diagram of the output mode after torsion and an interference diagram of a corresponding mode;
s5, comparing the mode field diagram of the target mode with the mode field diagram of the output mode after torsion, and comparing the interference diagram of the mode corresponding to the mode field diagram of the target mode with the interference diagram of the mode field diagram corresponding to the output mode after torsion to realize the switching of the optical fiber modes.
Detecting data
The detection system shown in fig. 2 uses the switching method to detect the multi-wavelength optical fiber mode switching system based on the few-mode phase shift grating. The beam (beam) coming out of the light source 201 is divided into an upper path and a lower path by a 50:50 coupler 203, and the lower beam is used for detecting the switched mode. The lower beam is transmitted in a single mode fiber 202 as a reference beam that passes through the polarization controller 104, the collimator 204, and the collimator 204 in sequence to reach the optical combiner 208. The beam on the upper path is used for mode switching, the beam on the upper path is incident on an SLM (spatial light modulator) 205 through a collimator 204, so that input of any mode can be realized, a polarization controller 104 can adjust the polarization state of the input mode, then the beam on the upper path enters a mode switching system 114 through the collimator 204 and the polarization controller 104, dynamic switching between the two modes is realized through adjusting a torsion device 102 in the mode switching system 114, the beam on the upper path output by the mode switching system 114 reaches a beam combiner 208 through a 40x objective lens 207, the beam combiner 208 combines the mode on the upper path and the reference beam on the lower path, and the mode switching is verified through an interference pattern observed by a CCD 209. 206 represents a spatial beam.
Fig. 3 (a) -3 (b) show the mode switching results when the phase-shifted long-period fiber grating 105 is untwisted with an input mode of OAM l=0 and a lasing wavelength of 1537 nm. Namely, fig. 3 (a) and 3 (b) respectively correspond to the mode field pattern of the output mode and the interference pattern of the corresponding mode. Fig. 3 (c) -3 (d) show the mode switching results when the phase-shifted long-period fiber grating 105 is twisted 240 degrees with an input mode of OAM l=0 and a lasing wavelength of 1537 nm. That is, fig. 3 (c) and 3 (d) correspond to the mode field pattern of the output mode and the interference pattern of the corresponding mode, respectively. The results show that in the input mode OAM l=0, the phase-shifted long-period fiber grating 105 twists such that OAM l=0 switches to OAM l=2 at 1537 nm.
Fig. 4 (a) -4 (b) show the mode switching results when the phase-shifted long-period fiber grating 105 is untwisted with an input mode of OAM l=2 and a lasing wavelength of 1537 nm. Namely, fig. 4 (a) and 4 (b) respectively correspond to the mode field pattern of the output mode and the interference pattern of the corresponding mode. Fig. 4 (c) -4 (d) show the mode switching results when the phase-shifted long-period fiber grating 105 is twisted 240 degrees with an input mode of OAM l=2 and a lasing wavelength of 1537 nm. Namely, fig. 4 (c) and 4 (d) correspond to the mode field pattern of the output mode and the interference pattern of the corresponding mode, respectively. The results show that in the input mode OAM l=2, the phase-shifted long-period fiber grating 105 twists such that OAM l=2 switches to OAM l=0 at 1537 nm.
Fig. 5 (a) -5 (b) show the mode switching results when the phase-shifted long-period fiber grating 105 is untwisted with an input mode of OAM l=0 and a laser wavelength of 1558 nm. That is, fig. 5 (a) and 5 (b) correspond to the mode field pattern of the output mode and the interference pattern of the corresponding mode, respectively. Fig. 5 (c) -5 (d) show the mode switching results when the phase-shifted long-period fiber grating 105 is twisted 240 degrees with an input mode of OAM l=0 and a laser wavelength of 1558 nm. That is, fig. 5 (c) and 5 (d) correspond to the mode field pattern of the output mode and the interference pattern of the corresponding mode, respectively. The results show that in the input mode OAM l=0, the phase-shifted long-period fiber grating 105 twists such that OAM l=2 switches to OAM l=0 at 1558 nm.
Fig. 6 (a) -6 (b) show the mode switching results when the phase-shifted long-period fiber grating 105 is untwisted with an input mode of OAM l=2 and a laser wavelength of 1558 nm. That is, fig. 6 (a) and 6 (b) correspond to the mode field pattern of the output mode and the interference pattern of the corresponding mode, respectively. Fig. 6 (c) -6 (d) show the mode switching results when the phase-shifted long-period fiber grating 105 is twisted 240 degrees with an input mode of OAM l=2 and a laser wavelength of 1558 nm. That is, fig. 6 (c) and 6 (d) correspond to the mode field pattern of the output mode and the interference pattern of the corresponding mode, respectively. The results show that in the input mode OAM l=2, the phase-shifted long-period fiber grating 105 twists such that OAM l=0 switches to OAM l=2 at 1558 nm.
Summarizing the above, by twisting the phase-shifted long-period fiber grating 105, the mutual switching between OAM l=2 and OAM l=0 can be achieved at a plurality of wavelengths. In addition, with the multi-wavelength optical fiber mode switching system, switching between any two modes (OAM l=n, n=0, 1,2, 3) can be realized.
The above embodiments are preferred examples of the present invention, and the present invention is not limited thereto, and any other modifications or equivalent substitutions made without departing from the technical aspects of the present invention are included in the scope of the present invention.
Claims (10)
1. A multi-wavelength optical fiber mode switching system based on a few-mode phase shift grating, comprising: few-mode optical fibers, a torsion device and a polarization controller; n high-order guided-mode long-period fiber gratings are arranged on the few-mode fiber, N is more than or equal to 2, and the N high-order guided-mode long-period fiber gratings are cascaded to form a phase-shift long-period fiber grating; the number of the torsion devices is 2, one torsion device is fixed, and the other torsion device can twist; two ends of the few-mode optical fiber are respectively fixed on 2 torsion devices, and the phase-shift long-period optical fiber grating is positioned between the 2 torsion devices; one end of the few-mode optical fiber is connected with the polarization controller;
the manufacturing method of the phase-shift long-period fiber grating comprises the following steps: the high-temperature ablation is carried out on the single-side repetition of the few-mode optical fiber by setting the cycle size, the cycle number and the processing power of the high-frequency carbon dioxide laser, so that the fiber core and the cladding structure of the few-mode optical fiber are changed, and the few-mode phase-shift long-period fiber grating with the refractive index emphasized and asymmetrically distributed is obtained.
2. The multi-wavelength optical fiber mode switching system based on the few-mode phase shift grating according to claim 1, wherein the periods of the N high-order guided-mode long-period optical fiber gratings are the same, the interval between the high-order guided-mode long-period optical fiber gratings is half of the period, and the interval length is the phase shift.
3. The system of claim 1, wherein the torsional devices are each provided with a clamp for fixing the few-mode fiber.
4. The few-mode phase shift grating-based multi-wavelength fiber mode switching system of claim 1, wherein the core mode of the phase shift long period fiber grating is a conducting mode.
5. The system of claim 1, wherein the few-mode fiber is one of a four-mode fiber, a six-mode fiber, a seven-mode fiber, a nine-mode fiber, and a twelve-mode fiber.
6. A switching method of a multi-wavelength optical fiber mode switching system based on a few-mode phase shift grating according to any one of claims 1 to 5, comprising:
s1, inputting laser into at least a mode fiber, and coupling the laser to a target mode through a grating mode coupling effect of a phase-shift long-period fiber grating;
s2, acquiring a mode field diagram of a target mode and an interference diagram of a corresponding mode;
s3, twisting the twisting device at the output end to twist the phase-shift long-period fiber grating, and changing the refractive index change of the phase-shift long-period fiber grating;
s4, acquiring a mode field diagram of the output mode after torsion and an interference diagram of a corresponding mode;
s5, comparing the mode field diagram of the target mode with the mode field diagram of the output mode after torsion, and comparing the interference diagram of the mode corresponding to the mode field diagram of the target mode with the interference diagram of the mode field diagram corresponding to the output mode after torsion to realize the switching of the optical fiber modes.
7. The switching method according to claim 6, wherein n=2, the wavelength of light input into the few-mode fiber is 1537nm, the optical mode input into the few-mode fiber is OAM l=0, the grating output mode is still OAM l=0 when not twisted, and the output optical mode is OAM l=2 after twisted if the twist device at the input end is twisted by 240 °.
8. The switching method according to claim 6, wherein n=2, the wavelength of light input into the few-mode fiber is 1537nm, the optical mode input into the few-mode fiber is OAM l=2, the grating output mode is still OAM l=2 in the case of no twist, and the twisted optical mode is OAM l=0 if the twist device at the input end is twisted by 240 degrees.
9. The switching method according to claim 6, wherein n=2, the wavelength of light input into the few-mode optical fiber is 1558nm, the optical mode input into the few-mode optical fiber is OAM l=0, and in the case of no twist, OAM l=0 realizes output OAM l=2 through the coupling effect of the grating, and if the twist device at the input end is twisted by 240 degrees, the output optical mode after the twist is OAM l=0.
10. The switching method according to claim 6, wherein n=2, the wavelength of light input into the few-mode optical fiber is 1558nm, the optical mode input into the few-mode optical fiber is OAM l=2, and in the untwisted condition OAM l=2 realizes output OAM l=0 through the coupling effect of the grating, and if the twist device at the input end is twisted by 240 degrees, the twisted optical mode is OAM l=2.
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| CN108107509B (en) * | 2017-11-13 | 2023-06-23 | 暨南大学 | High-order vortex mode generation method and device based on few-mode optical fiber |
| CN112305673A (en) * | 2020-08-07 | 2021-02-02 | 上海大学 | All-fiber mode conversion device and method and detection device |
| CN112162364B (en) * | 2020-09-25 | 2021-06-22 | 中南大学 | Phase-shift fiber Bragg grating capable of switching wavelength and wavelength switching method |
| CN113311525A (en) * | 2021-05-17 | 2021-08-27 | 华侨大学 | Phase-shift fiber Bragg grating preparation method based on femtosecond laser direct writing system |
| CN113484953A (en) * | 2021-07-05 | 2021-10-08 | 朱国轩 | Efficiency-adjustable all-fiber mode converter |
| CN115343806B (en) * | 2022-06-15 | 2023-07-25 | 暨南大学 | Multi-wavelength high-order mode generation method based on cascade long-period fiber bragg grating |
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