CN111323903A - Optical fiber orbital angular momentum mode separation method based on spiral structure - Google Patents
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Abstract
The invention discloses a method for separating an optical fiber orbital angular momentum mode based on a helical structure, which comprises the following steps: calculating the angular effective refractive index difference between the newly formed modes in the spiral optical fiber, which meets the requirement of the effective separation of the orbital angular momentum mode, according to the requirement of the total effective refractive index difference between the modes required by the effective separation of the orbital angular momentum mode and the longitudinal effective refractive index value of the orbital angular momentum mode in the original optical fiber; calculating the specific designed spiral period length meeting the requirement of the angular effective refractive index difference calculated in the previous step by utilizing the characteristic that the angular effective refractive index newly formed in the spiral optical fiber is related to the spiral period length; heating the original optical fiber, and controlling the movement and rotation speed of the original optical fiber to make it twist to form the spiral optical fiber. The invention ensures the reliable, stable and multiplexed long-distance transmission of the orbital angular momentum mode in the designed spiral optical fiber and realizes the common multiplexing of the circular polarization direction and the orbital angular momentum order.
Description
Technical Field
The invention relates to the technical field of optical communication and optical sensing, in particular to a method for separating an optical fiber orbital angular momentum mode based on a helical structure.
Background
The optical orbital angular momentum is widely applied in the fields of optical communication, optical sensing, particle control and the like, and the optical fiber supporting stable multiplexing transmission of various orbital angular momentum modes is an important optical device for realizing the application of the optical orbital angular momentum. In a conventional optical fiber, the refractive index difference between the core and the cladding is increased, or the refractive index difference between the HE mode and the EH mode (or TE/TM mode) belonging to the same degenerate mode is increased by a method of designing an optical fiber with a special structure, so that mode separation of an orbital angular momentum mode (orbital angular momentum formed based on the HE mode) in which spin and orbital angular momentum are the same and an orbital angular momentum mode (orbital angular momentum formed based on the EH or TE/TM mode) in which spin and orbital angular momentum are the same is realized. Common methods include few-mode, multi-mode, hollow-core, ring-core, multi-core, and photonic crystal fiber schemes. However, the above methods cannot separate orbital angular momentum modes having the same order of orbital angular momentum but different spin directions, and require complicated optical fiber design techniques and processing processes. Meanwhile, such specially designed optical fibers are difficult to realize low-loss connection with conventional optical fibers in optical fiber communication and sensing systems.
A great number of patents and papers at home and abroad discuss how to design optical fibers capable of stably transmitting a plurality of orbital angular momentum modes, but all the optical fibers are designed from the angle of increasing the effective refractive index of the light propagation direction (longitudinal direction), and a method for increasing the angular effective refractive index by adopting optical fibers with a spiral structure to realize reliable, stable and multiplexed long-distance transmission of different orbital angular momentum modes in the optical fibers is not adopted. In addition, the method of increasing the refractive index in the propagation direction can only increase the refractive index difference between the orbital angular momentum modes having the same orbital angular momentum order but different spin directions (HE mode angular momentum) and the opposite direction (EH mode angular momentum), and cannot increase the refractive index difference between the orbital angular momentum modes having the same orbital angular momentum order, thereby realizing effective separation and multiplexing transmission of such modes.
There are also a lot of papers at home and abroad discussing the manufacture of spiral long-period fiber gratings for various orbital angular momentum generators, or circular polarization converters, and sensors for torsion, etc. However, most of such orbital angular momentum generators generate a high-order mode through mode coupling, and then a phase difference of pi/2 is generated between an odd mode and an even mode belonging to the same vector mode HE mode (EH mode or TE/TM mode) to form an orbital angular momentum mode, and a method for realizing mode separation of different orbital angular momenta by increasing an angular effective refractive index through a helical structure in an optical fiber is not provided. In addition, the spiral fiber grating has mode conversion characteristics near the coupling wavelength, so that the modes participating in coupling cannot be stably and reliably transmitted.
Disclosure of Invention
The technical problem to be solved by the present invention is to provide a method for separating an optical fiber orbital angular momentum mode based on a spiral structure, which can ensure reliable, stable and multiplexed long-distance transmission in a designed spiral optical fiber, and realize common multiplexing of a circular polarization direction and an orbital angular momentum order.
In order to solve the technical problem, the invention provides a method for separating an optical fiber orbital angular momentum mode based on a helical structure, which comprises the following steps:
(1) calculating the angular effective refractive index difference between the modes newly formed in the spiral optical fiber and meeting the requirement of the effective separation of the orbital angular momentum mode according to the requirement of the total effective refractive index difference between the modes required by the effective separation of the orbital angular momentum mode and the longitudinal effective refractive index value of the orbital angular momentum mode in the original optical fiber, wherein the total effective refractive index of the orbital angular momentum mode in the spiral optical fiber consists of the longitudinal effective refractive index in the original optical fiber and the angular effective refractive index newly formed in the spiral optical fiber;
(2) calculating the specially designed spiral period length required by the angular effective refractive index difference calculated in the step (1) by utilizing the characteristics of the newly formed angular effective refractive index in the spiral fiber, the circular polarization state of the orbital angular momentum mode in the spiral fiber, the orbital angular momentum order, the working wavelength and the spiral period length of the spiral fiber;
(3) heating the original optical fiber, and controlling the movement and rotation speed of the original optical fiber to make the original optical fiber be twisted to form the spiral optical fiber with the specific designed spiral period length calculated in the step (2).
Preferably, in step (1), the original fiber is any fiber with a circularly symmetric structure, and the fiber types include single-mode fiber, few-mode fiber, multi-mode fiber, hollow-core fiber, ring-core fiber, multi-core fiber and photonic crystal fiber.
Preferably, in step (2), the period length Λ of the spiral with a specific design satisfies the following formula:
Λ＝min{Λp,q}
wherein subscripts p and q represent two orbital angular momentum modes p and q in the original fiber, min { } represents the minimum operation sign for obtaining the minimum spiral period length required by any two mode separations, Λp,qThe length of the spiral period of a particular design required to separate orbital angular momentum modes p and q is expressed specifically as:
wherein the subscripts p and q represent two orbital angular momentum modes p and q in the helical fiber; the | | is an absolute value calculation symbol; spAnd sqThe spin quantum numbers of the two orbital angular momentum modes are respectively, and the values of +1 or-1 respectively represent the left-handed and right-handed circular polarization states; lpAnd lqThe orders of the orbital angular momentum of the two orbital angular momentum modes are respectively integers; lambda [ alpha ]minIs the minimum wavelength in the operating wavelength range of the orbital angular momentum mode, and is the effective refractive index difference between the orbital angular momentum modes expected to be obtained, generally, the value of delta n is more than 1 × 10-4；
Respectively the longitudinal effective refractive indexes of the two orbital angular momentum modes in the original optical fiber before torsion, and meet the condition
Preferably, in the step (3), the heating and twisting method is to perform coaxial twisting around the center of the heated original optical fiber, and finally form the spiral optical fiber with a coaxial spiral structure with a specially designed spiral period length; the heating mode of the optical fiber is selected from an oxyhydrogen flame or a carbon dioxide laser.
The invention has the beneficial effects that: the manufacturing method is simple, can be realized on the traditional optical fiber processing equipment, and solves the problems that the traditional orbital angular momentum optical fiber (optical fibers with few modes, hollow cores, ring cores, multiple cores, photonic crystals and the like) needs special optical fiber design and processing technology and is difficult to produce in large scale and at low cost; the surface of the optical fiber processed according to the proposed design and manufacturing method basically has no deformation and damage, can keep the original transmission characteristic and can be connected with the original optical fiber before torsion in a low-loss manner; the invention can also solve the problem that the prior orbital angular momentum optical fiber can not separate orbital angular momentum modes with the same orbital angular momentum order and different circular polarization directions, namely, the spiral structure designed and manufactured by the invention can realize multiplexing transmission of orbital angular momentum and circular polarization; the application range of the invention not only comprises the spiral optical fiber, but also comprises devices such as a spiral optical fiber-based orbital angular momentum mode coupler, a converter, a generator, an amplifier and the like which are designed by using the method.
Drawings
FIG. 1 is a schematic diagram of the structure of the spiral optical fiber according to the present invention.
FIG. 2 is a schematic diagram of the experimental principle of fabricating a spiral optical fiber according to the present invention.
FIG. 3 is a schematic view of a single mode fiber based spiral fiber actually fabricated by the microscope of the present invention.
FIG. 4 is a diagram showing the simulation result of the mode effective refractive index of the original single mode fiber before the spiral structure is formed according to the present invention.
FIG. 5 is a schematic diagram showing the mode effective refractive index of the helical single-mode optical fiber after the helical structure is formed according to the present invention.
FIG. 6(a) is a schematic diagram of interference fringes of the +1 st order orbital angular momentum mode and Gaussian spherical wave separated by the present invention.
FIG. 6(b) is a schematic diagram of interference fringes of-1 order orbital angular momentum mode and Gaussian spherical wave separated by the present invention.
FIG. 6(c) is a schematic diagram of a separated light spot of the +1 orbital angular momentum mode according to the present invention.
FIG. 6(d) is a schematic diagram of a light spot of the separated-1 orbital angular momentum mode according to the present invention.
FIG. 7 is a graph showing the simulation results of the mode effective refractive index of the original four-mode optical fiber before the spiral structure is formed according to the present invention.
FIG. 8 is a diagram illustrating the simulation result of the mode effective refractive index of the spiral four-mode optical fiber after the spiral structure is formed.
FIG. 9(a) is a schematic diagram of interference fringes of the +2 order orbital angular momentum mode and Gaussian spherical wave separated by the present invention.
FIG. 9(b) is a schematic diagram of interference fringes of-2 order orbital angular momentum mode and Gaussian spherical wave separated by the present invention.
FIG. 9(c) is a schematic diagram of a separated spot of +2 orbital angular momentum mode according to the present invention.
FIG. 9(d) is a schematic diagram of a separated-2 orbital angular momentum mode of the invention.
FIG. 10 is a schematic view of the observation principle of observing and confirming mode separation according to the present invention.
Detailed Description
The method comprises the steps of synchronously controlling heating, moving and rotating of an original optical fiber, synchronously moving and rotating the original optical fiber heated to a molten state, and forming a spiral optical fiber with a specially designed spiral period length structure, wherein the specially designed spiral period length Λ is determined by the moving speed v (mm/s-mm/s) and the rotating speed w (turn/s-turn/s) of the original optical fiber and is expressed as Λ ═ v/w (mm/turn-mm/turn). due to the torsional tangential force when the original optical fiber is heated, the specially designed spiral period length structure is formed in the spiral optical fiber after cooling and has a uniform spiral refractive index distribution characteristic.
Assuming that the effective longitudinal refractive index of the orbital angular momentum mode (l, m) in the original fiber before twisting is
Where l and m denote the angular and radial order, respectively, in the cross-section. The effective refractive index of the orbital angular momentum mode in the twisted helical optical fiber forming the helical structure
Can be expressed as:
in the above formula
The part is the embodiment that the angular phase of the orbital angular momentum mode (l, m) in the optical fiber with the spiral structure changes along the propagation direction, namely the angular effective refractive index, wherein s is the spin quantum number, s is 1 and-1 respectively represents the left-handed and right-handed circular polarization states, sigma is the torsion direction of the spiral optical fiber, sigma is 1 or-1 respectively represents the left-handed or right-handed spiral structure, lambda is the working period of the orbital angular momentum mode, and Λ is the length of the specially designed spiral period.
To effectively separate the different orbital angular momentum modes, it is generally desirable that the effective refractive index difference between the two modes satisfy an Δ n > 1 × 10-4The conditions of (1). Since the angular effective refractive index is equivalent to the longitudinal effective refractive index, the longitudinal effective refractive index difference can be realized only by specially designed optical fiber structures or by increasing the refractive index difference between the fiber core and the cladding. Therefore, in the invention, the requirement of the effective refractive index difference is innovatively provided to be realized through the change of the angular effective refractive index, and in order to realize the effective refractive index difference required by the separation of any two orbital angular momentum modes p and q, the spiral period in the manufactured spiral optical fiber at least meets the following requirements:
wherein subscripts p and q represent any two orbital angular momentum modes p and q in the helical fiber; the | | is an absolute value calculation symbol; spAnd sqThe spin quantum numbers of the two modes are respectively, and when the value is 1 or-1, the spin quantum numbers respectively represent the left-handed and right-handed circular polarization states; lpAnd lqThe orders of orbital angular momentum of the two modes are respectively, and the values are integers; lambda [ alpha ]minIs the minimum wavelength within the operating wavelength range of the mode, and Δ n is the effective refractive index difference between the modes desired to be achieved, typically taken to be Δ n > 1 × 10-4；
The longitudinal effective refractive indices of the two modes in the original fiber before twisting,
when multiple orbital angular momentum modes are present in a helical fiber, the period length Λ of the particular design of the helix should satisfy the formula:
Λ＝min{Λp,q}(3)
wherein subscripts p and q denote two orbital angular momentum modes p and q in the original fiber; min { } represents the minimum operator sign, i.e., takes the minimum value in the spiral period required to separate any two modes.
When the above conditions are satisfied, the difference in effective refractive index between two orbital angular momentum modes having the same angular momentum order and different spin directions, that is, an HE mode in which spin and orbital angular momentums belong to the same degenerate mode and an EH mode in which spin and orbital angular momentums are in the same direction can reach 2 × 10-4Meanwhile, the effective refractive index difference between two orbital angular momentum modes with the same spin direction and different angular momentum directions can reach 1 × 10-4For any other different orbital angular momentum mode, due to the different spin direction or orbital angular momentum orders, the effective refractive index difference between any two orbital angular momentum modes can reach at least 1 × 10-4By the method, the effective separation of the optical fiber in the designed spiral optical fiber can be realized, and the requirements of long-distance stable, reliable and multiplexing transmission of different modes in the optical fiber are met.
When period Λ satisfies the resonance condition between certain modes in the spiral fiber grating in a specific wavelength interval, the coupled energy exchange between these modes at the specific wavelength will occur, i.e. the orbital angular momentum mode conversion is achieved.
The method comprises the following steps of fixing an optical fiber to be processed between a holder and a rotator, wherein the holder and the rotator are respectively fixed on two translation stages, heating the optical fiber by a carbon dioxide laser or oxyhydrogen flame, synchronously controlling the movement of the translation stages and the rotation of the rotator when the optical fiber is heated to a molten state, and synchronously controlling the movement speed and the rotation speed of the spiral optical fiber, wherein a period Λ for forming the spiral structure is determined by the movement speed v (mm/s-mm/s) and the rotation speed w (turn/s-turn/s), and is represented as Λ -v/w (mm/turn-mm/turn).
Example 1: taking a single-mode fiber as an example, the separation and transmission of 1 st order orbital angular momentum in the cladding are realized.
The structure of figure 2 was used to align a pristine single mode fiber (Fujikura Inc,
) Heating and twisting are carried out. In the figure, in order to ensure the uniformity of the heating zone, a Sapphire tube (Sapphire tube) is used to form the heating zone, and a carbon dioxide laser (CO) is controlled by a photoswitch (Shutter)2laser), one end of the original fiber to be processed (Optical fiber) is fixed (Clamp), and the original fiber to be processed is kept straight by a Weight (Weight), the other end is fixedly installed into a Rotator (Rotator), a wide light source (ASE) and a spectrum analyzer (OSA) for observing the characteristics of the spiral fiber in the process, such as loss characteristics and the like, when the original fiber is heated to a certain temperature, a moving Stage (Stage) and a rotating Stage (Rotator) work synchronously under the control of control software in a Computer (Computer) to realize simultaneous movement and rotation, a period Λ for forming the spiral structure is determined by a movement speed v (mm/s-mm/s) and a rotation speed w (turn/s-turn/s), which is expressed as Λ ═ v/w (mm/turn-mm/turn), fig. 3 is a single mode fiber based microscope (Fujikura Inc,
) Actually fabricated spiral optical fiber. As can be seen from the figure, the diameter deformation of the optical fiber after heating and twisting is about 1-3um, the transmission characteristic of the original single-mode optical fiber is hardly changed, and the formed spiral optical fiber can realize low-loss connection with the original optical fiber. Single mode fibers before and after forming the helix-structure (Fujikura Inc,
) The different mode effective refractive indices in (a) are shown in fig. 4 and 5. Figure 4 is a graph of the original single mode fiber before the helix-structure was formed (Fujikura Inc,
) The mode effective refractive index simulation result of (1). The fiber core and cladding radii are shown as 4.1um and 62.5um, respectively, and the refractive indices are 1.4580 and 1.4536, respectively, the effective index results of which are shownAnd (4) carrying out simulation calculation by adopting a finite element method. As can be seen, HE23、TE03And TM03The effective refractive index difference of the modes (the mode subscripts sequentially indicate the azimuthal and radial orders of the modes, respectively) is extremely small, and degenerates in the original fiber, making it difficult to separate independent propagation. Figure 5 shows a spiral single mode fiber after forming the spiral structure (Fujikura Inc,
) The radius of the fiber core and the cladding in the graph are respectively 4.1um and 62.5um, the refractive index is respectively 1.4580 and 1.4536, the spiral radius is 1cm, and the result in the graph is obtained by finite element method simulation calculation. It can be seen that different orbital angular momentum modes HE in the wavelength range of 1450nm to 1650nm23 +、HE23 -And TE/TM03 +/-(the signs in the superscript indicate different circular polarizations, + indicates a left-hand circular polarization state, -indicates a right-hand circular polarization state), the effective refractive index difference between the different orbital angular momentum modes is at least about 3 × 10-4And the requirement of effective separation of orbital angular momentum modes is completely met.
With the structure of fig. 10, the transmission conditions of the optical fiber in the helical structure formed by different orbital angular momentum modes are observed. The Tunable Laser (Tunable Laser) outputs light with a corresponding observation wavelength, the light is coupled by a Coupler (Coupler), one path of the light is input into a Mode converter (Mode converter) to obtain a corresponding orbital angular momentum Mode, the light is transmitted by a fiber forming a helical structure and then interferes with a Gaussian spherical wave reference signal output by the other path of the light, interference fringes are observed by a CCD, and a Polaroid (PC) and an Attenuator (attentuator) are used for adjusting the definition of the interference fringes. When no Gaussian spherical wave reference signal is added, the circular light spot corresponding to the orbital angular momentum mode is displayed, and the observed results are shown in FIGS. 6(c) and (d); when the gaussian spherical wave reference signal is added, it shows helical interference fringes, and the observed results are shown in fig. 6(a), (b). Wherein FIGS. 6(a), (c) show the post-interference fringes and pre-interference spots of the +1 order orbital angular momentum mode, respectively; FIGS. 6(b) and (d) show interference fringes of the-1 st order orbital angular momentum mode and a spot before interference, respectively.
Example 2: taking a four-mode optical fiber as an example, the separation transmission of 2-order orbital angular momentum in the fiber core is realized.
The structure of fig. 2 is used for heating and twisting an original four-mode optical fiber (long flying company, step-type four-mode optical fiber), and the heating and twisting mode is consistent with that of a single-mode optical fiber. The effective refractive indices of the different modes in the four-mode fiber (long-fiber, step-type four-mode fiber) before and after the formation of the spiral structure are shown in fig. 7 and 8. Fig. 7 shows the mode effective index simulation results of the original four-mode fiber (long femtolier, step four-mode fiber) before the spiral structure is formed. In the figure, the radius of the fiber core and the radius of the cladding are respectively 9.5um and 62.5um, the refractive index is respectively 1.4499 and 1.444, and the effective refractive index result in the figure is obtained by simulation calculation by a finite element method. As can be seen, HE31And EH11(the mode indices sequentially indicate the azimuthal and radial order of the mode, respectively.) the mode's effective index difference is extremely small, creating degenerate modes in the fiber that are difficult to separate for independent propagation. Fig. 8 shows a simulation result of the mode effective refractive index of a spiral four-mode fiber (long fiber, step-type four-mode fiber) after the spiral structure is formed. In the figure, the radius of the fiber core and the radius of the cladding are respectively 9.5um and 62.5um, the refractive index is 1.4499 and 1.444, the radius of the helix is 1cm, and the effective refractive index result in the figure is obtained by finite element method simulation calculation. It can be seen that different orbital angular momentum modes HE are available in the wavelength range of 1450nm to 1650nm31 +、HE31 -、EH11 +And EH11 -(the signs in the superscript indicate different circular polarizations, + indicates the HE-mode left-hand circular polarization state and the EH-mode right-hand circular polarization state, -indicates the HE-mode right-hand circular polarization state and the EH-mode left-hand circular polarization state), and the difference in refractive index between the different orbital angular momentum modes is at least about 3 × 10-4And the requirement of effective separation of orbital angular momentum modes is completely met. With the structure of fig. 10, the transmission conditions of the optical fiber in the helical structure formed by different orbital angular momentum modes are observed. When no Gaussian spherical wave reference signal is added, the circular light spot corresponding to the orbital angular momentum mode is displayed,the observed results are shown in FIGS. 9(c) and (d); when the gaussian spherical wave reference signal is added, it shows helical interference fringes, and the observed results are shown in fig. 9(a), (b). Wherein FIGS. 9(a), (c) show the post-interference fringes and pre-interference spots of the +2 order orbital angular momentum mode, respectively; FIGS. 9(b) and (d) show interference fringes of the-2 nd order orbital angular momentum mode and a spot before interference, respectively.
Claims (4)
1. A method for separating an optical fiber orbital angular momentum mode based on a helical structure is characterized by comprising the following steps:
(1) calculating the angular effective refractive index difference between the modes newly formed in the spiral optical fiber and meeting the requirement of the effective separation of the orbital angular momentum mode according to the requirement of the total effective refractive index difference between the modes required by the effective separation of the orbital angular momentum mode and the longitudinal effective refractive index value of the orbital angular momentum mode in the original optical fiber, wherein the total effective refractive index of the orbital angular momentum mode in the spiral optical fiber consists of the longitudinal effective refractive index in the original optical fiber and the angular effective refractive index newly formed in the spiral optical fiber;
(2) calculating the specially designed spiral period length required by the angular effective refractive index difference calculated in the step (1) by utilizing the characteristics of the newly formed angular effective refractive index in the spiral fiber, the circular polarization state of the orbital angular momentum mode in the spiral fiber, the orbital angular momentum order, the working wavelength and the spiral period length of the spiral fiber;
(3) heating the original optical fiber, and controlling the movement and rotation speed of the original optical fiber to make the original optical fiber be twisted to form the spiral optical fiber with the specific designed spiral period length calculated in the step (2).
2. The method for separating orbital angular momentum modes of optical fibers based on a helical structure according to claim 1, wherein in the step (1), the original optical fiber is any optical fiber with a circularly symmetric structure, and the optical fiber types include single mode optical fiber, few mode optical fiber, multi-mode optical fiber, hollow core optical fiber, ring core optical fiber, multi-core optical fiber and photonic crystal optical fiber.
3. The method for separating orbital angular momentum modes of an optical fiber based on a helical structure as claimed in claim 1, wherein in the step (2), the period length Λ of the specially designed helix satisfies the following formula:
Λ＝min{Λp,q}
wherein subscripts p and q represent two orbital angular momentum modes p and q in the original fiber, min { } represents the minimum operation sign for obtaining the minimum spiral period length required by any two mode separations, Λp,qThe length of the spiral period of a particular design required to separate orbital angular momentum modes p and q is expressed specifically as:
wherein the subscripts p and q represent two orbital angular momentum modes p and q in the helical fiber; the | | is an absolute value calculation symbol; spAnd sqThe spin quantum numbers of the two orbital angular momentum modes are respectively, and the values of +1 or-1 respectively represent the left-handed and right-handed circular polarization states; lpAnd lqThe orders of the orbital angular momentum of the two orbital angular momentum modes are respectively integers; lambda [ alpha ]minIs the minimum wavelength in the working wavelength range of the orbital angular momentum mode, and is the effective refractive index difference between the orbital angular momentum modes expected to be obtained, and is taken as delta n > 1 × 10-4；
Respectively the longitudinal effective refractive indexes of the two orbital angular momentum modes in the original optical fiber before torsion, and meet the condition
4. The method for separating orbital angular momentum mode of optical fiber based on helical structure as claimed in claim 1, wherein in the step (3), the heating and twisting method is to perform coaxial twisting around the center of the heated original optical fiber, and finally form the helical optical fiber of coaxial helical structure with specially designed helical period length; the heating mode of the optical fiber is selected from an oxyhydrogen flame or a carbon dioxide laser.
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| WO2022160453A1 (en) * | 2021-01-28 | 2022-08-04 | 深圳大学 | Spiral fiber grating and preparation method therefor, and all-fiber orbital angular momentum beam generator |
| CN115296771A (en) * | 2022-10-01 | 2022-11-04 | 深圳市子恒通讯设备有限公司 | Optical system of all-fiber mode converter |
| WO2023092484A1 (en) * | 2021-11-23 | 2023-06-01 | 深圳大学 | Method for preparing helical refractive-index-change-type fiber grating for all-fiber orbital angular momentum beam generator |
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| CN113484953A (en) * | 2021-07-05 | 2021-10-08 | 朱国轩 | Efficiency-adjustable all-fiber mode converter |
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