Optical fiber type tunable circularly polarized light conversion device and manufacturing method thereof

Abstract

The invention discloses an optical fiber type tunable circularly polarized light conversion device and a manufacturing method thereof, and the conversion device consists of a spiral optical fiber grating and a transmission optical fiber connected with the spiral optical fiber grating. Wherein the spiral fiber bragg grating is a long-period fiber bragg grating which is manufactured on the manufacturing fiber supporting the LP1v mode of the transmission fiber and has a set spiral direction C and a set period lambda, and the transmission fiber is an optical fiber which has a set length L and supports the LP1v mode of the transmission fiber. Based on the mode coupling characteristic of the spiral fiber grating and the spin-orbit mapping characteristic of the LP1v mode in the transmission fiber, the conversion device can convert an input fiber fundamental mode with any set conversion wavelength lambda and any polarization state into a high-purity left / right-handed circular polarization LP1v mode. The invention is compatible with various optical fiber devices and systems, has the characteristics of miniaturization, easiness in integration, low cost and the like of the optical fiber devices, and has the unique advantages of simple manufacturing process, no power loss and the like.

Description

Technical Field

[0001] The present invention relates to the fields of optical fiber communication, sensing, imaging and measurement, and in particular to an optical fiber type tunable circularly polarized light conversion device and a manufacturing method thereof. Background Art

[0002] Polarized light, as an important characteristic inherent in light, plays an important role in scientific research and has been widely used in fields such as communication, sensing, imaging and measurement. For example, in the field of optical fiber communication, polarization encoding or multiplexing can be used to achieve high-speed, large-capacity data transmission. In addition, since different substances absorb, scatter and refract the polarization state of light differently, the properties and structure of the substance can be sensed and analyzed by measuring the change in the polarization state of light after it passes through the substance. Specific polarized light helps to improve the accuracy of imaging. Compared with linearly polarized light, circularly polarized light carries spin angular momentum and can be used to detect chiral substances and realize the measurement of current, magnetic field, etc.

[0003] The patents related to circularly polarized light generating devices at home and abroad are as follows:

[0004] Chinese patent CN211786404U, a polarized light generating device with adjustable polarization degree;

[0005] Chinese patent CN110082924A, a circularly polarized light generating device based on a vector beam with radial polarization variation;

[0006] Chinese patent CN117580428A, a wavelength-adjustable high-efficiency circularly polarized electroluminescent device based on photon spin-orbit coupling;

[0007] Chinese patent CN118778174 A, an all-fiber polarization converter and its manufacturing method.

[0008] At present, polarized light generating devices are mainly based on the principle of transmission and reflection of light at the interface, and commonly used devices include wave plates, liquid crystals and prisms. For example, a polarization polarizer can be used to obtain specific linearly polarized light, and an optical prism (using the birefringence principle of crystals) can be used to achieve polarization separation, but the linearly polarized light generated by this method will lose more than half of the optical power. The linearly polarized light generating device proposed in the patent "A polarized light generating device with adjustable polarization degree (Chinese patent CN211786404 U)" requires that the polarization azimuth of the incident light is completely parallel or perpendicular to the reflecting surface. Based on the existing optical device processing technology, it is difficult to achieve this precise requirement for the polarization angle, and what is generated is linearly polarized light. Natural light is converted into linearly polarized light through a linear polarizer and then converted into left-handed or right-handed circularly polarized light through a 1 / 4 wave plate, but based on this method, more than half of the optical power will be lost. In the patent "A circularly polarized light generating device for vector light beams based on radial polarization changes (Chinese patent CN110082924 A)", specific circularly polarized light is obtained by setting the input optical power and the transmission distance of light; the patent "Wavelength-adjustable high-efficiency circularly polarized electroluminescent device based on photon spin-orbit coupling (Chinese patent CN117580428A)" uses organic single crystals to convert linearly polarized light into circularly polarized light based on the spin-orbit coupling effect, but the above methods based on spin-orbit interaction require specific media such as liquid crystal media, which has the disadvantage of high cost. The above existing conversion methods based on space devices have the disadvantages of large volume, difficulty in integration, additional coupling loss when coupled with optical fiber devices, and can only generate or convert polarized light in a specific wavelength range. In the patent "An all-fiber polarization converter and its manufacturing method (Chinese patent CN118778174 A)", it is necessary to use a special elliptical core optical fiber and accurately align the first and second optical fiber devices, which is difficult to implement and costly, and half of the power will be lost during the linear polarization conversion process. The paper “Strong circular dichroism for the HE11 mode in twisted single-ring hollow-core photonic crystal fiber, Optica, 5(10), 2018” uses the circular dichroism of spiral fiber gratings to achieve the output of specific circular polarization, but this method will lose half of the power. The paper “All-fiber circular polarization filter realized by using helical long-period fiber gratings, PTL, 30(22), 2018” uses the mode selection characteristics of spiral fiber gratings to achieve circular polarization conversion and filtering, but this method has low conversion efficiency. The above-mentioned conversion devices based on optical fiber devices have the disadvantages of high cost, low conversion efficiency and conversion power.So far, there is no all-fiber tunable circularly polarized light conversion device with simple manufacturing process, no power loss, miniaturization, easy integration and low cost. Summary of the invention

[0009] Purpose of the invention: In view of the problems existing in the prior art, the present invention provides an all-fiber tunable circularly polarized light conversion device with a simple manufacturing process and no power loss.

[0010] To achieve the above object, the present invention provides the following technical solutions:

[0011] A fiber-type tunable circularly polarized light conversion device, which is composed of a spiral fiber grating and a transmission fiber, can convert the input fiber fundamental mode with any set conversion wavelength λ and any polarization state into high-purity left / right circularly polarized LP 1v model;

[0012] The helical fiber Bragg grating is composed of a supporting transmission fiber LP 1v The mode is made of a long-period fiber grating with a set spiral direction C and period Λ made of optical fiber;

[0013] The transmission fiber is a fiber with a set length L, supporting the transmission fiber LP 1v Mode of optical fiber;

[0014] Furthermore, the preset spiral direction C of the aforementioned spiral fiber grating can be set to +1 or -1. When C is set to +1, it corresponds to a left-handed spiral fiber grating (counterclockwise spiral structure). At this time, the circularly polarized light conversion device converts the input fiber fundamental mode of any polarization state into the output left-handed circularly polarized LP 1v mode; when C is set to -1, it corresponds to a right-handed spiral fiber grating (clockwise spiral structure). At this time, the circularly polarized light conversion device converts the input fiber fundamental mode of any polarization state into the output right-handed circularly polarized LP 1v model.

[0015] Furthermore, the period of the aforementioned spiral long-period fiber grating is set to:

[0016] Λ=λ / (n 01 -n 1v ),

[0017] In the formula, λ represents the set conversion wavelength, n 01 and n 1v They represent the LP in the optical fiber used to make the grating. 01 and LP 1v The effective refractive index of the mode, where LP lv Represents the linear polarization mode of the optical fiber with angular and radial orders l and v respectively.

[0018] Furthermore, the aforementioned supporting transmission optical fiber LP 1v The transmission fiber length L of the mode is set as:

[0019] L=(2×q+1)×λ×|n TEv -n TMv | / 2,

[0020] In the formula, q is a natural number, n TEv and n TMv Respectively represent the optical fiber LP in the transmission optical fiber 1v Degenerate angular polarization mode TE 0v and radial polarization mode TM 0v The effective refractive index is λ, and λ represents the set conversion wavelength.

[0021] Furthermore, the aforementioned production fiber and transmission fiber used to produce the spiral fiber grating are supported by the transmission fiber LP 1v Any of the step-index or graded-index few-mode fibers, ring-core fibers, hollow-core fibers and photonic crystal fibers.

[0022] Furthermore, the aforementioned spiral fiber grating can be manufactured by any one of the fiber grating manufacturing methods including ultraviolet, mechanical, electric arc, carbon dioxide laser or heating twisting.

[0023] A method for manufacturing an optical fiber-type tunable circularly polarized light conversion device comprises the following steps:

[0024] S1, in support of transmission optical fiber LP 1v Pattern production: a spiral fiber grating (1) having a set spiral direction C and period Λ is produced on an optical fiber;

[0025] S2. Reserve or connect a supporting transmission optical fiber LP with a length of L at the output end of the manufactured spiral fiber Bragg grating. 1v A section of transmission optical fiber for the mode.

[0026] Compared with the prior art, the beneficial technical effects of the above technical solutions adopted in the present invention are as follows: the all-fiber tunable circularly polarized light conversion device proposed in the present invention has the characteristics of optical fiber devices such as miniaturization, easy integration and low cost, and can convert input light of any set wavelength and any polarization state, and has unique advantages such as simple manufacturing process and no power loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a structural diagram of the fiber-type tunable circularly polarized light conversion device provided by the present invention, C is the spiral direction of the spiral fiber grating, Λ is the period of the spiral fiber grating, L is the length of the transmission fiber, 1 is the spiral fiber grating, and 2 is the transmission fiber.

[0028] Figure 2 A schematic diagram of a method for preparing a fiber-type tunable circularly polarized light conversion device provided as a case.

[0029] Figure 3 For this case, a two-mode optical fiber is selected as the production optical fiber, and a relationship curve between the wavelength λ and the set period Λ is set in the range of 1500nm-1700nm.

[0030] Figure 4 For this case, a two-mode optical fiber is selected as the transmission optical fiber. A curve diagram showing the relationship between the set length L of the external transmission optical fiber required for realizing a fully circularly polarized light conversion device in the range of 1500nm-1700nm and the set wavelength λ is shown.

[0031] Figure 5 This is case 1, where the wavelength λ is set to 1540nm, q is set to 0, and a left-handed helical fiber Bragg grating (counterclockwise helical structure) is used to convert the input linear polarization fundamental mode into a completely left-handed circularly polarized light LP. 11 Demonstration diagram of the device structure and mode evolution process of the model.

[0032] Figure 6 For case 2, the wavelength λ is set to 1550nm, q is set to 1, and a left-handed helical fiber Bragg grating (counterclockwise helical structure) is used to convert the input right-handed circularly polarized fundamental mode into a completely left-handed circularly polarized light LP. 11 Demonstration diagram of the device structure and mode evolution process of the model.

[0033] Figure 7 This is case 3, where the wavelength λ is set to 1560nm, q is set to 1, and a right-handed spiral fiber Bragg grating (clockwise spiral structure) is used to convert the input left-handed circularly polarized fundamental mode into a completely right-handed circularly polarized light LP. 11 Demonstration diagram of the device structure and mode evolution process of the model.

[0034] Figure 8 This is case 4, where the wavelength λ is set to 1570nm, q is set to 0, and a right-handed spiral fiber Bragg grating (clockwise spiral structure) is used to convert the input elliptically polarized fundamental mode into a completely right-handed circularly polarized light LP. 11 Demonstration diagram of the device structure and mode evolution process of the model. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0036] like Figure 1As shown in the figure, a fiber-type tunable circularly polarized light conversion device of the present invention is composed of a spiral fiber grating (1) and a connected transmission fiber (2). The spiral fiber grating is supported by the transmission fiber LP. 1v The long-period fiber grating with a set spiral direction C and period Λ is made on the optical fiber. The transmission optical fiber is a supporting transmission optical fiber LP with a set length L. 1v Mode of optical fiber. Figure 1 In the figure, the light gray part is the cladding, the medium gray part is the core, the dark gray spiral part is the manufactured spiral fiber grating, and the external part of the spiral fiber grating is the transmission optical fiber.

[0037] This embodiment provides a method for preparing a fiber-type tunable circularly polarized light conversion device, such as Figure 2 As shown, the following steps are included:

[0038] (1) Fixing the fabricated optical fiber between the center of a fixture and a rotator, wherein the fixture and the rotator are respectively located on a translation stage 1 and a translation stage 2, and the translation stage 1 and the translation stage 2 are located on a translation stage 3;

[0039] (2) Putting a sapphire tube on the optical fiber to be manufactured and fixing it;

[0040] (3) Turn on the switch of the carbon dioxide laser, and the laser light emitted by the laser passes through the reflector and reaches the sapphire tube, thereby uniformly heating the optical fiber to be produced to a molten state;

[0041] (4) controlling the rotation direction of the rotator according to the set spiral direction C, and controlling the moving speed and the rotation angular velocity of the rotator according to the set period Λ, so as to form a spiral fiber grating with the set spiral direction C and period Λ;

[0042] (5) Retain or connect a supporting transmission optical fiber LP with a length of L at the output end of the manufactured spiral fiber grating 1v A section of transmission optical fiber for the mode.

[0043] In the above method, the heating, movement and specific rotation direction of the optical fiber are synchronously controlled to produce a spiral fiber grating. The optical fiber to be produced, which is heated to a molten state, is synchronously moved and rotated in the same direction to form a spiral fiber grating with a set spiral direction C and period Λ. When C is set to +1, it corresponds to a left-handed spiral fiber grating, that is, the optical fiber to be produced is twisted counterclockwise along the moving direction of the produced optical fiber; when C is set to -1, it corresponds to a right-handed spiral fiber grating, that is, the optical fiber to be produced is twisted clockwise along the moving direction of the produced optical fiber. The size of the spiral period Λ formed is determined by the moving speed v (mm / s-millimeter / second) and the rotation speed w (turn / s-turn / second) of the optical fiber, expressed as Λ=v / w (mm / turn-millimeter / turn). Due to the torsional tangential force during heating, a specifically designed spiral periodic structure is formed in the cooled spiral optical fiber, which has a spiral refractive index distribution characteristic.

[0044] The following experiment is conducted using this embodiment, and four cases are used. In all cases, the production fiber and transmission fiber are two-mode fiber (Yangtze-Flying Company's step-index two-mode fiber). The diameters of the core and cladding of the two-mode fiber are 14.5um and 125um, respectively, and the refractive indexes of the core and cladding are 1.4485 and 1.4440, respectively. The two-mode fiber is used as the production fiber in the case, and the finite element method can be used to calculate the scalar mode LP in the wavelength range of 1500nm-1700nm. 01 and LP 11 The modal effective refractive index n 01 and n 11 , and according to Λ=λ / (n 01 -n 11 ) calculates the required grating period Λ within the set wavelength range of 1500nm-1700nm, and the relationship curve between the set wavelength λ and the grating period Λ is shown in Figure 3 As shown, the four points marked in the figure correspond to cases 1-4 respectively.

[0045] In this case, a two-mode optical fiber is selected as the transmission optical fiber. The finite element method can be used to calculate the vector mode TE in the wavelength range of 1500nm-1700nm. 01 and TM 01 The modal effective refractive index n TE01 and n TM01 , and according to L=(2×q+1)×λ×|n TE01 -n TM01 | / 2, and calculate the relationship between the length L of the external transmission optical fiber required and the set wavelength λ in the set wavelength range of 1500nm-1700nm when q is 0 and 1 respectively. Figure 4 As shown, the four points marked in the figure correspond to cases 1-4 respectively.

[0046]

Case 1

[0047] like Figure 5 As shown in the device structure, the output polarized light wavelength is set to λ = 1540nm, then according to Figure 3 The period of the spiral fiber grating to be manufactured is Λ=822.93um, and C=+1 is used to manufacture a left-handed spiral fiber grating (counterclockwise spiral structure). Figure 4 The length of the grating external two-mode optical fiber L = 29.83cm. Figure 5 As shown in the mode evolution, according to the mode coupling characteristics of the spiral fiber grating, the manufactured left-handed spiral fiber grating converts the input fiber fundamental mode LP with linear polarization state at the set wavelength λ = 1540nm 01 Mode coupling is converted into LP with +1st-order orbital angular momentum in the same linear polarization state. 11 Mode. Linear polarization state + 1st-order orbital angular momentum LP 11 The mode can be decomposed into left-hand circular polarization mode and right-hand circular polarization mode. The left-hand circular polarization mode (spin angular momentum is +1, in the same direction as orbital angular momentum) consists of an odd-mode HE with a phase difference of π / 2. 21 Mode and even mode HE 21 mode; while the right-handed circular polarization mode (spin angular momentum is -1, opposite to the orbital angular momentum) is composed of the TM with a phase difference of π / 2 01 Mode and TE 01 Mode composition. Based on LP 11 Spin-orbit mapping properties of modes in two-mode transmission fibers, odd-mode HE in left-handed circularly polarized modes in transmission fibers 21 Mode and even mode HE 21 The effective refractive index difference between the modes is extremely small (generally about 10 -9 ), the phase difference is negligible when the transmission distance L = 29.83 cm, so the mode state is stable during the transmission process; while in the right-handed circular polarization mode of the transmission fiber, the TM 01 Mode and TE 01 The effective refractive index difference of the mode is large (generally greater than 10 -6 ), a phase difference of Δφ=π is generated at a transmission distance of L=29.83 cm, so the right-handed circular polarization state flips to the left-handed circular polarization state. The final linear polarization state LP 11 The mode is converted into completely left-handed circularly polarized light LP at the end of the transmission fiber 11 The device realizes the conversion of the input linear polarization state into the fundamental mode LP 01 Mode conversion to completely left-hand circularly polarized light LP 11 mold.

[0048]

Case 2

[0049] like Figure 6As shown in the device structure, the output polarized light wavelength is set to λ = 1550nm. Figure 3 The period of the spiral fiber grating to be manufactured is Λ=822.65um, and C=+1 is used to adopt a left-handed spiral fiber grating (counterclockwise spiral structure). Figure 4 The length of the grating external two-mode optical fiber L = 91.96cm. Figure 6 As shown in the mode evolution, according to the mode coupling characteristics of the spiral fiber Bragg grating, the manufactured left-handed spiral fiber Bragg grating converts the input fiber fundamental mode LP with right-handed circular polarization state at the set wavelength λ = 1550nm 01 Mode coupling is converted into LP with +1st-order orbital angular momentum in the same right-hand circular polarization state. 11 Mode. Right-handed circular polarization state + 1st-order orbital angular momentum LP 11 mode (spin angular momentum is -1, opposite to orbital angular momentum) is composed of TM with a phase difference of π / 2 01 Mode and TE 01 Mode composition. Based on LP 11 Spin-orbit mapping properties of modes in a transmission two-mode fiber, TM in a right-handed circularly polarized mode in a transmission fiber 01 Mode and TE 01 The effective refractive index difference of the mode is large (generally greater than 10 -6 ), a phase difference of Δφ=3π is generated at a transmission distance of L=91.96 cm, so the right-handed circular polarization state flips to the left-handed circular polarization state. 11 The mode is converted into completely left-handed circularly polarized light LP at the end of the transmission fiber 11 The device realizes the conversion of the input right-hand circular polarization state into the fundamental mode LP 01 Mode conversion to completely left-hand circularly polarized light LP 11 mold.

[0050]

Case 3

[0051] like Figure 7 As shown in the device structure, the output polarized light wavelength is set to λ = 1560nm, then according to Figure 3 The period of the spiral fiber grating to be manufactured is Λ=822.46um, and C=-1 is used to adopt a right-handed spiral fiber grating (clockwise spiral structure). Figure 4 The length of the grating external two-mode optical fiber L = 92.93cm. Figure 7 As shown in the mode evolution, according to the mode coupling characteristics of the spiral fiber Bragg grating, the right-handed spiral fiber Bragg grating produced converts the input fiber fundamental mode LP with left-handed circular polarization state at the set wavelength λ = 1560nm 01 Mode coupling is converted into LP carrying -1st-order orbital angular momentum in the same left-handed circular polarization state. 11Mode. Left-handed circular polarization state - 1st-order orbital angular momentum LP 11 mode (spin angular momentum is +1, opposite to orbital angular momentum) is composed of TM with a phase difference of π / 2 01 Mode and TE 01 Mode composition. Based on LP 11 Spin-orbit mapping properties of modes in transmission two-mode fibers, TM in left-handed circularly polarized modes in transmission fibers 01 Mode and TE 01 The effective refractive index difference of the mode is large (generally greater than 10 -6 ), a phase difference of Δφ=3π is generated at a transmission distance of L=92.93 cm, so the left-hand circular polarization state flips to the right-hand circular polarization state. 11 The mode is converted into completely right-handed circularly polarized light LP at the end of the transmission fiber 11 The device realizes the conversion of the input left-handed circular polarization state into the fundamental mode LP 01 Mode conversion to fully right-handed circularly polarized LP light 11 mold.

[0052]

Case 4

[0053] like Figure 8 As shown in the device structure, the output polarized light wavelength is set to λ = 1570nm, then according to Figure 3 The period of the spiral fiber grating to be manufactured is Λ=822.34um, and C=-1 is used to adopt a right-handed spiral fiber grating (clockwise spiral structure). Figure 4 The length of the grating external two-mode optical fiber L = 31.60cm. Figure 8 As shown in the mode evolution, according to the mode coupling characteristics of the spiral fiber Bragg grating, the right-handed spiral fiber Bragg grating is designed to input the elliptically polarized fiber fundamental mode LP at the set wavelength λ = 1570nm. 01 Mode coupling is converted into an LP carrying -1st-order orbital angular momentum in the same elliptical polarization state. 11 Mode. Elliptical polarization state-1st order orbital angular momentum LP 11 The mode can be decomposed into left-hand circular polarization mode and right-hand circular polarization mode. The left-hand circular polarization mode (spin angular momentum is +1, opposite to orbital angular momentum) is composed of TM with a phase difference of π / 2. 01 Mode and TE 01 Mode composition; the right-hand circular polarization mode (spin angular momentum is -1, in the same direction as the orbital angular momentum) is composed of an odd-mode HE with a phase difference of π / 2 21 Mode and even mode HE 21 Mode composition. Based on LP 11 Spin-orbit mapping properties of modes in two-mode transmission fibers, odd-mode HE in right-handed circularly polarized modes in transmission fibers21 Mode and even mode HE 21 The effective refractive index difference of the modes is extremely small (generally less than 10 -9 ), the phase difference is negligible when the transmission distance L = 31.60 cm, so the mode state is stable during the transmission process; while in the left-handed circularly polarized mode of the transmission fiber, the TM 01 Mode and TE 01 The effective refractive index difference of the mode is large (generally greater than 10 -6 ), a phase difference of Δφ=π is generated at a transmission distance of L=31.60 cm, so the left-handed circular polarization state flips to the right-handed circular polarization state. The final LP with elliptical polarization state 11 The mode is converted into completely right-handed circularly polarized light LP at the end of the transmission two-mode fiber 11 The device realizes the conversion of the input elliptically polarized state into the fundamental mode LP 01 Mode conversion to fully right-handed circularly polarized LP light 11 mold.

[0054] In summary, the present invention is based on the mode selection of spiral fiber grating and LP 1v The spin-orbit mapping characteristics of the mode in the transmission fiber realize a fiber-type tunable circularly polarized light conversion device, which can convert the input fiber fundamental mode with any polarization state at any set conversion wavelength λ into high-purity left / right circularly polarized LP 1v The present invention is compatible with various optical fiber devices and systems, has a simple manufacturing process, no power loss, and has unique characteristics such as miniaturization, integration and low cost.

[0055] The above are only preferred embodiments of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principles of the present invention, and these improvements and modifications should also be considered as the protection scope of the present invention. The structures, devices and operating methods not specifically described and explained in the present invention shall be implemented according to conventional means in the art unless otherwise specified and limited.

Claims

1. A fiber-type tunable circularly polarized light conversion device, characterized in that: The invention is composed of a spiral fiber grating (1) and a transmission fiber (2) connected together, and is used to convert an input fiber fundamental mode with an arbitrary polarization state and an arbitrarily set conversion wavelength λ into a high-purity left / right circularly polarized LP 1v model; The spiral fiber grating (1) is composed of a supporting transmission optical fiber LP 1v The mode is made of a long-period fiber grating with a set spiral direction C and period Λ made of optical fiber; The transmission optical fiber (2) is a fiber having a set length L, supporting the transmission optical fiber LP 1v Mode of optical fiber.

2. The optical fiber type tunable circularly polarized light conversion device according to claim 1, characterized in that: The period Λ of the spiral fiber grating (1) is set to: Λ=λ / (n 01 -n 1v ), In the formula, λ represents the set conversion wavelength, n 01 and n 1v They represent the LP in the optical fiber used to make the grating. 01 and LP 1v The effective refractive index of the mode, where LP lv Represents the linear polarization mode of the optical fiber with angular and radial orders l and v respectively.

3. The optical fiber type tunable circularly polarized light conversion device according to claim 1, characterized in that: The preset spiral direction C of the spiral fiber grating (1) is set to +1 or -1. When C is set to +1, it corresponds to a left-hand spiral fiber grating, that is, a counterclockwise spiral structure. At this time, the circularly polarized light conversion device converts the input fiber fundamental mode of any polarization state into a left-handed circularly polarized LP. 1v mode; when C is set to -1, it corresponds to a right-handed spiral fiber grating, that is, a clockwise spiral structure. At this time, the circularly polarized light conversion device converts the input fiber fundamental mode of any polarization state into a right-handed circularly polarized LP 1v model.

4. The optical fiber type tunable circularly polarized light conversion device according to claim 1, characterized in that: The supported transmission fiber LP 1v The length L of the transmission fiber (2) of the mode is set to: L=(2×q+1)×λ×|n TEv -n TMv | / 2, In the formula, q is a natural number, n TEv and n TMv Respectively represent the optical fiber LP in the transmission optical fiber 1v Degenerate angular polarization mode TE 0v and radial polarization mode TM 0v is the effective refractive index, and λ is the set conversion wavelength.

5. The optical fiber type tunable circularly polarized light conversion device according to claim 1, characterized in that: The production optical fiber and the transmission optical fiber (2) used to produce the spiral fiber grating (1) are used to support the transmission optical fiber LP 1v Any of the step-index or graded-index few-mode fibers, ring-core fibers, hollow-core fibers and photonic crystal fibers.

6. The optical fiber type tunable circularly polarized light conversion device according to claim 1, characterized in that: The spiral fiber grating (1) can be manufactured by any one of the fiber grating manufacturing methods including ultraviolet, mechanical, electric arc, carbon dioxide laser or heating twisting.

7. A method for manufacturing an optical fiber-type tunable circularly polarized light conversion device, characterized in that: The optical fiber type tunable circularly polarized light conversion device according to any one of claims 1 to 6 comprises the following steps: S1, in support of transmission optical fiber LP 1v Pattern production: a spiral fiber grating (1) having a set spiral direction C and period Λ is produced on an optical fiber; S2. A supporting transmission optical fiber LP with a length of L is reserved or externally connected at the output end of the manufactured spiral fiber grating (1). 1v A section of transmission optical fiber (2) for the mode.

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