121 results about "Refractive index modulation" patented technology

The invention discloses a fiber bragg grating femtosecond laser direct writing system and method based on light field regulation and control. The system comprises a femtosecond laser source, a polarization control module, a light beam expanding module, a light field modulation module, a 4f filtering imaging module, an oil immersed objective lens, a precision positioning and optical fiber clamping module, an observation module and a computer control module. The method comprises the following steps: firstly, fixing a standard single-mode optical fiber to be processed on a three-dimensional precision displacement platform; then programmable wavefront modulation is carried out on the femtosecond laser through a light field modulation module, and a multi-focus array is generated; then focusing the multi-focus array into the fiber core through an oil-immersed objective lens to realize one-time parallel inscribing of a plurality of refractive index modulation RIM regions; and finally, the computer control module controls the three-dimensional precision displacement platform to move at a constant speed in the axial direction of the optical fiber, and parallel integrated inscribing of a plurality of FBG structures is completed. According to the invention, the inscribing precision and inscribing efficiency of fiber bragg grating femtosecond laser direct writing are improved.

The invention discloses a preparation method of a polymer dispersed liquid crystal holographic grating with s polarization high diffraction characteristics, and belongs to the technical field of holographic optics. Raw materials comprise 60-90% of a thiol-ene monomer, 10-40% of liquid crystals, a photoinitiator accounting for 1.25% of the mass of the monomer, and a coinitiator accounting for 1.56% of the mass of the monomer. Light with the wavelength of 532 nm and the light intensity of 5-30 mW / cm < 2 > is used for carrying out double-interference photoetching to generate photochemical reaction so as to generate the polymer grating film, and the light is s polarized light. Under the optimal recording condition, delta n under s polarization can reach 1.93 * 10, and delta n under p polarization can reach 1.21 * 10. In combination with morphology analysis, it is found that refractive index modulation strongly depends on the proportion of a liquid crystal-rich phase to a polymer-rich phase in the grating. It is proved that the size of liquid crystal microdroplets formed by holographic recording is larger due to low recording intensity, and therefore the threshold driving voltage of the HPDLC grating is reduced.

The invention provides an acrylate monomer with a high refractive index and a preparation method and application thereof, the acrylate monomer has a structure as shown in a formula G1, G2 or G3, the refractive index of the acrylate monomer is 1.75 or above, so that a holographic recording medium has higher sensitivity and higher diffraction efficiency, and the holographic recording medium can be applied to the field of holographic recording. The holographic recording medium is used for a holographic grating, so that the holographic grating has high diffraction efficiency and high refractive index modulation degree.

The invention discloses a thiophene monomer, a holographic recording medium, a preparation method and a related device, the structural general formula of the thiophene monomer is shown in the specification, the refractive index of the monomer is larger than 1.8 and smaller than 1.9, the diffraction efficiency can be remarkably improved, the thiophene monomer is applied to preparation of a photopolymer type holographic recording medium, and the photopolymer type holographic recording medium with the sensitivity larger than 100 cm / mJ can be obtained. According to the holographic recording medium, the diffraction efficiency of the recording grating is larger than 95%, the refractive index modulation degree is larger than 0.1, and the shrinkage rate is lower than 1%, and further, the holographic recording medium can be used for preparing a volume holographic grating, a holographic optical element and an optical device.

The invention relates to the technical field of optical fiber device manufacturing, and discloses a femtosecond laser inscribing low-polarization-dependent-loss optical fiber grating method and system, and the method comprises the steps: firstly, synthesizing an initial phase comprising a flat-topped beam phase, an astigmatism correction phase and a defocus phase, and loading the initial phase to a spatial light phase modulator; therefore, a preset circular flat-top focusing light spot is generated. Secondly, collecting a three-dimensional light field image sequence of a focusing light spot in a low-power detection mode, reconstructing light intensity distribution, extracting effective focal depth and ovality characteristic parameters, dynamically optimizing a phase through a closed-loop feedback mechanism until light field characteristics reach a preset target, and obtaining an optimized phase; and finally, loading an optimized phase in a high-power inscribing mode, and controlling the axial scanning of the optical fiber to inscribe the grating. Accurate active regulation and control of the three-dimensional shape of the focused light field and closed-loop self-optimization of process parameters are realized, birefringence caused by anisotropy of a refractive index modulation area is inhibited from a physical mechanism, and polarization dependent loss of the fiber bragg grating is fundamentally reduced.

The invention discloses a 4, 4 '-bis (omega-alkenyl thioether) diphenyl sulfide monomer and a preparation method, the structural general formula of the 4, 4'-bis (omega-alkenyl thioether) diphenyl sulfide monomer is shown in the specification, n represents the number of methylene and is a positive integer, n = 1-10, the refractive index of a polymer obtained after the monomer and 4 '4-dimercapto diphenyl sulfide are polymerized is larger than 1.65 and smaller than 1.8, diffraction efficiency is remarkably improved, the preparation method is easy to operate, and the preparation method is suitable for industrial production. The invention further provides a photopolymer type holographic recording medium containing the monomer and a preparation method of the photopolymer type holographic recording medium, the sensitivity of the holographic recording medium is larger than 100 cm / mJ, the diffraction efficiency of a recording grating is larger than 95%, the refractive index modulation degree is larger than 0.1, the shrinkage rate is lower than 1%, and the preparation method is simple, controllable and suitable for industrial production. The invention also provides a volume holographic grating containing the holographic recording medium, a holographic optical element and an optical device.

The present invention belongs to the technical field of optical fiber sensing. Provided are a ring-type small-period long-period fiber grating sensor, and a preparation method therefor and the application thereof. A ring-type small-period long-period fiber grating provided in the present invention matches the cross-sectional shape of an optical fiber, and rings can more effectively expand the area of each refractive index modulation region in the cross section of the optical fiber, such that the ring-type grating has large refractive index modulation regions in both the axial direction and longitudinal direction of the optical fiber, and the intensities of a Bragg resonance peak and a cladding mode resonance peak can thus be simultaneously enhanced. Therefore, the Bragg resonance peak and the cladding mode resonance peak can be simultaneously observed in a transmission spectrum of the ring-type grating, such that simultaneous measurement of an ambient refractive index and temperature can be realized, and there is no longer a need to observe a reflection peak, thereby simplifying multi-parameter sensing test steps of the small-period long-period fiber grating.

The invention discloses a dithiocarbamate monomer, a holographic recording medium, a preparation method and a related device, the structural general formula of the monomer is as shown in G1 and G2, R1 represents any one of hydrogen, halogen and C1-C4 alkyl, R3 represents any one of hydrogen, halogen and C1-C4 alkyl, A1 represents C1-C4 alkyl, A2 represents hydrogen or methyl, n is a positive integer, and n = 1-10. The dithiocarbamate monomer provided by the invention has high refractive index, and the holographic recording medium with high sensitivity, high diffraction efficiency and high refractive index modulation degree can be obtained by applying the dithiocarbamate monomer to preparation of the photopolymer holographic recording medium; holographic recording media can be used to prepare volume holographic gratings, holographic optical elements, and optical devices.

The invention provides a photopolymer system, a grating device containing a chirp structure and a preparation method of the grating device. Visible light and ultraviolet light dual initiators and azobenzene polymerizable acrylate monomers are introduced into the photopolymer system; by utilizing the characteristics that an acrylate group can be used as a writing monomer to participate in a copolymerization process and an azobenzene group can be subjected to continuous photoisomerization during holographic exposure, a visible light photoinitiator and an ultraviolet light initiator driving system are reacted and cross-linked in sequence; a chirp structure is induced to be generated in the formed volume holographic grating while the photopolymer system records interference fringes, so that grating period change caused by material shrinkage is effectively compensated, the angle response bandwidth of the grating is remarkably widened, the requirement for refractive index modulation of the photopolymer system is reduced, and the optical grating has a wide application prospect. According to the invention, the selection range of the photopolymer system is widened, the overall aging resistance of the material system is improved, and the service life of the grating device is prolonged.

The invention relates to a quaii-BIC chiral metasurface device based on refractive index modulation and a preparation method and application thereof.The chiral metasurface device comprises a plurality of sub-wavelength structure partitions which are sequentially arranged along the X axis, and every two adjacent sub-wavelength structure partitions are rotationally and symmetrically arranged relative to the Y axis; a sub-wavelength structure in the sub-wavelength structure partition comprises at least two optical dielectric layers which are stacked along the Z axis, at least one sub-wavelength structure in the sub-wavelength structure partition is obliquely arranged relative to the Y axis, and a refractive index difference exists between the at least two optical dielectric layers, so that the metasurface device realizes intrinsic chirality. The metasurface device realizes tunable strong intrinsic chirality at multiple wavelengths, and the preparation method has the advantages that the processing difficulty is low, the thickness of the optical dielectric layer is low, the thickness and the inclination angle of the optical dielectric layer do not need to be accurately controlled, the lift-off process is compatible, and high-precision large-area metasurface device preparation can be realized.

The invention discloses a chirp grating design method and device, equipment and a storage medium, and relates to the technical field of optical fibers, and the disclosed chirp grating design method comprises the steps: analyzing a preset target spectrum function to obtain a target grating structure parameter; layering the initial grating into a plurality of sub-grating regions with uniform periods based on the target grating structure parameters, and establishing a layered transmission matrix model; determining a refractive index modulation depth range of each sub-gate region according to the layered transmission matrix model; and performing iterative optimization on grating structure parameters of the initial grating according to the layered transmission matrix model, the target spectral function, the refractive index modulation depth range and a preset error function to obtain a target grating. The performance of the chirp grating can be optimized.

The invention discloses a dual-channel all-optical switch device based on two-dimensional Bi2O2Se and a design method of the dual-channel all-optical switch device. The core of the device is an optical interference structure formed by two-dimensional Bi2O2Se nanosheets arranged on a mica substrate. The same group of transient absorption spectrum data is obtained through a pumping-detection system, and is decoupled into two independent switching channels: a channel I is based on carrier relaxation dynamics, and switching is realized by detecting a ground state bleaching signal at a wave band of 560-670 nm; the channel II is based on refractive index modulation caused by a Kramers-Kronig relationship, and realizes switching by analyzing interference fringe signals formed by probe light between the upper surface of the nanosheet and the lower surface of the mica substrate. The invention also provides a quantitative design method of the device, and the method achieves the fitting of an interference fringe signal through building a transient refractive index model, and precisely solves the relative refractive index change dynamics. The dual-channel device realizes picosecond-level ultrafast response (the channel I is 38.1 ps, and the channel II is 65.8 ps) and low-power-consumption operation (mJ / cm < 2 > magnitude), and the channel switch ratios respectively reach 1.74 and 1.93.

The invention provides a polymer composition, a polymer film material, a holographic grating, a preparation method of the holographic grating, an optical film material and display equipment. The polymer composition comprises a first polymerizable monomer, a second polymerizable monomer and a film-forming resin. The first polymerizable monomer is a non-liquid crystal monomer; the second polymerizable monomer is a liquid crystal monomer, the second polymerizable monomer comprises an active group, and the second polymerizable monomer can be subjected to a copolymerization reaction with the first polymerizable monomer through the active group under illumination. The refractive index modulation degree of the optical film material can be improved by using the polymer composition.

The invention relates to the technical field of holographic gratings, in particular to a holographic grating with a high refractive index modulation degree and a preparation method thereof, and the preparation method comprises the steps: coating a grating substrate with a precursor material to form a coating, and preparing a holographic dry plate with a holographic material layer; performing interference exposure on the holographic plate to obtain a semi-finished grating; bleaching the semi-finished product grating, and soaking the semi-finished product grating in an extraction liquid to obtain a grating precursor with a groove; and filling the groove with a fluorine-containing polymer dopant to obtain the holographic grating. The part, corresponding to the exposure bright area, of the grating precursor with the grooves is a polymer with a high refractive index, the inert body in the exposure dark area is removed, air is left, the grooves are formed in the surface of the grating, the appearance of the grooves fluctuates, the grooves are filled with low-refractive-index substances, and finally the high-refractive-index substances in the bright area are formed. The dark area is of a grating structure made of a low-refractive-index material; by adopting a two-step processing method, the holographic grating without light leakage in the reverse direction can be manufactured.

A dynamically tunable optical mirror named as a resonant cavity switching (RCS) device and a refractive index modulating (RIM) device are disclosed. The RCS device is comprising a nanoporous piezoelectric III-nitride material layer, such as GaN, AlN, AlScN, AlGaScN or their alloys sandwiched between a high-reflectivity distributed Bragg reflector (DBR) and a lower-reflectivity output DBR. The RIM devise is comprising the nanoporous III-nitride material layer. The nanoporous layer, patterned with interdigital transducers (IDTs), is actuated via surface acoustic waves (SAWs) or electric fields to induce rapid, reversible modulation of its effective refractive index. This enables sub-nanosecond switching between resonant and off-resonant optical states, facilitating efficient energy extraction, optical pulse carving, or phase control.

The invention discloses an unsaturated phenyl ether monomer, a holographic recording medium, a preparation method and a related device, the structural general formula of the monomer is as shown in G1 and G2, R1 represents any one of R2, A1 and A2 independently represent any one of hydrogen and phenyl, A3 represents hydrogen or methyl, A4 represents C1-C4 alkyl or phenyl, n is a positive integer and n = 1-5. The unsaturated phenyl ether monomer provided by the invention has high refractive index and is in a liquid state, and the holographic recording medium with high sensitivity, high diffraction efficiency and high refractive index modulation degree can be obtained by applying the unsaturated phenyl ether monomer to preparation of the photopolymer type holographic recording medium.

This optical integrated circuit comprises an optical waveguide device, a light-emitting device, and a support unit. The optical waveguide device includes a substrate, and an optical waveguide layer that is disposed on the substrate and includes an input coupler and an optical waveguide. The light-emitting device is spaced apart from the optical waveguide device. The light-emitting device includes a light-emitting layer and a phase modulation layer. The phase modulation layer includes a base layer and a plurality of different refractive index regions. The support unit includes a first support portion in which one device is disposed, and a second support portion that supports the other device. The distance between the optical waveguide device and the light-emitting device is smaller than the width of the second support portion in the direction in which the one device and the second support portion are lined up.

The invention relates to the technical field of optical fiber sensing and optical fiber device manufacturing, and discloses a femtosecond laser-inscribing polarization-maintaining fiber grating method and system for vector sensing, and the method comprises the following steps: obtaining a stress region image of a polarization-maintaining fiber through a CCD camera, recognizing the slow axis direction of the fiber through image processing, rotating the fiber, and obtaining the stress region image of the polarization-maintaining fiber; an included angle of 45 degrees is formed between the slow axis direction and a preset incident plane of the femtosecond laser; calculating a conjugate phase of wavefront aberration generated when femtosecond laser penetrates through a fiber coating layer and a cladding and is focused to a fiber core, and generating a phase diagram for loading a spatial light modulator; after being modulated by the spatial light modulator, a light beam emitted by the femtosecond laser enters and is focused on the fiber core along the direction of an included angle of 45 degrees, and a grating structure is formed by combining axial scanning and inscribing. Accurate automatic alignment in the fast and slow axis direction and active compensation of transmission aberration are achieved, refractive index modulation birefringence forming a specific included angle with the inherent birefringence axis of the optical fiber can be effectively induced, and therefore the polarization-maintaining fiber grating with the highly controllable reflection spectrum and the asymmetric double-peak characteristic is engraved.

The invention discloses a liquid crystal composition which comprises at least one of compounds in a general formula I, at least one of compounds in a general formula II and at least one of compounds in a general formula III. According to the invention, the liquid crystal composition has a high refractive index. Specifically, the compound as shown in the general formula I can increase the intersolubility of the liquid crystal composition while providing a relatively high refractive index for the liquid crystal composition, and has good stability to both photoelectricity and thermoelectricity; the compound in the general formula II can keep good solubility with other compounds while providing a relatively high refractive index for the liquid crystal composition; and the compound in the general formula III is an ester liquid crystal monomer compound, so that the liquid crystal composition has more diversity, and the stability of the whole liquid crystal system is higher. The invention also discloses a holographic polymer dispersed liquid crystal grating which has higher diffraction efficiency and refractive index modulation degree.

The invention relates to the technical field of multimode interference, and provides a central wavelength tunable multimode interference device which comprises an input waveguide region, a multimode interference region and an output waveguide region which are connected in sequence, the multimode interference region comprises a core layer, the core layer is made of a high-refractive-index material, and the output waveguide region is made of a high-refractive-index material. And a modulation electrode structure for modulating the refractive index of the core layer is arranged on the multimode interference region. The invention further provides a manufacturing method of the multimode interference device with the tunable central wavelength and a coherent modulator. Refractive index modulation is carried out on the core layer of the multi-mode interference area through the modulation electrode structure, in the multi-mode interference area, the effective refractive index directly determines the self-mapping point positions of different wavelengths, therefore, the effect of tunable central wavelength can be achieved through refractive index modulation, and through selection of different bias voltages, the tunable wavelength of the multi-mode interference area can be achieved. And the output effect of the optical power in the output waveguide is tuned.

The invention discloses an apodized FBG circle-by-circle inscribing system and method based on a variable radius method, and relates to the technical field of optical fiber inscribing, and the system comprises a laser beam shaping module, an optical fiber track control module and an optical fiber real-time monitoring module. The laser beam shaping module generates laser and focuses the laser to form a refractive index modulation area; the optical fiber real-time monitoring module monitors the side mode rejection ratio and the reflectivity of a reflection spectrum in real time, observes the pose of the ring core optical fiber and adjusts the pose through the optical fiber track control module, and it is ensured that a modulation area is located on the fiber core all the time. The optical fiber track control module clamps the ring core optical fiber, controls the ring core optical fiber to move on the Y axis and the Z axis according to sine and cosine functions respectively to form an annular inscribing track and step along the X axis (axial direction) according to a preset grating period, and the radius of each annular track changes along the X axis according to Gaussian-like distribution to achieve apodization distribution. The system effectively improves the side mode suppression ratio to 20-25dB (optimal Gaussian distribution), keeps high reflectivity, remarkably improves the spectrum quality, and is suitable for the fields of mode division multiplexing, optical fiber sensing and the like.

The application discloses a kind of optical fiber side light extraction structure and method, belong to optical fiber side light extraction technical field, structure has including femtosecond grating light extraction component, filter component including filter layer and with slit light shielding layer, and detection component.The method includes: with grating diffraction separation optical signal in fiber core, with filter component filters optical signal, with detector receives signal.The application is by femtosecond laser in fiber core and writes small refractive index modulation area, with diffraction effect will transport light be introduced with specific angle to side, again cooperate external filter and metal slit and constitute spatial filter, physically block the stray light deviating from preset angle.This internal diffraction+external filter synergic mechanism avoids physical damage optical fiber surface, and realizes high purity, high directional signal extraction under micro size.

The application discloses a phase mask plate preparation method for inhibiting a Fabry-Perot effect, and comprises the following steps: a dispersion fiber grating model is established, and reflection spectrum, transmission spectrum and group delay curve of the dispersion fiber grating are obtained through simulation; an ultra-Gaussian cut-off function model is established; according to the reflection spectrum and the transmission spectrum of the dispersion fiber grating and the ultra-Gaussian cut-off function, the reflection spectrum, the transmission spectrum and the group delay curve of the optimized dispersion fiber grating are obtained through simulation, and then a refractive index modulation depth distribution curve of a grating area of the phase mask plate is obtained; the refractive index modulation depth distribution curve of the grating area of the phase mask plate is optimized to obtain an optimized refractive index modulation depth distribution curve; a diffraction efficiency distribution curve and a groove depth of the phase mask plate are calculated; and the phase mask plate is obtained according to the groove depth of the phase mask plate. According to the application, the groove depth distribution of the phase mask plate used for writing is only adjusted, the Fabry-Perot effect can be effectively inhibited, and therefore the reflection spectrum flatness of the dispersion fiber grating is improved.

The invention belongs to the field related to information security and identity authentication, and particularly relates to a reconfigurable optical PUF (Physical Unclonable Function) based on a photorefractive effect and an authentication system and method thereof, the reconfigurable optical PUF has the stable cross-linked structure characteristic of a solid optical PUF, and a reconfiguration principle based on refractive index modulation of the photorefractive effect is fused. On the basis, the authentication method and system of the reconfigurable optical PUF based on the photorefractive effect are constructed; in the system, two paths of laser illumination PUF (Physical Unclonable Function) of detection and pumping are coupled from a light path structure by adopting a coupling device, an arranged laser power regulation module can regulate the power of the pumping laser, control the total energy of pumping photons injected into the optical PUF, excite a carrier self-built field to modulate the carrier self-built field or other polar molecules, and control the light path of the optical PUF. Therefore, the scattering characteristic of the optical PUF can be dynamically reconstructed in a controllable state. The PUF is illuminated by detection laser to form speckles to generate a key for identity authentication. The method has the advantages of high safety, high reliability and the like, and is suitable for the field with high safety requirements.

The invention discloses a photopolymer material, application thereof and a volume holographic grating, and relates to the technical field of polymer photosensitive materials. The photopolymer material comprises the following raw materials: a binder, an active monomer, a photoinitiator, a photosensitizer, a hydrogen donor and a sensitizer, the molar ratio of the active monomer to the photoinitiator is (8-12): 1; the molar ratio of the photosensitizer to the photoinitiator is 1: (15-25); the active monomer comprises a high-refractive-index monomer with the refractive index of 1.55-1.72 and a low-refractive-index monomer with the refractive index of 1.44-1.50, and the molar ratio of the high-refractive-index monomer to the low-refractive-index monomer is (0.7-1.3): 1. The photopolymer material meeting holographic recording can be prepared, and the prepared material is good in heat resistance, rapid in film forming, short in oxygen isolation exposure response time (as long as several seconds), high in refractive index modulation degree, high in sensitivity, high in diffraction efficiency, good in mechanical property and high in transmittance and can be prepared in a large area.

The application discloses a few-mode fiber double-cascaded mode converter and a high-power few-mode fiber laser. A core base mode and a core high-order mode converter and a core high-order mode and a cladding mode converter are cascaded on the few-mode fiber. The refractive index modulation distribution of the core base mode and the core high-order mode converter is uniformly distributed in the core center, and is used for coupling the core base mode to the core high-order mode. The refractive index modulation distribution of the core high-order mode and the cladding mode converter is distributed at the junction of the core and the cladding, and is used for coupling the core high-order mode to the cladding to form loss. The few-mode fiber double-cascaded mode converter is connected before an output end cap of the high-power few-mode fiber laser, and can inhibit stimulated Raman scattering in the large-mode-field few-mode fiber laser, so as to improve the output performance of the fiber laser.

The invention provides an epitaxial wafer with a refractive index modulation structure and a preparation method, and relates to the technical field of semiconductor lasers. The epitaxial wafer comprises a substrate, a buffer layer, an N limiting layer, an N waveguide layer, a quantum well layer, a P waveguide layer, a P limiting layer and a cap layer are sequentially arranged on the substrate from bottom to top, and the N waveguide layer sequentially comprises an N passive waveguide layer, an N reverse waveguide layer and an N active waveguide layer in the direction away from the N limiting layer. Along the direction away from the N waveguide layer, the In content in the quantum well layer is gradually reduced, and the As content is gradually increased. The content of Al in the P waveguide layer is gradually increased in the direction away from the quantum well layer. According to the epitaxial wafer with the refractive index modulation structure and the preparation method provided by the invention, a high catastrophe optical damage (COD) threshold, high output power and high photoelectric conversion efficiency are ensured, and resistance and thermal resistance are effectively reduced.

The invention concerns a hybrid optical device combining a silicon-on-insulator (SOI) waveguide platform (1) comprising a silicon waveguide (1a) with a thin-film electro-optical (EO) material such as lithium niobate or barium titanate forming a waveguide structure (2). The EO material waveguide structure (2) is bonded in optical contact with the SOI waveguide (1a), and electrodes (6) on its sides enable refractive index modulation via the electro-optical material Pockels effect. A coupling section (7), preferably comprising a tapered SOI waveguide (7a), transfers light between the SOI and EO structures with low loss. The device may include Bragg gratings (4a) or periodically poled sections (4b) in the EO layer for tunable or wavelength-selective modulation. The structure allows fast, reconfigurable light modulation, filtering, and signal routing on a CMOS-compatible platform, suitable for high-speed communication, optical computing, and sensing, offering a compact and efficient electro-optic integration solution.

The invention relates to the technical field of fiber bragg grating preparation, in particular to a method for preparing a fiber bragg grating through longitudinal line-by-line cold machining based on femtosecond laser direct writing, which comprises the following steps of: S10, controlling a femtosecond laser spot to move point by point along the axial direction of an optical fiber by taking a grating period as a step length, and applying a laser pulse at a corresponding position of each grating period, a local refractive index modulation area is formed; the at least m local refractive index modulation areas are periodically arranged in the axial direction of the optical fiber to form a longitudinal modulation track; s20, the femtosecond laser spot is controlled to move by a preset distance in the first direction perpendicular to the axial direction of the optical fiber; and the steps S10 and S20 are repeated until n longitudinal modulation tracks are formed, so that the local refractive index modulation areas located in the same cross section of the optical fiber can form a refractive index modulation plane, m refractive index modulation planes are obtained, and processing of the optical fiber grating is completed. Energy relaxation of the optical fiber material is facilitated, and a refractive index modulation structure is stably formed.

This invention provides a photopolymer composition, a holographic film, and a volume holographic grating. The photopolymer composition of this invention comprises a polymer matrix, a photopolymerizable monomer, and a photoinitiator; the polymer matrix comprises linear polyurethane, and the photopolymerizable monomer comprises a compound represented by Formula I. By using linear polyurethane as the polyurethane matrix and a compound represented by Formula I as the photopolymerizable monomer, the photopolymer composition of this invention possesses high refractive index modulation capability and low viscosity, enabling the formation of a holographic film with uniform material distribution, thereby achieving high diffraction efficiency in the volume holographic grating.