CN112910598B - Broadband optical orbital angular momentum multiplexing and demultiplexing method, device and storage medium - Google Patents
Broadband optical orbital angular momentum multiplexing and demultiplexing method, device and storage medium Download PDFInfo
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Abstract
The invention discloses a broadband optical orbital angular momentum multiplexing and demultiplexing method, a device and a storage medium, which are characterized in that signal light is emitted by a plurality of independent polarized and independent wavelength light sources, and is incident on a super-surface grating from different angles to generate OAM light beams with different topological charges and synthesize a beam of coaxial light beams in a 0-order diffraction direction, and the OAM light beams are emitted to realize OAM multiplexing; the coaxial light beam is incident on the ultra-surface grating, the OAM light beam is reduced into Gaussian light on different diffraction orders, and signal light is obtained after small-hole filtering, so that OAM demultiplexing is realized, and the complexity of a system is reduced. The problem of the broadband optical orbital angular momentum multiplexing and demultiplexing system complexity in the prior art is solved.
Description
Technical Field
The invention relates to the technical field of orbital angular momentum channel multiplexing and demultiplexing, in particular to a broadband optical orbital angular momentum multiplexing and demultiplexing method and device.
Background
The vortex beam carrying OAM (orbital angular momentum) has a circular ring shaped intensity profile and a helical phase wavefront exp (ilθ), where l is the topological charge number and θ is the azimuth angle. The OAM of the light may be implemented as a stand-alone information carrier for free-space optical communication. Due to the physical infinity of the OAM mode, it would present unprecedented opportunities for ultra-high capacity free-space optical communication.
OAM mode has the advantage of high bit rate and low bit error rate as a communication channel. A very critical issue with OAM multiplexed communications is the generation and multiplexing/demultiplexing of OAM beams. Traditionally, methods of generation/demultiplexing are based on bulk optical elements such as Q-plates, spiral phase plates and cylindrical mode converters, but are generally expensive and only respond to a specific polarization state. In addition, multiple optical couplers split the multi-channel OAM beam to create a re-coaxial combination, resulting in additional energy loss. The optical device has large volume and large number of optical elements, and further limits the application of the optical device in the current integration trend optical communication. To solve this problem, one solution is to replace the conventional optical element with a flat optical element. In recent years, a great deal of research has been conducted on chip-level OAM generation, and for example, binary optical devices such as dammann optical vortex gratings (Dammann optical vortex grating, DOVG) are also used for OAM mode division multiplexing. However, since the phase difference is determined by the refractive index, thickness, and wavelength of incident light of the material, it cannot be used as an optical device for broadband response. The OAM beam generated by the research based on the dielectric elliptic resonator on the silicon platform on the standard insulator also shows excellent performance, corresponding phase distribution is obtained by superposing a plurality of fork gratings, and then the arrangement of subsurface unit structures is obtained through the phase-rotation angle corresponding relation (P-B phase), so that the multiplexing and the de-multiplexing of the broadband OAM beam are realized; however, as the number of multiplexed channels increases, the energy utilization efficiency decreases, the energy of the higher order center spot is very weak, and it is a polarization sensitive multiplexer and demultiplexer since it follows the P-B phase principle. Therefore, a large number of polarization control devices such as half-wave plates or quarter-wave plates are required to adjust the polarization state of the light beam in the system, which further increases the complexity of the system. Therefore, in practical communication applications, the prior art has a disadvantage in consideration of the complexity of the practical communication situation.
Accordingly, there is a need for improvement and advancement in the art.
Disclosure of Invention
The invention aims to solve the technical problems of the prior art, provides a broadband optical orbital angular momentum multiplexing and demultiplexing method and device, and aims to solve the problem of system complexity in broadband optical orbital angular momentum multiplexing and demultiplexing in the prior art.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
in a first aspect, the present invention provides a broadband optical orbital angular momentum multiplexing and demultiplexing method, including:
a plurality of independent polarized and independent wavelength light sources emit signal light;
the signal light is incident on the super-surface grating from different angles to generate OAM light beams with different topological charges;
the OAM light beam is synthesized into a coaxial light beam in the 0-order diffraction direction to be emitted, so that OAM multiplexing is realized;
the coaxial light beam is incident on the ultra-surface grating, and the OAM light beam is restored to Gaussian light on different diffraction orders;
and the Gaussian light is subjected to small-hole filtering to obtain the signal light, so that OAM demultiplexing is realized.
In a second aspect, an embodiment of the present invention further provides a broadband optical orbital angular momentum multiplexing and demultiplexing device, including:
the signal light generation module is used for generating signal lights emitted by a plurality of independent polarized and independent wavelength light sources;
the OAM beam generation module is used for making the signal light incident on the ultra-surface grating from different angles to generate OAM beams with different topological charges;
the OAM beam synthesis coaxial beam module is used for synthesizing the OAM beams with different topological charges into a coaxial beam in the 0-order diffraction direction and emitting the coaxial beam;
the OAM beam reduction Gaussian light module is used for making the coaxial beam incident on the super-surface grating consistent with the device parameters used in the multiplexing process, and the OAM beams with different topological charges are reduced into Gaussian light on different diffraction orders;
and the signal light acquisition module is used for filtering the Gaussian light through a small hole to obtain the signal light.
In a third aspect, the present invention also provides a computer readable storage medium having stored thereon a broadband optical orbital angular momentum multiplexing and demultiplexing program which, when executed by a processor, implements the steps of the broadband optical orbital angular momentum multiplexing and demultiplexing method of any one of the above aspects.
The beneficial effects are that: compared with the prior art, the invention provides a broadband optical orbital angular momentum multiplexing and demultiplexing method and device, wherein the method comprises the steps of firstly, emitting signal light through a plurality of independent polarized and independent wavelength light sources, entering a super-surface grating from different angles, generating OAM light beams with different topological charges, synthesizing a coaxial light beam in a 0-order diffraction direction, and emitting the OAM light beam to realize OAM multiplexing; the coaxial light beam is incident on the ultra-surface grating, the OAM light beam is reduced into Gaussian light on different diffraction orders, and signal light is obtained after small-hole filtering, so that OAM demultiplexing is realized, and the complexity of a system is reduced.
Drawings
Fig. 1 is a flowchart of a specific implementation of a broadband optical orbital angular momentum multiplexing and demultiplexing method according to an embodiment of the invention.
Fig. 2 is a block diagram of a specific implementation of a broadband optical orbital angular momentum multiplexing and demultiplexing device according to an embodiment of the invention.
Detailed Description
In order to make the objects, technical solutions and effects of the present invention clearer and more specific, the present invention will be described in further detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
The vortex beam carrying OAM has a circular ring shaped intensity distribution and a helical phase wavefront exp (ilθ), where l is the topological charge number and θ is the azimuth angle. The OAM beam has wide application in the fields of optical operation, quantum information processing, super-resolution imaging and the like. Furthermore, the number of OAM eigenstates is theoretically infinite and the different OAM beams are mutually orthogonal. The OAM mode provides a new degree of freedom in addition to other inherent physical properties of the light, such as amplitude, frequency and phase. Thus, the OAM of the light may be implemented as a stand-alone information carrier for free-space optical communication. Due to the physical infinity of the OAM mode, it would present unprecedented opportunities for ultra-high capacity free-space optical communication.
OAM mode has the advantage of high bit rate and low bit error rate as a communication channel. A very critical issue with OAM multiplexed communications is the generation and multiplexing/demultiplexing of OAM beams. Because of the conservation law of the OAM mode, the generation and demultiplexing of the OAM beam can be generally performed by the same device, i.e., if one device can generate an OAM beam with a topology charge number of l, the OAM beam can be restored to a normal gaussian beam by passing the OAM beam through the same device with a reverse topology charge number (-l), and then the OAM beam is filtered by a small-hole filter to filter other topology charge components, thereby realizing demultiplexing. Traditionally, methods of generation/demultiplexing are based on bulk optical elements such as Q-plates, spiral phase plates and cylindrical mode converters, but are generally expensive and only respond to a specific polarization state. In addition, multiple optical couplers split the multi-channel OAM beam to create a re-coaxial combination, resulting in additional energy loss. The optical device has large volume and large number of optical elements, and further limits the application of the optical device in the current integration trend optical communication. To solve this problem, one solution is to replace the conventional optical element with a flat optical element. In recent years, a great deal of research has been conducted on the production of OAM at the chip level. For example, binary optical devices such as dammann optical vortex gratings (Dammann optical vortex grating, DOVG) are also used for OAM mode division multiplexing. However, since the phase difference is determined by the refractive index, thickness, and wavelength of incident light of the material, it cannot be used as an optical device for broadband response. Another study based on dielectric elliptical resonators on standard silicon-on-insulator platforms also showed excellent performance in the resulting OAM beam. Corresponding phase distribution is obtained by superposing a plurality of fork-shaped gratings, and then the arrangement of the subsurface unit structure is obtained through the phase-rotation angle corresponding relation (P-B phase), so that the multiplexing and the de-multiplexing of the broadband OAM wave beam are realized. However, as the number of multiplexed channels increases, the energy utilization efficiency decreases, and the energy of the center bright spot of the higher order is very weak. And is a polarization sensitive multiplexer and demultiplexer as it follows the P-B phase principle. Therefore, a large number of polarization control devices such as half-wave plates or quarter-wave plates are required to adjust the polarization state of the light beam in the system, which further increases the complexity of the system. In practical communication applications, therefore, the prior art is still to be improved and developed in consideration of the complexity of the practical communication situation.
In order to solve the problems in the prior art, the present embodiment provides a broadband optical orbital angular momentum multiplexing and demultiplexing method, by which the complexity of the system can be greatly reduced. When the embodiment is implemented, signal light is emitted by a plurality of independent polarized and independent wavelength light sources, and is incident on the ultra-surface grating from different angles, OAM light beams with different topological charges are generated, and a beam of coaxial light beams is synthesized in a 0-order diffraction direction and emitted, so that OAM multiplexing is realized; the coaxial light beam is incident on the ultra-surface grating, the OAM light beam is reduced into Gaussian light on different diffraction orders, and signal light is obtained after small-hole filtering, so that OAM demultiplexing is realized, and the complexity of a system is reduced.
Exemplary method
The broadband optical orbital angular momentum multiplexing and demultiplexing method of the present embodiment may be applied to a terminal device, as shown in fig. 1, and includes the following steps:
step S100, a plurality of independent polarized and independent wavelength light sources emit signal light.
The multiple light sources with independent polarization states and wavelengths described in the present invention, in particular, multiple Orbital Angular Momentum (OAM) channels that need multiplexing and demultiplexing, and allow multiple operating wavelengths and arbitrary polarization states.
And step 200, the signal light is incident on the super-surface grating from different angles to generate OAM light beams with different topological charges.
The super surface grating is an Au-SiO2-Au super surface grating, and is formed by a plurality of unit structure arrays on the same plane, the unit structure has higher reflectivity or transmissivity in a plurality of working wave bands through parameter optimization, and the phase modulation of 0 to 2 pi can be carried out on left-handed circularly polarized light or right-handed circularly polarized light.
Specifically, the plurality of cell structure arrays are two-layer structures or multi-layer structures. When the unit structure array is a two-layer structure, the two-layer structure is composed of a substrate and nano bricks arranged on the substrate. When the unit structure is a multilayer structure, the multilayer structure is formed by superposing a substrate, a dielectric layer and a nano brick from bottom to top.
And step S300, the OAM light beams are combined into a beam of coaxial light beams in the 0-order diffraction direction to be emitted, so that OAM multiplexing is realized.
The ultra-surface grating in the broadband OAM multiplexing and demultiplexing device with any polarization response is a binary phase vortex Dammann grating based on a P-B phase ultra-surface. The optical transfer function of the binary phase vortex Dammann grating based on the P-B phase ultrasonic surface can be expressed as follows:
is the phase delay of the beam through the grating, T is the period of the super surface grating, N is the number of channels to be multiplexed, m is the number of channels to be multiplexed from +.>To->Diffraction order of>Is normalized to the total power to an nth order power, deltal is the interval of the topological charge number and θ is the azimuth angle. To realize the function of a P-B phase ultra-surface grating, according to phi (x, y) =phi DOVG And (x, y) determining to obtain corresponding phase distribution, and then obtaining the arrangement of the subsurface unit structure through the phase-rotation angle corresponding relation.
Since light beams with any polarization state can be linearly combined by left circularly polarized light and right circularly polarized light, light beams incident with any polarization state can be divided into left circularly polarized light and right circularly polarized light. When the phase response of left circularly polarized light of the super surface grating is:
according to the characteristic that the phase response of the P-B phase left circularly polarized light and the right circularly polarized light are mutually conjugated and the binarization phase characteristic of the Dammann grating, the phase response of the right circularly polarized light of the super surface grating is as follows:
although the phase response of left circularly polarized light and right circularly polarized light are opposite, the grating phaseAnd simultaneous flipping of the vortex phase exp (im delta l theta) results in no change in the diffraction order and the topological charge number of each diffraction order. Since light beams of any polarization state can be linearly combined by left circularly polarized light and right circularly polarized light, the gratings have the same response to light beams of any polarization. The Dammann grating can realize the same response in a wide band by the broadband response characteristic of the super surface. Therefore, the binary phase vortex Dammann grating based on the P-B phase ultrasonic surface can be combined with means such as wavelength division multiplexing, partial division multiplexing and the like.
When a beam of light E m Incident on the super-surface grating from a specific diffraction angle, the emergent light in the 0-order diffraction direction is A m ＝E m *exp(iml m θ). When N beams of light are incident on the super-surface grating from different diffraction angles, the emergent light in the 0-order diffraction direction isThe N beams pass through the ultra-surface grating, load different orbital angular momentum and synthesize a coaxial beam in the 0-order diffraction direction for emergent, thus realizing broadband OAM multiplexing of arbitrary polarization.
In step S400, the coaxial light beam is incident on the super-surface grating, and the OAM light beam is reduced to gaussian light at different diffraction orders.
And S500, filtering the Gaussian light through a small hole to obtain the signal light, and realizing OAM demultiplexing.
The specific demultiplexing process in step S400 and step S500 is to reverse the processes described in step S200 and step S300, so as to implement wideband OAM demultiplexing with arbitrary polarization.
In practice, a special optimization scheme combines mode division multiplexing, wavelength division multiplexing and polarization division multiplexing, and can realize ultra-large capacity optical communication by using multiple operation mode and multiple working wavelengths and two orthogonal polarization multiplexing.
Specifically, a laser, a wavelength division multiplexing module, an IQ modulator, a frequency division multiplexing module, a 1×n fiber coupler and a super surface grating are sequentially placed as multiplexing ends, and the laser is used for emitting light beams with different wavelengths; the wavelength division multiplexing module is used for performing wavelength division multiplexing on the light beam; the IQ modulator is used for modulating a signal to be transmitted onto the light beam; the polarization multiplexing module is used for dividing the modulated light beam into two orthogonal light beams, and synthesizing one light beam after polarization multiplexing; the 1 XN optical fiber coupler divides the light beam into N light sources simulating a plurality of independent polarization states and independent wavelengths. The N beams are incident on the ultra-surface grating along a specific diffraction angle, OAM beams with different topological charges are generated, and a coaxial beam is synthesized in a 0-order diffraction direction to be emitted, so that the combination of OAM mode division multiplexing, wavelength division multiplexing and polarization division multiplexing is completed.
In summary, the present embodiment provides a broadband optical orbital angular momentum multiplexing and demultiplexing method, and the present embodiment firstly emits signal light through a plurality of independent polarized and independent wavelength light sources, and the signal light is incident on a super-surface grating from different angles, so as to generate OAM light beams with different topological charges, and synthesize a coaxial light beam in a 0-order diffraction direction, and the OAM multiplexing is implemented; the coaxial light beam is incident on the ultra-surface grating, the OAM light beam is reduced into Gaussian light on different diffraction orders, and signal light is obtained after small-hole filtering, so that OAM demultiplexing is realized, and the complexity of a system is reduced.
Exemplary apparatus
As shown in fig. 2, an embodiment of the present invention provides a broadband optical orbital angular momentum multiplexing and demultiplexing device, the device comprising: the signal light generation module 10, the OAM beam generation module 20, the OAM beam synthesis coaxial beam module 30, the OAM beam restoration gaussian optical module 40, and the signal light acquisition module 50.
Specifically, the signal light generating module 10 is configured to generate signal light emitted by a plurality of independently polarized, independent wavelength light sources. The plurality of light sources with independent polarization states and wavelengths, in particular a plurality of Orbital Angular Momentum (OAM) channels which need multiplexing and demultiplexing, and allow a plurality of working wavelengths and any polarization states.
The OAM beam generation module 20 is configured to make the signal light incident on the super surface grating from different angles, and generate OAM beams with different topology charges. The super surface grating is an Au-SiO2-Au super surface grating, and is formed by a plurality of unit structure arrays on the same plane, the unit structure has higher reflectivity or transmissivity in a plurality of working wave bands through parameter optimization, and the phase modulation of 0 to 2 pi can be carried out on left-handed circularly polarized light or right-handed circularly polarized light.
Specifically, the plurality of cell structure arrays are two-layer structures or multi-layer structures. When the unit structure array is a two-layer structure, the two-layer structure is composed of a substrate and nano bricks arranged on the substrate. When the unit structure is a multilayer structure, the multilayer structure is formed by superposing a substrate, a dielectric layer and a nano brick from bottom to top.
The OAM beam synthesis coaxial beam module 30 is configured to synthesize the OAM beams with different topological charges into a coaxial beam in the 0-order diffraction direction, and eject the coaxial beam. The ultra-surface grating in the broadband OAM multiplexing and demultiplexing device with any polarization response is a binary phase vortex Dammann grating based on a P-B phase ultra-surface. The optical transfer function of the binary phase vortex Dammann grating based on the P-B phase ultrasonic surface can be expressed as follows:
is the phase delay of the beam through the grating, T is the period of the super surface grating, N is the number of channels to be multiplexed, m is the number of channels to be multiplexed from +.>To->Diffraction order of>Is the nth order power normalized to the total power, Δl is the interval of the topological charges and θ is the azimuth angle. To realize the function of a P-B phase ultra-surface grating, according to phi (x, y) =phi DOVG And (x, y) determining to obtain corresponding phase distribution, and then obtaining the arrangement of the subsurface unit structure through the phase-rotation angle corresponding relation.
Since light beams with any polarization state can be linearly combined by left circularly polarized light and right circularly polarized light, light beams incident with any polarization state can be divided into left circularly polarized light and right circularly polarized light. When the phase response of left circularly polarized light of the super surface grating is:
according to the characteristic that the phase response of the P-B phase left circularly polarized light and the right circularly polarized light are mutually conjugated and the binarization phase characteristic of the Dammann grating, the phase response of the right circularly polarized light of the super surface grating is as follows:
although the phase response of left circularly polarized light and right circularly polarized light are opposite, the grating phaseAnd simultaneous flipping of the vortex phase exp (im delta l theta) results in no change in the diffraction order and the topological charge number of each diffraction order. Since light beams of any polarization state can be linearly combined by left circularly polarized light and right circularly polarized light, the gratings have the same response to light beams of any polarization. The Dammann grating can realize the same response in a wide band by the broadband response characteristic of the super surface. Therefore, the binary phase vortex Dammann grating based on the P-B phase ultrasonic surface can be combined with means such as wavelength division multiplexing, partial division multiplexing and the like.
When a beam of light E m Incident on the super-surface grating from a specific diffraction angle, the emergent light in the 0-order diffraction direction is A m ＝E m *exp(iml m θ). When N beams of light are incident on the super-surface grating from different diffraction angles, the emergent light in the 0-order diffraction direction isThe N beams pass through the ultra-surface grating, load different orbital angular momentum and synthesize a coaxial beam in the 0-order diffraction direction for emergent, thus realizing broadband OAM multiplexing of arbitrary polarization.
The OAM beam reduction gaussian optical module 40 is configured to make the coaxial beam incident on the super surface grating consistent with the device parameters used in the multiplexing process, where the OAM beams with different topological charges are reduced to gaussian light in different diffraction orders.
The signal light acquisition module 50 is configured to obtain the signal light after the gaussian light is subjected to pinhole filtering.
Those skilled in the art will appreciate that implementing all or part of the above-described methods may be accomplished by way of a computer program stored on a non-transitory computer readable storage medium, which when executed, may comprise the steps of the above-described method embodiments. Any reference to memory, storage, database, or other medium used in embodiments provided herein may include non-volatile and/or volatile memory. The nonvolatile memory can include Read Only Memory (ROM), programmable ROM (PROM), electrically Programmable ROM (EPROM), electrically Erasable Programmable ROM (EEPROM), or flash memory. Volatile memory can include Random Access Memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in a variety of forms such as Static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double Data Rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous Link DRAM (SLDRAM), memory bus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM), among others.
In summary, the invention discloses a broadband optical orbital angular momentum multiplexing and demultiplexing method and device, which are characterized in that signal light is emitted by a plurality of independent polarized and independent wavelength light sources, and is incident on a super-surface grating from different angles, OAM light beams with different topological charges are generated, and a coaxial light beam is synthesized in a 0-order diffraction direction and emitted, so that OAM multiplexing is realized; the coaxial light beam is incident on the ultra-surface grating, the OAM light beam is reduced into Gaussian light on different diffraction orders, and signal light is obtained after small-hole filtering, so that OAM demultiplexing is realized, and the complexity of a system is reduced.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and are not limiting; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims (5)
1. A method for multiplexing and demultiplexing broadband optical orbital angular momentum, comprising:
the plurality of light sources emit signal light; the polarization and the wavelength of each light source are not mutually interfered and are different;
the signal light is incident on the super-surface grating from different angles to generate OAM light beams with different topological charges;
the OAM light beam is synthesized into a coaxial light beam in the 0-order diffraction direction to be emitted, so that OAM multiplexing is realized;
the coaxial light beam is incident on the ultra-surface grating, and the OAM light beam is restored to Gaussian light on different diffraction orders;
the Gaussian light is subjected to small-hole filtering to obtain the signal light, so that OAM demultiplexing is realized;
using a plurality of OAM modes, a plurality of working wavelengths and two orthogonal polarization multiplexing, making N beams incident on a super-surface grating along a specific diffraction angle, generating OAM beams with different topological charges, synthesizing a beam of coaxial beams in a 0-order diffraction direction and emitting the same, and realizing the combination of OAM mode division multiplexing, wavelength division multiplexing and polarization division multiplexing;
the ultra-surface grating is formed by a plurality of unit structure arrays on the same plane, and the unit structure arrays are of a two-layer structure or a multi-layer structure;
the unit structure array is of a two-layer structure and consists of a substrate and nano bricks arranged on the substrate;
the unit structure array is of a multilayer structure and is formed by superposing a substrate, a dielectric layer and a nano brick from bottom to top;
the unit structure array carries out 0 to 2 pi phase modulation on an incident light beam by changing the direction angle of the unit structure, and has high reflectivity or transmissivity in a plurality of working wave bands;
the super surface grating is specifically a binary phase vortex Dammann grating based on a P-B phase super surface, and the optical transfer function of the binary phase vortex Dammann grating can be expressed as:
wherein phi is x i is an imaginary unit, phi represents the phase of the vortex Dammann grating, T is the period of the space in the x direction of the grating, and m is the period of the space in the x direction of the gratingTo->Cm is a normalization coefficient, N is the number of OAM channels to be multiplexed, +.>Is the interval of the topological charge number, θ is the azimuth angle.
2. The broadband optical orbital angular momentum multiplexing and demultiplexing method according to claim 1, wherein the plurality of independently polarized, independent wavelength light sources are a plurality of orbital angular momentum OAM channels requiring multiplexing and demultiplexing, and comprise a plurality of operating wavelengths and an arbitrary polarization state.
3. The method for multiplexing and demultiplexing according to any of claims 1-2, wherein the light beam of any polarization state is formed by linearly combining left circularly polarized light and right circularly polarized light, the light beam of polarization state incident comprises left circularly polarized light and right circularly polarized light, and the optical transfer function of the phase response of the left circularly polarized light of the super surface grating is:
according to the characteristic that the phase responses of the P-B phase left circularly polarized light and the right circularly polarized light are mutually conjugated and the binarization phase characteristic of the Dammann grating, the optical transfer function of the right circularly polarized light phase response of the super-surface grating is as follows:
4. a broadband optical orbital angular momentum multiplexing and demultiplexing device, comprising:
the OAM beam synthesis coaxial beam module comprises a signal light generation module, an OAM beam synthesis coaxial beam module, an OAM beam restoration Gaussian light module and a signal light acquisition module;
the signal light generation module is used for generating signal lights emitted by the light sources; the polarization and the wavelength of each light source are not mutually interfered and are different;
the OAM beam generation module is used for making the signal light incident on the super-surface grating from different angles to generate OAM beams with different topological charges;
the OAM beam synthesis coaxial beam module is used for synthesizing the OAM beams with different topological charges into a coaxial beam in the 0-order diffraction direction and emitting the coaxial beam;
the OAM beam reduction Gaussian light module is used for making the coaxial beam incident on the super-surface grating consistent with the device parameters used in the multiplexing process, and the OAM beams with different topological charges are reduced into Gaussian light on different diffraction orders;
the signal light acquisition module is used for filtering the Gaussian light through a small hole to obtain the signal light;
using a plurality of OAM modes, a plurality of working wavelengths and two orthogonal polarization multiplexing, making N beams incident on a super-surface grating along a specific diffraction angle, generating OAM beams with different topological charges, synthesizing a beam of coaxial beams in a 0-order diffraction direction and emitting the same, and realizing the combination of OAM mode division multiplexing, wavelength division multiplexing and polarization division multiplexing;
the ultra-surface grating is formed by a plurality of unit structure arrays on the same plane, and the unit structure arrays are of a two-layer structure or a multi-layer structure;
the unit structure array is of a two-layer structure and consists of a substrate and nano bricks arranged on the substrate;
the unit structure array is of a multilayer structure and is formed by superposing a substrate, a dielectric layer and a nano brick from bottom to top;
the unit structure array carries out 0 to 2 pi phase modulation on an incident light beam by changing the direction angle of the unit structure, and has high reflectivity or transmissivity in a plurality of working wave bands;
the super surface grating is specifically a binary phase vortex Dammann grating based on a P-B phase super surface, and the optical transfer function of the binary phase vortex Dammann grating can be expressed as:
wherein phi is x i is the imaginary unit, the vortex phi represents the phase of the dammann grating, T is the period of the space in the x direction of the grating, n is the number of channels to be multiplexed, and m is the slaveTo->Cm is a normalization coefficient, N is the number of OAM channels to be multiplexed,is the interval of the topological charge number, θ is the azimuth angle.
5. A computer readable storage medium, having stored thereon a broadband optical orbital angular momentum multiplexing and demultiplexing program, which when executed by a processor, implements the steps of the broadband optical orbital angular momentum multiplexing and demultiplexing method according to any of claims 1-3.
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| CN105162587A (en) * | 2015-09-25 | 2015-12-16 | 华南师范大学 | Multi-user orbital angular momentum multiplexing network system and quantum key distribution method thereof |
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