Light beam control device, light beam control device setting method and light beam control method

Abstract

The present invention discloses a light beam control device, a setting method of the light beam control device and a light beam control method. The device comprises: a light source, multiple sections of optical fiber, a plurality of optical fiber controllers, and a direct / coherent photodetector. The present invention uses a simple and easy-to-implement optical fiber controller to control the curvature and other geometric parameters of multiple sections of optical fiber, so as to change the transmission matrix of the multiple sections of optical fiber, thereby changing the spatial, time and frequency domain characteristics of the optical signal in the multi-mode optical fiber.

Description

Technical Field

[0001] The present invention relates to optical control, and in particular to a light beam control device, a setting method of the light beam control device and a light beam control method. Background Art

[0002] Currently, because multimode optical fibers are manufactured by drawing fused silica preforms, there are inherent undetectable random deviations between the light beam propagating through them and the ideal structure of the fiber. Therefore, theoretical models of light beams in ideal multimode optical fibers are often considered to be inadequate to describe practical multimode optical fibers.

[0003] It is generally believed that random deviations are unpredictable and their effects grow with the increase of fiber length. Despite this, the transmission of light beams in multimode fibers is still deterministic. In recent years, multimode fibers have become one of the many hot research topics aimed at enhancing the capacity of optical communications and endoscopic imaging systems. Ideally, people hope to achieve multiple channels to communicate simultaneously through the transverse modes of the fiber. However, interference between different transmission modes and coupling errors between the guided modes of the fiber lead to interference between transmission channels. For example, the optical wavefront is shaped at the proximal end of the fiber to obtain the desired output light field at the distal end, which can achieve compensation of modal dispersion, distal beam convergence, image transmission, and mode set orthogonalization. In a system based on wavefront shaping, the control of the optical wavefront occurs in free space, and a spatial light modulator, digital micromirror device, or nonlinear crystal is generally used to control the incident wavefront. The shaped wavefront is coupled into the fiber and superimposed with the fiber guided mode. For a fixed transmission matrix of the fiber, this superposition determines the light field at the output end of the fiber. Therefore, in a fiber that supports N guided modes, wavefront shaping can provide up to N complex control degrees. However, the above methods are mainly limited by two aspects: (i) the high requirement of computing power, which makes the system time-consuming to implement; (ii) the lack of bending flexibility. Any bending or looping of the optical fiber will cause the change of its transformation matrix, which will seriously damage the imaging quality. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a light beam control device, which can control the curvature and other geometric parameters of a multimode optical fiber through an optical fiber controller to change the transmission matrix of the multimode optical fiber, thereby changing the light field distribution of the optical signal in the multimode optical fiber and the spatial, temporal and frequency domain characteristics of the optical signal in the optical fiber system.

[0005] In a first aspect, an embodiment of the present invention provides a light beam control device, comprising: a light source, multiple sections of optical fiber, a plurality of optical fiber controllers, and a direct / coherent photodetector;

[0006] The light source is used to provide a light signal;

[0007] If the pigtail of the device at the input end of the beam control device is a single-mode fiber, the single-mode fiber of the pigtail of the device at the input end is coupled and connected with the multiple sections of optical fiber; if the pigtail of the device at the input end of the beam control device is a multi-mode fiber, the multi-mode fiber is coupled and connected with the multiple sections of optical fiber; the multiple sections of optical fiber are composed of multiple sections of optical fibers of different specifications connected in series or in parallel, including: multi-mode fiber and / or few-mode fiber and / or large mode field fiber and / or single-mode fiber;

[0008] The direct / coherent photodetector is used to receive and detect the optical signal;

[0009] The optical fiber controller is used to control the stretching, squeezing, bending and twisting of the multiple sections of optical fiber.

[0010] A light beam control device according to an embodiment of the present invention has at least the following beneficial effects: through a simple and easy-to-implement optical fiber controller, the optical fiber controller is used to control the curvature and other geometric parameters of multiple sections of optical fiber to change the transmission matrix of the multiple sections of optical fiber, thereby changing the spatial, time and frequency domain characteristics of the optical signal in the multi-mode optical fiber.

[0011] According to some other embodiments of the light beam control device of the present invention, the optical fiber controller includes a single-mode optical fiber polarization controller;

[0012] The single-mode optical fiber polarization controller can act on a winding and twisting mechanical structure, including a 3-ring cat-ear type single-mode optical fiber polarization controller and an electrically controlled single-mode optical fiber polarization controller.

[0013] According to some other embodiments of the light beam control device of the present invention, each of the optical fiber controllers includes a plurality of adjustment sites, through which the plurality of adjustment sites are used to perform multi-point adjustment on the plurality of sections of optical fiber.

[0014] According to some other embodiments of the present invention, the light beam control device further includes: an optical subsystem for controlling the light signal, wherein the control includes: convergence control, divergence control, collimation control, beam expansion control, or one or more of the above.

[0015] According to some other embodiments of the present invention, the light beam control device further includes: a signal modulator for performing intensity modulation and / or phase modulation on the light signal.

[0016] According to some other embodiments of the present invention, the optical beam control device further includes: a feedback unit for detecting parameters of the direct / coherent photodetector output signal, wherein the parameters include: optical signal power and / or optical signal phase and / or optical signal delay and / or high-order dispersion.

[0017] In a second aspect, an embodiment of the present invention provides a method for setting a light beam control device, comprising:

[0018] The light source provides a light signal;

[0019] The pigtail of the input device to be regulated is coupled and connected with the multiple sections of optical fiber. If the pigtail of the device at the input end of the light beam regulation device is a single-mode fiber, the single-mode fiber of the pigtail of the device at the input end is coupled and connected with the multiple sections of optical fiber; if the pigtail of the device at the input end of the light beam regulation device is a multi-mode fiber, the multi-mode fiber is coupled and connected with the multiple sections of optical fiber; the multiple sections of optical fiber are composed of multiple sections of optical fibers of different specifications connected in series or in parallel, including: multi-mode fiber and / or few-mode fiber and / or large mode field fiber and / or single-mode fiber;

[0020] A plurality of optical fiber controllers are provided, and the plurality of optical fiber controllers are used to stretch, squeeze, bend, and twist the plurality of optical fiber segments, so that the time domain, frequency domain, and space domain parameters of the optical signals transmitted by the plurality of optical fiber segments are regulated;

[0021] A direct / coherent photodetector is provided to detect the optical signal and convert it into an electrical signal.

[0022] In the third aspect, an embodiment of the present invention provides a light beam control method, wherein the light beam is spatially controlled by the light beam control device to control the optical signal light field distribution and propagation direction of the light beam, and the light beam is applied to a line-of-sight beam deflection transmitter or a beam deflection transmitter receiver or a non-line-of-sight scattering convergence optical communication system.

[0023] The following beneficial effects can be obtained by the light beam control method:

[0024] The optical fiber controller is used to control the multiple sections of optical fiber, adjust the light field distribution and propagation direction of the optical signal, and realize spatial domain control of the light beam.

[0025] In a fourth aspect, an embodiment of the present invention provides a light beam control method, wherein the light beam is controlled in the time domain by the light beam control device to control the delay and high-order delay of the signal carried by the optical electric field intensity of the light beam, or the delay and high-order delay of the optical envelope signal, which is applied to a tuned optical delay line or an optoelectronic oscillator.

[0026] The following beneficial effects can be obtained by the light beam control method:

[0027] The optical fiber controller is used to control the multiple sections of optical fiber to adjust the delay and high-order delay of the signal carried by the optical electric field intensity, or the delay and high-order delay of the optical envelope signal, so as to achieve the control of the time domain characteristics of the light beam.

[0028] In the fifth aspect, an embodiment of the present invention provides a light beam control method, in which the light beam is controlled in the frequency domain by the light beam control device to control the frequency characteristics of the signal carried by the optical electric field intensity of the light beam or the frequency characteristics of the optical envelope signal, thereby realizing the control of the frequency response characteristics of the transmission link of the light beam, which is applied to a multimode optical fiber bandwidth extender or a microwave photonic filter or an optical filter.

[0029] The following beneficial effects can be obtained by the light beam control method:

[0030] By using a plurality of the optical fiber controllers to control the plurality of optical fiber sections at a plurality of locations in a transmission link, the frequency characteristics of the signal carried by the optical electric field intensity or the frequency characteristics of the optical envelope signal are regulated, thereby achieving regulation of the frequency response characteristics of the transmission link. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a schematic diagram of a framework of a light beam control device in an embodiment of the present invention;

[0032] Figure 2 It is a schematic diagram of the structure of a light beam control device in an embodiment of the present invention and a schematic diagram of its relationship with the optical fiber;

[0033] Figures 3A-3D is a schematic diagram of the output light field distribution of a light beam control device in an embodiment of the present invention;

[0034] Figure 4 It is a schematic diagram of the spatial light field control structure of a line-of-sight wireless optical communication transmitting end of a light beam control device in an embodiment of the present invention;

[0035] Figure 5 It is a schematic diagram of the optical field control structure of a line-of-sight wireless optical communication receiving end of a light beam control device in an embodiment of the present invention;

[0036] Figure 6 2 is a schematic diagram of a non-line-of-sight optical wireless communication system application of a light beam control device in an embodiment of the present invention;

[0037] Figure 7 is a schematic diagram of a time domain system application of a light beam control device in an embodiment of the present invention;

[0038] Figure 8 It is a schematic diagram of a frequency domain system application of a light beam control device in an embodiment of the present invention.

[0039] Figures 9A-9C 4.5 km MMF transmission 2 GBd / s signal bandwidth distribution diagram under different control states in an embodiment of the present invention. DETAILED DESCRIPTION

[0040] The following will be combined with the embodiments to clearly and completely describe the concept of the present invention and the technical effects produced, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0041] In the description of the present invention, if it involves a description of orientation, for example, the orientation or position relationship indicated by "upper", "lower", "front", "back", "left", "right", etc. is based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention. If a feature is referred to as being "set", "fixed", "connected", or "installed" on another feature, it can be directly set, fixed, or connected to the other feature, or it can be indirectly set, fixed, connected, or installed on the other feature.

[0042] In the description of the embodiments of the present invention, if "several" is involved, it means more than one, if "multiple" is involved, it means more than two, if "greater than", "less than" or "exceed" is involved, it should be understood as not including the number itself, if "above", "below" or "within" is involved, it should be understood as including the number itself. If "first" or "second" is involved, it should be understood as being used to distinguish technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0043] Embodiment 1

[0044] Reference Figure 1 , shows a schematic diagram of a beam control device in an embodiment of the present invention. A beam control device includes: a light source, a pigtail 10 of a beam control device input end device, a plurality of multi-segment optical fibers 20, a plurality of optical fiber controllers 30, and a direct / coherent photodetector.

[0045] If the pigtail 10 of the device at the input end of the beam control device is a single-mode optical fiber, the single-mode optical fiber 10 of the pigtail of the device at the input end is coupled and connected to the multi-segment optical fiber 20; if the pigtail 10 of the device at the input end of the beam control device is a multi-mode optical fiber, the multi-mode optical fiber is coupled and connected to the multi-segment optical fiber 20; the multi-segment optical fiber 20 is composed of multiple sections of optical fibers of different specifications connected in series or in parallel, including: multi-mode optical fiber and / or few-mode optical fiber and / or large mode field optical fiber and / or single-mode optical fiber.

[0046] A direct / coherent photodetector is used to receive and detect the optical signal;

[0047] The optical fiber controller 30 is used to control the stretching, squeezing, bending and twisting of the multiple sections of optical fiber 20 .

[0048] The light source generates an optical signal, which is transmitted to a direct / coherent photodetector for detection. Since the multi-section optical fiber 20 is provided with a plurality of optical fiber controllers 30, multi-node adjustment can be performed to change the transmission matrix of the multi-section optical fiber 20. The optical fiber controller 30 adjusts the nodes in the multi-section optical fiber 20 one by one to regulate the spatial / temporal / frequency characteristics of the optical signal.

[0049] The following describes the mechanism effect of using a single-mode fiber polarization controller to stretch, squeeze, bend, and twist a multimode optical fiber to control the propagation characteristics of optical signals.

[0050] Since the multimode optical fiber is bent, the longitudinal wave number in the cross-sectional direction of the multimode optical fiber is a non-constant number, and β′ represents the propagation parameter at the center of the optical fiber at x=0.

[0051] For optical signals propagating in multimode optical fibers, the propagation mode satisfies that the optical field characterized by phase is perpendicular to the optical fiber axis in any plane:

[0052] k z (x)θxθρ=β(x)θρ(x)=cst (1)

[0053] The curvature ρ(x) can be expressed as ρ(x)=ρ-x, and the expression of the longitudinal wave number is further obtained as:

[0054]

[0055] The approximate curvature radius in the above formula is much larger than the core radius. Therefore, in the Helmholtz equation function, the following exists:

[0056]

[0057] Due to the compression bending on the surface of the multimode optical fiber, the core of the multimode optical fiber undergoes uneven deformation, with x>0 along the y-axis representing compression and x<0 representing expansion. Conversely, the longitudinal deformation will cause the material Poisson's coefficient σ to produce lateral deformation, and the components of the deformation tensor can be expressed as:

[0058] ∈ xx =∈ zz =-σ∈ yy (4)

[0059]

[0060] The relative change in fiber density can be expressed as

[0061]

[0062] Based on the above, the Gladstone–Dale relationship can be approximated as (n-1) / η, which is a constant.

[0063]

[0064] By deducing the approximate relationship between the radius of curvature and the core radius, we can obtain

[0065]

[0066] In the Helmholtz equation n' appears only in The term, β', is approximately the first-order term k0n in the bent fiber, and it can be deduced that:

[0067]

[0068] It can be seen from equations (3) and (9) that the bending geometry effect and the compression effect have similar effects on the wave number, but they are produced in opposite directions, and the compression effect has an additional factor term.

[0069]

[0070] Therefore, when there is a compression effect, the Helmholtz equation can be rewritten as

[0071]

[0072] where ψ'> represents the light field of the bent fiber.

[0073] Multimode fiber transmission matrix

[0074] When the transmitting end has N modes, after the light beam is transmitted through the multimode optical fiber for a certain distance, the light field distribution of the light beam at the receiving end can be expressed as:

[0075]

[0076] Where xi and yi represent the input and output optical signals, respectively, 1≤i≤N. N orthogonal modes can be represented as an N-dimensional diagonal matrix, where each element represents a mode. Each mode is a function of the amplitude and propagation parameters and is related to the wavelength of the incident optical signal, as shown in the matrix in equation (12). TM NN represents an N*N dimensional transmission matrix, which is a random matrix.

[0077] According to the Eisenbud–Wigner–Smith eigenstate theory, when a light beam passes through a scattering medium (including multimode optical fiber), the main mode is a set of independent spatial / polarization input and output states, where the main mode is defined as an input state with a corresponding output state (speckle), and the output state remains constant as the wavelength of the light source changes.

[0078] In the Helmholtz equation, the principal mode is the eigenstate of the operator, which is usually called the Eisenbud–Wigner–Smith delay operator in quantum mechanics and generalized scattering phenomena, and the group delay operator in MMF, characterized by where T is the transfer matrix of the fiber and ω is the optical frequency. The dominant modes have the smallest wavelength dependence of any kind and correspond to the most abrupt temporal characteristics when Fourier transformed into the time domain. By minimizing the wavelength dependence, the dominant modes maximally decouple the spatial, spectral, and temporal properties of the medium, with a single state sufficient to describe the output over a wide range of wavelengths. Since the dominant modes also determine the fastest and slowest paths through the medium, they can be used to maximize or minimize the time light spends in the medium.

[0079] For the N orthogonal modes of the incident light, there is no coupling between the modes, and the transmission matrix can be regarded as a unit diagonal matrix. When the N orthogonal modes propagate a certain distance in the multimode fiber, the transmission matrix becomes randomized and coupling occurs between the modes. The commonly used method generally only controls the incident light beam x i In this embodiment, the transmission matrix of the multimode optical fiber is adjusted to obtain N degrees of freedom without changing the transmission matrix. 2 It reduces the inter-mode coupling and diagonalizes the transfer matrix.

[0080] Embodiment 2

[0081] Reference Figure 2 , shows a schematic diagram of the structure of a beam control device in an embodiment of the present invention and a schematic diagram of its working relationship with an optical fiber. The optical fiber controller in this embodiment is a single-mode optical fiber polarization controller to control the transmission matrix of a multi-mode optical fiber. The single-mode optical fiber polarization controller is a winding and twisting mechanical structure, through which the optical fiber is stretched, squeezed, bent, and twisted. The single-mode optical fiber polarization controller includes a 3-ring cat-ear single-mode optical fiber polarization controller and an electrically controlled single-mode optical fiber polarization controller.

[0082] If each fiber controller carries 3 adjustment sites, 3n adjustment sites can be introduced when n fiber controllers are used. The light source can be a continuous wave single mode laser.

[0083] like Figure 2As shown, multiple sections of optical fiber are wound around the optical fiber controller, and the curvature radius and Poisson coefficient of the multiple sections of optical fiber are changed by changing the different position states of the optical fiber controller. Therefore, the transmission matrix of the multiple sections of optical fiber can be continuously adjusted, and the output light field can be arbitrarily adjusted.

[0084] Reference Figures 3A-3D , shows a schematic diagram of the output light field distribution of a light beam control device in an embodiment of the present invention. The output light field distribution is adjusted by controlling the optical fiber controller to control multiple sections of optical fiber. As shown in the figure, Figures 3A-3D The dotted circles are the light field distribution centers. The light field distribution is inconsistent under different control states.

[0085] Embodiment 3

[0086] Reference Figure 4 , shows a schematic diagram of the structure of a beam control device for beam steering and beam forming in an optical wireless communication system in an embodiment of the present invention. In this embodiment, the direct / coherent photodetector is specifically in the form of a charge coupled device (CCD) receiving module. By setting an optical subsystem, the defocus angle of the light beam output by the beam control device is expanded to achieve the conversion of the spatial characteristics of the light beam after the beam control device into a free space light field distribution, thereby achieving free space light beam steering and beam forming. At the same time, by setting one or more CCD receiving modules, the power distribution of the optical signal in different spaces is detected, and it is used as a feedback signal for further using the beam control device to achieve beam steering and beam forming. In an actual optical wireless communication system, the CCD can be replaced by a photodiode, and the different spatial received powers are used as feedback signals for beam steering and beam forming through a low-speed radio frequency link.

[0087] Embodiment 4

[0088] Reference Figure 5 , showing a schematic diagram of wireless communication reception of a light beam control device in an embodiment of the present invention. There are complex media in the light beam transmission signal channel, such as atmosphere and water with turbulence effects. Due to the uneven medium, the light beam will flicker and the light spot will be distorted when passing through the complex medium, resulting in signal transmission interruption. As shown in the figure, the optical signal is generated by a light source and propagated in the form of a light beam. The light beam is transmitted to the optical subsystem through the complex medium in free space, and the optical subsystem converges the light beam for transmission to the light beam control device. By adjusting the optical fiber controller in the light beam control device to change the transmission matrix of the multiple optical fibers in the light beam control device, the distorted light beam is controlled to be at the center of the output light field and transmitted to the direct / coherent photodetector.

[0089] Embodiment 5

[0090] Reference Figure 6 , shows a schematic diagram of a non-line-of-sight optical wireless communication system application of a beam control device in an embodiment of the present invention. In this embodiment, the light beam is generated by a light source, and the light beam is subjected to light field control by a beam control device. The optical subsystem collimates and focuses the light beam after light field control and transmits it to the surface of the scattering medium. When the light beam is transmitted to the surface of the scattering medium, the light beam will be diffusely scattered, and only part of the light beam can be transmitted to the direct / coherent photodetector.

[0091] The light field of the light beam is adjusted by a beam control device to change the spatial distribution of the light field, thereby making the diffusely scattered light beam more concentrated and transmitted to the direct / coherent photodetector.

[0092] Embodiment 6

[0093] Reference Figure 7 , shows a schematic diagram of a time domain control system application of a light beam control device in an embodiment of the present invention. The system also includes: a direct / coherent photodetector to detect the delay and high-order delay of the signal carried by the optical field intensity, or the delay and high-order delay of the optical envelope signal.

[0094] The light beam generated by the light source is modulated by a signal modulator, and the delay and high-order delay of the signal carried by the optical field intensity of the modulated light beam, or the delay and high-order delay of the optical envelope signal, are regulated by a light beam control device. The regulated light signal is detected by a direct / coherent photodetector and converted into an electrical signal. During the regulation process, the electrical signal is observed by a direct / coherent photodetector, and the signal detected by the direct / coherent photodetector is fed back to the signal modulator through a vector network analyzer to feedback-regulate the modulation signal of the signal modulator, so that the delay and high-order delay carried by the detected optical field after multiple adjustments reach the optimal value. After the regulation process is completed, no feedback unit is required.

[0095] Since the relative delay between modes of a multimode fiber mainly depends on the eigenvalue of the modal solution of the multimode fiber, that is, the propagation wave number, the corresponding group delay is expressed as

[0096]

[0097] c is the speed of light in a vacuum. In a scattering medium, the pulse propagates at a group velocity that depends on The modal delay can therefore be calculated from the wavelength-dependent refractive index profile n(r). A small change in the value of n(r) is sufficient to change the relative modal delay.

[0098] According to the Eisenbud–Wigner–Smith eigenstate theory, when a light beam passes through a scattering medium (including multimode optical fiber), the main mode is a set of independent spatial / polarization input and output states, where the main mode is defined as an input state with a corresponding output state (speckle), and the output state remains constant as the wavelength of the light source changes.

[0099] In the Helmholtz equation, the principal mode is the eigenstate of the operator, which is usually called the Eisenbud–Wigner–Smith delay operator in quantum mechanics and generalized scattering phenomena, and the group delay operator in MMF, characterized by where T is the transfer matrix of the fiber and ω is the optical frequency. The dominant modes have the smallest wavelength dependence of any kind and correspond to the most abrupt temporal characteristics when Fourier transformed into the time domain. By minimizing the wavelength dependence, the dominant modes maximally decouple the spatial, spectral, and temporal properties of the medium, with a single state sufficient to describe the output over a wide range of wavelengths. Since the dominant modes also determine the fastest and slowest paths through the medium, they can be used to maximize or minimize the time light spends in the medium.

[0100] In an optical fiber system, modes with the same mode number M (M=2m+1) have the same propagation parameters, and these single modes with the same propagation parameters are divided into the same mode group. In a multimode optical fiber, there is strong coupling between the modes in the same group, and each group tends to appear in the form of a single pulse delay, and the delay of each group is the arithmetic mean of the delays of the modes in the group. For a standard OM3 or OM4 optical fiber with 18 (or sometimes 19) mode groups, the output pulse will show 18 independent delay amounts. In this embodiment, these 18 delay amounts can be changed by adjusting the beam control device, thereby realizing a tunable optical delay line and optoelectronic oscillator.

[0101] Embodiment 7

[0102] Reference Figure 8 , shows a schematic diagram of a frequency domain system application of a light beam control device in an embodiment of the present invention. The features of this embodiment include: a light source, a signal modulator, and a direct / coherent photodetector.

[0103] The light beam generated by the light source is modulated by a signal modulator, and multiple fiber controllers are used to control multiple sections of optical fiber in multiple locations in a transmission link. The fiber controller is used to regulate the frequency characteristics of the signal carried by the modulated optical field intensity or the frequency characteristics of the optical envelope signal, thereby regulating the frequency domain response characteristics after the transmission of multiple sections of optical fiber. During the regulation process, the electrical signal is observed by a direct / coherent photodetector, and the signal detected by the photodetector is fed back to the signal modulator through a vector network analyzer to feedback and adjust the modulation signal of the signal modulator, so that the frequency domain response of the detected optical signal reaches the optimal value after multiple adjustments. After the regulation process is completed, no feedback unit is required.

[0104] The frequency domain response control includes two application scenarios. The first is to introduce one or more beam control devices in a multimode fiber or few-mode fiber transmission link to expand the bandwidth limitation caused by inter-mode dispersion, thereby enhancing the transmission rate of multimode fiber and few-mode fiber. The second is the frequency domain processing of the signal modulated on the electric field intensity or power (envelope) of the optical signal, including but not limited to filtering, frequency domain dispersion control, frequency domain sampling and signal shaping. Figures 9A-9C , shows the bandwidth distribution diagram of 2GBd / s signal transmitted by 4.5km MMF under different control states in an embodiment of the present invention.

[0105] As mentioned above, by regulating the coupling of different modes to change the main mode transmission characteristics, the frequency response function (bandwidth) of optical fiber transmission can be regulated, which is suitable for: a. multimode optical fiber bandwidth extender; b. microwave photon filter; c. optical filter.

[0106] Embodiment 8

[0107] Please refer to Figure 1 , an embodiment of the present invention provides a method for setting a light beam control device, comprising: a light source provides a light signal;

[0108] The pigtail of the input device to be regulated is coupled and connected with the multiple sections of optical fiber. If the pigtail of the device at the input end of the light beam regulation device is a single-mode fiber, the single-mode fiber of the pigtail of the device at the input end is coupled and connected with the multiple sections of optical fiber; if the pigtail of the device at the input end of the light beam regulation device is a multi-mode fiber, the multi-mode fiber is coupled and connected with the multiple sections of optical fiber; the multiple sections of optical fiber are composed of multiple sections of optical fibers of different specifications connected in series or in parallel, including: multi-mode fiber and / or few-mode fiber and / or large mode field fiber and / or single-mode fiber;

[0109] A plurality of optical fiber controllers are provided, and the plurality of optical fiber controllers are used to stretch, squeeze, bend, and twist the plurality of optical fiber segments, so that the time domain, frequency domain, and space domain parameters of the optical signals transmitted by the plurality of optical fiber segments are regulated;

[0110] A direct / coherent photodetector is provided to detect the optical signal and convert it into an electrical signal.

[0111] The light source generates an optical signal, which is transmitted to a direct / coherent photodetector to be observed. Since a plurality of optical fiber controllers 30 are respectively provided on the multi-section optical fiber 20, the multi-section optical fiber 20 can be adjusted at multiple nodes to change the transmission matrix of the multi-section optical fiber 20. The optical fiber controller 30 adjusts the nodes of the multi-section optical fiber 20 one by one to regulate the spatial / temporal / frequency domain characteristics of the optical signal. The optical fiber controller 30 regulates the curvature and geometric parameters of the multimode optical fiber 20 to change the transmission matrix of the multimode optical fiber 20, thereby changing the spatial / temporal / frequency domain characteristics of the optical signal in the multimode optical fiber 20.

[0112] In other embodiments, by combining a squeezing structure and a bending structure to regulate a single-mode optical fiber or a multi-mode optical fiber, the stretching, squeezing, bending, and twisting control of the single-mode optical fiber or the multi-mode optical fiber can be achieved.

[0113] The following describes the mechanism effect of using a single-mode fiber polarization controller to stretch, squeeze, bend, and twist multiple sections of optical fiber to control the propagation characteristics of optical signals.

[0114] Since the multimode optical fiber is bent, the longitudinal wave number in the cross-sectional direction of the multimode optical fiber is a non-constant number, and β′ represents the propagation parameter at the center of the optical fiber at x=0.

[0115] For optical signals propagating in multimode optical fibers, the propagation mode satisfies that the optical field characterized by phase is perpendicular to the optical fiber axis in any plane:

[0116] k z (x)θxθρ=β(x)θρ(x)=cst (1)

[0117] The curvature ρ(x) can be expressed as ρ(x)=ρ-x, and the expression of the longitudinal wave number is further obtained as:

[0118]

[0119] The approximate curvature radius in the above formula is much larger than the core radius. Therefore, in the Helmholtz equation function, the following exists:

[0120]

[0121] Due to the compression bending on the surface of the multimode optical fiber, the core of the multimode optical fiber undergoes uneven deformation, with x>0 along the y-axis representing compression and x<0 representing expansion. Conversely, the longitudinal deformation will cause the material Poisson's coefficient σ to produce lateral deformation, and the components of the deformation tensor can be expressed as:

[0122] ∈ xx =∈ zz =-σ∈ yy (4)

[0123]

[0124] The relative change in fiber density can be expressed as

[0125]

[0126] Based on the above, the Gladstone–Dale relationship can be approximated as (n-1) / η, which is a constant.

[0127]

[0128] By deducing the approximate relationship between the radius of curvature and the core radius, we can obtain

[0129]

[0130] In the Helmholtz equation n' appears only in The term β' is approximately the first-order term k0n in the bent fiber, and it can be deduced that:

[0131]

[0132] It can be seen from equations (3) and (9) that the bending geometry effect and the compression effect have similar effects on the wave number, but they are produced in opposite directions, and the compression effect has an additional factor term.

[0133]

[0134] Therefore, when there is a compression effect, the Helmholtz equation can be rewritten as

[0135]

[0136] where ψ'> represents the light field of the bent fiber.

[0137] Multimode fiber transmission matrix

[0138] When the transmitting end has N modes, after the light beam is transmitted through the multimode optical fiber for a certain distance, the light field distribution of the light beam at the receiving end can be expressed as:

[0139]

[0140] where x i and iRepresent the input and output optical signals respectively, 1≤i≤N. N orthogonal modes can be represented as an N-dimensional diagonal matrix, where each element in the diagonal matrix represents a mode. Each mode is a function of the amplitude and propagation parameters and is related to the wavelength of the incident optical signal, as shown in the matrix in equation (12). TM NN represents an N*N dimensional transmission matrix, which is a random matrix.

[0141] According to the Eisenbud–Wigner–Smith eigenstate theory, when a light beam passes through a scattering medium (including multimode optical fiber), the main mode is a set of independent spatial / polarization input and output states, where the main mode is defined as an input state with a corresponding output state (speckle), and the output state remains constant as the wavelength of the light source changes.

[0142] In the Helmholtz equation, the principal mode is the eigenstate of the operator, which is usually called the Eisenbud–Wigner–Smith delay operator in quantum mechanics and generalized scattering phenomena, and the group delay operator in MMF, characterized by where T is the transfer matrix of the fiber and ω is the optical frequency. The dominant modes have the smallest wavelength dependence of any kind and correspond to the most abrupt temporal characteristics when Fourier transformed into the time domain. By minimizing the wavelength dependence, the dominant modes maximally decouple the spatial, spectral, and temporal properties of the medium, with a single state sufficient to describe the output over a wide range of wavelengths. Since the dominant modes also determine the fastest and slowest paths through the medium, they can be used to maximize or minimize the time light spends in the medium.

[0143] For the N orthogonal modes of the incident light, there is no coupling between the modes, and the transmission matrix can be regarded as a unit diagonal matrix. When the N orthogonal modes propagate a certain distance in the multimode fiber, the transmission matrix becomes randomized and coupling occurs between the modes. The commonly used method generally only controls the incident light beam x i In this embodiment, the transmission matrix of the multimode optical fiber is adjusted to obtain N degrees of freedom without changing the transmission matrix. 2 It reduces the inter-mode coupling and diagonalizes the transfer matrix.

[0144] Please refer to Figure 4 The method for setting up the light beam control device also includes: setting up an optical subsystem to defocus and expand the light signal.

[0145] By setting up an optical subsystem to expand the light beam output by the beam control device, the spatial characteristics of the light beam after the beam control device are converted into a free-space light field distribution, thereby realizing free-space optical beam guidance and beam forming. At the same time, by setting up one or more CCD receiving modules, the power distribution of the optical signal in different spaces is detected, and it is used as a feedback signal for further using the beam control device to realize beam guidance and beam forming. In actual optical wireless communication systems, CCDs can be replaced by photodiodes, and the different spatial receiving powers are used as feedback signals for beam guidance and beam forming through low-speed radio frequency links.

[0146] Please refer to Figure 7 / 8, the method for setting up the light beam control device also includes: setting up a signal modulator for modulating the light signal. The light beam generated by the light source is modulated by the signal modulator to change the optical electric field intensity and / or optical power at different times, thereby modulating the signal to be transmitted or processed. If the signal is modulated on the optical electric field intensity, it can be detected by a coherent photodetector. If the signal is modulated on the optical envelope (power), it can be detected by an intensity photodetector. Please refer to Figure 1 , a plurality of optical fiber controllers 30 are used to change the transmission matrix of the multimode optical fiber 20 to change the relative delay of the transmission mode.

[0147] The method for setting up the light beam control device also includes: setting up a feedback unit, and during the control process, feeding back the electrical signal parameters output by the direct / coherent photodetector to the signal modulator through a vector network analyzer.

[0148] Reference Figure 7 In the process of time domain system regulation, the delay and high-order delay of the signal carried by the optical electric field intensity in the multi-segment optical fiber transmission process, or the delay and high-order delay of the optical envelope signal can be changed by regulating the optical beam control device, thereby realizing a tunable optical delay line, an optoelectronic oscillator, a multimode optical fiber bandwidth extender, a microwave photon filter and an optical filter. The above delay is fed back to the signal modulator through a feedback unit composed of a network analyzer to feedback and adjust the optical beam. When the system reaches the optimal state, no feedback unit is required.

[0149] Reference Figure 8 In the frequency domain system regulation process, the frequency domain response characteristics that appear in the multi-segment optical fiber transmission process can be changed by regulating the beam control device, thereby realizing a tunable bandwidth extender, microwave photon filter and optical filter. The above frequency response parameters are fed back to the signal modulator through the feedback unit composed of the network analyzer to feedback and adjust the beam. When the system reaches the optimal state, no feedback unit is required.

[0150] An embodiment provides a beam control method, specifically referring to Embodiment 3, the beam is spatially controlled by the beam control device to control the optical signal light field distribution and propagation direction of the beam, and the beam is applied to a line-of-sight beam deflection transmitter or a beam deflection transmitter receiver or a non-line-of-sight scattering convergence optical communication system.

[0151] An embodiment of the present invention provides a light beam control method, specifically referring to Example 6, the light beam is controlled in the time domain by the light beam control device to control the delay and high-order delay of the signal carried by the optical electric field intensity of the light beam, or the delay and high-order delay of the optical envelope signal, which is applied to a tuned optical delay line or an optoelectronic oscillator.

[0152] An embodiment of the present invention provides a light beam control method. Specifically referring to Example 7, the light beam is controlled in the frequency domain by the light beam control device to control the frequency characteristics of the signal carried by the optical electric field intensity of the light beam or the frequency characteristics of the optical envelope signal, thereby realizing the control of the frequency response characteristics of the transmission link of the light beam, which is applied to a multimode optical fiber bandwidth extender or a microwave photonic filter or an optical filter.

[0153] The following beneficial effects can be obtained by the light beam control method:

[0154] By using a plurality of the optical fiber controllers to control the plurality of optical fiber sections at a plurality of locations in a transmission link, the frequency characteristics of the signal carried by the optical electric field intensity or the frequency characteristics of the optical envelope signal are regulated, thereby achieving regulation of the frequency response characteristics of the transmission link.

[0155] The embodiments of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in the relevant technical field without departing from the purpose of the present invention. In addition, the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

Claims

1. A light beam control device, characterized in that: include: Light source, multiple sections of optical fiber, several optical fiber controllers, direct / coherent photodetectors; The light source is used to provide a light signal; If the pigtail of the device at the input end of the beam control device is a single-mode optical fiber, the single-mode optical fiber is coupled and connected with the multiple sections of optical fiber; if the pigtail of the device at the input end of the beam control device is a multi-mode optical fiber, the multi-mode optical fiber is coupled and connected with the multiple sections of optical fiber; The multi-section optical fiber is composed of multiple sections of optical fibers of different specifications connected in series or in parallel, and the multi-section optical fiber includes: multi-mode optical fiber and / or few-mode optical fiber and / or large mode field optical fiber and / or single-mode optical fiber; The direct / coherent photodetector is used to receive and detect the optical signal; The optical fiber controller is used to control the stretching and / or squeezing and / or bending and / or twisting of the multiple sections of optical fiber.

2. The light beam control device according to claim 1, characterized in that: The optical fiber controller comprises a single-mode optical fiber polarization controller; The single-mode optical fiber polarization controller is a winding and twisting mechanical structure, including a 3-ring cat-ear type single-mode optical fiber polarization controller and / or an electrically controlled single-mode optical fiber polarization controller.

3. The light beam control device according to claim 1, characterized in that: Each of the optical fiber controllers includes a plurality of adjustment sites, through which the plurality of optical fiber sections can be adjusted at multiple points.

4. The light beam control device according to claim 1, characterized in that: Also includes: The optical subsystem is used to regulate the optical signal, and the regulation includes one or more of the following: convergence regulation, divergence regulation, collimation regulation, and beam expansion regulation.

5. The light beam control device according to claim 1, characterized in that: Also includes: A signal modulator is used to perform intensity modulation and / or phase modulation on the optical signal.

6. The light beam control device according to claim 5, characterized in that: Also includes: The feedback unit is used to detect the parameters of the direct / coherent photoelectric detector output signal, wherein the parameters include: optical signal power and / or optical signal phase and / or optical signal delay and / or high-order dispersion.

7. A method for setting a light beam control device, characterized in that: include: The light source provides a light signal; The pigtail of the input-end device to be regulated is coupled and connected with the multiple sections of optical fiber. If the pigtail of the input-end device of the light beam regulating device is a single-mode optical fiber, the single-mode optical fiber is coupled and connected with the multiple sections of optical fiber; if the pigtail of the input-end device of the light beam regulating device is a multi-mode optical fiber, the multi-mode optical fiber is coupled and connected with the multiple sections of optical fiber; The multi-section optical fiber is composed of multiple sections of optical fibers of different specifications connected in series or in parallel, and the multi-section optical fiber includes: multi-mode optical fiber and / or few-mode optical fiber and / or large mode field optical fiber and / or single-mode optical fiber; A plurality of optical fiber controllers are provided, and the plurality of optical fiber controllers are used to stretch, squeeze, bend, and twist the plurality of optical fiber segments, so that the time domain, frequency domain, and space domain parameters of the optical signals transmitted by the plurality of optical fiber segments are regulated; A direct / coherent photodetector is provided to detect the optical signal and convert it into an electrical signal.

8. A light beam control method, characterized in that: The light beam is spatially regulated by the light beam regulation device according to any one of claims 1 to 6 to control the light field distribution and propagation direction of the optical signal of the light beam.

9. A light beam control method, characterized in that: The light beam is controlled in the time domain by the light beam control device described in any one of claims 1 to 6 to control the delay and high-order delay of the signal carried by the optical electric field intensity of the light beam, or the delay and high-order delay of the optical envelope signal.

10. A light beam control method, characterized in that: The light beam is regulated in the frequency domain by the light beam regulation device described in any one of claims 1 to 6 to control the frequency characteristics of the signal carried by the optical electric field intensity of the light beam or the frequency characteristics of the optical envelope signal, thereby achieving regulation of the frequency response characteristics of the transmission link of the light beam.

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