CN106788703A - The OAM detection means of OV light beams - Google Patents

Abstract

A kind of OAM detection means of OV light beams is disclosed herein, including：DMD DMD, lens, multi-module optical fiber coupler, multimode fiber array and light power meter；Wherein, the lens are arranged at the diffraction pattern that the DMD is produced；The multi-module optical fiber coupler is arranged on the focal plane of the lens, and is connected to the multimode fiber array；The multi-module optical fiber coupler is accessed in one end of the multimode fiber array, and the other end connects the light power meter.The OAM detection means of this paper, can carry out parallel detection to the energy of multichannel OV light beams, substantially increase detection efficiency, and capacity usage ratio is greatly improved, and operate also more convenient and reliable.

Description

OAM detection device for OV beam

technical field

The present application relates to the technical field of optical communication, and in particular to an orbital angular momentum (Orbital Angular Momentum, OAM) detection device of an optical vortex (Optical Vortices, OV) light beam.

Background technique

With the rapid development of optical communication technology and the wide application of Dense Wavelength Division Multiplexing (DWDM) technology, devices used for optical signal transmission and processing are developing towards high integration and arraying. Various high-performance and ultra-high-speed switching systems are The communication connections between its internal elements and other external systems have put forward the requirements of high density, high bandwidth and low loss. As the demand for bandwidth increases, electrical interconnects have become a bottleneck between high-speed processors and high-speed networks. It has become an inevitable development trend to replace electrical interconnection with optical interconnection. At the same time, with the development of parallel technologies such as parallel multiprocessors, parallel optical interconnection has received extensive attention. Optical interconnection uses photons as information carriers to realize information exchange between computing units. Due to the high speed of optical interconnection, the independent propagation of light waves without interference, the large number of interconnections, the high interconnection density, low power consumption, the ability to avoid "electronic bottlenecks", and the realization of wavelength channels, etc., in computer systems, information processing The application of technology and other aspects is indispensable, mainly in data exchange, elimination of "electronic bottleneck" and topology. From the perspective of structure, the classification of optical interconnection can be divided into: interconnection within the chip, interconnection between chips, interconnection between circuit boards, and interconnection between computers; from the channel used for interconnection Look, it can be divided into: optical fiber interconnection, waveguide interconnection, free space interconnection, etc. Various structures have their own information processing functions. At the same time, optical interconnection technology also has great advantages compared with electrical interconnection in terms of communication bandwidth, equal distance transmission, anti-electromagnetic interference and low energy consumption.

Optical vortices (OV) are beams with a helical wavefront propagation direction. When the phase of the light wave has a helical wavefront structure, the wavefront rotates in a helical manner around the propagation axis. Optical vortex photons all have a definite orbital angular momentum (Orbital Angular Momentum, OAM) Orbital angular momentum is a characteristic parameter that characterizes optical vortices. Due to the destructive interference of the vortex beam itself, the far-field diffraction pattern of the beam appears as a bright ring with a dark spot in the center. Spiral wavefront and phase singularity are its two main features. According to the helical phase of the electric field that rotates around the optical axis by an integer multiple of 2π within the optical path of one wavelength, different orbital angular momentum beams can be characterized by topological charge L (Topological Charge), where L can take any integer. Theory and experiments show that each photon in the light field of such an orbital angular momentum beam has a specific orbital angular momentum L. In theory, the possible value range of L is all integers. Therefore, the topological charge of the optical vortex can be used to complete numerical control, so that it can be fully applied in photon computing, superconducting thin films, quantum information, free space optical communication, etc.

In the related art, the detection end of the OAM detection system uses a single-mode optical fiber to detect one of the signals. First of all, it is necessary to restore the coaxial multi-channel OAM signal to a Gaussian point, couple one of the Gaussian points into a single-mode fiber, and then use an optical power meter to obtain the energy of the signal. This method is not only cumbersome to operate, but also has errors in measurement results. larger.

Based on the above reasons, there is a need for an OAM detection solution that can implement parallel detection and improve detection efficiency.

Contents of the invention

In order to solve the existing technical problems, an embodiment of the present invention provides an OAM detection device for an OV light beam.

In order to achieve the above object, the technical solution of the embodiment of the present invention is achieved in this way:

A detection device for orbital angular momentum OAM of an optical vortex OV light beam, comprising: a digital micromirror device DMD, a lens, a multimode fiber coupler, a multimode fiber array and an optical power meter; wherein,

The lens is arranged at the diffraction spot generated by the DMD;

The multimode fiber coupler is arranged at the focal plane of the lens and is connected with the multimode fiber array;

One end of the multimode fiber array is connected to the multimode fiber coupler, and the other end is connected to the optical power meter.

An embodiment of the present invention provides an OAM detection device for an OV light beam, which uses a multimode optical fiber array to simultaneously couple coaxial multi-channel signals carrying OAM, and restores the coaxial multi-channel OAM signals to Gaussian points at the detection end of the optical communication system , and then directly coupled into the multimode fiber array, so that the energy of multiple OV beams can be detected in parallel, which greatly improves the detection efficiency and the energy utilization rate has been greatly improved.

In addition, in the embodiment of the present invention, a multimode optical fiber array is used for detection, and the operation is more convenient and reliable.

Description of drawings

In the drawings (which are not necessarily drawn to scale), like reference numerals may describe like parts in different views. Similar reference numbers with different letter suffixes may indicate different instances of similar components. The drawings generally illustrate the various embodiments discussed herein, by way of example and not limitation.

1 is a frame diagram of an OAM detection device for parallel detection of 49 OAM signals;

Fig. 2 is a schematic diagram of a 7×7 multimode fiber coupler;

Figure 3 is a schematic diagram of the incident DMD light path in the Flat state;

Figure 4 is a schematic diagram of the incident DMD light path in the ON state;

Fig. 5 is the schematic diagram of the spatial position of m=1 level after passing through the f=40mm lens under the Flat state;

Figure 6 shows the 7×7 array arrangement after passing through the f=40mm lens in the Flat state;

Figure 7 shows the 7×7 array arrangement after f=40mm lens in the ON state.

detailed description

The present application provides an OAM detection device, which may include: a multimode fiber coupler, a lens, a DMD, a multimode fiber array, and an optical power meter; wherein the lens is arranged at the position of the diffraction spot generated by the DMD; The multimode fiber coupler is arranged at the focal plane of the lens and is connected with the multimode fiber array; one end of the multimode fiber array is connected to the multimode fiber coupler, and the other end is connected to the multimode fiber coupler. Optical power meter.

In some implementation manners, the DMD panel and the coaxial multiple OV light beams carrying multiple OAM signals may form an angle of 24° to maximize the detection effect.

In this application, the OAM detection device for OV light beams relates to the parallel detection technology of free space optical communication, and simultaneously couples the restoration points of coaxial multi-channel carrying OAM signals. Specifically, a multimode fiber array is used to simultaneously couple and parallel detect multiple coaxial restored OAM signals. The multimode fiber array is placed at the focal plane of the lens, the multi-channel OAM signals are restored to multiple Gaussian points, and converge at the focal point of the lens, and the multiple Gaussian points are directly coupled into the multimode fiber array at the focal point of the lens. The energy of any signal is detected in parallel. In this way, using the orthogonality of the OV beam to achieve multi-channel multiplexing, greatly improving the capacity of the information transmission system, using the optical fiber array to simultaneously couple the coaxial multi-channel OAM recovery point, greatly improving the detection efficiency, and the energy utilization rate has been improved. Substantial improvement.

As shown in FIG. 1 , it is a schematic structural diagram of an OAM detection device for parallel detection of 49 channels of OAM signals. It may include: a multimode fiber array 11 , a multimode fiber coupler 12 , a lens 13 , and a DMD14 . As shown in Figure 1, after the coaxial OV beam 10 carrying OAM is diffracted by DMD14 loaded with different specially designed Dammann grating holograms, a 7×7 array is generated in space to restore these coaxial multi-channel OAM signals One or more Gaussian points are focused in space after passing through the lens 13, and a multimode fiber coupler 12 is placed at the focal plane of the lens 13, and the restored one or more Gaussian points are coupled into the multimode fiber array 11 , an optical power meter (not shown in FIG. 1 ) is connected to the other end of the multimode fiber array 11, and the optical power meter can measure the energy level of the channel to achieve the purpose of parallel detection. In practical applications, its structure can be adjusted according to the number of optical paths of the OV beam. In particular, the structure of the multimode fiber array 11 and the multimode fiber coupler 12 can be adjusted according to the number of input coaxial OAM signals and the focal length of the lens. Specifically For the adjustment method, reference may be made to the example shown in FIG. 1 , which will not be repeated here.

FIG. 2 is a schematic cross-sectional view of a multimode fiber coupler. According to the focal length of different lenses, a variety of 7×7 array multimode fiber couplers can be used. Each multimode fiber coupler corresponds to two pieces. Figure 2 shows a 7×7 multimode fiber array. The white dots are connected to 49 multimode fibers, and the multimode fiber coupler is placed on lenses with different focal lengths. At the focal plane of , the coaxial multi-channel OAM signal can be correspondingly coupled into the multimode fiber coupler after being restored to a Gaussian point, so that parallel detection of any channel of OAM signal can be realized.

The program data is stored in the memory of the DMD, and the program data makes the multiple coaxial OV beams incident on the DMD panel output to a preset area in the form of diffraction. In practical application, the substrate of DMD is silicon, and the memory is produced on the silicon chip with large-scale integrated circuit technology. Each memory has two address electrodes (address electrodes) set on two support columns, and through the hinge (torsion hinge ) to install a miniature mirror, just like a "seesaw" structure. Each micro-mirror can reflect light from two directions, and the actual reflection direction depends on the state of the underlying memory cell; when the memory cell is in the "ON" state, the mirror will rotate to +12 degrees, If the memory cell is in the "OFF" state, the reflector will rotate to -12 degrees. In addition, the reflector without addressing signal corresponds to the 0 degree "Flat" state. That is to say, each unit of DMD has three stable states: +12 degrees, -12 degrees, and 0 degrees. As long as the DMD is combined with an appropriate light source and projection optical system, the micro-mirror will reflect the incident light into or out of the light hole of the projection lens, making the mirror in the "ON" state very bright, and the mirror in the "OFF" state is dark . Grayscale effects can be obtained by using 2-bit pulse width modulation. If fixed or rotating color filters are used, and one or three DMD chips are used, color display effects can be obtained. In practical applications, the program data of the DMD can be written into its memory through the computer, so that the light beam incident on the DMD panel can be output to the preset area in the form of diffraction, and the preset area can be placed by the lens The position after the lens is focused is the spatial position of the multimode fiber array.

In practical applications, the main working method of DMD is to adjust the rotation position of each micromirror on the chip according to different signals transmitted by the back-end circuit to the CMOS chip, so that the light irradiated on the micromirror can be selectively reflected in different directions. A DMD may include a circuit part, a mechanical part, and an optical part. Among them, the circuit part is a control circuit, the mechanical part is used to control the mechanical structure of the mirror rotation, and the optical part includes a rotatable mirror, which is distributed on the DMD panel and has a small volume. When the DMD works normally, light enters the DMD, and the mirrors on the DMD panel reflect the light by rotating, and the rotation of each mirror is controlled by the circuit unit.

In this application, the energy is evenly distributed between each diffraction order and written into the DMD binarized amplitude modulation hologram, which is output into a 7×7 array to correspond to a 7×7 multimode fiber array, and the DMD loads the DMD to load the binary value. The amplitude modulation hologram is used to restore the coaxial multi-channel OAM signal. In this way, at the detection end of the optical communication system, through the multimode fiber array, the energy of any path can be directly measured to achieve the purpose of parallel detection and greatly improve the detection efficiency of the system. In addition, since the core diameter of the multimode fiber is thicker than that of the single-mode fiber, and the numerical aperture is large, more optical power can be coupled from the light source, and the operation is more convenient and reliable than the single-mode device.

In practical applications, after the coaxial and multi-channel OV beams carrying multiple OAM signals are transmitted through free space, a series of digital micromirror devices (DMD, Digital Micromirror Device) loaded with different holograms are generated in space at the detection end. Diffraction spots converge on the focal plane of the lens after being focused by the lens. According to the reflective grating equation and the diffraction properties of the DMD, the spatial coordinates of the 7×7 array (that is, 49 coaxial OAM signals) under the focus of different focal length lenses can be determined. , the spatial coordinates are the spatial coordinates of the 7×7 multimode fiber array. In this way, the specific spatial position of the multimode fiber array can be determined to accurately receive 49 coaxial OAM signals, and then measure the energy of the OAM signal , to achieve the purpose of parallel detection.

In some implementations, the spatial coordinates of the multimode fiber array are different due to different steady states of the DMD.

The method for determining the spatial coordinates of the multimode fiber array will be described in detail below by taking a 7×7 multimode fiber array as an example.

The specific calculation method of the spatial coordinates of the 7×7 multimode optical fiber array may include the following steps:

(1) As shown in Figure 3, when the DMD is in the Flat state, the DMD is loaded with a Dammann grating, and the grating period d ₁ =0.157mm. Angle i=8°, θ ₀ =i=0.1396 (radians), according to the grating equation d ₁ (sini-sinθ ₁ )=mλ, the diffraction angle θ ₁ =0.1297 (radians) on the order of m=1 is obtained.

(2) As shown in Figure 4, when the DMD is in the ON state, the microlens array on the DMD is flipped by 12°, and the DMD starts to work, keeping the angle of the incident light unchanged. The normal at this time is the dotted line without arrows in Figure 4 As shown, at this time, the incident light angle is i'=20°, and the grating period is the period d ₂ =13.68μm of the DMD lens. According to the grating equation d ₂ (sini'-sinθ' ₁ =mλ, the diffraction order m= Diffraction angle θ' ₁ on the 1st order = 0.2307 (radian).

(3) As shown in Figure 5, when the lens of the DMD is rotated, the m=1 order is blazed to a higher order, and for the same m=1 diffraction line, the included angle is: α =Δθ-Δi=(θ'-θ)-(i'-i), according to this formula, calculate the angle α ₁ =(θ′ ₁ -θ ₁ ) of the spectral line angle of m=1-level DMD in the two states -(i'-i)=-0.1085 (radian).

(4) Calculate the spatial coordinates of the diffraction spectrum of m=1 order under the Flat state:

When the diffraction spectrum of m=1st order is focused by f=40mm lens: L=ftan(θ ₀ -θ ₁ )=0.396mm, which is the distance from point 0 to point 7 in Figure 6.

(5) Calculate the spatial coordinates of the 7×7 array in the Flat state after the f=40mm lens is focused, and the distance from point 0 to point 7 obtained from (4) is L=0.396mm, which is m=level 1 According to the above steps (1)(2)(3)(4), the position of m=level 2 (point 8) and the position of m=level 3 (point 9) are obtained, and the distance from point 0 to point 8 is calculated is 0.7961mm, and the distance from point 0 to point 9 is 1.1964mm. When the DMD is in the Flat state, the 7×7 array is arranged in a square. According to the distance from point 0 to point 7, the distance from point 0 to point 8, and the distance from point 0 to point 9, the spatial coordinates of each point in the array can be obtained. This space coordinate is the space coordinate of the 7×7 multimode optical fiber array in the Flat state.

(6) Calculate the spatial coordinates of the 7×7 multimode fiber array after being focused by the lens of f=40mm in the ON state: as shown in Figure 7, the array at this time is arranged in a diamond shape, and the position coordinates in the y direction remain unchanged , and in the x direction due to the change of the diffraction order, there will be a transverse stretch. From (2), it can be seen that the angle between point 7 and the y axis becomes π/4+α ₁ , based on (5) The position coordinates of point 7 at this time can be obtained from above, and point 7 is the middle point between point 1 and point 4. If the position of point 1 remains unchanged, the position coordinates of point 4 can be obtained. Combined with the structure of (5), the coordinates of each point in the 7×7 array at this time can be obtained, that is, the spatial coordinates of the multimode fiber coupler. Combined with the focal length f of different lenses, the spatial coordinates of the 7×7 multimode fiber array under the focus of various focal lengths f can be obtained.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention.

Claims (7)

1. a kind of orbital angular momentum OAM detecting device of optical vortex OV beam, it is characterized in that, comprise: digital micromirror device DMD, lens, multimode fiber coupler, multimode fiber array and optical power meter; Wherein, The lens is arranged at the diffraction spot generated by the DMD; The multimode fiber coupler is arranged at the focal plane of the lens and is connected with the multimode fiber array; One end of the multimode fiber array is connected to the multimode fiber coupler, and the other end is connected to the optical power meter. 2. The OAM detection device according to claim 1, wherein the DMD forms a specified angle with the coaxial multi-channel OV beam to be detected, and the coaxial multi-channel OV beam carries multiple OAM signals. 3. The OAM detection device according to claim 2, wherein the DMD forms an angle of 24° with the OV light beam to be detected. 4. The OAM detection device according to claim 1, wherein the lens is arranged at a distance of 2cm to 3cm from the DMD panel, and the diffraction spot generated by the DMD is kept at the center of the lens. 5. The OAM detection device according to claim 1 or 2, wherein when the coaxial multi-channel OV beams to be detected are 49 coaxial OV beams, the multimode fiber array is a 7×7 multimode fiber array, the multimode fiber coupler is a 7×7 array of multimode fiber couplers. 6. The OAM detection device according to claim 1, wherein the DMD includes a memory, and program data is stored in the memory, and the program data makes the multi-channel coaxial OV light beam incident to the DMD panel to diffract The form is output to the preset area, and the corresponding OAM signal is restored to a Gaussian point for the detection of the OAM signal. 7. The OAM detection device according to claim 1 or 6, wherein the spatial coordinates of the multimode optical fiber array are different due to the different steady states of the DMD.