An optical mode selection switch

Abstract

The application discloses an optical mode selection switch, comprising a platform, the platform surface is fixedly connected with a spatial light modulator, an optical processing device and a phase modulation module, the spatial light modulator, the optical processing device and the phase modulation module are parallel to each other, the optical processing device is located between the spatial light modulator and the phase modulation module, a plurality of phase units are uniformly fixed on the phase modulation module, the phase modulation module is a mode demultiplexing element array module, and the phase unit is a mode demultiplexing device unit of the same coordinate transformation or multi-plane light field conversion. The application can carry out N mode inputs, N mode outputs, and can freely select, separate and group propagation modes, improve the freedom degree of mode selection, and is not limited to optical fiber input or spatial light input, optical fiber or spatial light output, so that the mode division multiplexing is not limited to being carried out in an optical waveguide.

Description

Technical Field

[0001] This invention relates to the field of optical communication technology, specifically to an optical mode selection switch. Background Technology

[0002] Optical communication is a communication method that uses light waves as carriers. Optical mode switches are commonly used devices in optical communication. An optical mode switch is a device with one or more selectable transmission windows that can convert or perform logical operations on optical signals in optical transmission lines or integrated optical circuits. The basic form of an optical switch is 2×2, meaning there are two optical fibers at both the input and output ends, allowing for two connection states: parallel connection and cross connection. Its basic principle lies in optical fiber propagation. In the propagation of light in an optical waveguide, the mode that can propagate stably under certain conditions is called the optical mode of that fiber / waveguide. An optical fiber capable of propagating a single mode is called a single-mode fiber, and an optical fiber capable of propagating multiple modes is called a multimode fiber. Vortex light is a structured light with orbital angular momentum of different orders l (topological charge). It carries an angular phase factor eilθ, causing its wavefront to be distributed in a spiral shape. Vortex lights of different orders are orthogonal to each other. These orthogonal vortex lights can constitute different modes of light propagation in waveguides or free space. Optical mode switches utilize the optical propagation of vortex light. However, current optical mode switches have the following drawbacks:

[0003] In optical communication systems, different modes (such as different electromagnetic field modes in multimode fiber, different topological charge numbers of vortex light, etc.) can carry different information, thereby increasing the amount of information carried by optical communication. However, the number of input and output modes of current optical mode switches is limited, and the transmission mode cannot be freely selected, separated, or grouped for propagation. The degree of freedom in selecting the transmission mode is low, which in turn leads to a low amount of information carried.

[0004] To address this issue, we propose an optical mode selection switch. Summary of the Invention

[0005] The purpose of this invention is to provide an optical mode selection switch to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: an optical mode selection switch, comprising a platform, wherein a spatial light modulator, an optical processing device, and a phase modulation module are fixedly mounted on the surface of the platform, the spatial light modulator, the optical processing device, and the phase modulation module are parallel to each other, and the optical processing device is located between the spatial light modulator and the phase modulation module.

[0007] Multiple phase units are uniformly fixed on the phase modulation module, which is a mode demultiplexing element array module.

[0008] The phase unit is a mode demultiplexing device unit with the same coordinate transformation or multi-plane optical field transformation. The same coordinate transformation is a logarithmic polar coordinate transformation or a spiral transformation demultiplexing method, and multiple phase units are oriented in the same direction.

[0009] The optical processing device is a lens or a superlens.

[0010] Compared with the prior art, the beneficial effects of the present invention are:

[0011] This invention can perform N modes of input and N modes of output, and can freely select, separate, and group the propagation methods, which improves the freedom of mode selection and is not limited to fiber optic input or spatial light input and fiber optic or spatial light output, so that mode division multiplexing is not limited to optical waveguides. Attached Figure Description

[0012] Figure 1 These are schematic diagrams of the main structure in the first and second embodiments of the present invention;

[0013] Figure 2 This is a schematic diagram of one side of the logarithmic-polar coordinate transformation phase plate, cut to 1 mm, in the fourth embodiment of the present invention;

[0014] Figure 3 This is a schematic diagram of the other side of the logarithmic-polar coordinate transformation phase plate, which is cut off to 1 mm, in the fourth embodiment of the present invention.

[0015] Figure 4 This is a schematic diagram of one side of the spiral transformation phase plate, which is cut to 1 mm, in the fourth embodiment of the present invention;

[0016] Figure 5 This is a schematic diagram of the other side of the spiral transformation phase plate, which is cut to 1 mm, in the fourth embodiment of the present invention;

[0017] Figure 6 This is a schematic diagram of twice the reverse phase of the first-order demodulated spot in the logarithmic-polar coordinate transformation according to the fourth embodiment of the present invention;

[0018] Figure 7 This is a schematic diagram of the grating phase in the fourth embodiment of the present invention;

[0019] Figure 8 This is a schematic diagram of the total modulation phase in the fourth embodiment of the present invention, showing the superposition of twice the reverse phase and the grating phase, and the effective area (covering the demodulated spot) is extracted.

[0020] Figure 9 This is a schematic diagram of the light field intensity after passing through the phase modulation module in the reverse direction in the fourth embodiment of the present invention;

[0021] Figure 10This is a phase diagram of the final annular light spot in the fourth embodiment of the present invention.

[0022] In the figure: 1. Spatial light modulator 1; 2. Optical processing device; 3. Phase modulation module; 4. Platform; 31. Phase unit. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1:

[0025] Please see Figure 1 The present invention provides a technical solution: an optical mode selection switch, including a platform 4, on which a spatial light modulator 1, an optical processing device 2 and a phase modulation module 3 are fixedly mounted. The spatial light modulator 1, the optical processing device 2 and the phase modulation module 3 are parallel to each other. The optical processing device 2 is located between the spatial light modulator 1 and the phase modulation module 3. In actual use, the phase modulation module 3 and the spatial light modulator 1 should be positioned on the object plane and image plane of the optical processing device 2.

[0026] Example 2:

[0027] Please see Figure 1 This is the second embodiment of the present invention. This embodiment is based on the previous embodiment. Multiple phase units 31 are uniformly fixed on the phase modulation module 3. The phase modulation module 3 is a mode demultiplexing element array module.

[0028] Phase unit 31 is a mode demultiplexing device unit for the same coordinate transformation or multi-plane optical field transformation. The same coordinate transformation is either logarithmic polar coordinate transformation or spiral transformation demultiplexing. Multiple phase units 31 are oriented in the same direction. If they are oriented in the same direction, they can pass through the unit from the same direction and achieve the same demultiplexing effect.

[0029] The optical processing device 2 is a lens or a superlens, configured to allow the incident demultiplexed light to be incident parallel to the spatial light modulator 1, and to allow the reflected light from the spatial light modulator 1 to be incident parallel to the phase modulation module 3.

[0030] Example 3:

[0031] The third embodiment of the present invention is based on the above two embodiments, and the control requirements of the present invention are as follows:

[0032] The diameter of the input composite light spot used should not be greater than the effective side length of each demultiplexing unit of the phase modulation module, where the radius of the composite light spot is defined as the distance from the center of the circle to the light intensity attenuation point. The length of the maximum light intensity, where e is a natural constant.

[0033] The effective area captured by the spatial light modulator 1 should cover the size of the demodulated light spot generated by the input light spot, that is, the strip area.

[0034] The spatial light modulator 1 is divided into regions, and the demodulated light spot is given a corresponding double reverse phase. The demodulated light spot that needs to be modulated and deflected is given a grating phase of a corresponding angle, so that the reflected light can pass through the center of a phase unit 31 of the phase modulation module 3.

[0035] Example 4:

[0036] Please participate Figure 1-10 This is the fourth embodiment of the present invention, based on the above three embodiments. This embodiment provides a specific implementation method for using composite vortex light with different orders as input to the optical mode selection switch. In this embodiment, the input light spot uses vortex light with a diameter of 0.9 mm. In order to cover the input vortex light, the phase plate used for demultiplexing only needs to be cut by 1 mm (see the pattern after cutting). Figure 2-3 );

[0037] In this embodiment, the phase modulation module 3 is an array of vortex optical logarithmic-polar coordinate transformation demultiplexing elements, that is, the same logarithmic-polar coordinate demultiplexing elements are arranged horizontally, which has coordinate transformation (see...). Figure 2 ) and phase compensation (see Figure 3 The phase structure consists of two planes, each element with a side length of 1 mm, a spacing of 0.5 mm, and a thickness of 4.95 mm. The logarithmic polar coordinate demultiplexing device can demultiplex incident -1 to +1 order vortex light into three vertically arranged light spots. The input light passes through the central phase unit 31 of the phase modulation module 3 in the forward direction and is demultiplexed into vortex light arrays of different orders (see...). Figure 6 The spatial light modulator 1 propagates; the optical processing device 2 used in this embodiment is a lens with a focal length of 100mm. The vortex light array passes through the optical processing device 2 and is projected parallel onto the spatial light modulator 13. The vortex light demultiplexing element array and the spatial light modulator 13 are respectively placed at a distance of 100mm from the lens, i.e., on the object plane and the image plane.

[0038] The spatial light modulator 1 used in this embodiment is a reflective liquid crystal spatial light modulator 1. This type of spatial light modulator 1 performs pure phase modulation and reflection on the incident light. Each pixel size d is 3.8μm. The spatial light modulator 1 is divided into regions and loaded with twice the reverse phase of each order of light spot (see...). Figure 8 ) and grating phase (see Figure 9 The total phase is composed of multiple phases. It's worth noting that if a symmetrical grating is used, diffraction spots will form on both sides of the grating, resulting in significant energy loss and limiting the freedom of the optical mode selection switch to modulate the deflection in both positive and negative directions. Therefore, a unidirectional grating is used here; the maximum deflection angle of the grating is set as (0, ...). ,

[0039] The maximum deflection angle θmax depends on the pixel size of the spatial light modulator 1. However, considering that the optical processing device 2 has a certain size and numerical aperture, the limiting parameters of the optical modulation element in the spatial light modulator 1 should be considered when setting the deflection angle. After the demodulated light spot undergoes phase modulation and reflection by the spatial light modulator 1, it passes through the optical processing device 2 again. Taking a +1 order vortex light as an example, if the grating deflection angle θ applied to the demodulated light spot of the +1 order vortex light is 0.86° (since the spatial light modulator 1 is an active device, the angle of the applied grating can be freely selected within a limited range), then the demodulated light spot passes through the optical processing device 2 again. When the lens is offset by a distance f1tan(θ) of 1.5mm from the center, the light spot will then converge and hit the first unit on the side opposite to the center unit. Similarly, when the grating deflection angle θ is applied to -0.86°, the demodulated light spot will deviate by a distance of -1.5mm, hitting the first unit on the other side opposite to the center unit. Similarly, the same modulation can be performed for the 0th and -1st orders. Since the demultiplexed light spots are separated and reach different positions of the spatial light modulator 1, the phase applied by the spatial light modulator 1 in different regions will only act on the light spot in that region and will not change the phase of the light spot in other regions. Therefore, the modulation between the demodulated light spots of each order is independent of each other.

[0040] Since the demodulated light spot is subjected to phase modulation of the grating and double-inverse phase modulation to make its phase conjugate, when the reflected light passes through the vortex light demultiplexing element in reverse, the phase of the reflected light is the same as that during demultiplexing but the modulation order is reversed. This allows the demodulated light spot to be inverted back to the original vortex light. Therefore, the corresponding vortex light spot can be obtained from the phase unit 31 in the corresponding phase modulation module 3.

[0041] In this embodiment, by increasing the number of units N of the vortex optical demultiplexing array, the number of output ports can be increased to N. By adding a corresponding deflection phase to the L-order vortex beam position of the spatial light modulator 1, the desired order of vortex beam can be freely selected to any window, thereby achieving the mode selection effect.

[0042] Example 5:

[0043] The fifth embodiment of the present invention is based on the above four embodiments. As seen in the fourth embodiment, when multiple modes of light are input into the optical mode selection switch provided by the present invention, they first pass through the phase modulation module 3, which employs a mode separation element array module. The mode separation element array module separates the multi-mode input light into spatial light that propagates through multiple paths. Then, phase modulation is applied to these spatial lights according to different deflection requirements. The applied phase modulation is a composite of the phase of the light spot to be modulated (twice the reverse phase, the purpose of which is to make the light spot phase conjugate) and the grating phase (the purpose of which is to deflect the light spot), resulting in a total phase that allows the multi-mode light to pass through the optical mode selection switch provided by the present invention. The light is deflected under the action of the grating phase as required, thus being freely selected. Finally, the reflected light is reversed and passed through the unit of the mode separation element array to re-multiplex the separated multipath transmission spatial light into a newly set path (not fixed to a single path). This achieves the effect of free selection, separation, and group propagation of multimode light. Therefore, this invention can perform N mode inputs and N mode outputs, and can freely select, separate, and group propagation methods, improving the degree of freedom of mode selection. It is not limited to fiber optic input or spatial light input, or fiber optic or spatial light output, so that mode division multiplexing is not limited to optical waveguides.

[0044] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An optical mode selection switch, comprising a platform (4), characterized in that: The platform (4) is fixed with a spatial light modulator (1), an optical processing device (2) and a phase modulation module (3). The spatial light modulator (1), the optical processing device (2) and the phase modulation module (3) are parallel to each other. The optical processing device (2) is located between the spatial light modulator (1) and the phase modulation module (3). Multiple phase units (31) are uniformly fixed on the phase modulation module (3), and the phase modulation module (3) is a mode demultiplexing element array module; The phase unit (31) is a mode demultiplexing device unit of the same coordinate transformation or multi-plane optical field transformation. The same coordinate transformation is a logarithmic polar coordinate transformation or a spiral transformation demultiplexing method. The multiple phase units (31) are oriented in the same direction. The optical processing device (2) is a lens or a superlens.

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