Spatial light field coding device and coding method based on orthogonal time division multiplexing

Abstract

The invention relates to a spatial light field coding device and a spatial light field coding method for light field beam driving guidance, in particular to a spatial light field coding device and a spatial light field coding method based on orthogonal time division multiplexing. The technical problems that an existing space coding technology for light field beam driving guiding is low in coding frequency and poor in reliability are solved. The device comprises a photoelectric sensor, a laser, a collimating lens, a composite prism, a projection lens and a spatial light modulator. The composite prism comprises a lower prism and an upper prism; output light of the laser is collimated by the collimating lens to form collimated laser, the collimated laser is projected to the spatial light modulator through the composite prism to perform light field intensity coding modulation, and the modulated light field returns to the composite prism and is projected by the projection lens to form an imaging spatial light field; and the photoelectric sensor is arranged on the to-be-guided device and used for receiving the code of the image space light field, decoding the code to obtain the position of the to-be-guided device and adjusting the steering engine according to the position to enable the to-be-guided device to move towards a preset position.

Description

Technical Field

[0001] The present invention relates to a spatial light field coding method for light field beam driving guidance, and in particular to a spatial light field coding device and coding method based on orthogonal time division multiplexing. Background Art

[0002] Spatial light field coding technology is mainly used in light field beam steering technology. Light field beam steering refers to a technology that uses a modulated light field to control the movement of the device to be guided. During the guidance process, the device to be guided is always located in the light beam, so it is also called light field beam steering.

[0003] In the light field beam-riding guidance system, the device to be guided determines its own position through spatial coding. First, the spatial light illuminator needs to spatially encode the output light field. The encoded beam cross-section has different spatial positions with different information codes. The device to be guided placed in the light field can obtain its own position after decoding, and then feed it back to the control system and adjust its own motion mechanism to move to the specified spatial position, finally realizing long-distance guidance. Its principle is as follows: Figure 1 shown.

[0004] Existing spatially coded light illuminators are mainly used in ground environments, and their core components use a mechanical modulation disk to encode spatial light fields. Figure 2 and Figure 3 As shown, Figure 2 This is a schematic diagram of a mechanical modulation disk. Figure 3 This is a diagram of the mechanism of a mechanical modulation disk. The mechanical modulation disk is a disk. For the coordinate point in the light field, its coordinate position can be calculated from the time proportion of different frequencies. The calculation formula is: K = 2(τ1-τ2) / T, where K represents the position coefficient, that is, the degree of deviation from the center, and the range is (-1, 1); τ1 represents the scanning time of the spatial frequency f1, τ2 represents the scanning time of the spatial frequency f2, and T represents the scanning period of the modulation disk. The spatial encoding method of the modulation disk requires a motor to drive the modulation disk to operate continuously at high speed, which consumes a lot of power, has a low encoding frequency, and has poor reliability. Summary of the invention

[0005] The purpose of the present invention is to solve the technical problem that the existing spatial coding for light field beam driving guidance adopts a mechanical modulation disk, resulting in low coding frequency and poor reliability, and to provide a spatial light field coding device and coding method based on orthogonal time division multiplexing.

[0006] The technical solution of the present invention is:

[0007] A spatial light field encoding device based on orthogonal time division multiplexing, which is special in that it includes a photoelectric sensor, a collimator and a composite prism arranged in sequence on the laser light path, a projection lens arranged on one side of the composite prism, and a spatial light modulator arranged on the opposite side of the composite prism;

[0008] The composite prism comprises a lower prism and an upper prism which are arranged opposite to each other and both have a triangular prism structure;

[0009] The lower bottom surface of the lower prism constitutes the coded light incident surface of the composite prism;

[0010] One of the side surfaces of the lower prism constitutes a first composite surface of the composite prism;

[0011] The other side surface of the lower prism constitutes the laser incident surface of the composite prism;

[0012] The upper bottom surface of the upper prism constitutes the coded light emitting surface of the composite prism;

[0013] The surface of the upper prism that is parallel to and opposite to the first composite surface constitutes the second composite surface of the composite prism;

[0014] An air gap is provided between the first composite surface and the second composite surface;

[0015] The angle between the laser incident surface and the coded light incident surface is an obtuse angle;

[0016] The angle between the first composite surface and the laser incident surface is 45°;

[0017] The coded light incident surface is parallel to the coded light emitting surface;

[0018] The output light of the laser is collimated by a collimator to form a collimated laser, and the collimated laser is projected to a spatial light modulator through a composite prism for light field intensity coding modulation. The modulated light field returns to the composite prism and is projected through a projection lens to form an image space light field, and the image space light field covers the motion range of the device to be guided;

[0019] The photoelectric sensor is arranged on the device to be guided, and is used to receive and decode the encoding of the image space light field to obtain the position of the device to be guided, and adjust the steering gear according to the position to make the device to be guided move to a preset position.

[0020] Furthermore, the refractive index n of the composite prism is 1.5, and the critical angle for total reflection is 41.8°.

[0021] Furthermore, the material of the composite prism is H-K9.

[0022] Furthermore, the inclination angle of the micromirror of the spatial light modulator relative to the horizontal plane is ±12°; and the gap between the spatial light modulator and the coded light incident surface is 3.5 mm.

[0023] Furthermore, the resolution of the spatial light modulator is 1024×768, the diagonal of the micromirror array is 0.55 inches, the micromirror spacing is 10.8μm, the micromirror crossing time is 2.5μs, the micromirror reflectivity is 88%, the array diffraction efficiency is 86%, the array fill factor is 92%, and the input data clock rate is 400MHz.

[0024] Furthermore, the length of the spatial light modulator is 40.64 mm, the width is 31.75 mm, and the height is 5.98 mm; the size of the micromirror array in the spatial light modulator is 25.05 mm in length and 17.27 mm in width; the widths of the coded light incident surface and the laser incident surface are 43.35 mm and 30 mm respectively, and the widths of the second composite surface and the coded light exit surface are 48.25 mm and 55.09 mm respectively.

[0025] Furthermore, the parameters of the laser are as follows: wavelength is 808nm, maximum power is 2W, half-wave width is 3nm, output fiber core diameter is 400μm, and numerical aperture is 0.22; the parameters of the collimator are as follows: material is N-BK7, shape is a plano-convex lens, outer diameter is 25.4mm, center thickness is 4.7mm, and back focus is 56.7mm; the parameters of the projection lens are as follows: focal length is 20mm, relative aperture is F2.8, and image field of view is ≥30mm.

[0026] At the same time, the present invention also provides a spatial light field coding method based on orthogonal time division multiplexing, which adopts the above-mentioned spatial light field coding device based on orthogonal time division multiplexing, and its special feature is that it includes the following steps:

[0027] 1) After the laser is vertically incident on the laser incident surface of the compound prism, it is reflected by the compound prism to the spatial light modulator;

[0028] 2) The spatial light modulator encodes the laser:

[0029] If a certain micromirror in the spatial light modulator is in the on state, the laser reflected by the micromirror is emitted from the coded light emission surface in a vertical direction to the moving area of ​​the device to be guided;

[0030] If a certain micromirror in the spatial light modulator is in the off state, the laser reflected by the micromirror is emitted from the coded light emission surface in an inclined direction to outside the moving area of ​​the device to be guided;

[0031] 3) The coded laser is projected into the moving area of ​​the device to be guided to form an image space light field;

[0032] 4) The device to be guided receives and decodes the encoding of the image space light field through a photoelectric sensor, obtains its own position, and adjusts the steering gear according to the position to make the device to be guided move to a preset position.

[0033] Further, in step 4), the encoding specifically includes:

[0034] S1) Selection of the working area of ​​the spatial light modulator:

[0035] The central area of ​​the spatial light modulator is taken as the working reflection surface, and the working reflection surface is divided into M×M independent areas according to the resolution requirements for operation, and each area includes N×N micromirrors;

[0036] S2) Perform spatial orthogonal time division multiplexing encoding on the incident laser:

[0037] First, a group of start synchronization codes are sent to the device to be guided, and the device to be guided starts to receive the encoded optical signal in the horizontal direction; the spatial light modulator encodes the incident laser and sends two images with grayscale gradients in the horizontal direction to the device to be guided, where the grayscale of one image gradually increases from left to right, and the grayscale of the other image gradually decreases from left to right. After the two images are sent, a group of end synchronization codes are sent;

[0038] Then, a group of start synchronization codes are sent to the device to be guided, and the device to be guided starts to receive the encoded optical signal in the vertical direction; the spatial light modulator encodes the incident laser and sends two images with grayscale gradient in the vertical direction to the device to be guided, wherein the grayscale of one image gradually increases from top to bottom, and the grayscale of the other image gradually decreases from top to bottom. After the two images are sent, a group of end synchronization codes are sent;

[0039] In step 4), the decoding specifically includes:

[0040] The guided device receives four images and calculates the coordinates (△x, △y) of point A at any position in space according to the following formula:

[0041] △x=(Ix1-Ix2) / (Ix1+Ix2)

[0042] △y=(Iy1-Iy2) / (Iy1+Iy2)

[0043] Ix1 and Ix2 are the grayscales of the two images in the horizontal direction;

[0044] Iy1 and Iy2 are the grayscales of the two images in the vertical direction respectively.

[0045] Further, in step 4), the start synchronization code is 101010, and the end synchronization code is 0101; the grayscale levels of the four images are all 20;

[0046] In step S1), the size of the working reflective surface is 760×760, and is divided into 20×20 independent areas for operation, each area including 38×38 micromirrors.

[0047] Beneficial effects of the present invention:

[0048] 1. The present invention is a spatial light field coding device based on orthogonal time division multiplexing, which adopts a spatial light modulator for spatial coding. Compared with the existing modulation disk coding technology, the device is simple, has the characteristics of high coding frequency, no moving parts, high reliability and low power consumption, and can be applied to high reliability and low power consumption platforms such as satellites.

[0049] 2. The present invention provides a spatial light field coding method based on orthogonal time division multiplexing, which uses a spatial light modulator to perform spatial coding of orthogonal time division multiplexing, has simple operation, high coding efficiency and strong reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 It is the schematic diagram of the light field beam-riding guidance system;

[0051] Figure 2 It is a schematic diagram of the spatial encoding principle of the modulation disk in the prior art;

[0052] Figure 3 It is a schematic diagram of the representation principle of the expansion position information of the modulation disk code channel in the prior art;

[0053] Figure 4 It is a structural schematic diagram of a spatial light field encoding device based on orthogonal time division multiplexing of the present invention;

[0054] Figure 5 It is a circuit diagram of a spatial light field encoding device based on orthogonal time division multiplexing of the present invention;

[0055] Figure 6 It is a structural schematic diagram of a composite prism in an embodiment of a spatial light field encoding device based on orthogonal time division multiplexing of the present invention;

[0056] Figure 7 It is a diagram showing the size parameters of a composite prism in an embodiment of a spatial light field encoding device based on orthogonal time division multiplexing of the present invention;

[0057] Figure 8 It is a schematic diagram of edge light rays when the spatial light modulator is in the "on" state (+12°) in an embodiment of a spatial light field encoding device based on orthogonal time division multiplexing of the present invention;

[0058] Fig. 9 It is a schematic diagram of edge light rays when the spatial light modulator is in the "off" state (-12°) in an embodiment of a spatial light field encoding device based on orthogonal time division multiplexing of the present invention;

[0059] Fig.10 It is a schematic diagram of DMD working area selection in an embodiment of a spatial light field encoding device based on orthogonal time division multiplexing of the present invention;

[0060] Fig.11 It is a schematic diagram of the light field modulation principle of a spatial light modulator in an embodiment of a spatial light field encoding device based on orthogonal time division multiplexing of the present invention;

[0061] Fig.12 1 is a schematic diagram of spatial orthogonal time division multiplexing encoding (horizontal direction) of an embodiment of a spatial light field encoding method based on orthogonal time division multiplexing of the present invention;

[0062] Fig.13 1 is a schematic diagram of spatial orthogonal time division coding (vertical direction) of an embodiment of a spatial light field coding method based on orthogonal time division multiplexing of the present invention;

[0063] Fig.14 It is a spatial orthogonal time division coding timing diagram of an embodiment of a spatial light field coding method based on orthogonal time division multiplexing of the present invention;

[0064] Fig.15 The present invention is a timing diagram of a spatial light modulator sending data in an embodiment of a spatial light field encoding method based on orthogonal time division multiplexing.

[0065] Figure numerals: 1-laser; 2-collimator; 3-compound prism, 31-lower prism, 311-coded light incident surface, 312-first compound surface, 313-laser incident surface, 32-upper prism, 321-coded light exit surface, 322-second compound surface; 4-projection lens; 5-spatial light modulator. DETAILED DESCRIPTION

[0066] The present invention mainly adopts a spatial light modulator, a laser light source and an optical component as a spatial coding light irradiator, and adopts orthogonal time division multiplexing spatial light field coding technology to modulate the two-dimensional light field, so that the device to be guided receives the coding of the external two-dimensional light field through its own photoelectric sensor and decodes it to determine its own position, and then adjusts the steering gear to move to the preset position to realize beam steering. The principle is as follows Figure 1 shown.

[0067] The present invention provides a spatial light field encoding device based on orthogonal time division multiplexing, such as Figure 4As shown, it includes a photoelectric sensor, a collimator 2 and a compound prism 3 arranged in sequence on the optical path of the laser 1, a projection lens 4 arranged on one side of the compound prism 3; and a spatial light modulator 5 arranged on the opposite side of the compound prism 3. The gap between the spatial light modulator 5 and the coded light incident surface 311 is 3.5 mm. Among them, the laser 1 adopts a fiber laser, and a fiber laser with good monochromaticity is used as a light source; the photoelectric sensor is arranged on the device to be guided, and is used to receive the encoding of the image space light field and decode it to obtain the position of the device to be guided, and adjust the steering gear according to the position to make the device to be guided move to a preset position.

[0068] like Figure 6 As shown, the composite prism 3 includes a lower prism 31 and an upper prism 32 which are arranged opposite to each other and both have a triangular prism structure. The lower bottom surface of the lower prism 31 constitutes a coded light incident surface 311 of the composite prism 3; the upper bottom surface of the upper prism 32 constitutes a coded light exit surface 321 of the composite prism 3; one of the side surfaces of the lower prism 31 constitutes a first composite surface 312 of the composite prism 3, and the surface of the upper prism 32 opposite to the first composite surface 312 constitutes a second composite surface 322 of the composite prism 3, and an air gap is provided between the first composite surface 312 and the second composite surface 322; the other side surface of the lower prism 31 constitutes a laser incident surface 313 of the composite prism 3; the angle between the laser incident surface 313 and the coded light incident surface 311 is an obtuse angle; the angle between the first composite surface 312 and the laser incident surface 313 is 45°; the coded light incident surface 311 is parallel to the coded light exit surface 321. The parameters of the composite prism 3 are as follows: the material is H-K9, the refractive index n is 1.5, and the critical angle for total reflection is 41.8°.

[0069] The main principle of the device of the present invention is: the output light of the fiber laser is collimated by the collimator 2 to form a collimated laser, the collimated laser is projected to the spatial light modulator 5 through the compound prism 3 for light field intensity coding modulation, and after two-dimensional light field modulation by the spatial light modulator 5 (object space), it returns to the compound prism 3 and is projected through the projection lens 4 to form an image space light field, which covers the motion range of the device to be guided.

[0070] The main components of the control circuit in the device of the present invention are Altera Cyclone III EP3C40F324 FPGA, and the main parameters are as follows: 16Mbits EPCS16 configuration chip; 1Mbytes SRAM (256K×32bit); 64Mbytes DDRIISDRAM (32M×16Bit); 8Mbytes NOR Flash ROM; 64Mbytes NAND Flash ROM; serial interface MiniUSB2.0. The control circuit is mainly responsible for controlling the laser and spatial light modulator 5. The laser emitted by the laser 1 passes through the collimator 2 and the compound prism 3, and then modulates the light field through the reflector array in the spatial light modulator 5 and emits it into space. The control circuit realizes time-sharing modulation of the amplitude of the two-dimensional light field by writing different display patterns to the spatial light modulator 5 module at different times. The display pattern is written into the memory of the FPGA in advance through the serial communication interface. The functional block diagram of the control system is shown in the figure. Figure 5 shown.

[0071] In this embodiment, the main design parameters of each component in the device are as follows:

[0072] 1) Fiber laser: wavelength is 808nm; laser output mode is fiber output, continuous (CW); maximum power is 2W; full width at half maximum (FWHM) is 3nm; output fiber core diameter is 400um; numerical aperture (NA) is 0.222).

[0073] 2) Collimator 2: Material is N-BK7; shape is a plano-convex lens, outer diameter is 25.4mm, center thickness is 4.7mm; back focus is 56.7mm.

[0074] 3) Compound Prism 3:

[0075] The structure of the composite prism 3 used in the present invention is shown in FIG. Figure 6 As shown, it is composed of two prisms. The angle to be determined is the angle of the coded light incident surface 311 of the lower prism 31 (i.e. Figure 7 The surface where the middle mark ③ is located), the first composite surface 312 (i.e. Figure 7 The inclination angle of the surface marked with the middle mark ②) and the second composite surface 322 (i.e. Figure 7 The angle of the plane with the middle mark ④ is calculated below. The material of the composite prism 3 is H-K9, with a refractive index of n=1.5, and a critical angle of 41.8° when total reflection occurs.

[0076] When the spatial light modulator 5 is in the "on" state +12°, Figure 8As shown. In order to make the entire outgoing light enter the projection system vertically, the light must be incident on the micro-mirror surface of the spatial light modulator 5 at an angle of 24°. According to the principle of reversible optical path, the light is refracted at 24° at surface ① to reach surface ②. At surface ②, the light is totally reflected at an incident angle of 45°. The light is vertically emitted from surface ③ at 90°. The angle between the outgoing light and the horizontal direction is 15.7°. The light emitted from surface ② and entering surface ④ is deflected and still enters the projection system from surface ⑤ in a vertical direction.

[0077] When the spatial light modulator is in the "off" state -12°, Fig. 9 As shown. The incident light enters the composite prism 3 perpendicular to the ③ surface, is totally reflected at the ② surface and reaches the ① surface, and then refracts to enter the micro-mirror surface of the spatial light modulator 5 at 24° for reflection. The reflected light is refracted at the ① surface at an incident angle of 45° and at the ② surface at an incident angle of 0.4° to reach the ④ surface. The light passing through the ④ surface is deflected but still reaches the ⑤ surface at a perpendicular incident light to the ② surface for refraction. The angle between the outgoing light and the vertical direction is 48°.

[0078] The calculation process of the side length of the composite prism 3 is as follows: the incident light spot enters the ③ surface with a size of Φ25mm. Due to the design and processing of the composite prism 3, a 2.5mm margin is left on both sides. The side length of the ③ surface is taken as 30mm. According to the position of the edge incident light, the optical mapping method is used and the state of the spatial light modulator +12° and -12° is used to determine the length of each side, such as Figure 7 As shown, the size design of the composite prism 3 in this embodiment, the thickness of the composite prism 3 is 30mm, the widths of the coded light incident surface 311 (i.e., surface ①) and the laser incident surface 313 (i.e., surface ③) are 43.35mm and 30mm respectively, and the widths of the second composite surface 322 (i.e., surface ④) and the coded light exit surface 321 (i.e., surface ⑤) are 48.25mm and 55.09mm respectively.

[0079] The rotation axis of the spatial light modulator 5 is in the diagonal direction of the micromirror. In order to ensure that both the incident light and the reflected light are within the main interface of the composite prism 3, the installation direction of the spatial light modulator 5 should have an angle of 45° with the long side of the composite prism 3, that is, the rotation axis of the micromirror of the spatial light modulator 5 is parallel to the working surface of the composite prism 3 and perpendicular to the main cross-section.

[0080] 4) Projection lens 4: The function of projection lens 4 is to project the two-dimensional plane light field modulated by spatial light modulator 5 into the object space to form spatial light fields of different angles. The parameters of projection lens 4 are as follows: focal length is 20mm; relative aperture is F2.8; image field of view ≥ 30mm.

[0081] 5) The main parameters of the spatial light modulator 5 are as follows: the resolution is 1024×768; the diagonal of the micromirror array is 0.55 inches; the spacing between the micromirrors is 10.8μm; the tilt angle of the micromirrors is ±12° (relative to the plane); the crossing time of the micromirrors is 2.5μs; the reflectivity of the micromirrors is 88%; the diffraction efficiency of the micromirror array is 86%; the array filling factor is 92%; the input data clock rate is 400MHz; the overall dimensions are 40.64mm×31.75mm×5.98mm (length×width×height), and the size of the micromirror array is 25.05mm×17.27mm (length×width).

[0082] The display principle of the spatial light modulator 5 is:

[0083] The spatial light modulator 5 is an array composed of many tiny mirrors (referred to as micromirrors). Each pixel of the spatial light modulator can be operated individually by a computer. A pulse drive signal with different frequencies or duty cycles is applied to each pixel to achieve intensity modulation of the output reflected light. In the laser irradiation system, the light field projected onto the spatial light modulator chip can be spatially modulated by the spatial light modulator to achieve spatial encoding of the light field.

[0084] Selection of the working area of ​​the spatial light modulator 5:

[0085] like Fig.10 As shown, the pixel resolution of the spatial light modulator 5 is 1024×768. In order to make full use of the light source and facilitate the equal division of the area, a square area of ​​760×760 is selected, and the central area is taken as the working reflection surface. According to the resolution requirement of the illumination surface, this embodiment divides the working reflection surface into 20×20, that is, (P(1,1) to P(20,20)) 400 independent areas for operation, and each area is composed of 38×38 pixels (micromirrors).

[0086] Grayscale realization principle of spatial light modulator 5:

[0087] The spatial light modulator 5 is a reflective device. By changing the state of the micromirror, a binary operation is realized, that is, there are only two states, "On" and "Off". In the "On" state, the incident light is fully reflected, and in the "Off" state, the incident light is not reflected. In the device of the present invention, it is necessary to grayscale modulate the incident light to realize the display of grayscale images. In the spatial light modulator module, grayscale modulation can be realized by controlling the length of time each micromirror is turned on. Within a certain pulse period, grayscale modulation is performed by setting different two-dimensional codes for different micromirrors or blocks of the DMD module. Fig.11 This is a schematic diagram of 3-bit light field modulation. When 101 (decimal 5) is transmitted to the DMD device, the value obtained by time integration at the receiving end is 4.9, which is approximately equal to 5.

[0088] At the same time, the present invention also provides a spatial light field coding method based on orthogonal time division multiplexing, using the above-mentioned spatial light field coding device based on orthogonal time division multiplexing, comprising the following steps:

[0089] 1) After the laser is vertically incident on the laser incident surface 313 of the composite prism 3, it is reflected by the composite prism 3 to the spatial light modulator 5;

[0090] 2) The spatial light modulator 5 encodes the laser:

[0091] If a certain micromirror in the spatial light modulator 5 is in the on state, the laser reflected by the micromirror is emitted from the coded light emission surface in a vertical direction to the moving area of ​​the device to be guided;

[0092] If a certain micromirror in the spatial light modulator 5 is in the off state, the laser reflected by the micromirror is emitted from the coded light emitting surface in an inclined direction to outside the moving area of ​​the device to be guided;

[0093] 3) The coded laser is projected into the moving area of ​​the device to be guided to form an image space light field;

[0094] 4) The device to be guided receives the coding of the image space light field through a photoelectric sensor and decodes it to obtain its own position, and adjusts the steering gear according to the position to make the device to be guided move to a preset position.

[0095] The present invention adopts spatial orthogonal time division multiplexing coding, which means that in a certain plane in space, the light field is encoded horizontally and vertically according to the time series, and the light intensity coding technology is adopted, that is, a step grayscale image is displayed, and the spatial position is determined according to the intensity of light.

[0096] The encoding process includes the following steps:

[0097] S1) Selection of the working area of ​​the spatial light modulator 5:

[0098] The central area of ​​the spatial light modulator 5 is taken as the working reflection surface, and the working reflection surface is divided into M×M independent areas for operation according to the resolution requirement, and each area includes N×N micromirrors. In this embodiment, the size of the working reflection surface is 760×760, and it is divided into 20×20 independent areas for operation, and each area includes 38×38 micromirrors.

[0099] S2) Perform spatial orthogonal time division multiplexing encoding on the incident laser:

[0100] First, a set of start synchronization codes is sent to the device to be guided, the start synchronization code is 101010, and the device to be guided starts to receive the encoded optical signal in the horizontal direction; the spatial light modulator 5 encodes the incident laser and sends two images with grayscale gradients in the horizontal direction to the device to be guided, such as Fig.12 As shown, the grayscale of one image increases gradually from left to right, and the grayscale of the other image decreases gradually from left to right. In practice, the grayscale does not change continuously, but changes in steps. The current grayscale level is 20. After the two images are sent, a group of end synchronization codes are sent, and the end synchronization code is 0101.

[0101] Then a group of start synchronization codes are sent to the device to be guided, and the device to be guided starts to receive the encoded optical signal in the vertical direction; the spatial light modulator 5 encodes the incident laser and sends two images with grayscale gradients in the vertical direction to the device to be guided, such as Fig.13 As shown, the grayscale of one image gradually increases from top to bottom, and the grayscale of the other image gradually decreases from top to bottom. In practice, the grayscale does not change continuously, but changes in a step-like manner, with a grayscale level of 20. After the two images are sent, a group of end synchronization codes are sent.

[0102] The decoding is as follows:

[0103] At spatial position point A, when the first grayscale image is displayed, its grayscale is Ix1, and when the second grayscale image is displayed, its grayscale is Ix2. The horizontal position of point A in the spatial position can be calculated using the following formula.

[0104] △x=(Ix1-Ix2) / (Ix1+Ix2)

[0105] The absolute value of △x indicates the distance between point A and the horizontal center, and the sign of △x indicates whether point A is on the left or right side of the spot space.

[0106] Similarly, for two images in the system that display grayscale gradients in the vertical direction, the vertical position of a spatial point can be calculated using the following formula.

[0107] △y=(Iy1-Iy2) / (Iy1+Iy2)

[0108] The absolute value of △y indicates the distance between point A and the vertical center, and the sign of △y indicates whether point A is on the upper or lower side of the spot space.

[0109] The position coordinates (△x, △y) of point A can be determined through the horizontal position and the vertical position.

[0110] The timing of the four images sent in this embodiment is shown in Fig.14, the first and second frames are two pictures in the horizontal position, corresponding to the time sequences T1 and T2 respectively, the third and fourth frames are two pictures in the vertical position, corresponding to the time sequences T3 and T4 respectively, and the ordinate of each picture represents the light intensity of the spatial position.

[0111] In order to distinguish the two grayscale gradient images, a group of start synchronization codes 101010 need to be sent before sending the grayscale gradient images. After receiving this group of synchronization codes, the receiving end starts to receive the grayscale images. After sending two horizontal or two vertical grayscale gradient images, a group of end synchronization codes 0101 are sent so that the device to be guided can distinguish the received grayscale images. Fig.15 shown.

Claims

1. A spatial light field encoding device based on orthogonal time division multiplexing, characterized in that: It comprises a photoelectric sensor, a collimator (2) and a composite prism (3) arranged in sequence on the optical path of a laser (1), a projection lens (4) arranged on one side of the composite prism (3), and a spatial light modulator (5) arranged on the opposite side of the composite prism (3); The composite prism (3) comprises a lower prism (31) and an upper prism (32) which are arranged opposite to each other and both have a triangular prism structure; The lower bottom surface of the lower prism (31) constitutes the coded light incident surface (311) of the composite prism (3); One of the side surfaces of the lower prism (31) constitutes a first composite surface (312) of the composite prism (3); The other side surface of the lower prism (31) constitutes a laser incident surface (313) of the composite prism (3); The upper bottom surface of the upper prism (32) constitutes the coded light exit surface (321) of the composite prism (3); The surface of the upper prism (32) which is parallel to and opposite to the first composite surface (312) constitutes a second composite surface (322) of the composite prism (3); An air gap is provided between the first composite surface (312) and the second composite surface (322); The angle between the laser incident surface (313) and the coded light incident surface (311) is an obtuse angle; The angle between the first composite surface (312) and the laser incident surface (313) is 45°; The coded light incident surface (311) is parallel to the coded light exit surface (321); The output light of the laser (1) is collimated by a collimator (2) to form a collimated laser, and the collimated laser is projected to a spatial light modulator (5) through a composite prism (3) for light field intensity coding modulation, and the modulated light field returns to the composite prism (3) and is then projected through a projection lens (4) to form an image space light field, and the image space light field covers the motion range of the device to be guided; The photoelectric sensor is arranged on the device to be guided, and is used to receive and decode the encoding of the image space light field to obtain the position of the device to be guided, and adjust the steering gear according to the position to make the device to be guided move to a preset position.

2. The spatial light field encoding device based on orthogonal time division multiplexing according to claim 1, characterized in that: The refractive index n of the composite prism (3) is 1.5, and the critical angle for total reflection is 41.8°.

3. The spatial light field encoding device based on orthogonal time division multiplexing according to claim 2, characterized in that: The material of the composite prism (3) is H-K9.

4. A spatial light field encoding device based on orthogonal time division multiplexing according to any one of claims 1 to 3, characterized in that: The tilt angle of the micromirror of the spatial light modulator (5) relative to the horizontal plane is ±12°; The gap between the spatial light modulator (5) and the coded light incident surface (311) is 3.5 mm.

5. The spatial light field encoding device based on orthogonal time division multiplexing according to claim 4, characterized in that: The spatial light modulator (5) has a resolution of 1024×768, a micromirror array diagonal of 0.55 inches, a micromirror spacing of 10.8 μm, a micromirror crossing time of 2.5 μs, a micromirror reflectivity of 88%, an array diffraction efficiency of 86%, an array filling factor of 92%, and an input data clock rate of 400 MHz.

6. The spatial light field encoding device based on orthogonal time division multiplexing according to claim 3, characterized in that: The spatial light modulator (5) has a length of 40.64 mm, a width of 31.75 mm and a height of 5.98 mm; The dimensions of the micromirror array in the spatial light modulator (5) are 25.05 mm in length and 17.27 mm in width; The widths of the coded light incident surface (311) and the laser incident surface (313) are 43.35 mm and 30 mm respectively, and the widths of the second composite surface (322) and the coded light exit surface (321) are 48.25 mm and 55.09 mm respectively.

7. The spatial light field encoding device based on orthogonal time division multiplexing according to claim 6, characterized in that: The parameters of the laser (1) are as follows: wavelength of 808 nm, maximum power of 2 W, half-wave width of 3 nm, output fiber core diameter of 400 μm, and numerical aperture of 0.22; The parameters of the collimator (2) are as follows: the material is N-BK7, the shape is a plano-convex lens, the outer diameter is 25.4 mm, the center thickness is 4.7 mm, and the back focus is 56.7 mm; The parameters of the projection lens (4) are as follows: focal length is 20 mm, relative aperture is F2.8, and image field of view is ≥30 mm.

8. A spatial light field coding method based on orthogonal time division multiplexing, using the spatial light field coding device based on orthogonal time division multiplexing according to any one of claims 1 to 7, characterized in that: The following steps are involved: 1) After the laser light is vertically incident on the laser incident surface (313) of the composite prism (3), it is reflected by the composite prism (3) to the spatial light modulator (5); 2) The spatial light modulator (5) encodes the laser: If a certain micromirror in the spatial light modulator (5) is in an on state, the laser light reflected by the micromirror is emitted from the coded light emission surface in a vertical direction to the movement area of ​​the device to be guided; If a certain micromirror in the spatial light modulator (5) is in an off state, the laser light reflected by the micromirror is emitted from the coded light emission surface in an inclined direction to outside the moving area of ​​the device to be guided; 3) The coded laser light is projected into the moving area of ​​the device to be guided to form an image space light field; 4) The device to be guided receives and decodes the encoding of the image space light field through a photoelectric sensor, obtains its own position, and adjusts the steering gear according to the position to make the device to be guided move to a preset position.

9. The spatial light field encoding method based on orthogonal time division multiplexing according to claim 8, characterized in that: In step 4), the encoding specifically includes: S1) Selection of the working area of ​​the spatial light modulator (5): Taking the central area of ​​the spatial light modulator (5) as the working reflection surface, dividing the working reflection surface into M×M independent areas according to the resolution requirement for operation, each area includes N×N micromirrors; S2) Perform spatial orthogonal time division multiplexing encoding on the incident laser: First, a group of start synchronization codes are sent to the device to be guided, and the device to be guided starts to receive the encoded optical signal in the horizontal direction; the spatial light modulator (5) encodes the incident laser and sends two images with grayscale gradients in the horizontal direction to the device to be guided, wherein the grayscale of one image gradually increases from left to right, and the grayscale of the other image gradually decreases from left to right; after the two images are sent, a group of end synchronization codes are sent; Then, a group of start synchronization codes are sent to the device to be guided, and the device to be guided starts to receive the encoded optical signal in the vertical direction; the spatial light modulator (5) encodes the incident laser light, and sends two images with grayscale gradients in the vertical direction to the device to be guided, wherein the grayscale of one image gradually increases from top to bottom, and the grayscale of the other image gradually decreases from top to bottom; after the two images are sent, a group of end synchronization codes are sent; In step 4), the decoding specifically includes: The guided device receives four images and calculates the coordinates (△x, △y) of point A at any position in space according to the following formula: △x=(Ix1-Ix2) / (Ix1+Ix2) △y=(Iy1-Iy2) / (Iy1+Iy2) Ix1 and Ix2 are the grayscales of the two images in the horizontal direction; Iy1 and Iy2 are the grayscales of the two images in the vertical direction respectively.

10. The spatial light field encoding method based on orthogonal time division multiplexing according to claim 9, characterized in that ； In step 4), the start synchronization code is 101010, and the end synchronization code is 0101; the grayscale levels of the four images are all 20; In step S1), the size of the working reflective surface is 760×760, and is divided into 20×20 independent areas for operation, each area including 38×38 micromirrors.

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