A spatial light field encoding device and method based on orthogonal time division multiplexing

Abstract

The application relates to a spatial light field coding device and method for light field beam guiding, in particular to a spatial light field coding device and method based on orthogonal time division multiplexing. The technical problem of low coding frequency and poor reliability of the existing spatial coding technology for light field beam guiding is solved. The device comprises a photoelectric sensor, a laser, a collimating mirror, a composite prism, a projection lens and a spatial light modulator; the composite prism comprises a lower prism and an upper prism; the output light of the laser is collimated by the collimating mirror to form collimated laser, the collimated laser is projected to the spatial light modulator by the composite prism to perform light field intensity coding modulation, the modulated light field returns to the composite prism and is projected to form an image spatial light field by the projection lens; the photoelectric sensor is arranged on a device to be guided and is used for receiving the coding of the image spatial light field, decoding the position of the device to be guided, and adjusting a rudder to make the device to be guided move to a preset position.

Description

TECHNICAL FIELD

[0001] The application relates to a spatial light field encoding method for light field beam riding guidance, in particular to a spatial light field encoding device and method based on orthogonal time division multiplexing. BACKGROUND

[0002] The spatial light field encoding technology is mainly applied to the light field beam riding guidance technology. The light field beam riding guidance refers to a technology of controlling a to-be-guided device to move by using a modulated light field. In the guidance process, the to-be-guided device is always located in the light beam, and therefore the light field beam riding guidance is also called.

[0003] In the light field beam riding guidance system, the to-be-guided device determines its own position through spatial encoding. First, the spatial light irradiator needs to perform spatial encoding on the output light field. Different spatial positions of the encoded light beam section have different information codes. The to-be-guided device placed in the light field can obtain its own position after decoding, and then feedback to the control system and adjust the motion mechanism to move to the specified spatial position, so as to finally realize long-distance guidance. The principle is shown in Figure 1 .

[0004] The existing spatial encoding light irradiator is mainly applied to the ground environment, and the core component adopts a mechanical modulation disc to perform spatial light field encoding. As shown in Figure 2 and Figure 3 , a mechanical modulation disc is shown in Figure 2 , and a mechanical modulation disc mechanism is shown in Figure 3 . The mechanical modulation disc is a disc. For a coordinate point in the light field, the coordinate position can be obtained from the time proportion of different frequencies. The calculation formula is: K = 2 (τ1-τ2) / T, wherein 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 disc. The spatial encoding mode of the modulation disc needs to drive the modulation disc to continuously rotate at a high speed by using a motor, so the power consumption is large, the encoding frequency is low, and the reliability is poor. SUMMARY

[0005] The application aims to solve the technical problems of low encoding frequency and poor reliability caused by the mechanical modulation disc used in the existing spatial encoding for light field beam riding guidance, and provide a spatial light field encoding device and method based on orthogonal time division multiplexing.

[0006] The technical solution of the application is:

[0007] The application discloses a spatial light field encoding device based on orthogonal time division multiplexing, and has the characteristics that the device comprises a photoelectric sensor, a collimating mirror and a compound prism which are sequentially arranged in the light path of a laser, a projection lens arranged on one side of the compound prism, and a spatial light modulator arranged on the opposite side of the compound prism.

[0008] The compound prism comprises a lower prism and an upper prism which are oppositely arranged and both have a triangular prism structure.

[0009] The lower bottom surface of the lower prism forms an encoding light incident surface of the compound prism.

[0010] One side surface of the lower prism forms a first composite surface of the compound prism.

[0011] The other side surface of the lower prism forms a laser light incident surface of the compound prism.

[0012] The upper bottom surface of the upper prism forms an encoding light exit surface of the compound prism.

[0013] The surface of the upper prism which is parallel to and opposite to the first composite surface forms a second composite surface of the compound prism.

[0014] An air gap is arranged between the first composite surface and the second composite surface.

[0015] The included angle between the laser light incident surface and the encoding light incident surface is an obtuse angle.

[0016] The included angle between the first composite surface and the laser light incident surface is 45 degrees.

[0017] The encoding light incident surface is parallel to the encoding light exit surface.

[0018] The output light of the laser is collimated by the collimating mirror to form collimated laser light, the collimated laser light is projected to the spatial light modulator by the compound prism to perform light field intensity encoding modulation, the modulated light field returns to the compound prism and is projected to form an image space light field by the projection lens, and the image space light field covers the movement range of a device to be guided.

[0019] The photoelectric sensor is arranged on the device to be guided, and is used for receiving the encoding of the image space light field, decoding the position of the device to be guided, and adjusting a rudder to make the device to be guided move to a preset position.

[0020] Further, the refractive index n of the compound prism is 1.5, and the critical angle of total reflection is 41.8 degrees.

[0021] Further, the material of the compound prism is H-K9.

[0022] Further, the inclination angle of the micro-mirror of the spatial light modulator relative to the horizontal plane is ±12°; and the gap between the spatial light modulator and the coded light incidence surface is 3.5 mm.

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

[0024] Further, the length, width and height of the spatial light modulator are 40.64 mm, 31.75 mm and 5.98 mm respectively; the length and width of the micro-mirror array in the spatial light modulator are 25.05 mm and 17.27 mm respectively; the width of the coded light incidence surface and the laser incidence surface is 43.35 mm and 30 mm respectively; and the width of the second composite surface and the coded light exit surface is 48.25 mm and 55.09 mm respectively.

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

[0026] Meanwhile, the application also provides a spatial light field encoding method based on orthogonal time division multiplexing, which adopts the spatial light field encoding device based on orthogonal time division multiplexing.

[0027] 1) After the laser is vertically incident on the laser incidence surface of the laser self-composite prism, the laser is reflected to the spatial light modulator through the composite prism;

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

[0029] If a micro-mirror in the spatial light modulator is in an open state, the laser reflected by the micro-mirror is vertically emitted from the coded light exit surface to the movement region of the device to be guided;

[0030] If a micro-mirror in the spatial light modulator is in a closed state, the laser reflected by the micro-mirror is emitted from the coded light exit surface to the outside of the movement region of the device to be guided in an inclined direction;

[0031] 3) The encoded laser projected into the movement region of the device to be guided forms an image spatial light field;

[0032] 4) the to-be-guided device receives the code of the spatial light field through the photoelectric sensor, decodes the code to obtain the position of the to-be-guided device, and adjusts the steering engine to move the to-be-guided device to the preset position.

[0033] Further, in step 4), the code 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 reflective surface, and the working reflective surface is divided into MxM independent areas according to the resolution requirement, and each area includes NxN micromirrors;

[0036] S2) spatial orthogonal time division multiplexing coding of the incident laser:

[0037] A group of start synchronization codes are first sent to the to-be-guided device, and the to-be-guided device starts to receive the coded light signals in the horizontal direction; the spatial light modulator codes the incident laser and sends two images with gradually changing gray scales in the horizontal direction to the to-be-guided device, one of which gradually increases from left to right, and the other of which gradually decreases from left to right, and a group of end synchronization codes are sent after the two images are sent;

[0038] A group of start synchronization codes are further sent to the to-be-guided device, and the to-be-guided device starts to receive the coded light signals in the vertical direction; the spatial light modulator codes the incident laser and sends two images with gradually changing gray scales in the vertical direction to the to-be-guided device, one of which gradually increases from top to bottom, and the other of which gradually decreases from top to bottom, and a group of end synchronization codes are sent after the two images are sent;

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

[0040] The to-be-guided device receives four images, and calculates the coordinates (△x, △y) of any position A 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 gray scales of the two images in the horizontal direction, respectively;

[0044] Iy1 and Iy2 are the gray scales 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 gray scales of the four images are all 20.

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

[0047] Advantages of the present application:

[0048] 1. The spatial light field encoding device based on orthogonal time division multiplexing adopts a spatial light modulator for spatial encoding, and compared with the existing modulation disc encoding technology, the device is simple, has a high encoding frequency, no moving parts, high reliability and low power consumption, and can be applied to a satellite and other high-reliability and low-power-consumption platforms.

[0049] 2. The spatial light field encoding method based on orthogonal time division multiplexing adopts a spatial light modulator for spatial encoding of orthogonal time division multiplexing, and has the advantages of simple operation, high encoding efficiency and strong reliability. BRIEF DESCRIPTION OF DRAWINGS

[0050] Figure 1 is a schematic diagram of a light field pilot guidance system;

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

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

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

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

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

[0056] Figure 7 is a size parameter display diagram of the composite prism in the embodiment of the spatial light field encoding device based on orthogonal time division multiplexing;

[0057] Figure 8 is an edge light ray schematic diagram of the spatial light modulator in the “on” state (+12°) in the embodiment of the spatial light field encoding device based on orthogonal time division multiplexing;

[0058] Figure 9 is an edge light ray schematic diagram of the spatial light modulator in the “off” state (-12°) in the embodiment of the spatial light field encoding device based on orthogonal time division multiplexing;

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

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

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

[0062] Figure 13 is a spatial orthogonal time division multiplexing encoding schematic diagram (vertical direction) of an embodiment of a spatial light field encoding method based on orthogonal time division multiplexing of the application;

[0063] Figure 14 is a spatial orthogonal time division multiplexing encoding timing diagram of an embodiment of a spatial light field encoding method based on orthogonal time division multiplexing of the application;

[0064] Figure 15 is a spatial light modulator data transmission timing diagram of an embodiment of a spatial light field encoding method based on orthogonal time division multiplexing of the application.

[0065] The figure mark: 1-laser; 2-collimating mirror; 3-composite prism, 31-lower prism, 311-encoding light incident surface, 312-first composite surface, 313-laser incident surface, 32-upper prism, 321-encoding light exit surface, 322-second composite surface; 4-projection lens; 5-spatial light modulator. DETAILED DESCRIPTION

[0066] The application mainly adopts a spatial light modulator, a laser light source and an optical assembly as a spatial encoding light illuminator, adopts an orthogonal time division multiplexing spatial light field encoding technology to modulate a two-dimensional light field, so that a to-be-guided device receives an external two-dimensional light field encoding through a photoelectric sensor of the device and decodes the encoding to determine the position of the device, and then adjusts a steering engine to move to a preset position to realize guidance, and the principle is as shown in Figure 1 .

[0067] An embodiment of a spatial light field encoding device based on orthogonal time division multiplexing of the application is as shown in Figure 4As shown, it comprises a photoelectric sensor, a collimating mirror 2 and a compound prism 3 arranged in sequence in the light path of the laser 1, a projection lens 4 arranged at one side of the compound prism 3, and a spatial light modulator 5 arranged at the opposite side of the compound prism 3. The gap between the spatial light modulator 5 and the coded light incident surface 311 is 3.5mm. The laser 1 is a fiber laser, and a fiber laser with good monochromaticity is used as the light source. The photoelectric sensor is arranged on the device to be guided, and is used to receive the coded spatial light field and decode to obtain the position of the device to be guided, and adjust the rudder to make the device to be guided move to the preset position.

[0068] As shown in the figure, Figure 6 The compound prism 3 comprises a lower prism 31 and an upper prism 32 arranged oppositely and both in the form of triangular prism. The lower bottom surface of the lower prism 31 constitutes the coded light incident surface 311 of the compound prism 3, the upper bottom surface of the upper prism 32 constitutes the coded light exit surface 321 of the compound prism 3, one of the side surfaces of the lower prism 31 constitutes the first compound surface 312 of the compound prism 3, and the surface of the upper prism 32 opposite to the first compound surface 312 constitutes the second compound surface 322 of the compound prism 3, and an air gap is arranged between the first compound surface 312 and the second compound surface 322. The other side surface of the lower prism 31 constitutes the laser incident surface 313 of the compound prism 3. The included angle between the laser incident surface 313 and the coded light incident surface 311 is obtuse. The included angle between the first compound 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 compound prism 3 are as follows: the material is H-K9, the refractive index n is 1.5, and the critical angle of total reflection is 41.8°.

[0069] The main principle of the device is that the output light of the fiber laser is collimated by the collimating mirror 2 to form collimated laser, the collimated laser is projected to the spatial light modulator 5 by the compound prism 3 to perform light field intensity coding modulation, and after two-dimensional light field modulation (object space) by the spatial light modulator 5, it returns to the compound prism 3 and is projected by the projection lens 4 to form an image spatial light field, which covers the movement 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 as follows: 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: Made of N-BK7; Plano-convex lens with an outer diameter of 25.4 mm, a center thickness of 4.7 mm, and a back focal length of 56.7 mm.

[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 that needs 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 ②) and the second composite surface 322 of the refractive surface of the upper prism 32 (ie Figure 7 The angle of the plane marked with number ④ is calculated below for each of the two prisms. The material used for composite prism 3 is H-K9, with a refractive index of n = 1.5. The critical angle for total internal reflection is 41.8°.

[0076] When the spatial light modulator 5 is in the "on" state +12°, Figure 8As shown in the figure. To ensure that the entire outgoing light enters the projection system vertically, the light must be incident on the micromirror 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 and reaches surface ②. At surface ②, the light is totally reflected at an incident angle of 45°. The light is then emitted vertically from surface ③ at 90°, with an angle of 15.7° with the horizontal direction. The light emitted from surface ② and entering surface 4 is deflected and still enters the projection system vertically from surface ⑤.

[0077] When the spatial light modulator is in the "off" state -12°, Figure 9 As shown in the figure, the incident light enters the composite prism 3 perpendicular to surface ③, undergoes total internal reflection at surface ② and reaches surface 1. It is then refracted at 24° and reflected by the micromirror surface of the spatial light modulator 5. The reflected light is refracted at surface 1 at an incident angle of 45° and at surface 2 at an incident angle of 0.4° to reach surface 4. The light is deflected by surface 4 but still reaches surface 5 at an incident angle perpendicular to surface 2 and is refracted. 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 states of the spatial light modulator +12° and -12° are used to determine the length of each side, as shown in the figure below: Figure 7 As shown in the figure, the size design of the composite prism 3 in this embodiment is as follows: the thickness of the composite prism 3 is 30 mm, the widths of the coded light incident surface 311 (i.e., surface ①) and the laser incident surface 313 (i.e., surface ③) are 43.35 mm and 30 mm 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 48.25 mm and 55.09 mm 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: Projection Lens 4 projects the two-dimensional planar light field modulated by SLM 5 into the object space, forming spatial light fields at various angles. The parameters of Projection Lens 4 are as follows: focal length 20 mm; relative aperture F2.8; image-side field of view ≥ 30 mm.

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

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

[0083] The spatial light modulator 5 is an array of tiny mirrors (micromirrors). Each pixel of the spatial light modulator can be individually controlled by a computer. By applying pulsed drive signals of varying frequencies or duty cycles to each pixel, the intensity of the output reflected light can be modulated. In a laser illumination system, the spatial light modulator can spatially modulate the light field projected onto the spatial light modulator chip, achieving spatial encoding of the light field.

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

[0085] like Figure 10 As shown, the spatial light modulator 5 has a pixel resolution of 1024×768. To fully utilize the light source and facilitate equal area division, a square area of ​​760×760 is selected, with the center area serving as the working reflective surface. Based on the required resolution of the illumination surface, this embodiment divides the working reflective surface into 400 independent regions (20×20, i.e., (P(1,1) to P(20,20)) for operation, each of which consists of 38×38 pixels (micromirrors).

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

[0087] The spatial light modulator 5 is essentially a reflective device that achieves binary operation by changing the state of its micromirrors. Specifically, it can only have two states: "On" and "Off." In the "On" state, it fully reflects incident light, while in the "Off" state, it does not reflect incident light. In the device of the present invention, grayscale modulation of the incident light is required to display grayscale images. In the spatial light modulator module, grayscale modulation can be achieved by controlling the duration of each micromirror's on-time. Grayscale modulation is achieved by setting different two-dimensional codes for different micromirrors or blocks of the DMD module within a certain pulse period. Figure 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] Meanwhile, the application also provides a spatial light field encoding method based on orthogonal time division multiplexing, which adopts the spatial light field encoding device based on orthogonal time division multiplexing.

[0089] 1) After the laser is vertically incident on the laser incidence surface 313 of the laser self-combination prism 3, the laser is reflected to the spatial light modulator 5 through the combination prism 3;

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

[0091] If a micro-mirror in the spatial light modulator 5 is in an open state, the laser reflected by the micro-mirror is emitted from the encoding light exit surface to the motion region of the device to be guided in the vertical direction;

[0092] If a micro-mirror in the spatial light modulator 5 is in a closed state, the laser reflected by the micro-mirror is emitted from the encoding light exit surface to the outside of the motion region of the device to be guided in the inclined direction;

[0093] 3) The encoded laser projected into the motion region of the device to be guided forms an image spatial light field;

[0094] 4) The device to be guided receives the encoding of the image spatial light field through the photoelectric sensor and decodes to obtain the position of itself, and adjusts the rudder according to the position to make the device to be guided move to the preset position.

[0095] In the application, the spatial orthogonal time division multiplexing encoding is adopted, which refers to that in a certain plane in space, the light field at the place is encoded in the horizontal and vertical directions according to the time sequence, and the light intensity encoding technology is adopted, that is, the step grayscale image is displayed, and the spatial position is determined according to the light intensity.

[0096] The encoding specifically includes the following steps:

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

[0098] The central region of the spatial light modulator 5 is taken as the working reflection surface, the working reflection surface is divided into MxM independent regions according to the resolution requirement for operation, and each region includes NxN micro-mirrors. In the embodiment, the size of the working reflection surface is 760x760, and the working reflection surface is divided into 20x20 independent regions for operation, and each region includes 38x38 micro-mirrors.

[0099] S2) Spatial orthogonal time division multiplexing encoding of 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. 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 Figure 12 As shown in the figure, 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 a step-like manner. The current grayscale level is 20. After the two images are sent, a set of end synchronization codes is sent, and the end synchronization code is 0101.

[0101] Then a set of start synchronization codes is sent to the device to be guided, and the device to be guided begins to receive the vertically encoded optical signal; the spatial light modulator 5 encodes the incident laser and sends two vertical grayscale gradient images to the device to be guided, such as Figure 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 location 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 space 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 by the position in the horizontal direction and the position in the vertical direction.

[0110] The timing of the four images sent in this embodiment is shown in Figure 14, the first frame and the second frame are two images in horizontal position, corresponding to time sequence T1 and T2 respectively, the third frame and the fourth frame are two images in vertical position, corresponding to time sequence T3 and T4 respectively, the vertical coordinate of each image represents the light intensity of the spatial position.

[0111] In order to distinguish the two gray scale transition images, a group of start synchronization code 101010 is sent before sending the gray scale transition image, and the receiving end starts to receive the gray scale image after receiving the group of synchronization code. A group of end synchronization code 0101 is sent after sending the two horizontal or two vertical gray scale transition images, so as to distinguish the received gray scale image by the guiding device, as shown in Figure 15 ​

Claims

1. A spatial light field encoding device based on orthogonal time-division multiplexing, characterized by: It comprises a photoelectric sensor, a collimating mirror (2) and a compound prism (3) arranged in sequence in the light path of a 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 compound prism (3) comprises a lower prism (31) and an upper prism (32) arranged oppositely and both in a triangular prism structure. A lower bottom surface of the lower prism (31) constitutes an encoded light incident surface (311) of the compound prism (3). One side surface of the lower prism (31) constitutes a first compound surface (312) of the compound prism (3). Another side surface of the lower prism (31) constitutes a laser light incident surface (313) of the compound prism (3). An upper bottom surface of the upper prism (32) constitutes an encoded light exit surface (321) of the compound prism (3). A surface of the upper prism (32) parallel to and opposite to the first compound surface (312) constitutes a second compound surface (322) of the compound prism (3). An air gap is arranged between the first compound surface (312) and the second compound surface (322). An included angle between the laser light incident surface (313) and the encoded light incident surface (311) is obtuse. An included angle between the first compound surface (312) and the laser light incident surface (313) is 45°. The encoded light incident surface (311) is parallel to the encoded light exit surface (321). Output light of the laser (1) forms collimated laser light after collimation by the collimating mirror (2), the collimated laser light is projected to the spatial light modulator (5) to perform light field intensity encoding modulation by the compound prism (3), the modulated light field returns to the compound prism (3) and then is projected to form an image space light field by the projection lens (4), and the image space light field covers a movement range of a device to be guided. The photoelectric sensor is arranged on the device to be guided, receives and decodes the encoding of the image space light field to obtain a position of the device to be guided, and adjusts a rudder to move the device to be guided to a preset position.

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

3. The spatial light field encoding device based on orthogonal time division multiplexing according to claim 2, wherein a material of the compound prism (3) is H-K9.

4. The spatial light field encoding device based on orthogonal time division multiplexing according to any one of claims 1 to 3, wherein an inclination angle of a micromirror of the spatial light modulator (5) relative to a horizontal plane is ±12°, and a gap between the spatial light modulator (5) and the encoded 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, wherein ​ ​ ​ ​ The resolution of the spatial light modulator (5) is 1024×768, the diagonal of the micromirror array is 0.55 inches, the micromirror spacing is 10.8 μm, the micromirror crossing time is 2.5 μs, the micromirror reflectivity is 88%, the array diffraction efficiency is 86%, the array fill factor is 92%, and the input data clock rate is 400 MHz.

6. The spatial light field encoding device based on orthogonal time division multiplexing according to claim 3, characterized in that: The length, width and height of the spatial light modulator (5) are 40.64 mm, 31.75 mm and 5.98 mm, respectively; The length and width of the micromirror array in the spatial light modulator (5) are 25.05 mm and 17.27 mm, respectively; The widths of the encoding 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 encoding 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 is 808 nm, maximum power is 2 W, half-wave width is 3 nm, output fiber core diameter is 400 μm, and numerical aperture is 0.22; The parameters of the collimating mirror (2) are as follows: material is N-BK7, shape is plano-convex lens, outer diameter is 25.4 mm, central thickness is 4.7 mm, and back focal length 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 of any of claims 1-7, characterized in that, The steps include: 1) After the laser is perpendicularly incident on the laser incident surface (313) of the laser self-composite prism (3), the laser is reflected to the spatial light modulator (5) through the composite prism (3); 2) The spatial light modulator (5) encodes the laser: If a micromirror in the spatial light modulator (5) is in an open state, the laser reflected by the micromirror is perpendicularly emitted from the encoding light exit surface to the motion region of the device to be guided; If a micromirror in the spatial light modulator (5) is in a closed state, the laser reflected by the micromirror is obliquely emitted from the encoding light exit surface to the outside of the motion region of the device to be guided; 3) The encoded laser projected into the motion region of the device to be guided forms an image spatial light field; 4) The device to be guided receives the encoding of the image spatial light field through a photoelectric sensor and decodes it to obtain its position, and adjusts the rudder to make the device to be guided move to the preset position.

9. The spatial light field coding 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): The central region of the spatial light modulator (5) is taken as the working reflection surface, and the working reflection surface is divided into M×M independent regions according to the resolution requirement for operation, and each region includes N×N micromirrors; S2) Spatial orthogonal time division multiplexing encoding of the incident laser: A set of start synchronization code is sent to the device to be guided first, and the device to be guided starts to receive the coded light signal in horizontal direction; the spatial light modulator (5) codes the incident laser light and sends two images with gray scale gradually changing in horizontal direction to the device to be guided, one of the images has gray scale gradually increasing from left to right, and the other has gray scale gradually decreasing from left to right, after the two images are sent, a set of end synchronization code is sent; Then a set of start synchronization code is sent to the device to be guided, and the device to be guided starts to receive the coded light signal in vertical direction; the spatial light modulator (5) codes the incident laser light and sends two images with gray scale gradually changing in vertical direction to the device to be guided, one of the images has gray scale gradually increasing from top to bottom, and the other has gray scale gradually decreasing from top to bottom, after the two images are sent, a set of end synchronization code is sent; In step 4), the decoding specifically comprises: The device to be guided receives four images, and the coordinates (△x, △y) of any position A in space are calculated according to the following formula: △x = (Ix1-Ix2) / (Ix1+Ix2) △y = (Iy1-Iy2) / (Iy1+Iy2) Ix1 and Ix2 are the gray scales of the two images in horizontal direction respectively; Iy1 and Iy2 are the gray scales of the two images in vertical direction respectively.

10. The spatial light field coding 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 gray scales of the four images are all 20. In step S1), the size of the working reflective surface is 760×760, and the working reflective surface is divided into 20×20 independent areas for operation, each area includes 38×38 micromirrors.

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