CN104698802A - Large-size calculation holographic representation method - Google Patents

Abstract

The invention proposes a large-scale computational holographic reconstruction method. The method includes loading a discrete phase grating and space division multiplexing in a phase hologram. The present invention utilizes the method of space division multiplexing, first divides the selected picture into four sub-pictures, in order to realize the movement of the reproduced image position, load the phase of the discrete phase grating into the hologram in the process of making the phase hologram, and then The spatial light modulator (SLM) is divided into four parts, each part is loaded with the phase hologram of the corresponding sub-picture. During the optical reproduction process, the computer controls the change of the discrete phase grating in the hologram loaded into the corresponding scene, adjusts the positions of the four reproduced images, realizes the seamless splicing of the reproduced images, and obtains a large-scale computational holographic reconstruction.

Description

A Large-scale Computational Holographic Reconstruction Method

technical field

The present invention relates to computing holographic display technology, more specifically, the present invention relates to a large-scale computing holographic display technology.

Background technique

Holographic display is a true three-dimensional display technology, and viewers can watch stereoscopic images without wearing vision aid glasses. With the rapid development of computer technology, people widely use computer to simulate and process various optical processes, and derived computational holographic display technology. With the improvement of computer performance and the development of optoelectronic devices, the advantages of computational holographic displays based on spatial light modulators (SLM) have become more prominent, which has brought a lot of room for development of holography, which mainly loads holograms on SLMs. , to replace the chemical recording dry plate in traditional optical holography, thereby avoiding the harsh requirements of traditional optical holography on the optical path and experimental environment. At the same time, since the SLM can be erased and written in real time, real-time reproduction can be realized. However, limited by the structure of existing spatial light modulators, the reconstructed image size of computational holography is very small, which cannot meet people's actual needs.

In order to obtain a systematic and simple large-scale computational holographic reconstruction, researchers at home and abroad have conducted a series of studies. Japan's Kenji Yamamoto and his team proposed to divide the scenes to be reproduced and make them into holograms, and then load them on the corresponding SLM, and use multiple SLM array splicing methods to realize computational holographic large-scale display. However, in order to realize seamless splicing of reproduced images in this system, a lens array and a special large lens are introduced, which increases the complexity and operation difficulty of the system. Tomoyoshi Shimobaba of Chiba University in Japan proposed to expand the size of the computational holographic reconstruction by changing the sampling interval of the original image. Although the method system is simple and easy to implement, this method does not expand the size of the entire reconstructed image in essence, but only discards the edge information of the original image and locally expands the required information. The reproduced image size of the figure is the same.

Contents of the invention

The invention proposes a large-scale calculation holographic reproduction method, which combines the space division multiplexing method and loading discrete phase gratings in the phase hologram to realize large-scale calculation holographic display.

The space division multiplexing method is to process a picture whose length and width are x and y respectively in MATLAB, and the obtained dimensions are respectively The four sub-pictures are shown in Figure 1, and then their pixels are interpolated by bilinear interpolation to match the SLM pixels; the four sub-pictures are processed by Fourier iterative method to obtain four holograms ; Then synthesize a new hologram from the four holograms and load it on the SLM, which is equivalent to dividing the effective area of the SLM into four parts, each area is loaded with a corresponding hologram, and after optical reproduction, the four Regions will get their respective reconstructions.

Calculate the size h of the holographic reconstruction image and the focal length f of the imaging lens, the wavelength λ of the light source, and the SLM pixel size p to satisfy:

h = f λ ∕ p (1)

It can be seen that for the same optical path, that is, the optical path with the same f , λ , and p has the same size of the reproduced image of any picture. Therefore, it can be seen that the size of the reproduced image of the four sub-pictures and the original image is the same.

In order to splice the reconstructed images of the four parts together, an appropriate discrete phase grating is added in the process of generating the phase hologram, and the steps of generating the hologram are shown in Figure 2. During the optical reproduction process, the reproduction optical path is shown in Figure 3. The computer controls the change of the discrete phase grating loaded into the hologram of the corresponding scene, adjusts the positions of the four reproduction images, and realizes the seamless splicing of the reproduction images, thereby Computational holographic large-scale reconstructions are obtained.

Preferably, the structure of the discrete phase grating is shown in Figure 4, which has the function of phase modulation. Generally, the phase modulation is performed on the light wave with a period of 2 π , thereby changing the diffraction direction of the light and causing the position of the reproduced image to shift. The method of loading discrete phase gratings in the hologram is to add the phase modulation factor of the discrete phase grating in the phase hologram. By changing the phase modulation factor and changing the outgoing direction of the light, the position of the calculated holographic reconstruction image can be within the reconstruction area. Move freely.

Specifically, the phase of a discrete phase grating can be expressed as:

φ _g = mod( bm+cn , T ) × (2 π / T ) (2)

In the formula, mod represents the modulo operation, T represents the period of the grating, m and n represent the horizontal and vertical ranges of the grating respectively, b and c represent the grating loaded in the m and n directions respectively. Different b and c values can be used to obtain gratings in different directions, and different T values can be used to obtain gratings with different light deflection angles. It can be seen that after the light passes through the grating, it is equivalent to performing linear phase compensation on the light. During computer coding, the phase distribution of the grating is loaded into the phase hologram of the object, and the reproduced image is shifted to a specific position by changing the size of b , c , and T through program control. Let the phase of the object generated by the iterative Fourier algorithm be φ , then the phase finally loaded on the SLM should be:

φ _new = mod( φ+φ _g , 2 π ) (3)

Description of drawings

Accompanying drawing 1 is the recorded picture and four sub-pictures after division.

Accompanying drawing 2 is the production flowchart of the hologram of the present invention.

Accompanying drawing 3 is the structural representation of the present invention.

Accompanying drawing 4 is the structure diagram of discrete phase grating.

Accompanying drawing 5 is the reproduction image of original picture.

Accompanying drawing 6 is the reconstructed image that the present invention obtains.

The pictorial labels in the above-mentioned accompanying drawings are:

1 laser, 2 filter, 3 collimator lens, 4 spatial light modulator, 5 Fourier lens, 6 receiving screen, 7 computer.

It should be understood that the above drawings are only schematic and not drawn to scale.

Detailed ways

The specific implementation of a large-scale computational holographic reconstruction method proposed by the present invention will be described in detail below to further describe the present invention. It is necessary to point out that the following examples are only used for further description of the present invention, and cannot be interpreted as limiting the protection scope of the present invention. Those skilled in the art make some non-essential improvements and improvements to the present invention according to the above-mentioned content of the invention. Adjustment still belongs to the protection scope of the present invention.

In this implementation case, a green laser with a wavelength of 532nm is used, the filter is located on the optical axis of the reproduced light exiting at 100mm behind the laser, the collimator lens is located at 300mm from the filter, the SLM is located at 500mm behind the collimator lens, and the imaging lens and The distance between the SLMs is 150 mm; in the present invention, the Fourier imaging lens is used as the imaging lens, and the receiving screen is located at 500 mm behind the Fourier imaging lens. Among them, the SLM adopts a reflective phase-type SLM with a resolution of 1920 × 1080, a pixel size of 8 μm, and an effective area size of 8.64 mm × 15.36 mm ; the focal length of the Fourier imaging lens is 500 mm. The image source used is a grayscale image with 512 × 512 pixels.

In this example, after sample discretization, bilinear interpolation is used to interpolate the image to a size of 1920 × 1080; after that, Fourier iteration is performed to obtain its phase. In this implementation case, in order to reduce the speckle noise of the reproduced image, the iteration The number of positioning is 50 times; then the phase of the discrete phase grating is added to the obtained phase; then it is encoded into a computational hologram; and then the holograms of the four sub-pictures are synthesized into a new hologram.

In this example, the effective area of the SLM is divided into four parts, and the size of each part is 4.32 mm × 7.68 mm , and then the holograms of the four sub-pictures are respectively loaded on the corresponding areas of the SLM. The green light source emitted by the laser becomes collimated light through a filter and a collimating lens, and then irradiates the reflective SLM loaded with a hologram at an incident angle of 3°, and is imaged on its focal plane after passing through a Fourier lens .

In order to achieve seamless splicing of the four reconstructed images, the coefficients of the discrete phase grating added to the upper left corner of the original image are b = 1, c = 1, T = 6; the discrete phase grating added to the upper right corner of the original image The coefficients of the discrete phase grating are b = -1, c = 1, T = 6; for the figure in the lower left corner, the coefficients of the discrete phase grating are b = -1, c = -1, T = 6; for the figure in the lower right corner The coefficients of the discrete phase grating are b = 1, c = -1, T = 6. Finally, the four reconstructed images are regularly adjacent to obtain a seamless spliced large-scale computed holographic reconstructed image. Accompanying drawing 5 and accompanying drawing 6 are respectively the reproduced image of original picture and the reconstructed image that the present invention obtains, and it can be seen that the result of the present invention is enlarged four times than the result of reproduced image of original picture.

Claims (3)

1. a large scale calculation holographic reproducting method, is characterized in that, the method is by spatial division multiplexing usage and in phase hologram, load discrete phase grating combine, and achieves the display of large scale calculation holographic.

2. large scale calculation holographic reproducting method according to claim 1, is characterized in that, utilize spatial division multiplexing usage one width length and width are respectively into xwith ypicture process in MATLAB, obtain size and be respectively four width sub-pictures, then by bilinear interpolation by their pixel respectively interpolation itself and slm pixel are matched; Utilize Fourier's process of iteration to be processed respectively by this four width figure, obtain four width holograms; Then four width holograms are synthesized the new hologram of a width, be loaded in spatial light modulator (SLM), with regard to being equivalent to, the effective coverage of SLM is divided into four parts like this, each region loads corresponding hologram respectively, through optical reproduction, these four regions will obtain respective reproduction image, and its size is all identical with the size of former figure reproduction image, then the holographic reconstructed image through four sub-pictures splices, and just obtains large-sized reproduction image.

3. large scale calculation holographic reproducting method according to claim 1, it is characterized in that, discrete phase grating has the function of phase-modulation, the diffraction direction of light can be changed, so load discrete phase grating in phase type hologram, changing the exit direction of light, by changing the discrete phase grating be loaded in phase type hologram, the position of calculation holographic reproduction image can be moved freely in reproduction regions; Discrete phase grating is generally with 2 πfor the cycle carries out phase-modulation to light wave, its phase place can be expressed as φ _g =mod ( bm+cn, t) × (2 π/ t), in formula, mod represents modulo operation, trepresent the cycle of grating, m, nthe transverse and longitudinal scope of grating, b, crepresent respectively and be loaded into mwith ngrating on direction; Get different bwith cvalue can obtain the grating of different directions, gets different value can not be shared the same light the grating of deflection angle, can see that light is by being equivalent to after grating carry out linear phase compensation to light; When computer code, the PHASE DISTRIBUTION of grating is loaded in the phase type hologram of object, makes reproduction image be displaced to specific position by programmed control; The phase place making iterative Fourier transform algorithm produce object is φ, then the phase place be finally loaded on SLM should be φ _new =mod ( φ+φ _g , 2 π).