CN103995454A - A method for real-time 3D display of color holography with a single spatial light modulator - Google Patents

Abstract

The invention discloses a method for realizing color holographic real-time three-dimensional display by a single spatial light modulator. This method is a color holographic three-dimensional display method that can not only reduce the volume of the system, but also realize calculation acceleration. Compared with the prior art, the present invention uses a single spatial light modulator to realize color holographic 3D display in the technical solution proposed by the present invention, which simplifies the system and provides an effective way for miniaturization of color holographic 3D display equipment.

Description

A method for real-time 3D display of color holography with a single spatial light modulator

technical field

The invention relates to the technical field of holographic display, and more particularly relates to a method for realizing real-time three-dimensional display of color holography by a single spatial light modulator.

Background technique

Today, with the rapid development of information and science and technology, traditional display technology can no longer meet people's visual needs. People not only pursue higher resolution and more realistic color effects, but also hope to provide the same three-dimensional (3D) display in space as real objects. 3D display can show the layering and depth of images, and can be widely used in military affairs, education, film and television entertainment, and medicine. Computational holographic 3D projection display can completely record and reconstruct the wavefront of three-dimensional objects, and provide all the depth information required by the human visual system, so it has become one of the research hotspots in the field of 3D display.

Computational holographic 3D display technology is an organic combination of holography and computer display technology. Computational holographic color display technology can be divided into two categories according to the number of LC-SLMs required to achieve true color display. One requires three LC-SLMs, and the other requires only one LC-SLM to achieve true color display. .

Three LC-SLMs to achieve true color: In 1994, Sato and other Japanese scholars analyzed the characteristics of phase holograms, and proposed the use of three SLMs to achieve color holographic display. The experimental system consists of three SLMs, and the reproduced images of red, green, and blue (RGB) color components are synthesized in space by using light-combining elements to realize holographic color display. However, this solution requires a complex optical path design to ensure that the reproduced images of the three RGB channels are accurately combined, which greatly increases the volume of the system.

Single LC-SLM to achieve true color: In order to reduce the cost and complexity of the system, the holographic color display method based on a single LC-SLM has become one of the research hotspots. At present, there are two main color display methods based on a single-chip spatial light modulator: time-division multiplexing and space division.

Since T. Shimobaba and other Japanese scholars proposed a method of using time-division multiplexing to display color holographic display in 2003, research on holographic color display technology based on this method has made great progress. The time-division multiplexing method is also called the time-series color display method. Under the control of the synchronous control circuit, the RGB three-color reproduction light illuminates the single-chip LC-SLM according to a certain timing, and the hologram is also loaded into the LC-SLM according to a certain timing. In the SLM, the RGB three-color component holographic reconstruction images are received and displayed in time series on the receiving screen. This solution requires the spatial light modulator to have a higher frame rate. When the rate reaches a certain level, the human eye perceives a temporally synthesized color image through the integral effect. In the principle of this solution, for a color component, there is energy loss on the time axis, so its imaging effect will be affected to a certain extent. The advantage of the time series display method is that only one information bearing medium device is needed to realize color display, and the system structure is relatively simple. However, this method needs to precisely control the synchronization between the working time of the RGB light source and the loading of the hologram corresponding to the RGB color components, which requires a higher response speed for the hardware loading the hologram.

In 2004, Japanese scholar I. Tomoyoshi et al. proposed a way of using space segmentation to realize true color display. The system uses RGB three-color LEDs to synthesize multicolor light sources, and then irradiates them on a single LC-SLM at different angles simultaneously to realize a three-dimensional true-color holographic display. The research group improved the system again in 2011, but the system used an iterative algorithm for optimization when calculating holograms, making it difficult to achieve real-time display effects.

Contents of the invention

(1) Technical problems to be solved

The technical problem to be solved by the present invention is to provide a color holographic three-dimensional display method that can reduce the volume of the system and realize calculation acceleration.

(2) Technical solution

In order to solve the above technical problems, the present invention provides a method for real-time three-dimensional display of color holography, the steps of which are as follows:

Step 1: Divide the 3D color object on the object plane into three components: red, green, and blue, and propagate freely through space to reach the hologram surface respectively. The distance from the origin of the object plane to the origin of the hologram plane is z;

Step 2: The three beams of RGB plane reference light are irradiated on the holographic surface at different angles, and interfere with the corresponding object light color components to obtain three holograms, that is, the red reference light interferes with the object light red component to obtain H ₁ (x,y,z), the green reference light interferes with the green component of the object light to obtain H ₂ (x,y,z), the blue reference light interferes with the blue component of the object light to obtain H ₃ (x,y,z );

Step 3: Interfering different color components with their corresponding reference light to form a hologram is superimposed to form a hologram, and then add a y-axis direction tilt phase factor to the hologram, the expression can be written as:

Among them, where k _i =2π/λ _i , λ _i is the wavelength, and ψ is the tilt angle in the y-axis direction, which can shift the zero-order diffracted light of the spatial light modulator during the image reconstruction process, A(x ,y) represents the amplitude distribution of the hologram, represents the phase distribution of the hologram;

Step 4: Normalize the amplitude distribution, and then multiply it with the phase to get the final hologram,

Further, the obtained hologram is loaded into a single spatial light modulator, and then the three beams of RGB reproduced light are respectively irradiated on the hologram at the angle of recording, and a color image is obtained at a distance from the object plane.

(3) Beneficial effects

Compared with the prior art, the present invention uses a single spatial light modulator to realize color holographic 3D display in the technical solution proposed by the present invention, which simplifies the system and provides an effective way for miniaturization of color holographic 3D display equipment.

Our program runs on a PC with a core of 2.6GHz, and the software used is Matlab2011b. For the traditional color hologram calculation, the original color image is generally divided into RGB three-color components, and then the corresponding holograms are calculated separately. Without iterative optimization, it takes about 1.7 seconds to calculate three holograms with 1080×1080 pixels using the angular spectrum method, but the quality of the reconstructed color images is very poor. In order to improve the image quality, iterative algorithms are generally used to optimize the hologram, but this will be very time-consuming. However, it only takes about 1.3 seconds to calculate a 1080×1080 pixel hologram with our method, and the quality of the reconstructed image is high.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. Those skilled in the art can also obtain other drawings based on these drawings without creative work.

Fig. 1 is a schematic diagram of the hologram recording process of the present invention;

Fig. 2 is a schematic diagram of the reproduction process of a 3D color object in the present invention;

Fig. 3 is a schematic structural diagram of the full-color holographic display system of the present invention;

Fig. 4 is a schematic diagram of the hologram generation process of the 3D color object of the present invention;

Fig. 5 is a diagram of the optical reproduction result of a color 3D object according to the present invention, where (a) focuses on "RMB", and (b) focuses on "YGC".

Detailed ways

Embodiments of the present invention will be further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but should not be used to limit the scope of the present invention.

The present invention can use a single spatial light modulator to realize true-color holographic three-dimensional display, which greatly reduces the volume of the color holographic three-dimensional display system; at the same time, the final hologram is obtained through an analytical method, and no iterative algorithm is needed to optimize the hologram. Thus, the time for calculating the hologram is greatly saved.

The process of the computational generation process of the computational hologram is shown in Fig. 1.

Step 1: Divide the 3D color object on the object plane into three components: red, green, and blue, and propagate freely through space to reach the hologram surface respectively. The distance from the origin of the object plane to the origin of the hologram plane is z;

Step 2: The three beams of RGB plane reference light are irradiated on the holographic surface at different angles, and interfere with the corresponding object light color components to obtain three holograms, that is, the red reference light interferes with the object light red component to obtain H ₁ (x,y,z), the green reference light interferes with the green component of the object light to obtain H ₂ (x,y,z), the blue reference light interferes with the blue component of the object light to obtain H ₃ (x,y,z );

Step 3: Interfering different color components with their corresponding reference light to form a hologram is superimposed to form a hologram, and then add a y-axis direction tilt phase factor to the hologram, the expression can be written as:

Among them, where k _i =2π/λ _i , λ _i is the wavelength, and ψ is the tilt angle in the y-axis direction, which can shift the zero-order diffracted light of the spatial light modulator during the image reconstruction process, A(x ,y) represents the amplitude distribution of the hologram, represents the phase distribution of the hologram;

Step 4: Normalize the amplitude distribution, and then multiply it with the phase to get the final hologram,

The process of reconstructing 3D color objects is shown in Fig. 2.

The obtained hologram is loaded into the spatial light modulator, and then the three beams of RGB reproduced light are respectively irradiated on the hologram at the angle of recording, and the desired color image can be obtained at a distance from the object plane.

Construct a simple colored three-dimensional object, use the above principles to calculate the hologram and load it on the spatial light modulator, so that the spatial light modulator can reproduce the color holographic 3D image. The structure of the full-color holographic display system is shown in Figure 3. In the figure, BS is a semi-reflective half-mirror, and SLM is a reflective pure-phase liquid crystal spatial light modulator. The three-color lasers are coupled out by three couplers to output planar light waves, and they irradiate the spatial light modulator at different angles at the same time. The reconstructed color image is reflected to the output plane by a BS, and the CCD detector is used to record the experimental results.

Further illustrate the present invention with embodiment below.

We assume that this 3D object is composed of two pictures (both 1024×1024 pixels) before and after, and the distances from the holographic surface are z1=650mm and z2=500mm respectively. The size of the hologram is 8.64mm×8.64mm, the number of pixels is 1080×1080, the sampling interval of the holographic surface is 8.0μm×8.0μm, and the wavelengths of the red, green and blue recording lasers are still λ _R = 671nm, λ _G = 532nm , λ _B =473nm, the incident angles of the reference light red light and blue light are 2° and -2° respectively, and the incident angle of the green light is 0°. Using our proposed method to calculate the final hologram, the hologram generation process is shown in Figure 4. and load it into the spatial light modulator. When the RGB three-color lasers are incident from different angles at the same time, we can get a reproduced three-dimensional object on the output surface, as shown in Figure 5(a), focusing on "RMB", and 5(b), focusing on "YGC". Thus, it can be seen that the colored 3D object is reproduced relatively clearly.

The above embodiments are only used to illustrate the present invention, but not to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that various combinations, modifications or equivalent replacements of the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all should cover Within the scope of the claims of the present invention.

Claims (2)

1. A method for color holographic real-time three-dimensional display, characterized in that the steps are as follows: Step 1: Divide the 3D color object on the object plane into three components: red, green, and blue, and propagate freely through space to reach the hologram surface respectively. The distance from the origin of the object plane to the origin of the hologram plane is z; Step 2: The three beams of RGB plane reference light are irradiated on the holographic surface at different angles, and interfere with the corresponding object light color components to obtain three holograms, that is, the red reference light interferes with the object light red component to obtain H ₁ (x,y,z), the green reference light interferes with the green component of the object light to obtain H ₂ (x,y,z), the blue reference light interferes with the blue component of the object light to obtain H ₃ (x,y,z ); Step 3: Interfering different color components with their corresponding reference light to form a hologram is superimposed to form a hologram, and then add a y-axis direction tilt phase factor to the hologram, the expression can be written as: Among them, where k _i =2π/λ _i , λ _i is the wavelength, and ψ is the tilt angle in the y-axis direction, which can shift the zero-order diffracted light of the spatial light modulator during the image reconstruction process, A(x ,y) represents the amplitude distribution of the hologram, represents the phase distribution of the hologram; Step 4: Normalize the amplitude distribution, and then multiply it with the phase to get the final hologram, 2. The method for real-time three-dimensional display of color holography according to claim 1, characterized in that, the obtained hologram is loaded into a single spatial light modulator, and then three beams of RGB reproduced light are respectively irradiated on the hologram at the angle of recording , get a color image at a distance from the object plane.