Laser-based 3D holographic technology

1.3D Technology Principle

(1) Polarized glasses method

It uses the method of observing scenery with the human eye, using two parallel-placed movie cameras, representing the left and right eyes of a person, to simultaneously shoot two movie images with slight horizontal parallax.

When the audience wears special polarized glasses, the left eye can only see the left image, and the right eye can only see the right image. Through the binocular convergence function, the left and right images are superimposed on the retina, and the brain nerves produce a three-dimensional visual effect. This 3D technology is not a true 3D technology, and its imaging is still a projection technology based on a two-dimensional plane.

(II) Holographic 3D Technology

1. Principle of holography

Holography consists of two steps: interference recording of the wavefront and reconstruction of the wavefront diffraction[7]. Taking Fresnel holography as an example, the first step is interference recording of the wavefront. Figure 1 shows the recording optical path of Fresnel holography.

Figure 1. The optical path of holographic recording

As shown in the figure, the laser beam passes through the shutter and is divided into two beams by the beam splitter: the transmitted beam is reflected by the plane mirror M2, expanded by the beam expander L2, and then projected onto the holographic dry plate E as the reference light; the reflected beam is reflected by the plane mirror M1, expanded by the beam expander L1, and then shines on the object, and then diffusely reflected by the object as the object beam and projected onto E. The optical axis of the entire optical path is on the same horizontal plane, and the beam passes through the center of each component. The angle between the object light and the reference light is about 45o.

In the dark, clamp the holographic plate on the plate rack, with the emulsion side facing the object light and the reference light, and start the timer after standing for one minute. Remove the plate, develop it in the darkroom, fix it for a while, rinse it with water, and finally dry it. The hologram is ready.

Next, let’s talk about the reconstruction of holograms [8]. Fresnel laser holography is reproduced using lasers. The method of observing virtual images is shown in Figure 2:

Figure 2 Observation of virtual image

Place the prepared hologram back to the position of the original object when shooting, illuminate the hologram with reference light, and the virtual image of the object can be observed at the position of the original object behind the hologram.

If you want to observe the real image of the original object, you need to use the conjugate light of the reference light to illuminate the hologram. Then you can use a light screen behind the hologram to receive the real image of the object, as shown in the optical path in Figure 3.

Figure 3 Observation of real image

2. Holographic imaging principle

The imaging of holographic projection technology does not require a traditional silver screen, but is projected on an air fog screen. Air fog screen projection imaging is a new air imaging device. The device uses the imaging principle of a mirage to present light and shadow images with the help of particles in the air. A very thin layer of water mist wall is used instead of a traditional projection screen, so that you can freely shuttle through the screen image to achieve the illusory effect that real people can enter the video screen. A large amount of artificial fog is produced by using atomization equipment, and a screen that can produce plane fog is produced by combining the principle of air flow. Then the projection equipment is projected on the screen, which can form an illusory three-dimensional image in space, forming a three-dimensional spatial three-dimensional image, giving people a new three-dimensional visual enjoyment. The image gives people the feeling of walking in a painting, painting in people, real and illusory, like being in a fairyland or in Yaochi. The flickering, mysterious and attractive characteristics develop some amazing display projects. On the confused fog screen, a mythological story that seems like a dream is shown. It will bring the audience an unprecedented audio-visual experience.

Features of air fog screen stereoscopic imaging display: 1. The air fog screen imaging system includes a projector and an air screen system. The air screen system can create a fog wall formed by water vapor, and use rear projection technology to project images into an almost invisible air wall. What the viewer sees will be images or films floating in the air. 2. The air fog screen imaging generator can project computers, programs, infrared rays, lasers, and radars onto the fog screen through the projector light speed and wind field to form a variety of dynamic and virtual images. 3. The air fog screen imaging system uses an integrated ultrasonic movement inside, without mechanical drive, quiet and noiseless, high atomization efficiency, produces a certain concentration of negative ions, low failure rate, and simple maintenance.

Air fog screen stereoscopic imaging system principle: This system includes a proprietary projector and basic parts, in which the aerial image display is used from the front. The system does not require any additional screen. The main principle of forming the image is to use air and a small cabinet. No special chemicals are used or harmful to the environment. The design of the Heliodisplay projection system is inspired by the imaging principle of mirage. A projection system includes a projector and an air screen system. The air screen system can create a fog wall formed by water vapor. The projector projects the picture on it. Due to the uneven molecular vibration of the air and the fog wall, a layered and three-dimensional image can be formed.

2. Application of 3D holographic projection technology

(I) Realizing true naked-eye 3D movies

We all know that so far in the film projection technology, we have adopted the use of polarized glasses to achieve 3D technology. But we all know that this is not true 3D, because its final image is formed on a two-dimensional screen. If holographic technology is applied to film technology, then the real 3D movie will be separated from the screen and performed in a three-dimensional space, and polarized glasses will be completely removed to achieve naked eye 3D technology. In the 2010 "Hatsune Miku" concert in Japan, it was the anime singer who was virtualized by holographic technology. With the increasing maturity of holographic technology, holographic 3D will enter the cinema in the near future.

(II) Application to communication equipment

1. Virtual Keyboard

With the advancement of technology, the development of microelectronics and integrated circuits, various electronic devices have gradually transitioned from large devices to highly integrated mini devices. From desktop computers to notebooks, and now to the iPad led by Apple, electronic products have developed into a highly integrated field. However, while we enjoy the convenience brought by high integration, we have also overturned our traditional definition of PC. For example, the keyboard has been changed to a touch screen type. The use of holographic technology can virtualize a keyboard, and the use of laser sensing technology allows us to operate on the virtual keyboard.

2. Holographic Video

With the advent of the 3G era, video chat is no longer exclusive to computers. We can use our mobile phones to chat via video. In holographic technology, we will image the three-dimensional image of the person we want to chat with in front of us. This will be another great milestone for mankind after the computer communication era.

(III) Application in medicine

1. Holographic microscopy

Holographic microscopy is a technology that combines holography and microscopy. Compared with general microscopy technology, it can store the whole specimen. There is no need to prepare slices of the specimen. Especially for some living specimens, high-power continuous light or pulsed laser can be used to illuminate the hologram, which can be preserved for a long time. The reproduced image is three-dimensional and can show the details of the sample. There are two main types of holographic microscopy: one is to combine holographic technology with microscope, called "holographic microscope", which solves the contradiction between resolution and depth of field in the microscope, avoids the influence of aberration and reaches a very small diffraction limit, and can obtain a larger field of view; the other is to use the characteristics of the hologram itself to enlarge, called "holographic magnification". If different wavelengths and different diffraction angles are used during shooting, it is equivalent to adjusting the hologram accordingly, which can achieve image magnification. Holographic microscopy is widely used in medicine, biology, and scientific research.

2. Medical devices

Holography has solved many problems that are difficult to solve with other technologies with its unique advantages, and has made contributions to the diagnosis and treatment of diseases. Laser holography technology was first successfully applied in the diagnosis and treatment of ophthalmic diseases. The information provided by a holographic photo is equivalent to the information provided by 480 ordinary fundus photos. In the diagnosis of ophthalmic diseases, laser holographic imaging technology can provide a three-dimensional image of the entire eye, and a microscope can be used to observe and study different positions of the entire eye image (such as the cornea, anterior chamber, lens, vitreous body, and retina, etc.) layer by layer. Laser holographic imaging technology can also be used to provide separate three-dimensional images of various parts of the eye for in-depth examination. In clinical examinations, breast cancer with a diameter of 1mm can be detected using holographic diagnostic methods, which is conducive to the early diagnosis and treatment of cancer.

(IV) Holographic Information Storage

Optical holographic storage stores information in the form of holographic photography based on the principle of holography. It uses the coupling and decoupling between the two to combine the functions of information storage with the comparison, identification and even association between information, that is, it can combine information storage with information processing. Holographic information storage is a new storage method that emerged in the 1960s with the development of laser information. It is characterized by large capacity, high density, high diffraction rate, low noise, high resolution and high fidelity. Optical holographic storage not only has large capacity, but also has fast data transmission rate and short addressing time.

(V) Military Utilization

Holographic technology can make up for the shortcomings of general air and underwater surveillance systems. For example, general radar systems can only detect the distance, direction and movement speed of the target, while holographic surveillance systems can provide three-dimensional images of the target. This is of great significance in national defense and military, because timely identification of whether the target is an aircraft or a missile, a submarine or a torpedo is extremely important for taking countermeasures. The application of holography in the military has brought substantial changes to technologies such as communication, navigation, and positioning detection. Holography is a booming branch of optics, and its application is developing in depth and has penetrated into many fields. It has become an effective testing tool in modern scientific research, industry and economic construction.