3D Holographic Display Using Strontium Barium Niobate

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3D Holographic Display Using Strontium Barium Niobate

An innovative technique for generating a three dimensional holographic display using strontium barium niobate SBN is discussed. The resultant image is a hologram that can be viewed in real time over a wide perspective or field of view FOV. The holographic image is free from system-induced aberrations and has a uniform, high quality over the entire FOV. The enhanced image quality results from using a phase conjugate read beam generated from a second photorefractive crystal acting as a double pumped phase conjugate mirror DPPCM. Multiple three dimensional images have been stored in the crystal via wavelength multiplexing.
Descriptors:

HOLOGRAPHY DISPLAY SYSTEMS HOLOGRAMS MIRRORS NIOBATES PHASE CONJUGATION PHOTOREFRACTIVE MATERIALS REAL TIME THREE DIMENSIONAL WAVELENGTH DIVISION MULTIPLEXING

Subject Categories:
Holography

Present holographic displays, such as those generated by computers or emulsion films, usually require intermediate preprocessing or postprocessing and are, therefore, not capable of real-time production and viewing and have limited information storage capacity. The use of photo-refractive crystals, such as strontium barium niobate (SBN), as a holographic storage medium eliminates these and other limiting factors. For example, when a photorefractive storage medium is used, holograms may be recorded and projected without time-consuming processing and with
greater storage capacity through various forms of multiplexing. Additionally, the photorefractive recording medium is sensitive to low level intensity and is reusable. Therefore, previously stored holograms may be erased, and the crystal can be reused to store other holograms. Until recently, however, research in photorefractive holography has been limited to the production of two-dimensional (2-D) holograms and very limited field-of-view (FOV) 3-D holograms.
The proposed method employs a volume hologram recorded and read in real time in a photorefractive crystal to produce a 3-D image. This innovative technique is simple, and it differs from previous attempts at 3-D displays. We used a photorefractive material, SBN, to record a hologram, and a phase-conjugate read beam, which is generated from a double-pumped phase-conjugate mirror (DPPCM), to accurately reproduce the holographic image in space over a large perspective. The resultant holographic image is free from system-induced aberrations, may be viewed over a wide range of angles that can be expanded by the use of a mosaic of crystals, and has uniform high quality over the entire FOV.

The three-dimensional hologram is a real image of the object and can be
displayed in free space. The image can be viewed by projection, via lens
relays, directly into the eye or a camera. Figure 3 shows the hologram of
two dice earrings recorded in the SBN:60 photorefractive crystal. The dice
have dimensions of 2 mm on a side. We verified the third dimension of the
image by viewing the hologram at different perspectives, which demon-
strated parallax when we rotated the viewing angle by placing the camera
on a pivot arm. The FOV of the hologram (fig. 3) was measured to be ~14°.
We determined the FOV by the angular range in which the hologram was7
clearly visible. The expected FOV can be calculated from the diagram
shown in figure 4. The photorefractive recording crystal of length L c is
tilted so that the normal to the crystal’s largest face bisects the angle be-
tween the reference and object beams,
φ. The object of width s is located a
distance d from the projection of the recording crystal, where the projection
of the crystal is in the plane perpendicular to v
d . The effective length of the
recording material is

[delmarphotonics]

Crystal wafers are used in 3D holographic displays for several reasons, primarily due to their optical properties and suitability for holographic applications. Here are the key reasons why crystal wafers are chosen for 3D holographic displays:

1. Optical Clarity: Crystal wafers, especially those made from materials like lithium niobate (LiNbO3) or other photorefractive crystals, offer high optical clarity. This is crucial for recording and reconstructing holograms accurately, as any impurities or imperfections in the material can degrade image quality.

2. Nonlinear Optical Properties: Certain crystal materials exhibit nonlinear optical properties, such as the ability to change their refractive index in response to an applied electric field. This property is exploited in the recording and manipulation of holograms, allowing for dynamic control over the holographic display.

3. High Damage Threshold: Crystal wafers often have a high damage threshold, making them capable of withstanding the intense laser light used in holographic recording. This is important for ensuring the durability and reliability of the holographic display.

4. Birefringence and Phase Matching: Some crystals used in wafer form exhibit birefringence, which means they have different refractive indices for light polarized in different directions. This property, along with phase matching techniques, can be utilized to enhance the efficiency of holographic recording and reconstruction.

5. Piezoelectric Properties: Certain crystal wafers, like lithium niobate, are piezoelectric, meaning they generate an electric charge in response to mechanical stress. This property can be harnessed for the precise control of the crystal's properties during holographic processes.

6. Large Size and Homogeneity: Crystal wafers can be grown in large, homogeneous sizes, providing a suitable substrate for recording holograms over a significant area. This is advantageous for creating holographic displays with a wide field of view.

7. Temperature Stability: Some crystal materials exhibit good temperature stability, allowing for consistent holographic performance over a range of operating conditions.

8. Reproducibility: Crystal wafers can be manufactured with a high degree of reproducibility, ensuring consistent optical properties across different wafers. This is essential for mass production of holographic displays.

In summary, crystal wafers are chosen for 3D holographic displays due to their optical clarity, nonlinear properties, high damage threshold, birefringence, piezoelectricity, large size, homogeneity, temperature stability, and reproducibility, all of which contribute to the effectiveness and reliability of holographic imaging.

Keywords: Crystal wafers, 3D holographic displays, optical clarity, nonlinear optical properties, birefringence, piezoelectricity, holographic recording, holographic reconstruction.

[delmarphotonics]

Photorefractive holography is a technique that combines holography with the photorefractive effect exhibited by certain crystal materials. The photorefractive effect involves changes in the refractive index of a material induced by exposure to light. Here's an overview of photorefractive holography and its uses:

1. Recording Holograms:
- Photorefractive holography involves using a photorefractive material, often a crystal like lithium niobate (LiNbO3) or similar, as the recording medium.
- The material exhibits a change in refractive index in response to the interference pattern formed by the combination of an object beam and a reference beam during hologram recording.

2. Dynamic Holography:
- Photorefractive materials enable dynamic holography, allowing for real-time recording and reconstruction of holograms.
- This dynamic capability is particularly useful in applications where the holographic scene or object is changing over time.

3. Self-Developing Holograms:
- One of the advantages of photorefractive holography is the ability of the material to self-develop the hologram during recording. The changes in refractive index persist after exposure to light, allowing for the reconstruction of holograms without additional processing steps.

4. Real-Time 3D Imaging:
- Photorefractive holography is employed in applications where real-time 3D imaging is crucial, such as medical imaging, industrial inspection, and scientific visualization.

5. Holographic Storage:
- The photorefractive effect in crystals allows for the storage of holographic information in the crystal lattice. This has potential applications in holographic data storage, where large amounts of data can be stored and retrieved using holographic techniques.

6. Optical Phase Conjugation:
- Photorefractive materials can be used for optical phase conjugation, allowing for the correction of distortions and aberrations in optical systems.

7. Nonlinear Optical Processes:
- Photorefractive materials exhibit nonlinear optical properties, which can be harnessed for applications such as beam coupling, two-wave mixing, and four-wave mixing.

8. Holographic Interferometry:
- Photorefractive holography is used in holographic interferometry, a technique for measuring changes in the shape or deformation of objects. This is valuable in fields like material science and structural engineering.

In summary, photorefractive holography leverages the photorefractive effect in crystal materials for dynamic, real-time holography. Its uses span from 3D imaging and holographic storage to optical phase conjugation and holographic interferometry.

Keywords: Photorefractive holography, photorefractive effect, hologram recording, dynamic holography, real-time 3D imaging, holographic storage, optical phase conjugation, holographic interferometry.