We have developed a full-color full-parallax digital 3D holographic display system by using 24 physically tiled SLMs, an optical scan tiling approach and two sets of RGB lasers, which could display 378-Mpixel holograms at 60 Hz, with a displayed image size of 10 inch in diagonal. In this paper, we will review and compare three different holographic display systems developed by our group from various aspects, including SLMs, lasers, optics designs, hologram computation, data transmission, and system synchronization. We will also discuss the bottlenecks and prospects of further development of the system for practical applications.
KEYWORDS: Holograms, Holography, Spatial light modulators, 3D displays, Data transmission, Video, Data processing, Video acceleration, 3D modeling, Visualization
The pixel count of hologram for a holographic 3D display system increases rapidly with the increase in reconstructed
object size and viewing angle. According to our analysis, for 10 inch reconstructed object size with 5° viewing angle, a
hologram with a pixel count of 378 Million is required. Such a large pixel count is a challenge for both hologram
computation and hologram data transmission. The computation load is analyzed to be a few hundreds of Tflop for the
object with a few million object points, and the hologram data transmission rate required is analyzed to be 22.3 Gbps and
67.0 Gbps for monochrome display and color display using time division multiplexing at 60 Hz, respectively. A
computer cluster with 32.7 Tflops GPU computing ability and 60 Gbps transmission bandwidth was built to meet the
hardware requirements for large-pixel-count hologram computation and transmission. A distributed computation method
was implemented for computing large-pixel-count holograms. Computation time of 5.6 seconds was achieved for 378-
Mpixel hologram containing information of 1.7 M object points. During the playback of holographic video using our
holographic 3D display system, the hologram data was read out from SSDs, transmitted over the high speed network,
and finally launched onto SLMs for reconstruction. A data transmission rate of 31.8 Gbps was achieved, which
corresponded to 378-Mpixel hologram at 84 Hz for monochrome reconstruction and full color reconstruction using space
division multiplexing. The increasing demand for computation power and data transmission rate of large-pixel-count
hologram video displays has been effectively addressed.
We propose a new and simple method to reconstruct the refractive-index modulation of a symmetric fiber Bragg grating (FBG) from its magnitude reflection spectrum (i.e., phase information is not required). The reconstruction method uses an FBG model based on some known parameters of the fabricated FBG (grating length, number of subgratings, and grating period) and an optimization technique, namely, the Quasi-Newton method, to find the local parameter values of the FBG. To our knowledge, this is the first time that the reconstruction of FBG is experimentally realized by an optimization technique. Compared with other reconstruction methods, the proposed method is so simple that it requires only the reflection spectrum of the fabricated FBG.
This paper focuses on optical fiber laser-based wide range temperature measurement applications, under circumstances
where different strain values were applied to the chirped fiber Bragg grating at a fixed temperature and the uniform type IIA fiber Bragg grating was used temperature-tuned. This grating forms the end reflector in the laser cavity feedback configuration. Erbium doped fiber was used as the laser gain medium and was pumped by using light from a 1480 nm laser diode. The response of the sensor was achieved over the tunable-temperature range from 70°C to 500°C when a fixed strain value of 1000 με was applied to the chirped Bragg grating, with a root mean square error of 10°C, using linear fitting over the above measurement range.
A Tabu Search (TS) algorithm, to our knowledge, for the first time, is introduced into the optimized design of Fiber Bragg gratings (FBGs). By combining the Transfer Matrix Method (TMM) for calculating the reflection spectrum and the TS algorithm, we obtained a new method for synthesis the FBGs with advanced characteristics. A new appodization profile is proposed as an example to demonstrate the effectiveness of the method that is general to be useful for inverse problems in FBGs application.
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