In recent years, three-dimensional (3D) display has received widespread attention. The light field display technology based on multi-layer translucent structures enables observers to directly acquire 3D scenes without wearing any auxiliary equipment, and has the advantages of high resolution and low cost. The use of liquid crystal panels as translucent structures makes it possible to realize dynamic 3D display. However, interactive 3D display can hardly be achieved due to the unacceptable long time to generate each frame of a 3D animation. In this paper, we reduce the time consumption for each frame by optimizing acquisition of the four-dimensional light field and calculation of the multi-layer LCD images. With the help of powerful rendering capabilities of OpenGL, we easily obtain the light field information of 3D scenes within less than 0.5s. The light field is rapidly decomposed into multiple LCD images utilizing parallel computing of graphics processing units. Human-computer interaction is realized through the development of Kinect. A 3D display system based on multi-layer LCDs is built, information flow between various components in the system is created, and interactive 3D display is implemented.
Three-dimensional (3D) display technology, which aims at presenting almost-realistic 3D images to the observer without any auxiliary devices, has drawn great attention from both academia and industry these years. The 3D display based on multi-layer translucent structure is a new parallax-based 3D display model. Compared with conventional parallax barrier and integrated imaging, it can effectively ensure the utilization of light energy and image resolution of the system, expand the screen depth at the same time, and display a realistic virtual 3D scene. In this paper, we implement a flat 3D display using multi-layer translucencies. Based on our prototype of flat 3D display, we further extend it to spatial 3D display using mirroring of a square pyramid, which allows observers to see virtual 3D objects from different directions in the air.
Optical-electronic Integrated Neural Co-processor takes vital part in optical neural network, which is mainly realized by optical interconnects. Because of the accuracy requirement and long-term goal of integration, optical interconnects should be effective and pint-size. In traditional solutions of optical interconnects, holography built on crystalloid or law of Fresnel diffraction exploited on zone plate was used. However, holographic method cannot meet the efficiency requirement and zone plate is too bulk to make the optical neural unit miniaturization. Thus, this paper aims to find a way to replace holographic method or zone plate with enough diffraction efficiency and smaller size. Metasurfaces are composed of subwavelength-spaced phase shifters at an interface of medium. Metasurfaces allow for unprecedented control of light properties. They also have advanced optical technology of enabling versatile functionalities in a planar structure. In this paper, a nanostructure is presented for optical interconnects. The comparisons of light splitting ability and simulated crosstalk between nanostructure and zone plate are also made.
Photomultiplier tubes (PMTs) are the most common photoelectric conversion apparatus used as photon counters. Because of the sensitivity of the PMTs to the interference, calibration is necessary during the application of the PMTs. Traditional solutions for calibration are either based on the inverse square law of illumination, or using light-emitting diodes (LEDs) as standard light sources. However, rigid experimental techniques are required for these solutions. And the emission spectrum of LEDs does not cover the entire spectrum of detection. In this paper, a calibration method is presented by using a customized standard light source which can provide full spectrum of weak light from the dark count level to the saturation level of the PMTs. The photon counter in a light-shielding cavity is connected, via an optical fiber, to the customized standard light source attached with an intensity detector. The calibration process is discussed and experimental results with chemical reference substance are also presented for comparison.
Visible light communication (VLC) based on light emitting diodes has been regarded as an effective complement to radio frequency signal transmission. The color filter in VLC system plays the pivotal role for boosting signal-noise-ratio. In this paper, a tri-band color transmission filter with bandwidths consisting with LED’s 30nm is designed based on guided mode resonance, incorporating a sub-wavelength aluminum grating on slab dielectric waveguide made of titanium dioxide on silica substrate. Parameters of grating structure, including the grating period, duty cycle, grating thickness, and waveguide thickness, are optimized by employing particle swarm optimization toolbox. The far field spectrum is calculated by rigorous coupled-wave analysis to verify the effectiveness of the designed filter. Three center-wavelength of transmission bands are 440nm, 530 and 630 nm. The full-width-at-half-maximum (FWHM) bandwidths of three bands are about 30nm which consist with LED’s bandwidth.
Many kinds of optimization algorithm have been applied to design diffractive optical elements (DOEs) for beam shaping. However, only the selected sampling points are controlled by these optimization algorithms, the intensity distribution of other points on the output plane is always far away from the ideal distribution. In our previous research, the non-selected points were well controlled by using a hybrid algorithm merging hill-climbing with simulated annealing, but this hybrid algorithm is time-consuming. In this paper, a new hybrid algorithm merging Gerchberg-Saxton algorithm with gradient method is presented. Because of the use of iterative algorithm, the optimization time is largely reduced. The intensity distribution of the non-selected points as well as that of the selected points is well controlled, and good performance of beam shaping is obtained. Finally the experimental results demonstrate the good performance of this algorithm.
Due to its low energy consumption, high efficiency and fast switching speed, light-emitted diode (LED) has been used as a new light source in optical wireless communication. To ensure uniform lighting and signal-to-noise ratio (SNR) during the data transmission, diffractive optical elements (DOEs) can be employed as optical antennas. Different from laser, LED has a low temporal and spatial coherence. And its impacts upon the far-field diffraction patterns of DOEs remain unclear. Thus the mathematical models of far-field diffraction intensity for LED with a spectral bandwidth and source size are first derived in this paper. Then the relation between source size and uniformity of top-hat beam profile for LEDs either considering the spectral bandwidth or not are simulated. The results indicate that when the size of LED is much smaller than that of reshaped beam, the uniformity of reshaped beam obtained by light source with a spectral bandwidth is significantly better than that by a monochromatic light. However, once the size is larger than a certain threshold value, the uniformity of reshaped beam of two LED models are almost the same, and the influence introduced by spectral bandwidth can be ignored. Finally the reshaped beam profiles are measured by CCD camera when the areas of LED are 0.5×0.5mm2 and 1×1mm2. And the experimental results agree with the simulations.
Recently, interferometric null-testing with computer-generated hologram has been proposed as a non-contact and high
precision solution to the freeform optics metrology. However, the interferometry solution owns some typical
disadvantages such as the strong sensitivity to the table vibrations or temperature fluctuations, which hinders its usage
outside the strictly controlled laboratory conditions. Phase retrieval presents a viable alternative to interferometry for
measuring wavefront and can provide a more compact, less expensive, and more stable experimental setup. In this work,
we propose a novel solution to freeform metrology based on phase retrieval and computer-generated hologram (CGH).
The CGH is designed according to the ray tracing method, so as to compensate the aspheric aberration related to the
freeform element. With careful alignment of the CGH and the freeform element in the testing system, several defocused
intensity images can be captured for phase retrieval. In this paper the experimental results related to a freeform surface
with 18×18mm<sup>2</sup> rectangular aperture (its peak-to-valley aspherity equals to 193um) are reported, meanwhile, we also
have compared them with the measurement results given by the interferometry solution, so as to evaluate the validity of
Fast optimization algorithms of the design of diffractive optical elements (DOEs) for beam shaping are often based on
fast Fourier transform (FFT), and the demand of the sampling theorem must be met when FFT is used to calculate the
light intensity. Limited by the fabricating technology, the pixel size of a DOE cannot be too small. For beam shaping in
Fresnel diffraction domain, given that the sampling interval of a DOE is fixed, if the diffraction distance is too short, all
FFT algorithms would not meet the demand of the sampling theorem, and then the results of beam shaping would
become worse. In this paper, the disadvantages of the FFT algorithms in near Fresnel diffraction domain are discussed,
and an area division method is proposed for the DOEs design. The simulation and experimental results show the validity
of the proposed area division method.
To deal with the problem of phase-shifting interefrometry with different unknown phase shifts, some special designed algorithms have been put forward by former researchers, such as the advanced iterative algorithm (AIA) and the principal component analysis (PCA) demodulation algorithms. This paper proposes a novel solution for it. Firstly, the captured phase-shifting interefrograms are differentiated to remove the additive background term. Then the trigonometric functions of the modulation phase can be extracted with the blind signal separation method. Simulations and experiments have been carried out to validate the feasibility of the proposed algorithm, where both open and closed fringe patterns are involved. Besides, the comparison results with the AIA and PCA algorithms are also provided.
We propose a holographic 3D display system which can produce images with adjustable viewing parameters and
eliminated zero-order interruption. The 3D scene is generated from a 3D CAD tool, and point source algorithm is used to
generate the holograms. A two-step model is introduced in the computing to generate precise Fourier holograms. A
phase-only spatial light modulator (SLM) is used in the optical reconstruction, which can replay clear images for 3D
diffusive objects. During optical reconstructing, the viewing angle and image size of the system can be adjusted by
changing the parameters of the replay lens. A filter is introduced in the replay system to eliminate the zero-order
interruption and increase the 3D image quality. Optical experiments are performed, and the results show that our
proposed holographic display system can produce noiseless 3D image reconstructions.
For applying to various error patterns, including random errors, burst errors, and inhomogeneously distributed errors, in
the holographic data storage (HDS) channel, a three-dimensional error correcting with matched interleaving (3DEC-MI)
scheme is proposed in this paper. The 3DEC-MI scheme combines the advantages of the three-dimensional error
correcting scheme and the matched interleaving scheme, makes full use of the priori knowledge of the error patterns in
the HDS channel, distributes errors more uniformly, and decodes data iteratively in three dimensions. It is able to
eliminate the influences of non-uniform distribution of errors within a page and across pages, overcome the effects of
burst errors, correct random errors, and effectively reduce the symbol error rate (SER) of the HDS channel.
The wavelength and defocus margins for collinear holographic data storage system are theoretically analyzed based on
the first Born approximation and the scalar diffraction theory. Explicit expressions for the decay of diffracted signal in
the center of the detector plane with the shift of the reading wavelength and with the defocus of the disc are presented.
The expressions predict that the defocus margin is independent of the media thickness while a thicker disc leads to a
narrower wavelength margin. Simulation results show that the wavelength margin of collinear holographic scheme is
larger than that of the conventional 2-axis holographic scheme. The influences of the properties of reference pattern on
both margins are also discussed.
To compensate misregistrations between a detector array and a spatial light modulator in page-oriented volume
holographic data storage, a method based on a three-pixel model is proposed against sub-pixel misalignment. Several
methods for pixel mismatch compensation are reviewed. The quadratic two-pixel method is inapplicable when the local
shift is negative or the size of the aperture is relatively small. The inter-pixel crosstalk model is revised and an improved
three-pixel model is developed, which can be used to compensate arbitrarily misaligned data pages. The compensation
method uses prior information of the pixels on the input spatial light modulator (SLM). Recursive solutions are carried
out to recover the real values of the SLM pixels. Both simulation and experimental results show that the signal-to-noise
ratio (SNR) can be doubled approximately by use of the compensation method based on the three-pixel model. The
proposed method is appropriate for both positive and negative pixel shifts, and has similar effects of equalization, which
effectively improves the SNR.
A cross-shaped aperture is proposed for the Holographic Data Storage System (HDSS). Based on the non-symmetric
HDSS model, numerical simulations are carried out to compare the sensitivity to pixel shift, magnification error and
noise level of the cross-shaped aperture with the ordinary square aperture. The simulation results show that equivalent
or lower bit error rate can be achieved with the optimized cross-shaped aperture than that with the square aperture, while
the area of the cross-shaped aperture is 20 percent less than the corresponding square aperture. Thereby the multiplexing
spacing can be reduced and the areal density can be increased in HDSS. Experimental results of the performances of the
cross-shaped aperture from a custom-built HDSS are presented.