A laser scanning device can be used for contour or pattern reconstruction with associated image processing or recognition algorithm. For a better accuracy or accommodating to a high efficiency algorithm, the laser beam often needs reshaping to a specific pattern, such as a line beam, or homogenization so as to reduce the spatial variation of the device performance. In addition, a scanning mechanics is normally inevitable. Both beam shaping and scanning module take quite a volume in the whole system, which could be an issue for the applications in which miniature device is highly desired. In this paper, a holographic scanner has been proposed to perform both laser beam shaping and scanning function. A pure phase modulation liquid crystal on silicon (LCoS) device is used for implementing the dynamic hologram. The LCoS has a pixel size of 3.74μm, and provides 16 phase level with a full phase depth of 2π. A line beam with 20mm and uniformity up to 70% is generated and it is scanned back and forth in the orthogonal direction of the line with a stroke of 20mm. The scanning line pattern is generated based on iterative Fourier transform algorithm (IFTA) and the first diffraction order pattern is exploited with the zero order being blocked and absorbed so that the noise in the scanning line pattern is minimized. The proposed scheme is a compact and versatile solutions for patterned laser beam scanning devices.
Liquid crystal on silicon (LCoS) can be devised as a pure phase type spatial light modulator (SLM) with proper
arrangement of incident light polarization and choice of liquid crystal mode. The applications include digital holography,
optical switching and adaptive optics etc. The phase retardation at each pixel on the LCoS SLM can be controlled by
driving voltage, but the relationship is dependent of temperature and wavelength. In this paper, a vertical aligned
nematics (VAN) mode LCoS has been used for investigation.
Consideration the application environment, temperature range was set in between 30 to 70°C, and the selected
wavelength was 623 nm, 526 nm and 462 nm. We measured the E-O curve and converted into phase shift by equation.
The result shows that the phase retardation decreases with both the increase of temperature and wavelength. The
dynamic behavior of LC material is also reported in this paper, and a digital hologram from a digital-drive LCoS SLM
with 6.4 μm pixel is demonstrated.
Invisible grid-pattern structure light has often been used for being shined on objects for contour reconstruction based on
the distortion of grid pattern, for vehicle collision prevention etc. However, the structure light can be easily disturbed by
surrounding nature light even if infra-red (IR) light source is used because natural light contains quite an amount of IR
spectrum. In this paper, it is proposed that the structure light is provided from a highly coherent laser source, so that the
structure light pattern reflected from the target object will contain not only the distorted irradiance distribution of grid
pattern, but also laser speckle associated with it. The laser speckle pattern depends on the surface roughness of the target
object, which provides extra information for extracting the distorted grid pattern from the background irradiance of
surrounding natural light. The laser speckle pattern therefore helps to improve the immunity for surrounding light
disturbance, and hence the robustness and reliability of contour reconstruction system. A binary surface relief phase-type
diffractive optical element(DOE) has been proposed for generating desired pattern directly at far field when working
together with laser light source. The design process is based on iterative Fourier transform algorithm(IFTA) in scalar
The major efficiency loss in current liquid crystal displays(LCD) are the absorption in polarizers and
color filter, and both can be resolved with decent backlight design which takes light polarization and color
separation into consideration. Those improvement schemes on the backlight normally will not trade off
the image quality readily achieved in the commercial LCD. Both polarization and color separation
schemes for the backlight are reviewed with categorization on the basic concept, followed by the proposal
of possible combinations for both direct lit and edge lit configuration with the consideration on the
availability of associated components. Two total solutions, including polarization conversion module for
LED and pixelized backlight with RGB LED for direct lit and edge lit respectively, are given with
demonstration of preliminary result achieved so far as the efficiency improvement schemes for LCD
A polarization conversion and angular shaping LED module has been proposed to improve the efficiency and uniformity
for direct type LCD backlighting. The design includes simulation based on nanostructure, polarization and geometrical
Laser is an ideal illumination light source for liquid crystal projection displays in terms of source Etendue and
polarization. In order to make a conversion from a circular Gaussian laser beam profile to a rectangular uniform
distribution on the microdisplay, a double side microlens array has been proposed as a homogenizer, and a cylindrical
lens is exploited for shaping the aspect ratio of illumination pattern. The design and simulation based on scalar
diffraction theory have shown that two identical lenslet arrays on each side of a thin plastic substrate with a lateral shift
of half diagonal pitch can convert laser beam into a uniform square illumination at a specified near field. The pitch and
curvature of the lenslet are major parameters for modifying the illumination distance, area and uniformity. The proposed
lenslet array will provide an economical solution for the illumination optics of laser based light valve projector due to its
regular and circular lenslet profile.
A refractive astigmatic lens is employed to generate a focus error signal (FES) for servo control in general optical pickup. In
this paper, a diffractive optical element (DOE) is designed to implement optical functions of astigmatic focusing for a
MEMS-based miniature optical pickup at 650nm wavelength. We present a diffractive astigmatic lens with its internal zones
and external zones quantized into four, two phase levels, respectively based on fabrication consideration. The optical
simulation based on scalar diffraction theory shows the efficiency of this quantized lens for astigmatic focusing and a
comparison of the FES in the optical pickup system has been plotted.