A color-filter liquid crystal-on-silicon (LCoS) pico optical engine has been designed with polarization recovery. By combing nonimaging collection optics and a collimation lens, the collimated light's aperture is reshaped so that both of its two polarized parts can be polarization recovered and then collected by the relay lens. No polarization conversion system of traditional polarization recovery method is used, and the aperture of illumination optics does not increase. A design example of color-filter LCoS pico optical engine with 640×360 resolution is listed. High light efficiency of about 9.3 lumens per light-emitting diode watt and high irradiance uniformity of about 94% have been achieved. The thickness of the optical engine is 11 mm.
A slope angle-based reflector profile optimization method is introduced at the first time. Compared to the traditional profile-based optimization method, better optimization results are obtained with this method. Design examples of reflectors for general lighting applications are given to compare both types of optimization methods. Disadvantages, such as range definition, range overlapping, and parameter-dependent problems, which existed in the traditional profile-based optimization method can be totally overcome with the proposed method.
The point spread function (PSF) is asymmetric in a wavefront coding (WFC) system with cubic phase mask (CPM). The image formation of the WFC system is described as the generalized Sylvester matrix equation. With Tikhonov regularization, a global generalized minimal residual method (Gl-GMRES) algorithm is used to obtain the restored sharp image. For this large-scale, linear, and discrete, ill-posed problem, we introduce a Kronecker product approximation of the blurring operator to reduce the computation consumption. To eliminate ringing effect, four boundary conditions (BCs) are considered in the image restoration: periodic BCs, zero BCs, reflective BCs, and antireflective BCs. Analysis and numerical results show that the antireflective BCs provide better results than others. The experiment results show that the Gl-GMRES algorithm with antireflective BCs is more effective than the classic Wiener filter.
Wavefront coding (WFC) used in 2D barcode scanners can extend the depth of field into a great extent with simpler
structure compared to the autofocus microscope system. With a cubic phase mask (CPM) employed in the STOP, blurred
images will be obtained in charge coupled device (CCD), which can be restored by digital filters. Direct methods are
used widely in real-time restoration with good computational efficiency but with details smoothed. Here, the results of
direct method are firstly filtered by hard-threshold function. The positions of the steps can be detected by simple
differential operators. With the positions corrected by projection algorithm, the exact barcode information is restored. A
wavefront coding system with 7mm effective focal length and 6
F-number is designed as an example. Although with the
different magnification, images of different object distances can be restored by one point spread function (PSF) with
200mm object distance. A QR code (Quickly Response Code) of 31mm X 27mm is used as a target object. The
simulation results showed that the sharp imaging objective distance is from 80mm to 355mm. The 2D barcode scanner
with wavefront coding extends field depth with simple structure, low cost and large manufacture tolerance. This
combination of the direct filter and projection algorithm proposed here could get the exact 2D barcode information with
good computational efficiency.
With the development of LED technology, LED will potentially replace the traditional light source for its cost and size
advantages, especially in the micro-projection system. And since the illumination uniformity and efficiency on spatial
light modulators (SLM) are two important factors in evaluating the performance of micro-projection system, tapered
light pipe (TLP) and square compound parabolic concentrator (SCPC) are often used as beam shaper in LED-based
micro projection system to provide SLM with uniform and efficient illumination. In this paper, in order to overcome the
disadvantage of insufficient compactness induced by the working length of TLP or SCPC for the illumination system, a
total internal reflection (TIR) lens with rotated and faceted structure is designed with an optimization method to couple
and transfer most of the light emitted from LED into a rectangular target plane (RTP) representing SLM. The TIR lens
has six surfaces controlled by 17 dimensional parameters and is designed by optimization of dimensional parameters
with generic algorithms. In order to provide RTP in fixed position with satisfied illumination uniformity and efficiency,
the illumination uniformity and efficiency on RTP are taken into account in the merit function for the optimization
process. In Tracepro program, the simulation result of the LED illumination system with the optimized TIR lens shows
that the illumination efficiency and uniformity has respectively achieved to 61.9%, 76% with considering the limitation
angle of light (15°).
Wavefront coding extended the depth of field to a great extent with simpler structure compared to confocal microscope.
With cubic phase mask (CPM) employed in the STOP of the objective lens, blurred images will be obtained in charge
coupled device (CCD), which will be restored to sharp images by Wiener filter. We proposed that one CPM is used in
one microscope although there are different objective lenses with different power indices. The microscope proposed here
is the wavefront coding one when the CPM is used in the STOP; while it is the traditional one when a plane plate is used
in the STOP. Firstly, make the STOP in the last surface of the lens, and then add a plane plate at the STOP with the same
material and the same center thickness of the CPM. Traditional objective lenses are designed, based on which wavefront
coding system will be designed with the plane plate replaced by a CPM. Secondly, the parameters of CPMs in different
objective lenses are optimized to certain ranges based on metric function of stability of modulation transfer function
(MTF). The optimal parameter is chosen from these ranges. A set of objective lenses is designed as an example with one
CPM. The simulation results shows that the depth of field of 4X, 10X, 40X, 60X and 100X objective lenses with the
same CPM can reach to 400um, 40um, 24um, 16um and 2um respectively, which is much larger than 55.5um, 8.5um,
1um, 0.4um and 0.19um of the traditional ones.
Strehl ratio is an important aspect in evaluating the performance of the optical imaging system. Even in wavefront
coding imaging systems, Strehl ratio also plays an important role. It can be used to evaluate the sensitivity of phase
masks to aberrations, and it can also be added as the penalty in the optimization of phase mask parameters to make sure
that the noise gain of the intermediate image recovery is not too large. However the conventional Strehl ratio analyses
are only suitable for the optical system with a small amount of aberration, while the wavefront coding imaging system is
an optical system with a large aberration, the most of which are the characteristic aberrations introduced by the phase
plate. In this paper, the approximate expressions of Strehl ratio are derived for the wavefront coding system with phase
plates of free order and free type. These expressions show a good coincidence with the numerical ones. Based on these
expressions, the impact of the phase mask's order can be analyzed. Besides, the sensitivity of Strehl ratio to all kinds of
aberrations can also be analyzed for the wavefront coding system with phase plates. Phase plates of different types are
shown to be sensitive to aberrations of different types, and the impact of the aberration order can also taken into account.
At last, some advice is given for taking Strehl ratio as one of the performance aspects while choosing phase plates.
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