An electroactive polymer (EAP)-based MOEMS spatial light modulator (SLM), which shows high reliability and fast response speed, is reported in this work. The reliability is achieved by designing the SLM without direct contact between electrodes and deformable EAP surface; while the fast response speed is obtained by optimizing the microstructure of the EAP material. The concept of SLM, material optimization approach, fabrication processes, as well as characterization methods, are described. The SLM is driven by relatively low voltage, which is 200 V dc and 60 V ac and the response time is 35 μs. The manufactured SLM shows no degradation or breakdown after millions of actuation cycles, indicating a good reliability of the device.
An array of diffraction gratings and a Random Phase Plate (RPP) are used to suppress laser speckle effect. Dynamic
diffraction spots are generated on the surface of the RPP, after which the scattering lights are perceived by a detector.
Speckle Contrast Ratio (CR) and Number of Independent Speckle Patterns (NISP) with different gratings rotation
orientations (<i>θ</i>), gratings frequencies (grooves per millimeter: <i>f</i>), diameters of laser beam (<i>D</i>), and distances between the array of diffraction gratings and the RPP (<i>Z</i>) are calculated based on ZEMAX simulations, and an optimized model is proposed.
Barker binary phase code of maximum length 13 has previously been used for speckle reduction in line-scan laser
projectors, and a speckle contrast factor decreased down to 13% has been achieved. In this article, Barker-like
binary phase codes of length longer than 13 are used at an intermediate image plane. It is shown by theoretical
calculation that much better speckle reduction with speckle contrast factor up to 6% can be achieved by using
longer binary phase codes other than the Barker code. Preliminary experimental results are also presented
indictaing good speckle reduction.
We report a polymer based multiple diffraction modulator, in which PDMS (polydimethylsiloxane) is utilized as the
actuation material, for speckle reduction. The properties of the PDMS are characterized based on its response time and
deformability, which are the key properties concerned in this work. The structure dependent properties of PDMS are
discussed. Using the described technique, the PDMS satisfy the system demand.
The modulator is used to create real-time diffraction patterns by dynamic gratings formed by flexible PDMS. The
diffracted light passes through a diffuser, which is placed after the modulator, and induces speckle patterns on the screen.
Speckle-reduction is achieved by adding the time-varying speckle patterns in the integration time of the detector. It is
observed that using the modulator which has two gratings, the speckle contrast ratio reaches to 50%, which shows fair
agreement with the simulation.
It has been suggested to use Hadamard matrices <i>H(M)</i> of order M for speckle reduction in laser based projection displays
by creating a set of <i>M</i> two-dimensional phase masks from rows or columns of the <i>H(M)</i> and introducing them sequentially into the intermediate image plane of the laser projector. The speckle contrast reduction can reach <i>M<sup>-1/2</sup></i>. In
this paper, we have analyzed the contrast reduction. The result presents that any matrices can be used to form phase mask
as long as its columns are orthogonal to each other, such as the parts of columns of Hadamard matrix. The speckle contrast reduction is determined by the number of projection resolution elements lying in single camera resolution
element. To get high quality image with low speckle contrast reduction by Hadamard matrix, its order should be as high
as possible. However, it is impossible to implement by vibrating diffuser with high order due to the large vibration
amplitude. The motionless time-vary diffuser with Hadamard matrix phase pattern based on MEMS technology and
Electro-optical effect can be a good choice.
We report on device properties of tunable spatial light modulators for high-resolution optical applications by a novel
fabrication process. Thin polydimethylsiloxane (PDMS) films (4ìm-13ìm) were sandwiched between a flexible gold
film(50nm) and a rigid substrate with a comb-like electrode either by compression molding or spin coating. By applying
voltage between the upper gold film and underlying electrode, the initial plane PDMS surface changes into a form of
grating. Far-field scattering pattern with high order light components was observed by illumination at the continuously
reflective gold film with laser beam. Characterization was done by measuring the grating profile of the PDMS and the
response time. The PDMS deformation was demonstrated to increase with driving voltage. The deformation for 6ìm
thick PDMS is measured around 100nm when driving voltage is applied as 230V. Modeling and simulation of the
modulator electro-mechanical behavior was done for varies structure design. The simulation results showed fair
agreement with the experimental results. The response time, which defines how fast the PDMS response to the applied
voltage, was measured as a function of the driving voltage. The measured rise time is around 1 micorseconds and the fall
time is around 0.2 microseconds.