Speckle Reduction in Imaging Projection Systems

Abstract

<p class="MsoNormal" style="text-align:justify;"> <span lang="EN-US">Diffractive diffusers (phase gratings) are routinely used for homogenizing and beam shaping for laser beam applications. Another use for diffractive diffusers is in the reduction of speckle for pico-projection systems. While diffusers are unable to completely eliminate speckle they can be utilized to decrease the resultant contrast to provide a more visually acceptable image. Research has been conducted to quantify and measure the diffusers overall ability in speckle reduction. A theoretical Fourier optics model is used to provide the diffuser’s stationary and in-motion performance in terms of the resultant contrast level. Contrast measurements of two diffractive diffusers are calculated theoretically and compared with experimental results. Having a working theoretical model to accurately predict the performance of the diffractive diffuser allows for the verification of new diffuser designs specifically for pico-projection system applications.</span> </p&gt

Non-moving Hadamard matrix diffusers for speckle reduction in laser pico-projectors

“…Simulation of the primary diffuser is accomplished first to ensure the proper contrast evaluation prior to a two-diffuser simulation [ 18 ]. Both contrast values will be compared with the expected theoretical values for accuracy.…”

Polychromatic speckle reduction in laser pico-projectors using stationary dual Hadamard diffusers

“…Previous work has been completed simulating DHDs for speckle reduction at 535 nm green laser light [6,7]. Speckle contrast of 0.43 (± 0.02) was achieved at the single wavelength.…”

“…Laser beam power was kept constant at 0.1 µm to decrease the possibility of light saturation disrupting speckle measurements. More specific details can be found within [6,7]. While the speckle reduction is not as low as other proposed reduction systems, the DHD do not require any rotation or vibration creating a completely stationary subsystem ideal for handheld electronic devices.…”

Multi-Wavelength Speckle Reduction for Laser Pico-Projectors Using Diffractive Optics

“…An initial modeling of the primary diffuser is accomplished first to ensure the proper contrast evaluation prior to a two diffuser simulation [47]. Both contrast values will be compared with the expected theoretical values for accuracy.…”

“…Previous work has been completed simulating DHDs for speckle reduction at 535 nm green laser light [47,48]. For contrast reduction purposes, the defined angular dispersion means the speckle spots will separate at a greater angle for red at 635 nm compared with blue at 450 nm.…”