Speckle reduction and maintaining contrast in a LASER pico-projector using a vibrating symmetric diffuser

Abstract

We proposed a design for a LASER pico-projector with a low speckle contrast value and high contrast ratio that maintains system efficiency. The method for speckle contrast reduction utilizes two diffusers and a Voice Coil Motor (VCM) oscillator. The two different diffusers for a high contrast ratio and high system efficiency can be divided into two categories. In Category 1, the speckle contrast value can be decreased to 2.80% by using a circular symmetric diffuser. At the same time, the full-on/full-off (FO:FO) contrast ratio can be maintained within 1200:1-1300:1, but the system efficiency decreases 1.50%. In Category 2, the speckle contrast value can be reduced to 6.50% by using an elliptically scattering diffuser. At the same time, the FO:FO contrast ratio can be maintained within 1300:1-1400:1, and the system efficiency decreases by only 1.00%.

Speckle-modulating optical coherence tomography in living mice and humans

“…For example, the use of partially coherent illumination, implemented by a moving diffuser in the optical path, has been previously explored for imaging122223, display2425 and holography2627. In some cases speckle can be utilized to improve imaging, as in quantitative phase microscopy28, holographic microscopy29 and wide-field microscopy30.…”

Speckle-suppressed phase-only holographic three-dimensional display based on double-constraint Gerchberg–Saxton algorithm

“…Other methods for speckle suppression aim to introduce some moving devices in the optical system to weaken the time coherence of the laser. For example, Pan and Shih [8] and Kuratomi et al [9] used some kind of vibrating device or moving screen to change the timing phase distribution on the image plane in order to reduce the speckle noise. These methods can achieve a highquality reconstruction, but extra devices are necessary in the optical path, which increases the complexity of the holographic display system.…”

Skin buttons

“…Moreover, laser light tends to produce a speckle pattern, which can make the icons appear to "sparkle", reducing the visibility and identifiability of the icon [5]. Despeckling methods exist that can reduce this effect (see e.g., [23]), but future work is needed to see if these techniques are compatible with small devices. Finally, the IR proximity sensors we use can be inadvertently triggered by movement or flexing of the arm and wrist, and also by proximate clothing and jewelry.…”