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Abstract-Two-dimensional (2D) optical intensity channels exist in a variety of applications including holographic storage, page-oriented memories, optical interconnects, 2D barcodes, as well as MIMO wireless optical links. This paper considers the capacity of such channels when the transmitted signal is binarylevel. Strict spatial alignment between transmitter and receiver is not required nor is independence among the spatial channels. Spatial discrete multitone modulation is combined with digital image halftoning to produce a binary-level transmit image. Unlike earlier work, this paper considers imagers with pixels of fixed size and quantifies the tradeoff between frame rate, array size and capacity per frame. An experimental prototype pixelated wireless optical channel is constructed, and the channel parameters are measured. With a measured channel model, rates on the order of 450 Mbps are predicted for a 1 m link using 0.5 megapixel arrays at a frame rate of 7 kfps.

This paper presents a novel application of compressive sensing (CS) to provide spatial diversity for free-space optical communication links. A CS receiver estimates the focal-plane signal distribution due to atmospheric turbulence. This estimate is then employed by a digital micromirror device to select the portions of the focal plane which contain significant energy for detection. The CS receiver is less complex, requires fewer highspeed optoelectronic components, has lower preamplifier noise and can operate at higher rates than a comparable multipledetector array receiver. Bit-error rates are simulated for a photon counting channel and performance improvements near 2.4 dB can be obtained over a single detector receiver.

A method of speckle reduction suitable for use in a laser projector was proposed in the paper. Speckle contrast ratio (SCR) reduction was achieved by combining wavelength diversity and angular diversity methods. First, wavelength diversity was demonstrated by the use of two green laser sources (a 520 nm laser diode (LD) and a 532 nm diode-pumped solid-state (DPSS) laser) at a power ratio of 4:1. Second, angular diversity was achieved via the vibration of two lenses in two orthogonal directions placed directly after the laser source. The vibrating lenses are small and do not require changes to the beam path of the laser source, allowing for more compact projector designs. The frequency of vibration of these lenses was optimized to minimize the SCR in the output image. A SCR of less than 4% was achieved without the use of optical diffusers, which significantly reduces optical losses. Optical transmission could be further increased with the optimization of optical coatings on the lenses. This result shows great promise for applications such as laser pico-projectors within the realm of heads-up displays (HUDs) and mobile devices.

In this paper, a compact speckle reduction method utilizing vibrating lenses for laser beam scanning is proposed and demonstrated. The maximum speckle reduction efficiency was found to be 75.6% and 81.25% for a 532 nm diode-pumped solid-state (DPSS) laser and a 520 nm laser diode (LD), respectively. The minimum speckle contrast ratio observed using our method was 0.11 for the DPSS laser and 0.06 for the LD. The proposed method can provide speckle reduction with minimal power requirements, a low implementation cost, and no bending for the optical path of the laser beam. Additionally, this method is promising to withstand high-power lasers for use in high lumen laser projectors by optimizing the lens parameters. The demonstrated technique has a small form factor while simultaneously demonstrating a high degree of speckle reduction, which shows potential for speckle reduction in mini-and pico-laser projector applications.