Experimental results are reported demonstrating non-line of sight short-range ultraviolet communication link losses, and performance of photon counting detectors, operating in the solar blind spectrum regime. We employ light emitting diodes with divergent beams, a solar blind filter, and a wide field-of-view detector. Signal and noise statistics are characterized, and receiver performance is demonstrated. The effects of transmitter and receiver elevation angles, separation distance, and path loss are included.

Abstract-We present a new approach to optical interconnections, based on microelectromechanical system tip/tilt mirror technology and the White cell. This is a free-space approach in which many beams circulate simultaneously in the device, each beam forming a unique spot pattern on the micromirror array. On each bounce, each beam can be switched to any of several White cells, each of which has a different effect on the spot pattern. By appropriate combinations of these White cells, any input beam can be directed to any output. A simple proof-of-concept prototype has been demonstrated, and output coupling loss addressed.Index Terms-Microelectromechanical systems (MEMS) devices, optical communications, optical interconnections, White cell.

Motivated by rapid advances in solar blind ultraviolet (UV) light emitting diodes (LEDs), filters and photomultiplier tubes (PMTs), together with unique UV atmospheric propagation characteristics, a non-line-of-sight (NLOS) UV communication test-bed has been recently built and utilized for extensive experimental evaluation of performance of NLOS UV links in outdoor environments. Towards this end, key link components are first characterized and their limitations are identified. The tradeoffs among communication range, received number of photons, and bit-error-rate are revealed via field measurement results. Wavelength diversity is achieved by utilizing combinations of sources and detectors centered at different wavelengths in the solar blind band. It is demonstrated that signals can be reliably transmitted to their destinations of dozens of meters away through an NLOS channel. Although all reported results in this paper are based on open field experiments, it is found that reflections from surrounding objects such as trees and buildings can enhance the received signal strength, up to an order of magnitude increase in the received number of photons in some cases, thus significantly improving link performance.

Abstract-An optical true-time delay device that uses a binary counting system in a modified White cell is demonstrated. The switching engine uses four spherical mirrors and a three-state digital micromirror array. The delay part, as designed, provides 6 bits of delay ranging from 78 ps to 5 ns, using a combination of dielectric blocks for short delays and lens trains for longer ones. Long lens trains are folded for compactness. The authors describe the design and demonstrate two of the 6 bits of delays experimentally. Delays were accurate to within the measurement resolution of 1.25 ps. The insertion loss varied from 3.1-5.2 dB, depending on delay. It was found that the micromirrors do not contribute significantly to the loss.Index Terms-Array signal processing, beam steering, microelectromechanical devices, optical delay lines, optical signal processing, phased array radars.

We propose to use optical correlation to measure the quality of an optical link in real time, staying completely within the optical domain. We transmit a test signal of 010 and correlate the received (degraded) signal with 010. The strength and shape of the output measure dispersion and attenuation in just 3 bit periods (75 ps at 40 Gb/s) compared with minutes by traditional methods. Correlation becomes feasible owing to the recent development of tapped delay lines with very large numbers of taps. We present simulations showing that this technique can detect attenuation, dispersion, noise, and jitter. With this instantaneous quality-of-service information available to all nodes in a network, new protocols will enable the network to select paths based on quality, allowing service providers to take into account the system's physical impairments when selecting new light paths or when restoring existing ones and to guarantee varying levels of service. We present one such protocol.