Random Access

Optical phased arrays represent an enabling new technology that makes possible simple, affordable, lightweight, optical sensors offering very precise stabilization, random-access pointing, programmable multiple simultaneous beams, a dynamic focus/defocus capability, and moderate to excellent optical power handling capability. These new arrays steer or otherwise operate on an already formed beam, as compared to modem microwave phased arrays which both generate a beam and direct it in a specific direction. A phase projile is imposed on an optical beam as it is either transmitted through or refected from the phase shifter array. The imposed phase projile steers, focuses, fans out, or corrects phase aberrations on the beam. The array of optical phase shifters is realized through lithographic palteming of an electrical addressing network on the superstrate of a liquid crystal waveplate. Refractive index changes suficiently large to realize full-wave diperential phase shifts can be effected using low (<IO V ) voltages applied to the liquid crystal phase plate electrodes. High eficiency large-angle steering with phased arrays requires phase shifter spacing on the order of a wavelength or less; consequently addressing issues make I-D optical arrays much m r e practical than 2 -0 arrays. Orthogonal oriented 1-D phased arrays are used to defect a beam in both dimensions. Optical phased arrays with apertures on the order of 4 cm by 4 cm have been fabricated for steering green, red, 1.06 pm, and 10.6 pm radiation. Steering eficiencies of about 60% at 4" and 85% at about 2' have been achieved to date with switching times as short as a few milliseconds in the visible. Fluences of several hundred W/cm2 have been demonstrated at 10.6 pm with nonoptimlly engineered devices. Higher fluences can be handled at shorter wavelengths. Larger apertures are feasible, as is operation at other wavelengths and significantly faster switching times. System concepts that include a passive acquisition sensor as well as a laser radar are presented.

There is intensive attention on improving random media access control protocols in wireless environments. This paper proposes low-complexity, portable and flexible development of the wireless transmitter employing Random Access (RA) protocol. To develop this RA solution, the software architecture is roughly divided into three modules. The host software (i.e., micro-PC interface), Universal Serial Bus (USB) and Radio Frequency (RF) module. In our transmitter based scheme, the generated packets move from the higher layer (i.e., MAC layer) to the physical layer and then transmit over the air. At the other end, the packets will be received by the evaluation board, which is acting as a receiver. By using packet sniffer tool, we are able to sniff the radio packets from the micro-PC based RF-fronted wireless transmitter. Our results have been conducted through various test scenarios and emphasize the validity of our development in which, by our new developed RA solution, the generated radio packets are transmitted over the air successfully without any packet loss.