Acousto-optic channel equalization for microwave digital radios

Abstract

Digital radio transmission systems use complex modulation schemes that require powerful signalprocessing techniques to correct channel distortions and to minimize bit error rates. Acousto-optic processors are used, in conjunction with adaptive digital equalizers, to reduce the bit error rate of the digital radio receiver. The acousto-optic processor implements an inverse channel filter that is rapidly adaptable to time-varying distortions. A specific architecture is identified and a laboratory system is tested to verify the ability of the processor to track and correct time-varying channels. Computer simulations are used to show that the hybrid acousto-optic and digital equalizer permits a fourfold increase in the modulation capacity of radio, relative to all digital equalization, while improving the bit error rate performance.

Acousto-optic channel equalization for digital communications

“…To produce a homodyne photodetector output, the diffracted and undiffracted beams are made collinear and overlapping by a grating in the mask. For area modulation, we write the binary mask transmittance as9 m(q,p) = h(q,p)grat(q,p), (7) where q and p are the spatial coordinates, h(p,q) encodes the filter impulse response, and grat(q,p) is a binary grating. A two section, shifted grating is used so that light incident on the bottom half of the mask is diffracted with a it phase shift relative to the light diffracted from the top half; this allows bipolar masks to be encoded.…”

Characteristics of Soliton Evolution in the Wave-Breaking-Free Regime in a Passively Mode-Locked Yb-Doped Fiber Laser

“…Researchers have theoretically found that the formation of a pulse with a parabolic shaped temporal profile and a linear instantaneous frequency chirp is essential for the avoidance of wave-breaking in optical fibers. [14] Many experiments have demonstrated that the self-similar propagation of pulses resists the accumulation of excess nonlinearity and allows energy scaling towards the high-power regime in the laser fiber cavity. [15,16] The bound states of solitons formed in fiber lasers operating in a wave-breaking-free regime have been intensively investigated recently.…”