Learning and recall algorithm for optical associative memory using a bistable spatial light modulator

M-pulse amplitude modulation of a flat-topped beam for aeronautical laser communications

Using the Rytov method, bit error rate (BER) performances of M-pulse amplitude modulation (M-PAM) are investigated for a flat-topped beam when such a beam is employed in an aeronautical laser communication system operating in vertical paths having weak atmospheric turbulence. By using the on-axis scintillation index and the log-normal distributed intensity, the average BER (⟨BER⟩) is evaluated for M-PAM when M=2,4,8. The scintillation indices of collimated flat-topped beams of various flatness orders N are compared against propagation lengths, source sizes, and zenith angle for laser communication vertical paths, including uplink and downlink. Also, the ⟨BER⟩ versus the average signal to noise ratio (⟨SNR⟩) is examined for various beam flatness orders. It is shown that as the flatness order increases, the scintillation index decreases. Taking one of the best flatness order values, N=15, for reducing the scintillations, ⟨BER⟩ versus propagation lengths, source sizes, zenith angle, and ⟨SNR⟩ are found for various values of M. When M is increased, the ⟨BER⟩ is found to deteriorate.

System performances of optical space code-division multiple-access-based fiber-optic two-dimensional parallel data link

Optical space code-division multiple access is a scheme to multiplex and link data between two-dimensional processors such as smart pixels and spatial light modulators or arrays of optical sources like vertical-cavity surface-emitting lasers. We examine the multiplexing characteristics of optical space code-division multiple access by using optical orthogonal signature patterns. The probability density function of interference noise in interfering optical orthogonal signature patterns is calculated. The bit-error rate is derived from the result and plotted as a function of receiver threshold, code length, code weight, and number of users. Furthermore, we propose a prethresholding method to suppress the interference noise, and we experimentally verify that the method works effectively in improving system performance.