Arbitrary femtosecond optical pulse shaping with a liquid crystal spatial light modulator

Free space optical (FSO) communications technology has potential applications in the military sector to provide a secure, high speed communication channel, and in the civilian sector as a "last mile" carrier solution. It was proposed by other researchers that a multi-rate communication system that utilizes Meyer wavelets would achieve the greatest bandwidth and highest reliability possible for an FSO system [1]. In order to generate Meyer wavelets from femtosecond laser pulses, filtering must be performed optically to produce the desired pulse shape. One of the simplest ways to produce an arbitrary pulse shape from a laser pulse is with a tunable liquid-crystal spatial light modulator (LC-SLM) in a zero-dispersion pulse compression system. The simplest approach to determine the correct mask pattern for an LC-SLM is to utilize adaptive, global optimization methods. Since it takes several milliseconds to adjust the attributes of each pixel of an LC-SLM and there are typically over one-thousand pixels, it is important to determine the fastest algorithm for determining the optimum mask pattern. Several global optimization methods, including simulated annealing, exhaustive search, and random search, a hybrid of the other two algorithms, were characterized. It was found that exhaustive search can be used to form waveforms with negligible inaccuracies at rates of about 5 times faster than simulated annealing and about 3 times faster than random search, but that simulated annealing provides the highest accuracy. However, the difference in accuracy between all of these algorithms is less than 10 ^-5.