Information processing with short optical pulses

Compact, practical, and cost effective femtosecond lasers are beginning to show up commercially both as solid-state and fiber lasers. These femtosecond sources can be used to great advantage in many communications and information processing applications. Interestingly enough, most of these applications are not related to the speed of these pulses, but rather use some other aspect of femtosecond laser pulses such as large spectral bandwidth, spectral coherence, intensity, short coherent length, or signal-to-noise advantages. For example, the 3 THz spectral bandwidth of a 100 fs laser pulse is wide enough to support 30 WDM channels spaced at 100 GHz, all covered by a single laser source. These channels can now be modulated using either a modulator array or even only a single modulator when the femtosecond pulses are chirped by propagation in optical fiber, as in chirped-pulse WDM. Using diode-pumped erbium fiber lasers, such a femtosecond WDM source can support many channels in a cost effective way. A single TDM modulator running at a multiple of the repetition rate of the laser can now both define as well as encode data onto the WDM channels sequentially. Interesting applications also result when we take advantage of space-time analogies in optical systems involving short pulses. This principle can be used for all-optical packet header recognition of terabit-per-second data streams. Using computer-generated holograms (CGH), we have generated and subsequently recognized 8-bit pulse sequences at a 1 Tb/s data rate.