Signal correlation using a one-dimensional electroabsorptive CCD spatial light modulator

Electrically addressed spatial light modulation (SLM) may be carried out in a GaAs charge-coupled device (CCD) by charge-transfer control of the electroabsorption in the individual storage wells. One-dimensional modulator arrays may be utilized in both space-integrating and time-integrating correlators operated as incoherent optical processors. In the space-integrating case, one SLM controlled by the input signal is operated in cascade with a second SLM controlled by a reference waveform. This arrangement yields a single-detector output which is the correlation as a function of time. In the time-integrating correlator, the input signal is carried by the light source while a single SLM with a traveling reference wave controls the output intensity to a detector array. The modulator arrays may be operated with the light at normal incidence to a CCD with transparent gates or in a guided-wave mode, where the light propagates beneath the gate electrodes and parallel to the surface. The calculated dynamic range is greater for the guided-wave case because of the greater depth of modulation, although the fabrication and optical coupling are more critical. Space-integrating correlator performance is limited by "bleaching" or well-filling by the modulated light and predicted dynamic ranges are 20 dB for normal-incidence operation and 40 dB for the guided-wave mode. In the time-integrating correlator, saturation of the detector array is limiting, but the 100-percent modulation available in the input optical source yields 35-dB dynamic range for normal-incidence and 55 dB for guided-wave operation.