Self-aligning optical heterodyne with four-wave mixing

We have demonstrated self-aligning optical heterodyning with a large acceptance angle, using four-wave mixing in a photorefractive crystal. The experiment was carried out in a 5 mm x 5 mm x 5 mm Ce-doped SBN crystal, grown at the Rockwell Science Center. It is a nonlinear optical central processing unit, utilizing three input beams to produce an output. The inputs are the local oscillator, and two collinear information beams, one a frequency probe beam, degenerate in frequency with the local oscillator, and the other a frequency-shifted information carrier. The unshifted beam and the local oscillator produce a grating in the crystal through the photorefractive effect. This grating diffracts the information carrier in the direction of the local oscillator, and aligns the two beams automatically for heterodyning in a detector. The electrical output, in the form of the beat signal between the carrier and the local oscillator can be easily detected and displayed. Detailed investigation of the sensitivity, and robustness of the receiver in a noisy environment is under progress.