Wide-angle self-aligning heterodyning with four-wave mixing

Self-aligning optical heterodyning is demonstrated with an acceptance angle as large as 40 degrees . The receiver consists of a strontium barium niobate (SBN) crystal, a detector, and collecting lenses. The incoming beam interferes with the local oscillator to create a real-time grating in the SBN crystal, which diffracts and aligns the signal with the local oscillator. Heterodyne detection occurs as long as the written grating can diffract the input signal. All alignment requirements between the signal and local oscillator are automatically satisfied by the diffraction process, which permits the large acceptance angle. Insensitivity with respect to crystal orientation and background radiation has also been demonstrated.