Real-time Fourier transformer using one acousto-optical cell

摘要

An optical Fourier transformer comprising an acousto-optical cell such as a Bragg cell upon which is impressed a chirp signal, a laser which is modulated by the signal to be analyzed, optical means for dividing the laser beam into two beams which strike one side of the acousto-optical cell with opposite orientations. The chirped acousto- optical cell diffracts the beams incident thereupon. The two diffracted beams are then recombined with their original orientations reestablished so that they interfere upon striking a time-integrating photo-detector array. The distribution of integrated intensities is related to the Fourier transform of the signal to be analyzed. Polarization discrimination can be used to split and recombine beams and to reduce extraneous beams. Background noise and direct current terms can be eliminated by comparing runs with 180° of phase shift added between runs.