Modern optical signal processing experiments demonstrating intensity and pulse-width modulation using an acousto-optic modulator

Abstract

Two experiments are presented to introduce undergraduate students in electrical engineering or physics to modern optical signal processing. Both experiments use an acousto-optic (AO) Bragg cell together with additional electronics to modify the intensity of a laser beam. Specifically, we show how an AO feedback system operating in the Bragg regime can be configured to produce amplitude modulated (AM) and pulse-width modulated optical signals. The basic components of the AO feedback system include a laser, an AO Bragg cell, an electronic AM modulator, a photodetector, an amplifier, and an electronic adder. Except for the laser, the AM modulator, and the Bragg cell, each of these components can be constructed with low cost electronics. A tutorial outlining the principles of acousto-optics is included to provide sufficient understanding of the Bragg cell. The project described in the paper has been used as a demonstration for junior- and senior-level undergraduate students in electrical engineering communications and optics classes.

On the fundamentals of optical scanning holography

“…In the actual experimental setup, the plane wave and the spherical wave are combined, though a beam splitter and the spherical wave can be derived from a focusing laser beam. The temporal frequency difference ⍀ between the two waves can be provided by using an acousto-optic modulator 8,19 or an electro-optic modulator 8 in the path of the plane wave.…”