Technique for translating light-wave frequency by using an optical ring circuit containing a frequency shifter

A new technique for the external frequency translation of light waves is proposed. The technique enables the stepwise sweeping of an optical frequency in time over a wide range. The frequency translator is composed of an optical pulse modulator and an optical ring circuit that contains an acousto-optic frequency shifter and an optical amplifier. The pulse launched into the ring circuit undergoes a frequency shift for each complete trip around the ring circuit, and the frequency is translated considerably from the original input pulse. We confirm a frequency translation of as much as 8 GHz for a 1.5-microm light wave, in which the sweeping is strictly linear with respect to time.