Dynamic electrooptic frequency shifter for pulsed light signals

We report continuous frequency shifting of a train of mode-locked pulses of light by up to /spl plusmn/400 GHz using electrooptic frequency shifting (EOFS). Dynamic, continuous, and accurate shifting of the optical pulses is achieved by controlling the phase and power of a single frequency microwave signal in a traveling wave phase modulator structure. Operation of the device under different microwave power and optical pulse length settings was investigated in order to study spectral distortion predicted to occur at high levels of frequency shifting and when using long pulses. Possible techniques for future device improvement were proposed and preliminary tests were performed. The use of a second-harmonic component of the microwave drive signal leads to a longer region of constant amplitude gradient and results in reduced distortion.