Abstract

We introduce and develop a novel mode locker based on microwave dielectric resonators made of LiNbO₃. We call this device a dielectric resonator/optical modulator (DROM). A 20-GHz DROM was used as an FM mode locker at the 84th harmonic of a conventional 238-MHz diode-pumped Nd:BEL (La₂Be₂O₅) laser cavity. Depending on the mode locker drive frequency, two distinct regimes of mode locking were observed: 2.9-ps pulses at a repetition rate of 238 MHz and 3.9-ps pulses at a repetition rate of 20 GHz. With 800 mW of diode pump power, 50 mW of average output power was obtained. Next, a 2.85 GHz resonant microwave optical modulator was developed by using a LiNbO₃ crystal in a cutoff metal waveguide. Round-trip phase modulation of 1 rad was measured with 0.5 W of microwave power. By using the modulator at the 12th harmonic of a 237.5 MHz diode-pumped Nd:YLF laser, again two regimes of mode locking were observed: 4.0-ps pulses at a repetition rate of 237.5 MHz and 4.5-ps pulses at a repetition rate of 2.85 GHz were obtained. The average laser power was about 400 mW for a diode pump power of 1.8 W.

© 1992 Optical Society of America