Abstract

Above-threshold operation of a cw phase-matched triply resonant ring degenerate optical parametric oscillator (OPO) as a function of the pump intensity is theoretically analyzed. The internal pump photon number is clamped at approximately the threshold level. As the pump is increased, additional pump photons are converted into signal photons until an instability point is reached when the internal signal photon number is 4 times the internal pump photon number. Above the instability point the steady state becomes unstable due to competition between the two processes of parametric downconversion and upconversion, each requiring a different relative phase. While this is very similar to the instability of second harmonic generation inside a cavity, this OPO instability has not been pointed out before. When internal losses and nondegenerate signal and idler are included, we obtain a similar conclusion. If the ring cavity is replaced with a special standing-wave configuration, cw operation is stable at all pump levels because the two processes can coexist. This has important implications in current squeezing experiments in which single-ended (basically ring) cavities are preferred and in monolithic ring OPO as efficient tunable radiation sources. The design parameters for a stable ring OPO are discussed.

© 1988 Optical Society of America