Coherence properties of optical parametric oscillators

Abstract

Most treatments of noise characteristics of optical parametric oscillators (OPOs) have been based on linearization of the equations of motion. This approach, valid far below and far above threshold, breaks down in the threshold region as it ignores the nonlinearity of interaction. We present a treatment that takes into account both the nonlinearity and the quantum mechanical nature of noise in these oscillators. Analytical expressions for the steady-state amplitude distribution functions are derived. Both the degenerate and the nondegenerate OPOs are considered. These steady-state distributions are used to study the coherence properties of the OPOs in the threshold region. These studies bridge the noise characteristics of the OPOs below and above threshold. Results are compared with classical oscillators and differences and similarities are discussed. Special attention is given to quantum mechanical features that survive even as the oscillator amplitude grows and reaches macroscopic proportions.