The pump amplitude fluctuation of a current-driven semiconductor laser can be suppressed to below the ordinary shot-noise level by ‘‘high-impedance suppression.’’ As a result of this pump-fluctuation suppression, the output of a current-driven semiconductor laser exhibits amplitude squeezing in the frequency region below the cavity bandwidth. The noise equivalent circuits and the quantum-mechanical Langevin equations are derived and discussed for clarifying the difference between an ordinary laser oscillator with shot-noise-limited pump fluctuation and a constant-current-driven semiconductor laser.

• Received 20 October 1986

DOI:https://doi.org/10.1103/PhysRevA.35.5114