QUANTUM STATE CONTROL IN SEMICONDUCTOR-P-N JUNCTIONS .1. SQUEEZED STATE GENERATION IN SEMICONDUCTOR-LASERS

Quantum statistical properties of laser light have been extensively st udied for the last thirty years by using an operator Langevin equation , a density operator master equation, and a quantum mechanical Fokker- Planck equation. It has been generally accepted among physicists and q uantum electronics engineers that an ideal laser operating at far abov e the threshold generates a coherent state of light. Various experimen tal facts such as the Poissonian photoelectron statistics, the shot no ise limited photocurrent fluctuations, and the Gaussian distributions of optical homodyne detector output seem to support this. However, rec ent careful studies on a semiconductor laser have revealed that a semi conductor laser does not necessarily produce a coherent state of light , but generates a number-phase squeezed state, in which the photon-num ber noise is smaller than the standard quantum limit (shot noise limit or Poisson limit). This paper reviews the theoretical and experimenta l aspects of number-phase squeezed state generation by a semiconductor laser.