Abstract

Number states of the electromagnetic field are ideal for optical communication and for a variety of high precision measurements. It has been shown theoretically that the light from a semiconductor laser can opproach a number state^1. In previous experiments^2,3 the observed amplitude noise reduction, below the standard quantum limit, was at most 1.5 db. In this experiment we have been able to reduce the effects of optical feedback, increase the collection efficiency and consequently further elucidate the basic device physics necessary for improvement in the noise reduction. We have observed that the measured squeezing is not limited by the laser overall quantum efficiency but only by the optical output coupling efficiency. An explanation is advanced based on the premise that current division does not introduce Poissonian noise but thermal noise.

© 1990 Optical Society of America