Abstract

The generation of light with amplitude-noise levels below the standard quantum limit (SQL) by constant-current operation of light-emitting and semiconductor laser diodes has been well established.¹ Nearly all of this work, however, has been conducted with the light source cooled to cryogenic temperatures. At room temperature, the highest observed squeezing levels were 0.6 dB for light-emitting diodes and 0.2 dB for laser diodes.² We presently report up to 1.8 dB of squeezing from a commercially available index-guided quantum-well laser (SDL-5410-C) operated at room temperature. Although cross-gain saturation can lead to amplitude squeezing of the total number of photons emitted by a multimode semiconductor laser in the limit of fast intraband scattering and the absence of wavelength-dependent loss,³ we found that it was necessary to suppress the >100 near-threshold longitudinal side modes of the laser to obtain squeezing at room temperature. This was accomplished either by using optical feedback from a grating in an external cavity configuration or by injection-locking the laser to a single-frequency laser. Both of these techniques allow the output wavelength of the laser to be named and thus the squeezing level as a function of wavelength to be studied.

© 1994 Optical Society of America