Polarization-dependent noise in photon-number squeezed light generated by quantum-well lasers

Amplitude noise spectra from the nonclassical output of an injection-locked low-temperature quantum-well laser analyzed along orthogonal polarization axes reveals correlated polarization-dependent noise. Using polarization-preserving balanced homodyne detection to suppress these effects, we demonstrate photon-number fluctuations 4.5 dB below the semiclassical shot-noise limit (within 95% of the expected squeezing based on the device efficiency). Polarization mixing through birefringent components and, more significantly, correlated fluctuations originating in the laser gain medium are shown to account for the observations.