Quantum Mode Correlations in Vertical Cavity Surface Emitting Lasers

Abstract

Considerable progress has been made during the past decade in understanding the quantum noise processes associated with the generation of photon-number squeezed light from conventional semiconductor lasers. Microcavity lasers, such as the vertical cavity surface emitting laser (VCSEL), have also been predicted to generate photon-number squeezed light based upon the high impedance pump noise suppression model1. Previous measurements, however, have only shown noise far above shot noise2. Several features of VCSELs are expected to lead to important differences from the quantum photon statistics in conventional edge-emitters. Because the cavity length is matched to the lasing wavelength, only a single longitudinal mode is present. This eliminates noise contributions from longitudinal mode competition noise. However, VCSELs often oscillate in multiple transverse modes, particularly for high efficiency devices operating at high pump rates, necessary for squeezing. Although quantum mode correlation effects between multiple longitudinal modes have been studied extensively in edge-emitting devices3, quantum correlations between different transverse modes have not been observed. Furthermore, because of the high mirror reflectivities (>99%) squeezed output from a VCSEL can provide confirmation of the high impedance pump noise suppression model predictions in the good cavity limit, for which the theory was formulated. The enhanced spontaneous emission into the lasing mode that is characteristic of these devices can potentially lead to squeezed output at all pump rates. In present devices, the microcavity effects contribute to a low threshold current that allows for the high pump rates necessary for squeezed output to be achieved at room temperature without damage to the laser.