Reduction of feedback-induced intensity noise in vertical-cavity surface-emitting laser by superposition of high-frequency current

Vertical-cavity surface-emitting lasers (VCSELs) have received considerable recent attention due to the ease with which one may fabricate compact, two dimensional arrays of these devices, which makes them potentially useful in optical interconnection. Unwanted optical feedback can be induced by a variety of means, and in densely two-dimensionally integrated systems, it may prove difficult to eliminate this feedback using conventional optical isolators. It has been demonstrated experimentally that the feedback sensitivity of VCSELs is comparable to that of conventional edge-emitting lasers. However, to couple a given amount of feedback into the active region of a conventional edge-emitting laser requires more stringent focusing and alignment than it does to couple the same amount of feedback into the active region of a VCSEL. For this reason, in a given application, VCSELs may be more likely to be influenced by optical feedback than edge-emitting lasers. We have measured the relative intensity noise of a VCSEL subjected to external feedback. The VCSEL used in this experiment is a 10 μm-diameter, bottom-emitting InGaAs device that operates at a wavelength of 958 nm