Integrated photodetection in VCSELs

We present the different approaches we have studied to integrate generically photo-detection in a VCSEL (vertical cavity surface emitting laser) thus increasing further the advantages of this laser device. Two main detection configurations for different applications are possible: either external detection (for telemetry, imagery, etc.) or internal detection (for power monitoring, feedback measurements, etc.). We have investigated these two possibilities in single-cavity devices with a standard geometry in order to keep the fabrication of optimised devices as simple as possible. In the first case (external detection) we have obtained an improvement of the detection quantum efficiency to 20% in a 850 nm-emitting VCSEL by chemical selective etching the first periods of the top Bragg reflector. In the second case, integrated detection for VCSELs monitoring, we have proposed to use an adjacent VCSEL to detect the part of guided light in the plane of the cavity. This signal comes mostly from the spontaneous emission escaping laterally from the VCSEL active zone, but can be nevertheless efficiently used to monitor the normal laser output power, since both signals are monotonously correlated. Furthermore, we propose a derived approach including a Schottky contact on the cavity. A significant value of photocurrent (> 100 /spl mu/A) is obtained and the slope variations of the collected current can be correlated to VCSEL threshold crossing and extinctions without the need of any signal treatment.