Surface micromachined long wavelength LED/photodetector with a continuous tuning range of 75 nm

We have investigated a new design for a highly tunable, vertical cavity, long wavelength LED/photodetector. A device operating at 1.5 mu m has been built with a tuning range spanning 75 nm, with an extinction ratio of greater than 20 dB throughout the tuning range. The device is composed of a bottom GaAs/AlAs distributed Bragg reflector (DBR) that is grown on a GaAs substrate, an InP-based active gain region, and a surface micromachined tunable top DBR mirror. The top mirror is suspended in air above the active region by selectively removing a sacrificial polyimide layer while leaving side posts intact to support the structure. A laser driver supplies the current to the active region, which results in light output from the top side of the device. A voltage can then be applied between the suspended top mirror and the contact to the InP-based active region, resulting in an electrostatic attraction between the mirror and the base structure. This causes the top mirror to move towards the active region, thus decreasing the Fabry Perot cavity length, and altering the output wavelength of the device. The device has potential applications in optical interconnects and communications.