850 nm IR transmissive electro-absorption modulator using GaAs micromachining

• A new transmissive electro-absorption modulator was proposed and verified.
• Epitaxial growth of multi-layer designs was performed by MOCVD process.
• Thick InGaP (4λ) layer with a multifunction was grown on the GaAs substrate.
• A transmissive structure was realized using GaAs wet etching process.
• The experiment verified a high transmittance variation and speed for 3D camera.

The paper relates to a transmissive electro-absorption modulator and a method of fabricating the optical modulator for 3D image capturing system. For 3D image capturing, the system utilizes Time-of-Flight (TOF) principle by means of high-speed optical shuttering. A 20 MHz-switching high speed optical shutter is realized by GaAs based multi-layer design with electro-absorption layers combining with optical resonance cavity and GaAs micromachining based on the etching process. Thick InGaP (4λ) layer was chosen for the transmissive membrane structure and etch-stop of GaAs wet etching. This layer also was n-type doped to enhance the electrical contact resistance. The transmissive window area is divided into 28 cells for a low device capacitance and a high switching speed, and the polyimide layer with low dielectric constant is embedded between p-pad and n-pad to reduce the leakage and parasitic capacitance. As a result, 49.5% of transmittance variation and above 37.7 MHz of switching speed are obtained to guarantee the functionality of Time-of-Flight operation of 3D camera.