1550 nm surface normal electroabsorption modulators for free space optical communications

We report on the design, fabrication and characterization of 1550 nm electroabsorption modulators based on InGaAs/InAlAs coupled quantum wells grown on InP substrate by MBE. Large and small single modulators and modulator arrays have been fabricated on a wafer scale with an optimized device fabrication technology. The modulator size, shape, contact arrangements, and the array configurations have been varied to achieve suitable device performance for different retro-reflective free-space optical communication links. The device electrical and optical properties have been characterized by I-V, photoluminescence, absorption, transmittance and reflectance measurements. Modulators exhibit contrast ratios of 2:1 at a 3V driving bias and contrast ratios of 2:1 over a 30 nm bandwidth at 6V. A maximum contrast ratio of 4:1 is obtained at a 12 V driving voltage.