Free space communication link using a grating light modulator

Abstract

This paper presents the design and operation of a free space communication link based on a grating light modulator (GLM) in a corner cube reflector configuration. A GLM is a micromachined optical phase grating whose grating efficiency can be controlled electrostatically. Combining the GLM with a corner cube to create a grating corner cube (GCC) modulator reduces the alignment requirements of the device. Our device has a measured acceptance angle of ≈6° in the plane of incidence of the GLM, limited by angle dependence of the grating. Significant improvement of the acceptance angle can be achieved by optimizing the layer thickness of the grating structure. The resonance frequency of our GLMs is 290 kHz. Their low damping leads to ringing that increases the switching time to 35 us. The ringing has been reduced using a pre-shaped actuation signal yielding switching times of 10 μs. Low misalignment sensitivity, low power consumption, and low switching times make the GCC ideal for use in free space optical communication links.