We present the design and fabrication of a dual air-bridge waveguide structure integrated with MEMS functionality. The structure is designed to function as a tunable optical buffer for telecommunication application.
The optical buffer structure is based on two parallel waveguides made of high refractive index material with subwavelength dimensions. They are suspended in air, and are separated by a sub-micron air gap. Due to the fact that the size of the waveguides is much smaller than the wavelength of light that propagates in the structure, a significant fraction of the optical mode is in the air gap between the waveguides. By changing the size of the air gap using MEMS techniques, we can vary this fraction and hence the effective refractive index of the waveguide structure, thus generating tunable optical delay.
The optical buffer structure was grown on an InP substrate by molecular beam epitaxy, and the device layer was made of InGaP. An InGaAs layer was sandwiched between the device layer and the substrate to serve as a sacrificial layer. The sub-micron waveguides, their supports in the form of side pillars with tapered shapes in order to minimize optical losses, and the MEMS structures were patterned using electron beam lithography and plasma etching. Electrodes were integrated into the structure to provide electrostatic actuation. After the sample patterning, the waveguide structure was released using HF etch. Our simulations predict that by varying the waveguide separation from 50 nm to 500 nm, we could achieve a change in propagation delay by a factor of two.
We present the design and fabrication of a tunable optical buffer device based on III-V semiconductor platform for
telecommunication applications. The device comprises two indium phosphide suspended parallel waveguides with cross
sectional dimension of 200 nm by 300 nm, separated by an air gap. The gap between the waveguides was designed to be
adjustable by electrostatic force. Our simulation estimated that only 3 V is required to increase the separation distance
from 50 nm to 500 nm; this translates to a change in the propagation delay by a factor of 2. The first generation of the
suspended waveguide structure for optical buffering was fabricated. The sample was grown on an InP substrate by
molecular beam epitaxy. The waveguide pattern is written onto a 300 nm thick InP device layer by electron beam
lithography and plasma etching. Electrodes were incorporated into the structure to apply voltages for MEMS actuation.