Integrated Nanophotonic Control of Thermal Bimorph Microactuators*

A new type of thermal bimorph microactuator is presented, in which energy delivery to the actuator is achieved through an integrated nanophotonics approach. This approach has been adopted from existing photonic device and optical communications technology. The microactuators are fabricated on a silicon nitride platform using a silicon nitride/aluminum bimorph structure. Integrated nanophotonic building blocks, such as waveguides, tapers and grating couplers are designed and fabricated using photonic design and nanofabrication tools. During operation, laser light from a telecommunications laser source at milliwatt levels is focused onto the device and is captured by the grating coupler. The captured light is routed on the surface of the microstructure and delivered to the bimorph limbs by the waveguides and subsequently converted to heat using chromium optical absorbers integrated onto the waveguides. To provide additional mechanical flexibility and increased bending range, solid rib waveguides are replaced in parts by arrays of etched ridges which are periodically spaced at a fraction of the laser wavelength. These 1-D photonic crystals act as flexible subwavelength grating waveguides. As an added feature, the grating couplers are implemented as 2D arrays of etched holes, enabling polarization-based beam separation on the device, thus enabling control of different limbs through polarization switching at the laser source. In addition to in situ characterization, the microstructures are also transferred to an optical fiber tip which delivers laser light to the device while also providing a useful means for packaging and using the microactuators.