Authors: E.P. Furlani
Affilation: Eastman Kodak Research Labs, United States
Pages: 398 - 401
Keywords: MOEMS grating, electrothermal diffraction grating, thermoelastic grating, electrothermal light modulator
We present a thermoelastically driven MOEMS light modulator in the form of an ElectroThermal Grating (ETG). The ETG consists of an array of equally spaced bilayer microbeams suspended at both ends above a substrate (Fig. 1). The bilayer microbeams have a conductive/reflective top layer that has highly resistive end sections, and a central portion with low resistance, and a nonconductive bottom layer. In an unactivated state, the microbeams are flat and the ETG reflects incident light like a mirror (Fig. 2a). Light modulation occurs when a potential difference is applied across the conductive layers of alternate microbeams. This causes current to flow through the resistive end sections which, in turn, expand due to joule heating. The top sections expand more than the corresponding bottom sections, which have a lower coefficient of thermal expansion. This causes a thermoelastically induced deformation of the heated microbeams downward, toward the substrate. A diffraction pattern is produced when the heated microbeams deform a distance of / 4 £f from their rest position ( £f is the wavelength of the incident light) (Fig. 2b). Since the deformation depends on the level of current, an ETG can operate in an analog mode wherein it selectively diffracts a range of wavelengths. In this presentation, we demonstrate the performance of an ETG. We present an analytical design formula for rapid parametric optimization, and demonstrate ETG viability at operating voltages below one volt.