Abstract

We recently presented a micromechanical modulator with a broad optical bandwidth, thus allowing its use in wavelength-division multiplexing (WDM) fiber-optic applications.¹ Surface-normal modulation is achieved in this device by suspending an antireflection coating or membrane above a substrate via an air gap, and causing the air gap to change by applying a voltage between an electrode on the membrane and the substrate (Fig. 1, inset). Because the modulator window can be much larger than the fiber mode, inexpensive packaging is possible. Suspension of the antireflection coating is achieved by complete undercutting of a sacrificial layer. The membrane’s refractive index (n) is the square root of that of the substrate (n_s), and its thickness (t) is λ/(4n). If the air gap is mλ/4, for m even the reflectivity of the device is zero, and for m odd the reflectivity is high. We therefore called the device the Mechanical AntiReflection Switch (MARS). For m = 1 operation (quiescent air gap is λ/4), very broad optical bandwidths result. The optical bandwidth is reduced for larger m, but still is sufficient for WDM applications. We have since demonstrated reliability and temperature invariance, and evaluated the manufacturing options of this device.² The MARS device has been packaged and operated in fiber-optic systems with 10⁻⁹ bit-error-rate transmission at 1.5 Mbits/sec.³

© 1996 Optical Society of America