Amorphous Silicon as an Active Material in Optical Resonators
- PDF / 964,154 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 44 Downloads / 266 Views
0910-A17-01
Amorphous Silicon as an Active Material in Optical Resonators Dennis Hohlfeld, and Hans Zappe Department of Microsystems Engineering, University of Freiburg, Georges-Koehler-Allee 102, Freiburg, 79110, Germany ABSTRACT The application of amorphous silicon as a thermo-optically active material in MEMS-based, tunable optical filters is presented. The thin film interference filter employs a solid-state silicon cavity and silicon-based distributed Bragg reflectors (DBR). Tuning is achieved by varying the resonator’s refractive index and thus its optical thickness through thermal modulation. The filter is configured as a membrane and operates up to a temperature of 450 °C. Such a filter is essential for monitoring and reconfiguration of optical data communication networks and is also applicable for chemical and gas sensing. INTRODUCTION Optical filters are essential components in a wide spectrum of instruments, including spectroscopic applications, such as gas sensors, and optical channel management in communication systems. The functionality of these devices is greatly improved if wavelengthtunable filters are employed. The demand for higher transmission capacity in optical communication networks is satisfied by adding individually modulated optical channels to already established transmission systems. Due to increasing channel numbers, high-quality tunable devices are already deployed in flexible network management solutions. As a result, miniaturized tunable filters represent key components in a number of integrated optical subsystems, such as wavelength-selective add-drop multiplexers, optical channel monitors, and tunable lasers. Micromechanically tunable devices feature DBRs in connection with a single air-cavity, whereby tuning is achieved by mechanically varying the distance between the mirrors through electro-static, thermal, or magnetic actuation [1]. Tuning through the thermo-optic effect has already been applied to planar waveguide filters, which are based on silicon oxy-nitride materials. Here, we present a class of tunable thin-film interference filters, which are fabricated using silicon MEMS technology and feature a tuning mechanism based on the thermo-optic effect. This optical filter consists of DBRs as semi-transparent mirrors and a solid-state cavity in between. The refractive indices of the optical layers are varied using controlled temperature changes thereby shifting the transmission wavelength of the filter. As the thin-film filter is configured as a membrane, our approach differs significantly from [2] and shows greatly improved heating efficiency. DESIGN The transmission wavelength of an etalon may be tuned by varying the resonator thickness. This tuning is usually accomplished by mechanically varying the distance between the mirrors using electrostatic, thermal, or magnetic actuation. Varying the temperature of the membrane
changes the refractive index of the cavity and accordingly the optical resonator thickness of the filter. In this work thin-film metal heaters are deposited o
Data Loading...
