Fabrication and characterization of a thermal tunable bulk-micromachined optical filter

Abstract

This paper presents and demonstrates a thermal tunable bulk-micromachined optical filter. The filter is based on a Fabry–Perot (F–P) interferometer which is realized by changing the refractive index of bulk silicon F–P cavity. Dense boron doped silicon resistors are used as the heater to achieve the function of wavelength tunable. Device silicon layer of SOI wafer is utilized for the parallel and high-quality bulk F–P cavity with a large dimension mirror structure in size of more than 700μm. Four fixed-fixed beams are designed to suspend the F–P cavity and provide a good thermal isolation. The tunable optical filter has been successfully fabricated and packaged. A pair of optical fiber collimators is used to couple the optical signal due to the large size of the mirror. The measured wavelength tuning range is about 17nm from 1565.32nm to 1582.36nm with driving voltage from 0V to 13.55V. The maximum power consumption is less than 130mW. The 3-dB bandwidth of the successfully fabricated filter is achieved in value of 0.29nm while the Free Spectral Range (FSR) is 21.9nm. The heating and cooling responding time is less than 50ms.