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

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 700 μm. 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 17 nm from 1565.32 nm to 1582.36 nm with driving voltage from 0 V to 13.55 V. The maximum power consumption is less than 130 mW. The 3-dB bandwidth of the successfully fabricated filter is achieved in value of 0.29 nm while the Free Spectral Range (FSR) is 21.9 nm. The heating and cooling responding time is less than 50 ms.