Widely tunable Fabry-Perot filters using high index-contrast DBRs

Realization of microelectromechanisally wavelength tunable Fabry-Perot filters using high index-contrast distributed Bragg reflectors (DBRs) comprising GaAlAs/AlOx and Si/SiO2 material systems are reported. Due to the broadband nature of these high index-contrast DBRs, the 3dB transmission bandwidth of the cavity resonance is narrow and stable over the tuning range. While the three different sets of GaAlAs/AlOx based filters with different number of DBRs exhibited linewidths of 0.5nm, 2.0nm and 0.47nm with tuning ranges of 59nm, 83nm and 60 nm respectively, the silicon-based filter exhibited a linewidth of 0.3 nm and a tuning range of 12 nm. Transmission spectra from these devices displayed varying magnitudes of higher order spatial modes in addition to a fundamental Fabry-Perot mode. These higher order spatial modes were attributed to lensing effect caused by partially oxidized AlGaAs layers within the mirror layers. One of the GaAlAs filters showed a frequency response of 500 KHz at 3dB cutoff point indicating a switching time of 2 microseconds.