Tunable Vernier Microring Optical Filters With p - i - p-Type Microheaters

We present thermally tunable microring optical filters using p - i - p-type microheaters. The use of Vernier effect in the cascaded two microring resonators significantly enlarges the free spectral range (FSR) and the thermal tuning range with reduced power consumption. Heat generated by the p - i - p-type microheaters interacts directly with the microring waveguides, providing a means to effectively tune resonances without incurring excess loss. Experimental results reveal that the filter passband can be discretely shifted in the wavelength range from 1520 to 1600 nm by tuning one resonator with a power tuning efficiency value of 2.5 nm/mW. The passband can be also continuously shifted by simultaneously tuning both resonators with a power tuning efficiency value of 0.11 nm/mW. The rise (fall) time of the p - i - p microheater is measured to be 460 ns (1.1 mu s) under a peak-to-peak driving voltage of 3.4 V.