Micron-sized channel-dropping filters using silicon waveguide devices

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Abstract
High density integrated optics on the scale of VLSI is of interest as it allows complicated optical interconnect circuitry to be mass produced. In this paper we present micron-sized high Q resonant cavity structures based on silicon on insulator devices. These resonant cavities may be used in channel dropping filters and modulators. Because of their small size, they have high packing densities on the order of one million devices per square centimeter. This technology has the added advantage in that it can utilize the embedded VLSI electronics manufacturing capacity. In previous work, we studied silicon on oxide photonic band gap (PBG) devices and demonstrated devices with a 400 nm stop band and with a defect which had a Q of 265 centered at a wavelength of 1560 nm. In addition, we fabricated 3 to 5 micrometer radii micro-rings with Qs of approximately 250 and free spectral widths of over 20 nm. In this work, we report results on micro-racetracks, which are oval shaped resonators, with resonances that are approximately 16 nm apart and Qs of about 1000. These racetracks incorporate a vertical coupling technology in which the bus waveguides and the ring are on separate planes. This vertical coupling scheme allows for independent control of the Q of the ring via the distance between the ring and the bus. We demonstrate higher order multi-resonator filters with similar Q and free spectral range to the single resonator filters. The individual resonators in each filter have slightly different resonant frequencies from each other resulting in multi-peaked resonances and lower drop efficiencies. Finally, we show that it is possible to thermally tune the resonances by 1 nm leading to a 10:1 contrast ratio.

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