Abstract
We demonstrate planar Si3N4 ring resonators with ultra-high quality factors (Q) of 19 million, 28 million, and 7 million at 1060 nm, 1310 nm, and 1550 nm, respectively. By integrating the ultra-low-loss Si3N4 ring resonators with laterally offset planar waveguide directional couplers, optical add-drop and notch filters are demonstrated to have ultra-narrow bandwidths of 16 MHz, 38 MHz, and 300 MHz at 1060 nm, 1310 nm, and 1550 nm, respectively. These are the highest Qs reported for ring resonators with planar directional couplers, and ultra-narrowband microwave photonic filters can be realized based on these high-Q ring resonators.
Highlights
Ultra-high-Q optical resonators are crucial to an assortment of applications including cavity quantum electrodynamics [1,2], nonlinear optics [3], bio-sensing [4], telecommunications [5,6,7], and microwave photonic filters [8,9]
Planar silicon microdisk resonators integrated with in-plane waveguides were reported to have Qs of 3 million at 1550 nm [11]; the resonance is in a high-order mode, and silicon is not transparent in the 750~1000 nm wavelength regime, which is important for some applications such as biosensing due to the low optical absorption in water and the transparency of proteins in this wavelength range [12]
Ultra-high Q ring resonators as ultra-narrowband filters. These ultra-high Q ring resonators are integrated with laterally offset planar directional couplers to construct optical notch and add-drop filters with ultra-narrow bandwidths for microwave photonic filter and high-sensitivity sensor applications
Summary
Ultra-high-Q optical resonators are crucial to an assortment of applications including cavity quantum electrodynamics [1,2], nonlinear optics [3], bio-sensing [4], telecommunications [5,6,7], and microwave photonic filters [8,9]. An ideal platform for these resonators-on-achip would combine ultra-high-Q with planar processing capability, lasers, photodetectors and other photonic components for integration, and transparency across a wide range of wavelengths. Whispering-gallery-mode (WGM) resonators with ultra-high quality factor (Q) of 100 million have been demonstrated in microtoroidal structures made from thermally grown silica [10]. Due to their nonplanar structure, it is difficult to integrate such resonators with other optical devices for complex functionality. The resonators are fabricated with recently demonstrated ultra-low-loss high-aspect-ratio waveguide technology [15] and have integrated directional couplers. We discuss the suitability of these ultra-high-Q resonators with planar directional couplers for a specific application, namely ultra-narrowband filters (Section 4)
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