Zhang Y, Zhong K, Zhou X, Tsang HK. Broadband high-Q multimode silicon concentric racetrack resonators for widely tunable Raman lasers.
Nat Commun 2022;
13:3534. [PMID:
35725566 PMCID:
PMC9209424 DOI:
10.1038/s41467-022-31244-0]
[Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2021] [Accepted: 06/10/2022] [Indexed: 11/23/2022] Open
Abstract
Multimode silicon resonators with ultralow propagation losses for ultrahigh quality (Q) factors have been attracting attention recently. However, conventional multimode silicon resonators only have high Q factors at certain wavelengths because the Q factors are reduced at wavelengths where fundamental modes and higher-order modes are both near resonances. Here, by implementing a broadband pulley directional coupler and concentric racetracks, we present a broadband high-Q multimode silicon resonator with average loaded Q factors of 1.4 × 106 over a wavelength range of 440 nm (1240–1680 nm). The mutual coupling between the two multimode racetracks can lead to two supermodes that mitigate the reduction in Q factors caused by the mode coupling of the higher-order modes. Based on the broadband high-Q multimode resonator, we experimentally demonstrated a broadly tunable Raman silicon laser with over 516 nm wavelength tuning range (1325–1841 nm), a threshold power of (0.4 ± 0.1) mW and a slope efficiency of (8.5 ± 1.5) % at 25 V reverse bias.
The authors demonstrate a new approach for multimode resonators to maintain high-quality-factor resonances across a broad wavelength range using the detuning between the symmetric and anti-symmetric supermodes in concentric racetrack resonators.
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