Whispering gallery mode optical resonators integrated on silicon have demonstrated low threshold Raman lasers. One of the primary reasons for their success is their ultra-high quality factors (Q) which result in an amplification of the circulating optical field. Therefore, to date, the key research focus has been on maintaining high Q factors, as that determines the lasing threshold and linewidth. However, equally important criteria are lasing efficiency and wavelength. These parameters are governed by the material, not the cavity Q. Therefore, to fully address this challenge, it is necessary to develop new materials. We have synthesized a suite of metal-doped silica and small molecules to enable the development of higher performance Raman lasers. The efficiencies and thresholds of many of these devices surpass the previous work. Specifically, the silica sol-gel lasers are doped with metal nanoparticles (eg Ti, Zr) and are fabricated using conventional micro/nanofabrication methods. The intercalation of the metal in the silica matrix increases the silica Raman gain coefficient by changing the polarizability of the material. We have also made a new suite of small molecules that intrinsically have increased Raman gain values. By grafting the materials to the device surface, the overall Raman gain of the device is increased. These approaches enable two different strategies of improving the Raman efficiency and threshold of microcavity-based lasers.
Andrea Armani, Hyungwoo Choi, Xiaoqin Shen, Dongyu Chen, and Andre Kovach, "Hybrid ultra-high-Q silica microcavity Raman lasers," Proc. SPIE 10535, Integrated Optics: Devices, Materials, and Technologies XXII, 1053509 (Presented at SPIE OPTO: January 29, 2018; Published: 23 February 2018); https://doi.org/10.1117/12.2289930.
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