High-Q germanium optical nanocavity
Mid-infrared (MIR) integrated photonics has attracted broad interest due to its promising applications in biochemical sensing, environmental monitoring, disease diagnosis, and optical communication. Among MIR integration platforms, germanium-based platforms hold many excellent properties, such as wide transparency windows, high refractive indices, and high nonlinear coefficients; however, the development of MIR germanium photonic devices is still in its infancy. Specifically, MIR high-Q germanium resonators with comparable performance to their silicon counterparts remain unprecedented. Here we experimentally demonstrate an MIR germanium nanocavity with a Q factor of ～18,000, the highest-to-date of reported nanocavities across MIR germanium-based integration platforms. This is achieved through a combination of a feasible theoretical design, Smart-Cut methods for wafer development, and optimized device fabrication processes. Our nanocavity, with its high Q factor and ultrasmall mode volume, opens new avenues for on-chip applications in the MIR spectral range.
基金项目：Konica Minolta Imaging Science Encouragement Award; Ministry of Education, Culture, Sports, Science and Technology (MEXT)10.13039/501100001700; Japan Society for the Promotion of Science (JSPS)10.13039/501100001691 (JP26220605, JP18K13798); New Energy and Industrial Technology Development Organization (NEDO)10.13039/501100001863; Burroughs Wellcome Foundation.
Ziqiang Zhao：Department of Electrical Engineering and Information Systems, The University of Tokyo, Tokyo 113-0033, Japan
Wen Zhou：Department of Electronic Engineering, The Chinese University of Hong Kong, Shatin, Hong Kong SAR, China
Mitsuru Takenaka：Department of Electrical Engineering and Information Systems, The University of Tokyo, Tokyo 113-0033, Japan
Hon Ki Tsang：Department of Electronic Engineering, The Chinese University of Hong Kong, Shatin, Hong Kong SAR, China
Zhenzhou Cheng：Department of Chemistry, The University of Tokyo, Tokyo 113-0033, Japan
Keisuke Goda：Department of Chemistry, The University of Tokyo, Tokyo 113-0033, JapanDepartment of Electrical Engineering, University of California, Los Angeles, California 90095, USAe-mail: email@example.com
【1】R. Soref, “Mid-infrared photonics in silicon and germanium,” Nat. Photonics 4 , 495–497 (2010).
【2】N. Hiramatsu, F. Kusa, K. Imasaka, I. Morichika, A. Takegami, and S. Ashihara, “Propagation length of mid-infrared surface plasmon polaritons on gold: impact of morphology change by thermal annealing,” J. Appl. Phys. 120 , 173103 (2016).
【3】Q. S. Guo, A. Pospischil, M. Bhuiyan, H. Jiang, H. Tian, D. Farmer, B. C. Deng, C. Li, S. J. Han, H. Wang, Q. F. Xia, T. P. Ma, T. Mueller, and F. N. Xia, “Black phosphorus mid-infrared photodetectors with high gain,” Nano Lett. 16 , 4648–4655 (2016).
【4】H. T. Lin, L. Li, Y. Zou, S. Danto, J. D. Musgraves, K. Richardson, S. Kozacik, M. Murakowski, D. Prather, P. T. Lin, V. Singh, A. Agarwal, L. C. Kimerling, and J. J. Hu, “Demonstration of high-Q mid-infrared chalcogenide glass-on-silicon resonators,” Opt. Lett. 38 , 1470–1472 (2013).
【5】A. G. Griffith, R. K. W. Lau, J. Cardenas, Y. Okawachi, A. Mohanty, R. Fain, Y. H. D. Lee, M. J. Yu, C. T. Phare, C. B. Poitras, A. L. Gaeta, and M. Lipson, “Silicon-chip mid-infrared frequency comb generation,” Nat. Commun. 6 , 6299 (2015).
【6】B. Kuyken, T. Ideguchi, S. Holzner, M. Yan, T. Hansch, J. Van Campenhout, P. Verheyen, S. Coen, F. Leo, R. Baets, G. Roelkens, and N. Picque, “An octave-spanning mid-infrared frequency comb generated in a silicon nanophotonic wire waveguide,” Nat. Commun. 6 , 6310 (2015).
【7】Y. Zou, S. Chakravarty, C. J. Chung, X. C. Xu, and R. T. Chen, “Mid-infrared silicon photonic waveguides and devices [Invited],” Photon. Res. 6 , 254–276 (2018).
【8】T. Hu, B. W. Dong, X. S. Luo, T. Y. Liow, J. F. Song, C. Lee, and G. Q. Lo, “Silicon photonic platforms for mid-infrared applications [Invited],” Photon. Res. 5 , 417–430 (2017).
【9】W. Bogaerts, P. De Heyn, T. Van Vaerenbergh, K. De Vos, S. K. Selvaraja, T. Claes, P. Dumon, P. Bienstman, D. Van Thourhout, and R. Baets, “Silicon microring resonators,” Laser Photon. Rev. 6 , 47–73 (2012).
【10】F. X. Li, S. D. Jackson, C. Grillet, E. Magi, D. Hudson, S. J. Madden, Y. Moghe, C. O’Brien, A. Read, S. G. Duvall, P. Atanackovic, B. J. Eggleton, and D. J. Moss, “Low propagation loss silicon-on-sapphire waveguides for the mid-infrared,” Opt. Express 19 , 15212–15220 (2011).
【11】C. J. Smith, R. Shankar, M. Laderer, M. B. Frish, M. Loncar, and M. G. Allen, “Sensing nitrous oxide with QCL-coupled silicon-on-sapphire ring resonators,” Opt. Express 23 , 5491–5499 (2015).
【12】J. Chiles, and S. Fathpour, “Mid-infrared integrated waveguide modulators based on silicon-on-lithium-niobate photonics,” Optica 1 , 350–355 (2014).
【13】S. Khan, J. Chiles, J. Ma, and S. Fathpour, “Silicon-on-nitride waveguides for mid- and near-infrared integrated photonics,” Appl. Phys. Lett. 102 , 121104 (2013).
【14】S. A. Miller, M. J. Yu, X. C. Ji, A. G. Griffith, J. Cardenas, A. L. Gaeta, and M. Lipson, “Low-loss silicon platform for broadband mid-infrared photonics,” Optica 4 , 707–712 (2017).
【15】R. Shankar, R. Leijssen, I. Bulu, and M. Loncar, “Mid-infrared photonic crystal cavities in silicon,” Opt. Express 19 , 5579–5586 (2011).
【16】R. Shankar, I. Bulu, R. Leijssen, and M. Loncar, “Study of thermally-induced optical bistability and the role of surface treatments in Si-based mid-infrared photonic crystal cavities,” Opt. Express 19 , 24828–24837 (2011).
【17】H. T. Lin, Z. Q. Luo, T. Gu, L. C. Kimerling, K. Wada, A. Agarwal, and J. J. Hu, “Mid-infrared integrated photonics on silicon: a perspective,” Nanophotonics 7 , 393–420 (2018).
【18】N. K. Hon, R. Soref, and B. Jalali, “The third-order nonlinear optical coefficients of Si, Ge, and Si1-xGex in the midwave and longwave infrared,” J. Appl. Phys. 110 , 011301 (2011).
【19】A. Malik, S. Dwivedi, L. Van Landschoot, M. Munceb, Y. Shimura, G. Lepage, J. Van Campenhout, W. Vanherle, T. Van Opstal, R. Loo, and G. Roelkens, “Ge-on-Si and Ge-on-SOI thermo-optic phase shifters for the mid-infrared,” Opt. Express 22 , 28479–28488 (2014).
【20】S. Radosavljevic, N. T. Beneitez, A. Katumba, M. Muneeb, M. Vanslembrouck, B. Kuyken, and G. Roelkens, “Mid-infrared Vernier racetrack resonator tunable filter implemented on a germanium on SOI waveguide platform [Invited],” Opt. Mater. Express 8 , 824–835 (2018).
【21】W. Li, P. Anantha, S. Y. Bao, K. H. Lee, X. Guo, T. Hu, L. Zhang, H. Wang, R. Soref, and C. S. Tan, “Germanium-on-silicon nitride waveguides for mid-infrared integrated photonics,” Appl. Phys. Lett. 109 , 241101 (2016).
【22】J. Kang, X. Yu, M. Takenaka, and S. Takagi, “Impact of thermal annealing on Ge-on-insulator substrate fabricated by wafer bonding,” Mater. Sci. Semicond. Process. 42 , 259–263 (2016).
【23】K. H. Lee, S. Y. Bao, G. Y. Chong, Y. H. Tan, E. A. Fitzgerald, and C. S. Tan, “Fabrication and characterization of germanium-on-insulator through epitaxy, bonding, and layer transfer,” J. Appl. Phys. 116 , 103506 (2014).
【24】T. H. Xiao, Z. Zhao, W. Zhou, M. Takenaka, H. K. Tsang, Z. Cheng, and K. Goda, “Mid-infrared germanium photonic crystal cavity,” Opt. Lett. 42 , 2882–2885 (2017).
【25】J. Kang, Z. Cheng, W. Zhou, T. H. Xiao, K. L. Gopalakrisna, M. Takenaka, H. K. Tsang, and K. Goda, “Focusing subwavelength grating coupler for mid-infrared suspended membrane germanium waveguides,” Opt. Lett. 42 , 2094–2097 (2017).
【26】M. Sinobad, C. Monat, B. Luther-Davies, P. Ma, S. Madden, D. J. Moss, A. Mitchell, D. Allioux, R. Orobtchouk, S. Boutami, J. M. Hartmann, J. M. Fedeli, and C. Grillet, “Mid-infrared octave spanning supercontinuum generation to 8.5?μm in silicon–germanium waveguides,” Optica 5 , 360–366 (2018).
【27】L. Shen, N. Healy, C. J. Mitchell, J. S. Penades, M. Nedeljkovic, G. Z. Mashanovich, and A. C. Peacock, “Two-photon absorption and all-optical modulation in germanium-on-silicon waveguides for the mid-infrared,” Opt. Lett. 40 , 2213–2216 (2015).
【28】B. Troia, J. S. Penades, A. Z. Khokhar, M. Nedeljkovic, C. Alonso-Ramos, V. M. N. Passaro, and G. Z. Mashanovich, “Germanium-on-silicon Vernier-effect photonic microcavities for the mid-infrared,” Opt. Lett. 41 , 610–613 (2016).
Ting-Hui Xiao, Ziqiang Zhao, Wen Zhou, Mitsuru Takenaka, Hon Ki Tsang, Zhenzhou Cheng, and Keisuke Goda, "High-Q germanium optical nanocavity," Photonics Research 6(9), 925-928 (2018)