2019 Fiscal Year Annual Research Report
Development of rare-earth oxide based optical amplifiers and lasers integrated on Si by using magnetic light-matter interactions
| Project/Area Number |
19H02207
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| Research Institution | NTT Basic Research Laboratories |
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Principal Investigator |
徐 学俊 日本電信電話株式会社NTT物性科学基礎研究所, 量子光物性研究部, 主任研究員 (80593334)
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| Co-Investigator(Kenkyū-buntansha) |
後藤 秀樹 日本電信電話株式会社NTT物性科学基礎研究所, 量子光物性研究部, 主席研究員 (10393795)
俵 毅彦 日本電信電話株式会社NTT物性科学基礎研究所, 量子光物性研究部, 主幹研究員 (40393798)
尾身 博雄 日本電信電話株式会社NTT物性科学基礎研究所, 量子光物性研究部, 主任研究員 (50257218)
澤野 憲太郎 東京都市大学, 理工学部, 教授 (90409376)
稲葉 智宏 日本電信電話株式会社NTT物性科学基礎研究所, 量子光物性研究部, 研究員 (90839119)
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| Project Period (FY) |
2019-04-01 – 2022-03-31
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| Keywords | 希土類イオン / 光増幅器 / レーザー / シリコンフォトニクス / 光導波路 / ナノ共振器 |
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| Outline of Annual Research Achievements |
High quality single-crystal rare-earth oxide (REO) thin films, including Er2O3 and compound (ErGd)2O3 with different Er compositions, have been successfully grown on silicon-on-insulator (SOI) substrate. Well-resolved Stark-split photoluminescence (PL) emission peaks in the telecommunication band has been observed in all samples. Specifically, (ErGd)2O3 with Er concentration of 3.3X10^21 cm-3 demonstrates a PL lifetime of ~0.81 ms and a lifetime-concentration product as large as 2.67X10^18 s*cm-3, which is on the same order as other Er-incorporated materials shown to have high optical gain.
A ridge-type horizontal slot waveguide, with large power confinement factor within low refractive index REO and simple fabrication process, has been proposed and demonstrated, as a basic waveguide structure for optical amplifiers. For (ErGd)2O3 based waveguides, a large waveguide modal absorption of 88 dB/cm related to Er3+ ions has been achieved, indicating a large potential optical gain. Strong light emission from the waveguides have also been observed, with a radiation-efficiency on the order of 10-4. Although the waveguide propagation loss is still too large to demonstrate net optical gain in current stage, the main loss mechanism has been identified and the problem can be alleviated through dedicated material and device optimization.
These results suggest that the combination of REO thin film and horizontal slot waveguide is a very promising platform for realizing high performance optical amplifiers and lasers for silicon photonic integrated circuits.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
The most important techniques towards realization of optical amplifiers and lasers, including gain material growth and waveguide structure fabrication, have been established in the first year of the project. First, high quality single-crystal Er-incorporated REO thin films with large lifetime-concentration product have been successfully grown on SOI substrate. Second, a promising waveguide structure featuring strong optical confinement and simple fabrication process has been demonstrated, showing ultra-high potential optical gain and light emission efficiency of REO thin films embedded in. For the proposed subwavelength dielectric resonator (SWDR) suggested in the proposal application, it is found that the fabrication process is quite complicated. To solve this problem, an alternative SWDR structure based on nanodisk dimer with enhanced magnetic field as well as much simpler fabrication process has been proposed and being subject to device simulation and design. Furthermore, a peer-reviewed journal paper [X. Xu et al, Opt. Express 28(10), 14448 (2020)] has been published based on experimental results mentioned above. Based on these achievement, we therefore think that the project is generally progressing well as planned.
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| Strategy for Future Research Activity |
The future work in this project will be organized as follows:
(1) The propagation loss of horizontal slot waveguides will be reduced by optimizing the material growth conditions and device geometric parameters. After that, the optical gain will be characterized by pump-probe measurement method. Theoretical analysis, such as rate-equation modeling, will be performed and compared with experimental results to get insights and guidelines for further increasing optical gain.
(2) A simple subwavelength dielectric resonator (i.e., nanodisk dimer) with strong magnetic field enhancement will be designed and fabricated. Several measurements will be performed on the fabricated device structure, to confirm selective excitation and strong Purcell enhancement for magnetic dipole transitions of Er3+ in REO.
(3) High Q-factor optical resonators by using single nanodisk dimer as a building block, will be designed and fabricated. Once the Q-factor is high enough, lasers will be readily achieved through optical pumping. The lasing behavior will be evidenced through several characterizations.
(4) The laser threshold will be reduced through dedicated material and device optimization. Then, Ge quantum dot based light emitting diodes with significantly improved light output will be integrated with the low threshold optically pumped REO lasers in order to realize electrically driven lasers on Si substrate.
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