| 研究課題/領域番号 |
19H02207
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| 研究機関 | 日本電信電話株式会社NTT物性科学基礎研究所 |
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研究代表者 |
徐 学俊 日本電信電話株式会社NTT物性科学基礎研究所, フロンティア機能物性研究部, 主任研究員 (80593334)
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| 研究分担者 |
後藤 秀樹 日本電信電話株式会社NTT物性科学基礎研究所, 企画, 所長 (10393795)
俵 毅彦 日本電信電話株式会社NTT物性科学基礎研究所, フロンティア機能物性研究部, 主幹研究員 (40393798)
尾身 博雄 大和大学, 理工学部, 教授 (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, フロンティア機能物性研究部, 研究員 (90839119)
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| 研究期間 (年度) |
2019-04-01 – 2022-03-31
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| キーワード | 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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| 研究実績の概要 |
A low loss waveguide platform for optical amplifiers and lasers based on rare-earth oxide (REO) thin films grown on Si substrate has been proposed and demonstrated. It is fabricated by patterning SiN thin film on REO/SOI substrate, the so-called SiN/REO/SOI strip-loaded waveguide. The waveguide exhibits lateral leakage loss for TM polarization. However, the leakage loss can be minimized at specific waveguide widths, due to the mechanism of bound states in the continuum. Ultra-low propagation loss of < 5 dB/cm has been experimentally demonstrated. Based on this waveguide structure, microring resonators with high Q-factor on the order of 10^4 have also realized. In such SiN/(ErGd)2O3/SOI strip-loaded waveguides with Er composition of ~5.7%, large optical signal enhancement of ~16 dB/cm at ~1536 nm has been observed upon optical pumping. The signal enhancement could be further improved by optimizing material quality and waveguide structure.
To investigate and manipulate light emission of electric dipole (ED) and magnetic dipole (MD) transitions of Er3+ ions in REO thin films, optical structures with enhanced electric or magnetic field in REO are desired. Metasurface structure based on Si/REO/SOI layer stacks has been designed. The unit cell structure is an asymmetric mesa of patterned Si on REO thin film. By adjusting geometric parameters, high-Q resonances in the wavelength range of optical transitions of Er3+ ions can be realized, with enhanced electric and magnetic fields, respectively. The proposed structure can be used to selectively enhance ED and MD emission.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
3: やや遅れている
理由
In FY2020, low loss waveguide platform, high Q-factor microring resonators, and large optical signal enhancement from the waveguides have been experimentally demonstrated, and high Q-factor metasurfaces for ED/MD enhancement have been designed. However, due to COVID-19 pandemic and multiple times of announcement of state of emergency, the research time, especially, experiment time, has been significantly reduced to less than half compared with FY2019. One of the planned targets of demonstration of net optical gain is not achieved. For this reason, it is concluded that the progress in FY2020 is a little delayed. However, this target is expected to be achieved in FY2021.
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| 今後の研究の推進方策 |
(1) The observed signal enhancement is not enough to compensate absorption loss of Er3+ ions due to low population inversion ratio. The reasons are considered to be large population loss due to energy transfer upconversion and inefficient pump laser absorption. Therefore, further optimization of (a) Er concentration and material quality of REO thin films and, (b) optical confinement factor in REO and propagate on loss of the SiN/REO/SOI waveguides, will be performed to increase the signal enhancement and realize net optical gain.
(2) Optically pumped lasers will be demonstrated by using REO gain medium and high-Q factor microring resonators as realized in FY2020.
(3) Optical properties of ED and MD transitions of Er3+ ions in REO thin films will be characterized. After that, the designed metasurface structures will be fabricated and characterized to demonstrate light emission enhancement for ED and MD transitions. The effect of selective enhancement of MD transitions on suppression of energy transfer upconversion will be also investigated and utilized to realize optical amplifiers and lasers with low thresholds.
(4) Light emitting diodes (LEDs) based on Ge quantum dots (QDs) with high output power will be demonstrated through embedding them into optical microcavities. The monolithic integration process for Ge QDs LEDs and REO thin film based lasers will be investigated and finally to realize electrically driven lasers by using Ge QDs LEDs as on-chip pump sources.
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