2001 Fiscal Year Final Research Report Summary
Investigation of an ultrafast all optical modulation device using three levels in a GaN/AlGaN quantum well
| Project/Area Number |
11555014
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 展開研究 |
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| Research Field |
Applied optics/Quantum optical engineering
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| Research Institution | KYOTO UNIVERSITY |
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Principal Investigator |
NODA Susumu Kyoto Univ., Dept. of Electron. Sci. and Eng., Professor, 工学研究科, 教授 (10208358)
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| Co-Investigator(Kenkyū-buntansha) |
IIZUKA Norio Toshiba, R&D Center, Researcher, 研究開発センター, 研究員
ASANO Takashi Kyoto Univ., Dept. of Electron. Sci. and Eng., Assistant, 工学研究科, 助手 (30332729)
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| Project Period (FY) |
1999 – 2001
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| Keywords | GaN / AlGaN Quantum dot / Intersubband transition / All-optical modulation / Ultra fast relaxation / Carrier dynamics / Intersubband relaxation time / Monte Carlo simulation |
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| Research Abstract |
(1) The purpose of this research project is to develop an ultrafast all-optical modulation device which can operate at a speed of T-bits/s. The points of the developments are (a) utilization of the all-optical modulation method which has been proposed and investigated by the representative researcher, and (b) utilization of GaN / AlGaN quantum wells which are expected to have an ultra fast population relaxation time of 100 fs.
(2) At first, the growth condition of GaN / AlGaN quantum well was investigated to maximize the numbers of quantum wells. It was found that the generation of the crack in the growth layer due to the lattice mismatch can be avoided by introducing a GaN buffer layer in between the AlGaN barrier layers. Therefore a multiple-quantum-well with 200 well layers has been successfully grown, which showed a strong intersubband absorption peak of 30-40% at a wavelength of 4.5 μm.
(3) Next, the intersubband population relaxation time, which determines the modulation speed of t
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he device, was measured by one-color pump-probe method. It was experimentally shown for the first time that the relaxation time is as short as 100-200 fs. The result indicated that the response time of the modulation device can be as short as 100 fs.
(4) The measurement system for the all-optical modulation experiment has been developed, which utilizes a differential frequency mixing crystal to generate a mid-infrared pulse and a water cell to generate a white-light generation in the water cell. For the comparison and trial, the modulation characteristics of the device consist of conventional GaAs/AlGaAs quantum wells was measured. The deference of the carrier relaxation dynamics between the GaAs/AlGaAs quantum wells and GaN/AlGaN quantum wells was precisely investigated.
(5) The shortening of the intersubband transition wavelength in a GaN/AlGaN quantum well was investigated for the purpose of practical applications. By changing the growth method from MOVPE to MBE, a transition wavelength shorter than 1.55fj.m has been obtained. This is a very encouraging result since we can utilize a small semiconductor laser for the source of the control (pump) light. Less
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