研究内容
Membrane-DFB laser
A high index contrast (HIC) waveguide structure which enables ultra-small and highly integrated optical circuits is very attractive. The reflactive index difference between semiconductor core and low index polymer cladding layer is about 40%, which enhanced the optical field in its core layer compared with that of conventional double hetero structures. A semiconductor membrane laser which composed of thin (150nm) core and polymer claddings, shows 3 times higher optical confinement factor due to the HIC effect.

Fig. 1 Comparison between conventional DH and membrane structure
　

@Low threshold operation under optically pumped condition

　 By utilizing the high optical confinement structure, very low threshold operations of semiconductor lasers are theoretically expected. With this polymer (Insulator) cladding structure, however, it is very difficult to inject carriers to the core layers, while conventional injection type laser has p-type and n-type semiconductor layers as its upper and lower claddings. In addition, these layers are prepared by crystal growth technique in which lattice-matched material systems are required. We try to design and test optically pumped devices to examine the high optical confinement effect, then reported low threshold single-mode operation as shown fig.2 and 3.

Fig. 2 Schematic structure and cross sectional SEM view

　

Fig.3 Light output characteristic and a lasing spectrum
　

AInjection type membrane laser

One of most important project is realization of injection type membrane lasers. A very low threshold operation of the optically pumped membrane DFB laser has been obtained. But an external light source is required in this system, which is not preferable for the device integration. It is difficult to combine the membrane and vertical pn-junction structure as mentioned before. Then, we introduced a lateral current injection (LCI) structure to our membrane based devices.
Up to now, we have realized LCI laser on semi-insulated substrate with GaInAsP thin (400 nm) core layers including 5 quantum wells by organic metallic vapor phase epitaxy regrowth technique. Then, investigations for electrical and optical properties are currently in progress in the thin LCI structure.

Fig. 4 (Left) Schematic structure and cross sectional SEM view. (Right) Light output characteristic of LCI laser
　

BDevice integration

Not only the membrane laser, some applications for other optical functional devices are expected on membrane based platform with the realization of electrically driven laser. We study photodetector and optical modulator for integration devices.
　

CAthermal membrane laser

A temperature-insensitive light source is strongly desirable in cost effective dense wavelength-division-multiplexed systems available without temperature control. A lasing wavelength of semiconductor tends to shift to longer side. On the other hand, benzocyclobutene (BCB) cladding layer which has a negative temperature coefficient of refractive index. By controlling the thicknesses of the semiconductor core layer and BCB cladding layers, membrane lasers have possibility to realize an athermal operation.
　
List of reports
Journal Papers

(1) T. Okamoto, N. Nunoya, Y. Onodera, S. Tamura and S. Arai, “Continuous wave operation of optically pumped membrane DFB laser,” Ellectron. Lett., vol. 37, no. 24, pp. 1455-1456, Nov. 2001.

(2) T. Okamoto, N. Nunoya, Y. Onodera, S. Tamura and S. Arai, “Single-Mode Operation of Optically Pumped Membrane Buried Heterostructure Distributed-Feedback Lasers,” Jpn. J. Appl. Phys., vol. 41, no. 3A, pp. L249-L251, Mar. 2002.

(3) T. Okamoto, N. Nunoya, Y. Onodera, S. Tamura and S. Arai, “Low-Threshold Singlemode Operation of Membrane BH-DFB Lasers,” Ellectron. Lett., vol. 38, no. 23, pp. 1444-1446, Nov. 2002.

(4) T. Okamoto, N. Nunoya, Y. Onodera, T. Yamazaki, S. Tamura and S. Arai, “Optically Pumped Membrane BH-DFB Lasers for Low-Threshold and Single-Mode Operation,” IEEE J. Select. Topics in Quantum Electron., vol. 9, no. 5, pp. 1361-1366, Sept. /Oct. 2003.

(5) T. Okamoto, T. Yamazaki, S. Sakamoto, S. Tamura and S. Arai, “Low Threshold Membrane BH-DFB Laser Arrays with Precisely Controlled Wavelength over a Wide Range,” IEEE Photon. Technol. Lett., vol. 15, no. 5, pp. 1242-1244, May 2004.

(6) S. Sakamoto, T. Okamoto, T. Yamazaki, S. Tamura and S. Arai, “Multiple-Wavelengths Membrane BH-DFB Laser Arrays,” IEEE J. Select. Topics in Quantum Electronics, No. 11, Vol. 5, pp. 1174-1179, Sep. /Oct. 2005.

　
International Conferences

(1) T. Okamoto, N. Nunoya, Y. Onodera, S. Tamura and S. Arai, “CW Operation of Optically Pumped Membrane DFB Laser,” The 4th Pacific Rim Conf. On Lasers and Electro-Optics (CLEO/PR2001), WJPD1-10, pp.44-45 (PD), Makuhari Chiba, Japan), July 2001.

(2) T. Okamoto, N. Nunoya, Y. Onodera, S. Tamura and S. Arai, “Single Mode Operation of Optically Pumped Membrane BH-DFB Lasers,” The 14th Annual Meeting of The IEEE Lasers & Electro-Optics Society (LEOS2001), PD1.1, San Diego (USA), Nov. 2001.

(3) T. Okamoto, N. Nunoya, Y. Onodera, S. Tamura and S. Arai, “1550nm Wavelength Membrane DFB Laser Cladded by BCB Polymer,” 5th International Symposium on Contemporary Photonics Technology (CPT2002), Tokyo, E-21, pp. 101-102, Jan. 2002.

(4) T. Okamoto, N. Nunoya, Y. Onodera, S. Tamura and S. Arai, “Low threshold operation of membrane buried heterostructure distributed feedback laser,” 14th Indium Phosphide and Related Materials Conf. (IPRM2002), Stockholm, PI-4, pp.115-118, May, 2002.

(5) T. Okamoto, Y. Onodera, T. Yamazaki, S. Tamura and S. Arai, “Membrane Distributed Feedback Lasers for Ultra Low Threshold Current Operation,” The 9th Int'l Symposium on Quantum Effect Electronics, 9, pp. 58-61, Tokyo, Nov. 2002.

(6) T. Okamoto, Y. Onodera, T. Yamazaki, S. Tamura and S. Arai, “Low Threshold Membrane BH-DFB Laser Arrays for 1490-1565nm Wavelength Range,” 15th Indium Phosphide and Related Materials Conf. (IPRM2003), Santa Barbara, FA2.5, pp. 558-561, May, 2003.

(7) S. Arai, T. Okamoto, Y. Onodera, T. Yamazaki, S. Tamura, “Low Threshold GaInAsP/InP Membrane BH-DFB Lasers,” (Invited), The 8th Optoelectronics and Communications Conference (OECC2003), Shanghai, Oct. 2003.

(8) T. Okamoto, T. Yamazaki, S. Sakamoto, S. Tamura and S. Arai, “Low Threshold Operation of Optically Pumped Membrane BH-DFB Laser Arrays with a Wide Wavelength Range,” The 16th Annual Meeting of The IEEE Lasers & Electro-Optics Society (LEOS2003), WT 2, pp. 636-637, Tucson (USA), Oct. 2003.

(9) T. Okamoto, T. Yamazaki, S. Sakamoto, S. Tamura and S. Arai, “Short Cavity Membrane BH-DFB Laser with l/4 Phase Shift,” 16th Indium Phosphide and Related Materials Conf. (IPRM2004), WA-3-3, pp. 519-523, Kagoshima, May, 2004.

(10) T. Okamoto, T. Yamazaki, S. Sakamoto, S. Tamura and S. Arai, “Improved Temperature Insensitivity of Membrane BH-DFB Laser with Polymer Cladding Layers”, The 9th Optoelectronics and Communication Conference (OECC2004), 14E2-3, pp. 528-529, Yokohama, July, 2004.

(11) T. Okamoto, T. Yamazaki, S. Sakamoto, S. Tamura and S. Arai, “Multiple-Wavelengths Low-Threshold Membrane BH-DFB Laser Arrays”, 2004 IEEE 19th International Semiconductor Laser Conference, WC1, Matsue, Sept., 2004.

(12) S. Sakamoto, T. Okamoto, T. Yamazaki, H. Kawashima, Tang Jing-Long, S. Tamura and S. Arai, “Narrow Stripe Membrane BH-DFB Lasers for Lateral-Mode Control,” The 6th Pacific Rim Conf. On Lasers and Electro-Optics (CLEO/PR2005), CTuJ 4-6, Tokyo, July 2005

(13) S. Sakamoto, H. Kawashima, H. Naitoh, S. Tamura, T. Maruyama and S. Arai, “Narrow Stripe Membrane BH-DFB Lasers with Surface Corrugation for Stable Single-Mode Operation”, The 18th International Conference on Indium Phosphide and Related Materials (IPRM2006), TuA1-7, Princeton, USA, May 2006.

(14)S. Sakamoto, H. Kawashima, H. Naitoh, S. Tamura, T. Maruyama and S. Arai, “Narrow Stripe Membrane BH-DFB Lasers with Surface Corrugation for Stable Single-Mode Operation”, The　11th International Conference on Optical Electrical Comunication Conference (OECC2006),5E1-3, Kaohsiung, Taiwan, July 2006.

(15)S. Sakamoto, H. Naitoh, H. Kawashima, Y. Nishimoto, S. Tamura, T. Maruyama and S. Arai, “1-step OMVPE Grown Strongly Index-Coupled Membrane DFB Laser with Surface Corrugation Grating Structure,” 2006 IEEE 19th International Semiconductor Laser Conference (ISLC2006),P 10, Hawai, USA, Sep. 2006.
　
Meeting Report

(1) T. Okamoto, Y. Onodera, T. Yamazaki, S. Tamura and S. Arai, “A Study of Semiconductor Membrane BH-DFB Laser Arrays,” 「半導体薄膜BH-DFBレーザに関する研究」 Technical Report of IEICE, OPE2003-30 (2003-07), pp.35-38, Tokyo (Japan), July 2003.

(2) T. Okamoto, T. Yamazaki, S. Sakamoto, S. Tamura and S. Arai, “Polymer Cladded Semiconductor Membrane BH-DFB Lasers,” 「誘電体クラッド半導体薄膜BH-DFBレーザ」 Technical Report of IEICE, OPE2004-20 (2004-07), pp.11-14, Tokyo (Japan), July 2004.

(3) S. Sakamoto, H. Naitoh, S. Tamura, T. Maruyama and S. Arai, “Membrane BH-DFB Laser with Surface Corrugation Grating”, 「凹凸形状回折格子を用いた半導体薄膜BH-DFBレーザ」, Technical Report of IEICE, OPE2006-19 (2004-06), pp.1-6, Tokyo (Japan), June 2006.

　
Domestic Conferences

(1) K. Matsui, T. Okamoto, N. Nunoya and S. Arai, “Analysis of threshold current of membrane DFB lasers with wirelike active regions,” 「半導体薄膜活性層分離型DFBレーザの閾値電流解析」 Nat. Conv. Res. of Japan Soc. Appl. Phys., 30a-ZS-7, Digest III pp. 1152, Tokyo, Mar. 2001.

(2) T. Okamoto, N. Nunoya, Y. Onodera, S. Tamura and S. Arai, “Room Temperature CW Operation of Optically-Pumped Membrane DFB Lasers,” 「半導体薄膜構造DFBレーザの光励 起室温連続動作」 Nat. Conv. Res. of Japan Soc. Appl. Phys., 13p-B-14, Digest III pp. 869, Aichi, Sep. 2001.

(3) T. Okamoto, N. Nunoya, Y. Onodera, S. Tamura and S. Arai, “Single-Mode Operation of Optically Pumped Membrane BH-DFB Lasers,” 「BH構造を導入した光励起半導体薄膜DFBレーザの単一モード動作」 Nat. Conv. Res. of Japan Soc. Appl. Phys., 29a-YS-9, Digest III pp. 1144, Kanagawa, Mar. 2002.

(4) Y. Onodera, T. Okamoto, N. Nunoya, S. Tamura and S. Arai, “Low Threshold Operation of Membrane BH-DFB Lasers,” 「半導体薄膜DFBレーザの低しきい値動作」 Nat. Conv. Res. of Japan Soc. Appl. Phys., 29a-YS-9, Digest III pp. 1144, Kanagawa, Mar. 2002.

(5) T. Okamoto, Y. Onodera, T. Yamazaki, S. Tamura and S. Arai, “Proposal of Multiple Wavelength Membrane DFB Laser Array,” 「位相シフト変調型半導体薄膜DFB多波長アレイ光源の提案」Nat. Conv. Res. of Japan Soc. Appl. Phys., 26p-A-12, Digest III pp. 996, Niigata, Sep. 2002.

(6) T. Okamoto, Y. Onodera, T. Yamazaki, S. Tamura and S. Arai, “Wavelength Controllability of Membrane BH-DFB Lasers,” 「半導体薄膜BH-DFBレーザの波長制御性」 Nat. Conv. Res. of Japan Soc. Appl. Phys., 28p-ZQ-16, Digest III pp. 1241, Kanagawa, Mar. 2003.

(7) T. Okamoto, Y. Onodera, T. Yamazaki, S. Tamura and S. Arai, “Fabrication of Multiple Wavelength Membrane BH-DFB Laser Arrays,” 「半導体薄膜BH-DFB多波長レーザアレイの試作」Nat. Conv. Res. of Japan Soc. Appl. Phys., 28p-ZQ-17, Digest III pp. 1241, Kanagawa, Mar. 2003.

(8) T. Okamoto, T. Yamazaki, S. Tamura and S. Arai, “Room Temperature CW Operation of Phase Shifted Membrane BH-DFB Laser,” 「位相シフト半導体薄膜BH-DFBレーザの室温連続動作」Nat. Conv. Res. of Japan Soc. Appl. Phys., 30p-YB-11, Digest III pp. 1041, Fukuoka, Aug. 2003.

(9) T. Yamazaki, T. Okamoto, S. Tamura and S. Arai, “Low Threshold Operation of Membrane BH-DFB Laser Arrays,” 「半導体薄膜BH-DFBレーザアレイの低しきい値動作」 Nat. Conv. Res. of Japan Soc. Appl. Phys., 30p-YB-12, Digest III pp. 1042, Fukuoka, Aug. 2003.

(10) T. Okamoto, T. Yamazaki, S. Sakamoto, S. Tamura and S. Arai, “Athermal effect of polymer cladded membrane BH-DFB laser,” 「誘電体クラッドを用いた半導体薄膜BH-DFBレーザにおけるアサーマル効果の観測」Nat. Conv. Res. of Japan Soc. Appl. Phys., 30a-ZZ-5, Digest III pp. 1260, Tokyo, Mar. 2004.

(11) T. Yamazaki, T. Okamoto, S. Sakamoto, S. Tamura and S. Arai, “Multiple wavelength membrane BH-DFB laser arrays,” 「一括励起半導体薄膜BH-DFB多波長レーザアレイの試作」Nat. Conv. Res. of Japan Soc. Appl. Phys., 30a-ZZ-6, Digest III pp. 1260, Tokyo, Mar. 2004.

(12) S. Sakamoto, T. Okamoto, T. Yamazaki, S. Tamura and S. Arai, “Athermal effect of polymer cladded membrane BH-DFB laser,” 「誘電体クラッドを用いた半導体薄膜BH-DFBレーザにおけるアサーマル効果の観測」Nat. Conv. Res. of Japan Soc. Appl. Phys., 1a-ZN-9, Digest III Miyagi, Sept. 2004.

(13) T. Okamoto, S. Sakamoto, T. Yamazaki, S. Tamura and S. Arai, “Membrane BH-DFB laser array with exposure control,” 「EB露光量制御による微小波長間隔半導体薄膜BH-DFBレーザアレイ」Nat. Conv. Res. of Japan Soc. Appl. Phys., 1a-ZN-10, Digest III Miyagi, Sept. 2004.

(14) T. Okamoto, S. Sakamoto, T. Yamazaki, S. Tamura and S. Arai, “Membrane BH-DFB Laser with High Index Difference Waveguide”, 「高屈折率差導波路構造を用いた半導体薄膜BH-DFBレーザ」, The 65th Autumn Meeting, 2004; The Japan Society of Applied Physics., 1a-ZN-10, Digest III -p. 1020, Sendai, Sep. 2004.

(15) S. Sakamoto, T. Okamoto, T. Yamazaki, H. Kawashima, Tang Jing-Long, S. Tamura and S. Arai, “Membrane BH-DFB Laser Array with Asperity Corrugation Structure”, 「凹凸形状回折格子を用いた半導体薄膜BH-DFBレーザアレイ」, The 52nd Spring Meeting, 2005; The Japan Society of Applied Physics and Related Societies., 31p-ZH-5, Saitama, Mar./Apr. 2005.

(16) H. Kawashima, S. Sakamoto, T. Okamoto, T. Yamazaki, Tang Jing-Long, S. Tamura and S. Arai, “Lateral-Mode Control of Membrane BH-DFB Lasers with Narrow Stripe”, 「狭ストライプ半導体薄膜BH-DFBレーザの横モード制御」, The 52nd Spring Meeting, 2005; The Japan Society of Applied Physics and Related Societies.,31p-ZH-6, Saitama, Mar./Apr. 2005.

(17)S. Sakamoto, H. Kawashima, H. Naitoh, S. Tamura, T. Maruyama, and S. Arai, “Narrow Stripe Membrane BH-DFB Laser Array using Surface Corrugation”「凹凸形状回折格子を用いた狭ストライプ半導体薄膜BH-DFBレーザアレイ」, The 53rd Spring Meeting, 2006; The Japan Society of Applied Physics and Related Societies.,23a-Za-4, Tokyo, Mar. 2006.

(18)S. Sakamoto, H. Naitoh, H. Kawashima, Y. Nishimoto, S. Tamura, T. Maruyama, and S. Arai, “High Temperature Continuous Wave Operation of Membrane BH-DFB Laser”「 半導体薄膜BH-DFBレーザの高温連続動作」, The 67th Autumn Meeting, 2006; The Japan Society of Applied Physics., 29a-ZT-5, Digest III pp.1046 , Shiga, Aug. 2006.

(19)S. Sakamoto, H. Naitoh, H. Kawashima, S. Tamura, T. Maruyama, and S. Arai, “Low Threshold Operation of Short Cavity Membrane BH-DFB Laser using Surface Corrugation Grating”「凹凸形状回折格子を用いた短共振器半導体薄膜BH-DFBレーザの低しきい値動作」, The 67th Autumn Meeting, 2006; The Japan Society of Applied Physics., 29a-ZT-6, Digest III pp.1046 , Shiga, Aug. 2006.

(20)H. Naitoh, S. Sakamoto, H. Kawashima, Y. Nishimoto, S. Tamura, T. Maruyama, and S. Arai, “1-step OMVPE Grown Index Coupled Membrane DFB Laser with Surface Corrugation Structure,”「1回OMVPE成長による凹凸形状半導体薄膜DFBレーザ」, The 67th Autumn Meeting, 2006; The Japan Society of Applied Physics., 29a-ZT-7, Digest III pp.1047 , Shiga, Aug. 2006.
　
Awards
(1) T. Okamoto, “Continuous Wave Operation of Optically Pumped Membrane DFB Laser,” Student Paper Contest, Third Place, IEEE Student Branch at Tokyo Institute of Technology, Dec. 2001.

(2) T. Okamoto, “Membrane Distributed Feedback Lasers for Ultra Low Threshold Current Operation,” Student Paper Contest, Third Place, IEEE Student Branch at Tokyo Institute of Technology, Dec. 2002.

(3) T. Okamoto, “Low Threshold and Precisely Wavelength Controlled Membrane BH-DFB Laser Arrays with a Wide Wavelength Range,” Student Paper Contest, First Place, IEEE Student Branch at Tokyo Institute of Technology, Dec. 2003.

(4) 岡本健志　「位相シフト半導体薄膜BH-DFBレーザの室温連続動作」　第15回応用物理学会講演奨励賞2004年3月.
(5) 黒川宗高　「OMVPE再成長法による薄膜クラッド層を有する横方向電流注入型レーザ」　第25回応用物理学会講演奨励賞2008年9月