Reseach
Membrane-DFB laser

　　　　　Fig. 1 Schematic structure and cross sectional SEM view
　

　　Fig. 2 Light output characteristic and SMSR
　

Fig. 3 Spectra
left figure: Membrane DFB laser
right figure: Membrane BH-DFB laser 　

　

Fig. 4 Membrane BH-DFB laser arrays
left figure: Layout
right figure: Lasing wavelength controllability
　
Ultralow threshold current operation of semiconductor lasers would be indispensable for parallel optical data transmissions and optical interconnections. In order to realize them, several types of membrane-based semiconductor lasers, for example microdisk lasers and 2-D photonic crystal lasers, have been investigated because of their advantage of a large optical confinement factor to the active region due to a large refractive index difference.

Novel semiconductor laser structure, that is, membrane laser which has the Benzocyclobutene (BCB) cladding layers, enables to increase optical confinement into active layer due to a large refractive index difference between active layer and cladding layers. A room temperature continuous wave operation of membrane DFB laser consisting of deeply etched single-quantum-well wire-like active regions was demonstrated for the first time under optical pumping. A threshold power of 38mW was obtained for 10.7µm-wide and 40µm-long device. From spontaneous emission spectrum, a large stop-band width of 65nm and a low equivalent refractive index of 2.30, which are peculiar to a thin membrane waveguide structure, were observed.


In order to realize single mode and low threshold operation of 1.5µm-wavelength GaInAsP/InP membrane DFB laser, buried heterostructure (BH) was innovated by slightly changing the fabrication process. A threshold pump power of 1.5mW and a sub-mode suppression-ratio of 42dB were obtained for a 142nm-thick semiconductor membrane core layer with a cavity length of 120µm and a stripe width of 2µm under room-temperature continuous wave optical pumping. The corresponding threshold for current injection was roughly estimated to be 27µA.

High optical confinement and high index coupling in 1.55 µm-wavelength GaInAsP/InP membrane buried heterostructure distributed feedback (BH-DFB) lasers consisting of deeply etched single-quantum-well wire-like active regions were demonstrated under room-temperature (RT) continuous-wave (CW) optical pumping. We have realized membrane BH-DFB laser arrays by arranging the laser cavities (10 µm spaced 15 elements with 5 different grating periods). A total wavelength span of 72 nm was achieved with a small lasing wavelength fluctuation of up to +-1.2 nm at RT-CW condition under optical pumping. From this value, membrane thickness fluctuation was estimated to be +-0.4 nm. Threshold pump power of 3.4 mW and SMSR of 45 dB were achieved in a typical device.
　
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.
(13) 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.
(14) 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.
(15) 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.
(16)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.
(17)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.
(18)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.
(19)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.