Prof.  Fumio  Koyama
Tokyo Institute of Technology,  Japan

Title: New Function and Integration of VCSEL Photonics

Abstract:

A vertical cavity surface emitting laser (VCSEL) was invented in 1977. The 40 years’ research and developments opened up various applications including datacom, sensors, optical interconnects, spectroscopy, optical storages, printers, laser displays, laser radar, atomic clock and high power sources. A lot of unique features have been already proven. A key challenge is to establish a platform to integrate functional devices with VCSELs. While the vertical integration of coupled cavities and modulators with VCSELs were reported, there are still challenges we need toward smart integration platforms involving various optical devices such as a modulator, amplifier, switch, detector, beam scanner and so on.
In this paper, our recent activities on new functions and integration of VCSEL photonics will be reviewed. We address a lateral integration platform and new functions, including high speed coupled cavity VCSELs, high power VCSEL amplifiers, high-resolution beam scanners, and their integrations.
We proposed and demonstrated the lateral integration scheme for VCSEL photonics. A VCSEL structure can be used as an optical waveguide in the lateral direction, which is called as a Bragg reflector waveguide. Slow light can be excited in Bragg reflector waveguides with their large waveguide dispersion. The distributed Bragg reflectors (DBR) used in VCSELs are composed of quarter-wavelength stack multi-layers. The slow down factor is the ratio of the group velocity of slow light versus that in conventional semiconductor waveguides. When we propagate light operating near the cutoff wavelength in the device, we are able to obtain a large slow down factor. The low group velocity is caused by the large waveguide dispersion in a Bragg reflector waveguide. The low group velocity dramatically reduces the size of various optical devices such as optical amplifiers, optical switches and nonlinear optical devices. In addition, the large waveguide dispersion enables high-resolution beam steering. The lateral integration platform enables us to form a transverse coupled cavity (TCC) VCSEL, which shows a significant bandwidth extension thanks to “photon-photon resonances”. A record 3-dB bandwidth of over 30 GHz was realized for 850 nm & 980 nm TCC VCSEL with a bow-tie shape or battledore-shape oxide aperture. The 3- dB modulation bandwidth can be 3 times larger than a conventional VCSEL without optical feedback. In addition, we demonstrate the lateral integration of an ultra-compact electro-absorption modulator. We obtained a sub-volt low driving voltage, and the bandwidth beyond 30 GHz. Our ultra-compact modulator integrated VCSEL can boost the modulation speed far beyond the direct modulation bandwidth with low-power consumption for use in nextgeneration computing and communication networks.
We also proposed a slow light VCSEL amplifier. It is similar to our reported beam scanner based on a Bragg reflector waveguide structure. Its epitaxial structure is the same as oxide-confinement VCSELs. An input light is coupled through a lensed fiber to a lateral propagation mode. A portion of the propagating light radiated from the amplifier surface which forms a uniform wave fronts. The light decays exponentially due to radiation and absorption loss, but its intensity becomes uniform along the VCSEL amplifier by injecting a current above the lasing threshold of the VCSEL. In this case, power of the amplified light is proportional to the amplifier length, and the beam divergence is getting smaller and smaller with increasing the length. We are able to obtain sharp beam steering and high power simultaneously. The proposed device is easy to integrate with a VCSEL laterally, and a slow light mode can be excited efficiently. Thus, we are able to form an ultra-compact, hig

Biography:

Fumio Koyama received the B.S., M.S., and Ph.D. degrees in physical electronics from the Tokyo Institute of Technology, Tokyo, Japan, in 1980, 1982 and 1985, respectively. He is a professor, Institute of Innovative Research, Tokyo Institute of Technology. He served as the dean, Institute of Innovative Research between 2018- 2020. His research interest includes VCSEL photonics, photonic integrated devices, 3D optical sensing and LiDAR. He has authored or co-authored more than 1,000 journal and conference papers, including more than 100 invited talks.
For more than 30 years, Fumio Koyama has been one of leading researchers whose work contributed to VCSEL photonics and single-mode lasers for broadband optical communications. He received various awards, including the IEEE Student Paper Award in 1985, the IEE Electronics Letters Premium in 1985 and in 1988, IEICE Paper Awards in 1990, 2002, 2004 and 2007, Marubun Scientific Award in 1998, the Ichimura Award in 2004, the IEICE Electronics Society Award in 2006, the MEXT Prize for Science and Technology in 2007, IEEE/LEOS William Streifer Scientific Achievement Award in 2008, the 2012 Izuo Hayashi Award from the Japanese Society of Applied Physics, Tokyo Metropolitan Government Award in 2015 and the Ichimura Prize in Industry for Excellent Achievement from the New Technology Development Foundation in 2016, the 32nd Kenjiro Sakurai Memorial Award from the Optoelectronics Industry and Technology Development Association in 2017, Okawa Award in 2018 and Nick Holonyak, Jr. Award from OSA in 2019 and IEICE Achievement Award in 2019. He is Fellow of IEEE, OSA, IEICE and the Japan Society of Applied Physics.
He was a deputy editor for IEEE/OSA Journal of Lightwave Technology (2011-2016) and a topical editor for OSA Optics Letters (2009-2013), and was the Guest Editor of IEEE JSTQE (2002 and 2007). He has served as the IEEE David Sarnoff Award Committee Member (2009-2012) and the IEEE Fink and Baker Awards Committee Member (2013-2014). He also has served as various committee members, including General Chair (2010), Program Chair (2008) and Sub-committee Chair (2006) of IEEE International Semiconductor Laser Conferences, Subcommittee Co-Chair of ACP 2009-2010, Steering Committee Chair of CLEO Pacific-Rim (2012-), CLEO/QELS TPC member (2006-2008), LEOS Annual Meeting TPC member (1998-2003), General Co-chair (2007) and Program Co-chair (2005) OECC. He was the chair of IEEE Photonics Society Japan Chapter and Board Member of IEEE Tokyo Section. He also served as President of Electronics Society, the Institute of Electronics, Information and Communication Engineers (IEICE) (2011-2012) and the member of IEEE Photonics Society Board of Governors (2012-2014)