Directly modulated membrane lasers with 108 GHz bandwidth on a high-thermal-conductivity silicon carbide substrate

• Published in: Nature photonics Vol. 15; no. 1; pp. 28 - 35
• Main Authors: Yamaoka, Suguru, Diamantopoulos, Nikolaos-Panteleimon, Nishi, Hidetaka, Nakao, Ryo, Fujii, Takuro, Takeda, Koji, Hiraki, Tatsurou, Tsurugaya, Takuma, Kanazawa, Shigeru, Tanobe, Hiromasa, Kakitsuka, Takaaki, Tsuchizawa, Tai, Koyama, Fumio, Matsuo, Shinji
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.01.2021; Nature Publishing Group
• Subjects: 140/125; 142/126; 639/624/1020/1085; 639/624/1020/1093; 639/624/1020/1095; Active regions (lasers); Applied and Technical Physics; Bandwidths; Carrier density; Conductivity; Damping; Electrical resistivity; Energy costs; Injection current; Laser applications; Lasers; Membranes; Optical feedback; Photons; Physics; Physics and Astronomy; Pulse amplitude modulation; Quantum Physics; Relaxation oscillations; Semiconductor lasers; Silicon; Silicon carbide; Silicon substrates; Waveguides
• ISSN: 1749-4885; 1749-4893
• DOI: 10.1038/s41566-020-00700-y

Increasing the modulation speed of semiconductor lasers has attracted much attention from the viewpoint of both physics and the applications of lasers. Here we propose a membrane distributed reflector laser on a low-refractive-index and high-thermal-conductivity silicon carbide substrate that overcomes the modulation bandwidth limit. The laser features a high modulation efficiency because of its large optical confinement in the active region and small differential gain reduction at a high injection current density. We achieve a 42 GHz relaxation oscillation frequency by using a laser with a 50-μm-long active region. The cavity, designed to have a short photon lifetime, suppresses the damping effect while keeping the threshold carrier density low, resulting in a 60 GHz intrinsic 3 dB bandwidth ( f 3dB ). By employing the photon–photon resonance at 95 GHz due to optical feedback from an integrated output waveguide, we achieve an f 3dB of 108 GHz and demonstrate 256 Gbit s −1 four-level pulse-amplitude modulations with a 475 fJ bit −1 energy cost of the direct-current electrical input. Directly modulated membrane distributed reflector lasers are fabricated on a silicon carbide platform. The 3 dB bandwidth, four-level pulse-amplitude modulation speed and operating energy for transmitting one bit are 108 GHz, 256 Gbit s −1 and 475 fJ, respectively.