Low Energy Consumption Direct Modulation of Lambda-Scale Embedded Active-Region Photonic-Crystal Lasers

Koji Takeda^1,2, Tomonari Sato^1,2, Akihiko Shinya^1,3, Eiichi Kuramochi^1,3,
Masaya Notomi^1,3, Koichi Hasebe^1,2, Takaaki Kakitsuka^1,2, and Shinji Matsuo^1,2
¹NTT Photonics Laboratory ²Optical Science Laboratory, ³NTT Nanophotonics Center

　There have been many attempts to form optical interconnects on CMOS chips with a distance ranging from core-to-core and chip-to-chip level. Light sources used in such short-distance optical interconnects have to be driven with ultra-low energy consumptions, e.g. 10 fJ/bit [1]. We have developed lambda-scale embedded active-region photonic-crystal (LEAP) lasers to use them as light sources for on- and off-chip optical interconnect [2]. In this paper, we report how much energy the LEAP lasers consumed under direct modulations.
　Device fabrication procedures were similar to that we have reported elsewhere [3]. Ion implantations and thermal diffusions of dopants formed lateral p-i-n junction. Photonic-crystals were formed by electron-beam lithography and dry etching, followed by wet etching.
　We measured a light output and an applied voltage versus an injected current, and the result is shown in Fig. 1. We obtained a threshold current of 32 µA, and the maximum output power was 39.3 µW at a current injection of 300 µA. There was an optical coupling loss of approximately 8 dB, and the plot shows calibrated output power at the waveguides. We then drove the LEAP lasers with a pseudo-random bit sequence of 2³¹ – 1 at a bit rate of 10 Gb/s. Output light was monitored by a digital sampling oscilloscope via an optical amplifier that was used to compensate an optical coupling loss. Figure 2 shows the eye diagram of the LEAP lasers. We needed only 80-µA current injection to achieve a clear eye opening with an extinction ratio of 10 dB. We achieved the energy consumption of smaller than 10 fJ/bit under this operating condition.
　Part of this work was supported by the New Energy and Industrial Technology Development Organization (NEDO).