Thresholdless Oscillation in High-β Buried Multiple-quantum-wellPhotonic Crystal Lasers

Masato Takiguchi1,2, Hideaki Taniyama1,2, Hisashi Sumikura1,2,
Muhammad Danang Birowosuto1,2, Eiichi Kuramochi1,2, Akihiko Shinya1,2,
Tomonari Sato1,3, Koji Takeda1,3, Shinji Matsuo1,3, and Masaya Notomi1,2
1NTT Nanophotonics Center, 2Optical Science Laboratory,
3NTT Device Technology Laboratories

 A photonic crystal (PhC) cavity is promising for photonic network-on-chip architecture because its ultra-small mode volume and high quality factor will enable efficient and high-speed lasers and LEDs. To realize them, we study nano-emitters using buried multiple quantum wells (MQW) PhC cavities [Fig.1(a)]. Conventional QW-PhC have been extensively investigated, however they suffer from poor carrier confinement and surface non-radiative recombination. On the other hands, our buried MQW PhC cavities can exhibit distinctive spontaneous emission control [1] because of strong carrier confinement and low surface non-radiative recombination. Therefore spontaneous coupling factor (β) of our devices can be unity and theoretically-predicted thresholdless laser can be realised.
 In this study, we have investigated the characteristics of high-β buried MQW PhC lasers to clarify the thresholdless operation. To compare the nature of lasing operation for high and low β values, we performed systematic measurements, such as L-L measurement and time resolved measurement, under a large and small detuning condition (2 nm and 15 nm detuning) as shown Fig. 1(b). From these results, we have unambiguously demonstrated high-β lasing with a smoothed transition. In addition, we systematically investigated the dependence of β on the detuning frequency, which was in good agreement with a numerical simulation based on the finite-difference time-domain method [Fig. 1(c)].

Fig. 1. (a) Schematic of L3 PhC cavity. (b) L-L curve. (c) Experimental and simulated β.