A micrometre-scale Raman silicon laser with a microwatt threshold

Abstract

The application of novel technologies to silicon electronics has been intensively studied with a view to overcoming the physical limitations of Moore's law, that is, the observation that the number of components on integrated chips tends to double every two years. For example, silicon devices have enormous potential for photonic integrated circuits on chips compatible with complementary metal-oxide-semiconductor devices, with various key elements having been demonstrated in the past decade. In particular, a focus on the exploitation of the Raman effect has added active optical functionality to pure silicon, culminating in the realization of a continuous-wave all-silicon laser. This achievement is an important step towards silicon photonics, but the desired miniaturization to micrometre dimensions and the reduction of the threshold for laser action to microwatt powers have yet to be achieved: such lasers remain limited to centimetre-sized cavities with thresholds higher than 20 milliwatts, even with the assistance of reverse-biased p-i-n diodes. Here we demonstrate a continuous-wave Raman silicon laser using a photonic-crystal, high-quality-factor nanocavity without any p-i-n diodes, yielding a device with a cavity size of less than 10 micrometres and an unprecedentedly low lasing threshold of 1 microwatt. Our nanocavity design exploits the principle that the strength of light-matter interactions is proportional to the ratio of quality factor to the cavity volume and allows drastic enhancement of the Raman gain beyond that predicted theoretically. Such a device may make it possible to construct practical silicon lasers and amplifiers for large-scale integration in photonic circuits.

High-Q silicon photonic crystal cavity for enhanced optical nonlinearities

“…The computed mode profile ( Fig. 1(c)) resembles that of the basic design and, most importantly, the modal volume remains extremely small: V ¼ 0.34(k/n) 3 . We additionally simulated the optimal structure using a 3D finite-difference time-domain method, 25 which confirms the GME-computed volume and gives Q ideal ¼ 1.7 Â 10 6 -in good agreement with the GME value.…”

“…It displays nonlinear effects, including high-contrast optical bistability, at a threshold power among the lowest ever reported for a silicon device. With a theoretical modal volume as small as V ¼ 0.34(k/n) 3 , this cavity ranks among those with the highest Q/V ratios ever demonstrated, while having a small footprint suited for integration in photonic circuits. V C 2014 AIP Publishing LLC.…”

“…[1][2][3][4] Considerable effort has been devoted in the last decade to the optimization of these structures. In particular, several studies have been aiming at developing designs with the highest quality factor Q, combined with the smallest modal volume V as the nonlinear optical response of these devices-as well as the Purcell effect and radiation-matter coupling-are enhanced as Q increases and V decreases.…”

“…1,6,11,15,17,[34][35][36] In the present work, we have additionally investigated an alternate optimal design 13 characterized by a smaller modal volume, that was obtained by introducing a stricter upper bound S 1x < 0.25a in the optimization procedure. The design has an ideal GMEcomputed Q-factor 1.05 Â 10 6 (FDTD: 1.0 Â 10 6 ) and a smaller modal volume V ¼ 0.25(k/n) 3 . The shifts defining this design are as follows:…”

A Thresholdless Tunable Raman Nanolaser using a ZnO–Graphene Superlattice

“…In recent years, miniaturization of Raman silicon laser has been successfully achieved with the assistance of reverse-biased p-i-n diode at centimeter size or photonics-crystal with high-quality-factor nanocavity at micrometer size. [7][8][9] However, for applications such as high-resolution medical imagings or on-chip optical communications, 'ultimate' nanolasers with scalable, thresholdless, …”