Nanocavity-Enhanced Giant Stimulated Raman Scattering in Si Nanowires in the Visible Light Region

Abstract

Silicon photonics has been a very active area of research especially in the past two decades in order to meet the ever-increasing demand for more computational power and faster device speeds and their natural compatibility with complementary metal-oxide semiconductor. In order to develop Si as a useful photonics material, essential photonic components such as light sources, waveguides, wavelength convertors, modulators, and detectors need to be developed and integrated. However, due to the indirect electronic bandgap of Si, conventional light emission devices such as light-emitting diodes and lasers cannot be built. Therefore, there has been considerable interest in developing Si-based Raman lasers, which are nonlinear devices and require large stimulated Raman scattering (SRS) in an optical cavity. However, due to the low quantum yield of SRS in Si, Raman lasers have very large device footprints and high lasing threshold, making them unsuitable for faster, smaller, and energy-efficient devices. Here, we report strong SRS and extremely high Raman gain in Si nanowire optical cavities in the visible region with measured SRS threshold as low as 30 kW/cm2. At cavity mode resonance, light is confined into a low mode volume and high intensity electromagnetic mode inside the Si nanowire due to its high refractive index, which leads to strong SRS at low pump intensities. Electromagnetic calculations reveal greater than 6 orders of magnitude increase in Raman gain coefficient at 532 nm pump wavelength, compared to the gain value at 1.55 μm wavelength reported in literature, despite the 108 higher losses at 532 nm. Because of the high gain in such small structures, we believe that this is a significant first step in realizing a monolithically integrable nanoscale low-powered Si Raman laser.

Cavity Engineering of Photon–Phonon Interactions in Si Nanocavities

“…for any of the measurements that may reflect formation of stronger photon–phonon polaritons and/or photon dressed states. In fact, as demonstrated in one of our earlier works even at much higher pumping powers when stimulated Raman scattering was observed, no significant changes in the Raman spectra were observed that may indicate formation of phonon–photon hybrid states. The detailed balance is also not being violated as the system is in a quasiequilibrium state while being pumped by light and, depending on the cavity modes, produces a specific response.…”

“…13 In addition we have also shown bright white light emission in the Si nanowire integrated with plasmonic cavities even though bulk Si does not emit light because of its indirect band gap. 14,15 Recently, we also demonstrated stimulated Raman scattering in the visible wavelength range in Si nanowires for the first time, 16 which is promising for fabricating nanoscale monolithic Raman lasers. Raman scattering is the process of inelastic scattering of photons from phonons in the ground or excited state which leads to generation or annihilation of phonons via Stokes or anti-Stokes scattering resulting in emission of a photon of slightly lower or higher energy.…”

Nonlinear optical heating of all-dielectric super-cavity: efficient light-to-heat conversion through giant thermorefractive bistability

“…Moreover, we have revealed bistability regime in the optical heating at intensity around 1 mW/𝜇m 2 . Our results are also helpful for resolving the thermal challenges for all-dielectric resonator-based photonic devices [39], Raman microlasers [40,41], and nanoscale photo-thermal chemistry and sensing [42][43][44]. As an outlook, we believe that the developed bistability approach is quite universal and can be further applied not only for various types of nonlinearities based on Kerr effect [45,46], electron-hole plasma generation [32,33,47] and excitonic effects [48][49][50].…”

Integrated Raman Laser: A Review of the Last Two Decades

“…In reference [109], Agarwal et al reported a strong SRS and very high Raman gain in optical cavities made of Si nanowire of various diameters in the visible region [109]. The authors evaluated by electromagnetic calculations an enhancement of the Raman gain coefficient of Si nanowire by a factor greater than 10 6 at 532 nm excitation with respect to the gain value at the 1.55 µm wavelength reported in literature [56], even though the losses are 10 8 higher at 532 nm.…”