Microwatts continuous-wave pumped second harmonic generation in few- and mono-layer GaSe

Abstract

We demonstrate the first achievement of continuous-wave (CW) pumped second harmonic generation (SHG) in few- and mono-layer gallium selenide (GaSe) flakes, which are coated on silicon photonic crystal (PC) cavities. Because of ultrahigh second order nonlinearity of the two-dimensional (2D) GaSe and localized resonant mode in the PC cavity, SHG’s pump power is greatly reduced to microwatts. In a nine-layer GaSe coated PC cavity, while the optical power inside the GaSe flake is only 1.5% of that in the silicon PC slab, the SHG in GaSe is more than 650 times stronger than the third harmonic generation in silicon slab, indicating 2D GaSe’s great potentials to strengthen nonlinear processes in silicon photonics. Our study opens up a new view to expand 2D materials’ optoelectronic applications in nonlinear regime and chip-integrated active devices.

Controlling Defects in Continuous 2D GaS Films for High‐Performance Wavelength‐Tunable UV‐Discriminating Photodetectors

“…In addition, due to difficulties in exfoliation and lack of thickness‐controlled synthesis methods, previous reports were unable to study layered‐dependent properties of the 2D layered material, and to our knowledge, characterization or properties of GaS less than 3 layers (3L) are missing. Furthermore, although other members in the group‐III monochalcogenide‐layered materials with similar structures (GaSe, GaTe, InSe) have attracted intense attention as they have demonstrated superior optical properties, including ultra‐high second‐harmonic generation, giant piezo‐phototronic response, polarization‐dependent absorption, etc., properties of GaS with wide potential remain unexplored as a result of unanswered stability issues and unsatisfying samples. Recently, our group has developed a simple and atmospheric pressure chemical vapor deposition (CVD) method for the growth of 2D GaS crystals, which paved way for further study of the material's stability and layer‐dependent properties.…”

Low‐Power Continuous‐Wave Second Harmonic Generation in Semiconductor Nanowires

“…We characterize the resonant mode and SHG of the NW‐PPC cavity using a vertically coupled cross‐polarization microscope (see Supporting Information) . Figure c plots the resonant peak of a PPC cavity before and after the NW‐integration.…”

“…For instance, the SHG could be measured reliably even with a 50 W CW laser power focused on the device (Figure a). And only 6% of the CW pump light could be coupled into the cavity mode with the employed objective lens, that is, the effective pump power is only W. In the previously reported NW SHG results, pulsed light sources with a peak power around 100 W were typically used .…”

Cavity nonlinear optics with layered materials

“…A promising solution will be to use make a doubly resonant cavity out of wide bandgap materials, such as silicon nitride [38] or silicon dioxide [83]. Researchers also recently demonstrated continuous wave second harmonic generation using GaSe coupled with silicon photonic crystal cavity with a pump laser at ~1550 nm [84]. The required optical power in this work is only microwatts, primarily due to the high Q-factor and small mode-volume of the photonic crystal cavities.…”