Supercontinuum generation in integrated GaN waveguides

Supercontinuum in integrated GaN waveguides is demonstrated for the first time. We observe gap-free spectra spanning more than two octaves and extending into the mid-infrared to wavelengths approaching 4 µm. The waveguides are pumped by a robust off-the-shelf erbium-based femtosecond laser with sub-nJ pulse energies and also allow f-2f self-referencing for precision spectroscopy.

webpage_GaN_supercontinuum_photo1.JPG

Photograph of a GaNOS chip pumped by a C-band femtosecond laser.

GaN is widely used in high-power LEDs and high-frequency electronics. More recently, it has attracted interest as a new material for nonlinear integrated photonics due to its large bandgap, strong nonlinearities and wide transparent window.

Here we exploit these material properties and demonstrate for the first time supercontinuum generation in integrated GaN waveguides. By pumping the system in the technologically mature telecom wavelength window, optical bandwidths of more than 1.5 octaves (30 dB) are achieved in short 2 mm long waveguides with pico-Joule pulse energy. In longer waveguides with a tailored variable-width profile, more than two octaves of gapless supercontinuum is achieved reaching up to 4 µm wavelength, ideal for multi-species molecular sensing. By exploiting the second-order nonlinearity, we also demonstrate on-chip f-2f self-referencing. Our results demonstrate the potential of GaN waveguides in broadband integrated nonlinear photonics, bridging the gap from erbium-based lasers in the telecom wavelength regime and emerging applications in the mid-infrared wavelength range.

Reference:

Supercontinua from integrated gallium nitride waveguides; Weichen Fan, Markus Ludwig, Ian Rousseau, Ivo Arabadzhiev, Bastian Ruhnke, Thibault Wildi, and Tobias Herr;  Optica  11, 1175-1181 (2024).