26th Australian Institute of Physics Congress and the Australian and New Zealand Conference on Optics and Photonics

Brillouin Dynamic Gratings in Low-loss Heterogeneous Chalcogenide-Germanosilicate Chips

Not scheduled

20m

Belinda Hutchinson Building (The University of Sydney )

Contributed Oral ANZOS | Photonics and Optics (ANZCOP)

Description

Brillouin dynamic gratings (BDGs) provide a versatile mechanism for realizing reconfigurable narrowband optical filtering through optoacoustic interactions. While BDGs have been extensively studied in optical fibres, systematic investigations in integrated photonic platforms remain limited. Here, we demonstrate strong BDGs in low-loss heterogeneous As$_2$S$_3$–Ge:SiO$_2$ waveguides and present, to our knowledge, the first systematic study of BDG reflection and bandwidth characteristics in this platform.

The BDGs are generated via stimulated Brillouin scattering using two counter-propagating transverse-electric pump waves, while a transverse-magnetic probe interrogates the induced acoustic grating. Measurements were performed in waveguides with lengths of 3 cm, 20 cm, and 40 cm. We observe wavelength-selective reflections with peak reflectivities of up to 6.5%, demonstrating efficient light-sound interactions in heterogeneous chalcogenide devices.

The measured reflection spectra are analysed using coupled-mode-equation (CME) modelling incorporating optical attenuation and a spatially varying coupling coefficient. Excellent agreement between experiment and theory is obtained using a coupled-mode model that employs an exponential grating-strength profile. Furthermore, the measured reflection bandwidth decreases systematically with increasing waveguide length, exhibiting the expected inverse-length scaling, $\mathrm{FWHM}\propto 1/L$, with linewidths reducing from 14.9 GHz for a 3 cm device to 1.56 GHz for a 40 cm device.

Figure 1: a) Measured BDG reflection spectrum for the 20 cm device with coupled-mode-equation (CME) fit, showing a peak reflectivity of 6.46%. (b) BDG bandwidth as a function of inverse waveguide length, confirming the expected scaling $\mathrm{FWHM}\propto 1/L$ (R² = 0.997).

These results establish heterogeneous chalcogenide waveguides as a promising platform for compact, reconfigurable and highly selective optical filtering, with applications in integrated microwave photonics and programmable photonic signal processing.