Speaker
Description
Brillouin microwave photonic (MWP) filters harness stimulated Brillouin scattering to frequency-selectively manipulate the amplitude of microwave signals in the optical domain, realising either a passband or notch response. A high-performance Brillouin MWP filter requires a low-phase-noise laser, high-bandwidth modulators, a high-gain Brillouin nonlinear medium, and high-bandwidth photodetectors. Ultimately, these components must be integrated on a single chip to reduce size, weight, and power. Thin-film lithium niobate on insulator (LNOI) has become a popular material for electro-optic modulators owing to its large electro-optic coefficient, which enables high-bandwidth, linear, and low-loss modulation. Although Brillouin gain has been demonstrated on this platform via surface-acoustic-wave-mediated scattering, the net gain remains below 10 dB, limiting bandpass-filter performance. By contrast, chalcogenide glass (ChG)—particularly arsenic trisulfide (As₂S₃)—has recently shown a net gain of nearly 50 dB.
In this work, we combine LNOI and ChG to simultaneously achieve a low half-wave-voltage–length product (2.24 V·cm), high modulation bandwidth, and high Brillouin gain with MHz-scale RF linewidths on a single platform. An As₂S₃ vertical taper is overlaid onto a silicon-nitride (SiNx)-loaded LNOI platform by shadow-mask deposition, transitioning light between platforms at 1 dB interface loss. The SiNx interlayer enables an etchless strip-loaded LNOI waveguide while preserving Brillouin nonlinearity, yielding an experimental gain coefficient of 270 m⁻¹W⁻¹. While initial results demonstrate a Brillouin bandpass filter tunable over 10 GHz with only a 2 dB extinction ratio due to high fibre-chip coupling loss (8 dB/facet), our model predicts 30 dB raw gain in a 20 cm ChG waveguide at 25 dBm pump power. Further incorporating an over- or under-coupled ring resonator would enable a versatile, low-power Brillouin passband and notch filter, as well as opening opportunities for other Brillouin MWP devices such as optoelectronic oscillators, true-time delay, and light storage.
| I am the presenting author | Yes |
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