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Surface acoustic wave devices are ubiquitously used for signal processing and filtering, as well as mechanical, chemical, and biological sensing and show promise as quantum transducers. While surface acoustic waves (SAWs) are primarily excited and driven using electromechanical coupling and interdigital transducers, there is a strong desire for novel methods that enable the coherent excitation and detection of SAWs all-optically interfacing with photonic integrated circuits. In this work, we numerically model and experimentally demonstrate SAW excitation in integrated photonic waveguides made from GeAsSe glass via backward stimulated Brillouin scattering (SBS). We measure a Brillouin gain coefficient of 203 W−1 m−1 for the surface acoustic resonance at 3.81 GHz, with a linewidth narrowed to 20 MHz. Experimental access to this new regime of SBS not only opens up opportunities for novel on-chip sensing applications by harnessing the waveguide surface but also paves the way for strong Brillouin interactions in materials lacking sufficient acoustic guidance in the waveguide core, as well as the excitation of SAWs in non-piezoelectric materials.

Brillouin enhanced four wave mixing in the form of a Brillouin dynamic grating (BDG) enables a uniquely tunable filter whose properties can be tuned by purely optical means. This makes the BDG a valuable tool in microwave photonics (MWP). BDGs have been studied extensively in fibers, but the only observation in an integrated platform required exotic materials. Unlocking BDG in a standard and mature platform will enable its integration into large-scale circuits. Here, we demonstrate the first observation of a BDG in a silicon nitride (Si3N4) waveguide. We also present a new and optimized design, which will enhance the BDG response of the waveguide, unlocking the path to large-scale integration into MWP circuits.

Nonlinear optical effects including stimulated Brillouin scattering (SBS) and four-wave mixing (FWM) play an important role in microwave photonics, optical frequency combs, and quantum photonics. Harnessing SBS and FWM in a low-loss and versatile integrated platform would open the path to build large-scale Brillouin/Kerr-based photonic integrated circuits. In this letter, we investigate the Brillouin and Kerr properties of a low-index (n = 1.513 @ 1550 nm) silicon oxynitride (SiON) platform. We observed, for the first time, backward Brillouin scattering in SiON waveguides with a Brillouin gain coefficient of 0.3 m−1 W−1, which can potentially be increased to 0.95 m−1 W−1 by just tailoring the waveguide cross section. We also performed FWM experiments in SiON rings and obtained the nonlinear parameter γ of 0.02 m−1 W−1. Our results point to a low-loss and low-index photonic integrated platform that is both Brillouin and Kerr active.

Photonic integration, advanced functionality, reconfigurability, and high radio frequency (RF) performance are key features in integrated microwave photonic systems that are still difficult to achieve simultaneously. In this work, we demonstrate an integrated microwave photonic circuit that can be reconfigured for two distinct RF functions, namely, a tunable notch filter and a phase shifter. We achieved >50 dB high-extinction notch filtering over 6–16 GHz and 2π continuously tunable phase shifting over 12–20 GHz frequencies. At the same time, we implemented an on-chip linearization technique to achieve a spurious-free dynamic range of more than 120 dB · Hz4/5 for both functions. Our work combines multi-functionality and linearization in one photonic integrated circuit and paves the way to reconfigurable RF photonic front-ends with very high performance.

Optical modulation plays arguably the utmost important role in microwave photonic (MWP) systems. Precise synthesis of modulated optical spectra dictates virtually all aspects of MWP system quality including loss, noise figure, linearity, and types of functionalities that can be executed. However, for such a critical function, the versatility to generate and transform analog optical modulation is severely lacking, blocking the pathways to truly unique MWP functions including ultra-linear links and low-loss high rejection filters. Here, we demonstrate a versatile radiofrequency (RF) photonic spectral shaper integrated in a silicon photonic circuit. The spectral shaper controls the two modulation bands generated from an electro-optic modulation process in their relative amplitude and phase, offering an enhanced versatility for microwave-photonic modulation applications. Using the spectral shaper, we show electrically tailorable modulation transformations. Furthermore, we show a series of unprecedented RF filtering experiments through monolithic integration of the spectral shaper with a network of reconfigurable ring resonators.

Signal processing using on-chip nonlinear or linear optical effects has shown tremendous potential for RF photonic applications. Combining nonlinear and linear elements on the same photonic chip can further enable advanced functionality and enhanced system performance in a robust and compact form. However, the integration of nonlinear and linear optical signal processing units remains challenging due to the competing and demanding waveguide requirements, specifically the combination of high optical nonlinearity in single-pass waveguides, which is desirable for broadband signal processing with low linear loss and negligible nonlinear distortions required for linear signal processing. Here, we report the first demonstration of integrating Brillouin-active waveguides and passive ring resonators on the same integrated photonic chip, enabling an integrated microwave photonic notch filter with ultradeep stopband suppressions of >40 dB, a low filter passband loss of