Localized high resolution Brillouin spectrum measurement of a photonic integrated circuit

Abstract

Stimulated Brillouin scattering (SBS) is a phonon-photon interaction in which the energy of an optical pump transfers to a Stokes wave through an acoustic wave. Chalcogenide glass (As 2 S 3 ) photonic integrated circuits (PIC) are among the most efficient platforms for SBS and have been extensively developed for several applications, including microwave photonic filters, lasers and optical memory. In these applications, the acoustic properties of the waveguide are paramount to achieve high performance. A distributed SBS measurement with high spatial resolution reveals information about the local phonon-photon interactions along the waveguide in contrast to traditional techniques, which only capture an integrated SBS response. Among different SBS-based distributed measurement techniques, Brillouin optical correlation domain analysis (BOCDA) has achieved the highest spatial resolution, which is essential for scanning cm-scale PICs. Different implementations of BOCDA use frequency and phase modulation [1] [2] or are based on amplified spontaneous emission (ASE) [3]. The latter requires only a simple ASE source, however the drawback is that this technique typically leads to a low signal-to-noise ratio (SNR). In this work, we use an ASE-based BOCDA system with a lock-in amplifier to achieve higher SNR by rejecting the excess noise from the ASE spectrum. We scan the local SBS response of a chalcogenide PIC with 2.5 mm spatial resolution. This approach provides critical information about acoustic properties of the waveguide.