On-chip stimulated Brillouin scattering in As2S3 waveguides with soft claddings of Benzocyclobutene

On-chip stimulated Brillouin scattering (SBS) can be implemented with arsenic trisulfide (As2S3) waveguides and benefits various applications of microwave photonic, signal processing and sensing. While stiff top-claddings of silica on the waveguides can help to enhance the opto-acoustic interaction in SBS, the soft cladding can facilitate the realization of narrow linewidth Brillouin lasers. Herein, we systematically study the on-chip SBS characteristics of the ridge As2S3 waveguides with soft claddings of Benzocyclobutene (BCB). Specifically, an optical propagation loss lower than 0.2 dB/cm and a Brillouin gain coefficient of approximately 300 m−1 W−1 at the Brillouin frequency of 7.70 GHz have been demonstrated. In particular, the linewidth of the Brillouin gain spectrum is broadened to be about 60 MHz. The influence of waveguide width on the SBS properties is systematically studied and the mostly-concerned linewidth broadening effect with respect to different waveguide dimensions has been found to be negligible. As an application of the fabricated BCB-cladded As2S3 waveguide, we have demonstrated the microwave bandpass filter with a suppression ratio of up to 23 dB. The As2S3 waveguides with BCB claddings may provide an effective and economic platform for on-chip SBS applications, such as integrated notch filter, Brillouin amplifiers, Brillouin lasers.