In this study, we develop mid-infrared (MIR) waveguides and beamsplitters for applications such as spectroscopy, chemical sensing, and remote sensing using ultrafast laser inscription (ULI) within chalcogenide glass IG2 (Ge33As12Se55). MIR photonic integrated circuits (PICs) enable compact and efficient optical layouts. IG2 glass is ideal for MIR PICs because of its broad transparency window, low absorption, and compatibility with atmospheric windows at 3-5 and 8-12 µm.
The waveguiding properties at 1.064 µm (Near-IR) and 4.55 µm (MIR) were investigated by examining the effects of inscription parameters and geometries, particularly the impact of pulse energy and the number of layers for a multi-scan strategy on the mode confinement and the morphology the waveguide cross-section. We determine that higher pulse energy or a higher number of layers is required to achieve guided modes at the longer wavelength. For example, for the single-layer configuration, the threshold pulse energy that enables the guided modes at the 1.064 and 4.55-µm wavelength is 3 and 6 nJ, respectively. Mode confinement at MIR was further achieved at 6nJ when two or more vertical layers were applied, achieving a minimum propagation loss of 1.8 dB/cm with a four-layer configuration. Waveguides with cross-sections larger than two layers exhibited higher-order modes at MIR in addition to the fundamental mode. We further demonstrate MIR 1x4 beamsplitters, achieving uniform splitting ratios of over 96 %. Our results highlight the potential of ULI-inscribed IG2 waveguides and beamsplitters for developing mid-infrared photonic devices and integrated circuits.