Fig. 1. Optical properties of GeSbS material. (a) Measurement of transmittance window and refractive index of GeSbS bulk material^[47]; (b) measurement of the change in the resonant frequency of GeSbS resonators with temperature for determination of thermal-optic coefficient (TOC)^[48]

Fig. 2. Deposition and device fabrication based on GeSbS material. (a) Fabrication of 4 inch thin film based on GeSbS material; (b) uniformity of thin film thickness; (c) uniformity of thin film refractive index; (d) SEM image of fabricated waveguide structure; (e) fabricated micro-ring resonator device with racetrack waveguide coupling; (f) cross-sectional view of the waveguide device

Fig. 3. GeSbS photonic chip preparation technology. (a) Schematic of ChG thin film fabrication process; (b) on-chip device packaging with an array of optical fiber inputs and outputs; (c) microring resonator structure with a high Q factor of 6.40×10⁵; (d) distribution of Q factors for microring resonators; (e) distribution of loaded Q and intrinsic Q over the wavelength range of 1500‒1590 nm, with an average Q factor of 6.97×10⁵

Fig. 4. Sensors based on different optical principles. (a) Microscale suspended structure ultrasound sensor based on a micron-scale silicon chip^[80]; (b) miniaturized ultrasound detector developed using SOI technology^[81]; (c) silicon substrate waveguide design with air-gap acoustic enhancement^[82]; (d) silicon-based platform with PDMS acoustic enhancement^[83]

Fig. 5. Research on the performance of on-chip ultrasonic detector based on ChG. (a) Fabrication process of on-chip ultrasound detectors based on ChG^[22]; (b) on-chip ChG microring resonator ultrasound detector with a Q factor of 1.48×10^6［22］; (c) design of a cascaded structure with 3 on-chip ultrasound detectors based on ChG^［22］; (d) parallel spectral and ultrasound signal demodulation from the three ultrasound detectors^［22］; (e) fabrication process of a suspended ChG microring resonator^[99]; (f) fabricated suspended ChG microring resonator with an optical quality factor of 1.1×10^6［99］

Fig. 6. Application of photoacoustic tomography using a ChG-based ultrasound detector array^[100]. (a) Conceptual diagram of the imaging process; (b) schematic of a digital optical frequency comb system for parallel spectral demodulation of the array devices; (c) ChG-based ultrasound detectors and their array structure; (d) physical ultrasound detector array after fiber-coupled packaging; (e) photoacoustic image of a leaf vein; (f) photoacoustic imaging results of a 7-day-old zebrafish; (g) photoacoustic imaging results of a 21-day-old zebrafish

Fig. 7. Acousto-optic modulators of different structures. (a) Schematic of an on-chip push-pull acousto-optic modulator^[130]; (b) simulation of acoustic surface wave mode field^[129]; (c) on-chip aluminum nitride (AlN) isolator based on the acousto-optic effect^[131]; (d) fully integrated acousto-optic modulator optical image using surface acoustic wave (SAW) and Lamb wave techniques^[122]; (e) cross-section of an integrated acousto-optic modulator with a SiO₂-clad silicon rib waveguide and an AlN thin film surface acoustic wave^[126]; (f) (g) acousto-optic modulators based on different structural designs of on-chip AlN thin films^[127-128]

Fig. 8. Related research of ChG in other fields. (a) Advances in research on flexible thin films^[134-135]; (b) progress in on-chip devices based on chalcogenide materials for mid-infrared gas detection^［137］; (c) optimization studies of on-chip devices based on chalcogenide materials for mid-infrared gas detection^［138］