Chalcogenide microfiber-assisted silica microfiber for ultrasound detection

An ultra-compact ultrasound sensor with a chalcogenide (ChG) microfiber and a silica microfiber is fabricated. It can detect the ultrasound wave generated by a piezoelectric transducer peaked at 3.7 MHz. The sensor shows the broadband ultrasound frequency response with a high signal-to-noise ratio (SNR), owing to the high refractive index and small Young's modulus of ChG material. A ChG (${{\rm As}_2}{{\rm Se}_3}$As₂Se₃) microfiber of 2 µm diameter is adhered to the surface of a silica microfiber with a diameter of 5 µm via Van der Waals force; the transmission spectrum has high contrast due to multi-mode interference in this hybrid structure. The SNR response could be up to 70 dB, especially at low frequency due to the soft ChG microfiber as a sensing unit to magnify the ultrasound signal, along with an SNR over 12 dB at ultrasound of 31.2 MHz. As a comparison, a silica taper with the same size as the ChG microfiber is also placed on the silica microfiber with a diameter of 5 µm to detect an ultrasound signal from 18 kHz to 9.4 MHz with an SNR lower than that based on the ChG microfiber up to 38.8 dB, showing the high sensitivity of the ChG microfiber.