Direct laser writing of smart polymer photonic devices for ultrasound detection

With the development of micro/nano-scale fabrication technologies, smart active/passive photonic devices have been fabricated by using silicon/polymer materials, which show great potential applications in photonics and optoelectronics. The current fabrication techniques such as electron-beam lithography give a high resolution, but they are expensive and time-consuming. Here, we present some polymer-based photonic devices fabricated by 3D femtosecond laser writing through two-photon polymerization. The resolution can reach up to ~100 nm, which is less than 1/10 wavelength within the C-band. Hence, the fabricated photonic devices can be used for micro lasing and sensing application. In this research, we show the spectral characteristics of several photonic devices such as phase-shifted Bragg grating waveguides. Due to the properties of polymer materials, the devices have a higher sensitivity on acoustic waves that can modify the geometry of the waveguide and thus induce a change in the effective index of the mode, which can be utilized for designing ultrasonic sensors. Although the fabricated quality is lower than that of photonic devices fabricated by the electron-beam lithography, the results show our fabricated devices can be useful for inexpensive sensors for ultrasound detection, demonstrating the usability of the femtosecond laser writing technique for photonic applications.