Three-dimensional-printed Fabry–Perot interferometer on an optical fiber tip for a gas pressure sensor

We demonstrate a three-dimensional (3D)-printed miniature optical fiber-based polymer Fabry-Perot (FP) interferometric pressure sensor based on direct femtosecond laser writing through two-photon polymerization. An unsealed cylinder column with a suspended polymer diaphragm is directly printed on a single-mode fiber tip to form an FP cavity. Here, two FP cavities with different lengths and the same diaphragm thickness (5 µm) are presented. The fabricated FP interferometer has a fringe contrast larger than 15 dB. The experimental results show that the fabricated device with a 140 µm cavity length has a linear response to the change of pressure with a sensitivity of 3.959 nm/MPa in a range of 0-1100 kPa, and the device with a 90 µm cavity length has a linear pressure sensitivity of 4.097 nm/MPa. The temperature sensitivity is measured to be about 160.2 pm/°C and 156.8 pm/°C, respectively, within the range from 20 to 70°C. The results demonstrate that 3D-printing techniques can be used for directly fabricating FP cavities on optical fiber tips for sensing applications.