Deep wet etching on fused silica material for fiber optic sensors

Abstract

In this paper, deep microstructures on fused silica material, which are useful for fabrication of the fiber optic sensors, were obtained by using a wet chemical etching process. The etching solutions and the masking materials used for developing deep structure are described in this paper. The etch rate of a fused silica diaphragm in room temperature ranged from 46nm per minute to 83nm per minute with different concentrations of Buffered Hydrogen Fluoride (BHF). The etch depth of one step etching was 25μm with the surface roughness less than 20nm (peak-to-peak value). The optical reflectance from the deep etched surface was 4%, which is the same as a well-cleaved fiber end face. This result made the visibility of interference fringes from the single mode fiber optic sensors to be as high as 96%. Furthermore, two-step structures on the fused silica diaphragms with the total depth greater than 35μm are demonstrated. To the best knowledge of the authors, this is the deepest structure produced by wet etching process on fused silica material. Fiber optic pressure sensors based on deep etched diaphragms were fabricated and tested. Fabrication of microstructures on the fiber end faces by using this process is therefore possible.