A new application of optical fiber surface plasmon resonance for micro-displacement measurement

Abstract

We provided an effective method that optical fiber surface plasmon resonance (SPR) can be used to displacement measurement. By fabricating a Kretschmann configuration on a micro-structure fiber which is produced by splicing a short segment of graded-index fiber (GIF) with a plastic-clad silica (PCS), we made a novel micro-displacement sensor. We employed a single-mode fiber (SMF) to change the radial position of the incident beam as the displacement. In the GIF, the angle between light beam and fiber axis, which is changed by the displacement, will lead to changes of resonance angle in the PCS. Thus the resonance wavelength shifts. The detection range of the proposed sensor is 0–25 μm; and its sensitivity is related to the refractive index (RI) of liquid surrounding in which the sensing zone is immersed (named cladding liquid). The higher the cladding liquid RI, the higher the sensitivity. Under cladding liquid RI of 1.41, the resonance wavelength redshifts from 801 nm to 839 nm when the displacement changes from 0 μm to 25 μm. When the displacement is close to 25 μm, the sensitivity reaches a maximum of 2.43 nm/μm, which transcends almost all of other optical-fiber micro-displacement sensors. The proposed micro-displacement sensor will have potential applications in high precision instruments.