*Article* **NOA61-Polymer Fiber Fizeau Interferometer with a Flexible NOA65-Polymer Taper for Simultaneous Measurement of Tilt Angle and Temperature**

**Cheng-Ling Lee \* , Chi-Shiang Chen, Chun-Ren Yang and Rui-Cheng Zeng**

Department of Electro-Optical Engineering, National United University, No. 2 Lien-Da, Miaoli City 36003, Taiwan; U0723013@gm.nuu.edu.tw (C.-S.C.); alanboy927@gmail.com (C.-R.Y.); watermelon5424@gmail.com (R.-C.Z.)

**\*** Correspondence: cherry@nuu.edu.tw; Tel.: +886-37-382568; Fax: +886-37-382555

**Abstract:** This study proposes and experimentally demonstrates a NOA61-polymer fiber Fizeau interferometer (PFFI) connected to a flexible NOA65-polymer taper (PT) for simultaneous measurement of tilt angle and temperature (T). The PT/PFFI fiber sensor consists of a taper-shaped flexible NOA65 polymer and single-mode fiber with an endface that is attached to a NOA61-polymer. The NOA61-polymer of PFFI is highly sensitive to variations of T with high repeatability and enables the simultaneous measurement of tilt angle by connecting with the highly flexible NOA65-PT. the interference fringe visibility of optical spectra in the PFFI can be highly controlled by the tilt angle of the PT and is thus capable of measuring tilt angles with high sensitivity. On the other hand, wavelength shifts of the spectra in the PFFI only occur when T varies. The proposed PT/PFFI can simultaneously detect the tilt state and the variation of surrounding T by measuring the optical spectral responses and eliminating cross sensitivity. Experimental results demonstrate the PT/PFFI can simultaneously measure tilt angles and T with good sensitivities and obtain averages of 0.4 dB/◦ and 0.17 nm/◦C, respectively.

**Keywords:** fiber tilt sensor; NOA61; NOA65; polymer; simultaneous measurement; fiber Fizeau interferometer; taper
