**4. Conclusions**

This study proposes a new sensing configuration combining the high T sensitivity and repeatability NOA61-PFFI to the flexible NOA65-PT. Thus, the sensor can achieve the simultaneous measurement of φ and T. The experimental results show that the interference FV of the optical spectra is only correlated with φ and the wavelength shifts (Δλ) of the interference spectra are only affected by T variations. Consistent results illustrate that by using the proposed sensing scheme with the specific characteristics of the used materials (NOA61 and NOA65 polymers), the fiber device can simultaneously and effectively measure T and φ with small errors. Furthermore, the proposed PT/PFFI can independently discriminate the tilt angle state and the surrounding T variations from the measured spectra. The sensing results demonstrate that the PT/PFFI can measure φ and T simultaneously with good sensitivities and averages of 0.4 dB/◦ and 0.17 nm/◦C, respectively. The obtained results of the T and φ sensitivities may not be high but are comparable with those based on the FBG sensors, however, the advantages of this solution are that it is simple, flexible, easy to fabricate, and does not require an expansive laser system for writing the FBGs.

**Author Contributions:** This work was carried out in collaboration between all authors. The first author and corresponding author C.-L.L., proposed the sensing concept, verified the mathematical method, analyzed the data, wrote and revised the manuscript. Author, C.-S.C., an undergraduate student in the Department of EOE, finished the experiments, managed figures and data. Authors, C.-R.Y. and R.-C.Z., the graduated students in the Department of EOE, performed the first stage experiments, managed figures, and data. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by The Ministry of Science and Technology of Taiwan, MOST 108-2221-E-239-020 and the APC was funded by MOST 109-2221-E-239-029.

**Conflicts of Interest:** The authors declare no conflict of interest.
