| Title |
Study on Separate Measurement of Refractive Index and Temperature Using Fiber Multi-Mode Interference and Grating Resonance |
| Authors |
Minchan Bae ; Yong Wook Lee |
| DOI |
http://doi.org/10.5207/JIEIE.2024.38.1.015 |
| Keywords |
Grating resonance; Multi-mode interference; Refractive index; Temperature |
| Abstract |
In this paper, we demonstrated the separate measurement of refractive index(RI) and temperature using a combination of the multi-mode interference(MMI) of no-core fiber(NCF) and the grating resonance of double-clad fiber(DCF). An NCF segment concatenated with a long-period fiber grating (LPFG) inscribed on DCF was utilized as the sensor head. We selected two resonance dips in the transmitted spectrum generated by the MMI and the grating resonance as sensor indicators DMMI and DLPFG. First, we observed how the two sensor indicators responded to external RI variations by increasing the concentration of the sucrose solution injected around the sensor head from 0% to 50%(1.3330 ∼ 1.4201RIU) with increments of 10%. While one sensor indicator DMMI formed by the MMI showed a total wavelength shift of ∼6.6nm with an adjusted R2 value of 0.99821, another sensor indicator DLPFG formed by the grating resonance of the LPFG written on DCF showed a total wavelength shift of ∼0.28nm with an adjusted R2 value of 0.43149. This result indicates that DMMI is 23 times more sensitive to RI than DLPFG and that DMMI can be employed to measure RI almost independently of ambient temperature changes. On the other hand, to investigate the temperature response of the sensor indicators, the sensor head was placed inside the glass container filled with distilled water, and the temperature of the incubated distilled water(0% sucrose solution) was increased using a hot plate. With the increase of the applied temperature from 30 to 55℃, DLPFG showed a total wavelength shift of ∼1.86nm with an adjusted R2 value of 0.9991. In contrast, for the same temperature change, DMMI exhibited a total wavelength shift of ∼0.18nm with an adjusted R2 value of 0.92857. This implies that DLPFG is sufficient to be used for temperature measurement nearly independent of external RI variations. As a result, the two sensor indicators DMMI and DLPFG of the proposed sensor head can be utilized for the separate measurement of RI and temperature changes, respectively. |