Hetero Core Arrangement of Optical Fibers as an Effective Tool for Different Sensing Applications

In the similar note, the alternative arrangement can also be reckoned. When we look at the propagation characteristics, the transmission characteristics get influenced drastically. It is widely known that light propagates by means of total internal reflection in optical fiber [3-5]. Again, the signal is chiefly conveyed by guided mode or core modes. However, if there is a small exposed region in the cladding of the fiber, there happens to be another entry of cladding modes/leaky modes. When we talk SMS arrangement, there is a lead in fiber and lead out fiber. The signal in the form of light enters through lead in fiber and modulated light intensity is received through lead out fiber. There is no hard and fast rule of applying single mode fiber as the lead in or lead out. Instead, multimode fibers can be effectively placed as the lead in/lead out fiber. When fibers of dissimilar cores are spliced together, there arises multimode interference (MMI). This precisely occurs from the interference of the light beams within the joints. This MMI leads to self-image process. Self-image signifies the reproduction of the input signal after traversing a certain length of the mid fiber in case of SMS. When we go for the alternative

arrangement where multimode fibers are placed side by side, thereby sandwiching a single mode fiber in between [4-7]. As per reports, the power distribution within these aforementioned arrangements is a function of the mid-length of the fiber as well as core-diameter. Even, the refractive index also plays a pivotal role in sensing applications. When we modulate these features, there is a considerable fluctuation of transmittance. Simultaneously, by injecting analytes with different refractive indices, one can assess different physical variables in the form of pressure, humidity, temperature etc. Regarding assessment of physical variables, there are various approaches. However, the modulation of transmitted signal can be interrogated in two domains: wavelength interrogation and intensity interrogation. The former category is sensitive to minute change which manifests itself in the form of shifted wavelengths. On the contrary, the intensity fluctuations are assessed through voltage change, power change or current change. However, the former category is expensive while the latter one is inexpensive.

Although several adaptations have been reported till now regarding sensing applications, there are certain challenges that need special mention. Detection of couple of parameters through these adaptations (hetero-core arrangement) is another challenge. The sensitivity as well as limit of detection plays an important criterion for sensing approaches. While augmenting these two, complications arise from the fabrication of these hetero schemes. Hence, there is a need to synergistic fabrication procedure which will cater ease interrogation as well as inexpensiveness. It is believed that these hurdles may be overcome in near future with state-of-the-art fusion splicers and highly sensitive receivers.

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2. Paul D, Biswas R, Bhattacharya NS (2015) Investigating photonic crystal fiber within E to L communication band with different material composites. Optik 126(23): 4640- 4645.

3. Paul D, Biswas R, Bhattacharya NS (2015) Modal parameter analysis for crown glass and phosphate glass photonic crystal fiber. Ind J Phys 89(7): 737-741.

4. Paul D, Biswas R, Bhattacharya NS (2015) Predicting different losses of photonic crystal fibers in material and hetero-core domain. Optical Materials 48: 110-120.

5. Biswas R, Karmakar P (2016) All fiber optic hetero-core spliced multimode single mode multimode filter. Optical and Quantum Electronics 48(8): 1-7.

6. Biswas R (2017) Low cost wavelength selective evanescent fiber optic temperature and refractive Index sensor. European Physical Journal Plus (in Press). Eur Phys J Plus 132: 207.

7. Biswas R, Karmakar PK, Gogoi C, Sarma D (2017) A Comparative Analysis of Hetero Core Spliced MSM and SMS System in terms of Transmittance. International Journal of Photonics and Optical Technology 3(9): 16-19.