M. S. Aruna Gandhi

A novel fiber Michelson interferometer (FMI) based on parallel dual polarization maintaining fiber Sagnac interferometers (PMF-SIs) is proposed and experimentally demonstrated for temperature sensing. The free spectral range (FSR) difference of dual PMF-SIs determines the FSR of envelope and sensitivity of the sensor. The temperature sensitivity of parallel dual PMF-SIs is greatly enhanced by the Vernier effect. Experimental results show that the temperature sensitivity of the proposed sensor is improved from -1.646 nm/°C (single PMF-SI) to 78.984 nm/°C (parallel dual PMF-SIs), with a magnification factor of 47.99, and the temperature resolution is improved from ±0.03037°C to ±0.00063°C by optimizing the FSR difference between the two PMF-SIs. Our proposed ultrasensitive temperature sensor is with easy fabrication, low cost and simple configuration which can be implemented for various real applications that need high precision temperature measurement.

The survey focuses on the most significant contributions in the field of fiber optic plasmonic sensors (FOPS) in recent years. FOPSs are plasmonic sensor-based fiber optic probes that use an optical field to measure the biological agents. Owing to their high sensitivity, high resolution, and low cost, FOPS turn out to be potential alternatives to conventional biological fiber optic sensors. FOPS use optical transduction mechanisms to enhance sensitivity and resolution. The optical transduction mechanisms of FOPS with different geometrical structures and the photonic properties of the geometries are discussed in detail. The studies of optical properties with a combination of suitable materials for testing the biosamples allow for diagnosing diseases in the medical field.

We propose a simple geometric, highly responsive and miniaturized surface plasmon polariton microbiosensor using a photonic quasicrystal fiber. Here, we consider gold as plasmonic material as the external coating for exciting the surface plasmon to detect the refractive index of the external analyte sensing to facilitate the practical realization. Further, we carry out detailed characteristics evaluations such as wavelength and amplitude sensitivities, resolution, full-width at half maximum, the figure of merit, signal to noise ratio and detection limit for both 6-fold and 8-fold plasmonic sensors. The proposed 6 and 8-fold sensors show a maximum sensitivity of 28,000 nm/RIU for an analyte range of 1.41–1.42 and 27,000 nm/RIU for an analyte range of 1.4–1.41, respectively. While the figure-of-merit of the 6-fold sensor is 491, for the 8-fold sensor, it is 231. Besides, the structural parameters and the arrangements of the air-holes in cladding region add to the sensing performance. The proposed sensing systems operate for a wide range of wavelengths from 600 to 1300 nm. Thus, the proposed sensors might turn out to be promising candidates for the refractive index-based biological and chemical detections. Keywords: Photonic quasicrystal fiber, Surface plasmonic polariton, Microbiosensor, External sensing approach

A highly-sensitive temperature sensor with controllable sensitivity based on Vernier effect by cascading a tunable extrinsic Fabry-Perot interferometer (FPI) and a fixed reflective Lyot filter (RLF) is theoretically investigated and experimentally demonstrated. The temperature sensitivity can be tuned by modulating the cavity length of the extrinsic FPI and online monitoring the envelope of superimposed spectrum with optical spectrum analyzer (OSA). The FPI works as the reference arm to tune the temperature sensitivity of the sensing system, while the RLF with 1-meter polarization maintaining fiber (PMF) acts as the sensing probe. Experimental results prove that by changing the cavity length of the FPI, the sensitivities of −3.82 nm/°C, −8.33 nm/°C and −14.63 nm/°C can be achieved. Compared with the single sensing element, the sensitivities are magnified by 3.78, 8.25 and 14.49 times. The proposed temperature sensor is feasible to be applied practically in scenarios which require different temperature sensitivities in demanded temperature detection ranges.

Using finite-element method, we propose a photonic quasi-crystal fiber-based refractive index biosensor (PQF-RIBS), which works based on the surface plasmon polariton. We determine the loss spectra for two different variations of the refractive index of analyte, na. From the detailed numerical analysis, we find that the PQF-RIBS exhibits a maximum refractive index sensitivity of 6000 nm/RIU and a resolution of 1.6 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> RIU when na is increased from 1.45 to 1.46. Besides, this sensor does exhibit the negative refractive index sensitivity of -4000 nm/RIU and a resolution of 2.5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> RIU for a sensing range from 1.52 to 1.53. Furthermore, we carry out selective filling of liquid in the selective holes of the proposed biosensor for a sensing wavelength range from 900 to 1200 nm. Finally, we also study the influence of the structural parameters, namely, diameter of the core and diameter of the air holes in the cladding over the loss spectra of a fundamental mode for a particular n <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</sub> of 1.47.