Abstract
The long period fiber grating (LPFG) is widely used as a sensor due to its high sensitivity and resolution. However, the broad bandwidth of the attenuation bands formed by the mode coupling between the fundamental core mode and the cladding modes constitutes a difficulty when the device is used as a conventional sensor. To overcome this limitation, a Michelson interferometer-type sensor configuration has been developed, using an LPFG grating pair formed by coating a mirror at the distal end of the LPFG. This sensor configuration is more convenient to use and is able to overcome the limitations of the single LPFG based sensor as the shifts in the attenuation bands being more easily detectable due to the formation of the sharp spectral fringe pattern in the LPFG based Michelson interferometer. In this work, I studied the LPFG based Michelson interferometer as the refractive index sensor and discussed the sensitivity enhancement of the LPFG based Michelson interferometer as a refractive index sensor by employing higher order cladding modes and by reducing the cladding radius. The results demonstrated the HE17 mode with a cladding radius of 62.5 μm, in the range of surrounding refractive index (SRI) of 1–1.45, and its resonant peak showed a wavelength shift of 26.99 nm/RIU. When the cladding region was further reduced to 24 μm, the resonant peak showed a wavelength shift of 569.88 nm/RIU, resulting in a sensitivity enhancement of nearly 21 times. However, as the cladding region was etched further, then the HE17 order cladding mode and higher mode would be cut off. Therefore, the implementation of high sensitivity for SRI sensing with the reduced cladding in the LPFG based Michelson interferometer is dependent on the proper combination of the cladding radius and cladding mode order.
Highlights
The development of various devices for external refractive index sensing has become increasingly important for numerous applications in various industrial processes, biomedical analysis, and environmental monitoring
Greater attention has been paid to sensors based on long period fiber grating (LPFG) because of their high sensitivity, relatively simple fabrication, and simple signal detection
An LPFG based Michelson interferometer is presented, which is termed as the SILPFG that includes a long-period grating operating in the reflection mode for refractive-index sensing
Summary
The development of various devices for external refractive index sensing has become increasingly important for numerous applications in various industrial processes, biomedical analysis, and environmental monitoring. The widely used fiber optic sensors usually employ the long-period fiber grating (LPFG) [1, 2], etched fiber Bragg grating [3], and plasmon resonance sensing structure [4]. Greater attention has been paid to sensors based on LPFGs because of their high sensitivity, relatively simple fabrication, and simple signal detection. Amit SINGH: Long Period Fiber Grating Based Refractive Index Sensor With Enhanced Sensitivity Using Michelson. ) in the perturbed region, and the transmission spectrum is formed, which consists of series of attenuation bands at various discrete resonant wavelengths [6]. Where λres is the resonant wavelength corresponding to mth cladding mode, neff,co is the effective refractive. Photonic Sensors and it does not require the manufacture of two identical gratings, which is a technically challenging task [10]
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