A cost-effective fiber Bragg grating (FBG) temperature sensor package was designed and developed with two distinct sensing probes and demodulation schemes. U-shaped and capillary shape probes were designed and tested using an optical spectrum analyzer and two different indiginously developed intensity demodulation schemes. The temperature sensitivities were measured as 12.94 ± 0.15 pm °C⁻¹, 11.57 ± 0.12 pm °C⁻¹, and 12.03 ± 0.14 pm °C⁻¹ for a bare FBG and for FBGs encapsulated in the U-shaped and capillary probes, respectively, with negligible hysteresis and a repeatability of 1 °C–3 °C. The performance of the probes was demonstrated by twin-FBG intensity demodulation schemes, the range of which was increased up to 181.50 °C with a resolution of 0.120 °C by the development of a CFBG-FBG intensity demodulation scheme.

Thermal metrology is critical in many high-energy industrial processes to optimize the process efficiency, energy consumption and quality of end product. Here, we present the design and development of a double thimble type standard type-1 fiber Bragg grating (FBG) high temperature sensing probes. Two different probes named probe-1 and probe-2 are developed by encapsulating type-1 FBGs in two stainless steel thimbles with ceramic filling. The probes are experimentally tested in a high temperature box furnace and their responses are interrogated by an optical spectrum analyzer. FBGs encapsulated in both probe-1 and probe-2 exhibited a linear red-shift in their Bragg wavelength with increase in temperature from 30 °C to 700 °C with sensitivities of 13.86 ± 0.1 pm/°C and 14.10 ± 0.2 pm/°C which are 4.8% and 3.16% lower than temperature sensitivity of bare FBG, respectively. A deformation in the Bragg spectrum of probe-1 is observed at temperatures above 500 °C however, probe-2 is found to be thermally stable up to 700 °C. An estimated life-time of about 6 years is offered by the optimized probe-2 with a negligible hysteresis and repeatability of 1°C–5°C.

A target-type cantilever based temperature compensated fiber Bragg grating (FBG) flow sensor is designed and developed with economical demodulation and data acquisition schemes. FBG is glued on the surface of a thin elastic stainless steel cantilever in pre-strained condition. The cantilever is mounted inside a flow channel by a special purpose brass holder with a height and direction adjustable threaded stem. The sensor is interrogated by an optical spectrum analyzer (OSA) and indigenously developed twin FBGs and chirped FBG—FBG intensity demodulation schemes. Response of the sensor is investigated in the flow rate range of 0–10 l min⁻¹ in both forward and reverse flow directions. In spectral demodulation, the flow sensor offered a linear response in the full investigated range with a sensitivity of 19.2 pm/(L/min). However, the twin FBGs demodulation scheme presented a linear behaviour in the range of 4–10 l min⁻¹ with sensitivities of 1.22 ± 0.03 μW/(L/min) and 29.89 ± 0.55 mV/(L/min) detected by the high speed power meter and photodetector, respectively. The novel CFBG-FBG intensity demodulator offered a linear response throughout its tested range and can offer a flow rate detection up to 265 l min⁻¹ at the present sensitivity of the sensor with the condition that the cantilever-FBG system must be strong enough to withstand the higher flow rates. The temperature of the fluid is monitored by an FBG temperature sensing probe connected to the flow channel using intensity demodulation scheme by another pair of twin FBGs. Temperature compensation of the flow sensor is performed by arithmetic operations over the reflection intensities due to temperature probe to the results of the flow rates using a cost-effective data acquisition scheme.