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The sensing of carbon dioxide (CO2) at room temperature, which has potential applications in environmental monitoring, healthcare, mining, biotechnology, food industry, etc., is a challenge for the scientific community due to the relative inertness of CO2. Here, we propose a novel gas sensor based on clad-etched Fiber Bragg Grating (FBG) with polyallylamine-amino-carbon nanotube coated on the surface of the core for detecting the concentrations of CO2 gas at room temperature, in ppm levels over a wide range (1000 ppm-4000 ppm). The limit of detection observed in polyallylamine-amino-carbon nanotube coated core-FBG has been found to be about 75 ppm. In this approach, when CO2 gas molecules interact with the polyallylamine-amino-carbon nanotube coated FBG, the effective refractive index of the fiber core changes, resulting in a shift in Bragg wavelength. The experimental data show a linear response of Bragg wavelength shift for increase in concentration of CO2 gas. Besides being reproducible and repeatable, the technique is fast, compact, and highly sensitive.

Multi-parameter sensing in the form of sensor arrays functionalized with multiple receptors, is an approach for attaining selectivity in sensing. We have demonstrated a novel fiber sensor based on an etched Bragg grating whose core is coated with materials such as polyelectrolytes, carbon nanotubes, and polyallylamine-amino-carbon nanotubes, and can be used for detecting gases, pH, humidity, refractive index, proteins and other biomolecules. In this approach, the target molecules interact with the functionalized core of the etched FBG resulting in a change in the effective refractive index of the fiber core leading to a subsequent shift in the Bragg wavelength. The experimental data shows that the wavelength shift varies linearly with the concentration of the target analyte. Besides being reproducible and repeatable, the technique is fast, compact, and highly sensitive.

Here, we describe a novel FBG interrogation system in which FBGs are used as both sensing and reference elements. The reference FBGs is bonded to a mechanical flexure system having a linear amplification of 1:3.5, which is actuated using a piezo-actuator by applying a 0-150 V ramp. The lengths of the reference gratings decide the maximum strain that can be applied to the reference grating, which in turn decides that strain range which can be interrogated. The main advantages of the present system are the on-line measurement of the wavelength shifts, small size, good sensitivity, multiplexing capability and low cost.