Abstract
The simple and highly sensitive measurement of the refractive index (RI) of liquids is critical for designing the optical instruments and important in biochemical sensing applications. Intensity modulation-based polymer optical fiber (POF) RI sensors have a lot of advantages including low cost, easy fabrication and operation, good flexibility, and working in the visible wavelength. In this review, recent developments of the intensity modulation POF-based RI sensors are summarized. The materials of the POF and the working principle of intensity modulation are introduced briefly. Moreover, the RI sensing performance of POF sensors with different structures including tapered, bent, and side-polished structures, among others, are presented in detail. Finally, the sensing performance for different structures of POF-based RI sensors are compared and discussed.
Highlights
The refractive index (RI) is an important optical parameter of material
The fiber gratings usually refer to the fiber Bragg gratings (FBG), the long-period gratings (LPG), and the titled Bragg gratings, which are fabricated on the single-mode silica fibers [106] or the single-mode polymer fibers [48]
The results showed that a higher RI sensitivity can be obtained when the LPG structure was imprinted on a thin polymer optical fiber (POF)
Summary
The refractive index (RI) is an important optical parameter of material. Some physical quantities such as concentration, temperature, and pressure, etc., can be reflected by the change of RI [1]. Compared with the wavelength modulation, the intensity modulation method does not need the complex fabrication processing and expensive equipment; usually, the cheap LED and photodetectors can be used as the light source and detector [53] for the sensor system. This type of sensor is very easy to implement and goes very well with multimode fiber, which could provide a low-cost solution for RI measurement. Reviewed the optical fiber-based RI sensors and tried to make a comparative study of various existing devices and systems in this field All of these existing reviews, are completely lacking information about intensity-modulated POF-based RI sensors.
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