Temperature independent refractive index measurement using a fiber Bragg grating on abrupt tapered tip

Abstract

a b s t r a c tA fiber Bragg grating was inscribed in an abrupt fiber taper using a femtosecond laser and phase-mask interferometer. The abrupt taper transition allows to excite a broad range of guided modes with different effective refractive indices that are reflected at different wavelengths according to Bragg's law. The multimode-Bragg reflection expands over 30 nm in the telecom-C-band. This corresponds to a modefield overlap of up to 30% outside of the fiber, making the device suitable for evanescent field sensing. Refractive index and temperature measurements are performed for different reflection peaks. Temperature independent refractive index measurements are achieved by considering the difference between the wavelength shifts of two measured reflection peaks. A minimum refractive index sensitivity of 16 ± 1 nm/RIU was obtained in a low refractive index regime (1.3475-1.3720) with low influence of temperature (À0.32 ± 0.06 pm/°C). The cross sensitivity for this structure is 2.0 Â 10 À5 RIU/°C. The potential for simultaneous measurement of refractive index and temperature is also studied.

An Optical Sensor Designed From Cascaded Anti-Resonant Reflection Waveguide and Fiber Ring-Shaped Structure for Simultaneous Measurement of Refractive Index and Temperature

“…Fiber gratings, such as (LPFG) and fiber Bragg gratings (FBG), are commonly used to measure RI and temperature simultaneously in a cascade with other sensing structures due to their temperature-sensitive and RI insensitive characteristics. These sensors are usually composed by cascading fiber gratings with another structure, such as special optical fiber [11], s-shaped taper [12], droplet-like fiber structure [13], core-offset MZI [14], microfiber knot resonators [15],etc., or by embedding another structure, abrupt tapered tip [16] and in-line MZI [17]. However, in the manufacturing process of these hybrid sensors, whether fiber gratings or other cascaded structures, complex preprocessing usually requires the use of expensive equipment, such as femtosecond lasers or high precision cutting equipment, all of which limit their development in large-scale production and practical applications.…”

Phenomenological models of the main characteristics of a step optical fiber

“…Наприклад, не складно довести, що будь-яка залежність може моделюватись поліномом нульового ступеню (тобто, константою), якщо діапазон значень параметрів достатньо малий. Для діапазону хвиль DWDM значення параметра K попередньо можна визначити за рекомендаціями МСЕ-Т [25], де коефіцієнт хроматичної дисперсії пропонується апроксимувати лінійним поліномом:…”

Optical Fiber Refractometer Based Metal Ion Sensors

“…A normal uniform FBG is not inherently sensitive to ambient RI as it mostly influences the core guided modes that are tightly confined in the fiber core with no interaction with the ambient environment. However, fiber sensitization techniques such as fiber tapering [53,54] and cladding modification [55,56] can be employed to sensitize the Bragg grating. A special FBG known as the tilted FBG (TFBG) shown in Figure 7, can be used without modification for RI sensing [57,58].…”