Investigation of Bending Sensitivity in Partially Doped Core Fiber for Sensing Applications

Abstract

A fiber based high sensitive bend sensor is proposed and demonstrated using a uniquely designed partially doped core fiber (PDCF). The fabrication method of PDCF with two core regions, namely an undoped outer region with a diameter of ∼9.5 µm encompassing a doped, inner core region with a diameter of 4.00 µm is explained. The mechanism of bending effect in proposed PDCF and the experimental setup for amplified spontaneous emission (ASE) based sensor and fiber laser based sensor is illustrated. For ASE sensor, the higher ASE power level loss as the spooling radius is reduced from 20 to 3 cm is measured. The gain peak shift to shorter wavelength with respect to the decrease of the spooling radius from 20 to 3 cm due to higher bending loss at smaller bending radius is observed. The results are in agreement with overlap factor variation of PDCF. As expected from ASE peaks variation, the fiber laser sensor spectral operation is changed from 1539 to 1530 nm range. This phenomenon is due to higher mode field diameter of longer wavelength and result of optical filtering at longer wavelengths. The experimental results showed the output of the ASE is also highly stable, with no observable variation in the power output over a measurement period of 1 h. The PDCF is also temperature insensitive.Index Terms-Optical sensors, partially doped core fiber, fiber laser sensor. 1530-437X

Passively mode-locked laser using an entirely centred erbium-doped fiber

“…This paper details a passively mode-locked fiber laser using a two-core optical fiber, with an undoped outer region of 9.38 μm diameter that surrounds a 4.00 μm diameter central core region doped with erbium ions at 400 ppm concentration. This optical fiber, abbreviated as TC-EDF, was developed in-house, with a designated application as a bend-sensitive active optical fiber sensor [23,24]. This same fiber was also used to demonstrate mode-locked behaviour using CNT as a saturable absorber.…”

“…TC-EDF is a new type of fiber in which the fiber core comprises two annular regions, these being a concentrated erbium-doped inner core region and a surrounding undoped outer core region. The concentrated inner core acts as the source mechanism for the amplified spontaneous emission (ASE) spectrum, and the high concentration of erbium dopant in this region results in the propagating Gaussian beam achieving maximum intensity at the core, causing excitation of erbium ions within this inner core of the fiber [23,24]. Recent experiments reported in [24] demonstrate the ASE output is relatively stable with negligible variation in output power over a measurement period of one hour.…”