Three-hole microstructured optical fiber for efficient fiber Bragg grating refractometer

Abstract

We present a photosensitive three-hole microstructured optical fiber specifically designed to improve the refractive index sensitivity of a standard fiber Bragg grating (FBG) sensor photowritten in the suspended Ge-doped silica core. We describe the specific photowriting procedure used to realize gratings in such a fiber. We then determine their spectral sensitivity to the refractive index changes of material filling the holes surrounding the core. The sensitivity is compared with that of standard FBGs photowritten in a six-hole fiber with a larger core diameter. We demonstrate an improvement in the sensitivity by two orders of magnitude and reach a resolution of 3 x 10(-5) and 6 x 10(-6) around mean refractive index values of 1.33 and 1.40, respectively.

A refractometer based on a micro-slot in a fiber Bragg grating formed by chemically assisted femtosecond laser processing

“…Figure 6(c) gives its response to a variation of the LRI in terms of its wavelength and the strength. In the low LRI region, both change almost monotonically with a trend similar to previous reports [3,7] and the sensitivity reaches 116nm/refractive index unit (RIU) (or 8.6×10 -6 /pm) for an LRI from 1.44 to 1.46. Once in regime II, the scenario changes substantially, showing obvious less reflectivity and unpredictable wavelength.…”

“…Traditional optical fibers with a solid core seem unsuitable in this respect and microstructure optical fibers (MOF) appear as the only option. MOFs have been reported interacting with liquids either still using the evanescent wave [7] or guiding light in liquidfilled hollow core [8]. But writing FBGs in MOFs is not trivial, it is either impractical because of the huge hollow core [8] or requires special preparation of photosensitive fiber [7].…”

“…MOFs have been reported interacting with liquids either still using the evanescent wave [7] or guiding light in liquidfilled hollow core [8]. But writing FBGs in MOFs is not trivial, it is either impractical because of the huge hollow core [8] or requires special preparation of photosensitive fiber [7]. Most reported MOF based liquid or gas sensors also incur difficulties in pumping the measurands to the functional region of the fiber.…”

Observation of symmetrical reflection sidebands in a silica suspended-core fiber Bragg grating

“…The suspendedcore fiber was connected to high NA fibers (Nufern-UHNA4) at both ends via strong fusion splicing [15]. This ensured the air-holes were sealed, allowing enough loaded hydrogen to be retained in the core for sufficient time during the FBG inscription [12]. The spliced fibers were left in a hydrogen chamber with pressure of 2000 psi for one month at room temperature.…”

“…By doping a suspended-core fiber with germanium, the fiber nonlinearity is enhanced, at the same time this also enables fiber Bragg grating (FBG) to be photo-written in the core [12]. New optical phenomena can be expected in a FBG written on an ultra-small-core fiber.…”