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

Abstract

A liquid core waveguide as a refractometer is proposed. Microtunnels were created in standard optical fiber using tightly focused femtoscond laser inscription and chemical etching. A 1.2(h)×125(d) ×500(l) μ m micro-slot engraved along a fiber Bragg grating (FBG) was used to construct liquid core waveguide by filling the slot with index matching oils. The device was used to measure refractive index and sensitivity up to 10 -6 /pm was obtained.

Note: Optical fiber milled by focused ion beam and its application for Fabry-Pérot refractive index sensor

“…The fiber constitutes the backbone conduit for light guiding, and effective light-fluid interaction is achieved when the microfluidic channel intersects the optical pathway. In recent years, devices such as microchannels, microslots, and FP interferometers have been fabricated in single-mode fibers (SMFs) by the use of femtosecond laser micromachining, [8][9][10][11][12] which can be effectively utilized for RI sensing with low temperature sensitivity and large dynamic range. However, a relative low fringe visibility of the interference pattern is achieved when using this technique for making FP fiber sensors.…”

Microchanneled Chirped Fiber Bragg Grating Formed by Femtosecond Laser-Aided Chemical Etching for Refractive Index and Temperature Measurements

“…It has been reported that regions modified by the fs laser have much higher etching rate than the pristine material, of which the contrast ratio can be up to 100 : 1 [5]. Recently, a micro-slot superimposed on an FBG fabricated by the same technique has also been reported [6]. The fs/etching combined approach represents a low-cost but effective microstructuring technique compared to fs laser direct machining.…”

“…The proposed MCFBG shows not only enhanced RI sensitivity but also nondegrading mechanical strength, representing a more ideal candidate for implementation of in-fiber bio-chemical sensors for a range of potential applications. The introduction of a microchannel to a CFBG results in the change of effective index due to the infusion of the surrounding medium in this region [6], and thus the change of the spectral response of the MCFBG. By applying the transfer matrix method, we have simulated the spectral property of the proposed MCFBG structure.…”

In-fiber polymer–glass hybrid waveguide Bragg grating

“…Tightly focused femtosecond laser pulses have been used to induce refractive changes for writing optical waveguides [9] and, with the aid of chemical etching, have been applied in micromachining [10]. Holes have been opened on the surface or through the fiber with this technique [11][12][13], and we have employed a microslot engraved through the fiber to make a liquid core waveguide [14]. In this Letter we further the work and report on a novel in-fiber hybrid waveguide grating structure that features a polymer core and a glass cladding.…”

“…As explained in [14], with high refractive index material filling in the slot, a hybrid slab waveguide with the filling material as its core and the glass as its cladding can be produced. Polymers not only present a higher refractive index than the glass but can also undergo a transition from a liquid or viscous amorphous state to a solid state, making them superb candidates as the filling material in the hybrid waveguide.…”