Long-Period Gratings in Highly Germanium-Doped, Single-Mode Optical Fibers for Sensing Applications

Abstract

Long-period fiber gratings (LPGs) are well known for their sensitivity to external influences, which make them interesting for a large number of sensing applications. For these applications, fibers with a high numerical aperture (i.e., fibers with highly germanium (Ge)-doped fused silica fiber cores) are more attractive since they are intrinsically photosensitive, as well as less sensitive to bend- and microbend-induced light attenuations. In this work, we introduce a novel method to inscribe LPGs into highly Ge-doped, single-mode fibers. By tapering the optical fiber, and thus, tailoring the effective indices of the core and cladding modes, for the first time, an LPG was inscribed into such fibers using the amplitude mask technique and a KrF excimer laser. Based on this novel method, sensitive LPG-based fiber optic sensors only a few millimeters in length can be incorporated in bend-insensitive fibers for use in various monitoring applications. Moreover, by applying the described inscription method, the LPG spectrum can be influenced and tailored according to the specific demands of a particular application.

Evaluating the Performance of Functionalized Carbon Structures with Integrated Optical Fiber Sensors under Practical Conditions

“…Furthermore, the measurement of the spatial strain profile along the OGF was achieved based on an OFDR technique using Corning SMF28E XB fiber with acrylate coating and two Fibercore SM1500 fibres (with FBG sensors and acrylate coating) that had been integrated in the FCS, which is illustrated in Figure 1 . The FBGs have been inscribed in-house in photosensitive Fibercore SM1500 fiber using a KrF excimer laser and the phase mask technique [ 15 ]. The length of the fabricated FBGs was 7 mm and the Full Width Half Maximum (FWHM) of the resulting spectral reflection peaks was 0.53 nm.…”

Long-Period Gratings and Microcavity In-Line Mach Zehnder Interferometers as Highly Sensitive Optical Fiber Platforms for Bacteria Sensing

“…LPGs can be arc-induced using a fiber splicer [23], fabricated using UV pulsed [24], femtosecond laser or CO 2 laser. Comparative analysis shows that UV-written and arc-induced LPGs may offer similar sensitivities [25].…”

“…This system is based on the natural affinity of bacteria to specific carbohydrates, a moiety occurring in almost every living organism, which is a basis of the bacteria-host cell recognition. Therefore, they are able to naturally attract bacteria, facilitate biofilm formation, and promote bacteria adhesion [24]. In this sensing schema, the detection of pathogenic bacteria is carried out via protein-carbohydrate interactions, which are very similar to the antibody-antigen, or enzyme-substrate reactions.…”

Morphological and Surface-State Challenges in Ge Nanoparticle Applications

“…Ge possesses a variety of interesting properties, such as its narrow band gap (0.67 eV at 300 K), high ion intercalation capacity (4.4:1 Li/Ge ratio and 1:1 Na/Ge ratio), high refractive index, high charge carrier mobilities (μ e = 3900 cm 2 V –1 s –1 and μ h = 1900 cm 2 V –1 s –1 ), and low toxicity . These attractive properties have already resulted in Ge-based materials being applied in solid-state electronics, semiconductors, and optical fibers as well as in more specialized applications such as infrared optical transistors, as alloying agents, or as catalysts for the production of plastics. ,− Recently, new advances in the theoretical understanding and experimental design related to NPs and QC effects have fueled renewed interest in Ge NPs. As the NP dimensions decrease, the surface area and its free energy increase, QC becomes stronger, and the behavior of the material changes more dramatically from that of its bulk counterpart.…”