Grating resonances in air–silica microstructured optical fibers

Abstract

We report what is believed to be the first demonstration of optical fiber gratings written in photonic crystal fibers. The fiber consists of a germanium-doped photosensitive core surrounded by a hexagonal periodic air-hole lattice in a silica matrix. The spectra of these gratings allow for a detailed characterization of the fiber. In particular, the gratings facilitate coupling to higher-order leaky modes. We show that the spatial distribution and the effective index of these modes are determined largely by the design of the lattice and that the grating spectra are unaffected by the refractive index surrounding the fiber. We describe these measurements and corresponding simulations and discuss their implications for the understanding of such air-hole structures.

Review of long period fiber gratings written by CO2 laser

“…85 UVlaser exposure is a common technique for writing a FBG/ LPFG in a Ge-doped PCF with a photosensitivity. 12,86,87 In contrast, CO 2 laser irradiation is a highly efficient, low cost technique for writing a LPFG in a pure-silica PCF without photosensitivity. 20,24,25,27 Kakarantzas et al 20,88 reported, as shown in Fig.…”

“…Periodic index modulations are usually required to realize mode coupling in in- fiber gratings. Although this presents no difficulties in conventional glass fibers, 16,21 solid-core PCFs, 12,20,25 and solid-core PBFs, 50,[94][95][96][97][98] it is very difficult, even impossible, to directly induce index modulations in an air-core PBF due to the air core structure, thereby seriously obstructing the development of PBF-based gratings over the past decade.…”

Role of Flexible Macro Fibre Composite (MFC) Actuator on Bragg Wavelength Tuning in Microstructure Polymer Optical Fibre Long Period Grating for Strain Sensing Applications*

“…In general, multiple microscopic air-holes lattice runs down longitudinally along the length of the optical fibre with different microstructure pattern. A novel waveguides property can be achieved by designing various air hole structures, size, shape and distribution of the holes, which may not be readily achieved in conventional optical fibres [1][2][3][4].…”

A dual wavelength distributed-feedback fiber laser

“…[37][38][39] By doping the core of air-silica structured fibers with germanium, improved dispersion characteristics were achieved 40 showing larger customization. Germanium doping in the core allowed Bragg gratings to be written, 41 although some of the advantages of the structured fiber, particularly the evanescent field extending into the holes, are lost. Core cladding interactions also become problematic.…”