A simple and wavelength-flexible procedure for fabricating phase-shifted fibre Bragg gratings

Abstract

A simple procedure for fabricating phase-shifted fibre Bragg gratings (PSFBGs) that does not require the use of a phase-shifted phase mask is presented. Two standard fibre Bragg gratings (FBGs) of equal length and with the same Bragg wavelength are inscribed sequentially in single mode optical fibre, such that the FBGs overlap physically by one grating period. This procedure induces a spectral-hole in the middle of the reflection spectrum, equivalent to a -phase shifted FBG. PSFBGs have been fabricated in the 1300 nm and 1550 nm wavelength bandwidths, demonstrating flexibility in the choice of the centre wavelength. The PSFBGs fabricated are compared with a model based on a modified Rouard's method which is subsequently used to investigate the influence of translation stage errors on the fabrication of the PSFBGs. The model demonstrates that the strength/reflectivity of the PSFBG influences the spectral-hole linewidth as well as the finesse of the device while the length of the PSFBG affects only the linewidth of the spectral-hole but not the finesse of the device. The PSFBG devices produced by this technique are reproducible and the fabrication process is fast and is well suited for the fabrication of WDM PSFBGs.

Novel fabrication technique for phase-shifted fiber Bragg gratings using a variable-velocity scanning beam and a shielded phase mask

“…Over the past decade, an extensive variety of methods have been reported for phase-shifted FBG fabrication, such as Moire method [14], moving fiber-scanning beam method [8,15], and shielded phase mask method [16], Other techniques have included the creation of internal micro-structures [13], overexposure to a near-infrared femtosecond laser with a uniform phase mask [17]. However, these methods have specific disadvantages as detailed in the comparison of phase-shifted FBG fabrication methods presented by Chehura et al [18]. These methods feature fabrication limitations, such as complex systems, poor tolerance, insufficient repeatability, and high processing time.…”

“…However, the resulting phase-shifted FBG exhibited a relatively wide transmission passband (i.e. ∼82 pm FWHM) [18]. In 2014, Sergio et al demonstrated a new type of phase-shifted superstructure FBG which was inscribed into the optical fiber by opening and closing the laser shutter at preset locations [16].…”

Phase-shifted fiber Bragg grating inscription by fusion splicing technique and femtosecond laser

“…This technique possesses high quality, whereas it requires a high precise control and is time consuming. A simple PS-FBG inscription technique is presented based on a sequential double UV laser exposure process, in which two uniform FBGs with same parameters are overlapped physically by one grating period [12]. This technique is repeatable and arbitrary phase shift can be achieved, but it requires a high precise control.…”

Multiplexing a serial array of tapered optical fibre sensors using coherent optical frequency domain reflectometry

“…Coherent optical frequency domain reflectometry (OFDR) has been shown to be capable to identifying changes in attenuation of an optical fibre with high spatial resolution, and instrumentation is available commercially. OFDR is a distributed measurement technique that offers the ability to monitor the power of light backscattered along the length of an optical fibre under test, which might be as a result of Rayleigh scattering or of reflections from splices and components such as fibre Bragg gratings, with very high spatial resolution 5,6,7,8 . The basis of OFDR is swept wavelength homodyne interferometry, in which the output from a tuneable laser is input to an interferometer with one path containing the fibre under test and the other to a reference arm of fixed length.…”