Over 70 nm Wideband Tuning of Fiber Bragg Gratings Using a Compressive Bending Technique

We demonstrate, for the first time, a silica-based fiber Bragg grating (FBG) with a wavelength tuning range over 70 nm, using compressive bending given by a simple tuning package. The wide tuning range of the device (from 1614 nm to 1544 nm), covers the entire Lband and a half of the C-band. Its polarization-mode dispersion (PMD) and polarization-dependent loss (PDL) remain low over the full operating regime. Introduction The expansion of DWDM systems from the conventional band (C-band) to the short band (S-band) and the long band (L-band) calls for the development of various wavelength tunable optical devices. In the near-future dynamic reconfigurable networks, which will encompass operation bandwidth over 150 nm, it requires wavelength-selective filters with a large tuning range. In addition, the capability of the filters to tune into the dead band between the C and L bands, which is not in service, is necessary to prevent crosstalk in DWDM systems with tight channels separation. The fiber Bragg gratings (FBG) is the most suitable for selecting DWDM signals with channel spacing ≤50 GHz owing to its narrow bandwidth and steep spectral edge. Its center wavelength can typically be shifted either by the strain or thermal effect. However, strain tuning is more preferable to achieve a wider tuning range. Recent demonstrations of widely tunable FBG are carried by using a compressive strain. This is because the silica fiber is 23 times stronger in a compression-strain mode than in a tensile-strain mode [1,2]. In this paper, we demonstrate a 70-nm wavelength tuning range of an FBG using compressive bending [3] given by a simple tuning package. To the best of our knowledge, this is the widest tuning range ever achieved with a silica-based FBG. We also find that the polarization-mode dispersion (PMD) and polarization-dependent loss (PDL) of the device are low enough under various compressive strains, showing applicability of the device to DWDM networks. Principle of Operation and Fabrication of the Device