Cascade Connection of Two Long-Period Fiber Gratings with a π-Phase Shift to Expand the Rejection Bandwidths


IEICE TRANSACTIONS on Electronics   Vol.E98-C    No.6    pp.512-517
Publication Date: 2015/06/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.E98.C.512
Type of Manuscript: PAPER
Category: Optoelectronics
long-period fiber grating,  band-rejection filter,  widening rejection bandwidth,  cascade connection,  arc-discharge,  

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A novel method was developed to expand and adjust the bandwidth of long-period fiber gratings (LPFGs) as band-rejection filters. The band-rejection filters were constructed by concatenating two LPFGs with an appropriate space, that causes a π-phase shift. The component LPFGs with the same period and the different numbers of periods are designed to have -3-dB transmission at wavelengths on both sides of a resonance wavelength symmetrically, and the transmission loss of the concatenated LPFGs peaks at the -3-dB transmission wavelengths. The rejection bandwidth was widened by changing the interval between the -3-dB transmission wavelengths. The concatenated LPFGs were simulated by using a transfer-matrix method based on a discrete coupling model, and were fabricated by a point-by-point arc discharge technique on the basis of the simulation results. It was demonstrated that the rejection bandwidth at 20-dB attenuation reached 26.6 nm and was 2.7 times broader than that of a single uniform LPFG.