Novel long-period fiber gratings written by high-frequency CO2 laser pulses and applications in optical fiber communication

In this paper, we report novel long-period fiber gratings (LPFGs) fabricated by using a new writing technique that is mainly based on the thermal shock effect of focused high-frequency CO2 laser pulses at several kHz. Several unique characteristics of these LPFGs, such as bend and transverse-load, etc., are observed by experiments, for the first time, to our knowledge. These unique features of the LPFGs are mainly due to the asymmetrical distribution of the refractive index on the cross-section of the LPFG induced by high-frequency CO2 laser pulses. Based on these novel LPFGs, an amplified spontaneous emission noise filter and a gain equalizer have been demonstrated for the noise figure reduction and the gain spectrum flattening of Er-doped fiber amplifiers (EDFAs), respectively. By means of the unique bending and loading features of the LPFG, two tunable gain equalizers have been demonstrated for dynamic gain flattening of EDFAs. (C) 2003 Elsevier B.V. All rights reserved.