Saitoh Kunimasa, Varshney Shailendra K, Koshiba Masanori
Graduate School of Information Science and Technology, Hokkaido University, Sapporo 060-0814, Japan.
Opt Express. 2007 Dec 24;15(26):17724-35. doi: 10.1364/oe.15.017724.
We propose a new design of hole-assisted fiber (HAF) that can compensate for the accumulated dispersion in single-mode fiber link along with dispersion slope, thus providing broadband dispersion compensation over C-band as well as can amplify the signal channels by utilizing the stimulated Raman scattering phenomena. The proposed dispersion-compensating HAF (DCHAF) exhibits the lowest dispersion coefficient of -550 ps/nm/km at 1550 nm with an effective mode area of 15.6 microm(2). A 2.52 km long module of DCHAF amplifies incoming signals by rendering a gain of 4.2 dB with +/-0.8 dB gain flatness over whole C-band. To obtain accurate modal properties of DCHAF, a full-vector finite element method (FEM) solver is employed. The macro-bend loss characteristics of the proposed DCHAF are evaluated using FEM solver in cylindrical coordinate systems of a curved DCHAF, and low bending losses (<10(-2) dB/m for 1 cm bending radius) are obtained for improved DCHAF design while keeping intact its dispersion compensation and Raman amplification properties. We have further investigated the birefringence characteristics that can give significant information on the polarization mode dispersion of DCHAF by assuming a certain deformation (eccentricity e = 7%) either in air-holes or in the doped core or in both at a same time. It is noticed that the distortion in air-holes induces a birefringence of 10(-5), which is larger by a factor of 10 than the birefringence caused due to the core ellipticity. A PMD of 11.3 ps/ radicalkm is obtained at 1550 nm for distorted air-holes DCHAF structure.
我们提出了一种新型的空穴辅助光纤（HAF）设计，它能够补偿单模光纤链路中累积的色散以及色散斜率，从而在C波段提供宽带色散补偿，并且还能利用受激拉曼散射现象放大信号通道。所提出的色散补偿空穴辅助光纤（DCHAF）在1550nm处展现出最低色散系数为-550ps/nm/km，有效模面积为15.6平方微米。一个2.52km长的DCHAF模块通过在整个C波段提供4.2dB的增益且增益平坦度为+/-0.8dB来放大输入信号。为了获得DCHAF准确的模态特性，采用了全矢量有限元方法（FEM）求解器。利用FEM求解器在弯曲DCHAF的柱坐标系中评估所提出的DCHAF的宏弯曲损耗特性，对于改进后的DCHAF设计，获得了低弯曲损耗（弯曲半径为1cm时<10^(-2)dB/m），同时保持其色散补偿和拉曼放大特性不变。我们进一步研究了双折射特性，通过假设在气孔、掺杂纤芯或两者同时存在一定变形（偏心率e = 7%），这可以给出有关DCHAF偏振模色散的重要信息。值得注意的是，气孔中的畸变会引起10^(-5)的双折射，这比纤芯椭圆度引起的双折射大10倍。对于畸变气孔DCHAF结构，在1550nm处获得的偏振模色散为11.3ps/√km。
