Large negative dispersion in dual-concentric-core photonic crystal fiber with hybrid cladding structure based on complete leaky mode coupling Jinhui Yuan a, ⁎, Xinzhu Sang a , Chongxiu Yu a , Cang Jin a , Xiangwei Shen a , Guiyao Zhou b , Shuguang Li b , Lantian Hou b a State Key Laboratory of Information Photonics and Optical Communications (Beijing University of Posts and Telecommunications), P.O. Box163 (BUPT), 100876 Beijing, China b Institute of Infrared Optical Fibers and Sensors, Physics Department, Yanshan University, 066004 Qinhuangdao, China abstract article info Article history: Received 2 December 2010 Received in revised form 28 August 2011 Accepted 29 August 2011 Available online 14 September 2011 Keywords: Dual-concentric-core photonic crystal fiber (DCCPCF) Large negative dispersion Complete mode coupling Coupled-mode theory Considering the optical stability of solution, the sugar-solution is infused into the outer core ring of dual- concentric-core photonic crystal fiber (DCCPCF). The influences of structure parameters and solution concen- tration on the phase and loss matching are comprehensively analyzed. By choosing the appropriate outer core mode to completely couple with the inner core fundamental mode, the large negative dispersion PCF around 1.55 μm is designed, which has the dispersion value of -39,500 ps/km/nm as well as bandwidth of 7.4 nm and effective mode area of 28.3 μm 2 . The designed PCF with hybrid cladding structure can effectively compensate the positive dispersion of conventional single mode fiber, and suppress the system perturbation caused by a series of nonlinear effects. Considering the mode field mismatching between the DCCPCF and the tapered fiber, the calculated connection loss around 1.55 μm is below 3 dB. In addition, the equivalent prop- agation constants of two leaky modes are deduced from the coupled-mode theory, and the complete mode coupling case can be well predicted by comparing the real and imaginary parts of propagation constants. © 2011 Elsevier B.V. All rights reserved. 1. Introduction The dispersion must be compensated in the long-distance optical data transmission system to suppress the broadening of pulse. One way to realize this is to use the dispersion compensating fibers (DCFs), which are designed to have large negative dispersion [1–10]. To minimize the insertion loss and reduce the cost, the DCFs should be as short as possible, and the magnitude of negative dispersion should be as large as possible. Recently, the photonic crystal fibers (PCFs) have attracted lots of attentions in many fields due to its novel properties such as large effective mode area and controllable dispersion, and so on [11–14]. Some investigations on DCFs and dispersion compensating photonic crystal fibers (DCPCFs) have been reported [2–17]. The disper- sion value of over -500000 ps/km/nm was achieved in Bragg-fiber [6]. Ganuck et al. reported that the higher-order mode in multimode fiber exhibited the dispersion value of less than -1000 ps/km/nm [7]. Hut- tunen et al. showed a dispersion value of -55000 ps/km/nm in the higher-order modes of dual-concentric-core PCF (DCCPCF) with doped high-index inner core [12]. Zhang et al. showed a dispersion peak value of -36000 ps/km/nm around 1.55 μm in DCCPCF with an inner low-index core and an outer high-index core [17]. The large negative dispersion in DCCPCF is mainly caused by the leaky mode coupling. Roberts et al. showed the mode coupling be- tween the inner core fundamental mode of PCFs and outer core defect mode at the anti-crossing point [18]. Renversez et al. explained a core mode transition induced by avoided crossing between a core leaky mode and a high-index cylinder leaky mode in the anti-resonant guiding PCFs [19]. Zhang et al. investigated the dependence of leaky mode coupling on loss in the PCF with hybrid cladding structure, and showed the crucial role of effective index imaginary part in the leaky mode coupling [20]. In above reports, although the large negative dispersions were achieved based on the leaky mode coupling, the higher-order modes were mainly used, and the suppression of nonlinear effects wasn't well considered. In addition, in DCCPCFs with solution infused into the outer core ring, the influences of the structure parameters and optical stability of solution on the mode coupling characteristics weren't analyzed, which are very important in actual application. In this paper, considering the optical stability, the DCCPCF with hybrid cladding structure is formed by infusing the sugar-solution into the outer core ring. The influences of the structure parameters and sugar-solution concentration on the characteristics of leaky mode coupling are comprehensively investigated based on the Multi-pole method (MPM) [21]. The large negative dispersion PCF around 1.55 μm, which can suppress the system perturbation caused by a se- ries of nonlinear effects, is designed by choosing appropriate outer core mode to completely couple with the inner core fundamental Optics Communications 284 (2011) 5847–5852 ⁎ Corresponding author. Tel.: + 86 10 62281179. E-mail address: yuanjinhui81@163.com (J. Yuan). 0030-4018/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.optcom.2011.08.075 Contents lists available at SciVerse ScienceDirect Optics Communications journal homepage: www.elsevier.com/locate/optcom