Photonic Crystal Multi-Core Fibers for Future High-Capacity Transmission Systems

Since the internet traffic is rapidly growing, it is expected that the current transmission fibers will become inadequate in around 2015–2020 [1], [2]. Therefore, some innovations with transmission fibers for future high-capacity transmission have been strongly required. Expanding the transmission bands from the current C and/or L-Band by utilizing new transmission fibers is one interesting direction. For example, photonic crystal fibers (PCFs), which have an endlessly single mode (ESM) property, are one of the interesting candidates to realize ultra wide-band transmissions [3]– [6]. In addition, PCFs, which are designed to realize large effective core area (Aeff), have been also investigated and reported [7]–[9]. These reports said that PCFs had a large potential in realizing larger Aeff than conventional solid fibers. For these aspects, PCFs can offer very interesting optical properties as future high-capacity transmission lines. Recently, another important direction, namely using space division multiplexing (SDM) by using multi-core fibers (MCFs), has been paid considerable attention [10]– [13]. A multi-core fiber literally multiples the core number within a fiber dimension, which enables multiple transmission capacity per one fiber. Naturally, the ultra highcapacity transmission, by combining both ultra wide-band wavelength division multiplexing (WDM) and SDM, can be realized by applying PC-MCFs [10]. In addition, PC-MCFs give another interesting possibility, namely SDM with large Aeff cores [11]. Merits of using PCFs and PC-MCFs compared to conventional fiber types will be demonstrated and discussed in this paper, with some novel R&D results.