Applications of highly nonlinear dispersion tailored lead silicate fibres for high speed optical communications

Abstract

Recent advances in optical fibre technology, most notably in the area of microstructured optical fibres (MOFs), offer a host of new opportunities within future high speed communication systems. Herein we review how our recent progress on the implementation of lead silicate fibre designs, allowing both flexible dispersion control and a high effective nonlinearity, can be integrated into various all-optical signal processing devices for high speed optical communication systems. Highly nonlinear lead silicate fibres have already proven to be well suited for achieving efficient four-wave mixing (FWM) due to their high effective nonlinear coefficient, low dispersion profile and short length. Keywords: All-optical signal processing, nonlinear optics, optical communications, four-wave mixing. INTRODUCTIONThe ability to fabricate small core soft-glass holey fibres (HFs) with tailored dispersion properties (in particular with flattened and near-zero values) and 2-3 orders of magnitude higher effective nonlinearity than silica fibres opens new prospects in the implementation of compact, all-optical nonlinear devices [1], such as wavelength conversion, signal regeneration and the like, which can radically transform future optical networks. Four-wave-mixing (FWM)-based switches are particularly attractive, since they offer transparency both in terms of modulation formats and repetition rates. Key fibre parameters for achieving broadband, highly efficient FWM processes are: (i) a highly nonlinear medium, (ii) low dispersion values over a broad wavelength range and (iii) short lengths in order to enhance the phase matching process. While several high-nonlinearity and dispersionflattened air/glass HFs have been demonstrated using either silica [2] or non-silica [1] glass as the host material, the precise control of their corresponding dispersion is extremely hard to achieve. This is because precise dispersion control requires extreme precision in the dimensions and spacing of the µm-scale holes of the microstructure. The complex interdependence between temperature, surface tension and internal pressure within the holes, however, causes small-scale longitudinal cross sectional variations, which are very difficult to control in practice. To solve this issue we have proposed in [3] a new all-solid fibre concept based on the use of three commercial lead silicate glasses (Schott SF57, LLF1, SF6) arranged in a W-type index profile. The fabricated fibre presents a flattened and near-zero dispersion profile and a high nonlinearity of 820W -1 km -1 at the telecom wavelengths. Accurate polishing of the glass preform before the fibre drawing has allowed us to reduce the propagation losses from an initial value of ~5dB/m [3] down to ~2dB/m [4] in the 1.55µm region. In this talk we will review some examples of successful applications of the fabricated single-mode, highly nonlinear dispersion tailored lead silicate glass fibre for high speed optical communication.