Planar lightwave circuits for FTTH and photonic networks

Integrated-optic waveguide devices become more and more complicated to realize high functionality. Optical functional devices are important to solve electrical bottleneck issues. Ultra-compact and CMOS compatible silicon waveguides are important for the integration of an optical component and an electronic circuit aiming at higher level of functionalities. This paper reviews the recent progress and future prospects of PLC devices and their applications to FTTH and photonic networks.

Optical splitters for FTTH

Single-mode 1xN splitters are essential optical components for PDS-PON (passive double star type passive optical network) systems. For greater levels of splitting such as 1×64 and 1×128, the excess loss and PDL of Y-branch splitters increase as more and more Y branches are cascaded. Funnel-type splitter configuration (Fig. 1) becomes advantageous for large port splitters [1]–[3]. In 1xN funnel splitter, an array of N output waveguides are positioned at the end of the slab region. The output waveguides are positioned so that they all point at the input waveguide. The width of the outer funnel waveguides is designed to be wider than that of the inner one to obtain a uniform coupling efficiency in all output waveguides. Experimental transmission spectra of 1×64 funnel splitter is shown in Fig. 2, where , and W = 6.5~26 µm. Some of the radiated light leaks out from the outermost funnel waveguides. This causes excess loss in the funnel splitter (about 0.8 dB theoretical loss). Although the radiation pattern varies in accordance with the wavelength, an almost flat splitting spectrum is obtainable. The maximum insertion loss (IL) is 19.6 dB, IL uniformity is 1.22 dB, and the maximum polarization-dependent loss (PDL) is 0.17 dB, respectively.