Interleaved Waveband MUX/DEMUX Developed on Single Arrayed-Waveguide Grating
OFC/NFOEC 2008 - 2008 Conference on Optical Fiber Communication/National Fiber Optic Engineers Conference
We propose a novel interleaved waveband MUX/DEMUX developed on a single AWG. The device configuration is very simple and resolves the major difficulties raised by the previously proposed concatenated AWG arrangement. Introduction Broadband access is rapidly penetrating the world. Significant traffic expansion is envisaged in the near future with the introduction of IP-TV and IP-based High-Definition (HD) and super-HD video services. In order to create cost-effective, bandwidth-abundant future
... h-abundant future networks, hierarchical optical path networks are recognized as playing a key role [1, 2]. They exploit grouping and routing wavelength paths as a bundle, the waveband [1, 2]. Wavebands have been proven to substantially reduce the size of optical cross-connect systems . One of the key components in realizing the hierarchical optical path cross-connect is the waveband multi/demultiplexer (MUX/DEMUX). A dielectric multilayer filter has been fabricated that offers 8-skip-0 band operation at 100-GHz spacing , however, it requires 409 layers  and the manufacturing challenge is significant. Another band-filter that consists of two specially designed arrayed-waveguide gratings (AWG) has been reported . The output/input ports of the two AWGs need to be connected with waveguides of exactly the same length and the level of precision required is high. A more recent proposal [5, 6] uses concatenated conventional AWGs to realize the waveband MUX/DEMUX. The key to the device is that it retains multi/demultiplexing granularity at the individual wavelength channel level. This means that conventional individual wavelength channel AWGs can be utilized. The salient feature of the waveband MUX/DEMUX is that it can accommodate multiple input fibers simultaneously, which makes it very effective in reducing the cost and size of the waveband cross-connect. Regarding waveband arrangements, two different configurations have been identified : continuous and interleaved waveband arrangements. This paper proposes a novel interleaved waveband MUX/DEMUX. It is developed on a single conventional AWG, and as a result, it simultaneously eliminates the major two shortcomings seen in the previous development . First, the proposed device can remove all the waveguide crossings that were used to connect the two AWGs. Second, the single AWG configuration substantially relaxes fabrication tolerance and increases yields, while the previous device demanded minimization of the performance variance between the two AWGs. Comparison of continuous and interleaved waveband arrangements The generic hierarchical optical cross-connect architecture is shown in Fig.1 . It is divided into two parts; one part consists of a waveband MUX/DEMUX and waveband cross-connect (WBXC) for routing waveband paths, and the other part consists of a wavelength MUX/DEMUX and WXC for routing wavelength paths. Figures 2 and 3 depict two different waveband arrangements: continuous waveband arrangement and interleaved waveband arrangement. A continuous waveband accommodates continuous wavelength paths on the ITU-T grid. An interleaved waveband accommodates interleaved wavelength paths on the ITU-T grid. From the networking point of view, the waveband arrangement has virtually no effect on network OAM&P (Operation, Administration, Maintenance, and Provisioning). However, the wavelength MUX/DEMUX required depends on the arrangement selected. The channel spacing between wavelength paths is much wider for an interleaved waveband than for continuous waveband, so the wavelength path MUX/DEMUX required for an interleaved waveband can be realized with an AWG without any temperature control. The fabrication tolerance is also rather large and the integration of many wavelength MUX/DEMUX devices on a single chip becomes easier. Thus, the interleaved waveband arrangement can ease wavelength MUX/DEMUX fabrication. The interleaved waveband MUX/DEMUX can use cyclic AWGs (FSR = channel spacing x # of wavebands). There is, however, one significant problem with cyclic AWGs. It is inherently difficult to precisely align the center frequency of each channel on the ITU-T grid among the multiple wavebands; the frequency deviation causes transmission signal distortion and large optical loss, particularly at or close to the edge channels of each waveband, and for wavebands near the edge of the total band (i.e. C or/and L-band). On the other hand, the previously proposed interleaved waveband MUX/DEMUX in  can be realized by using wide FSR AWGs (cyclic approach is not utilized). However the device still has two shortcomings; the substantial number of waveguide crossings needed between the two component AWGs, and the requirement that the characteristics of the two AWGs must be exactly matched. The proposed device explained below simultaneously eliminates these 1 a1555_1.pdf OThE1.pdf OFC/NFOEC 2008 978-1-55752-855-1/08/$25.00 ©2008 IEEE Authorized licensed use limited to: Georgia State University. Downloaded on June 27, 2009 at 23:25 from IEEE Xplore. Restrictions apply.