Research on loss-imbalance equalization of AWG-based OADM

Integrated-Optic Arrayed Waveguide Grating (AWG) NxN multiplexers are a new focus in All Optical Networks (AON) for their unique N input and N output geometry and have been used in a variety of applications. All AWGs fabricated so far have shown loss-imbalance among FDM channels due to non-umiform diffraction efficiency. It is fatal in AON because it will accumulate after each AWG. Uniform diffraction efficiency obtained in ideal design limit is one ideal solution, but it is nearly impossible to achieve the ideal limit with present fabrication technology. This paper applies a new method-shifted connection-on equalizing loss-imbalance of AWG-based OADM. The basic idea is simple and the result is of great significance. We theoretically analyze the effect of 8 various shifted configurations and predict each effectiveness. We find the relationship between the loss-imbalance and shift delta is a quadratic equation We extend the method to cascaded AWGs. Also we deduce the limit of the equalization which is independent of m and AWG's loss-imbalance parameter alpha, beta. Experiment results accord with theory very well and show that we successfully reduce a worst case loss-imbalance (9.5 dB) to a best case loss-imbalance (3dB) in a single AWG-based OADM. We find that equalization configuration with foldback path is superior to loopback path configurations, when no more than Nn wavelengths are used. The method is very simple and effective in equalizing AWG's loss-imbalance and the idea can be applied to other equalizations in AON.