A Reconsideration of Birefringent Interleaver

摘要

Wavelength interleaver is an important component of dense wavelength division multiplexing systems. Various techniques are proposed to implement the wavelength interleaver. Among these approaches, the one based on the birefringent crystal might be the first ever been proposed and manufactured. The birefringent wavelength interleaver has a de facto standard structure consisting of n pieces of birefringent crystal with designed rotation angles. One important yet often overlooked issue regarding this structure is worthy of discussion. It is well known that the lossless finite impulse response (FIR) filter pair can be used to model the "standard" birefringent interleaver without material loss, and a "standard" interleaver consisting of n pieces of birefringent crystals implements nth-order Z-transform transfer functions. However, it is seldom mentioned that, this popular birefringent interleaver diagram can not represent arbitrary nth-order Z-transform functions of a lossless FIR filter pair. In other words, for an nth-order lossless FIR filter whose transfer function is derived from signal processing theory, it might not be feasible with the standard birefringent wavelength interleaver diagram. This fact makes it difficult to apply signal processing techniques to birefringent wavelength interleaver design. In this article, we present an alternative birefringent wavelength interleaver diagram to solve this problem.