A design methodology to simplify WDM Benes photonic switches

In wavelength division multiplexing (WDM) networks, wavelength cross-connect (WXC) is an important device which consists of space switching elements (SSEs) and wavelength converters (WCs) to provide the switching functionality of connection between its inputs and outputs. Wavelength-exchange optical crossbar (WOC) is a novel photonic switching element which enables performing space switching and wavelength converting in a single-step. By replacing some conventional 2×2 space switching elements with WOCs, a new class of photonic switch architectures called wavelength-exchanging cross connect (WEX) has been proposed to eliminate all WCs used in all of the existing WXC designs. In order to achieve nonblocking connection, the photonic switch architectures are designed to provide connections of full-permutation, which indicate that the outputs are all possible permutations of the inputs. We observe that some permutations, such as to mutually exchange the wavelengths within the same fiber, are equivalent and hence may not be necessary. Since the number of connection permutations of a photonic switch is proportional to its hardware complexity, the switch architecture with only sufficient permutations consequently has low complexity. We propose a design methodology to construct such new WDM photonic switches based on Benes WEX type with 2 fibers, by eliminating some switching elements whose control states are always in bar or cross for sufficient permutations. Our study results show that (i) in cases of Benes WEX switch with 2 wavelengths in each fiber, 2 out of 6 switching elements can be eliminated; (ii) in cases of Benes WEX switch with 4 wavelengths in each fiber, 4 out of 18 switching elements can be eliminated.

I. Introduction

In wavelength division multiplexing (WDM) networks, wavelength cross-connect (WXC) [1]–[8] is an important device which provides the switching functionality of connections between its inputs and outputs. Basically, a WXC consists of two types of main elements: space switching elements (SSEs) and wavelength converters (WCs). SSEs are capable of connecting input ports to the required output ports without performing any wavelength converting on input signals [9]. WCs are usually employed to relax the wavelength continuity constraint and hence improve the blocking performance of the networks [10]. As the number of wavelengths per fiber increases, the numbers of both SSEs and WCs of a WXC grow rapidly. Thus, to reduce the hardware complexity of WXC architecture is a large challenge [11].