NxN switching arrangement of two planar arrays without waveguide crossings

#This invention relates to N×N optical crossconnect switches, and more particularly, to an N×N crossconnect switching arrangement of two planar arrays without waveguide crossings.

#In high capacity optical networks, an essential device is the N×N crossconnect switch. The function of this device is to provide at each node full connectivity among several incoming fibers, each carrying several wavelength channels. The switch must be nonblocking, and it must be fast and efficient [1-3]. These properties can be realized with minimal depth 2log N and low crosstalk by using a crossbar arrangement of binary trees, consisting of 2N(N−1)1×2 and 2×1 elements [1-3]. This approach, however, is difficult to realize in integrated form on a single wafer, because of its large number of waveguide crossings.

#What is needed is an N×N crossconnect switch, which can be implemented without the use of waveguide crossings.

#In the drawings,

#FIG. 1 illustrates an imaging arrangement of two periodic slabs.

#FIG. 2 shows an array element combined with an input 1×N switch.

#In the following description, identical element designations in different figures represent identical elements. Additionally in each element designation, the first digit refers to the figure in which that element is first located (e.g., 104 is first located in FIG. 1).

#1. Imaging Arrangement of Two Arrays of Binary Trees

#The classical N×N crossconnect switch arrangement consists of a 1×N switch array and an N×1 switch array, which requires a total of N2 connections, between the various switches. The N2 connections make the arrangement difficult to realize in integrated form for large N on a single wafer, because of the large number of waveguide crossings required by the various connections. In the present application we propose, as a remedy to this problem, a planar imaging arrangement of two arrays combined with a cylindrical reflector. We first describe an equivalent arrangement without cylindrical reflector. Thus, we initially assume a planar free-space between the two arrays. The following configuration is closely related to the confocal arrangement used in [4]. Here we consider an arrangement of switches, but the following considerations also apply to any crossbar switching arrangement, for instance including wavelength routers instead of ordinary 1×N and N×1 switches. Thus a variety of such switching arrangements can be constructed, for instance by using ordinary 1×N and N×1 switches for both arrays, a 1×N switch for the first array and wavelength routers for the second array, wavelength routers for the first array and N×1 switches for the second array, or using wavelength grating routers for both arrays. The 1×N and N×1 switch arrangements may be implemented as described in pending U.S. patent application Ser. No. 09/687,346, filed on Oct. 13, 2000 and entitled “LARGE N×N OPTICAL SWITCH USING BINARY TREES.” The wavelength routers may be implemented as described in U.S. Pat. No. 5,136,671, issued on Aug. 4, 1992 and entitled “OPTICAL SWITCH, MULTIPLEXER, AND DEMULTIPLEXER.”