Wavelength division multiplexed optical networks

DETAILED DESCRIPTION FIG.
1 shows schematically a 16 channel ADM 10 illustrative of an embodiment of the invention.
Of course, fewer or more channels are feasible.
An input waveguide, typically an optical fiber 12, serves as the input of the ADM.
An optical circulator with ports 14A, 14B and 14C is included in the input path for reasons to be discussed later.
The input supplies by way of port 14A a sixteen channel input AWGR 16 advantageously of the kind to be described with reference to FIG.
2.
Sixteen optical waveguides 18A-18P, typically planar waveguides, interconnect the input AWGR to the output AWGR 20 also to be described with reference to FIG.
2 and its output comprises the output waveguide 22, typically an optical fiber.
A directional coupler 24 is coupled to the output waveguide 22 by means of which optical signals of channels to be added are introduced into the waveguide 22 for travel to the next node in the optical network.
Each of the waveguides 18A-18P between the input and output AWGRs includes along its wave path an optical switch 26A-26P, advantageously a MEMS switch of the kind shown in FIGS.
3 and 4.
When closed, as with switches 26A-26D, a switch permits any optical signal exiting an output wave path of AGWR 16 to pass through to an input wavepath of AWGR 20 with minimum loss for further travel along output waveguide 22.
When open, as with switches 26E-26L, a switch reflects, desirably with high efficiency, an incident optical signal back through AGWR 16 to exit at the input of AGWR 16 from which it passes into port 14B of circulator 14 and exits at port 14C to enter into waveguide 28, which typically can be an optical fiber, for further independent travel.
Such a signal corresponds to a dropped channel.
Wavepaths 18M-18P are provided with three dB couplers so that half of the signal power in each of these passes through the closed switch in its wavepath to the input of waveguide 22.
The other half of the signal power in wavepaths 18M-18P that is abstracted by the 3 db couplers passes out in waveguides for use for local reception