Multi-wavelength cross-connect optical network

Details Multi-wavelength cross-connect optical network Multi-wavelength cross-connect optical network

1999-11-22

2001-01-16

Pascal, Leslie (Department: 2733)

Optical: systems and elements

Deflection using a moving element

Using a periodically moving element

C359S199200

Reexamination Certificate

active

06175432

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to optical communication systems, and more particularly, to optical multi-wavelength cross-connect networks for wavelength division multiplex (WDM) optical communications.
2. Statement of the Problem
WDM optical communications systems that can carry information at rates up to terabits per second are becoming the next wave in optical communications development. In current WDM systems, information is optically coded within each of the WDM channels and the network is linked using a point-to-point architecture. Signal routing and switching are performed electronically (i.e., optical information is translated back to electronic format and then processed at each network node). As data rates increase, these opto-electronic and electro-optic conversions are becoming the bottleneck for the network. To improve the efficiency and reduce to cost of networks, routing and switching performed in the optical domain are preferred.
Thus, national and international researches for all-optical networks have become the current focus in the fiber optics industry. A recent technical journal, “Multi-Wavelength Optical Technology and Networks,”
Journal of Lightwave Technology
(vol. 14, no. 6, 1996), has gathered about 40 papers reviewing the current status of all-optical networks. Three basic WDM cross-connect networks were listed (shown herein as prior art in
FIG. 1
) as the basic building blocks for WDM networks. Recently, a national Optical Multi-Wavelength Optical Networking (MONET) Consortium has been formed to study all-optical networks. In its recent demonstration, three all-optical network test beds have been constructed: a WDM long distance test bed; a WDM cross-connect test bed; and a local-exchange test bed (R. C. Alferness, el. al., “MONET: New Jersey demonstration network results,” Optical Fiber Conference 1997, Paper WI1, and “All Optical Test Beds Prove National Networking,”
Lightwave
(April 1997)). Wavelength cross-connect networks using array waveguide gratings (AWG) together with opto-mechanical space switches and LiNbO3-based cross-connect switches have been used in such networks. International efforts, such as the ACTS (Advanced Communications Technologies and Services) program launched by the European Commission projects, are specifically addressing the problems of trans-European optical transport networks using WDM (M. Berger et al., “Pan-European Optical Networking using Wavelength Division Multiplexing,”
IEEE Comm. Mag.
p. 82, (April 1997)). A similar architecture to the MONET project is proposed, except another approach using the wavelength conversion technique is also planned in this European effort.
3. Solution to the Problem
The present invention uses two arrays of unique 1×N wavelength switches to form the wavelength cross-connect network. Because the wavelength filtering and optical switching are accomplished within the same device, the switching elements needed to perform the wavelength cross-connect are reduced and optimized. Furthermore, because the wavelength switch has a built-in complementary spectra characteristic, where a wavelength-slicing concept is used, wavelength collision can be avoided.
SUMMARY OF THE INVENTION
The present invention provides an optical cross-connect network for wavelength routing of optical channels between two arrays of optical fibers carrying WDM signals using interconnected arrays of optical wavelength switches based on combinations of a 1×2 wavelength switch architecture. For example, a cross-connect network can be made by interconnecting two arrays of 1×4 wavelength switches, each of which is made by combining three 1×2 wavelength switches. A tree structure of 1×2 wavelength switches can also be used. Each 1×2 optical wavelength switch has a first polarization separation element (e.g., a birefringent element) that decomposes and spatially separates the input WDM signal into two orthogonally-polarized beams. A first polarization rotator selectably rotates the polarization of one of the beams to match the polarization of other beam, based on an external control signal. A wavelength filter (e.g., stacked waveplates) provides a polarization-dependent optical transmission function such that the first beam decomposes into third and fourth beams with orthogonal polarizations, and the second beam decomposes into fifth and sixth beams with orthogonal polarizations. The third and fifth beams carry a first spectral band at a first polarization and the fourth and sixth beams carry a second spectral band at an orthogonal polarization. A polarization-dependent routing element (e.g., a second birefringent element) spatially separates these four beams into two pairs of horizontally polarized and vertically polarized components. A second polarization rotator rotates the polarizations of the beams so that the third and fifth beams, and the fourth and sixth beams are orthogonally polarized. A polarization combining element (e.g., a third birefringent element) recombines the third and fifth beams (i.e., the first spectral band), and also recombines the fourth and sixth beams (i.e., the second spectral band) which are coupled to the output ports based on the control state of the wavelength switch.


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