Optical waveguides – With optical coupler – Switch
Reexamination Certificate
1999-06-24
2001-09-18
Lee, John D. (Department: 2874)
Optical waveguides
With optical coupler
Switch
C385S003000, C385S017000
Reexamination Certificate
active
06292599
ABSTRACT:
TECHNICAL FIELD
The invention relates to an optical wavelength selective device, and more particularly to a wavelength selective switch for re-routing wavelength channels in an optical network, in which each wavelength channel can be re-routed separately and independently on the other wavelength channels. The invention also relates to a method for re-routing wavelength channels in an optical network.
STATE OF THE ART
To be able to further increase the capacity on already existing optical networks, there are a number of different known methods. One way is to use so-called wavelength division multiplex (WDM) technology for improving the degree of operation of available bandwidth connection an optical fibre in the optical network. To be able to increase the flexibility of the network, devices which can provide re-routing of traffic in the optical network are necessary. Such devices for re-routing traffic are also suitable for employing the network in the most effective way as possible and at interruption in the network. To be able to provide re-routing for each wavelength channel individually, wavelength selective switches are required.
In “Wavelength Division Multiplexer with Photoinduced Bragg Gratings Fabricated in a planar Lightwave Circuit Type Asymmetric Mach Zehnder Interferometer on Si”, Y. Hibino et al, IEEE Photonics Technology Letters, Vol. 8, No. 1, January 1996, 99 84-86 an optical element is disclosed in which Bragg-gratings and phase control elements are used in a Mach Zehnder interferometer. The proposed applications are wavelength division multiplexing and wavelength division de-multiplexing.
However, the above disclosed switch cannot be used as a wavelength selective switch. If the above disclosed device is to used for add/drop of more channels, a number of devices are required equal to the number of handled add/drop pairs. This type of device is, relatively hard to re-configure, i.e. inflexible.
The problems with above the described technology as regards wavelength selective switches is that these require very large complicated structures or several components, which results in large power losses and a high cost.
DISCLOSURE OF THE INVENTION
To increase the capacity in an optical transfer system, a plurality of different methods may be employed, for instance, wavelength division multiplexing, transmission channels are multiplexed and de-multiplexed on different carrier wavelengths to and from an information flow. Said multiplexing and de-multiplexing require optical wavelength selective devices. It can also be desirable to determine transmission path through the optical network for each wavelength channel individually. For that purpose, switching components are required with wavelength selective properties.
One problem with known wavelength selective switches is that these contribute to large power losses.
Another problem with known wavelength selective switches is that known wavelength selective switches have a relatively complicated structure and in all known cases a relatively large number of different elements.
Yet another problem is that known wavelength selective switches are relatively expensive to manufacture based on above disclosed complicated structure and the number of comprised components.
The present invention tackles the problem by means of a wavelength selective switch comprising at least two multi-mode waveguides, at least one wavelength selective cross-connection structure, at least two phase control elements and at least four connection waveguides. The wavelength selective cross-connection structure is arranged between a first and a second multi-mode waveguide. Said first multi-mode waveguide is provided with at least one access waveguide on a first side and at least two access waveguides on a second side and said second multi-mode waveguide is provided with at least two access waveguides on a first side and at least one access waveguide on a second side. Said wavelength selective cross-connection structure is provided with at least two access waveguides on a first and a second side.
At a wavelength selective cross-connection structure, a first access waveguide on the second side of the first multi-mode waveguide is arranged to a first access waveguide on the first side of the wavelength selective cross-connection structure via a first connection waveguide, a second access waveguide on the second side of the first multi-mode waveguide arranged to a first access waveguide on the second side of the wavelength selective cross-connection structure via a second connection waveguide, and a second access waveguide on the first side of the wavelength selective cross-connection structure is arranged to a first access waveguide on the first side of the second multi-mode waveguide via a third connection waveguide and a second access waveguide on the second side of the wavelength selective cross-connection structure is arranged to a second access waveguide on the first side of the second multi-mode waveguide via a fourth connection waveguide.
The phase control elements are arranged in the connection waveguides on one of the sides of the wavelength selective cross-connection structure.
At a cross-connection structure there are two different so-called Mach-Zehnder paths for each particular wavelength in the optical signal. A first Mach-Zehnder path goes from a first access waveguide on the second side of the first multi-mode waveguide to the second access waveguide on the first side of the second multi-mode waveguide via the first and the fourth connection waveguide and via the wavelength selective cross-connection structure for wavelengths which are transmitted through the cross-connection structure.
A second Mach-Zehnder path goes from a second access waveguide on the second side of the first multi-mode waveguide to the first access waveguide on the first side of the second multi-mode waveguide via the second and the third connection waveguide and via the wavelength selective cross-connection structure for wavelengths which are transmitted through the cross-connection structure.
A third Mach-Zehnder path goes from a first access waveguide on the second side of the first multi-mode waveguide to a first access waveguide on the first side of the second multi-mode waveguide via the first and the third connection waveguide and via the wavelength selective cross-connection structure for wavelengths which are reflected by the cross-connection structure.
A fourth Mach-Zehnder path goes from a second access waveguide on the second side of a first multi-mode waveguide to the second access waveguide on the first side of the second multi-mode waveguide via the second and the fourth connection waveguide and via the wavelength selective cross-connection structure for wavelengths which are reflected by the cross-connection structure.
Only wavelengths which are reflected in any cross-connection structure can be controlled actively, i.e. the wavelength which goes via the third or fourth Mach-Zehnder path as disclosed above.
Said Mach-Zehnder paths are preferably equal in length in the wavelength selective switch element according to the invention.
Thus, for a wavelength selective cross-connection structure there are two different Mach-Zehnder paths for wavelengths which are reflected by the cross-connection structure and two different Mach-Zehnder paths for wavelengths which are transmitted by the cross-connection structure. Thus, for two different Mach-Zehnder paths for two different wavelengths and for N wavelength selective cross-connection structures there are 2×N different Mach-Zehnder paths for N wavelengths.
The first and the second multi-mode waveguide preferably have the same length-width ratio when they are of the same type, e.g., a 2×2 type. In an embodiment according to the invention the multi-mode waveguide can comprise a MMI waveguide.
At two or more wavelength selective cross-connection structures for each wavelength selective cross-connection structure, two phase control elements and two connection waveguides are added. Each wavelength selecti
Burns Doane Swecker & Mathis L.L.P.
Connelly-Cushwa Michelle R.
Lee John D.
Telefonaktiebolaget LM Ericcson (publ)
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