The present invention relates to an optical multi-wavelength selective device, more precisely a multi-wavelength selective switch for rerouting and switching of wavelengths in an optical network, in which each wavelength may be separately rerouted. The invention also comprises a method for rerouting and switching or add/drop multiplexing of wavelengths in an optical network.
In order to further increase the capacity on existing optical networks a number of methods are known. One means is to use so called wavelength division multiplexing (WDM) technique in order to improve the degree of utilization of the available bandwidth. In order to increase the network flexibility, devices able to reroute traffic in the optical network are necessary. Such devices for rerouting of the traffic are also suitable in order to utilize the network as efficiently as possible, and in case of network interrupts.
In xe2x80x9cWavelength Division Multiplexer with Photoinduced Bragg Gratings Fabricated in a Planar Lightwave Circuit Type Asymmetric Mach Zehnder Interferometer on Sixe2x80x9d Y. Hibino et.al., IEEE Photonics Technology Letters, Vol. 8, No. 1, January 1996 an optical element is described in which Bragg grating and a phase control element is used in a Mach Zehnder interferometer. The considered applications are wavelength division multiplexing and wavelength division de-multiplexing.
The above described device can however not be used as a multi-wavelength selective switch. If the described device is to be used for add/drop of several channels, as many devices are needed as the number of handled add/drop pairs. This type of device is comparatively hard to reconfigure, i.e. it is a non-adaptable device.
In K. W. Cheung, D. A. Smith, J. K. Baran, J. J. Johnson: xe2x80x9cWavelength-selective circuit and packet switching using acousto-optic tunable filtersxe2x80x9d Globecom ""90, pp 1541-1547, 1990, a manner is described of solving multi-wavelength selective rerouting of wavelength channels separate and independently of each other based on opto-aucoustic switches. This type of rerouting typically uses a number of micro-seconds, which may be a problem in high speed transmissions.
In R. C. Alferness, L. L. Buhl, U. Koren, B. I. Miller, M. Young, T. L. Koch.xe2x80x9d Broadly tunable InGaAsP/InP buried rib waveguide vertical coupler filterxe2x80x9d, Techn. Dig. Integrated Photonics Research, post-deadline paper, pp. 33-36, 1991 a tunable wavelength selective grating-assisted directional coupler comprising two waveguides having different effective refractive indexes and a grating described. This directional coupler can couple a wavelength from the first waveguide to the second waveguide.
The problem present in the known technique as regards multi-wavelength selective switches and re-directional devices is this demand very big and complicated structures or more components, which results in big power losses and high costs, or in that they can not be used in connection with high speed transmissions.
In order to increase the capacity in an optical transmission system several know methods may be used. In wavelength division multiplexing the transmission channels are multiplexed and de-multiplexed on different carrier wavelengths to respectively from an information flow. Said multiplexing and de-multiplexing demands optical multi-wavelength selective devices. It may also be desirable to change the transmission route through the optical net for certain wavelength channels. For this purpose components are needed having multi-wavelength selective performance characteristics such as a multi-wavelength selective switch.
A known problem related to multi-wavelength selective switches may be that these contribute to big power losses.
Another problem is that all by us known multi-wavelength selective switches known to us exhibited a relatively complicated structure or a great number of components.
Another problem is that known multi-wavelength selective switches are relatively expensive to manufacture depending on said complicated structures or the number of components comprised.
Yet a problem is that certain known multi-wavelength selective switches exhibit relatively slow switching speeds, typically a number of microseconds.
The present invention approaches the said problem through a multi-wavelength selective switch in the form of a directional coupler structure comprising two waveguides arranged having different effective refractive index. The waveguides are at one section arranged in the proximity of each other, such that an optical field in each of the waveguides may overlap the other wherein at least one grating is arranged for co-directional coupling.
In a method according to the invention for switching and re-direction of optical wavelengths in an optical network one branch in a directional coupler structure comprising optical wavelengths is excited. The optical wavelengths are thereafter transmitted through said branch to the directional coupler structure. The optical wavelengths are thereafter transmitted through a section where the waveguides are arranged in the proximity of each other whereby none or at least one wavelength is influenced by at least one in this section arranged grating for co-directional coupling and is coupled to the other waveguide.
In a second embodiment according to the invention at least one wavelength selective amplifier is comprised in at least one branch of the directional coupler structure, e.g. in the form of a distributed-Bragg-reflector-amplifier.
The object of the present invention is to obtain a multi-wavelength selective switch, the structure of which is so simple and compact as possible, such that the manufacturing thereby may be reduced compared to the available technique, and in which the switching speed still is relatively high.
An advantage of the present invention is that the power losses relatively seen may be kept low.
A further advantage of the present invention is that its remaining performance characteristics such as crosstalk and the like may be improved compared to know technique.
Still a further advantage of the present invention is that signal splitting only is performed when absolutely necessary.
The invention will now be described further using the preferred embodiments and with reference to the appended drawings.