Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2001-07-17
2004-10-19
Ullah, Akm Enayet (Department: 2874)
Optical waveguides
With optical coupler
Switch
C385S018000, C385S020000, C385S022000
Reexamination Certificate
active
06807329
ABSTRACT:
FIELD OF THE INVENTION
This invention is generally in the field of switching techniques and relates to a method and device for all-optical switching.
BACKGROUND OF THE INVENTION
Optical communication networks require cross-connect or switching mechanisms enabling direction, diversion, multiplexing or broadcasting (multicasting) of a plurality of information channels in a manner to meet the requirements of the network. Optical switches can also be used in Dense Wavelength Division Multiplexing (DWDM) telecommunication systems for routing the information, enabling optical add/drop multiplexing (OADM), as well as for protection purposes.
Switching modules have various forms, such as structures whereby N input channels are directed simultaneously to M output ports in various configurations. In a dynamic switch, this operation can be reshuffled in time.
The so-called “all-optical switches” are capable of performing the switching function without converting the signals from the optical domain to the electrical domain and back. Such an optical switch is disclosed, for example, in U.S. Pat. No. 6,041,151. This switch device utilizes a double refracting crystal operating as a polarizing beam displacer in conjunction with a controllable half wave gate that is able to rotate the polarization of an incident light beam by 90 degrees in accordance with a control input.
SUMMARY OF THE INVENTION
There is accordingly a need in the art to facilitate a switching technique by providing a novel all-optical switch device of a simple and compact design.
An all-optical switch device according to the invention does not depend on optics-electronics-optics (O-E-O) conversion, and does not need movement of the elements of the switch device. The switch device is characterized by fast operation exhibiting low insertion loss and minimal cross talk between output channels. The switch device is based on the electro-optic effect exhibited in a material of the kind capable of dynamically producing a phase delay for each polarization component of an incident light beam as a function of a voltage applied to the material. Such a material may be Lead Lanthanum Zirconate Titanate (PLZT), BSO or LiNbO
3
. The varying phase delay may result in a controllable polarization rotation.
The main idea of the present invention consists of designing a switch device having a polarizing beam splitting surface, controllable polarization rotating (CPR) means, and beam directing means. The CPR and/or beam directing means may be separate elements accommodated at opposite sides of the polarizing beam splitting surface. The polarizing beam splitting surface may be the surface of a beam splitter (e.g. cubic beam splitter). The CPR and beam directing means may be integral with the beam splitter, by making the entire beam splitter or respective portions thereof from a polarization rotating material and making respective surfaces of the beam splitter reflective. Alternatively, the CPR and beam directing means may be separate elements accommodated at respective surfaces of the beam splitter.
An input beam (either unpolarized or of a specific polarization) impinges onto the polarizing splitting surface, and can be split into two linearly polarized beam components (in the case of unpolarized input beam), which propagate along different optical paths. The beam components of the input beam interact with the CPR means and beam directing means, and return back to the polarizing beam splitting surface, where at least one output beam (e.g., of no particular polarization state, namely, consisting of different polarization components) is produced. It should be understood that, when a polarized input beam is used, the device of the present invention provides for directing this beam to a selected one of two output channels.
If the entire beam splitter is made of a polarization rotating material, then, in the operative state of the beam splitter, the different polarization components of an input beam undergo polarization rotation prior to being split by the polarizing beam splitting surface of the beam splitter. Depending on the current mode of the CPR means (which may and may not be integral with the beam splitter), namely, operative or inoperative modes of the CPR, the output beam can be directed towards one of the two output channels of the device, or two output beam components can be directed towards both output channels, respectively. The CPR in the inoperative and operative modes thereof does not affect and does affect, respectively, the polarization of the beam passing therethrough.
The controllable portion rotating medium is shiftable between its inactivated and activated states by application of an electric field to the medium. Depending on the type of the medium being used, one of its states presents an operative mode of the medium, and the other state presents an inoperative mode of the medium. Polarization rotating medium of the kind based on the electro-optic effect (e.g., ferroelectric crystals or ceramics) is in the operative mode (affecting the polarization of a beam), when in the activated state of the medium. The polarization rotating medium of the kind utilizing LC materials is in its inoperative mode (i.e., does not affect the polarization state of a beam), when in the activated state of the medium, and is in its operative mode (i.e., affects the polarization state of a beam), when in the inactivated state of the medium.
Hence, the terms “inoperative mode” and “operative mode” of a CPR medium are associated with effect of the medium with respect to an incident beam, irrespective of the terms “activated” and “inactivated” states which are associated with the application of an electric field to the CPR. In the inoperative mode of the CPR, it does not affect the polarization of the beam, and in the operative state of the CPR, it affects the polarization of the beam.
Thus, according to one aspect of the present invention, there is provided a switching method for selectively directing an input beam to at least one of two output channels, the method comprising the steps of:
(i) providing incidence of the input beam onto a polarizing beam splitting surface to thereby enable splitting of the input beam into two beam components of different polarizations propagating along different optical paths;
(ii) passing the input beam components of different polarizations through a controllable polarization rotating medium capable of affecting the polarization of each of the beam components; and
(iii) directing the beam components that have passed through said medium onto said polarizing surface, thereby producing at least one output beam propagating towards at least one selected output channel, depending on a current mode of the polarization rotating medium.
It should be understood that the input beam may be unpolarized, namely a randomly polarized beam (of no specific polarization state), containing beam components of different polarizations. Alternatively, the input beam may have a specific polarization. In this case, the interaction of the input beam with the polarizing beam splitting surface will result in the beam propagation along a specific optical path.
It should also be understood that the input beam may pass the CPR medium prior to being split into the two beam components of different polarizations. This may be implemented by utilizing a beam splitter having the polarizing beam splitting surface and being made from a controllable polarization rotating material.
According to another aspect of the present invention, there is provided an all-optical switch device operable for selectively directing an input beam to at least one of two output channels, the device comprising:
(a) a polarizing beam splitting surface capable of splitting an input beam into two beam components of different polarizations and directing the split beam components to propagate along different optical paths, and capable of combining two beam components of different polarizations to produce at least one output beam;
(b) controllable polarization rotating means accommodated
Goldenberg Efraim
Konforti Naim
Miron Yehuda
Shabtay Gal
Zalevsky Zeev
CIVCOM Devices & Systems Ltd.
Fenster & Company
Ullah Akm Enayet
Wood Kevin S.
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