Optical waveguides – With optical coupler – Particular coupling function
Reexamination Certificate
1998-07-08
2001-04-03
Palmer, Phan T. H. (Department: 2874)
Optical waveguides
With optical coupler
Particular coupling function
C385S009000, C385S010000, C385S037000
Reexamination Certificate
active
06212314
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to opto-mechanical electronic devices, and more particularly to a class of such devices that involves hybrid integrated micro-optic mechanics.
BACKGROUND OF THE INVENTION
Integrated optics is a well-established technology using lithography to define waveguiding paths on the surface of a planar substrate to create a variety of passive and active components. As used herein, passive components are those that route light without detection and retransmission of data signals.
Passive integrated optics devices provide robust components for power splitting, wavelength routing arid similar functions. Active integrated optics devices typically use a refractive index change from thermo- or electro-optic effects to switch light beams between optical paths.
Optomechanical components potentially provide electro-mechanical latching with no power dissipation. Micro-electro-mechanics is a rapidly developing field that exploits lithographic mass fabrication techniques to build miniature mechanical systems ranging in size from millimeters to microns. As used herein, a micromechanical element is a miniature element that has been shaped by lithographic patterning followed by deposition of and/or etching a workpiece, generally a multilayer structure of which several layers typically are of polysilicon. Some of the polysilicon layers are releasable by removal of intermediate sacrificial layers to form mechanical structures. Such an element is then used in a micro-electro-mechanical system (MEMS), for example in micromechanical optics. MEMS devices are available from many sources, as for example, the MEMS Technology Application Center at North Carolina (MCNC). There is now an extensive body of literature relating to such technology and its application to optical switching. Typical of such literature is a paper entitled “MEM'S the Word for Optical Beam Manipulation” published in
Circuits and Devices,
July 1997, pp. 11-18.
It is normally difficult to combine the properties of micro-mechanical optics and integrated optics in a single device because of the incompatibility of their materials and in their processing.
The present invention involves a new class of devices that are more compatible to the combining of the two technologies of micro-mechanical optics and integrated optics for use in hybrid integrated micro-opto-mechanics (HIMOM).
SUMMARY OF THE INVENTION
The basic principle of a new class of devices that use hybrid integrated micro-optics mechanics involves coupling to an optical waveguide for affecting an optical signal traveling therein through the evanescent electric field that accompanies the optical signal in the surrounding waveguide cladding as the optical signal travels along the waveguide. A basic advantage of a device that uses this approach is that it allows micro-mechanical switching and routing of the optical signal without the need for coupling the optical signal out of the waveguide, thereby increasing the efficiency and robustness of the resulting device, while lessening the need for the compatibility of the materials used for switching or waveguiding. Basically, this invention involves the movement of an element, such as a membrane, of a MEMS controllably in and out of the evanescent field of an optical signal traveling along a waveguide to affect its travel along the waveguide. Since the effect is stronger the closer the movable element is to the waveguide, for maximum effect the element should get as close as is feasible to the waveguide, typically as close as a fraction of a micron.
For an optical signal of the kind presently used in optical communication systems, the evanescent field does not extend in significant strength beyond 0.1 and 0.5 microns from the waveguide. This limited penetration into the space surrounding the waveguide would make macro-mechanical techniques ineffective in using the evanescent field for control purposes. Moreover, for maximum effect, it is advantageous to thin, in the region of interaction, the cladding that is normally used to cover the waveguide.
In a simple illustrative embodiment of the invention, a MEMS membrane is positioned adjacent a waveguide and controllably inserted in and out of the evanescent field of an optical signal traveling along the waveguide for scattering the optical signal and attenuating desirably further travel along the waveguide.
In another illustrative embodiment of the invention, a waveguide interferometer switch, a section of a MEMS that is readily deformable electromechanically is moved in, from out of, near contact with a selected one of two arms of a Mach-Zender interferometer so that then there is evanescent coupling by such arm with the guided mode in the dielectric cladding surrounding the waveguide. This coupling changes the effective index of refraction, and therefore the optical length, of the affected arm. Such a change affects the relative phase of the light waves in the two arms and produces an unequal division of the power of the light wave between the two output ports of the interferometer.
In another illustrative embodiment, a device that adds or drops selectively a wavelength channel in a wavelength multiplex division (WDM) system uses evanescent coupling to modify the reflective properties of MEMS optical gratings to add or drop a channel of a particular wavelength from a group of signal channels of different wavelengths.
In some instances, the MEMS element may even serve to provide some waveguiding.
The invention will be better understood from the following detailed description taken in conjunction with the accompanying drawing.
REFERENCES:
patent: 5854864 (1998-12-01), Knoesen et al.
Lucent Technologies
Palmer Phan T. H.
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