Optical waveguides – With optical coupler – Particular coupling structure
Reexamination Certificate
1999-08-13
2001-08-21
Healy, Brian (Department: 2874)
Optical waveguides
With optical coupler
Particular coupling structure
C385S042000, C385S043000, C385S051000, C385S123000, C356S340000, C065S385000, C065S406000, C065S408000
Reexamination Certificate
active
06278821
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a Mach-Zehnder interferometer for an optical communication system. More particularly, the present invention is directed to a Mach-Zehnder interferometer, formed from segmented cane structures, which provides access to the constituent optical fibers during the fabrication process.
2. Technical Background
There is an emerging need for narrowband wavelength division multiplexing (WDM) couplers and filters. Such optical devices are needed in the 1550 nm window for modifying the gain spectrum of erbium fiber amplifiers. These devices will also be widely used in trunk lines as well as in fiber-to-the-subscriber communication architectures. When used in these applications, these optical devices will need to be environmentally stable, unaffected by large temperature changes, and very reliable.
There is also a need for both wavelength tunable optical devices and fixed wavelength optical devices. In an all optical network, for example, the optical device can be tuned at the receiver end in order to detect the desired incoming signal. In a second approach, tunable lasers are used to send a plurality of signals, and the desired signal is detected by employing a receiver having a fixed filter. The transmission system could also employ both fixed lasers and filters. The wavelength separation capabilities of the filters for these systems needs to be on the order of tens of nanometers to as small as less then one nanometer.
The Mach-Zehnder interferometer is known for its narrowband wavelength filtering capabilities. It has been proposed that filters having pass bands as narrow as 1 nm be formed by connecting two evanescent couplers with unequal optical path lengths between them. However, it is difficult to achieve reproducibility and environmental stability with this approach, since the connecting fibers are subject to external destabilizing conditions such as temperature changes and random bending forces.
One technique for stabilizing a Mach-Zehnder interferometer is disclosed in U.S. Pat. No. 5,295,205, which is incorporated herein by reference, and commonly owned by the assignee of the present invention. As taught by this patent, the Mach-Zehnder interferometer is formed by threading first and second dissimilar optical fibers through the central bore of a continuous glass tube. The tube is evacuated and heated to collapse it onto the fibers. The tube is further heated and stretched at two spaced locations to form two couplers that are joined by the two optical fibers.
While the resulting Mach-Zehnder structure does improve the environmental stability of the optical device, this structure is still subject to thermal instability. Additionally, this structure does not allow access to the optical fibers in a region between the two coupling regions, known as the phase shift region. In view of these limitations of known Mach-Zehnder interferometers, it is desirable to provide a structure for realizing a Mach-Zehnder device which is highly insensitive to large temperature variations, or athermalized, and also allows physical access to the optical fibers within the phase shift region of the interferometer.
SUMMARY OF THE INVENTION
In accordance with the present invention, a Mach-Zehnder interferometer for performing an optical function on a plurality of optical fibers is disclosed. The interferometer includes a first cane segment surrounding the optical fibers. The first cane segment forms a first optical coupling region. The interferometer also includes a second cane segment surrounding the optical fibers. The second cane segment forms a second optical coupling region. A phase shift region is formed by a discontinuity between the first and second cane segments for exposing the optical fibers. The optical fibers are suspended between the first and second cane segments within the phase shift region. A substrate is provided for supporting the optical fibers within the phase shift region.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various features and embodiments of the invention, and together with the description serve to explain the principles and operation of the invention.
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Carberry Joel P.
Krol Mark F.
Miller William J.
Morrell Mark L.
Corning Incorporated
Harness & Dickey & Pierce P.L.C.
Healy Brian
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