Optical waveguides – With optical coupler – Particular coupling function
Reexamination Certificate
1999-01-19
2001-03-27
Bovernick, Rodney (Department: 2874)
Optical waveguides
With optical coupler
Particular coupling function
C385S039000, C385S015000
Reexamination Certificate
active
06208780
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable.
TECHNICAL FIELD
The present invention is generally related to optical monitoring and, more particularly, is related to a system and method for optical monitoring of multiple channels in a wavelength division multiplexing communications system.
BACKGROUND OF THE INVENTION
Network management in a communications network often requires information relative to the operation of the network. In the case of fiber optic communications networks, it is often desirable to know the precise condition of the optical signals transmitted through an optical fiber to perform channel diagnostics and to control the operation of the network. For example, in an optical fiber used to transmit up to sixteen channels or optical signals, certain information about each optical signal as it is transmitted through the optical fiber is important to ensure that the underlying information of the signal is relayed accurately.
For example, the actual channel presence is an important factor. This is important, for example, to inform a network monitor that a discontinuity has been created that prevents a single channel or multiple channels from being transmitted through the optical fiber. In such a circumstance, a network monitor function may be implemented that routes optical signals around the faulty pathway until the discontinuity is remedied.
Also, the power of each channel is another important factor used to maintain channel equalization. Specifically, the power of the optical signal over a channel may be affected by many different factors inherent in the optical network. In the case of a single fiber, different channels may operate at different power levels a which is undesirable due to the periodical use of optical amplifiers in an optical network and due to other factors. Determining the actual power of the optical signals in an optical fiber for each channel is important in order to determine necessary adjustments in performing channel equalization functions. Other important information may include the noise density across the various channels in an optical fiber as well as any frequency shift experienced by a particular channel.
SUMMARY OF THE INVENTION
The present invention provides for an optical filter, system, and method for detecting optical signals in an optical fiber trunk for purposes of diagnostics and control of a wavelength division multiplexing system using optical fiber network. According to one embodiment, an optical filter comprises a predetermined number N of cascaded Mach-Zender circuits, the optical filter having a predetermined transfer function with a predetermined scanning peak, the cascaded Mach-Zender circuits having an optical input and an optical output. In another embodiment, a system is provided which employs the aforementioned optical filter in which a control circuit is coupled to each of the Mach-Zender circuits that causes a phase shift in the Mach-Zender circuits, thereby allowing the optical filter to scan a predetermined frequency spectrum with the predetermined scanning peak to determine the existence and/or the condition of optical signals within the predetermined frequency spectrum.
In yet another embodiment, the present invention may be viewed as a method for monitoring optical signals in a wavelength division multiplexing system. This method comprises the steps of filtering an optical signal obtained from an optical fiber trunk in a wavelength division multiplexing system with a predetermined number N of cascaded Mach-Zender circuits having a predetermined transfer function with a predetermined scanning peak, the cascaded Mach-Zender circuits having an optical input and an optical output. The method further includes the steps of moving the scanning peak across a predetermined frequency band by adjusting the phase of an optical signal in a branch of each of the Mach-Zender circuits, and finally, measuring the optical signal at predetermined frequency points along the predetermined frequency band.
The present invention has numerous advantages, a few of which include, for example, an integrated optical filter and optical detector circuit which are without moving parts. In addition, the present invention is simple in design, user friendly, robust and reliable in operation, efficient in operation, and easily implemented for mass commercial production.
Other features and advantages of the present invention will become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional features and advantages be included herein as within the scope of the present invention.
REFERENCES:
patent: 5596661 (1997-01-01), Henry et al.
patent: 5680490 (1997-10-01), Cohen et al.
patent: 5712716 (1998-01-01), Vanoli et al.
patent: 5852505 (1998-12-01), Li
patent: 6031948 (2000-02-01), Chen
Kuznetsov, M. Cascaded Coupler Mach-Zehnder Channel Dropping Filters for Wavelength-Division-Multiplexed Optical Systems, Lightwave Technology, Journal of, vol. 12 Issue: 2, Feb. 1994 pp. 226-230.
Li Yuan
Wang Yan
Bovernick Rodney
Lucent Technologies - Inc.
Song Sarah U
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