Optical waveguides – With optical coupler – Plural
Reexamination Certificate
1999-03-18
2001-02-06
Palmer, Phan T. H. (Department: 2874)
Optical waveguides
With optical coupler
Plural
C385S043000, C385S016000, C385S014000, C359S199200
Reexamination Certificate
active
06185345
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to method and apparatus for providing ultra-stable optical wavelength division multiplexing and/or demultiplexing.
BACKGROUND OF THE INVENTION
The implementation of a low cost, low insertion loss, dense wavelength division multiplexer (DWDM) or demultiplexer (DWDD) is of great advantage in high capacity optical systems. Unfortunately, most DWDM of DWDD devices have high insertion loss or high cost associated with them.
U.S. Pat. No. 5,809,190 (Chen), issued on Sept. 15, 1998, discloses an unbalanced Mach-Zehnder (UMZ) interferometer capable of accomplishing dense wavelength division (DWD) multiplexing with low insertion loss. More particularly, Chen discloses apparatus and method of making a fused dense wavelength division multiplexer (DWDM) using a fused-biconical taper technique. The DWDM comprises multiple Multi-window Wavelength Division Multiplexers (MWDMs) which are cascaded in several stages where the MWDMs in each stage have an identical window spacing. For an N-channel DWDM, there are a predetermined plurality of DWDMs in each stage, and the stages are cascaded to form the MWDM. Unfortunately, the UMZ is by nature sensitive to temperature fluctuations of the environment, and typical temperature fluctuations expected in the terminal environment can render the DWDM device unusable. Therefore, the disclosed UMZ device is unstable because of the occurrence of variations in phase due to temperature fluctuations. A similar device is also discussed in an article titled “Fused-Coupler Technology for DWDM Applications” by F. Gonthier in the magazine
Fiber Optic Product News
, September 1998, at pages 54 and 56.
U.S. Pat. No. 5,647,037 (Byron), issued on Jul. 8, 1997, discloses an optical band-pass filter with tunable performance achieved by adding a variable time delay in one of two output legs of a 3 dB splitter. Both output legs containing separate matched Bragg grating reflectors at separate predetermined distances from a central optical coupling region of the filter to reduce any noise component in a channel signal by a predetermined amount. The optical filter is able to redirect the channel signal into either a launch leg or a band-pass leg of the filter. The filter, however, does not provide for any compensation for variations in phase due to environmental fluctuations.
It is desirable to provide an ultra-stable optical wavelength division multiplexing and/or demultiplexing arrangement to automatically compensate for any change in signal drift and/or transmission properties of an included filter.
SUMMARY OF THE INVENTION
The present invention is directed to method and apparatus for providing ultra-stable optical wavelength division multiplexing (WDM) and/or demultiplexing by automatically compensating for any change in signal drift and/or transmission properties in a WDM multiplexer or demultiplexer.
Viewed from one aspect, the present invention is directed to an unbalanced Mach-Zehnder interferometer for use in, for example, an optical wavelength division multiplexer or demultiplexer. The unbalanced Mach-Zehnder interferometer comprises first and second fused tapered couplers, and a variable delay providing means. Each of the first and second fused tapered couplers are responsive to the reception of at least one first and second optical input signals for generating separate predetermined first and second optical output signals. The first and second output signals from the first fused tapered coupler are coupled via first and second optical waveguides, respectively, to respective first and second optical inputs of the second fused tapered coupler. First and second output signals from the second fused tapered coupler are provided as first and second output signals from the unbalanced Mach-Zehnder interferometer. The variable delay providing means is coupled in one of the first and second waveguides coupling the first and second optical output signals from the first fused tapered coupler to the first and second optical inputs of the second fused tapered coupler. The variable delay providing means introduces a predetermined variable delay into an optical signal passing therethrough for maintaining a relative delay between the first and second waveguides at a constant value.
Viewed from another aspect, the present invention is directed to an optical wavelength division multiplexer or demultiplexer comprising a plurality of unbalanced Mach-Zehnder interferometers located in a plurality of stages of a cascading arrangement. Each unbalanced Mach-Zehnder interferometer comprises a first fused tapered coupler, a second fused tapered coupler, and a variable delay providing means. The first fused tapered coupler is responsive to the reception of at least one of first and second optical input signals for generating separate predetermined first and second optical output signals for transmission via first and second optical waveguides, respectively. The second fused tapered coupler is responsive to the reception of the first and second optical output signals from the first fused tapered coupler which are received at first and second optical inputs, respectively, from the respective first and second optical waveguides, for generating separate predetermined first and second optical output signals from the unbalanced Mach-Zehnder interferometer. The variable delay providing means is coupled in one of the first and second waveguides coupling the output signals from the first fused tapered coupler to the first and second optical inputs of the second fused tapered coupler for introducing a predetermined variable delay into the associated optical output signal from the first fused tapered coupler passing therethrough for maintaining a relative delay between the first and second waveguides at a constant value.
Viewed from still another aspect, the present invention is directed to a method of providing a unbalanced Mach-Zehnder interferometer that compensates for signal drift. In a first step, at least one of first and second optical input signals are received at a first fused tapered coupler for generating separate predetermined first and second optical output signals for transmission via first and second optical waveguides, respectively. In a second step, the first and second optical output signals generated by the first fused tapered coupler in step (a) are received at first and second optical inputs, respectively, of a second fused tapered coupler from the respective first and second optical waveguides. The second fused tapered coupler generates separate predetermined first and second optical output signals which are output signals from the unbalanced Mach-Zehnder interferometer. In a third step, a predetermined variable delay is introduced into one of the first and second optical output signal from the first fused tapered coupler generated in the first step in a variable delay providing means. The variable delay that is introduced maintains a relative delay between the first and second waveguides coupling the first and second output signals from the first fused tapered coupler to the first and second optical inputs of the second fused tapered coupler at a constant value.
The invention will be better understood from the following more detailed description taken with the accompanying drawings and claims.
REFERENCES:
patent: 5048909 (1991-09-01), Henry
patent: 5459801 (1995-10-01), Suizer
patent: 5633965 (1997-05-01), Bricheno et al.
patent: 5636309 (1997-06-01), Henry et al.
patent: 5647037 (1997-07-01), Byron
patent: 5703976 (1997-12-01), Cullen
patent: 5761351 (1998-06-01), Johnson
patent: 5809190 (1998-09-01), Chen
patent: 5930414 (1999-07-01), Fishman et al.
patent: 0778479 (1996-12-01), None
Article entitled “Fused Coupler Technology for DWMD Applications”, Gpnthier, Fiber Optic Product News, Sept., 1998, pp. 54 and 56.
Diner Fahri
Singh Harmeet
Hunton & Williams
Palmer Phan T. H.
Qtera Corporation
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