Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
1998-07-07
2001-04-03
Chang, Audrey (Department: 2872)
Optical waveguides
With optical coupler
Input/output coupler
C385S015000, C385S024000, C385S037000, C385S039000, C385S045000, C359S199200, C359S199200
Reexamination Certificate
active
06212315
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to Wavelength Division Multiplexed (WDM) systems and, more particularly, to a channel power equalizer for a WDM system.
BACKGROUND OF THE INVENTION
In wavelength-division mutiplexed (WDM) networks, a low-loss device that can dynamically equalize the channel powers is needed to compensate for residual gain ripple in the optical amplifiers, incorrect added channel powers in optical add/drops, and sudden channel-power changes. Devices that can dynamically equalize the powers on a broad spectral feature basis include Mach-Zehnder filters[1], acoustooptic filters[2, 3], holograms[4], and micro-mechanically driven mirrors[5]. (Note, the reference number(s) identified in brackets, e.g., [4], indicates the position of that reference(s) in the reference list in the attached Appendix). Devices that can dynamically equalize the power on a channel-by-channel basis conventionally consist of a demultiplexer, an array of programmable attenuators, and a multiplexer (or power combiner)[6, 7]. However, the transmission loss of a demultiplexer-multiplexer pair, 1/T (where T is the transmissivity of the pair), is often too high for many networks.
What is needed is an improved channel-by-channel power equalizer that can achieve a low insertion loss by sacrificing attenuation range.
SUMMARY OF THE INVENTION
My invention is a dynamically and chromatically variable transmissivity apparatus (e.g., a channel equalizer) which controls the power level of wavelength signals (e.g., channel powers) in wavelength-division multiplexed (WDM) systems. When the WDM signal includes wavelengths grouped into a plurality of wavelength channels, the apparatus functions as a WDM channel equalizer. The input WDM signal is split into two components, in one component a phase shift is added to the wavelengths needing equalization, the two signal components are then recombined. The phase shift added at each wavelength determines the amount of loss compensation or equalization obtained for that wavelength. For a decrease in attenuation (i.e., equalization) range the device exhibits a decrease in insertion loss.
More particularly, a chromatically variable transmissivity optical apparatus comprises 1) a first coupler having an input port for receiving a Wavelength Division Multiplexed (WDM) signal and two output ports for outputting first and second WDM signals; 2) a second coupler having two input ports and an output port for outputting an equalized WDM signal; 3) a first optical path for coupling a first WDM signal from the first output port of the first coupler to a first input port of the second coupler; 4) a second optical path for coupling the second WDM signal from a second output port of the first coupler to an input of a wavelength selective phase shifter apparatus for providing a phase shift to one or more wavelengths of the second WDM signal; 5) a third optical path for coupling the phase shifted second WDM signal from an output of the phase shifter apparatus to a second input port of the second coupler; and wherein the second coupler combines the first WDM signal with the phase shifted second WDM signal to form the equalized WDM signal.
According to another feature, the size of the apparatus is substantially reduced when it is implemented as a reflective chromatically variable transmissivity optical apparatus which includes a reflective facet at the midpoint of the selective phase shifter apparatus to reflect optical signals back their source. The incoming WDM signal would then be inputted to one input port of the input coupler and the equalized WDM signal would then be outputted from another input port of the input coupler.
According to other features, a variety of couplers and wavelength selective phase shifter apparatuses may be utilized. The apparatus can also be implemented using bulk components or using an integrated optical device.
REFERENCES:
patent: 5519796 (1996-05-01), Li et al.
patent: 5710848 (1998-01-01), Dumais et al.
patent: 5912750 (1999-06-01), Takeda et al.
patent: 5953467 (1999-09-01), Madsen
patent: 6049640 (2000-04-01), Doerr
Caccuro John A.
Chang Audrey
Lucent Technologies - Inc.
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