Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1999-09-13
2003-06-10
Tweel, John (Department: 2632)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200
Reexamination Certificate
active
06577416
ABSTRACT:
BACKGROUND TO THE INVENTION
Multi-wavelength optically amplified systems require selective pre-emphasis of channel powers to equalise signal to noise ratios at the receive terminal end. In one known architecture, individual channel powers are controlled by a respective optical attenuator or optical amplifier in the transmit tributary path prior to combining. This has the disadvantage that after setting each channel power, relative drifts in the output powers of the tributary components and/or changes to the spectral characteristics of the following aggregate path components can upset the pre-emphasis which results in a system signal to noise impairment in one or more channels.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, a channel control circuit for an optical wavelength division multiplexed (WDM) communications system comprises:
an optical coupling means having an optical input and an optical output;
an optical multiplexer for demultiplexing a WDM optical signal received at the optical input into separate channels;
a number of optical gain control elements for controlling the signal power of a respective channel to provide pre-emphasis control; and,
means for coupling each of the channels via a respective return path through the optical multiplexer to the optical output, where the channels appear as a WDM optical signal.
The present invention addresses problems associated with conventional tributary path channel control. The use of an optical coupler in combination with a WDM multiplexer enables pre-emphasis of the individual channels in a WDM optical signal to be carried out in the aggregate path and provides a compact and cost effective solution with minimal insertion loss. The WDM optical signal is demultiplexed and the relative powers of the individual channels set accordingly. The channels are subsequently multiplexed in a return path through the same multiplexer so that the output signal is a WDM signal with the required degree of pre-emphasis in each channel. The arrangement also has a degree of tributary independence in that a failure in one path carrying one channel will not totally remove the other channels.
Preferably, the optical gain control elements comprise optical attenuators. More preferably, each optical attenuator comprises a feedback circuit for providing active gain control to maintain channel power substantially at a predetermined level.
Preferably, each optical attenuator is coupled to an optical reflector for reflecting the optical signal along a return path to the optical multiplexer.
The optical multiplexer may, for example, be of a type manufactured using either multilayer dielectric or array waveguide interference technology.
Preferably, the channel control circuit comprises an optical circulator arranged to couple an optical signal between the optical input and the optical multiplexer, and between the optical multiplexer and the optical output. This form of optical coupler provides inherent optical isolation for the control circuit. As an alternative, a 3 dB coupler may be used.
According to a second aspect of the present invention, a transmit terminal for an optical wavelength division multiplexed (WDM) communications system comprises a channel control circuit in accordance with the first aspect of the present invention.
According to a third aspect of the present invention, a receive terminal for an optical wavelength division multiplexed (WDM) communications system comprises a channel control circuit in accordance with the first aspect of the present invention.
Preferably, the terminal further comprises an optical amplifier coupled to the optical output of the optical coupling means.
According to a fourth aspect of the present invention, an optical wavelength division multiplexed communications system comprises a terminal according to either of the second and third aspects of the present invention.
REFERENCES:
patent: 5548654 (1996-08-01), Fast
patent: 5745271 (1998-04-01), Ford et al.
patent: 5790289 (1998-08-01), Taga et al.
patent: 5877879 (1999-03-01), Naito
patent: 6151157 (2000-11-01), Ball et al.
patent: 6160659 (2000-12-01), Kinoshita
patent: 6185022 (2001-02-01), Harasawa
patent: 2 303 984 (1996-03-01), None
patent: 8-321824 (1996-12-01), None
patent: WO 97/06616 (1997-02-01), None
Alcatel
Sughrue & Mion, PLLC
Tweel John
LandOfFree
Channel control in a wavelength division multiplexed... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Channel control in a wavelength division multiplexed..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Channel control in a wavelength division multiplexed... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3110956