Optical: systems and elements – Optical amplifier – Optical fiber
Reexamination Certificate
1999-04-15
2001-05-22
Buczinski, Stephen C. (Department: 3662)
Optical: systems and elements
Optical amplifier
Optical fiber
C359S199200, C385S014000, C385S031000
Reexamination Certificate
active
06236499
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is directed to optical amplification in communication networks and more particularly to a highly scalable modular optical amplifier based subsystem.
2. Background Art
To achieve long haul optical transmission, regenerators (repeaters) and/or optical amplifiers are deployed along the optical transmission link in multiple locations, for boosting the signal on the fiber. For systems operating at data rates of GBps, regenerator sites could be spaced in the range between 35 to 80 Km, depending on the wavelength chosen for transmission. The distance between optical amplifiers may be almost doubled, being in the range between 80 to 160 km.
Optical amplifiers are based on a length of Erbium doped fiber (active fiber) pumped with light of a certain wavelength to amplify the optical signal passing through the amplifier. The active fiber is spliced in the optical fiber. An important element is the WDM coupler, which performs the function of coupling the pump source laser wavelength to the Erbium doped fiber. Optical amplifiers may also be bidirectional, in which case they use a pump for each direction of transmission, with the respective WDM couplers. Optical isolators are also used internal to an optical amplifier, for reducing reflections generated at the points of fiber discontinuities, such as couplers, splitters, etc.
Optical amplifiers are favoured in long-distance systems over electrical repeaters not only because they allow for longer distances between the modules, and can be easily spliced into the fiber transmission link, but more importantly, because they do not require optical/electrical and electrical/optical conversion. An optical amplifier can amplify multiband/multichannel optical signals without demultiplexing them, thereby avoiding the costs of multiple optical receivers, multiple regeneration circuits and multiple optical transmitters. Also, they amplify whatever bit rate comes down the fiber. Even if the transmission rate is boosted, the device will not need to be replaced.
Current optical amplifiers are equipped with power monitors which control the pump based on measurements of the output, and sometimes input signals. The measurement is effected by providing an optical tap coupler on the respective output and input optical signal and diverting a fraction (generally 3-5%) of the respective input and output signals to the monitor.
The 80 km limitation can be extended with the introduction of external modulation and use of dispersion shifted optical. WDM and dense WDM (DWDM) technologies reduce the strands of optical fiber cable needed to establish a communication link, and provide manifold capacity expansion on existing fiber links. In addition, the advances in fiber technology now permit optical amplifiers to work not only in the conventional band (C-band) of 1530-1563 nm, but also in an extended band (E-band) of 1570-1603 nm.
The number of amplifiers required for working and protection spans, the type of the optical amplifiers, and the number of wavelengths carried within the system are significant issues must be considered when designing multiband/multichannel transmission systems. As the optical amplifiers evolve in performance and functionality, so does their cost. Evolution of the network, e.g. in terms of bandwidth growth must also be taken into consideration. Currently, network providers use over-performing optical amplifiers than necessary at the first stage of network deployment for allowing for future growth.
The optical amplifiers available on the market accommodate up to 16 bands bidirectionally. These amplifiers are exclusively for bidirectional or unidirectional systems and are relatively inflexible to create various complex amplifier topologies. There are three types of optical amplifiers: post-amplifiers that connect to a transmitter to boost the output power; line amplifiers connected along a route between the transmitter and the receiver; and pre-amplifiers that improve the sensitivity of optical receivers. These different types of amplifiers provide different output powers, use different input power levels, and generally have different noise figure requirements. Being stand-alone units, they allow the network with little opportunity for growth or scalability, in that they must be replaced whenever the demand for bandwidth increases.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a highly scalable modular optical amplifier based subsystem, which solves totally or in part the drawbacks of the prior art optical amplifiers.
It is another object of the invention to provide a highly versatile, scalable and modular family of optical amplifier building blocks that can be arranged in a variety of ways to produce both unidirectional and bidirectional topologies.
The building blocks or modules of the optical amplifier architecture are intended to operate in a modular manner exploiting the entire conventional Erbium gain window (1530 nm-1563 nm) as well as the extended Erbium band (1570 nm-1603 nm). Used together, this set, or family of products can produce optical amplifier topologies which can either be unidirectional or bidirectional, which also offer scalability with respect to the number of wavelengths deployed.
The modules or building blocks are compatible with the current Northern Telecom Limited S/DMS TransportNode™ products, and could be mapped into the existing shelves. It is expected that the equipping restrictions, mostly surrounding the OSC circuit pack, need to be employed due to hardware or software limitations, or to simplify system operation and verification. These restrictions will be documented in the equipping rules for the appropriate S/DMS TransportNode OC-192 releases.
According to one aspect of the invention there is provided a dual optical amplifier building block comprising a first and a second optical amplifier (OA), for amplifying a first and a second optical signal, respectively, a first input WDM coupler connected at the input of the first OA for separating a first optical service channel (OSC) from the first optical signal, a first output WDM coupler connected at the output of the first OA for adding the first OSC to the first optical signal, a second input WDM coupler connected at the input of the second OA for separating a second OSC from the second optical signal, a second output WDM coupler connected at the output of the second OA for adding the second OSC to the second optical signal, a first line-in and a first line-out connector for coupling the first optical signal over a first transmission line, a second line-in and a second line-out connector for coupling the second optical signal over a second transmission line, a first drop-OSC and a first add-OSC connector for coupling the first OSC to the respective first input and output WDM coupler, and a second drop-OSC and a second add-OSC connector for coupling the second OSC to the respective second input and output WDM coupler, and unexpected additions of further first-group channels.
According to a further aspect of the invention, there is provided a booster optical amplifier building block comprising, an optical amplifier (OA) for providing a substantial increase in optical output power of an optical signal, a WDM coupler connected at the output of the OA for adding an OSC to the optical signal, a line-in and a line-out connector for coupling the optical signal over a transmission line, and an add-OSC connector for coupling the OSC to the WDM coupler.
The invention further includes an optical service channel (OSC) building block for transmitting and receiving service information over a first and a second service channel, comprising, a West OSC transceiver with a West receiver for the first OSC and a East transmitter for the second OSC, an East OSC with a West transmitter for the first OSC and a second East for the second OSC, a first West-in and a first East-out connector for coupling the first OSC to the West receiver and the West transmitter, respectively, and a second East-in and
Berg Loren S.
Hinds Mark R.
Keys Robert W.
May Gregory D.
Solheim Alan G.
Buczinski Stephen C.
Diaconescu Aprilia U.
Nortel Networks Limited
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