Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
2000-02-23
2003-06-24
Pascal, Leslie (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200, C359S199200, C359S199200, C359S199200
Reexamination Certificate
active
06583901
ABSTRACT:
FIELD OF THE INVENTION
This invention pertains to optical communications systems, in general, and to an optical network and a method of operating an optical network, in particular.
BACKGROUND OF THE INVENTION
As used herein, the term “optical network” relates to any network that interconnects a plurality of nodes and conveys information between nodes with optical signals. The term “optical communications system” as used herein refers to any system that utilizes optical signals to convey information between one node and one or more other nodes. An optical communications system may include one or more optical networks.
Telecommunications carriers began installing optical fiber cable about 15 years ago. At the time the optical fiber cables were installed, it was expected that the optical fiber infrastructure would provide communications systems and networks with ample capacity for the foreseeable future. However, the phenomenal growth of data traffic on the Internet has taxed the capabilities of the optical fiber infrastructure. In addition, new high bandwidth applications are being developed and are being made available for corporate applications. The result of this increased usage of the fiber infrastructure is serious network congestion and exhaustion of the fiber infrastructure. In the past, optical fiber systems relied on time division multiplexing to route traffic through a channel. Time division multiplexed systems add more capacity by time multiplexing signals onto an optical fiber. A disadvantage of time division multiplex systems is that data must be converted from light waves to electronic signals and then back to light. The system complexity is thereby increased.
As the demand for increasing traffic capacity continues, the limitations of existing optical networks and optical communications systems must be overcome. To do so, the capacity of the existing optical networks and optical communications systems needs to be increased. Capacity of existing optical infrastructure may be expanded by the laying of more fiber optic cable, for example. However, the cost of such expansion is prohibitive. Therefore a need exists for a cost-effective way to increase the capacity of existing optical infrastructure.
Wavelength Digital Multiplexing (WDM) and Dense Wavelength Digital Multiplexing (DWDM) are being used and/or proposed for use in long-haul telecom network applications for increasing the capacity of existing fiber optic networks. The advantage of both WDM and DWDM is that the conversion to electrical signals is not necessary. The devices that handle and switch system traffic process light and not electrical signals. WDM and DWDM would appear to many to be the solution to optical network limitations. In WDM, plural optical channels are carried over a single fiber optic, with each channel being assigned to a particular wavelength. By using optical amplifiers, multiple optical channels are directly amplified simultaneously thereby facilitating the use of WDM systems in long-haul optical networks. DWDM is a WDM system in which channel spacing is on the order of one nanometer or less. WDM and DWDM expand the capacity of an optical fiber by multiple wavelength channels into a single laser beam. Each wavelength is capable of carrying as much traffic as the original. Thus in one example set forth by Barry Greenberg in
Special Report: new growth markets/emerging OEMs: lighting the way to a network
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capacity solution,
Electronic Buyer News, 04-19-1999, pp. 50, “A fiber carrying four 2.5-Gbit/s DWDM channels, for example, has its capacity increased to 10 Gbit/s, without having to install additional fiber of use higher- speed transmission equipment.” With WDM and DWDM, traffic passes from one node of the network to its destination in the form of light waves without conversion to electrical signals. DWDM and WDM will permit increase in the capacity of the fiber infrastructure. Systems with up to 128 and 240 DWDM channels have been proposed and/or are being built. However, DWDM and WDM are both limited by the non-linear cost increase as the network is expanded. In each instance, expansion beyond an incremental increase in traffic handling capacity may trigger significant investment in new optical fiber and equipment that is significantly in excess of the incremental increase in network capacity. In addition, DWDM based systems are not scaleable in expansion because equipment typically has to be replaced rather than merely added to. Existing implementations of both WDM and DWDM are too limited for solving the congestion problems of the existing optical infrastructure. The present systems are limited in the number of available channels. The slight increase in channel occupancy in such systems will present severe restrictions on the traffic handling capacity of the network. Additional difficulties with present implementations of DWDM and WDM technology include lack of flexibility; difficulty in handling packet switched information, nonlinear optical effects and the already noted lack of incremental and scaleable upgrade capability.
It is therefor highly desirable to provide an optical communication system that has increased channel capacity. It is further desirable to provide an optical communication system that provides bandwidth based upon user demand. It is further desirable that any improved optical communication system is able to utilize the existing fiber optic infrastructure. Such a solution will prevent so called “fiber exhaust”. To effectively utilize the existing infrastructure in the face of the dramatic increases in traffic that will be encountered, it is highly desirable to increase channel capacity by a factor of 10 to 200 times that provided by DWDM to permit up to 20,000 channels to be served. It is also highly desirable that any improved optical communication system has a low cost per channel.
SUMMARY OF THE INVENTION
In accordance with the principles of the invention, fiber exhaust is substantially avoided by increasing the traffic handling capacity of existing fiber infrastructure. In the illustrative embodiment of the invention, the traffic handling capacity is increased by up to 200 fold over DWDM system technology.
In a method of operating an optical communications system in accordance with the invention, a plurality of optical channels is provided and the optical channels are utilized for communications among a plurality of communications nodes. Each optical channel is determined by at least two of three optical signal characteristics. A first one of the optical signal characteristics is selected from a plurality of predetermined optical wavelengths. A second one of the optical signal characteristics is selected from a plurality of predetermined optical phases, and a third one of said optical signal characteristics is selected from a plurality of optical modulation frequencies.
In one embodiment in accordance with the principles of the invention, two of the optical signal characteristics are utilized to determine the optical channels. In this first embodiment of the invention, each channel is defined by one optical wavelength of a plurality of optical wavelengths and by one modulation frequency of a plurality of optical modulation frequencies.
In a second embodiment in accordance with the principles of the invention, one wavelength of a plurality of optical wavelengths, one frequency of a plurality of optical modulation frequencies, and one phase of a plurality of optical signal phases define each channel.
Optical communication system apparatus and methods of operating an optical communications system in accordance with the invention may utilize existing optical fiber networks and provide significantly increased channel capacity. In accordance with one aspect of the invention the system apparatus provides for a plurality of communications channels and a processor unit receives requests for allocation of one or more channels from a node coupled to the optical communications system. In accordance with the principles of the invention a system and method are provided i
Ching Alexander B.
Pascal Leslie
Sedighian M. R.
Squire Sanders & Dempsey L.L.P.
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