Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-07-21
2002-09-10
Chan, Jason (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200, C359S199200, C359S199200, C359S199200, C385S016000
Reexamination Certificate
active
06449073
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
BACKGROUND OF THE INVENTION
The present invention is directed generally to network, transmission and communication systems. More particularly, the invention relates to optical information network, transmission and communication systems and optical components, such as cross connect switches, add/drop devices, demultiplexers, and multiplexers, for use therein.
The development of digital technology has provided electronic access to a vast amount of information. The increased access to information has fueled an increasing desire to quickly obtain and process the information. This desire has, in turn, placed ever increasing demands for faster and higher capacity electronic information processing equipment (computers) and transmission networks and systems linking the processing equipment (i.e., telephone lines, cable television (CATV) systems, local, wide and metropolitan area networks (LAN, WAN, and MAN)).
In response to these demands, many transmission systems in use today either have been or will be converted from electrical to optical networks. Optical transmission systems provide substantially larger information transmission bandwidths than electrical systems, which provides for increased information transmission capacities.
Early optical transmission systems were developed as space division multiplex (SDM) systems. In early SDM systems, one signal was transmitted as a single optical wavelength in each waveguide, i.e., fiber optic strand. A number of waveguides were clustered to form a fiber optic cable that provided for the transmission of a plurality of signals in spaced relationship.
As transmission capacity demands increased, optical transmission and receiving equipment was developed that provided for time division multiplexed (TDM) transmission of a plurality of distinct optical signals in a single waveguide. Optical TDM systems are generally analogous to electrical TDM systems in that the signals are transmitted on a common line, but spaced in time. The transmission of the signals is in a known sequence allows the plurality of distinct signals to be separated after transmission.
A problem with TDM transmission is the transmission bandwidth in the waveguide increases with each additional multiplexed signal. For example, information can be transmitted through a waveguide via a first series of optical signals separated in time by an interval &Dgr;t. Additional information can also be transmitted over the same waveguide using a second series of optical signals during the time interval &Dgr;t by merely offsetting the transmission of the first and second series of signals in time. While an optical signal in each series is only transmitted through the waveguide every &Dgr;t interval, two signals, or n signals in the general case, are passing through the waveguide during each interval. Therefore, the overall transmission rate in TDM systems increases directly with the number of signals transmitted.
Signal transmission rates in fiber optic waveguides are generally limited by the interactions between the optical signal (i.e., light pulse) and microstructural features of the waveguide material. As the transmission rate is increased, signal dispersion in the fiber and other transmission effects deleterious to signal quality begin to occur as a result of the interactions.
Optical signals are typically transmitted in wavelengths that minimize dispersion in the fiber. For example, older optical systems are commonly operated around 1310 nm and employ SMF-28 fiber manufactured by Corning, or its equivalent, which has minimum dispersion at or near 1310 nm. Another type of fiber, known as dispersion shifted fiber, has its minimum dispersion at or near 1550 nm. A third type of fiber sold by Corning as LS fiber and by Lucent Technology as TrueWave has its minimum dispersion at or near 1550 nm. In addition to having different minimum dispersion wavelengths, each fiber has varying immunity to other signal degradation mechanisms, such as four wave mixing, at increased transmission rates.
The transmission rates at which the signal quality begins to degrade are substantially lower (<40 Gbps) than the capacity of the transmission and receiving equipment. Therefore, TDM systems, which increase capacity by increasing transmission rates, generally have only a limited potential for further increasing the capacity of optical transmission systems.
The development of wavelength division multiplex (WDM) transmission systems has provided a way to increase the capacity of optical systems without encountering the waveguide limitations present in TDM systems. In a WDM system, a plurality of optical signals including information carrying wavelengths are combined to produce a multiple wavelength signal that is transmitted through the system to a receiver. After the multiple wavelength signal is received, the information carrying wavelengths are separated from the multiple wavelength signal and provided to a corresponding plurality of destinations. Unlike TDM systems, only one WDM signal is transmitted during a time interval &Dgr;t, although each WDM signal contains a plurality of signals including information carrying wavelengths.
Also unlike TDM systems, the waveguide material does not realistically limit the information bandwidth that can be placed on a single optical fiber in a WDM system. One skilled in the art can also appreciate that the number of wavelengths that can be used to transmit information over a single waveguide is currently limited by the complexity of the transmission and receiving equipment required to generate, transmit, receive, and separate the multiple wavelength signal.
Currently, many optical transmission systems must convert the optical signal to an electrical signal during transmission to perform transmission functions, such as signal amplification and switching. The optical to electrical conversion, and vice versa, substantially limits the overall transmission speed of the network, and increases transmission losses in the network. Thus, it has been an industry goal to develop optical amplifiers and optical cross-connect switches to provide for high speed, all optical transmission systems.
The development of optical fiber amplifiers produced by doping the optical fiber with Erbium ions (Er
3+
) or other elements has allowed for the elimination of electrical amplifiers and the requisite time delay and costs associated with signal conversion. In addition to simplifying and decreasing the cost of the equipment required to amplify a signal, optical fiber amplifiers have proven effective for amplifying a plurality of wavelengths without a commensurate increase in the complexity of the amplifier as additional wavelengths are included in the WDM signal.
Unlike optical amplifiers, optical cross-connect switches greatly increase in complexity as the number of waveguides entering and exiting the switch and the number of wavelengths per waveguide increases. As a result, the expansion of all optical systems has been somewhat inhibited by the lack of simple, efficient, and economically attractive optical cross-connect switching systems.
A number of optical cross-connect switches are based on one or more 1×2 signal splitters or 2×2 signal couplers used in conjunction with one or more wavelength filters, such as described in U.S. Pat. No. 5,446,809 issued to Fritz et al. The complexity of these types of switch increases not only with the number of inputs and outputs in the switch, but also with the number of wavelengths being switched. For example, if a 2×2 switch is provided to switch two eight wavelength WDM input signals to two output signals, the switch would have to include 32 gratings to allow all wavelengths to be switched. However, if a 4×4 switch is provided to switch four sixteen wavelength. WDM input signals to four output signals, 256 gratings will be required. In addition, the flexibility of the switch is limited because additional gratings or filters must be added to each wav
Chan Jason
Corvis Corporation
Sedighian M. R.
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