Optical waveguides – With optical coupler – Plural
Reexamination Certificate
2001-04-23
2003-10-21
Ngo, Hung N. (Department: 2874)
Optical waveguides
With optical coupler
Plural
C385S047000
Reexamination Certificate
active
06636658
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to multiple channel multiplexers and demultiplexers for fiber optic systems. In particular, the present invention relates to wavelength division multiplexer/demultiplexer systems that provide parallel multiplexing/demultiplexing of a multiple channel optical signal.
2. Background Technology
The increasing demand for bandwidth, coupled with the high cost of laying new optical fiber, has created a strong demand to find new and better ways to increase the carrying capacity on existing optical fiber systems. One such way to increase the capacity is by a technique called wavelength division multiplexing (WDM), which employs multiple wavelengths to carry multiple signal channels and thereby greatly increase the capacity of installed fiber optic networks.
Wavelength division multiplexing (WDM) technology has become a vital component of optical communication systems. In a WDM optical system, light from several lasers, each having a different central wavelength, is combined into a single beam that is introduced into an optical fiber. Each wavelength is associated with an independent data signal through the optical fiber. At the exit end of the optical fiber, a demultiplexer is used to separate the beam by wavelength into the independent signals. In this way, the data transmission capacity of the optical fiber is increased by a factor equal to the number of single wavelength signals combined into a single fiber.
A demultiplexer (DEMUX) device is designed to selectively direct several channels from a single multiple-channel input beam into separate output channels and a multiplexer (MUX) device provides a single multiple-channel output beam comprising the combinations of a plurality of separate input beams. A multiplexer-demultiplexer (MUX/DEMUX) device operates in either the multiplexing or demultiplexing mode depending on its orientation in application, i.e., depending on the choice of direction of the light beam paths through the device.
Thus, in a WDM system, optical signal channels are: (1) generated by light sources; (2) multiplexed to form an optical signal constructed of the individual optical signal channels; (3) transmitted over a single waveguide such as an optical fiber; and (4) demultiplexed such that each channel wavelength is individually routed to a designated receiver such as an optical detector.
Generally, applications for MUX/DEMUX technology include long haul communications and local area data networks. Both digital and analog systems have been demonstrated for voice, data and video. The scope of applications for WDM devices ranges from spacecraft and aircraft applications to closed circuit and cable television systems. In view of these diverse applications, much effort has been expended toward developing WDM technology.
Wavelength selectivity in MUX/DEMUX devices may be achieved through the use of the wavelength-selective characteristics of optical thin film interference filters, such as high and low bandpass filters and dichroic filters. Wavelength selectivity may also be achieved with angularly dispersive devices including prisms and various diffractive grating devices, e.g., prism grating devices, linear grating devices, and chirped grating devices. The grating devices may be of the Littrow-type, which uses a common lens of either a conventional lens type or a graded index (GRIN) rod lens type. No-lens systems are also known and may have, for example, only a concave grating or a combination of a slab waveguide with a grating device. Combinations of grating devices and optical filters are also known.
Conceptually, each wavelength channel in an optical fiber operates at its own data rate. In fact, optical channels can carry signals at different speeds. The use of WDM can push total capacity per fiber to hundreds of gigabytes per second. Generally, more space is required between wavelength channels when operating at 10 gigabytes per second than at 2.5 gigabytes per second, but the total capacities are nonetheless impressive. For example, in the case of 4 wavelength channels at a data rate per channel of 2.5 gigabytes per second, a total data rate of 10 gigabytes per second is provided. With 8 wavelength channels at a data rate per channel of 2.5 gigabytes per second, a total data rate of 20 gigabytes per second is provided. In fact, other wavelength channels can include, for example, 16, 32, 40, or more wavelength channels operating at 2.5 gigabytes per second or 10 gigabytes per second and allow much higher data transfer possibilities. Further, the use of multiple fibers in a single cable can provide even higher transmission rates.
Optical WDM networks typically allocate a portion of the spectrum about a center frequency of the nominal channel wavelength for signal transmission. For example, in dense wavelength division multiplexing (DWDM) systems, channel spacings of less than 1 nm are typically used with wavelength bands centering around 1550 nm. Other systems may require or allow narrower or wider channel widths or spacings. Whereas DWDM is commonly used in telecommunications where the dense channel spacing is ideal, DWDM is normally incompatible with local network data transfer because the narrow channel spacing leads to excessive crosstalk that is unacceptable in data transfer applications.
One solution to crosstalk and channel separation problems in local area networks (LAN), metropolitan area networks (MAN), and wide area networks (WAN) is wide wavelength division multiplexing (WWDM), which is an industry-defined term that indicates narrow bands of wavelengths that are spaced relatively far apart. Typically, the wavelength bands are about 10 nanometers (nm) wide and are spaced about 25 nm apart. The wavelength bands in WWDM bands are centered at about 1310 nm and typically contain four channels at 1275 nm, 1300 nm, 1325 nm, and 1350 nm, each within about ±5 nm of the designated wavelength. WWDM can be expanded to up to 100 gigabytes per second or more. Nevertheless, when more than 4 wavelengths, for example 8 or 16, are multiplexed, the demultiplexing needs become greater and the accompanying risk of excessive beam attenuation heightens.
An advantage of the wide channel spacing in WWDM is that it requires no temperature control over the range of 0° C. to 70° C. This is because, although laser wavelengths may drift by a few nanometers over the range of 0° C. to 70° C., WWDM has an acceptable wavelength variation of ±5 nm. Therefore, WWDM is not particularly limited by temperature conditions.
Similar to WWDM, coarse wavelength division multiplexing (CWDM) is another industry-defined term and is a solution to crosstalk and channel spacing problems. CWDM denotes wavelength bands that are about 10 nm wide and are spaced about 20 nm apart. The CWDM bands are centered at about 850 nm and about 1550 nm.
The 10-gigabit per second Ethernet standard (GbE) is based upon WWDM technology. However, the standard has numerous challenges. Various solutions have been proposed for the 10 GbE standard, including WWDM using multiple wavelength lower speed lasers. Currently, the 10 GbE industry is standardizing on a physical layer transceiver that incorporates WWDM technology. On the transmitter side, the standard uses a multiplexer that combines the output from four lasers at 1,310 nanometers and launches them into an optical fiber. On the receiver side there is a demultiplexer that has an input fiber for the four wavelengths or channels and an optical system with color separation capabilities to divide the four channels. The 10 GbE standard provides physical air solutions to support 65 meters on installed multimode fiber, 300 meters on multimode fiber, 2 kilometers on single mode fiber, 10 kilometers on single mode fiber, and 40 kilometers on single mode fiber. It should be noted that the WWDM physical medium dependent (PMD) solution (10 GBASE-LX4) is the only solution that meets all distance objectives of 10 km or less.
One example of a demultiplexer device is disclosed in U.S. Pat
Cooke Janeen
Egerton Clive
Goodman Timothy D.
Holme Roberts & Owen LLP
Ngo Hung N.
Optical Coating Laboratory, Inc.
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