Optical waveguides – With optical coupler – Plural
Reexamination Certificate
1999-12-21
2001-02-20
Ngo, Hung N. (Department: 2874)
Optical waveguides
With optical coupler
Plural
Reexamination Certificate
active
06192174
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates in general to optical communication and, in particular, to wavelength selection switches for optical application.
As multiple forms of communication traffic continue to place increasingly heavy burdens on fiber optic networks, users are looking for innovative ways to push more data through existing fiber. Dense Wavelength Division Multiplexing (DWDM) offers a state-of-the art alternative for increasing the transmission capabilities of fiber networks using optical technology. DWDM allows multiple streams of data to share a common communications channel by placing data streams onto different wavelengths. The result is a dramatic increase in the amount of bandwidth provided by a single optical fiber.
DWDM evolved from WDM (wave division multiplexing), which began as a dual-channel 1310/1550 nanometer (nm) system. Originally, this approach led to doubling of traffic capacity. DWDM increases the channel density up to 40 separate optical wavelengths, thus significantly increasing the net fiber capacity.
For a fiber optic network architecture using DWDM, it is necessary to route and switch optical signals based on their wavelength in order to optimize data traffic usage. Dropping signal from and adding signals back to the optical network is a rudimentary building block for an optical network architecture.
FIG. 1
illustrates the functionality and building elements for a conventional Add-Drop Module (AMD)
100
. As an example, four wavelengths &lgr;
1
, &lgr;
2
, &lgr;
3
and &lgr;
4
carried along the input port
101
arrive at the Add-Drop Module
100
. The AMD consists of two optical switches,
111
and
1
12
, and two Wavelength Division Multiplexers (WDM)
111
,
112
. In the normal ( default ) operation, the switch
111
and switch
112
are connected to the DROP WDM
121
and Add WDM
122
, respectively. The wavelength &lgr;
2
passes through the WDM
121
and arrive at the Drop port
131
. The remaining three wavelengths, &lgr;
1
, &lgr;
3
and &lgr;
4
are reflected by the WDM
121
and reflected again by WDM
122
. Then these three wavelengths are directed to the Output Port
135
by the switch
122
. Meanwhile, a new data signal in the same wavelength of &lgr;
2
′ transmitted from Add Port
132
is added back to the network through port
132
and WDM
122
and appears at Output Port
135
.
In the faulty case such as failure of Receiver or Transmitter in the Add-Drop ports, the two switches are toggled to be connected to the Express Path
125
. In this case the incoming light stream flows through the ADM
100
without interruption.
While the above-described Add-Drop module
100
may be satisfactory for some optical network applications, with the continual reduction in size of optical components in optical network applications, it may be desirable to provide an Add-Drop module which is smaller, cheaper and with better performance. The present invention reduce the numbers of components and cost in an Add-Drop module and further improve its optical performance in insertion loss.
SUMMARY OF THE INVENTION
This invention is based on the observation that, by making use of filters that selectively passes and reflects radiation of different wavelengths, it is possible to reduce the number of components as well as the overall size of the Add-Drop module.
Thus, one embodiment of the invention is directed towards an apparatus for transmitting radiation of multiple wavelengths. A first input channel carries radiation of one or more wavelengths and a second input channel carries radiation of a first wavelength to be added. At least one filter is placed between the channels. When a switch member is placed in a first position between the channels, radiation carried by the first input channel is received by an output channel and the radiation of the first wavelength carried by the second input channel is received by another output channel. When the switch member is in the second position between these channels, at least some of the radiation carried by the two input channels impinges on at least one filter. This causes radiation of all but one of the wavelengths carried by the first input channel and the radiation of the first wavelength to be directed towards a first one of the two output channels and radiation of the wavelength carried by the first input channel but not received by the first output channel be directed towards the remaining output channel.
REFERENCES:
patent: 5751868 (1998-05-01), Bala et al.
patent: 5915051 (1999-06-01), Damask et al.
“Optical Restorable WDM Ring Network Using Simple Add/Drop Circuitry,” B. Glance et al.,Journal of Lightwave Technology, vol. 14, No. 11, Nov. 1996, pp. 2453-2456.
“Arrayed-Waveguide Grating Multiplexer with Loop-Back Optical Paths and Its Applications,” Y. Tachikawa et al.,Journal of Lightwave Technology, vol. 14, No. 6, Jun. 1996, pp. 977-984.
Dicon Fiberoptics, Inc.
Ngo Hung N.
Skjerven Morril MacPherson LLP
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