Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
2002-08-28
2004-09-14
Kim, Ellen E. (Department: 2874)
Optical waveguides
With optical coupler
Input/output coupler
C385S024000, C385S014000
Reexamination Certificate
active
06792182
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to optical networks and their components. More specifically, the invention relates to optical cross connects for dense wavelength division multiplexing, or DWDM networks.
BACKGROUND OF THE INVENTION
Fibre optic networks allow very large amounts of information to be transmitted accurately over long and short distances. These networks transmit a plurality of optical signals with differing wavelengths into the same fibre to increase the overall bandwidth of the network. Referring to
FIG. 1
, an optical network is shown wherein a plurality of optical signals with different wavelengths, &lgr;
1
to &lgr;n, is transmitted from a first node
10
to a second node
12
multiplexed within a same fibre. At the second node
12
the optical signal whose wavelength is &lgr;
1
is separated, dropped, and the remainder of the multiplexed signal is transmitted to the third node
13
. Thus, this type of optical network has specific destinations serviced by signals at specific wavelengths. This simplifies the optical components tremendously because every signal characterized by a specific wavelength channel exits the network at a predetermined node. Unfortunately, this can also be disadvantageous because the network cannot be reconfigured conveniently. Reconfiguring the network is very beneficial because it allows the network to bypass equipment that is being serviced and it allows the network to boost the available bandwidth between specific nodes when there is a significant fluctuation in the bandwidth requirements between nodes.
Referring to
FIG. 2
, a configurable optical add/drop multiplexer, or COADM adds flexibility to the network. The COADM
20
has a wavelength dispersive element
21
for separating an optical signal at wavelength &lgr;
1
from the received multiplexed optical signals. While it only diverts one signal, in this case at wavelength &lgr;
1
, it does attenuate all of the optical signals. The wavelength dispersive element
21
is optically coupled to a switch
22
. The optical switch
22
can be set to either maintain the one signal within the network or optionally, the one signal is dropped from the network. If the one signal is dropped a new signal at wavelength &lgr;
1
, within the same wavelength channel as the one signal, is optionally provided. Recombining the optical signals requires a second wavelength dispersive element
23
. Similarly, a second COADM
25
is added to control signals at wavelength &lgr;
2
. As shown in
FIG. 2
, the second COADM
25
has been set to keep the one signal at wavelength &lgr;
2
within the multiplexed optical signal. Unlike a costly router, a COADM is not fast enough to switch individual packets of information, also known as internet protocol packets or IP packets; however, it is fast enough to allow the network to reconfigure itself based upon signal routing requirements. This solution is practical when the number of channels to be dropped is low, because each of the wavelength dispersing elements has a loss that all the optical signals experience. Generally, this approach is not recommend for serially add/dropping more than eight channels at each of more than eight nodes.
When larger numbers of wavelength channels must be added and dropped, an optical cross connect or OCX is used. Referring to
FIG. 3
, the OCX has two wavelength dispersive elements
31
and
32
in the form of arrayed waveguide gratings (AWGs). The first AWG
31
receives all the optical signals and separates them based upon their wavelength. Signals within each wavelength channel propagate down separate waveguides and into separate switches. The switch used to route each signal may drop it from the network or route it back into the network. The switch
33
is a 2×2 switch, which gives it the ability to substitute an added signal at a same wavelength for an optical signal that is dropped. The OCX shown in
FIG. 3
supports only four wavelength channels. The number of wavelength channels that an OCX can support is limited by the quality of the wavelength dispersive elements and the availability of the switches. Since optical signals propagate through the wavelength dispersive elements a maximum of two times the optical attenuation of the device is fairly low. Unfortunately, the OCX is very expensive. The two wavelength dispersive elements are expensive, the switches are expensive and handling the optical fibres during manufacture is time consuming and difficult. Additionally, the characteristics of the signals traveling through the OCX are very dependent on how well matched the two wavelength dispersive elements are one to another. Typically, the exact frequency response of one wavelength dispersive element is not precisely duplicated by any other. Using a tuning method, the frequency response of one such element can be tuned to another. This improves the matching of the two devices but unfortunately it is expensive. Alternatively, devices from a large batch may be tested, evaluated and paired with similarly performing devices. These tests and the handling of the devices is time consuming and require very expensive testing equipment. Additionally, the optical properties of the wavelength dispersive elements are subject to modification due to environmental changes, such as temperature; maintaining same environmental conditions on both wavelength dispersive elements adds to the complexity required to package the device. Clearly, it would be beneficial to have an OCX that is inexpensive, small, and reliable while having good optical properties associated with near perfectly matched wavelength dispersive elements.
SUMMARY OF THE INVENTION
The invention discloses an optical wavelength division multiplexer/demultiplexer device comprising: an input port for coupling a first multiplexed optical signal supporting a first plurality of wavelength channels; a plurality of output ports, each for providing a channelized signal of said first plurality of wavelength channels; a first plurality of input ports, each for coupling a channelized wavelength signal of a second plurality of wavelength channels; a first output port for providing a second multiplexed optical signal corresponding to said second plurality of wavelength channels; a second plurality of input ports, each for coupling a channelized wavelength signal of a third plurality of wavelength channels; a second output port for coupling a second multiplexed optical signal containing said third plurality of wavelength channels; and, an echelle grating disposed for separating the first multiplexed optical signal received from the input port into signals within individual wavelength channels and for directing each into a corresponding output port of the plurality of output ports, for combining a second plurality of signals within corresponding wavelength channels received from the first plurality of input waveguides into a second multiplexed optical signal and for providing the second multiplexed optical signal to first output port, and for combining a third plurality of optical signals within corresponding wavelength channels received from the second plurality of input ports into a third multiplexed optical signal and for providing the third multiplexed optical signal to the second output port.
Additionally, the invention describes an optical wavelength division multiplexer/demultiplexer device comprising: a first input waveguide; a first input port for coupling a first multiplexed optical signal containing a first plurality of wavelength channels to the first input waveguide; a second input waveguide; a second input port for coupling a second multiplexed optical signal containing a second plurality of wavelength channels to the second input waveguide; a first plurality of output ports, each for providing a channelized signal of said first plurality of wavelength channels from the first input port; a second plurality of output ports, each for providing a channelized signal of said first plurality of wavelength channels from the second input port; a first plurality of input w
Berolo Orazio
Davies Michael
Hichwa Bryant
Bernstein Jason A.
Kim Ellen E.
Metrophotonics Inc.
Powell, Goldstein, Fraze & Murphy LLP
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