Optical waveguides – With optical coupler – Plural
Reexamination Certificate
2002-01-02
2004-08-24
Ullah, Akm Enayet (Department: 2874)
Optical waveguides
With optical coupler
Plural
C385S042000, C385S050000, C398S068000, C398S082000, C398S093000
Reexamination Certificate
active
06782157
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to optical communication systems, and more particularly, to a bidirectional optical interleaver.
Demand for voice and data bandwidth in telecommunications networks continues to increase as population grows, work habits evolve (for example, the increased reliance on telecommuting and video/teleconferencing) and business and personal usage of internet-based telecommunications accelerates. Network operators and telecommunications service providers face an increasingly competitive environment that demands low operating and infrastructure costs, and fast supply of new capacity. Operators and service providers are thus motivated to deploy optical telecommunications equipment that maximizes feature and function density within their facilities.
The telecommunications industry has been actively working to develop new technologies to increase network capacity while continuing to meet the financial expectations experienced in today's less regulated telecommunication landscape. Of particular importance has been the emergence of wavelength division multiplexing (“WDM”), which supports the transmission of multiple optical channels (each channel having a different wavelength) on a single fiber. Each channel is modulated with a different information signal to thus provide a substantial increase in data and voice carrying capacity without requiring the installation of new transport media, such as optical cables, in the network.
Dense wavelength division multiplexing (“DWDM”) technology is developing as an approach to scale up network capacity even further. In DWDM technology, the optical channels are packed more tightly within the available transmission spectrum. Individual optical channels thus become more closely spaced. Recently, 400 and 200 GHz spacings were common for optical channels. As the state of the art improved, 100 GHz and then 50 GHz channel spacing has become more common. Optical interleaving products have been introduced to address capacity needs by interleaving multiple sets of optical channels into a more densely packed stream. In its simplest form, with 2×1 interleaving, two subsets of optical channels are multiplexed into a single set with half the channel spacing of the subsets. A 1×2 deinterleaver operates in a complementary manner to demultiplex a set of optical channels into two subsets of optical channels where each subset has twice the channel spacing of the input set. The single term “interleaver” is typically used to refer to both multiplexing and demultiplexing functions. Currently, interleavers may be used to support either multiplexing or demultiplexing, but not both functions simultaneously.
Interleavers are utilized in transmission applications include multiplexing (and demultiplexing) in DWDM networks. Optical Add/Drop Multiplexing (“OADM”) is another common application. In addition, interleavers may be deployed as an interface among transmission streams having unequal channel spacings to allow existing networks to be gracefully scaled upwards to meet future capacity demands. While current interleaver technology is entirely satisfactory in many applications, some classes of interleavers are physically large while others may be complex to manufacture and thus have high costs. Accordingly, it would be very desirable to reduce size and costs while increasing the feature set and functionalities provided in today's optical networking infrastructure.
SUMMARY OF THE INVENTION
An inventive method and apparatus is provided by a bidirectional optical 1×2 device formed by a cascade of three optical 2×2 devices. The first of two distal end ports of a first 2×2 device in the first tier of the cascade is optically coupled via a first bidirectional optical path to a proximal end port of a second 2×2 device (one of two 2×2 devices in the second tier of the cascade). The second distal end port of the first 2×2 device is optically coupled via a second bidirectional optical path to a proximal end port FL of the third 2×2 device (the other of the two 2×2 devices in the second tier of the cascade).
Each 2×2 device is bidirectional where optical signals propagate through the 2×2 device in the forward and backward directions simultaneously. An input WDM signal is received at a first proximal end port of the first 2×2 device. As the input WDM signal forward propagates through the first 2×2 device (from proximal end to distal end), it is demultiplexed into first and second subsets of optical channels. In some applications of the invention, the channel spacing in each of the first and second subsets may be approximately double that of the input WDM signal.
Third and fourth subsets of optical channels are received, respectively, at a distal end port of the second 2×2 device and a distal end port of the third 2×2 device. As the third and fourth subsets of optical channels backward propagate through the first 2×2 device (from distal end to proximal end), they are multiplexed into an output WDM signal that is output at the second proximal end port of the first 2×2 device. In some applications of the invention, the output WDM signal may have a channel spacing that is approximately half that of the third and fourth subsets. The demultiplexing in the forward direction and multiplexing in the backward direction occur simultaneously to thereby perform bidirectional 1×2 optical demultiplexing and 2×1 optical multiplexing in the 1×2 device.
In illustrative embodiments of the invention, a bidirectional 1×4 demultiplexer, 4×1 multiplexer is disclosed for demultiplexing an input WDM signal propagating in the forward direction into four discrete output channels while simultaneously multiplexing four discrete input channels propagating in the backward direction into an output WDM signal. The bidirectional 1×4 demultiplexer, 4×1 multiplexer is arranged from a two-tiered cascade of three 1×2 devices. The input WDM signal is received at the proximal end of the cascade and the four discrete input channels are received at the distal end. A bidirectional 1×8 demultiplexer, 8×1 multiplexer is also disclosed for demultiplexing an input WDM signal propagating in the forward direction into a eight discrete output channels while simultaneously multiplexing eight discrete input channels propagating in the backward direction into an output WDM signal. The bidirectional 1×8 demultiplexer, 8×1 multiplexer is arranged from a three-tiered cascade of seven 1×2 devices. Optical isolators are disposed at each input of the cascade in both the four and eight channel embodiments (i.e., at the proximal end input for the WDM signal and at each of the distal end inputs for the discrete input channels) to prevent feedback to the signal sources.
In another illustrative embodiment of the invention, an input WDM signal having N channels is received at a first proximal end port of a 1×2 device disposed in a first tier of a cascade of (N−1) 1×2 devices having m tiers where 2
m
=N. As the input WDM signal forward propagates through the cascade, 1×N demultiplexing thereby occurs to generate a set of N discrete output channels that are output at respective first distal end ports of the 2×2 devices in the last tier (i.e., the m
th
tier) of the cascade.
A set of N discrete input channels is received at second distal end ports of the 2×2 devices in the m
th
tier of the cascade. As the set of N input channels backward propagates through the cascaded array, N×1 optical multiplexing thereby occurs to generate an output WDM signal that is output at a second proximal end port of the 1×2 optical device in the
1
st
tier of the cascade. Optical isolators are disposed at the inputs of the cascade (i.e., at the proximal end input for the WDM signal and at each of the N distal end inputs) to prevent feedback to the signal sources.
Advantageously, t
Luo Huali Ariel
Sullivan Kevin
Mayer Fortkort & Williams PC
Mayer, Esq. Stuart H.
Rahll Jerry T
Ullah Akm Enayet
Wavesplitter Technologies, Inc.
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