WO2002054642A9 - High density reconfigurable optical multiplexer - Google Patents

High density reconfigurable optical multiplexer

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Publication number
WO2002054642A9
WO2002054642A9 PCT/US2001/023984 US0123984W WO02054642A9 WO 2002054642 A9 WO2002054642 A9 WO 2002054642A9 US 0123984 W US0123984 W US 0123984W WO 02054642 A9 WO02054642 A9 WO 02054642A9
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WO
Grant status
Application
Patent type
Prior art keywords
interleaver
output
optical
inputs
power combiner
Prior art date
Application number
PCT/US2001/023984
Other languages
French (fr)
Other versions
WO2002054642A3 (en )
WO2002054642A2 (en )
Inventor
Calvin J Martin
Zelda Gills
Jerome Case
Chiroll Tolliver
Original Assignee
Luxcore Networks Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date

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Classifications

    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04JMULTIPLEX COMMUNICATION
    • H04J14/00Optical multiplex systems
    • H04J14/02Wavelength-division multiplex systems

Abstract

An optical dense wavelength division multiplexer includes an interleaver and power combiners. Outputs of the power combiners feed the interleaver's inputs. The multiplexer provides a set of inputs of each power combiner, and a multiplexed signal output at the interleaver's output. Each input is not single wavelength-specific. The multiplexed signal has an improved optical signal to noise ratio because of the periodically spaced band reject regions of the interleaver.

Description

HIGH DENSITY RECONFIGU ABLE OPTICAL MULTIPLEXER

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to optical processing and, more particularly, to optical multiplexing and de-multiplexing systems.

2. Background The explosive growth of telecommunications is, to a large degree, both a cause and an effect of proliferation of fiber optic communication systems. Optical fiber has been used in telecommunications for several decades. In a typical system, light (including infrared light) modulated with a data signal is coupled to a fiber at a source node, transmitted by the fiber to a destination node, possibly through several intermediate nodes, received at the destination node, and demodulated and converted into an electrical data signal.

As the need for more bandwidth exerts its relentless pressure, wavelength division multiplexed (WDM) systems evolve to provide more fiber carrying capacity, h such systems, separate data channels are transmitted through the same fiber on different wavelengths. More and more distinct channels are being squeezed into a single fiber, resulting in progressively smaller separation between the channels. Channel separations of 100 or even 50 Ghz are replacing 200 Ghz separation common just a year or two ago. The specific wavelengths grids for various separations and spectrum regions are specified by the International Telecommunications Union (ITU), a standard-setting body based in Geneva, Switzerland.

Some of the more important components in DWDM systems are multiplexers and de-multiplexers. As one example, a multiplexer will combine several channels into a DWDM signal for transmission over a DWDM system's span. Obviously, the several channels will probably have to be separated at some point, so that individual data streams can be recovered. The separation function will be performed by a de-multiplexer.

As the maximum number of channels, i.e., wavelengths, on a single fiber grows, so does the size of multiplexers (and de-multiplexers). At the time of this writing, 128-wavelengths DWDM systems are on the horizon, and, doubtless, higher channel-count systems will be developed soon. Hence, the need for large optical multiplexers exists, and low cost of the product is always an important consideration. Several basic schemes are used for multiplexing DWDM signals. (They are also used for de-multiplexing; from here on, we will generically use the term multiplexing to refer to both processes, unless the context requires otherwise.) They include: (1) thin-film dielectric interference devices, (2) planar array waveguides, (3) Bragg gratings, (4) diffraction gratings, and (5) Mach-Zehnder interferometers.

Notably, power splitter/combiner elements — simple, small, robust, and inexpensive devices — generally are not used for multiplexing. This is so because of non-linearities existing in the combiners: multiple wavelengths do not merely combine, but also mix, creating sum and difference components, as well as higher- order products. This noise and cross-talk degrades optical signal-to-noise ratio of the channels.

A need exists for smaller, less expensive multiplexers with acceptable optical signal to noise ratios.

SUMMARY OF THE INVENTION h accordance with the broad principles of this invention, a wavelengths multiplexing circuit has at least an interleaver and a power combiner, with the output of the power combiner being optically coupled into one of the interleaver's inputs. The inputs of the combiner serve as non-differentiated inputs of the multiplexer, while the interleaver's output serves as the multiplexer's output.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 illustrates a l-by-2 interleaver. Figure 2 illustrates a two-stage l-by-4 interleaver. Figure 3 illustrates a multiplexer having ans interleaver and two power combiners.

Figure 4 illustrates a multiplexer with one interleaver and one power combiner. Figure 5 illustrates a multiplexer with a two-stage interleaver and four power combiners.

DETAILED DESCRIPTION Each of the multiplexing schemes discussed in the BACKGROUND section of this document has its uses and its shortcomings. Each scheme is challenged by the constantly narrowing channel separation requirements imposed by the high channel count systems. Interleaving is one such scheme often used in DWDM systems with narrow channel separations. An interleave multiplexer (interleaver) is essentially a l-by-2 comb filter with periodically spaced bandpass and band-reject sections. Referring now to Figure 1, an interleaver 100 has input ports 110 and 120, and an output port 130. (The interleaver will likely function in the reverse direction as well, i.e., as a demultiplexer, h that case, port 130 will be an input, while ports 110 and 120 will be outputs. As mentioned above, for simplicity we discuss multiplexing, although the same discussion will generally apply to de-multiplexing.) A first set of N channels (at wavelengths κ.\, κ3, . . . K^N-I)) spaced 2d nanometers (or Gigahertz) apart is input into port 110; a second set of N channels similarly spaced but appearing between and equidistant to the channels of the first set (at wavelengths κ , K4, . . . K(2N)) are input into port 120. Channels 1-2N (κι, κ2, K3, 4 . . . K(2N)) will then appear as a combined signal at port 130. The channel separation of the combined signal will be "d" ~ one half of the channel separation of each of the original sets of signals.

Note that if a channel from the second set, e.g., κ2, were input into port 110, it would be notched, i.e., significantly attenuated, at port 130. Similarly, a channel from the first set input into port 120 would also be notched at output port 130.

When used as a multiplexer, an interleaver's input is not wavelength- specific: it has the advantage of not requiring a single, predetermined wavelength at either of its input ports. This result is a direct consequence of bandwidth periodicity of the device. As illustrated above with reference to Figure 1, port 110 can accept any one, or any combination, of wavelengths of the first set, i.e., κls κ3, • • • ^N-i . This is beneficial because it provides system integrators with more flexibility in configuring a multiplexer node. By logical extension an interleaver may be combined with one or more additional stages of interleavers (or multiplexers in general) to provide multiplexing of additional channels. A two-stage setup is illustrated in Figure 2. There, input 110 of interleaver 100 is optically coupled to a l-by-8 multiplexer 210; input 120 is coupled to a second l-by-8 multiplexer 220. The combined device is therefore a l-by-16 multiplexer comprising two stages. The downside of such arrangement is its bulk and cost as compared to a more conventional l-by-16 multiplexer.

We have reasoned that the notching capability of an interleaver will increase optical signal to noise ratio of the combined signal because intra-channel noise will be attenuated in the interleaver. We have further reasoned that because of the noise attenuation, using power combiner elements for second stage (or higher stages) of a multiplexer may be feasible when the first stage (or any preceding stage) is an interleaver. Practical results have borne this out. A non-limiting embodiment of a multiplexer in accordance with this principle is illustrated in Figure 3. Multiplexer 300 has two stages. The first stage is a l-by-2 interleaver 310. The second stage includes two power combiners 320 and 330. Power combiner 320 has N non-differentiated inputs 322! through 322» and an output 324; power combiner 330 has non-differentiated inputs 332ι through 332N and an output 334. Outputs 324 and 334 are optically coupled to inputs 312 and 314 of interleaver 310, respectively. Output 316 of interleaver 310 is the output of multiplexer 300. Inputs 322i through 322N and 332! through 332N are inputs of the multiplexer.

As should be clear from the above discussion to those of ordinary skill in the art, multiplexer 300 has two non-interchangeable sets of non-differentiated inputs. Thus, the flexibility afforded by interleaver-based multiplexer has been preserved and extended to a higher number of inputs.

Many variations are possible on the basic scheme shown in Figure 3. For example, the two power combiners need not be identical and need not have the same number of ports. In some applications, one of the combiners may be replaced by a multiplexer, for example a second interleaver, a thin-film dielectric device, a planar array waveguide, a Bragg grating, a diffraction gratings, or a Mach-Zehnder interferometer. The second combiner (or multiplexer) may be eliminated altogether, resulting in a multiplexer with the number of input ports equal to the number of inputs of the first combiner, or the number of inputs of the first combiner plus the second input of the interleaver. This arrangement is illustrated in Figure 4. Multiplexer 400 has a l-by-2 interleaver 410 and a l-by-4 power combiner 420. Output 425 of combiner 420 is coupled to input 412 of interleaver 410. Input 414 to the interleaver and the four power combiner inputs 421 through 424 are the input ports of the multiplexer. Interleaver output 416 is the output of the multiplexer.

Furthermore, a combination of two interleavers or of an interleaver with a multiplexer of a different type may be substituted for interleaver 310 of Figure 3; in this case, more than two power combiners can be used, in accordance with the number of inputs of the combined device. Such multiplexer is shown in Figure 5, where outputs of interleavers 520 and 530 are coupled to the two inputs of interleaver 510. The four inputs of interleavers 520 and 530 are coupled to the outputs of four l-by-4 power splitters 540, 550, 560, and 570. Although immediate deployment of the invention in 1310 and 1550 nanometer bands is contemplated, the invention is not limited to operation in any specific region of the spectrum. Indeed, the invention is not limited to DWDM systems or other fiber optic telecommunication systems.

Many additional modifications are intended in the foregoing disclosure, and it will be appreciated by those of ordinary skill in the art that in some instances some features of the invention will be employed in the absence of a corresponding use of other features, without departure from the scope of the invention as set forth. The illustrative examples therefore do not define the metes and bounds of the invention, which function has been reserved for the following claims and their equivalents.

Claims

We claim:
1. A multiplexer comprising:
an interleaver comprising an input and an output;
a power combiner comprising an output and at least two inputs for receiving signals, the output of the power combiner being coupled to the input of the interleaver;
whereby the received signals are multiplexed and output through the output of the interleaver.
2. An optical multiplexer comprising: an optical interleaver comprising an output and at least two inputs, said at least two inputs comprising a first interleaver input and a second interleaver input; a first optical power combiner comprising an output and a plurality of inputs for receiving a first plurality of signals to be multiplexed into a combined signal, said output of said first optical power combiner being optically coupled to said first interleaver input; wherein the signals received by said inputs of said first optical power combiner are multiplexed into the combined signal and output through said output of said interleaver.
3. The optical multiplexer according to claim 2, further comprising: a second optical power combiner comprising an output and a plurality of inputs for receiving a second plurality of signals to be multiplexed into the combined signal, said output of said second optical power combiner being optically coupled to said second interleaver input; wherein the signals received by said inputs of said first optical power combiner and by said inputs of said second power combiner are multiplexed into the combined signal and output through said output of said interleaver.
4. The optical multiplexer according to claim 3, wherein said interleaver comprises a Mach-Zehnder interferometer.
5. The optical multiplexer according to claim 3, wherein said interleaver is a multi-stage interleaver, said at least two inputs of said interleaver further comprising a third interleaver input and a fourth interleaver input.
6. The optical multiplexer according to claim 5, wherein said multistage interleaver comprises three Mach-Zehnder interferometers.
7. A method of multiplexing a first plurality of optical signals and a second plurality of optical signals into a multiplexed optical signal, the method comprising: inputting the first plurality of the optical signals into inputs of a first optical power combiner; receiving a first combined signal from an output of the first optical power combiner; inputting the second plurality of the optical signals into inputs of a second optical power combiner; receiving a second combined signal from an output of the second power combiner; and multiplexing the first and the second combined signals in an optical interleaver to obtain the multiplexed optical signal.
8. The method of multiplexing according to claim 7, wherein said step of multiplexing the first and the second combined signals is performed in a Mach- Zehnder interferometer.
PCT/US2001/023984 2000-12-29 2001-07-31 High density reconfigurable optical multiplexer WO2002054642A9 (en)

Priority Applications (2)

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US75331700 true 2000-12-29 2000-12-29
US09/753,317 2000-12-29

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EP2919404B1 (en) * 2014-03-10 2016-07-20 Alcatel Lucent Multiplexing system and demultiplexing system for WDM channel transmission

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US5680490A (en) * 1995-09-08 1997-10-21 Lucent Technologies Inc. Comb splitting system and method for a multichannel optical fiber communication network
US6163393A (en) * 1996-10-29 2000-12-19 Chorum Technologies Inc. Method and apparatus for wavelength multipexing/demultiplexing
US5978114A (en) * 1997-08-29 1999-11-02 Amphenol Corporation Modular cascaded Mach-Zehnder DWDM components

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WO2002054642A3 (en) 2003-01-03 application
WO2002054642A2 (en) 2002-07-11 application

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