Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
2000-05-18
2003-04-08
Negash, Kinfe-Michael (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200
Reexamination Certificate
active
06545782
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to a method and system for demultiplexing wavelengths used in optical fiber technology. More particularly, this invention relates to a method and system for dense wavelength division multiplexing (DWDM) based on a new and improved technique of asymmetric wavelength slicing to flexibly configure a demultiplexing system more suitable for DWDM applications.
BACKGROUND OF THE INVENTION
The dense wavelength division multiplexing (DWDM) technology has been broadly employed to increase transmission capacity of existing fiber optic transmission systems. In the DWDM technology, optical signals generated with dense-spaced wavelengths from different sources are first combined into a single optical output. Then the single optical output is transmitted over a single optical fiber. Finally the single optical output is separated and de-multiplexed into individual optical signals having the same dense-spaced wavelengths, which are directed toward different destinations. The more narrow the spacing in wavelength between different optical signals, the greater transmission capacity the existing fiber optical transmission systems.
In the DWDM technology, the DWDM devices are needed to combine or separate optical signals having dense-spaced wavelengths. Several technologies, including the wavelength slicing, are currently being employed for providing the DWDM function. With rapid increasing demand for transmission capacity and thus decreasing wavelength spacing, the wavelength slicing technology is now becoming more and more popular for those of ordinary skill in the art to carry out the task of demultiplexing wavelengths.
FIG. 1
shows the current wavelength slicing based DWDM device as that disclosed in U.S. Pat. No. 6,040,932 entitled “Method and Circuit for Demultiplexing an Optical Signal” (issued on Mar. 21, 2000), the disclosure of U.S. Pat. No. 6,040,932 is hereby incorporated in this Application by reference. Duck et al. disclose in U.S. Pat. No. 6,040,932, the technique for the current wavelength slicing based DWDM with the incoming composite optical signals having dense-spaced wavelength channels. The composite optical signals are separated by an optical device comprising an etalon into two symmetrically complementary sets of composite output signals having wavelength spacing which is twice as that of incoming optical signals. Note that while all even wavelength channels are sliced into a set of output signals, all odd wavelength channels are sliced into the other output signals, and all channels have a equal bandwidth. Specifically, Ducks et al. implement a periodic multi-cavity Fabry-Perot etalon having a free spectral range of “2d” to couple to a circulator for launching an input beam. The first of the two composite optical signals carrying channels
1
,
3
,
5
, . . . , n, is reflected from the input port of the etalon and the second of the two optical signals carrying channels
2
,
4
,
6
, . . . , n−1 is transmitted through the etalon. The method is commonly referred to as symmetric optical slicing because of the symmetric characteristic in terms of wavelength and bandwidth. Many stages of symmetric optical slicers can be cascaded together to provide the DWDM to totally separate all wavelengths. Since current symmetric wavelength slicing based DWDM technology provides the symmetric wavelength and bandwidth characteristics, to completely demultiplexing the DWDM signals, slicers with different spectral ranges have to be used. For example, to demultiplex 0.8 nm (100 GHz) spaced signals, a slicer with a spectral range of 0.8 nm has to be used first to slice the signals to 200 GHz spacing. And, then a slicer with a spectral range of 1.6 nm (200 GHz) has to be used, and so on until the signals are completely demultiplexed. Another disadvantage of the conventional symmetric slicing is due to the fact that the bandwidth for each channel in both sliced arms is the same, therefore, the maximum bit-rate in each channel is the same, which limits the flexibility of the system.
Therefore, a need exists in the art of optical signal transmission with DWDM technique by implementing the optical channel slicing technology to overcome the difficulties discussed above. Specifically, a design to provide the wavelength slicing based DWDM which simplifies the system, and provides more flexibility is required.
SUMMARY OF THE PRESENT INVENTION
It is therefore an object of the present invention to provide an improved method and configuration for carrying out an asymmetric wave channel slicing such that the DWDM technology can be simplified without being limited by the difficulties of the symmetric wave-channel slicing technology. With a greater degree of freedom to design the system for wavelength channel separation by asymmetric channel slicing, aforementioned difficulties and limitations in the pending application can be overcome.
Another object of this invention is to flexibly design the asymmetric wavelength channel slicing device such that the wavelength spacing between adjacent channels can be flexibly adjusted to three, four, or five times of a very dense channel separation. The same asymmetric slicing devices can be cascaded to progressively separate the composite signals into individual optical signal transmitted in each of these wavelength channels.
Another object of this invention is to flexibly design the asymmetric wavelength channel slicing device such that the bandwidth of channels in one arm is different from that of the other to allow different maximum bit-rate to be transmitted in different wavelengths.
Briefly, in a preferred embodiment, the present invention discloses an improved wavelength slicing technique for demultiplexing a composite optical signal. The technique applies a method for demultiplexing the composite optical signal for transmitting data signals over a plurality of data channels of different wavelengths represented by &lgr;
1
, &lgr;
2
, &lgr;
3
, &lgr;
4
, . . . &lgr;
n
where n is a positive integer. The method includes a step a) of receiving the composite optical signal into an asymmetric wavelength-slicing device through a device-input port And step b) of slicing the composite signal and extracting a first composite optical signal comprising data signals transmitted in a first set of data channels &lgr;
1
, &lgr;
a
, &lgr;
b
, &lgr;
c
, . . . &lgr;
n−1
through a first output port. And, extracting a second composite optical signal comprising data signals transmitted in a second set of data channels &lgr;
2
, &lgr;
d
, &lgr;
e
, &lgr;
f
, . . . &lgr;
n
through a second output port wherein the second set of data channels is complimentary and asymmetric to the first set of data channels.
In another preferred embodiment, the present invention discloses an improved wavelength slicing technique for demultiplexing a composite optical signal. The technique applies a method for demultiplexing the composite optical signal for transmitting data signals over a plurality of data channels of different wavelengths represented by &lgr;
1
, &lgr;
2
, &lgr;
3
, &lgr;
4
, . . . &lgr;
n
where n is a positive integer. The method includes a step a) of receiving the composite optical signal into an asymmetric wavelength-slicing device through a device-input port And step b) of slicing the composite signal and extracting a first composite optical signal comprising data signals transmitted in a first set of data channels &lgr;
1
, &lgr;
3
, &lgr;
5
, &lgr;
7
, . . . &lgr;
n−1
through a first output port. And, extracting a second composite optical signal comprising data signals transmitted in a second set of data channels &lgr;
2
, &lgr;
4
, &lgr;
6
, &lgr;
8
, . . . &lgr;
n
through a second output port wherein the second set of data channels is complimentary and having different pass bandwidth than the first set of data channels.
REFERENCES:
patent: 6115155 (2000-09-01), Liu et al.
patent: 6163393 (2000-12-01), Wu et al.
patent: 6208444 (2001-03-01), Wong et al.
Wang Hongchuan
Yan Mei
Lin Bo-In
Negash Kinfe-Michael
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