Optical waveguides – With optical coupler – Plural
Reexamination Certificate
1999-06-04
2001-09-25
Lee, John D. (Department: 2874)
Optical waveguides
With optical coupler
Plural
C385S037000
Reexamination Certificate
active
06295396
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to method and apparatus for higher-order chromatic dispersion and dispersion slope compensation for virtually any type of optical fiber used in high-speed optical communication systems.
BACKGROUND OF THE INVENTION
Chromatic dispersion is one of the major sources for signal distortions in high-speed optical communications. For example, OC192 systems (10 Gbit/s Non-Return-to-Zero format) are limited about 70 km for conventional single mode fibers (SMF-28) without compensation for chromatic dispersion. Among a variety of techniques for dispersion compensation, dispersion compensating fibers (DCF) and fiber Bragg gratings (FBG) are the most techniques used in practical applications.
As the demand for bandwidth keeps increasing, the requirements for dispersion compensation also increases. The most efficient way to increase system capacity is to increase the number of channels using the wavelength-division-multiplexing (WDM) technology. However, the existence of higher-order chromatic dispersion in optical fibers makes it difficult to provide chromatic dispersion compensation for all of the channels. The dominating effect of higher-order dispersion is the third-order dispersion, which is also known as the dispersion slope. In other words, dispersion slope describes the different chromatic dispersion that each WDM channel experiences. The broader the optical bandwidth that the WDM channels occupy, or, the longer the transmission distances, the greater the effect of dispersion slope. Therefore, compensation for dispersion slope has become crucial for high capacity WDM systems.
Different types of optical fibers have different dispersion characteristics. In other words, different dispersion slope compensations are required for different fibers. For example, dispersion compensating fibers (DCFs) are considered one of the most reliable techniques for compensating for both dispersion and dispersion slope for the single mode fiber SMF-28. However, it is difficult to design a suitable DCF for dispersion-shifted fibers (DSF) due to the limitations of the optical fiber design. Ideally, fiber Bragg gratings (FBG) are preferable over DCFs for several attractive reasons such as, virtually no optical nonlinearity, low insertion loss, compact size, and flexibility for different fiber types. However, a group-delay ripple associated with an FBG makes it inferior in most applications when compared to a DCF. Therefore, it becomes desirable to provide a technique to compensate for a large amount of chromatic dispersion. Unfortunately, the group-delay ripple also becomes larger for larger amount of chromatic dispersion. Unless the group delay ripple of the FBG can be made small enough, the application of FBGs in dispersion compensation is limited.
It is desirable to provide a technique for higher-order chromatic dispersion and dispersion slope compensation for virtually any type of optical fibers used in high-speed optical communication systems without suffering severe degradation due to a group-delay ripple of fiber Bragg gratings.
SUMMARY OF THE INVENTION
The present invention is directed to method and apparatus for higher-order chromatic dispersion and dispersion slope compensation for virtually any type of optical fiber used in high-speed optical communication systems.
Viewed from one aspect, the present invention is directed to an optical arrangement for providing dispersion slope compensation to a received dispersion distorted input signal comprising N×M wavelength multiplexed channels. The optical arrangement comprises a plurality of N fiber Bragg gratings (FBGs) and first directing means. The plurality of N fiber Bragg gratings (FBGs) are serially coupled along an optical fiber. Each FBG is arranged to reflect a separate one of N groups of wavelength channels received in the input signal back along the optical fiber for providing a dispersion compensating value to each of the N groups of wavelength channels. The first directing means sequentially directs the input signal to the plurality of FBGs for providing dispersion slope compensation to the N×M wavelength multiplexed channels, and then directs a dispersion slope compensated output signal for the N×M wavelength multiplexed channels to an output from the optical arrangement.
Viewed from another aspect, the present invention is directed to an optical arrangement for providing dispersion slope compensation to a received dispersion distorted input signal comprising N×M wavelength multiplexed channels. The optical arrangement comprises first directing means, a plurality of N fiber Bragg gratings (FBGs), and a major dispersion compensating fiber (DCF). The first directing means comprises a first port, a second port, and a third port. The first port is coupled to receive the input signal via a first optical fiber. The second port is coupled to a second optical fiber, and the third port is coupled to a third optical fiber that provides a dispersion slope compensating output signal from the optical arrangement. The directing means directs the input signal from the first port to the second port for propagation along the second optical fiber, and then directs a signal returning on the second optical fiber to the third port for propagation on the third optical fiber. The plurality of N fiber Bragg gratings (FBGs) are serially formed along the second optical fiber. Each FBG is arranged to reflect a separate one of a plurality of N groups of wavelength channels back along the second optical fiber towards the second port of the first directing means for providing a predetermined dispersion compensating value for each of the N groups of wavelength channels. The major dispersion compensating fiber (DCF) is coupled to any one of the first, second, and third optical fibers for providing a predetermined overall dispersion correction value to all of the N×M wavelength channels. The combination of the dispersion compensating values provided by major DCF and in the reflected signals from each of the plurality of FBGs generating a dispersion slope compensated output signal from the optical arrangement wherein dispersion found in the input signal is substantially eliminated.
Viewed from still another aspect, the present invention is directed to a method of providing dispersion slope compensation to a received dispersion distorted input signal comprising N×M wavelength multiplexed channels comprising the following steps. In step (a), a separate one of N groups of wavelength channels is reflected back along an optical fiber from a separate one of a plurality of N fiber Bragg gratings (FBGs) which are serially coupled along the optical fiber for providing a first dispersion compensating value to each of the N groups. In step (b), a predetermined overall second dispersion compensating value is introduced to the N×M wavelength multiplexed channels by a major dispersion compensating fiber (DCF). In step (c), a dispersion slope compensated output signal is generated wherein the dispersion in the input signal is substantially eliminated after the N groups of wavelength signals have been reflected by each of the plurality of FBGs in step (a) and have propagated through the major DCF in step (b) to an output.
Viewed from still another aspect, the present invention is directed a method of providing dispersion slope compensation to a received dispersion distorted input signal comprising N×M wavelength multiplexed channels comprising the following steps. In step (a), the N×M wavelength multiplexed channels are demultiplexed in a band separator into a plurality of N groups of M wavelength channels each. A first section of the N groups of wavelength channels are directed along a first optical fiber, and a second section of the N groups of wavelength channels are directed along a second optical fiber. In step (b), each of groups of wavelength channels received in the first and second sections via the first and second optical fibers, respectively, are directed along a respectiv
Cao Xiang-Dong
Diner Fahri
Connelly-Cushwa Michelle R.
Hunton & Williams
Lee John D.
Qtera Corporation
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