Optical waveguides – Optical fiber waveguide with cladding – Utilizing multiple core or cladding
Reexamination Certificate
2001-05-09
2003-10-28
Sanghavi, Hemang (Department: 2874)
Optical waveguides
Optical fiber waveguide with cladding
Utilizing multiple core or cladding
C385S124000
Reexamination Certificate
active
06640038
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to dispersion managed fibers and, in particular, to dispersion managed fibers which exhibit reduced sensitivity to manufacturing variabilities, have relatively small changes in mode field diameter (MFD) at the junctions between fiber sections having positive dispersions and fiber sections having negative dispersions, and/or are readily manufactured using the “tablet” method.
BACKGROUND OF THE INVENTION
A. Dispersion Managed Fibers
Dispersion managed fibers are optical fibers which have a low to zero net dispersion by purposely incorporating, along the axial length of the fiber, sections that have a positive dispersion and sections that have a negative dispersion.
The discovery of dispersion managed fibers arose, at least in part, from the realization that transmission of light at high bit rates (>40 Gbs) requires not only handling linear impairment but also non-linear impairments. Initial work was done on understanding how dispersion management helped NRZ transmission. However, very soon it was realized that this concept applied equally well to other forms of data transmission (soliton, RZ, etc.).
Dispersion management has been proposed at various length scales, in the 100's of meters range and in the 10's of kilometers range, with names such as “dispersion managed fibers” used to refer to management in the 100's of meters range and “dispersion managed cable” referring to management on the 10's of kilometers range. For ease of discussion, the terminology “dispersion managed fiber” is used herein for both ranges.
In broadest outline, dispersion management achieves global near net zero dispersion while still having finite local dispersion. That is, by controlling the product of the length (L
i
) and dispersion (D
i
) of the individual fiber sections, the sum of those products for the entire fiber (&Sgr;L
i
·D
i
) can be made small, thus giving the fiber the desired low to zero net dispersion. As used herein, the sum of the L
i
·D
i
products for a dispersion managed fiber is referred to as the fiber's “overall” dispersion.
A key advantage of using fiber sections having substantial local dispersions (substantial D
i
values) is the avoidance of the adverse consequences of various non-linear effects, including four wave mixing. By avoiding these problems, higher power densities can be propagated in dispersion managed fibers than in conventional low dispersion fibers. This is an important advantage in terms of increasing the transmitted bit rate, the repeater spacing, and the total system length. It should be noted that these improvements in fiber performance are achieved irrespective of the transmission format, e.g., the improvements in performance are achieved for NRZ, RZ, and soliton transmission.
In addition to making the sum of the L
i
·D
i
products small, for fibers which are to carry signals at a plurality of wavelengths, i.e., WDM fibers, it is also important to control the change in dispersion with wavelength (dD/d&lgr;) for the fiber (referred to hereinafter as the “dispersion slope” or “S”). More particularly, a dispersion managed fiber which is to be used in a WDM setting needs to have sections whose individual slopes (S
i
) are controlled so that &Sgr;L
i
·S
i
is close to or preferably equal to zero for the entire fiber.
The combination of the requirement that &Sgr;L
i
·D
i
is approximately equal to zero and that &Sgr;L
i
·S
i
is also approximately equal to zero, means that the ratio of D
i
to S
i
needs to be substantially the same for each section.
In addition to the foregoing, for very high bit rates, the variation in D
i
within a section (i.e., D
i
(l) where l is length along the fiber axis within a section) also becomes important. Specifically, if the variation in D
i
(l) is large, the non-linear effects which dispersion management is designed to address can still have an adverse effect on individual bits. That is, the system's “Q” value can be considerably reduced even though the average properties are well controlled over the whole system length.
A discussion of dispersion managed fibers, including the effects of local variations in dispersion, can be found in Anis et al., “Continuous Dispersion Managed Fiber For Very High Speed Soliton Systems,”
ECOC'
99
Proceedings
, Vol. 1, pages 230-232, 1999, and the references referred to therein, all of which are incorporated herein by reference.
B. The Problem of Process Variabilities in the Manufacture of Dispersion Managed Fibers
Dispersion managed fibers can be manufactured in various ways known in the art. As with any manufacturing process, the processes used in making dispersion managed fibers result in at least some variations in the product due to process variabilities. As discussed above, the entire concept of dispersion management is based on tight control of both global and local dispersion, as well as dispersion slope. Accordingly, dealing with the problem of process variabilities is especially important in the area of dispersion managed fibers.
As described in detail below, in accordance with the invention, certain fiber profiles have been discovered which satisfy the optical properties needed for a dispersion managed fiber and which are significantly less sensitive to process variations. Such profiles allow for the manufacture of dispersion managed fibers with improved overall properties compared to those previously known in the art.
C. Fracture Problems Associated with the “Tablet” Method of Manufacturing Dispersion Managed Fibers
A particularly efficacious approach to making dispersion managed fibers involves the use of individual “tablets” having the desired dispersion properties which are assembled together to form an entire fiber. A description of this process can be found in commonly assigned, co-pending, U.S. patent application Ser. No. 08/844,997, filed Apr. 23, 1997, and entitled “Method of Making Optical Fibers,” the contents of which are incorporated herein by reference. This application was published as PCT Patent Publication No. WO97/41076 on Nov. 6, 1997.
The tablets used in this process tend to suffer from fracturing problems during manufacture. These tablets are formed from a core cane (i.e., a cane containing the core of the fiber and some cladding) by various cutting techniques, including scoring/snapping, laser cutting, water jet cutting, saw cutting, and the like. After cutting, the transverse surfaces of the tablet may be polished if desired.
In accordance with a further aspect of the invention, it has been discovered that the fracturing observed during the cutting of tablets is due to residual stresses introduced into the core cane by prior processing steps. Surprisingly, it has been found that the same types of profiles which reduce sensitivities to processing variabilities, also solve the fracturing problem.
It should be noted that the profiles of the invention which reduce sensitivities to processing variabilities can be used with manufacturing techniques which do not involve the cutting of tablets and thus do not have the fracturing problem.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the invention to provide fiber profiles for use in dispersion managed fibers which exhibit reduced sensitivities to manufacturing variabilities. More particularly, it is an object of the invention to provide dispersion managed fibers having a plurality of sections wherein the standard deviation of the dispersion values for the sections is reduced compared to prior dispersion managed fibers. It is also an object of the invention to provide sections whose dispersion values exhibit less variation along the length of a section.
It is another object of the invention to provide fiber profiles which lead to relatively small changes in mode field diameter (MFD) at the junctions between the positive and negative dispersion sections of a dispersion managed fiber. The problems associated with mode field diameter mismatches at such junctions are discussed below.
It is an additional object of the i
Chervenak William J.
Corning Incorporated
Rojas Omar
Sanghavi Hemang
Wayland Randall S.
LandOfFree
Dispersion managed fibers having reduced sensitivity to... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Dispersion managed fibers having reduced sensitivity to..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Dispersion managed fibers having reduced sensitivity to... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3134631