Dispersion managed optical waveguide fiber

Details Dispersion managed optical waveguide fiber Dispersion managed optical waveguide fiber

2000-02-07

2001-11-13

Spyrou, Cassandra (Department: 2872)

Optical waveguides

Optical fiber waveguide with cladding

Utilizing multiple core or cladding

C385S123000, C359S199200

Reexamination Certificate

active

06317552

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention is directed to an optical waveguide fiber having a multi-ring core design which provides for large negative dispersion. In particular, the large negative dispersion is achieved while maintaining low bend loss, low splice loss, and polarization mode dispersion comparable to that of the waveguide fiber comprising the link to be compensated.
Many telecommunications links designed to operate in a wavelength window near 1300 nm have been installed. In general the waveguides manufactured for such links were designed to have a zero dispersion wavelength near 1300 nm to avoid signal distortion due to dispersion over long, unregenerated link lengths. More recently, the capability of operating at a wavelength window near 1550 nm has been developed. The 1550 nm window is advantageous because the attenuation of a silica based waveguide has a minimum there and the window lies near the center of the erbium doped optical amplifier gain curve. In fact, for a typical waveguide the attenuation near 1550 nm is less than 60% of the attenuation near 1300 nm. This large gain in signal to noise ratio as well as the possibility of extending link length without adding regenerators has made telecommunications operations at 1550 nm very attractive.
However, if a telecommunication link originally made for 1300 nm window operation is to be upgraded to include 1550 nm operation, the dispersion penalty due to the location of the dispersion zero must be overcome. Because the waveguides in these links weredesigned to have zero dispersion near 1300 nm, the dispersion at 1550 nm increases rapidly with link length. The dispersion at 1550 nm is typically about 15-20 ps
m-km.
Two strategies which may be used to remove the 1550 nm dispersion penalty are:
employ very narrow line width 1550 nm lasers; or,
introduce dispersion compensating waveguide fiber into the link.
A dispersion compensating waveguide fiber is one which has a dispersion of opposite sign relative to the link dispersion which is to be compensated. For example, a 1300 nm telecommunications system may have 18 ps
m-km dispersion at 1550 nm. A link length of 60 km is common. Thus, for 1550 nm operation over this link 1080 ps per nm of laser line width must be compensated to avoid a dispersion penalty. Even though very narrow line width distributed feedback lasers have been developed a considerable amount of dispersion remains to compensated at operating wavelengths far from the zero dispersion wavelength. Thus the dispersion compensating waveguide fiber can be used to advantage in systems employing very narrow linewidth lasers as well as lasers having a relatively broad emission band.
The technical innovations required to implement either of these strategies are sophisticated. In the case of the compensation waveguide strategy, waveguide core profiles which provide the proper amount of compensating dispersion must be found. The problem is complicated by the fact that changing the core refractive index profile to obtain a negative, i.e., compensating, dispersion, changes other properties of the waveguide. In particular, waveguide fibers having negative dispersion have been found to be more susceptible to bending loss, have higher polarization mode dispersion, and increased attenuation when compared to the original waveguide fiber used in the system. See. for example U.S. Pat. No. 5,361,319, Antos, et al.
The telecommunications industry, therefore, has a need for a dispersion compensating waveguide fiber which:
is resistant to bending loss;
has a high negative dispersion so that the compensating fiber length is relatively short,
has a low attenuation;
exhibits low splice loss with the original system waveguide; and,
has comparatively low polarization mode dispersion.
DEFINITIONS
The radius or width of the regions of the core are defined in terms of the index of refraction of the core along a radius. A particular region begins at the point where the refractive index characteristic of that region begins and ends at the last point where the refractive index is characteristic of that region. Radius and width will be expressed in terms of these beginning and ending points unless otherwise noted in the text.
An alpha refractive index profile is n=n
0
(1−&Dgr;(r/a)
&agr;
), where n
0
is the refractive index at the first point of the alpha index profile, &Dgr; is defined below, r is radius, and a is the radius measured from the first to the last point of the alpha index profile, and r is chosen to be zero at the first point of the alpha index profile.
The width of an index profile segment is the distance between two vertical lines drawn from the respective beginning and ending points of the index profile segment to the horizontal axis of the chart of refractive index vs. radius.
The % index delta is % &Dgr;=[(n
1
2
−n
c
2
)/2n
1
2
]×100, where n
1
is a core index and n
c
is the clad index. Unless otherwise stated, n
1
is the maximum refractive index in the core region characterized by a % &Dgr;.
The zero reference for refractive index is chosen as the minimum refractive index in the clad glass layer. A region of refractive index in the core which is less than this minimum value is assigned a negative value.
Bend performance is defined by a standard testing procedure in which the attenuation induced by winding a waveguide fiber about a mandrel is measured. The standard test calls for waveguide fiber performance with one turn about a 32 mm mandrel and with 100 turns about a 75 mm mandrel. The maximum allowed bending induced attenuation is usually specified in the operating window around 1300 nm and around 1550 nm.
SUMMARY OF THE INVENTION
The invention set forth in this application meets the need for a high performance dispersion compensating optical waveguide fiber without using fluorine.
A first aspect of the invention is a dispersion compensating single mode optical waveguide fiber having a central core region surrounded by a clad layer. To make the structure a waveguide, at least a portion of the core refractive index must be higher than the maximum refractive index of the clad layer which abuts and surrounds the core region. The core region of the novel dispersion compensating waveguide comprises at least five segments, a center segment symmetric about the long axis of the waveguide, and at least four annular segments symmetrically layered about the center segment. The center segment has a relative index, &Dgr;
c
%, which is in the range of 1.5% to 3.5%. The upper limit on &Dgr;
c
% depends upon what is practical in terms of doping capability and in terms of added attenuation as dopant percent increases. Large negative dispersion can be obtained using a center relative index higher than 3.5%, but dopant levels high enough to produce such an index are usually impractical and not cost effective. A preferred range for &Dgr;
c
% is 2% to 3%.
The magnitudes of the relative indexes are all positive and are chosen as follows: the center relative index is largest; the successive odd numbered surrounding segments or layers, beginning with the number 1 for the layer abutting the center segment, are smaller in magnitude than &Dgr;
c
%; the successive even numbered surrounding layers are smaller in magnitude than &Dgr;
c
% but larger in magnitude than the odd numbered layers.
The center segment is characterized by a radius and the successive annular segments are characterized by widths. The novelty of the waveguide structure is defined by the choice of relatives indexes, &Dgr;%, and the center radius and widths of the annular segments which make up the core. In particular, the &Dgr;%'s and radius and widths are chosen such that the total dispersion of the waveguide is more negative than about −85 ps
m-km. The waveguide attenuation depends upon the relative index of the center segment, &Dgr;
c
%. For &Dgr;
c
% near 2% the attenuation is less than about 0.55 dB/km over a pre-selected band of wavelengths which lies in the wavelength range 1520 nm to 1600 nm. A wavelength of

Affiliated with

Also associated with

Rating

Dispersion managed optical waveguide fiber 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 optical waveguide fiber, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Dispersion managed optical waveguide fiber will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2603823