Optical waveguides – Optical fiber waveguide with cladding – Utilizing multiple core or cladding
Reexamination Certificate
1999-07-27
2002-01-29
Bovernick, Rodney (Department: 2874)
Optical waveguides
Optical fiber waveguide with cladding
Utilizing multiple core or cladding
C385S124000, C385S126000
Reexamination Certificate
active
06343176
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention is directed to a single mode optical waveguide fiber designed for long repeater spacing, high data rate telecommunication systems. In particular, the single mode waveguide combines excellent bend resistance, low attenuation, and large effective area, A
eff
, features that are desired for undersea applications.
A waveguide having large effective area reduces non-linear optical effects, including self phase modulation, four wave mixing, cross phase modulation, and non-linear scattering processes, all of which can cause degradation of signals in high power systems. In general, a mathematical description of these non-linear effects includes the ratio, P/A
eff
, where P is optical power. For example, a non-linear optical effect can be described by an equation containing a term, exp [P×L
eff
/A
eff
], where L
eff
is effective length. Thus, an increase in A
eff
produces a decrease in the non-linear contribution to the degradation of a light signal.
The requirement in the telecommunication industry for greater information capacity over long distances, without electronic signal regeneration, has led to a reevaluation of single mode fiber index profile design. The genera of these profile designs, which are called segmented core designs in this application, are disclosed in detail in U.S. Pat. No. 4,715,679, Bhagavatula.
The focus of this reevaluation has been to provide optical waveguides which:
reduce non-linear effects such as those noted above;
are optimized for the lower attenuation operating wavelength range around 1550 nm;
are compatible with optical amplifiers; and,
retain the desirable properties of optical waveguides such as high strength, fatigue resistance, and bend resistance.
The definition of high power and long distance is meaningful only in the context of a particular telecommunication system wherein a bit rate, a bit error rate, a multiplexing scheme, and perhaps optical amplifiers are specified. There are additional factors, known to those skilled in the art, which have impact upon the meaning of high power and long distance. However, for most purposes, high power is an optical power greater than about 10 mw. In some applications, signal power levels of 1 mW or less are still sensitive to non-linear effects, so that A
eff
is still an important consideration in such lower power systems.
A long distance is one in which the distance between electronic regenerators can be in excess of 100 km. The regenerators are to be distinguished from repeaters which make use of optical amplifiers. Repeater spacing, especially in high data density systems, can be less than half the regenerator spacing.
To provide a suitable waveguide for multiplexed transmission, the total dispersion should be low, but not zero, and have a low slope over the window of operating wavelength. In systems in which the suppression of potential soliton formation is important, the total dispersion of the waveguide fiber should be negative, so that the linear dispersion cannot counteract the non-linear self phase modulation which occurs for high power signals.
A typical application for such a waveguide fiber is undersea systems that, in order to be economically feasible, must carry high information rates over long distances without regenerators and over an extended window of wavelengths. The present invention describes a novel profile that is singularly suited to for use in these stringent conditions. The desired properties of the waveguide fiber for such a system are set forth in detail below.
Definitions
The following definitions are in accord with common usage in the art.
The radii of the segments of the core are defined in terms of the index of refraction. A particular segment has a first and a last refractive index point. The radius from the waveguide centerline to the location of this first refractive index point is the inner radius of the core region or segment. Likewise, the radius from the waveguide centerline to the location of the last refractive index point is the outer radius of the core segment.
The segment radius may be conveniently defined in a number of ways, as will be seen in the description of
FIGS. 1 & 2
below. In the case of
FIG. 2
, from which Tables 1 & 2 are derived, the radii of the index profile segments are defined as follows, where the reference is to a chart of &Dgr; % vs. waveguide radius:
the radius of the central core segment, r
1
, is measured from the axial centerline of the waveguide to the intersection of the extrapolated central index profile with the x axis, i.e., the &Dgr; %=0 point;
the outer radius, r
2
, of the first annular segment is measured from the axial centerline of the waveguide to the intersection of the first annular segment profile with a vertical line drawn through the &Dgr; % point which is half of the &Dgr; % difference between the first and the second annular segment profile;
the outer radius, r
3
, of the second annular segment is measured from the axial centerline of the waveguide to the intersection of the second annular segment profile with a vertical line drawn through the &Dgr; % point which is half of the &Dgr; % difference between the second and third annular segment profile;
the outer radius of any additional annular segments is measured analogously to the outer radii of the first and second annular segments; and,
the radius of the final annular segment is measured from the waveguide centerline to the midpoint of the segment.
The width, w, of a segment is taken to be the distance between the inner and outer radius of the segment. It is understood that the outer radius of a segment corresponds to the inner radius of the next segment.
No particular significance is attached to a particular definition of index profile geometry. Of course, in carrying out a model calculation the definitions must be used consistently as is done herein.
The effective area is
A
eff
=2&pgr;(∫E
2
r dr)
2
/(∫E
4
r dr), where the integration limits are 0 to ∞, and E is the electric field associated with the propagated light. The effective area is wavelength dependent. The wavelength at which the effective area is calculated is the wavelength at or near the center of the operating window for which the waveguide fiber is designed. More than one A
eff
may be assigned to a waveguide fiber which operates over a range of the order of hundreds of nanometers.
Effective diameter, D
eff
, may be defined as,
A
eff
=&pgr;(D
eff
/2)
2
.
The relative index, &Dgr; %, is defined by the equation,
&Dgr; %=100×(n
1
2
-n
2
2
)/2n
1
2
, where n
1
is the maximum refractive index of the index profile segment 1, and n
2
is a reference refractive index which is taken to be, in this application, the refractive index of the clad layer.
The term refractive index profile or simply index profile is the relation between &Dgr; % or refractive index and radius over a selected portion of the core.
The term &agr;-profile refers to a refractive index profile expressed in terms of &Dgr;(b) %, where b is radius, which follows the equation, &Dgr;(b)%=&Dgr;(b
0
)(1−[¦b-b
0
¦/(b
1
−b
0
)]
&agr;
), where b
0
is the radial point at which the index is a maximum and b
1
is the point at which &Dgr;(b)% is zero and b is in the range b
i
≦b≦b
f
, where delta is defined above, b
i
is the initial point of the &agr;-profile, b
f
is the final point of the &agr;-profile, and &agr; is an exponent which is a real number.
Other index profiles include a step index, a trapezoidal index and a rounded step index, in which the rounding is typically due to dopant diffusion in regions of rapid refractive index change.
Total dispersion is defined as the algebraic sum of waveguide dispersion and material dispersion. Total dispersion is sometimes called chromatic dispersion in the art. The units of total dispersion are ps
m-km.
The bend resistance of a waveguide fiber is expressed as induced attenuation under prescribed test conditions. Standard test conditions include 100 turns of wa
Li Ming-Jun
Stone Jeffery Scott
Bovernick Rodney
Chervenak William J.
Corning Incorporated
Song Sarah N
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