Optical waveguides – Optical fiber waveguide with cladding – Utilizing multiple core or cladding
Reexamination Certificate
2000-11-02
2002-07-16
Bovernick, Rodney (Department: 2874)
Optical waveguides
Optical fiber waveguide with cladding
Utilizing multiple core or cladding
C385S124000
Reexamination Certificate
active
06421491
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a waveguide fiber having large effective area, and particularly to such a fiber designed for use over an extended wavelength range.
2. Technical Background
Dispersion shifted optical waveguide fiber having large effective area, for example that disclosed and described in U.S. Pat. No. 5,835,655, Liu et al., has been developed for use in the wavelength range which spans the low attenuation wavelength window around 1550 nm. The large effective area of the waveguide serves to limit non-linear dispersion effects that can occur in high power or high data rate systems. In U.S. Pat. No. 5,748,824, Smith, is disclosed a dispersion shifted waveguide fiber having its zero dispersion wavelength outside the operating window to limit losses in wavelength division multiplexed systems due to four wave mixing and cross phase modulation. In particular, the zero dispersion wavelength is designed to be less than the lower wavelength of the operating window so that the linear dispersion is non-zero and positive over the operating window. In such a waveguide fiber design, non-linear self phase modulation as well as four wave mixing and cross phase modulation effects are curtailed.
The demand for additional capacity has encouraged a search for waveguide index profile designs that extend the operating window into the L-band, typically defined as the wavelength range 1565 nm to 1625 nm or 1650 nm. A successful design for this extended operating range would exhibit a dispersion magnitude over the entire operating wavelength range sufficient to limit the four wave mixing and cross phase modulation effects, which become larger in systems having relatively smaller channel spacing. Such waveguide fiber designs preferably would not sacrifice performance in the C-band, typically defined as the wavelength range from 1530 nm to 1565 nm. In addition, the total dispersion slope would preferably be low enough to preclude high linear dispersion at the upper end of the wavelength range.
The problem of designing a waveguide fiber having a desired magnitude of total dispersion over at least the S (1470 nm to 1530 nm), C (1530 nm to 1565 nm), and L (1565 nm to 1650 nm) bands is addressed by the present invention. An extended S band defined as the wavelength range from 1350 nm to 1530 nm is also addressed in this application.
Definitions
The following definitions are in accord with common usage in the art.
The refractive index profile is the relationship between refractive index or relative refractive index and waveguide fiber radius.
A segmented core is one that is divided into at least a first and a second waveguide fiber core portion or segment. Each portion or segment is located along a particular radial length, is substantially symmetric about the waveguide fiber centerline, and has an associated refractive index profile.
The radii of the segments of the core are defined in terms of the respective refractive indexes at respective beginning and end points of the segments. The definitions of the radii used herein are set forth in the figures and the discussion thereof.
Total dispersion of a waveguide fiber is the sum of the material dispersion, the waveguide dispersion, and the inter-modal dispersion. In the case of single mode waveguide fibers the inter-modal dispersion is zero.
The sign convention generally applied to the total dispersion is as follows. Total dispersion is said to be positive if shorter wavelength signals travel faster than longer wavelength signals in the waveguide. Conversely, in a negative total dispersion waveguide, signals of longer wavelength travel faster.
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 light propagated in the waveguide. An effective diameter, D
eff
, may be defined as,
A
eff
=&pgr;(D
eff
/2)
2
.
The relative refractive index percent, &Dgr;%=100×(n
i
2
−n
c
2
)/2n
i
2
, where n
i
is the maximum refractive index in region i, unless otherwise specified, and n
c
is the average refractive index of the cladding region.
The term &agr;-profile refers to a refractive index profile, expressed in terms of &agr; (b)%, where b is radius, which follows the equation,
&Dgr;(b)%=&Dgr;(b
o
)(1−[|b−b
o
|/(b
1
−b
o
)]
&agr;
),
where b
o
is the point at which &Dgr;(b)% is maximum, 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.
The pin array bend test is used to compare relative resistance of waveguide fibers to bending. To perform this test, attenuation loss is measured for a waveguide fiber with essentially no induced bending loss. The waveguide fiber is then woven about the pin array and attenuation again measured. The loss induced by bending is the difference between the two attenuation measurements. The pin array is a set of ten cylindrical pins arranged in a single row and held in a fixed vertical position on a flat surface. The pin spacing is 5 mm, center to center. The pin diameter is 0.67 mm. The waveguide fiber is caused to pass on opposite sides of adjacent pins. During testing, the waveguide fiber is placed under a tension just sufficient to make the waveguide conform to a portion of the periphery of the pins. The test pertains to macro-bend resistance of the waveguide fiber.
Another bend test referenced herein is the lateral load test. In this test a prescribed length of waveguide fiber is placed between two flat plates. A #70 wire mesh is attached to one of the plates. (The market code #70 mesh is descriptive of screen made of wire having a diameter of 0.178 mm. The screen openings are squares of side length 0.185 mm.) A known length of waveguide fiber is sandwiched between the plates and a reference attenuation is measured while the plates are pressed together with a force of 30 newtons. A 70 newton force is then applied to the plates and the increase in attenuation in dB per unit length is measured. This increase in attenuation is the lateral load attenuation of the waveguide. The test pertains to the micro-bend resistance of the waveguide fiber.
SUMMARY OF THE INVENTION
A first aspect of the present invention is an optical waveguide fiber, typically a single mode optical waveguide fiber, having a core region surrounded by a clad layer. The core region and the clad layer are characterized by respective refractive index profiles. The core region is divided into a central segment, a first annular segment surrounding the central segment, and a second annular segment surrounding the first annular segment. Each segment has a refractive index profile and an inner and an outer radius. The core segments are configured to provide a waveguide fiber having a positive total dispersion in the range of 1.0 ps
m-km to 16.0 ps
m-km over a wavelength range extending from 1470 nm to 1625 nm.
An extension of this aspect (aspect extension) of the invention is one in which the wavelength range of operation is 1450 nm to 1625 nm. The total dispersion (sometimes referred to as chromatic dispersion) is in the range of 0.1 ps
m-km to 18 ps
m-km over the range of operation, and the zero dispersion wavelength is less than 1450 nm. In a preferred embodiment of the aspect extension, the total dispersion at 1525 nm is no greater than 11 ps
m-km.
At 1550 nm the waveguide of this first aspect is characterized by an effective area greater than 60 &mgr;m
2
, preferably greater than 70 &mgr;m
2
, and an attenuation less than 0.25 dB/km, preferably less than 0.20 dB/km. In the aspect extension the effective area is greater than 70 &mgr;m
2
and preferably greater than 80 &mgr;m
2
. The attenuation at 1550 nm of the aspect extension is less than 0.20 dB/km. At 1600 nm the first aspect of the invention has e
Bovernick Rodney
Chervenak William J.
Corning Incorporated
Stahl Michael J.
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