Optical waveguides – Optical fiber waveguide with cladding – With graded index core or cladding
Reexamination Certificate
2000-07-07
2002-06-04
Spyrou, Cassandra (Department: 2872)
Optical waveguides
Optical fiber waveguide with cladding
With graded index core or cladding
C385S123000
Reexamination Certificate
active
06400879
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a single mode waveguide fiber having a refractive index profile, a core diameter, and a relative index which provide a high non-linearity coefficient. In particular, the high non-linearity coefficient is obtained together with pre-selected values for zero dispersion wavelength, cut off wavelength, and spectral attenuation in the 1550 nm operating window.
The &agr;-profile waveguide fiber core has been studied in considerable detail over the past several decades. The design of the first single mode waveguide to be manufactured included a step index profile in the central core region.
Core refractive index profile design has evolved as waveguide optical systems requirements have changed. The study of the core profile has been driven by the need for such waveguide features as:
positioning of cut off wavelength;
positioning of zero dispersion wavelength;
lower attenuation;
improved bend resistance; and,
lower total dispersion and dispersion slope.
More recently, the very high performance telecommunication systems, i.e., those which include multiplexing, high data rates, long regenerator spacing, soliton propagation, or optical amplifiers, have resulted in a broader study of core index profiles to include designs which have high effective area to minimize signal distortion and dispersion due to non-linear effects.
In certain devices, however, increase in non-linear index of refraction or decrease in effective area can improve performance. One notable case in which performance is enhanced by increased non-linearity is that of a wavelength conversion device based upon modulational instability.
What is required by devices which make use of highly non-linear waveguide fiber is that the non-linear waveguide retain such characteristics as those noted above. The difficulty of making non-linear waveguides is therefore compounded because increased non-linearity usually requires increased concentration of glass forming metal oxides, termed dopants, which alter the waveguide core refractive index. The increased dopant concentration results in higher attenuation and effects mode power distribution which in turn effects the waveguide properties required for efficient operation of a device using the non-linear waveguide. In particular, increased dopant concentration causes the zero dispersion wavelength to increase beyond the wavelength region useful for soliton propagation.
DEFINITIONS
The effective area is
A
eff
=2&pgr; (SE
2
r dr)
2
/(SE
4
r dr), where the integration limits are 0 to ∞, and E is the electric field associated with the propagated light. An 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;=(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 the refractive index in the reference region which is usually taken to be the minimum index of the clad layer.
For the particular profile described in this application, the core region has one segment. The notation &Dgr;
o
is used to describe the relative index of this single segment. The notation &Dgr;
c
is used to describe the relative index of the clad region.
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 alpha profile refers to a refractive index profile which follows the equation, n(r)=n
0
(1−&Dgr;[r/a]
&agr;
) where r is core radius, &Dgr; is defined above, a is the last point in the profile, r is chosen to be zero at the first point of the profile, and &agr; is an exponent which defines the profile shape. Other index profile shapes include a step index, a trapezoidal index and a rounded step index, in which the rounding is due to dopant diffusion in regions of rapid refractive index change.
SUMMARY OF THE INVENTION
The novel single mode waveguide of this application meets the need for a waveguide which is highly non-linear, but retains the required characteristics in terms of low attenuation in the 1550 nm window, properly positioned zero dispersion and cut off wavelengths, low, positive total dispersion, and low dispersion slope.
A first aspect of the invention is a single mode optical waveguide having a core region surrounded by a clad layer. The core region has a surface, a diameter, a relative refractive index, &Dgr;
o
, and a refractive index profile. The diameter of the core is measured from the central long axis of the single mode fiber to the core surface. The relative index of the core, &Dgr;
o
, is greater than &Dgr;
c
, the relative index of the clad. Both relative indexes are referenced to n
c
, the minimum refractive index of the clad layer.
The core region profile is an x-profile, for which the relative index is in the range 0.016 to 0.040, and the diameter is in the range 3 &mgr;m to 8 &mgr;m. Given this basic structure, two key waveguide fiber parameters, which serve to define the waveguide, are, a zero dispersion wavelength, &lgr;
o
, in the range of about 1500 nm to 1570 nm, and a non-linearity constant in the range of about
3
×
10
-
16
cm2
W
to
13
×
10
-
16
cm2
W
.
The non-linearity constant is n
2
in the equation for refractive index, n=n
o
+n
2
P/A
eff
, in which P is transmitted power, n
o
is the linear refractive index, and A
eff
is the effective defined above.
This novel waveguide, when incorporated in a wavelength conversion device, improves the performance thereof. In an embodiment of this aspect, the waveguide core has &agr; in the range of about 1.8 to 2.4, core diameter in the range 5 &mgr;m to 6 &mgr;m, and core relative index in the range of about 0.019 to 0.030. In this embodiment and in the first aspect of the invention, cut off wavelength is in the range of about 1400 nm to 1500 nm, attenuation at 1550 nm is not greater than 1 dB, the dispersion slope is in the range of 0.03 ps
m
2
-km to 0.10 ps
m
2
-km, and total dispersion over the wavelength range 1520 nm to 1600 nm is positive but not greater than about 2 ps
m-km.
Calculations have shown that the required waveguide properties together with the required waveguide non-linearity can be realized when the &agr; is very large, which means the &agr;-profile is essentially a step index profile. Thus, &agr; values in the range of 1.8 to infinity are contemplated by the inventors. Thus an embodiment of the invention is a step profile or a rounded step profile. The &Dgr; value and core diameter do not change in this embodiment of the profile shape.
In another embodiment of this first aspect the clad layer refractive index profile is flat and has a constant refractive index equal to the minimum index, n
c
.
The invention may also be described solely in terms of a particular geometry associated with a particular a of the waveguide &agr;-profile. Thus, the invention is a single mode optical waveguide fiber having a core and a clad as described in the first aspect of the invention above. The &agr; of the core region profile is in the range of about 1.8 to 2.4, the relative index of the core is in the range 0.019 to 0.030, and the core diameter is in the range 5 &mgr;m to 6 &mgr;m. In an embodiment preferred because of simplicity of manufacture, the clad layer refractive index profile is flat and has a refractive index equal to the minimum clad index, n
c
. Here again, higher values of &agr; are calculated to be effective in producing a waveguide having all the required properties. Thus, step index and rounded step index are also proper descriptors of the profile shape of the novel waveguide.
REFERENCES:
patent: 4755022 (1988-07-01), Ohashi et al.
Kato, T., et al., “Estimation of Nonlinear Refractive Index in Various Silica-Based Glasses for Optical Fibers”, Optics Letters, vol. 20, No. 22, Nov. 15, 1995, pp. 2279-2281.
Onishi, M. et al., “Highly Nonline
Hawk Robert M.
Nolan Daniel A.
Tarcza Steven H.
Amari Alessandro V.
Chervenak William J.
Corning Incorporated
Spyrou Cassandra
LandOfFree
Highly non-linear single mode waveguide does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Highly non-linear single mode waveguide, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Highly non-linear single mode waveguide will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2981845