Optical waveguide containing P.sub.2 O.sub.5 and GeO.sub.2

DETAILED DESCRIPTION It is an object of this invention to provide an economical and more easily formed optical waveguide fiber that overcomes the heretofore noted disadvantages.
Another object of this invention is to provide an optical waveguide fiber having a high numerical aperture.
A further object of this invention is to provide an optical waveguide in which both the thermal coefficient of expansion and the softening temperature of the core are compatible with those of the cladding regardless of the difference between the refractive indices of the core and cladding.
Briefly, according to this invention, an optical waveguide is produced comprising a cladding layer formed of relatively high purity glass and a core of high purity glass containing a sufficient amount of GeO.
sub.
2 and P.
sub.
2 O.
sub.
5 to increase the refractive index of the core to a value greater than that of the cladding layer.
The cation impurity level of the core does not exceed 10 parts per million of transition elements.
The waveguide of this invention is an improvement over germania doped waveguides which have recently been employed in an attempt to provide waveguides of increased numerical aperture.
The partial substitution of P.
sub.
2 O.
sub.
5 for GeO.
sub.
2 in the GeO.
sub.
2 -SiO.
sub.
2 glass system results in a decrease in the softening point temperature with substantially no change in expansion coefficient.
Depending upon the amount of P.
sub.
2 O.
sub.
5 and GeO.
sub.
2 in the resultant glass, there is often an increase in refractive index as compared with the corresponding GeO.
sub.
2 -SiO.
sub.
2 glass which contains the same amount of SiO.
sub.
2.
These features are advantageous in that they permit high NA optical waveguide fibers to be fabricated with less difficulty than was heretofore encountered.
By adjusting the ratio of GeO.
sub.
2 to P.
sub.
2 O.
sub.
5 in the core glass of an optical waveguide fiber the softening point temperature of the core glass can be made compatible with that of the cladding glass.
Moreover, the waveguides of the present invention possess the advantages of germania doped fibers, viz