Gradient index optical waveguide and method of making

The method of making an optical waveguide having a radial gradient index of refraction in the core thereof, comprising:

• forming a glass tubular member having at least three constituents including a silicon compound and dopants, a first of said constituents being a dopant which produces glass having a changing refractive index and thermal expansion coefficient with variations in concentration, a second of said constituents being a dopant producing changing thermal expansion coefficient with variations in concentration;
• radially changing the concentration of said first of said constituents while forming to produce a radially varying index of refraction;
• changing the concentration of said second of said constituents radially while forming to maintain the thermal expansion coefficient substantially constant throughout said radial gradient of said tubular member;
• coating said tubular member with a layer of cladding glass having an index of refraction less than that of the core formed by the preceding steps;
• and
• adding to the composition of said cladding layer a constituent producing substantially no increase in the index of refraction and which increases the thermal expansion coefficient of said cladding to approximately the composite thermal expansion coefficient of said core so that residual stresses in said core caused by a different expansion coefficient cladding become compressive.