On the thermo-optic coefficient of P₂O₅ in SiO₂

Measurements of the thermo-optic coefficient (dn/dT) are made on a binary phosphosilicate core glass optical fiber. Using these results, dn/dT for the P₂O₅ constituent is found to be -13.3 × 10^-6 ± 8.0% K^-1, a value much lower in magnitude than reported in the literature for this system. Its accurate elucidation is especially useful in guiding the design of low- or negative-thermo-optic glasses and optical fibers. The phosphosilicate core also has a coefficient of thermal expansion that is higher than that of the pure silica cladding. As a result, the clad fiber geometry slightly lessens the effectiveness of the negative-valued contribution to dn/dT by P₂O₅ relative to bulk glass.