MATERIAL HAVING SMALL OPTICAL PATH LENGTH CHANGE

PROBLEM TO BE SOLVED: To provide a material having a low temperature dependence of an optical path length, which is available for optical communication and an optical integrated circuit board.SOLUTION: A complex oxide material of Sr(Ti,Zr)O, in which strontium zirconate (SrZrO) is added to strontium titanate (SrTiO), has an optical path length temperature coefficient (OPD) that is controllable. Here, OPD=1/S×dS/dT=CTE + 1/n×dn/dT, where S is an optical path length; CTE is a linear thermal expansion coefficient; n is a refractive index; and dn/dT is a temperature coefficient of a refractive index. In particular, an absolute value of the OPD is 6 ppm/°C or less in a range of "0.20