A photonic thermometer module assembly includes: a sheath; a sheath bottom plug; a sheath top flange; a top sealing flange; a heat exchanger; a photonic thermometer disposed on the heat exchanger such that the photonic thermometer determines a temperature of the sheath; and an optical fiber array in optical communication with the photonic thermometer and that optically couples the photonic thermometer to an exterior environment of the photonic thermometer module assembly, wherein the photonic thermometer module assembly is compatible with International Temperature Scale of 0 (ITS-90) fixed-point cell infrastructure and conventional drywell and oil-bath calibrations, and the photonic thermometer module assembly provides temperature measurements from −200° C. to +700° C.