應用半導體雷射及超外差式相位檢測技術，量測鈮酸鉀晶體及光纖之光熱係數。外差拍差信號(heterodyne beating Signal)，由載波及上下旁波帶拍差而得，其相關於上下旁波及載波在共振腔行走之相位移，相位差信號由相位敏感檢測(phase sensitive detection)決定，並發現信號與溫度相依，由溫度相依，決定鈮酸鉀b 軸及c軸之光熱係數，各為-4×10-5及6.7×10-5℃-1單模光纖之光熱係數為9.2×10-6℃-1。 並使用新穎Fabry-Perot干涉儀技術，也可量測鈮酸鉀之光熱係數，由於共振腔穿透光之橫模變化與其溫度相依，並由此決定鈮酸鉀晶體b軸之光熱係數各為-4×10-5及6.7×10-5℃-1，此結果與超外式相位檢測干涉技術量測之數值相當一致。 A heterodyne interferometric technique is applied to determine the thermo-optic coefficients of a KNbO3 crystal and a single ode fiber with a GaAlAs diode laser. The heterodyne beats signal, resulting from the beating of the carrier and two side-band frequencies, is related to the phase shift difference between the carrier and the side-bands. This phase shift difference is determined with a phase sensitive detection technique and is found to be temperature dependent. From the temperature dependence, the thermo-optic coefficients of the KNbO3 crystal along the b and c cry-stallographic axis are determined to be -4.5×0.00001 and 6.7×0.00001/˚C ,respectively . The thermo-optic coefficient of a single mode fiber is found to be 9.2×0.000001/˚C .Using a novel Fabry-perot interferometer technique , we were also able to measured the thermo-optic coefficient of a KNbO3 crystal . In this technique the trausverse intensity distributions of the laser transmitted through the crystal were found to be temperature dependent , and the thermo optic coefficints along crystallongraphic axis b and c axis were determined to be and 6.1×0.00001/˚C , respectively . The results agreed well with the results obtained by heterodyne interferometric technique .