Abstract The demodulation character of 3 ×3 optic fiber couplers is analyzed , and the application in the coherent communication system and speech signal collection is pointed out in the paper. By the experiment , the feasibility of speech signal collection system by the way of the all light is verified. Key words optic fiber couplers , speech signal collection , full light 全光纖多功能研發(fā)平臺(tái)