The investigation results on phase optical sensors are presented. Phaseacoustic sensitivity of two- and three-layered (w-type) fibers with various polimeric jackets as well as without any coatings has been measured. To provide a rapid and reliable measurement of the phaseacoustic sensitivity of fibers it is suggested that a wideband acoustic noise signal should be employed. The operation of a fiber interferometer with alternating current automatic phase control (ACAPC) has been analysed. It has been shown that the detectability of this interferometer is about 1.7 times as low as that in the absence of ACAPC. Detectability characteristics of the autodyne laser sensor with a monomode fiber has been investigated.