A pressure transmitter for detection of a physical variable relative to a process fluid, comprising: a first and a second pressure-sensitive membrane suitable for interfacing with said process fluid; a pressure sensor having a supporting body provided with a cavity inside which a third pressure-sensitive membrane is positioned; an analysis and conditioning unit operationally coupled to at least one light source; a first and a second optical fiber having a first end operationally coupled to said power source; said first and second optical fibers transmitting the light signals emitted by said source to said third membrane and the signals reflected by the third membrane to said analysis and conditioning unit which generates signals indicating said physical variable.