In a preferred embodiment, the invention provides a 
fiber optic 
pressure sensor apparatus which includes a 
light source, a reflective sensor diaphragm movable in accordance with pressure in a medium and an 
optical fiber coupled to the 
light source for delivering a first 
wavefront of light to the reflective sensor diaphragm. The 
optical fiber has an endface which is separated from the reflective sensor diaphragm by a gap, the endface receiving a second 
wavefront of light reflected from the reflective sensor diaphragm. The first and second wavefronts constructively and destructively interfere to create a modulated optical 
signal. A 
spectrometer is coupled to the 
optical fiber for converting the optical 
signal into a series of digital values, and means for analyzing the digital values is provided for obtaining a measurement of the pressure in the medium. An 
optical coupler is preferably provided for 
coupling the 
light source, the optical 
fiber, and the 
spectrometer. A power monitoring 
optical detector means may be coupled to the light source by the 
optical coupler. A graded-index lens may be coupled to the endface of the optical 
fiber. The angle between the endface and a longitudinal axis of the optical fiber may be formed to be between zero and 11 degrees. A sealed or vented sensor body may be provided. In sealed embodiments, organic adhesives are preferably used to seal the sensor body. The means for analyzing the digital values preferably includes means for recovering phase information from the modulated optical 
signal by taking a 
Fourier transform of the modulated optical signal. Sensor gap measurements are then derived from this phase information.