A modular fiber optic sensor that uses a light source to transmits light through at least one optical fiber to a sensor support. The sensor support is releasably attached to the optical fiber(s) allowing the use of both a single and multiple fibers. Diaphragms are exchangably attached to the sensor support allowing numerous diaphragm configurations to be attached to the sensor support. The different diaphragm configurations allow the sensor to detect a wide range of physical phenomena. A detection system is coupled to the optical fiber(s) that determines the change in light intensity which is reflected from the diaphragm's reflector.