In this letter, we present a hollow fiber based miniature EFPI
(MEFPI) fiber-optic pressure sensor, which has a diameter of
only 125 m. The structure of the pressure sensor is shown in
Fig. 1. The length of the FP cavity (air gap) will decrease with
the reduction in length of the hollow fiber as a result of the applied
pressure. Light is injected into the lead-in optical fiber and
partially reflected (4%) by the end faces of the two fibers. Then
the two reflections propagate back through the same lead-in
fiber and generate interference fringes, which will be demodulated
to determine the air gap thickness. The FP cavity length
can be adjusted with high precision in a wide range, giving a
great deal of flexibility in the choice of light source or the signal
demodulation scheme selection.