A cleaved lead-in optical fiber [single-mode fiber (SMF-28)]
was spliced with a 3.3-mm-long hollow fiber with inside diameter
(I.D.) of 75 m and outside diameter (O.D.) about 125 m
by using a optical fiber fusion splicer (Sumitomo, Type-36).
Another cleaved optical fiber with O.D. of 60–65 m was inserted
into the hollow fiber from the other end as a reflecting
fiber to form an FP cavity between these cleaved two fiber end
faces. The thinner fiber can be obtained by etching or drawing
a standard optical fiber (125- m O.D.). The lead-in fiber was
connected to a white light interferometer system [8].