We theoretically and experimentally investigated the optical performance of fiber connections with various air-filled gaps. Such gaps might occur when a fiber connection realized using physical contact (PC) fails unexpectedly resulting in imperfect PC. The experimental results suggested that the optical performance of these fiber connections depends on both wavelength and gap width. When the air-filled gap between the fiber ends is narrow (of wavelength order) the insertion loss increases between 0.0 and 0.6 dB. The return loss varies greatly and the worst value is about 8.7 dB. When the gap is much wider than the wavelength, the insertion losses are mainly affected by the radiation loss in the air-filled gap between the fiber ends and the return losses are close to 14.7 dB, which is the Fresnel reflection value at a fiber end in air. We also found that in the worst case the insertion and return losses for fiber connections with imperfect PC can deteriorate respectively to ~18 and 9.4 dB at a wavelength of 1.31 μm and ~17 and 9.9 dB at a wavelength of 1.55 μm. In addition, we studied the characteristics of multi-connected PC-type connectors with an air-filled gap. We discovered that the total returned light from multi-connected joints with an air-filled gap could deteriorate to 5.9 dB at worst for four-connected connectors. These results support the practical use of PC-type connectors in the construction and operation of optical network systems.
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