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The multiplexing capacity of single-/multi-/single- mode (SMS) intrinsic Fabry-Pérot fiber sensor is dramatically enhanced by reducing its insertion loss. This improvement is achieved by controlling the cavity length to promote refocusing of the guided light when entering the lead-out single mode fiber. With this technique, the round-trip insertion loss of the sensor is reduced from about -3 dB on average to below -0.5 dB, and the signal-to-noise-ratio-defined multiplexing capacity is accordingly increased from six to more than twenty. The paper employs a mode theory based approach to rigorously treat the refocusing problem. Other engineering issues, such as splicing condition and sensor additional phase are analyzed and demonstrated as well.