We demonstrate a novel all-optical noninverted OC-192 return-to-zero (RZ) decision-gate by using a semiconductor optical amplifier (SOA) which is gain-controlled to achieve an extremely high cross-gain-modulation depth and a narrow gain window. A dark-optical-comb generated by reshaping the optical clock RZ data in a Mach-Zehnder intensity modulator is employed as an injecting source to temporally deplete most of the gain in the SOA. Such a dark-optical-comb injected SOA decision-gate exhibits improved 311 regeneration performances such as a timing tolerance of 33.5 ps, a Q-factor of 8.1, an input dynamical tolerance of 14 dB, and an extinction ratio (ER) of 14 dB. The deviation between the wavelengths of backward injected dark-optical-comb and input RZ data for optimizing the ER of the decision-gate is determined as Delta lambda = 19 nm. Under a threshold operating dark-optical-comb power of 7 dBm, such a decision-gate can recover the - 18.5-dBm degraded RZ data with a bit-error-rate of less than 10(-9) at 10 Gb/s. A negative power penalty of -4.2 dB is demonstrated for the RZ data after 50-km propagation and decision gating.