We propose and experimentally demonstrate a novel scheme to generate optical frequency-locked multicarriers by using double recirculation frequency shifter loops based on different frequency shifting direction single-sideband modulation in I/Q modulators driven by RF clock signals. By changing the phase difference of I and Q RF drive signal, each loop generates long wavelength and short wavelength subcarriers, respectively. The tone-to-noise ratio (TNR) performance with amplified spontaneous emission noise and the effect of polarization state are theoretically analyzed and experimentally investigated for the first time. Experimental results are in good agreement with the theoretical analysis. Using this scheme, we successfully generate 104 frequency-locked subcarriers with TNR larger than 17 dB and carrier spacing at 12.5 GHz covering 10.21 nm from 1545.01 to 1555.22 nm which shows that this scheme has great potential in future Tb/s per channel communications. The feasibility of this scheme is demonstrated by the experimental results.