Proposed is an approach to achieving a carrier-envelope-offset (CEO)-locked frequency comb with 25 GHz mode spacing in the telecommunications wavelength region. To achieve the approach, a 250 fs laser pulse train at a 25 GHz repetition rate was developed by intensity-and phase-modulating a seed light emitted from a continuous-wave laser diode and propagating it through a dispersive fibre. Using the authors' developed tellurite photonics crystal fibre with a high-nonlinear coefficient, octave-spanning supercontinuum generation in the 1.5 mu m band from a 250 MHz gated pulse train for CEO frequency detection was demonstrated.