We report a photonic crystal fiber (PCF) coupler having an ultrawide spectral bandwidth keeping single mode operation. The use of the PCF coupler in a fiber-based optical coherence tomography (OCT) system enables us to handle the wide spectral bands of various light sources, including superluminescent diodes (SLDs) at $1300\mathrm{nm}$ and $820\mathrm{nm}$ , Ti:sapphire lasers, and white-light sources. The multiband imaging performances of the PCF-based OCT system are demonstrated by obtaining dental images at $1300\mathrm{nm}$ and $820\mathrm{nm}$ with the same setup. In addition, we show that the PCF coupler could cover the spectrum over a one octave span and guide both the fundamental wave ( $1030\mathrm{nm}$ ) and the second harmonic wave ( $515\mathrm{nm}$ ) simultaneously.