When the center wavelength of the WaveShaper was fixed at 1550.05 nm while the passband spacing between the defined two wavelengths was varied from about 0.2 nm to 0.8 nm with a step of
0.2 nm, dual-wavelength single-frequency lasing with switchable wavelength spacing has been achieved by adjusting the drive currents of the FP-LD1 and FP-LD2 respectively from 50 mA to 30 mA and from 45 mA to 65 mA. The output optical spectra before and after being
filtered by the TOF are respectively shown in Fig.3 (a) and (b).