Low-Cost Dispersion-Tuned Active Harmonic Mode-Locked Laser With a 3-cm Coherence Length

We propose a low-cost dispersion-tuned actively mode-locked laser with long coherence length (up to 3 cm) by combining a wide-band, high reflectivity, and high-dispersion chirped fiber Bragg grating (CFBG) with a reflective semiconductor optical amplifier (RSOA). The dependence of the tuning characteristics on the varying physical length of CFBG in the cavity is studied experimentally and theoretically in the CFBG and RSOA based laser for the first time. The results show that the wavelength tuning range reduces when the harmonic number is increasing. Moreover, the high-dispersion and high-reflectivity CFBG yields high optical signal to noise ratio (>48 dB), narrow spectral width (lower than 0.033 nm), and more than 3-cm coherence length in the harmonically mode-locked laser. This low-cost dispersion tuned mode-locked laser with wide tuning range, stable and small time-bandwidth product, and long coherence length can lead to enhanced applications.