Integrated extended-cavity 1.5-μm semiconductor laser switchable between self- and anti-colliding pulse passive mode-locking configuration

We present the first integrated linear extended-cavity passively mode-locked (PML) semiconductor laser in which the operating mode can be switched electrically between two configurations. The first configuration is where the saturable absorber (SA) is located next to the output coupler, the so-called anti-colliding pulse mode-locking (ACPML) scheme. The second is where the SA is next to the high reflectance mirror, the self-colliding pulse mode-locking (SCPML) scheme. The 7.5-GHz PML was used to demonstrate experimentally the theoretical prediction that placing the SA next to the output coupler leads to a significant improvement in the laser stability and quality of the optical pulses. The experimental results show that the ACPML scheme allows for more deeply saturated SA due to the increase of optical power in the SA. The measurements of the RF spectra and autocorrelation traces confirm the superiority of the ACPML design in terms of pulse stability and width over the SCPML design for a wide range of operating conditions. The linewidth of the beat tone at the repetition rate was reduced by more than 60 times, the measured minimal autocorrelation width improved from 22 to 7.5 ps and a 3 dB increase in average output power was achieved.