Optical pulse generation using fabry-Pe/spl acute/rot lasers under continuous-wave operation

Optical pulse generation at 100 GHz using a 1.5-μm Fabry-Pe/spl acute/rot laser is experimentally demonstrated under continuous-wave operation. Although the output from the laser is almost constant, subpicosecond pulses at 100 GHz are obtained after propagation through a single-mode fiber with an adequate anomalous dispersion. The measured radio frequency spectrum confirms that the multiple longitudinal modes of the Fabry-Pe/spl acute/rot laser are passively mode locked. Mode-locking instabilities appearing as frequency jumps at different currents are observed.

I. Introduction

Semiconductor lasers with Fabry–Pérot (FP) cavities show multiple longitudinal modes, and the multimode nature of FP lasers has extensively been studied. The main-mode power increases as the injection current to the laser increases. However, the side-mode power saturates in the above-threshold regime because the carrier density is cramped at the threshold. According to conventional semiconductor laser theory [1], therefore, the side-mode suppression ratio (SMSR) increases as the injection current increases. Experimentally, however, a degradation in the SMSR and spectral broadening are observed in high-injection regimes. In particular, long-wavelength FP lasers show a broader spectrum compared with short-wavelength FP lasers. Anomalous behaviors of longitudinal modes such as spectral asymmetries and wavelength shifts have been reported [2]–[4]. Fig. 1. Experimental setup. All measurements are done after coupling to an SMF through an optical isolator with an isolation of 60 dB.