Effect of linewidth enhancement factor in actively modelocked ring laser.pdfVIP

Effect of linewidth enhancement factor in actively mode-locked ring laser Akira Takada, Makoto Saika, and Shigenori Nagano R D Center, General Engineering Quality Assurance Div., Topcon Corporation, 75-1 Hasunuma-cho, Itabashi-ku, Tokyo 174-8580, Japan ABSTRACT Fundamental performance of the swept-source optical coherence tomography (SS-OCT) system is defined by its wavelength-swept laser. Especially narrower instantaneous spectral linewidth of the laser has the advantage in deep- range tomography. We have demonstrated narrow-linewidth actively mode-locked ring lasers (AMLL), employing anomalous dispersion configuration. The linewidth of an AMLL is determined by anomalous dispersion and self-phase modulation (SPM) in the semiconductor optical amplifier (SOA). For such soliton-like phenomenon of AMLLs, numerical calculation predicts that both of large dispersion and small SPM make the linewidth narrower. Since the dispersion restricts wavelength sweeping range of AMLLs, too large dispersion cannot be used. To weaken the SPM effect, low linewidth enhancement factor α of SOA is desirable. Quantum-dot(QD)-based SOA offers low α-factor in comparison with quantum-well SOA (QWSOA). In this study, we employ a QDSOA as a gain medium in an AMLL and also use a QWSOA for comparison. The wavelength band of the QWSOA-AMLL is 1.5 µm and that of QDSOA-AMLL is 1.0 µm. Since we