Active Mode-Locking of a 13-μm Extended-Cavity Silicon Chip Bragg Reflector Laser

Abstract

Recently, we have demonstrated several experimental high speed transmission systems using optical time division multiplexing (OTDM) [1,2]. Unlike conventional high speed systems [3], where the data transmitted is modulated using a 50% duty cycle, these OTDM systems use short optical pulses generated by mode-locked extended-cavity semiconductor lasers [4]. Optimum performance in these OTDM systems [1,2], where up to four separate sources are time multiplexed, is limited by fiber dispersion caused by the wide spectral widths and unmatched wavelengths of the different mode-locked lasers [1,2]. In the absence of any frequency selective element within the composite cavity, the spectral characteristics of these lasers are difficult to control, and thus point to a need for a mode-locked laser structure which includes some form of frequency control. We describe here a laser which contains the desired intra-cavity frequency selective element; the external-cavity silicon chip bragg reflector (SCBR) [5] mode-locked laser. SCBR lasers with short passive cavities have demonstrated single frequency operation and very narrow linewidth [6]. We have used a long (~5 cm) passive cavity of the same type to achieve mode-locking at frequencies around 2 GHz.