Mode-locked extended cavity laser using fiber grating and its characterization with interferometric autocorrelation measurement

At 1.3 mm the low group velocity dispersion of standard single mode fibre would appear to make this wavelength attractive for high bit rate transmission applications. The transmissions of optical solitons is one possible technique for reaching the high bit rates required in future transmission systems. A key component in such a system is the soliton laser source. This device must be both a stable and reliable source of optical pulses at a high bit rate. For this purpose a Mode-Locked Extended Cavity Laser (ML-ECL) using a Bragg reflector as wavelength selective feedback component for generation of a > 10 Gbit/s pulse stream has been developed operating at 1.7 GHz in the fundamental mode. A semiconductor laser chip, anti-reflection coated at one facet and high reflection coated at the other, was coupled with a lensed fibre grating. In comparison to bulk optical components the use of fibre based components ensured a better mechanical stability and about 50 times more output power. Additionally, the integration of the device is generally simplified To use this mode-locked laser as a pulse source for a high-bit-rate telecommunications system detailed analysis of the ultrashort optical pulse performance is important. Adjacent pulse interaction in a fibre link may be enhanced or suppressed depending on their non-linear phase behaviour during transmission. We briefly present a recently developed interferometric autocorrelator which is capable of detemiing both, the temporal width (FWHM) and the non-linear phase of optical pulses by assuming a certain intensity shape and extrapolation the phase. By comparing the autocorrelation traces with simulated data on the basis of a Gaussian intensity profile and a quadratic phase behaviour a linear chirp of about 25 ps within the FWHM of the optical pulses was found. The developed ML-ECL is a prototype of a laser source which will be utilised in transmission experiments in the project UPGRADE in the European ACTS programme. The realisation of optical soliton transmission at 1.3 pm over standard single mode optical fibres is a goal of this project. A field trial of 10 Gbit/s, SDH based, soliton transmission will be demonstrated at the CeBIT exhibition in Hannover in 1997. The techniques reported here play an important role in achieving the project objectives