Qdash based Directly Modulated Lasers for next generation access network

As the standardization of next generation passive optical network (NGPON) is still open, it is necessary to develop innovative 10Gbit/s transmitters at 1.55µm for long reach, low cost and high capacity access and metropolitan networks. Directly modulated lasers (DML) are attractive candidates due to their high output power, high tolerance to optical feedback, and ability to operate in semi-cooled or un-cooled conditions. However, it remains difficult with DML to both reach transmission distances in the range of 60km, because of frequency chirp at 1.55µm inherent to direct high bit rate modulation, and to achieve high dynamic extinction ratio, typically more than 6dB, to fulfil the specifications of the next generation PON. Transmissions over 200km have already been demonstrated with DML by using many methods based on a proper management of the chirp. These methods use for instance dispersion compensation fibre1, specific filtering2-4, reduction of spectral broadening5 or electronic compensation6. However, these solutions require tightly stabilized optical filter, accurate temperature control or specific power consuming electronic detection schemes. It is therefore required to propose low cost and efficient solutions to cover access and metropolitan transmission distances (typically 10 to 80 km). Self-assembled semiconductor quantum-dots (QDots) and quantumdashes (QDashes) lasers appear to be promising materials since higher differential gain and lower chirp are expected. Recently, p-doping of the Qdash active layers led to further improvement of intrinsic dynamic properties7 and Henry's factor as low as 2.5 was reported.