Optimization of DFB lasers integrated with Franz-Keldysh absorptionmodulators

The influence of the residual facet reflectance on electroabsorption modulators monolithically integrated with DFB lasers is analyzed, for both index- and partly loss-coupled lasers. The optimum laser design is discussed from the standpoint of system requirements in long-distance 10 Gb/s transmission systems, requiring a minimum of chirp. The integrated device's performance will depend as much on the laser design as on the modulator. The DFB laser should be long (L>500 μm) with a coupling strength of about κ·L=2-3 and should have a high relaxation oscillation frequency. The residual reflectance should be less than 1·10^-4     

DFB laser monolithically integrated with an absorption modulator with low residual reflectance and small chirp

Transmission over 150 km of standard fibre at 5 Gbit/s, and over 75 km at 8 Gbit/s, is reported with a monolithically integrated DFB laser and Franz-Keldysh absorption modulator. The modulator facet reflectance is low. The device is stable over a range of operating parameters. The butt-joint, buried-heterostructure device is entirely grown by MOVPE.<>     

Dispersion compensation by differential time delay

A technique for optical pre- or postdistortion in order to compensate for fiber dispersion is discussed theoretically, The dispersion compensation device is based on differential time delay for the upper and the lower sideband of the modulated signal. The proposed scheme is primarily intended for high bit rate (>10 Gbit/s) time division multiplexed transmission, and in an ideal case the transmitting distance could be enhanced by a factor of 4 in a dispersive limited system. With more realistic demands on the dispersion compensation device, the gained distance is in the order of 2.5