Electrical and optical interactions between integrated InGaAsP/InP DFB lasers and electroabsorption modulators

Electrical and optical interactions occurring in InGaAsP/InP integrated light sources composed of DFB lasers and electroabsorption modulators have been studied. Static measurements indicated that an isolation resistance between the laser and the modulator should be as large as 100 kΩ or more in order to reduce a lasing wavelength shift associated with biasing the modulator. The useful guided light out of the modulator was about 1-2 percent of the laser output. At high frequency modulation, asymmetric sidebands were observed in dynamic spectra measured at the modulator facet, which were caused by additional modulation of the laser part. Such additional modulation was relatively large at the relaxation oscillation frequency of the laser, but it was reduced by connecting an RF bypass condenser in parallel to the laser diode and by depositing an antireflection coating at the modulator facet. After eliminating the additional modulation, an integrated device showed a high frequency response of 5.7-GHz 3-dB bandwidth and a small linewidth enhancement factor of α=0.8