Small chirp, low drive-voltage integrated 10 Gb/s DFB laser and bulk electroabsorption modulator on semi-insulating InP substrate

Abstract

Integrated lasers and electro-absorption modulators have attained large interest, [l]-[8], for long distance, high bitrate transmission. In this paper we report on monolithically integrated DFB lasers and bulk modulators on semi-insulating (SI) InP substrate. The main reasons to develop Si-substrate devices are (i) the reduced stray capacitances, (ii) possibilities to make arrays, (iii) easier integration with co-planar microwave waveguides, (iv) future integration with InP Heterojunction Bipolar Transistor (HBT) drive stages. By proper optimisation (i.e. choice of bandgap wavelength of the modulator with respect to the DFB lasing wavelength) we obtain zero-bias operation with low drive voltage and small chirp. Short modulator (150 pm) devices have a 3-dB bandwidth of up to 19 GHz and can be operated with a voltage swing from 0 to -2 V with 10 dB extinction ratio, and have good transmission properties in 10 Gb/s transmission experiments. In particular they operate penalty-free at 40 km standard fibre. With long modulator (300 μm) devices, less than 1 V drive voltage for 10 dB extinction with >9 GHz modulation bandwidth can be obtained. We believe this is the lowest drive voltage reported for integrated bulk modulators useful for 10 Gb/s. The temperature dependence is also investigated and conclusions made regarding the usefulness in WDM applications.