Technical Insight
Travelling wave lasers exceed 50 GHz (Research Review)
Electroabsorption modulators (EA) integrated with DFB lasers represent a key development in high capacity optical networks. However, much wider bandwidths will be required and the limitation caused by device capacitance needs to be overcome for bit rates over 40 Gbit/s. The authors, from NTT Photonics Laboratories in Japan (Y Akage et al. Elec. Lett. 2001 37(5) 299), describe a novel travelling wave design that integrates the EA and DFB laser with a bandwidth that can be tuned to well over 50 GHz (see ). The device was fabricated on Fe-doped InP to form a co-planar feeding electrode. The InGaAsP/InGaAsP MQW absorption layer of the modulator and the MQW of the DFB are monolithically integrated, and 2 m wide stripes (etched by RIE) form the co-planar travelling waveguide in the modulator section. Compared to conventional EA-DFBs with a lumped element electrode, the small signal frequency response falls off more gradually in the new design. Centered on a wavelength of 1552 nm, the optical output power of the emitter was 20 mW, and the extinction ratio of the EA was 21 dB at 3 V bias. The bandwidth is expected to exceed 100 GHz by optimizing the structure.
