InP photoreceiver OEICs for high-speed optical transmission systems

Photoreceivers based on InP are becoming increasingly important for 40 Gbit/s telecommunication systems operating at the wavelength of 1.55 mu m. Due to the monolithic integration, they are advantageous in respect of high-speed performance, small size and cost saving in high-frequency packaging. Research groups worldwide are engaged in developing such OEIC's, with varying architectures and types of the components. Our broadband photoreceiver OEIC consists of a waveguide-integrated GaInAs p-i-n photodetector and a distributed amplifier. The 5*20 mu m sized photodetectors, with a responsivity of 0.4 A/W, reveal a 3 dB cut-off frequency of 70 GHz. The electrical distributed amplifier is made of our high-electron mobility transistors. The HEMT devices with gate lengths of 0.25 mu m exhibit cut-off frequencies fT and fmax of up to 100 and 250 GHz, respectively. The integrated photoreceivers are characterized on-after using a heterodyne-measurement setup and finally packaged into modules for system experiments. On recently fabricated wafers, the receivers show a bandwidth of 40 GHz, whereas the amplifiers alone even exhibit values as high as 43 GHz, with gain ripple less than 1 dB.