Worldwide, higher-order modulation formats are intensively investigated to further increase the spectral efficiency for
building the next generation of high-speed metro systems. IQ-modulators, coherent receivers and electronic equalizers
are hereby discussed as key devices. We report on system design issues as well as on HHI's latest achievements in
developing InP based high-speed modulators and coherent receiver frontends.
The paper presents the development and optimization of ultra-broadband photodiodes (> 100 GHz) and balanced photodetectors (70 GHz). These developments are based on the waveguide-integrated photodiode type applying semi-insulating optical waveguide layers, grown on InP:Fe. The chip developments, characterizations in the frequency and time domain and the packaging of the chips into modules with fibre pigtail and 1 mm connector are described. The modules are tested at bit rates of 80, 100 and 160 Gbit/s, employing NRZ, RZ and DPSK modulation formats.
Recent development trends in InP-based optoelectronic devices are illustrated by means of selected examples. These include lasers for uncooled operation and direct modulation at 10 Gbit/s, complex-coupled lasers, which exhibit particularly low sensitivity to back reflections as well as monolithic mode-locked semiconductor lasers as ps-pulse sources for OTDM applications. Furthermore, a Mach-Zehnder interferometer modulator for high bit rate applications (40 Gbit/s and beyond) is described, and finally, photoreceivers and ultra high-speed waveguide-integrated photodiodes with > 100 GHz bandwidth are presented, which are key component for high bit rate systems, advanced modulation format transmission links, and for high speed measurement equipment as well.
Photoreceivers based on InP are becoming increasingly important for 40 Gbit/s telecommunication systems operating at the wavelength of 1.55 micrometers . 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 micrometers 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 micrometers 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.
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