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Coherent receiver front-end module including a polarization diversity waveguide OIC and a high-speed InGaAs twin-dual p-i-n photodiode OEIC both based on InP
The economic implementation of coherent optical systems requires practical integrated optical front-end receiver devices with reasonable degree of integration. As a precursor to such an OEIC, an InGaAsP/InP polarization diversity waveguide OIC, including two TE/TM-mode splitters, two TE-filters, two 3-dB couplers, and a planar front-illuminated InGaAs twin-dual-p-i-n photodiode-OEIC (including two balanced p-i-n photodiodes) was fabricated. The OIC depicts a TE/TM-mode separation of more than 13 dB, a 3-dB coupler imbalance of less than 10% and an intrinsic loss of less than 2 dB. A single detector device shows a responsivity of 1.05 A/W at a wavelength of 1.55 mu m, a total series resistance below 10 Omega , and a 3-dB bandwidth of more than 10 GHz. The O(E)ICs have been (packaged) in a versatile housing for system tests. The operation of the modules has been demonstrated in a heterodyne experiment yielding a bandwidth of more than 2.2 GHz for the whole module.