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The first results of an integrated hybrid photo-receiver based on a 850 nm two-terminal (2T) silicon germanium (SiGe) heterojunction bipolar photo-transistor (HPT) for low-cost radio-over-fibre (RoF) applications is presented. A hybrid module was realised with two cascaded low-noise amplifiers of 20 dB total gain and an SiGe 2T-HPT exhibiting a −15 dB opto-microwave gain at 5.15 GHz with a 1.6 GHz bandwidth. A 16% degradation of the error vector magnitude compared with back-to-back measurement for the transmission of a 2 GHz OFDM signal at 3 Gbit/s was measured based on the 60 GHz IEEE 802.15.3c standard transposed at the intermediate frequency (IF) of 5 GHz, according to an IF-RoF distribution mode.

Micron dimensioned on-chip optical links of 50 micron length, utilizing 650 -850 nm propagation wavelength, have been realized in a Si Ge bipolar process. Key design strategies is the utilization of high speed avalanche based Si light emitting devices (Si Av LEds) in combination with silicon nitride based wave guides and high speeds Si Ge based optical detectors. The optical source, waveguide and detector were all integrated on the same chip. TEOS densification strategies and state of the art Si-Ge bipolar technology were further used as key design strategies. Best performances show up to 25 GHz RF carrier modulation and -40dBm total optical link budget loss with a power consumption of only 0.1 mW per GHz bandwidth. Improvement possibilities still exist. The process used is in regular production. The technology is particularly suitable for application as optical interconnects utilizing low loss, side surface, waveguide to optical fibre coupling.

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The intrinsic frequency response of silicongermanium heterojunction bipolar phototransistors (HPTs) at 850 nm is studied to be implemented in multimode fiber systems. The experimental analysis of an HPT with an optical window size of 10 × 10 µm 2 is presented. An optomicrowave (OM) scanning near-field optical microscopy is performed to observe the variation of the HPT dynamic behavior versus the illumination location of the phototransistor. The photocurrent generated by the photodiode at the interface between the n ++ subcollector and the p + guard ring is analyzed, and its impact on the performance of the HPT is investigated. Then, we propose a technique to remove the substrate photocurrent effect on the optical transition frequency (f Topt ): f Topt value of 4.1 GHz given by raw measurement results increases up to 6 GHz after removing the substrate response. The influence of the 2-D carrier flows on the HPT intrinsic OM behavior is also studied. Design aspects of SiGe/Si HPT structures are finally discussed as a conclusion.Index Terms-Microwave photonics, opto-microwave scanning near-field optical microscopy (OM-SNOM), siliconbased photodetectors, SiGe phototransistor, substrate effect.

A 10 × 10 μm2SiGe heterojunction bipolar photo-transistor (HPT) is fabricated using a commercial technological process of 80 GHz SiGe bipolar transistors (HBT). Its technology and structure are first briefly described. Its optimal opto-microwave dynamic performance is then analyzed versus voltage biasing conditions for opto-microwave continuous wave measurements. The optimal biasing points are then chosen in order to maximize the optical transition frequency (fTopt) and the opto-microwave responsivity of the HPT. An opto-microwave scanning near-field optical microscopy (OM-SNOM) is performed using these optimum bias conditions to localize the region of the SiGe HPT with highest frequency response. The OM-SNOM results are key to extract the optical coupling of the probe to the HPT (of 32.3%) and thus the absolute responsivity of the HPT. The effect of the substrate is also observed as it limits the extraction of the intrinsic HPT performance. A maximum optical transition frequency of 4.12 GHz and an absolute low frequency opto-microwave responsivity of 0.805A/W are extracted at 850 nm.