We present the design of a bias-free uni-travelling-carrier photodiode (UTC-PD) that is operational above 110 GHz, and its application to 100-GBd fixed-fiber communication and 109-GHz carrier-photonic wireless communication for advanced optical networks. The design and analysis for bias-free operation were explained in detail using the carrier concentration in the photo-absorption layer and carrier collector layer. In the experimental results, the developed UTC-PD with back-illuminated structure exhibited a wide 3-dB bandwidth of over 110 GHz at 0 V. For fixed-fiber communications, a high-baud-rate photoreceiver based on the UTC-PD was fabricated. Eye diagrams showed clear openings at up to 107 GBd and high photo-currents of 3-7 mA at 100 GHz signal light were observed at zero-bias. Assuming photonic wireless communication using photonic power supply through optical fiber, the developed UTC-PD contributed to reducing bias feeds to the photoreceiver module. Additionally, low power consumption was achieved when using the newly developed 110 GHz InP-PHEMT amplifier with the UTC-PD.
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