As an important resource, entanglement light source has been used in developing quantum information technologies, such as quantum key distribution(QKD). There are few experiments implementing entanglement-based deterministic QKD protocols since the security of existing protocols may be compromised in lossy channels. In this work, we report on a loss-tolerant deterministic QKD experiment which follows a modified “Ping-Pong”(PP) protocol. The experiment results demonstrate for the first time that a secure deterministic QKD session can be fulfilled in a channel with an optical loss of 9 dB, based on a telecom-band entangled photon source. This exhibits a conceivable prospect of ultilizing entanglement light source in real-life fiber-based quantum communications.

Continuous-wave terahertz emitters based on photomixers with hybrid nanoelectrodes are investigated. The nanoelectrodes consist of a nitrogen-doped single layer of graphene and silver nanowires, placed on low-temperature-grown (LTG) GaAs as photoconductive material. Due to the high transparency of graphene and the low fill factor of nanowire nanoelectrodes, high photocurrents in the range from 260 μA to 1.8 mA can be reached. Despite their very small size nanoelectrodes provide the capability of handling rather high currents, leading to THz output signals reasonably three times higher than for conventional interdigitated finger electrodes for the whole measurement range. Measurement results of generated photocurrents and THz output signals are presented, showing the increased performance of our approach while maintaining highly reliable operation of the devices.

A new integrated lens-antenna is designed and implemented for a nanocontact based terahertz (THz) photomixer. The new design replaces the standard conventional bulky silicon lens, which normally no THz photomixer can avoid. The Fresnel Zone Plate is used to design the new lens-antenna and is simulated by the MIT open-source tool called Meep. The final design showed, with only two simple fabrication technology processing steps (standard optical lithography) that the lens-antenna can be monolithically integrated with the THz nanophotomixer. With its compact design, the THz measurements showed a comparable behavior to the conventional bulky silicon lens, therefore it would be ready for photonic integrated circuits based THz systems.

Antenna-coupled photomixers, serving as emitters and receivers of terahertz (THz) radiation, are the central active components of coherent optoelectronic THz systems. Here, we focus on the continuous-wave modality, which finds ample use for spectroscopy, sensing, and ranging and plays a major role in upcoming ultrahigh-frequency telecommunication applications. We demonstrate with planar receivers based on low-temperature-grown GaAs that the use of interdigital graphene electrodes instead of metal fingers enhances the responsivity by more than one order of magnitude. The increase in responsivity leads to a strongly enlarged dynamic range and doubles the frequency range covered in the detection process. We show by simulations that these improvements are a consequence of the transparency of the finger electrodes for visible/near-infrared laser radiation, which also activates the area under the fingers for the mixing process, not only their edges as in conventional devices with metal electrodes.

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