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Photodetection in the near- and mid-infrared spectrum requires a suitable absorbing material able to meet the respective targets while ideally being cost-effective. Graphene, with its extraordinary optoelectronic properties, could provide a material basis simultaneously serving both regimes. The zero-band gap offers almost wavelength independent absorption which lead to photodetectors operating in the infrared spectrum. However, to keep noise low, a detection mechanism with fast and zero bias operation would be needed. Here, we show a self-powered graphene photodetector with a > 400 GHz frequency response. The device combines a metamaterial perfect absorber architecture with graphene, where asymmetric resonators induce photothermoelectric directional photocurrents within the graphene channel. A quasi-instantaneous response linked to the photothermoelectric effect is found. Typical drift/diffusion times optimization are not needed for a high-speed response. Our results demonstrate that these photothermoelectric directional photocurrents have the potential to outperform the bandwidth of many other graphene photodetectors and most conventional technologies. Self-powered graphene photodetectors based on the photothermoelectric effect (PTE) could provide low-noise operation in the telecom and mid-infrared ranges, but their bandwidth is usually limited. Here, the authors report the realization of PTE graphene photodetectors integrated with a metamaterial perfect absorber, showing a 3-dB bandwidth above 400 GHz. [ABSTRACT FROM AUTHOR]

The study demonstrates high‐quality pulsed‐laser‐deposited (PLD) barium titanate (BTO) thin‐films on a magnesium oxide substrate. The frequency response of the relative permittivity (dielectric constant) and the linear electro‐optical coefficient (Pockels coefficient) are measured. At 0.2 GHz, the Pockels coefficient is fitted to be r42 ≈ 1030 pm V−1. It decreases to ≈390 pm V−1 at 10 GHz after which it remains constant up to 70 GHz. The unbiased BTO permittivity is measured to be εa ≈ 7600 at 0.2 GHz, dropping to ≈1100 at 67 GHz, while the biased BTO had a permittivity εa ≈ 2000 at 0.2 GHz, dropping to ≈500 at 67 GHz. These results fill an important experimental characterization gap for high‐speed BTO applications and show the high quality of PLD‐grown BTO films. Lastly, the material's crystalline quality is characterized and the domain distribution is imaged. The findings enable the design and fabrication of a new generation of BTO‐based components for sensing and communications. [ABSTRACT FROM AUTHOR]

Plasmonic hybrids are introduced to replace photonic optical hybrids for coherent reception. These plasmonic circuits offer a compact footprint and a fabrication compatible with many electronic platforms as one only relies on metallic layer stacks. To mitigate the plasmonic losses, we propose new designs with shortest propagation paths. Simulations predict plasmonic hybrids with compact footprints of less than 1 µm 2 and excess losses below 1 dB. In the experiment we fabricated plasmonic hybrids with 1 µm 2 , excess losses of 3.3 dB, and excellent broadband performance for signals over more than 100 nm. These results need to be compared against reference optical hybrids with typical excess losses of 0.5 dB in the C-band. Our demonstrations show a path towards a fabrication platform with increasingly complex and compact plasmonic devices that can be cointegrated with electronics.

This paper introduces a simple method for the measurement of the relative permittivity and the Pockels coefficient of electro-optic (EO) materials in a waveguide up to sub-THz frequencies. By miniaturizing the device and making use of plasmonics, the complexities of traditional methods are mitigated. This work elaborates the fabrication tolerance and simplicity of the method, and highlights its applicability to various materials, substrates and configurations. The method is showcased using drop-casted perovskite barium titanate (BaTiO3, BTO) nano-particle thin-films and it has previously been used to measure epitaxial thin film BTO. In this work we show the effective relative permittivity of drop casted BTO to be ε eff ∼ 30 at 200 MHz, dropping to ∼ 18 at 67 GHz and similarly, the effective Pockels coefficient was found to be r eff ∼ 16 at 350 MHz and ∼ 8 at 70 GHz. These values are a factor > 50 below the values found for thin film BTO. Yet, the fact that the method can be applied to such different samples and Pockels strengths gives testimony to its versatility and sensitivity.