AbstractPhotodetection 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.

We demonstrate a 110-GHz BTO Mach-Zehnder modulator integrated on foundry- produced silicon nitride for 340 Gbit/s data links. This approach, featuring nano-scale plasmonics and highly nonlinear BTO, proves to be a viable platform for next-generation Tbit/s links.

Abstract 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.

Efficient fiber-to-chip coupling is demonstrated for SiN photonics with simple and fabrication-tolerant amorphous silicon overlay gratings. This elegant approach offers coupling loss of only 0.43 dB and 1.11 dB with and without back-reflector, respectively.

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.

This paper presents a compact and power efficient one-chip optical phased array (OPA) transmitter (TX) for optical wireless communication (OWC). A traveling-wave-electrode Mach-Zehnder modulator (TWE-MZM) and mm-Wave driver, which would traditionally be implemented by bulky off-the-shelf components, are monolithically integrated with a silicon-based 1 x 64 OPA onto a single chip, reducing an active area of the entire system down to 6.4 mm(2). Moreover, a co-design and integration of TWE-MZM and mm-Wave driver largely minimizes the parasitics and mismatches of an interface between the TWE and mm-Wave driver. The 64-element optical antenna achieves beam divergence of 0.77 degrees and 4.23 degrees over transversal and longitudinal direction, respectively. The two-sided beam-steering angles of the array antenna in transversal and longitudinal direction are +/- 14.3 degrees and 6.1 degrees, respectively, while the side-lobe suppression ratio is 7.81 dB. The co-integrated TWE-MZM and driver support a measured data rate up to 15 Gbps and consume 210 mW. To the best of our knowledge, our proposed electronic-photonic integrated circuit is the first OWC-application OPA TX, which monolithically integrates TWE-MZM, CMOS driver, and OPA all in one-chip.

We demonstrate the first O-band BaTiO 3 -plasmonic modulator on SiN. Featuring symbol rates of up to 200 GBd, 2 dB on-chip loss, and 70 GHz bandwidth, this approach proves suitable for low-loss, high-speed, and low-complexity communication.

Fully integrated silicon-based optical phased arrays (OPAs) are promising devices due to their extremely narrow beam, compact size, and low power consumption. Their potential applications include light detection and ranging (LiDAR), three-dimensional (3D) imaging, holography and wireless optical communication (WOC) [1]–[6]. These applications require OPAs to have small size and efficient interfacing between the electronic and photonic integrated circuits (ICs). There have been substantial efforts to realize compact OPAs with CMOS ICs for LiDAR applications [2–3, 5]. [2] demonstrated a monolithic integration with 1024-element antennas and DACs into one single chip, and [3] employed 3D-integration to connect phase shifters in the OPA with DACs. For the interface between the phase shifters and their driving DACs, relatively low bandwidth (BW) signals below 200 MHz are sufficient [1]. In contrast, OPAs for WOC require broadband electrical driving signal up-to 30 Gbps from an RF-amplifier to a traveling-wave-electrode Mach-Zehnder modulator (TWE-MZM) [4]. For such broadband high frequencies, the electronic-to-photonic IC interface becomes highly vulnerable to parasitics, losses, and impedance mismatches. As a result, OPAs for high-speed WOC applications have only been presented using commercial MZMs and RF-amplifiers, which consume large area and power, as shown in Fig. 1 [4]–[6].

Highly efficient coupling of light from an optical fiber to silicon nitride (SiN) photonic integrated circuits (PICs) is experimentally demonstrated with simple and fabrication-tolerant grating couplers (GC). Fully etched amorphous silicon gratings are formed on top of foundry-produced SiN PICs in a back-end-of-the-line (BEOL) process, which is compatible with 248 nm deep UV lithography. Metallic back reflectors are introduced to enhance the coupling efficiency (CE) from -1.11 to -0.44 dB in simulation and from -2.2 to -1.4 dB in experiments for the TE polarization in the C-band. Furthermore, these gratings can be optimized to couple both TE and TM polarizations with a CE below -3 dB and polarization-dependent losses under 1 dB over a wavelength range of 40 nm in the O-band. This elegant approach offers a simple solution for the realization of compact and, at the same time, highly efficient coupling schemes in SiN PICs.

Plasmonic modulators have been assessed for operation up to 200 GBaud in a turbulent 53 km free-space-optical link. They are shown to withstand space radiation and large temperature ranges making them ideal for space applications.

Memristive devices have attracted significant attention due to their downscaling potential, low power operation, and fast switching performance. Their inherent properties make them suitable for emerging applications such as neuromorphic computing, in-memory computing, and reservoir computing. However, the different applications demand either volatile or nonvolatile operation. In this study, we demonstrate how compliance current and specific material choices can be used to control the volatility and nonvolatility of memristive devices. Especially, by mixing different materials in the active electrode, we gain additional design parameters that allow us to tune the devices for different applications. We found that alloying Ag with Sn stabilizes the nonvolatile retention regime in a reproducible manner. Additionally, our alloying approach improves the reliability, endurance, and uniformity of the devices. We attribute these advances to stabilization of the filament inside the switching medium by the inclusion of Sn in the filament structure. These advantageous properties of alloying were found by investigating a choice of six electrode materials (Ag, Cu, AgCu-1, AgCu-2, AgSn-1, AgSn-2) and three switching layers (SiO2, Al2O3, HfO2).

Although graphene has met many of its initially predicted optoelectronic, thermal, and mechanical properties, photodetectors with large spectral bandwidths and extremely high frequency responses remain outstanding. In this work, we demonstrate a >500 gigahertz, flat-frequency response, graphene-based photodetector that operates under ambient conditions across a 200-nanometer-wide spectral band with center wavelengths adaptable from <1400 to >4200 nanometers. Our detector combines graphene with metamaterial perfect absorbers with direct illumination from a single-mode fiber, which breaks with the conventional miniaturization of photodetectors on an integrated photonic platform. This design allows for much higher optical powers while still allowing record-high bandwidths and data rates. Our results demonstrate that graphene photodetectors can outperform conventional technologies in terms of speed, bandwidth, and operation across a large spectral range.

Achieving electrically driven light sources on a silicon substrate is one of the great challenges in integrated optics. For low-power applications, one possible candidate could be Light Emitting Tunnel Junctions (LETJs) [1] . Unlike many semiconductor light sources that rely on direct-bandgap materials, the emission characteristics of LETJs are not strongly dependent on the material choice, but are determined by the electrical and optical environment of the tunnelling interface. While most electrons tunnel elastically from one electrode to the other, some can couple to and excite electromagnetic modes in a broad range of frequencies, spanning the microwave to the visible [1] – [3] .

A 1 Tbit/s 53km single channel free-space optical (FSO) link is demonstrated. High bandwidth, high order modulation formats and advanced adaptive optics are utilized. We show that the absence of a nonlinear-Shannon limit in combination with adaptive optics enables record data-transmission with low link failures.

Graphene’s unique band structure leading to high carrier mobility and broad spectral absorption have successfully been exploited in high-speed photodetectors (PD) [1] . Several demonstrated graphene devices did not show any decline in performance over the tested frequency response even above 100 GHz [1] , [2] leading to speculations on how fast these graphene-based devices can actually be. Some reports indicate thermal- and carrier-based effects in graphene should offer device responses above 300-500GHz [3] , [4] , making graphene a promising material for next generation high-speed optoelectronics integrated into the silicon (Si) photonics platform.