Dominik Bisang

High-speed, integrated photodetectors are crucial for addressing the bandwidth bottlenecks in next-generation data centers and high-performance computing. While graphene offers exceptional intrinsic speed and broadband absorption, realizing its potential in scalable, high-responsivity integrated devices has proven challenging. Here, we demonstrate a waveguide-integrated plasmonic graphene photodetector architecture capable of operating in high-capacity data links. By utilizing plasmonic resonators to enhance light-matter interaction and facilitate photocarrier extraction, the device exhibits a 3 dB bandwidth of 155 GHz and a responsivity exceeding 200 mA/W in the L-band under bias. We validated the device’s capabilities for high-speed data communications through direct detection of intensity-modulated signals, achieving a single-lane line rate of 192 Gbit/s. To further illustrate the platform’s scalability, we cointegrated eight such photodetectors with a low-crosstalk silicon photonic 1 × 8 arrayed waveguide grating to form a wavelength-division multiplexing receiver. This integrated system yielded an aggregated line rate of 816 Gbit/s. These results, representing the fastest waveguide-coupled plasmonic graphene photodetectors reported to date, pave the way for a new generation of dense, high-capacity optical interconnects essential for future high-performance computing and AI infrastructure.

Next-generation superconducting quantum computers face scalability limitations due to the increasing number of required interconnects from room temperature into the cryogenic environment. Scalability can be improved by transitioning to photonic links, and even further scaling can be obtained by employing wavelength multiplexing. This would allow to replace multiple RF cables by a single optical fiber. However, experimental demonstration of a cryogenic multichannel optical-to-microwave converter, required for demultiplexing incoming optical signals and performing conversion to microwave signals inside the cryostat, is still missing. Here, we demonstrate the first cryogenic eight-channel optical-to-microwave converter. It combines an arrayed waveguide grating in silicon photonics for wavelength demultiplexing with eight waveguide-integrated plasmonic graphene photodetectors. The device has a compact footprint of 1.75 mm × 0.71 mm, enabling scalable and dense integration. We characterized all eight channels at 4 K and found electrical crosstalk below 30 dB, high bandwidth >45 GHz, subnanoampere dark current, and 4–5× increased responsivity compared to room temperature. Finally, as a proof of concept, we simultaneously transferred two RF signals modulated on two different optical carriers into the cryostat and achieved crosstalk isolation of >50 dB in the best case. Therefore, our device demonstrates the potential of wavelength-multiplexed photonic links for mitigating the cryogenic interconnect bottleneck.

Silicon–graphene hybrid photodetectors represent a promising platform by combining graphene’s high carrier mobility and pronounced electrostatic sensitivity with silicon’s superior light absorption capability. However, systematic comparisons of different detection mechanisms in such hybrids remain limited, making it challenging to identify the optimal architecture for different imaging applications. Here, we present a systematic comparison of three photodetection mechanisms in silicon–graphene hybrid photodetectors: interfacial photogating, Schottky photodiodes, and Schottky-assisted photogating. These devices have been implemented on the same chip and evaluated under identical conditions. By analyzing responsivity, noise, dynamic range, speed, and array-level imaging, including crosstalk and pixel variation in 5 × 5 arrays, we identify the key performance trade-offs. Interfacial photogating offers high gain and strong low light sensitivity, Schottky-assisted photogating provides higher gain but larger variability and slower response, while Schottky photodiodes enable fast, low-cross-talk imaging. These insights establish practical guidelines for selecting hybrid silicon–graphene detector architectures based on application-specific performance priorities.

Emerging cryogenic technologies suffer from scaling discrepancies due to limitations stemming from the electrical signal lines connecting the ambient to the cryogenic environment. Currently employed radio frequency cabling offers limited operation bandwidths, therefore requiring large amounts of valuable space and inherently also conducting large amounts of heat. Realizing the ambient-to-cryogenic signal transfer by optical fibers could resolve all of these issues. However, for this purpose, cryogenic-compatible, high-speed, zero-bias-operated photodetectors are required. In this work, we demonstrate a metamaterial-graphene photodetector able to generate high-speed electrical signals in a cryostat without any need for electrical feed lines. This is enabled by a nanostructured metamaterial-graphene architecture that utilizes nanoscale optical hot spots to simultaneously enhance absorption and enable zero-bias carrier extraction. Beyond that, the devices offer high-frequency operations above 100 GHz, a small footprint, and compatibility with various substrates. The signal transfer is further demonstrated by cryogenic optical communication with bit rates of >100 Gbit/s. These results demonstrate a robust platform for high-bandwidth optical-to-electrical conversion, providing a scalable pathway for low-power signal interfacing in next-generation cryogenic systems and quantum technologies.

Cryogenic quantum applications have a demand for an ever-higher number of interconnects and bandwidth. Photonic links are foreseen to offer data transfer with high bandwidth, low heat load, and low noise to enable the next-generation scalable quantum computing systems. However, they require high-speed and energy-efficient modulators operating at cryogenic temperatures for electro-optic signal conversion. Here, plasmonic organic electro-optic modulators operating at 4 K are demonstrated with a >100 GHz bandwidth, drive voltages as low as 96 mV, and a significant reduction in plasmonic propagation losses by over 40% compared to room temperature. Up to 160 Gbit/s and 256 Gbit/s cryogenic electro-optic signal conversion are demonstrated by performing data experiments using a plasmonic Mach-Zehnder modulator at around 1528 nm and a plasmonic ring-resonator modulator at around 1285 nm, respectively. This work shows that plasmonic modulators are ideally suited for future high-speed, scalable, and energy-efficient photonic interconnects in cryogenic environments.

Phototransistors are light-sensitive devices featuring a high dynamic range, low-light detection, and mechanisms to adapt to different ambient light conditions. These features are of interest for bioinspired applications such as artificial and restored vision. In this work, we report on a graphene-based phototransistor exploiting the photogating effect that features picowatt- to microwatt-level photodetection, a dynamic range covering six orders of magnitude from 7 to 10(7) lux, and a responsivity of up to 4.7 x 10(3) A/W. The proposed device offers the highest dynamic range and lowest optical power detected compared to the state of the art in interfacial photogating and further operates air stably. These results have been achieved by a combination of multiple developments. For example, by optimizing the geometry of our devices with respect to the graphene channel aspect ratio and by introducing a semitransparent top-gate electrode, we report a factor 20-30 improvement in responsivity over unoptimized reference devices. Furthermore, we use a built-in dynamic range compression based on a partial logarithmic optical power dependence in combination with control of responsivity. These features enable adaptation to changing lighting conditions and support high dynamic range operation, similar to what is known in human visual perception. The enhanced performance of our devices therefore holds potential for bioinspired applications, such as retinal implants.

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.