Photo thermal effect graphene detector featuring 105 Gbit s-1 NRZ and 120 Gbit s-1 PAM4 direct detection

Efficient Large-Area Graphene p-n Junction Terahertz Receivers on an Integrated Optical Platform

The integration of graphene-based p-n junctions into photonic or optoelectronic platforms can allow efficient guiding and absorption of the light signals into the detection element, promising a major improvement in the efficiency of the system, by minimizing optical losses and enhancing the light coupling. These platforms can also potentially provide additional functionalities, such as frequency filtering, modulation, or multiplexing of the signals. At terahertz (THz) frequencies, this can lead to a variety of new applications such as sensing, imaging, and communication, as well as advancements in high-speed electronics and wireless technologies. Here, we took advantage of large area industrial-scale graphene, realized via an inexpensive production process, to engineer an antenna-integrated graphene Salisbury screen (AgSS) p-n junction photodetector, in which the electromagnetic coupling between graphene and the free-space wavelength is optimized by controlling the antenna dimensions and its distance from a sub-wavelength thin reflective mirror. Room-temperature noise equivalent powers < 300 pWHz-1/2, response time < 5 ns and a power dynamic range larger than four orders of magnitude at 2.86 THz is reached, exceeding the performances of exfoliated graphene photodetectors technologies, and competitive with complementary metal-oxide semiconductor (CMOS) and micro-bolometer technologies at high THz frequencies.

Emerging Thermal Detectors Based on Low-Dimensional Materials: Strategies and Progress

Thermal detectors, owing to their broadband spectral response and ambient operating temperature capabilities, represent a key technological avenue for surpassing the inherent limitations of traditional photon detectors. A fundamental trade-off exists between the thermal properties and the response performance of conventional thermosensitive materials (e.g., vanadium oxide and amorphous silicon), significantly hindering the simultaneous enhancement of device sensitivity and response speed. Recently, low-dimensional materials, with their atomically thin thickness leading to ultralow thermal capacitance and tunable thermoelectric properties, have emerged as a promising perspective for addressing these bottlenecks. Integrating low-dimensional materials with metasurfaces enables the utilization of subwavelength periodic configurations and localized electromagnetic field enhancements. This not only overcomes the limitation of low light absorption efficiency in thermal detectors based on low-dimensional materials (TDLMs) but also imparts full Stokes polarization detection capability, thus offering a paradigm shift towards multidimensional light field sensing. This review systematically elucidates the working principle and device architecture of TDLMs. Subsequently, it reviews recent research advancements in this field, delving into the unique advantages of metasurface design in terms of light localization and interfacial heat transfer optimization. Furthermore, it summarizes the cutting-edge applications of TDLMs in wideband communication, flexible sensing, and multidimensional photodetection. Finally, it analyzes the major challenges confronting TDLMs and provides an outlook on their future development prospects.

Waveguide-integrated aluminum-MoTe2 Schottky photodetectors for the wavelength band extended to 2 µm

Transition metal dichalcogenide (TMDC) materials with excellent optoelectronic properties have attracted much attention in the fields of reconfigurable electronic devices, next-generation FETs, and photodetectors (PDs). While normal TMDC PDs have a bandgap-limited absorption edge of ∼1.3 µm, metal-TMDC Schottky PDs based on internal photoemission provide an operation band extension strategy. In this study, we demonstrate that a TMDC PD can even operate at the wavelength band as long as 2.0 µm by judiciously choosing TMDC and metal materials to construct a low barrier height Schottky PD. Specifically, a silicon waveguide-integrated Al-MoTe2 Schottky PD was measured with responsivities of 18 mA/W and 5.5 mA/W at 1.6 µm and 2 µm, respectively. Meanwhile, the dark current is as low as 2 µA. The linear response can be maintained when the input optical power is in the mW scale. A measured 3 dB bandwidth is much larger than 1.75 MHz. These findings offer a promising avenue for expanding the detection range of the TMDC-based PDs with overall good performance in responsivity, bandwidth, sensitivity, and linearity.

Four-channel graphene optical receiver

Silicon photonics with the advantages of low power consumption and low fabrication cost is a crucial technology for facilitating high-capacity optical communications and interconnects. The graphene photodetectors (GPDs) featuring broadband operation, high speed, and low integration cost can be good additions to the SiGe photodetectors, supporting high-speed photodetection in wavelength bands beyond 1.6 μm on silicon. Here we realize a silicon-integrated four-channel wavelength division multiplexing (WDM) optical receiver based on a micro-ring resonator (MRR) array and four p-n homojunction GPDs. These photo-thermoelectric (PTE) GPDs exhibit zero-bias responsivities of ∼1.1 V W-1 and set-up limited 3 dB-bandwidth >67 GHz. The GPDs show good consistence benefiting from the compact active region array (0.006 mm2) covered by a single mechanically exfoliated hBN/graphene/hBN stack. Moreover, the WDM graphene optical receiver realized 4 × 16 Gbps non-return-to-zero optical signal transmission. To the best of our knowledge, it is the first GPD-array-based optical receiver using high-quality mechanically exfoliated graphene and edge graphene-metal contacts with low resistances. Apparently, our design is also compatible with CVD-grown graphene. This work sheds light on the large-scale integration of GPDs with high consistency and uniformity, enabling the application of high-quality mechanically exfoliated graphene, and promoting the development of the graphene photonic integrated circuits.

Controlling photothermoelectric directional photocurrents in graphene with over 400 GHz bandwidth

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.

Field-Effect Thermoelectric Hotspot in Monolayer Graphene Transistor

Graphene is a promising candidate for the thermal management of downscaled microelectronic devices owing to its exceptional electrical and thermal properties. Nevertheless, a comprehensive understanding of the intricate electrical and thermal interconversions at a nanoscale, particularly in field-effect transistors with prevalent gate operations, remains elusive. In this study, nanothermometric imaging is used to examine a current-carrying monolayer graphene channel sandwiched between hexagonal boron nitride dielectrics. It is revealed for the first time that beyond the expected Joule heating, the thermoelectric Peltier effect actively plays a significant role in generating hotspots beneath the gated region. With gate-controlled charge redistribution and a shift in the Dirac point position, an unprecedented systematic evolution of thermoelectric hotspots, underscoring their remarkable tenability is demonstrated. This study reveals the field-effect Peltier contribution in a single graphene-material channel of transistors, offering valuable insights into field-effect thermoelectrics and future on-chip energy management.

Waveguide-integrated twisted bilayer graphene photodetectors

Graphene photodetectors have exhibited high bandwidth and capability of being integrated with silicon photonics (SiPh), holding promise for future optical communication devices. However, they usually suffer from a low photoresponsivity due to weak optical absorption. In this work, we have implemented SiPh-integrated twisted bilayer graphene (tBLG) detectors and reported a responsivity of 0.65 A W-1 for telecom wavelength 1,550 nm. The high responsivity enables a 3-dB bandwidth of >65 GHz and a high data stream rate of 50 Gbit s-1. Such high responsivity is attributed to the enhanced optical absorption, which is facilitated by van Hove singularities in the band structure of high-mobility tBLG with 4.1o twist angle. The uniform performance of the fabricated photodetector arrays demonstrates a fascinating prospect of large-area tBLG as a material candidate for heterogeneous integration with SiPh.

Recent trends in the transfer of graphene films

Recent years have witnessed advances in chemical vapor deposition growth of graphene films on metal foils with fine scalability and thickness controllability. However, challenges for obtaining wrinkle-free, defect-free and large-area uniformity remain to be tackled. In addition, the real commercial applications of graphene films still require industrially compatible transfer techniques with reliable performance of transferred graphene, excellent production capacity, and suitable cost. Transferred graphene films, particularly with a large area, still suffer from the presence of transfer-related cracks, wrinkles and contaminants, which would strongly deteriorate the quality and uniformity of transferred graphene films. Potential applications of graphene films include moisture barrier films, transparent conductive films, electromagnetic shielding films, and optical communications; such applications call different requirements for the performance of transferred graphene, which, in turn, determine the suitable transfer techniques. Besides the reliable transfer process, automatic machines should be well developed for the future batch transfer of graphene films, ensuring the repeatability and scalability. This mini-review provides a summary of recent advances in the transfer of graphene films and offers a perspective for future directions of transfer techniques that are compatible for industrial batch transfer.

2D Materials in Flexible Electronics: Recent Advances and Future Prospectives

Flexible electronics have recently gained considerable attention due to their potential to provide new and innovative solutions to a wide range of challenges in various electronic fields. These electronics require specific material properties and performance because they need to be integrated into a variety of surfaces or folded and rolled for newly formatted electronics. Two-dimensional (2D) materials have emerged as promising candidates for flexible electronics due to their unique mechanical, electrical, and optical properties, as well as their compatibility with other materials, enabling the creation of various flexible electronic devices. This article provides a comprehensive review of the progress made in developing flexible electronic devices using 2D materials. In addition, it highlights the key aspects of materials, scalable material production, and device fabrication processes for flexible applications, along with important examples of demonstrations that achieved breakthroughs in various flexible and wearable electronic applications. Finally, we discuss the opportunities, current challenges, potential solutions, and future investigative directions about this field.

Sub-THz wireless transmission based on graphene-integrated optoelectronic mixer

Optoelectronics is a valuable solution to scale up wireless links frequency to sub-THz in the next generation antenna systems and networks. Here, we propose a low-power consumption, small footprint building block for 6 G and 5 G new radio wireless transmission allowing broadband capacity (e.g., 10-100 Gb/s per link and beyond). We demonstrate a wireless datalink based on graphene, reaching setup limited sub-THz carrier frequency and multi-Gbit/s data rate. Our device consists of a graphene-based integrated optoelectronic mixer capable of mixing an optically generated reference oscillator approaching 100 GHz, with a baseband electrical signal. We report >96 GHz optoelectronic bandwidth and -44 dB upconversion efficiency with a footprint significantly smaller than those of state-of-the-art photonic transmitters (i.e., <0.1 mm2). These results are enabled by an integrated-photonic technology based on wafer-scale high-mobility graphene and pave the way towards the development of optoelectronics-based arrayed-antennas for millimeter-wave technology.

Metamaterial graphene photodetector with bandwidth exceeding 500 gigahertz

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.

Graphene Photonics I/Q Modulator for Advanced Modulation Formats

Starting from its classical domain of long distance links, optical communication is conquering new application areas down to chip-to-chip interconnections in response to the ever-increasing demand for higher bandwidth. The use of coherent modulation formats, typically employed in long-haul systems, is now debated to be extended to short links to increase the bandwidth density. Next-generation transceivers are targeting high bandwidth, high energy efficiency, compact footprint, and low cost. Integrated photonics is the only technology to reach this goal, and silicon photonics is expected to play the leading actor. However, silicon modulators have some limits, in terms of bandwidth and footprint. Graphene is an ideal material to be integrated with silicon photonics to meet the requirements of next generation transceivers. This material provides optimal properties: high mobility, fast carrier dynamics and ultrabroadband optical properties. Graphene photonics for direct detection systems based on binary modulation formats have been demonstrated so far, including electro-absorption modulators, phase modulators, and photodetectors. However, coherent modulation for increased data-rates has not yet been reported for graphene photonics yet. In this work, we present the first graphene photonics I/Q modulator based on four graphene on silicon electro-absorption modulators for advanced modulation formats and demonstrate quadrature phase shift keying (QPSK) modulation up to 40 Gb/s.

Real-time Fourier-domain optical vector oscilloscope

To meet the constant demands of high-capacity telecommunications infrastructure, data rates beyond 1 terabit per second per wavelength channel and optical multiplexing are widely applied. However, these features pose challenges for existing data acquisition and optical performance monitoring techniques because of bandwidth limitation and signal synchronization. We designed an approach that would address these limitations by optically converting the frequency limit to an unlimited time axis and combining this with a chirped coherent detection to innovatively obtain the full-field spectrum. With this approach, we demonstrated a real-time Fourier-domain optical vector oscilloscope, with a 3.4-terahertz bandwidth and a 280-femtosecond temporal resolution over a 520-picosecond record length. In addition to on-off keying and binary phase-shift keying signals (128 gigabits per second), quadrature phase-shift keying wavelength division-multiplexed signals (4 × 160 gigabits per second) are simultaneously observed. Moreover, we successfully demonstrate some high-precision measurements, which indicate them as a promising scientific and industrial tool in high-speed optical communication and ultrafast optical measurement.

All-silicon microring avalanche photodiodes with a >65 A/W response

We report an all-Si microring (MRR) avalanche photodiode (APD) with an ultrahigh responsivity (R) of 65 A/W, dark current of 6.5 µA, and record gain-bandwidth product (GBP) of 798 GHz at -7.36 V. The mechanisms for the high responsivity have been modelled and investigated. Furthermore, open eye diagrams up to 20 Gb/s are supported at 1310 nm at -7.36 V. The device is the first, to the best of our knowledge, low cost all-Si APD that has potential to compete with current commercial Ge- and III-V-based photodetectors (PDs). This shows the potential to make the all-Si APD a standard "black-box" component in Si photonics CMOS foundry platform component libraries.

Nanomaterial-assisted theranosis of bone diseases

Bone-related diseases refer to a group of skeletal disorders that are characterized by bone and cartilage destruction. Conventional approaches can regulate bone homeostasis to a certain extent. However, these therapies are still associated with some undesirable problems. Fortunately, recent advances in nanomaterials have provided unprecedented opportunities for diagnosis and therapy of bone-related diseases. This review provides a comprehensive and up-to-date overview of current advanced theranostic nanomaterials in bone-related diseases. First, the potential utility of nanomaterials for biological imaging and biomarker detection is illustrated. Second, nanomaterials serve as therapeutic delivery platforms with special functions for bone homeostasis regulation and cellular modulation are highlighted. Finally, perspectives in this field are offered, including current key bottlenecks and future directions, which may be helpful for exploiting nanomaterials with novel properties and unique functions. This review will provide scientific guidance to enhance the development of advanced nanomaterials for the diagnosis and therapy of bone-related diseases.

Monolithic Metamaterial-Integrated Graphene Terahertz Photodetector with Wavelength and Polarization Selectivity

The frequency spectra and polarization states of terahertz waves can convey significant information about physical interactions and material properties. Compact and miniaturized on-chip platforms for effective capturing of these quantities are being extensively investigated because of their promising potential for paramount applications of terahertz technology such as in situ sensing and characterization. Here, we present a metamaterial-graphene hybrid device that integrates the functions of photodetection, wavelength, and polarization selectivity into a monolithic architecture. Leveraging the ultrahigh design freedom of metamaterial optical properties and the electronically controllable hot-carrier-assisted photothermoelectric effect in graphene, our detector shows resonantly enhanced photoresponse at two specific target wavelengths with orthogonal polarizations. We demonstrate its versatile capabilities for spectrally selective and polarization resolved imaging on a single-chip platform that is free from advanced optical components. Our strategy is beneficial to the future development of multifunctional, compact, and low-cost terahertz sensors.

A highly tunable photoelectric response of graphene field-effect transistor with lateral P-N junction in channel

This paper reports a highly tunable photoelectric response of graphene field-effect transistor (GFET) with lateral P-N junction in channel. The poly(sulfobetaine methacrylate) (PSBMA) provides strong N-type doping on graphene due to the dipole moment of pendent groups after ultraviolet annealing in high vacuum. A lateral P-N junction is introduced into the channel of the GFET by partially covering the graphene channel with PSBMA. With such P-N junction in the channel, the GFET exhibits a highly tunable photoelectric response over a wide range of exciting photon wavelength. With a lateral P-N junction in the channel, the polarity of photocurrent (I_ph) of the GFET switches three times as the back-gate voltage (V_BG) scan over two Dirac-point voltages. The underlying physical mechanism of photoelectric response is attributed to photovoltaic and photo-induced bolometric effect, which compete to dominatingI_phat variousV_BG. This provides a possible strategy for designing new phototransistors or optoelectronic device in the future.

Intertwined-pulse modulation for compressive data telemetry

This paper presents a novel approach for anisochronous pulse-based modulation. In the proposed approach, referred to as the intertwined-pulse modulation (IPM), every pair of consecutive symbols overlap in time. This allows for shortening the time allocated for the transmission of the symbols, hence achieving temporal compaction while the data goes through the line encoding step in a digital communication system. The IPM is also uniquely superior to other existing anisochronous pulse-based modulation schemes in the fact that it exhibits robust symbol error rate against unwanted variations in both rise/fall times of the pulses in the modulated waveform, and in the threshold level used for data detection on the receiver side. An experimental setup was developed to implement an IPM encoder using standard digital hardware, and an IPM decoder as a part of the receiver system in software. According to the experimental results (supported by simulation results and theoretical studies), for the data mean value of mid-full-scale range, the proposed IPM scheme exhibits a time-domain compaction rate of up to 209.2%.

Highly stable semitransparent multilayer graphene/LaVO3vertical-heterostructure photodetectors

A heterostructure composed of a combination of semi-metallic graphene (Gr) and high-absorption LaVO₃is ideal for high-performance translucent photodetector (PD) applications. Here, we present multilayer Gr/LaVO₃vertical-heterostructure semitransparent PDs with various layer numbers (L_n). AtL_n= 2, the PD shows the best performance with a responsivity (R) of 0.094 A W^-1and a specific detectivity (D*) of 7.385 × 10⁷cm Hz^1/2W^-1at 532 nm. Additionally, the average visible transmittance of the PD is 63%, i.e. it is semitransparent. We increased photocurrent (PC) by approximately 13%, from 0.564 to 0.635μA cm^-2by using an Al reflector on the semitransparent PD. The PC of an unencapsulated PD maintains about 86% (from 0.571 to 0.493μA cm^-2) of its initial PC value after 2000 h at 25 °C temperature/30% relative humidity, showing good stability. This behavior is superior to that of previously reported graphene-based PDs. These results show that these PDs have great potential for semitransparent optoelectronic applications.

Unbiased Plasmonic-Assisted Integrated Graphene Photodetectors

Photonic integrated circuits (PICs) for next-generation optical communication interconnects and all-optical signal processing require efficient (∼A/W) and fast (≥25 Gbs-1) light detection at low ( Collapse

Key Words

• graphene
• photodetectors
• integrated photonics
• plasmonics
• photothermoelectric effect

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MESH Headings Collapse

Grants

• Horizon 2020 Framework Programme
• Quantum Flagship
• Engineering and Physical Sciences Research Council
• H2020 European Research Council

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Affiliation(s)

Ioannis Vangelidis Department of Materials Science and Engineering, University of Ioannina, Ioannina 45110, Greece
Dimitris V. Bellas Department of Materials Science and Engineering, University of Ioannina, Ioannina 45110, Greece Department of Informatics, Center for Interdisciplinary Research and Innovation, Aristotle University of Thessaloniki, Thessaloniki 57001, Greece
Stephan Suckow AMO GmbH, Advanced Microelectronic Center Aachen (AMICA), Otto-Blumenthal-Strasse 25, Aachen 52074, Germany
George Dabos Department of Informatics, Center for Interdisciplinary Research and Innovation, Aristotle University of Thessaloniki, Thessaloniki 57001, Greece
Sebastián Castilla ICFO - Institut de Ciències Fotòniques, The Barcelona Institute of Science and Technology, Castelldefels, Barcelona 08860, Spain
Frank H. L. Koppens ICFO - Institut de Ciències Fotòniques, The Barcelona Institute of Science and Technology, Castelldefels, Barcelona 08860, Spain ICREA - Institució Catalana de Recerca i Estudis Avançats, Barcelona 08010, Spain
Andrea C. Ferrari Cambridge Graphene Centre, University of Cambridge, Cambridge CB3 0FA, U.K.
Nikos Pleros Department of Informatics, Center for Interdisciplinary Research and Innovation, Aristotle University of Thessaloniki, Thessaloniki 57001, Greece
Elefterios Lidorikis Department of Materials Science and Engineering, University of Ioannina, Ioannina 45110, Greece University Research Center of Ioannina (URCI), Institute of Materials Science and Computing, Ioannina 45110, Greece

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Collaborators Collapse

Si/SnSe-Nanorod Heterojunction with Ultrafast Infrared Detection Enabled by Manipulating Photo-Induced Thermoelectric Behavior

Photothermal detectors have attracted tremendous research interest in uncooled infrared imaging technology but with a relatively slow response. Here, Si/SnSe-nanorod (Si/SnSe-NR) heterojunctions are fabricated as a photothermal detector to realize high-performance infrared response beyond the bandgap limitation. Vertically standing SnSe-NR arrays are deposited on Si by a sputtering method. Through manipulating the photoinduced thermoelectric (PTE) behavior along the c-axis, the Si/SnSe-NRs heterojunction exhibits a unique four-stage photoresponse with a high photoresponsivity of 106.3 V W^-1 and high optical detectivity of 1.9 × 10¹⁰ cm Hz^1/2 W^-1 under 1342 nm illumination. Importantly, an ultrafast infrared photothermal response is achieved with the rise/fall time of 11.3/258.7 μs. Moreover, the coupling effect between the PTE behavior and external thermal excitation enables an improved response by 288.4%. The work not only offers a new strategy to develop high-speed photothermal detectors but also performs a deep understanding of the PTE behavior in a heterojunction system.

Advances in integrated ultra-wideband electro-optic modulators [Invited]

Increasing data traffic and bandwidth-hungry applications require electro-optic modulators with ultra-wide modulation bandwidth for cost-efficient optical networks. Thus far, integrated solutions have emerged to provide high bandwidth and low energy consumption in compact sizes. Here, we review the design guidelines and delicate structures for higher bandwidth, applying them to lumped-element and traveling-wave electrodes. Additionally, we focus on candidate material platforms with the potential for ultra-wideband optical systems. By comparing the superiority and mechanism limitations of different integrated modulators, we design a future roadmap based on the recent advances.

Photo-modulated optical and electrical properties of graphene

Photo-modulation is a promising strategy for contactless and ultrafast control of optical and electrical properties of photoactive materials. Graphene is an attractive candidate material for photo-modulation due to its extraordinary physical properties and its relevance to a wide range of devices, from photodetectors to energy converters. In this review, we survey different strategies for photo-modulation of electrical and optical properties of graphene, including photogating, generation of hot carriers, and thermo-optical effects. We briefly discuss the role of nanophotonic strategies to maximize these effects and highlight promising fields for application of these techniques.

Silicon-Based Graphene Electro-Optical Modulators

With the increasing demand for capacity in communications networks, the use of integrated photonics to transmit, process and manipulate digital and analog signals has been extensively explored. Silicon photonics, exploiting the complementary-metal-oxide-semiconductor (CMOS)-compatible fabrication technology to realize low-cost, robust, compact, and power-efficient integrated photonic circuits, is regarded as one of the most promising candidates for next-generation chip-scale information and communication technology (ICT). However, the electro-optic modulators, a key component of Silicon photonics, face challenges in addressing the complex requirements and limitations of various applications under state-of-the-art technologies. In recent years, the graphene EO modulators, promising small footprints, high temperature stability, cost-effective, scalable integration and a high speed, have attracted enormous interest regarding their hybrid integration with SiPh on silicon-on-insulator (SOI) chips. In this paper, we summarize the developments in the study of silicon-based graphene EO modulators, which covers the basic principle of a graphene EO modulator, the performance of graphene electro-absorption (EA) and electro-refractive (ER) modulators, as well as the recent advances in optical communications and microwave photonics (MWP). Finally, we discuss the emerging challenges and potential applications for the future practical use of silicon-based graphene EO modulators.

Engineering sensitivity and spectral range of photodetection in van der Waals materials and hybrids

Exploration of van der Waals heterostructures in the field of optoelectronics has produced photodetectors with very high bandwidth as well as ultra-high sensitivity. Appropriate engineering of these heterostructures allows us to exploit multiple light-to-electricity conversion mechanisms, ranging from photovoltaic, photoconductive to photogating processes. These mechanisms manifest in different sensitivity and speed of photoresponse. In addition, integrating graphene-based hybrid structures with photonic platforms provides a high gain-bandwidth product, with bandwidths ≫1 GHz. In this review, we discuss the progression in the field of photodetection in 2D hybrids. We emphasize the physical mechanisms at play in diverse architectures and discuss the origin of enhanced photoresponse in hybrids. Recent developments in 2D photodetectors based on room temperature detection, photon-counting ability, integration with Si and other pressing issues, that need to be addressed for these materials to be integrated with industrial standards have been discussed.

Ultrahigh-speed graphene-based optical coherent receiver

Graphene-based photodetectors have attracted significant attention for high-speed optical communication due to their large bandwidth, compact footprint, and compatibility with silicon-based photonics platform. Large-bandwidth silicon-based optical coherent receivers are crucial elements for large-capacity optical communication networks with advanced modulation formats. Here, we propose and experimentally demonstrate an integrated optical coherent receiver based on a 90-degree optical hybrid and graphene-on-plasmonic slot waveguide photodetectors, featuring a compact footprint and a large bandwidth far exceeding 67 GHz. Combined with the balanced detection, 90 Gbit/s binary phase-shift keying signal is received with a promoted signal-to-noise ratio. Moreover, receptions of 200 Gbit/s quadrature phase-shift keying and 240 Gbit/s 16 quadrature amplitude modulation signals on a single-polarization carrier are realized with a low additional power consumption below 14 fJ/bit. This graphene-based optical coherent receiver will promise potential applications in 400-Gigabit Ethernet and 800-Gigabit Ethernet technology, paving another route for future high-speed coherent optical communication networks.

High-responsivity graphene photodetectors integrated on silicon microring resonators

Graphene integrated photonics provides several advantages over conventional Si photonics. Single layer graphene (SLG) enables fast, broadband, and energy-efficient electro-optic modulators, optical switches and photodetectors (GPDs), and is compatible with any optical waveguide. The last major barrier to SLG-based optical receivers lies in the current GPDs' low responsivity when compared to conventional PDs. Here we overcome this by integrating a photo-thermoelectric GPD with a Si microring resonator. Under critical coupling, we achieve >90% light absorption in a ~6 μm SLG channel along a Si waveguide. Cavity-enhanced light-matter interactions cause carriers in SLG to reach ~400 K for an input power ~0.6 mW, resulting in a voltage responsivity ~90 V/W, with a receiver sensitivity enabling our GPDs to operate at a 10-9 bit-error rate, on par with mature semiconductor technology, but with a natural generation of a voltage, rather than a current, thus removing the need for transimpedance amplification, with a reduction of energy-per-bit, cost, and foot-print.

Silicon/2D-material photodetectors: from near-infrared to mid-infrared

Two-dimensional materials (2DMs) have been used widely in constructing photodetectors (PDs) because of their advantages in flexible integration and ultrabroad operation wavelength range. Specifically, 2DM PDs on silicon have attracted much attention because silicon microelectronics and silicon photonics have been developed successfully for many applications. 2DM PDs meet the imperious demand of silicon photonics on low-cost, high-performance, and broadband photodetection. In this work, a review is given for the recent progresses of Si/2DM PDs working in the wavelength band from near-infrared to mid-infrared, which are attractive for many applications. The operation mechanisms and the device configurations are summarized in the first part. The waveguide-integrated PDs and the surface-illuminated PDs are then reviewed in details, respectively. The discussion and outlook for 2DM PDs on silicon are finally given.

Wafer-Scale Integration of Graphene-Based Photonic Devices

Graphene and related materials can lead to disruptive advances in next-generation photonics and optoelectronics. The challenge is to devise growth, transfer and fabrication protocols providing high (≥5000 cm2 V-1 s-1) mobility devices with reliable performance at the wafer scale. Here, we present a flow for the integration of graphene in photonics circuits. This relies on chemical vapor deposition (CVD) of single layer graphene (SLG) matrices comprising up to ∼12000 individual single crystals, grown to match the geometrical configuration of the devices in the photonic circuit. This is followed by a transfer approach which guarantees coverage over ∼80% of the device area, and integrity for up to 150 mm wafers, with room temperature mobility ∼5000 cm2 V-1 s-1. We use this process flow to demonstrate double SLG electro-absorption modulators with modulation efficiency ∼0.25, 0.45, 0.75, 1 dB V-1 for device lengths ∼30, 60, 90, 120 μm. The data rate is up to 20 Gbps. Encapsulation with single-layer hexagonal boron nitride (hBN) is used to protect SLG during plasma-enhanced CVD of Si3N4, ensuring reproducible device performance. The processes are compatible with full automation. This paves the way for large scale production of graphene-based photonic devices.