Si-substrate vertical-structure InGaN/GaN micro-LED-based photodetector for beyond 10  Gbps visible light communication

Li D., Ma C., Wang J., Hu F., Hou Y., Wang S., Hu J., Yi S., Ma Y., Shi J., Zhang J., Li Z., Chi N., Xia L., Shen C.

Visible light communication (VLC) is a promising technology for next-generation high-speed optical wireless data links. Among various transmitters, GaN-based superluminescent diodes (SLDs) show interesting characteristics, including a large modulation bandwidth, droop free and low speckle noise, which makes them attractive for VLC applications. In this work, we design and fabricate a blue-emitting SLD utilizing tilted facet configuration. Using SLD as the light source, a VLC system is experimentally demonstrated. A record data rate of 4.57 gigabit per second (Gbps) is achieved with adaptive bit-loading discrete multiple tone (DMT) modulation, while the highest modulation format reaches 256 quadrature amplitude modulation (QAM). The corresponding bit error rate (BER) is ~3.5 × 10−3, which is below the forward error correction (FEC) threshold of 3.8 × 10−3.

Hu J., Hu F., Jia J., Li G., Shi J., Zhang J., Li Z., Chi N., Yu S., Shen C.

Visible light communication (VLC), combining wireless communication with white lighting, has many advantages. It is free of electromagnetic interference, is rich in spectrum resources, and has a gigabit-per-second (Gbps) data rate. Laser diodes (LDs) are emerging as promising light sources for high-speed VLC communication due to their high modulation bandwidth. In this paper, we demonstrate a red/green/blue (R/G/B) LDs based VLC system with a recorded data rate of 46.41 Gbps, employing discrete multitone (DMT) and adaptive bit-loading technology to achieve high spectral efficiency (SE). The emission characteristics and transmission performance of R/G/B-LDs are discussed. The optimal data rates of R/G/B-LDs channels are 17.168/14.652/14.590 Gbps, respectively. The bit-error-ratio (BER) of each channel satisfies the 7% forward-error-correction (FEC) threshold (3.8×10−3) and greatly approaches the channel Shannon limit.

Chang Y., Hsu T., Liou F., Chow C., Liu Y., Kuo H., Yeh C., Yang P.

We propose and demonstrate a green semipolar (20-21) micro-light emitting diode (LED) acting as a high speed visible light communication (VLC) photodiode (PD). The micro-LED PD has the optical-to-electrical (OE) response of 228 MHz. A record data rate of 540 Mbit/s in on-off-keying (OOK) format with free-space transmission distance of 1.1 m was achieved, fulfilling the pre-forward error correction (FEC) limit. Many transmitters (Txs) and receivers (Rxs) is required to support the high density pico/femto-cells in future wireless networks, as well as the Internet-of-Things (IOT) networks. The proposed work could allow the realization of a low-cost, small-footprint and a high level of integration of VLC Txs and Rxs on the same platform.

Hu F., Chen S., Li G., Zou P., Zhang J., Hu J., Zhang J., He Z., Yu S., Jiang F., Chi N.

High-speed visible light communication (VLC) using light-emitting diodes (LEDs) is a potential complementary technology for beyond-5G wireless communication networks. The speed of VLC systems significantly depends on the quality of LEDs, and thus various novel LEDs with enhanced VLC performance increasingly emerge. Among them, InGaN/GaN-based LEDs on a Si-substrate are a promising LED transmitter that has enabled VLC data rates beyond 10 Gbps. The optimization on the period number of superlattice interlayer (SL), which is a stress-relief epitaxial layer in a Si-substrate LED, has been demonstrated to be an effective method to improve Si-substrate LED’s luminescence properties. However, this method to improve LED’s VLC properties is barely investigated. Hence, we for the first time experimentally studied the impact of SL period number on VLC performance. Accordingly, we designed and fabricated an integrated 4 × 4 multichromatic Si-substrate wavelength-division-multiplexing LED array chip with optimal SL period number. This chip allows up to 24.25 Gbps/1.2 m VLC transmission using eight wavelengths, which is the highest VLC data rate for an InGaN/GaN LED-based VLC system to the best of our knowledge. Additionally, a record-breaking data rate of 2.02 Gbps over a 20-m VLC link is achieved using a blue Si-substrate LED with the optimal SL period number. These results validate the effectiveness of Si-substrate LEDs for both high-speed and long-distance VLC and pave the way for Si-substrate LED design specially for high-speed VLC applications.

Lin R., Liu X., Zhou G., Qian Z., Cui X., Tian P.

Chi N., Zhou Y., Wei Y., Hu F.

6G networks are expected to provide extremely high capacity and satisfy emerging applications, but current frequency bands may not be sufficient. Moreover, 6G will provide superior coverage by integrating space/air/underwater networks with terrestrial networks, given that traditional wireless communications are not able to provide high-speed data rates for nonterrestrial networks. Visible light communication (VLC) is a high-speed communication technique with an unlicensed frequency range of 400-800 THz and can be adopted as an alternative approach to solving these problems. In this article, we present the prospects and challenges of VLC in 6G in conjunction with its advances in high-speed transmissions. Recent hot research interests, including new materials and devices, advanced modulation, underwater VLC (UVLC), and signal processing based on machine learning, are also discussed. It is envisaged that VLC will become an indispensable part of 6G given its high-speed transmission advantages and will cooperate with other communication methods to benefit our daily lives.

You X., Wang C., Huang J., Gao X., Zhang Z., Wang M., Huang Y., Zhang C., Jiang Y., Wang J., Zhu M., Sheng B., Wang D., Pan Z., Zhu P., et. al.

The fifth generation (5G) wireless communication networks are being deployed worldwide from 2020 and more capabilities are in the process of being standardized, such as mass connectivity, ultra-reliability, and guaranteed low latency. However, 5G will not meet all requirements of the future in 2030 and beyond, and sixth generation (6G) wireless communication networks are expected to provide global coverage, enhanced spectral/energy/cost efficiency, better intelligence level and security, etc. To meet these requirements, 6G networks will rely on new enabling technologies, i.e., air interface and transmission technologies and novel network architecture, such as waveform design, multiple access, channel coding schemes, multi-antenna technologies, network slicing, cell-free architecture, and cloud/fog/edge computing. Our vision on 6G is that it will have four new paradigm shifts. First, to satisfy the requirement of global coverage, 6G will not be limited to terrestrial communication networks, which will need to be complemented with non-terrestrial networks such as satellite and unmanned aerial vehicle (UAV) communication networks, thus achieving a space-air-ground-sea integrated communication network. Second, all spectra will be fully explored to further increase data rates and connection density, including the sub-6 GHz, millimeter wave (mmWave), terahertz (THz), and optical frequency bands. Third, facing the big datasets generated by the use of extremely heterogeneous networks, diverse communication scenarios, large numbers of antennas, wide bandwidths, and new service requirements, 6G networks will enable a new range of smart applications with the aid of artificial intelligence (AI) and big data technologies. Fourth, network security will have to be strengthened when developing 6G networks. This article provides a comprehensive survey of recent advances and future trends in these four aspects. Clearly, 6G with additional technical requirements beyond those of 5G will enable faster and further communications to the extent that the boundary between physical and cyber worlds disappears.

Hu F., A. Holguin-Lerma J., Mao Y., Zou P., Shen C., Khee Ng T., S. Ooi B., Chi N.

Wang W., Cheng C., Wang H., Lin G.

The visible wavelength-division multiplexing (VWDM) optical wireless communication beyond 30 Gbit/s with a white-light beam mixed by red/green/violet (R/G/V) laser diodes (LDs) and yellow (Y) LED is demonstrated via quadrature amplitude modulation discrete multitone modulation (QAM DMT). To facilitate both high-quality indoor lighting and high-speed optical wireless communication, the R/G/V-LD white-light module incorporates with a Y-LED to provide a high color rendering index (CRI) and encapsulates with a frosted glass to enlarge its divergent angle. By respectively encoding the R/G/V-LDs with the filtered QAM DMT data in a back-to-back case, the total raw data rate as high as 34.8 Gbit/s is achieved by encoded R/G/V-LDs with respective VWDM data rates of 18/7.2/9.6 Gbit/s. To fulfill the demanded CRI and correlated color temperature (CCT) for indoor white-lighting, the yellow LED contributes the yellowish-orange luminescence with flexible CCT and CRI varying from 3952 K to 3031 K and from 0 to 45.9, respectively. A cold white-light carrier at a CCT of 4852 K, CRI of 71.6, and CIE of (0.3652, 0.4942) is also approached by attenuating the red LD power, and such a cold white-light spot with an illuminance of 6800 lux and a divergent solid angle of 0.89 steradian (sr) can support VWDM data transmission at 28.4 Gbit/s.

Alkhazragi O., Kang C.H., Kong M., Liu G., Lee C., Li K., Zhang H., Wagstaff J.M., Alhawaj F., Ng T.K., Speck J.S., Nakamura S., DenBaars S.P., Ooi B.S.

Visible light communication (VLC) has drawn significant attention in recent years. Though high-speed visible-light sources have seen significant advances, commercially available photodetectors have low wavelength selectivity and modulation bandwidth in the near-violet-blue wavelengths, making them a bottleneck in VLC links. Here we show a record 7.4-Gbit/s visible-light communication link using a wavelength-selective, (2021)-oriented, semipolar InGaN/GaN multiple-quantum-well micro-photodetector (μPD) on GaN substrate. This is achieved by leveraging on the unique photodetection properties of semipolar μPDs, combined with an optimized communication system utilizing bit- and power-loading schemes in orthogonal frequency-division multiplexing (OFDM) modulation over a 2-GHz bandwidth. We used a 405-nm violet laser diode transmitter as the responsivity of the μPD was highest within the responsivity range of 360 - 420 nm. The investigation fully demonstrated the feasibility and favorable choice of semipolar InGaN/GaN μPDs for multi-Gbit/s optical wireless communication.

Xie E., Bian R., He X., Islim M.S., Chen C., McKendry J.J., Gu E., Haas H., Dawson M.D.

By employing a GaN-based series-biased micro-light emitting diode (μLED) array and orthogonal frequency division multiplexing modulation format, a high-speed free-space visible light communication system for long-distance applications has been demonstrated. The blue series-biased μLED array, which consists of 3 × 3, 20 μm-diameter μLED elements, presents promising performance with an optical power and -6dB electrical modulation bandwidth of over 10 mW and 980 MHz, respectively. Record data transmission rates have been successfully achieved at different free-space distances. Within 5 m transmission distances, over 10 Gbps data rates at the forward error correction (FEC) floor of 3.8 × 10 -3 are accomplished. Extending the transmission distances to 20 m, the data rates are maintained at the Gbps level at the FEC floor.

Zou P., Zhao Y., Hu F., Chi N.

Underwater visible light communication (UVLC) systems suffer from a strong nonlinear effect and high inter-symbol interference (ISI). In this study, to improve the performance of a UVLC system under such conditions, we propose a novel nonlinear hybrid modulation scheme named two-dimensional bit allocation (2DBA). By comparing the performance of 2DBA with the famous Levin-Campello (LC) algorithm and the quadrature amplitude modulation (QAM)–based time-domain hybrid modulation (TDHQ) algorithm, we have proved by analysis and experiment that 2DBA can outperform the power allocation–based LC algorithm and the TDHQ algorithm below the 3.8×10−3 hard decision forward error correction threshold (HD-FEC) when the system has a severe nonlinear effect and ISI. The data rate 3.24 Gb/s of 2DBA is measured after 1.2 m underwater transmission; as far as we know, this is the highest data rate reported in a blue LED chip based UVLC system.

Kang C.H., Liu G., Lee C., Alkhazragi O., Wagstaff J.M., Li K., Alhawaj F., Ng T.K., Speck J.S., Nakamura S., DenBaars S.P., Ooi B.S.

Abstract This paper investigated the use of semipolar InGaN/GaN multiple quantum well based micro-photodetectors (μPDs) as the optical receiver for visible light communication (VLC). The fabricated semipolar μPDs exhibited a low dark current of 1.6 pA at −10 V, a responsivity of 0.191 A W−1, and a −3 dB modulation bandwidth of 347 MHz. A high data rate of up to 1.55 Gbit s−1 was achievable by utilizing the extended bandwidth of more than −10 dB, and based on a straight-forward non-return-to-zero on–off keying modulation scheme. This development demonstrated the feasibility of wavelength-selective detection scheme using semipolar μPD for high-data-capacity VLC systems.

Liu X., Lin R., Chen H., Zhang S., Qian Z., Zhou G., Chen X., Zhou X., Zheng L., Liu R., Tian P.

This work reports the use of the chip-based GaN-based micro-LED (μLED) arrays for multifunctional applications as microdisplay, data transmitters, photodetectors, and solar cells. The functions of ...

Zong B., Fan C., Wang X., Duan X., Wang B., Wang J.

The key drivers of 6G result not only from the challenges and performance limits that 5G presents but also from the technology-driven paradigm shift and the continuous evolution of wireless networks. Intelligent driving and industry revolutions create core requirements for 6G that will lead to service classes of ubiquitous mobile ultrabroadband (uMUB), ultrahighspeed-with-low-latency communications (uHSLLC), and ultrahigh data density (uHDD).

Shen D., Ren T., Chen X., Lin R., Liao Y., Shan X., Cui X., Tian P.

Xu Z., Luo Z., Lin X., Cai J., Lu Z., Zhang J., Wang G., Wang X., Shen C., Shi J., Zhang J., Zhou Y., Chi N.

Sun Z., Shi F., Shi Z., Choi H.W., Liu Y., Wang Y., Yan J.

AbstractThe ultimate neuromorphic chip based on light‐stimulated artificial synapses requires suitable materials and platforms for optoelectronic integration. Herein, a GaN optoelectronic integrated chip with multifunctions of communication, sensing, and neuromorphic computing is proposed and fabricated on a GaN‐on‐Si light‐emitting diode (LED) epitaxial wafer. The monolithically integrated chip consists of an InGaN/GaN multiple‐quantum‐well LED and a GaN‐based optoelectronic synaptic metal‐oxide‐semiconductor field‐effect transistor connected in series. It can achieve multi‐mode switching, including self‐powered photodetector (PD), light‐emitting synapse, and gate‐voltage‐controlled light transmitter. For the PD mode, a great responsivity of 4393 A W−1 and a high specific detectivity of 1.56 × 1014 Jones are demonstrated. Notably, due to varying absorption of short wavelength light by different epitaxial layers, the integrated device shows differentiated wavelength selectivity for light illuminated from the front and back sides. When the integrated device is operating in synapse mode, excitatory postsynaptic currents induced by light stimuli can be read both optically and electrically with the assistance of built‐in optical‐to‐electrical‐to‐optical conversion. Moreover, direct bias‐voltage modulation and gate‐voltage modulation are both configured into this integrated device, achieving 60 and 5 Mbps modulation rates for visible light communication applications, respectively.

Chen L., Lin T., Chai J., Hao Q., Lei L., Chen J., Wang W., Li G.

InGaN-based pin-type visible light photodetectors (PDs), exhibiting enormous advantages of fast photoresponse speed and low noise, have drawn tremendous interest in visible light communication (VLC) applications. However, the insufficient light absorption capacity and low photoelectric conversion efficiency of InGaN-based pin heterojunction hinder the realization of high-sensitivity PDs for achieving this aim. Herein, plasmonic PDs based on InGaN/GaN multi-quantum wells (MQW) heterojunction with Ag nanoparticles (NPs) have been experimentally implemented, showing balanced abilities of enhanced photoresponse and polarization sensitivity in the blue light region. The PD's optimized responsivity, detectivity, and anisotropy ratio reach 0.176 A/W, 1.93 × 1010 Jones, and 1.395, respectively, under 405 nm illumination. The surface plasmon resonance-induced local field of Ag NPs enhances the electric field density and the light absorption density in the heterojunction region of InGaN/GaN MQWs, improving the photoresponse of PDs. This work proposes a valuable strategy for designing high-performance visible light PDs, providing an attractive stage for high-efficiency visible light communication applications.

Zhang Z., Gu Y., Liu X., Ruan Y., Shen D., Shan X., Jin Z., Cui X., Guo R., Zhang S., Tian P.

Chi N., Niu W., Zhou Y., Wang J., Chen H., He Z., Li J., Xu Z., Lin X., Luo Z., Lu Z., Zhang J., Shen C., Li Z., Shi J., et. al.

Liu J., Ma L., He Z.

The capability for real-time mobile communication is crucial for underwater visible light communication applications. In practical real-time underwater visible light mobile communication (UVLMC) systems, movement orientation significantly impacts communication performance. However, there is limited research on this aspect. We propose a real-time UVLMC system based on the conditional feedback threshold (CFT) to enhance performance under random receiver orientations. In experiments, we achieved real-time UVLMC over a distance of 60 meters with a data rate of 2 Mb/s under random receiver orientations in a tap water channel. The system can operate under a mean polar angle and azimuth angle as large as 40° and 120°, respectively, at a moving speed of 0.15 m/s with a dynamic range of 7 meters. This represents a 4.8-fold improvement in dynamic range compared to the system without the CFT mechanism.

Yang C., Huang W., Ning Q., Luo F.

Zhang Z., Cai T., Li Z., Wu B., Zheng Z., You C., Jiang G., Ma M., Xu Z., Shen C., Chen X., Song E., Cui J., Huang G., Mei Y.

AbstractThe implementation of an advanced light receiver is imperative for the widespread application of visible light communication. However, the integration of multifunctional and high‐performance visible light receivers is still limited by device structure and system complexity. Herein, a graphene‐readout silicon‐based microtube photodetector is proposed as the receiver for omnidirectional Mbps‐level visible light communication. The integration of graphene‐semiconductor material systems simultaneously ensures the effective absorption of incident light and rapid readout of photogenerated carriers, and the device exhibits an ultrafast response speed of 75 ns and high responsivity of 6803 A W−1. In addition, the microtube photodetector realizes the omnidirectional light‐trapping and enhanced polarization photodetection. As the receiving end of the visible light communication system, the microtube photodetector achieves a data rate of up to 778 Mbps, a field of view of 140°, and the encrypted visible light communication of polarized light, providing a new possibility for the future development of the internet of things and information security.

Ma T., Xue N., Muhammad A., Fang G., Yan J., Chen R., Sun J., Sun X.

Photodetectors are critical components in a wide range of applications, from imaging and sensing to communications and environmental monitoring. Recent advancements in material science have led to the development of emerging photodetecting materials, such as perovskites, polymers, novel two-dimensional materials, and quantum dots, which offer unique optoelectronic properties and high tunability. This review presents a comprehensive overview of the synthesis methodologies for these cutting-edge materials, highlighting their potential to enhance photodetection performance. Additionally, we explore the design and fabrication of photodetectors with novel structures and physics, emphasizing devices that achieve high figure-of-merit parameters, such as enhanced sensitivity, fast response times, and broad spectral detection. Finally, we discuss the demonstration of new applications enabled by these advanced photodetectors, including flexible and wearable devices, next-generation imaging systems, and environmental sensing technologies. Through this review, we aim to provide insights into the current trends and future directions in the field of photodetection, guiding further research and development in this rapidly evolving area.

Niu J., Wang J., Shi Y., Dong Z., Huang T., Dai X., Sha W., Long Y., Hu W.

Niu J., Bai X., Wang J., Chen Y., Zhao B., Sha W., Long Y., Wang Z., Hu W.

AbstractVisualization is a cornerstone in human–computer interaction, evolving from large screens to mobile devices and now to wearable display technology. However, conventional batteries and displays lack the softness and stretchability inherent to human skin. Here, a fully flexible, all‐in‐one electronic display skin by integrating a flexible microLED display, a stretchable circuit, and a Zn|PAM|V2O5 hydrogel battery pack is developed. Vapor‐phase bulk transfer is used to efficiently and accurately transfer 10 000 microLEDs onto a flexible substrate, ensuring high flexibility and ultra‐thin (240 µm). The flexible hydrogel battery pack provides sustainable energy, with a high specific capacity of 331.3 mAh g−1. Additionally, a transparent stretchable circuit board (maximum stretch 40%) is made by 3D printing technology. The skin display exhibited exceptional stretchability and biocompatibility, conforming to movements while maintaining high‐resolution dynamic visual outputs. These innovations pave the way for advanced skin‐implanted displays, promising transformative applications in information interaction, healthcare, and artificial intelligence.

Abdullah M., Younis M., Sohail M.T., Wu S., Zhang X., Khan K., Asif M., Yan P.

AbstractPhotodetectors are one of the most critical components for future optoelectronic systems and it undergoes significant advancements to meet the growing demands of diverse applications spanning the spectrum from ultraviolet (UV) to terahertz (THz). 2D materials are very attractive for photodetector applications because of their distinct optical and electrical properties. The atomic‐thin structure, high carrier mobility, low van der Waals (vdWs) interaction between layers, relatively narrower bandgap engineered through engineering, and significant absorption coefficient significantly benefit the chip‐scale production and integration of 2D materials‐based photodetectors. The extremely sensitive detection at ambient temperature with ultra‐fast capabilities is made possible with the adaptability of 2D materials. Here, the recent progress of photodetectors based on 2D materials, covering the spectrum from UV to THz is reported. In this report, the interaction of light with 2D materials is first deliberated on in terms of optical physics. Then, various mechanisms on which detectors work, important performance parameters, important and fruitful fabrication methods, fundamental optical properties of 2D materials, various types of 2D materials‐based detectors, different strategies to improve performance, and important applications of photodetectors are discussed.

Zhang J., Deng L., Xia S., Guo C., Liu K., Chen L., Liu W., Xiao H., Yang Z., Guo W., Ye J.

Abstract Solid-state ultraviolet (UV) photodetectors (PDs) have received significant attention due to their advantages of small size, absence of external cooling, high selectivity and the ability to utilize the energy band structure semiconductor materials to achieve detection across various wavelengths. III-nitride thin films, as typical wide bandgap semiconductors with mature n-type and p-type doping capabilities, are ideal candidates for solid-state UV-PDs. However, a combination of III-nitride and other wide bandgap materials can either enrich the functionality of devices such as spectrum-selective and broadband UV detectionor offer opportunities to enhance device performance, including high photoresponsivity, high external quantum efficiency, low dark current and fast response time. This topical review focuses on giving a thorough review of the III-nitride-based hybrid-type UV PDs, their recent progress and future prospects. We highlight the different optical and electrical properties of various materials including GaN, Ga2O3, ZnO, perovskite, etc. By carefully choosing the materials on both sides of the heterojunction and modulating the thickness and Fermi levels and corresponding layers, p–i–n, Schottky or metal–semiconductor–metal-type PDs were successfully fabricated. They displayed outstanding device performance and novel spectral-selective properties. The advantages for future development of these hybrid-type PDs will be discussed, such as inherently formed p–n junction with large depletion regions at the interface of two different materials and capability of bandgap engineering to tune the band offset between the conduction and valence bands, thus enabling large barrier height for one type of carrier without influencing the other. The drawbacks of hybrid-type UV-PD due to poor interface quality and challenges in forming electrical contact in nanostructured hybrid UV-PD will also be discussed.

Wang J., Hu J., Guan C., Hou Y., Xu Z., Sun L., Wang Y., Zhou Y., Ooi B., Shi J., Li Z., Zhang J., Chi N., Yu S., Shen C.

Visible light communication (VLC) based on laser diodes demonstrates great potential for high data rate maritime, terrestrial, and aerial wireless data links. Here, we design and fabricate high-speed blue laser diodes (LDs) grown on c-plane gallium nitride (GaN) substrate. This was achieved through active region design and miniaturization toward a narrow ridge waveguide, short cavity length, and single longitudinal mode Fabry–Perot laser diode. The fabricated mini-LD has a low threshold current of 31 mA and slope efficiency of 1.02 W/A. A record modulation bandwidth of 5.9 GHz (−3  dB) was measured from the mini-LD. Using the developed mini-LD as a transmitter, the VLC link exhibits a high data transmission rate of 20.06 Gbps adopting the bit and power loading discrete multitone (DMT) modulation technique. The corresponding bit error rate is 0.003, satisfying the forward error correction standard. The demonstrated GaN-based mini-LD has significantly enhanced data transmission rates, paving the path for energy-efficient VLC systems and integrated photonics in the visible regime.