Although the 5G wireless network has made significant advances,it is not enough to accommodate the rapidly rising requirement for broader bandwidth in post-5G and 6G eras.As a result,emerging technologies in higher fr...Although the 5G wireless network has made significant advances,it is not enough to accommodate the rapidly rising requirement for broader bandwidth in post-5G and 6G eras.As a result,emerging technologies in higher frequencies including visible light communication(VLC),are becoming a hot topic.In particular,LED-based VLC is foreseen as a key enabler for achieving data rates at the Tb/s level in indoor scenarios using multi-color LED arrays with wavelength division multiplexing(WDM)technology.This paper proposes an optimized multi-color LED array chip for high-speed VLC systems.Its long-wavelength GaN-based LED units are remarkably enhanced by V-pit structure in their efficiency,especially in the“yellow gap”region,and it achieves significant improvement in data rate compared with earlier research.This work investigates the V-pit structure and tries to provide insight by introducing a new equivalent circuit model,which provides an explanation of the simulation and experiment results.In the final test using a laboratory communication system,the data rates of eight channels from short to long wavelength are 3.91 Gb/s,3.77 Gb/s,3.67 Gb/s,4.40 Gb/s,3.78 Gb/s,3.18 Gb/s,4.31 Gb/s,and 4.35 Gb/s(31.38 Gb/s in total),with advanced digital signal processing(DSP)techniques including digital equalization technique and bit-power loading discrete multitone(DMT)modulation format.展开更多
The rapid growth of new services has led to a significant increase in data traffic,which brings challenges for data centers in supporting high-speed processing of large volumes of data.Traditional electrical interconn...The rapid growth of new services has led to a significant increase in data traffic,which brings challenges for data centers in supporting high-speed processing of large volumes of data.Traditional electrical interconnects are becoming increasingly inadequate,leading to increasing attention to optical interconnects to achieve high-speed data center interconnects(DCIs).Visible light laser communication(VLLC)inherits the advantages of free-space optics(FSO),allowing it to circumvent the limitations of conventional fiber-based optical interconnects.In addition,VLLC offers other advantages such as high thermal stability,low power consumption,and low packaging cost.In this Letter,a novel differential pilot coding(DPC)scheme is proposed to achieve precise channel estimation and compensation for linear impairments without halving the effective data rate.A data rate of 601.46 Gbps with a constellation size up to 1024QAM over a 1 m multimode fiber(MMF)-1 m FSO-1 m MMF link is successfully achieved based on a 50-channel wavelength division multiplexer(WDM)VLLC system utilizing DPC and bit-power-loading discrete multitone(DMT)modulation.To the best of our knowledge,this is the highest data rate and constellation size ever the reported for a WDM VLLC system,which proves that VLLC is a promising candidate solution for achieving high-capacity and cost-effective optical interconnects in data centers.展开更多
The next generation of mobile communication is committed to establishing an integrated three-dimensional network that encompasses air,land,and sea.The visible light spectrum is situated within the transmission window ...The next generation of mobile communication is committed to establishing an integrated three-dimensional network that encompasses air,land,and sea.The visible light spectrum is situated within the transmission window for underwater communication,making visible light laser communication a focus of intense research.展开更多
Visible light communication(VLC)has emerged as a promising communication method in 6G.However,the development of receiving devices is much slower than that of transmitting devices,limited by materials,structures,and f...Visible light communication(VLC)has emerged as a promising communication method in 6G.However,the development of receiving devices is much slower than that of transmitting devices,limited by materials,structures,and fabrication.In this paper,we propose and fabricate an InGaN/GaN multiple-quantum-well-based vertical-structure micro-LED-based photodetector(μPD)on a Si substrate.A comprehensive comparison of the photoelectrical performance and communication performance of three sizes ofμPDs,10,50,and 100μm,is presented.The peak responsivity of all threeμPDs is achieved at 400 nm,while the passband full-widths at half maxima are 87,72,and 78 nm for 10,50,and 100μmμPDs,respectively.The−20 dB cutoff bandwidth is up to 822 MHz for 50μmμPD.A data rate of 10.14 Gbps is experimentally demonstrated by bit and power loading discrete multitone modulation and the proposed digital pre-equalizer algorithm over 1 m free space utilizing the self-designed 4×450μmμPD array as a receiver and a 450 nm laser diode as a transmitter.This is the first time a more than 10 Gbps VLC system has been achieved utilizing a GaN-based micro-PD,to the best of our knowledge.The investigation fully demonstrates the superiority of Si substrates and vertical structures in InGaN/GaNμPDs and shows its great potential for high-speed VLC links beyond 10 Gbps.展开更多
In this paper,we propose a 36-quadrature amplitude modulation(QAM)superposition modulation technique that is featured with uneven symbol probability by nonlinear precoding,named nonlinear coded nonuniform superpositio...In this paper,we propose a 36-quadrature amplitude modulation(QAM)superposition modulation technique that is featured with uneven symbol probability by nonlinear precoding,named nonlinear coded nonuniform superposition(NCNS)QAM.Its aim is to alleviate the nonlinearity effect caused by high instantaneous power in multi-input single-output(MISO)visible light communication(VLC)system,with an uneven probabilistic-shaped constellation.The transmitter includes two LEDs to send signals independently,and the receiver uses a photo detector to receive the superposed QAM signal.The experiment results show that NCNS has a better robustness against nonlinearity than pulse amplitude modulation 4,approximately gaining a 16% increase in maximum usable peak-to-peak voltage and a 33% enlargement in dynamic range area.It is a simple but effective approach to solve the bandwidth limits related to signal power and hopefully be applied in large power VLC systems such as underwater VLC,or to improve the robustness against power fluctuation.展开更多
In recent studies, visible light communication(VLC) has been predicted to be a prospective technique in the future 6G communication systems. To suit the trend of exponentially growing connectivity, researchers have in...In recent studies, visible light communication(VLC) has been predicted to be a prospective technique in the future 6G communication systems. To suit the trend of exponentially growing connectivity, researchers have intensively studied techniques that enable multiple access(MA) in VLC systems, such as the MIMO system based on LED devices to support potential applications in the Internet of Things(IoT) or edge computing in the nextgeneration access network. However, their transmission rate is limited due to the intrinsic bandwidth of LED.Unfortunately, the majority of visible light laser communication (VLLC) research with beyond 10 Gb/s data rates concentrates on point-to-point links, or using discrete photodetector(PD) devices instead of an integrated array PD. In this paper, we demonstrated an integrated PD array device fabricated with a Si-substrated GaN/InGaN multiple-quantum-well(MQW) structure, which has a 4 × 4 array of 50 μm × 50 μm micro-PD units with a common cathode and anode. This single-integrated array successfully provides access for two different transmitters simultaneously in the experiment, implementing a 2 × 2 MIMO-VLLC link at 405 nm. The highest data rate achieved is 13.2 Gb/s, and the corresponding net data rate(NDR) achieved is 12.27 Gb/s after deducing the FEC overhead, using 2.2 GHz bandwidth and superposed PAM signals. Furthermore, we assess the Huffman-coded coding scheme, which brings a fine-grain adjustment in access capacity and enhances the overall data throughput when the user signal power varies drastically due to distance, weather, or other challenges in the channel condition. As far as we know, this is the first demonstration of multiple visible light laser source access based on a single integrated GaN/InGaN receiver module.展开更多
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)g...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(−3dB)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.展开更多
基金This research was funded by the National Key Research and Development Program of China(2022YFB2802803)the Natural Science Foundation of China Project(No.61925104,No.62031011,No.62201157,No.62074072).
文摘Although the 5G wireless network has made significant advances,it is not enough to accommodate the rapidly rising requirement for broader bandwidth in post-5G and 6G eras.As a result,emerging technologies in higher frequencies including visible light communication(VLC),are becoming a hot topic.In particular,LED-based VLC is foreseen as a key enabler for achieving data rates at the Tb/s level in indoor scenarios using multi-color LED arrays with wavelength division multiplexing(WDM)technology.This paper proposes an optimized multi-color LED array chip for high-speed VLC systems.Its long-wavelength GaN-based LED units are remarkably enhanced by V-pit structure in their efficiency,especially in the“yellow gap”region,and it achieves significant improvement in data rate compared with earlier research.This work investigates the V-pit structure and tries to provide insight by introducing a new equivalent circuit model,which provides an explanation of the simulation and experiment results.In the final test using a laboratory communication system,the data rates of eight channels from short to long wavelength are 3.91 Gb/s,3.77 Gb/s,3.67 Gb/s,4.40 Gb/s,3.78 Gb/s,3.18 Gb/s,4.31 Gb/s,and 4.35 Gb/s(31.38 Gb/s in total),with advanced digital signal processing(DSP)techniques including digital equalization technique and bit-power loading discrete multitone(DMT)modulation format.
基金supported by the National Natural Science Foundation of China(Nos.61925104 and 62031011)the National Key Research and Development Program of China(No.2022YFB2802803)。
文摘The rapid growth of new services has led to a significant increase in data traffic,which brings challenges for data centers in supporting high-speed processing of large volumes of data.Traditional electrical interconnects are becoming increasingly inadequate,leading to increasing attention to optical interconnects to achieve high-speed data center interconnects(DCIs).Visible light laser communication(VLLC)inherits the advantages of free-space optics(FSO),allowing it to circumvent the limitations of conventional fiber-based optical interconnects.In addition,VLLC offers other advantages such as high thermal stability,low power consumption,and low packaging cost.In this Letter,a novel differential pilot coding(DPC)scheme is proposed to achieve precise channel estimation and compensation for linear impairments without halving the effective data rate.A data rate of 601.46 Gbps with a constellation size up to 1024QAM over a 1 m multimode fiber(MMF)-1 m FSO-1 m MMF link is successfully achieved based on a 50-channel wavelength division multiplexer(WDM)VLLC system utilizing DPC and bit-power-loading discrete multitone(DMT)modulation.To the best of our knowledge,this is the highest data rate and constellation size ever the reported for a WDM VLLC system,which proves that VLLC is a promising candidate solution for achieving high-capacity and cost-effective optical interconnects in data centers.
基金National Natural Science Foundation of China(62031011,61925104)National Key Researchand Development Program of China(2022YFB2802803).
文摘The next generation of mobile communication is committed to establishing an integrated three-dimensional network that encompasses air,land,and sea.The visible light spectrum is situated within the transmission window for underwater communication,making visible light laser communication a focus of intense research.
基金National Natural Science Foundation of China(61925104,62031011,62201157)Major Key Project of PCL+1 种基金China Postdoctoral Science Foundation(2021M700025)National Postdoctoral Program for Innovative Talents(BX2021082).
文摘Visible light communication(VLC)has emerged as a promising communication method in 6G.However,the development of receiving devices is much slower than that of transmitting devices,limited by materials,structures,and fabrication.In this paper,we propose and fabricate an InGaN/GaN multiple-quantum-well-based vertical-structure micro-LED-based photodetector(μPD)on a Si substrate.A comprehensive comparison of the photoelectrical performance and communication performance of three sizes ofμPDs,10,50,and 100μm,is presented.The peak responsivity of all threeμPDs is achieved at 400 nm,while the passband full-widths at half maxima are 87,72,and 78 nm for 10,50,and 100μmμPDs,respectively.The−20 dB cutoff bandwidth is up to 822 MHz for 50μmμPD.A data rate of 10.14 Gbps is experimentally demonstrated by bit and power loading discrete multitone modulation and the proposed digital pre-equalizer algorithm over 1 m free space utilizing the self-designed 4×450μmμPD array as a receiver and a 450 nm laser diode as a transmitter.This is the first time a more than 10 Gbps VLC system has been achieved utilizing a GaN-based micro-PD,to the best of our knowledge.The investigation fully demonstrates the superiority of Si substrates and vertical structures in InGaN/GaNμPDs and shows its great potential for high-speed VLC links beyond 10 Gbps.
基金This work was partially supported by the National Natural Science Foundation of China(Nos.61925104,62031011,and 62074072)China National Postdoctoral Program for Innovative Talents(No.BX2021082)+1 种基金China Postdoctoral Science Foundation(No.2021M700025)Major Key Project of PCL(No.PCL2021A14).
文摘In this paper,we propose a 36-quadrature amplitude modulation(QAM)superposition modulation technique that is featured with uneven symbol probability by nonlinear precoding,named nonlinear coded nonuniform superposition(NCNS)QAM.Its aim is to alleviate the nonlinearity effect caused by high instantaneous power in multi-input single-output(MISO)visible light communication(VLC)system,with an uneven probabilistic-shaped constellation.The transmitter includes two LEDs to send signals independently,and the receiver uses a photo detector to receive the superposed QAM signal.The experiment results show that NCNS has a better robustness against nonlinearity than pulse amplitude modulation 4,approximately gaining a 16% increase in maximum usable peak-to-peak voltage and a 33% enlargement in dynamic range area.It is a simple but effective approach to solve the bandwidth limits related to signal power and hopefully be applied in large power VLC systems such as underwater VLC,or to improve the robustness against power fluctuation.
基金National Key Research and Development Program of China (2022YFB2802803)National Natural Science Foundation of China (61925104, 62031011)。
文摘In recent studies, visible light communication(VLC) has been predicted to be a prospective technique in the future 6G communication systems. To suit the trend of exponentially growing connectivity, researchers have intensively studied techniques that enable multiple access(MA) in VLC systems, such as the MIMO system based on LED devices to support potential applications in the Internet of Things(IoT) or edge computing in the nextgeneration access network. However, their transmission rate is limited due to the intrinsic bandwidth of LED.Unfortunately, the majority of visible light laser communication (VLLC) research with beyond 10 Gb/s data rates concentrates on point-to-point links, or using discrete photodetector(PD) devices instead of an integrated array PD. In this paper, we demonstrated an integrated PD array device fabricated with a Si-substrated GaN/InGaN multiple-quantum-well(MQW) structure, which has a 4 × 4 array of 50 μm × 50 μm micro-PD units with a common cathode and anode. This single-integrated array successfully provides access for two different transmitters simultaneously in the experiment, implementing a 2 × 2 MIMO-VLLC link at 405 nm. The highest data rate achieved is 13.2 Gb/s, and the corresponding net data rate(NDR) achieved is 12.27 Gb/s after deducing the FEC overhead, using 2.2 GHz bandwidth and superposed PAM signals. Furthermore, we assess the Huffman-coded coding scheme, which brings a fine-grain adjustment in access capacity and enhances the overall data throughput when the user signal power varies drastically due to distance, weather, or other challenges in the channel condition. As far as we know, this is the first demonstration of multiple visible light laser source access based on a single integrated GaN/InGaN receiver module.
基金National Key Research and Development Program of China(2022YFB2802803)National Natural Science Foundation of China(61925104,62031011,62274042)+2 种基金Natural Science Foundation of Shanghai Municipality(21ZR1406200)China Mobile Research Institute X-NETJiangsu Provincial Key Research and Development Program(BE2021008-5).
文摘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(−3dB)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.
