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Optical wireless communication (OWC) has emerged as a complementary or alternative technology to the radio-frequency (RF) communication. OWC based on image sensor, which is also called optical camera communication (OCC) has attracted much attention from industrial and academic societies. Here, we discuss several recent OCC technologies. We propose and demonstrate a light emitting diode (LED) light panel and rolling shutter image sensor based OCC system using frame-averaging background removal (FABR) technique, Z-score normalization, and neural network (NN). Here, a driver circuit for the LED display panel based on a bipolar-junction-transistor (BJT) and a metal-oxide-semiconductor field-effect-transistor (MOSFET) is also discussed. It can provide low enough driving frequency from a few Hz to kHz and high bias current for the LED light panel. Experimental results show that the proposed scheme can mitigate the inter-symbol interference (ISI) observed in the rolling shutter pattern produced by the high noise-ratio (NR) of the display contents.

Optical wireless communication (OWC) technology has attracted many attentions recently. Lighting luminaries equipped with red-green-blue (RGB) based light-emitting-diodes (LEDs) or laser-diode (LDs) can modify the perceived color of illumination. These highly directional light sources with adjustable perceived colors makes them very suitable for high speed and high security data transmissions. Here, we propose and demonstrate a two-level LD based color-shift-keying orthogonal-frequency- division-multiplexing (CSK OFDM) signal for the OWC systems. This scheme cannot only provide non-flickering effect to minimize human health concern, but also can enhance the transmission data rate of the CSK system. Here, the system model and the implementation of bit and power loading algorithm on the LD-CSK-OFDM are discussed. Experimentally results show that the demonstrated LD-CSK-OFDM signal can achieve data rate of 28.4 Gbit/s with 1.25 m free-space transmission distance satisfying the forward-error-correction (FEC) threshold.

In this study, a symmetric polarization-division-multiplexing (PDM) wavelength-division-multiplexing passive optical network (WDM-PON) with fiber to the extension (FTTE) architecture is presented and investigated. The proposed PON can also avoid the Rayleigh backscattering (RB) interference noise. Here, each WDM wavelength can produce 25 Gbit/s on-off keying (OOK) and 10 Gbit/s OOK modulation channels simultaneously in x- and y-polarizations (Polx and Poly) through PDM method for 25 and 105 km single-mode fiber (SMF) transmissions without dispersion compensation. The measured minimal power budget of 25 and 10 Gbit/s downstream and upstream signals are 29 and 35.1 dB and 29.8 and 31.5 dB, respectively, at the forward error correction (FEC) target. Therefore, the proposed PDM WDM-PON architecture can not only offer symmetric 35 Gbit/s downstream and upstream connections by the dual-polarized wavelength, but also can avoid the RB-induced interference noise. In addition, the presented dual-polarized downstream signal also can provide information security in physical layer, when the unauthorized user occupies unlawfully.

We propose and experimentally demonstrate a color-shift-keying embedded direct-current-optical-orthogonal-frequency-division-multiplexing (CSK-DCO-OFDM) scheme for the VLC systems. The proposed scheme can provide not only non-flickering aggregated optical power to reduce human health concerns, but also offers additional modulation dimension or flexibility to the CSK by including high data rate OFDM signal. The data rate is increased from 10 Mbit/s in the original CSK signal to 70.43 Mbit/s in the CSK-DCO-OFDM signal, and both the CSK and OFDM signals satisfy the forward-error-correction (FEC) threshold.

In this work, we first propose and demonstrate a bidirectional time-division-multiplexing (TDM) free space optical communication (FSO) traffic integrated in ring-based fiber access network together with fiber fault protection. Here, while we add the new designed optical devices in the central office (CO) and each optical wireless unit (OWU) respectively, the TDM-FSO fiber system can achieve the self-protected operation against fault. In addition, according to the proposed ring-based fiber network, the maximum numbers of eight OWUs can be provided for the symmetric 10 Gbps on-off keying (OOK) FSO downstream and upstream connections. As a result, the proposed FSO access network can allow 25 km fiber transmission and proper FSO transmission length depending on the atmospheric attenuation of different weather condition.

In this paper, we propose a long-reach star-ring-based time- and wavelength-division-multiplexing passive optical network (TWDM-PON) by using fiber- and free space optical (FSO)-protected architecture against fiber breakpoint. Here, the new fiber-based and FSO-based optical network unit (ONU) modules are designed in the PON system to achieve the self-protected operation. Thus, the adjacent ONU is linked to produce the fiber- or FSO-based reconnections. Thus, $4\times 10$ Gbit/s downstream and 10 Gbit/s upstream signals can be reached through 70 km fiber transmission and a length of free space link without signal amplification and dispersion compensation. Moreover, the relationships of splitter ratio and FSO link length in the proposed TWDM access network are also analyzed and discussed.

In the paper, we propose and design a ring-topology wavelength-division-multiplexing (WDM) access network for long-reach signal transmission. Here, the new central office (CO) and optical network unit (ONU) modules are designed to construct the ring-based architecture for symmetric data connection. Thus, the Rayleigh backscattering (RB) beat noise can be prevented due to the unidirectional downstream and upstream signal connections. In the demonstration, eight WDM wavelengths with 10 Gbit/s on-off keying (OOK) modulation are applied to serve as the symmetric downstream and upstream traffic through 105 km fiber connection without dispersion compensation. In addition, the minimum power budgets of 33.8, 36.1 and 35.4 dB among the eight WDM wavelengths can be obtained at the back-to-back (BtB), 51 and 105 km fiber links, respectively, under the forward error correction (FEC) target.

Visible light communication (VLC) is an advanced, highly developed optical wireless communication (OWC) technology that can simultaneously provide lighting and high-speed wireless data transmission. A VLC system has several key advantages: ultra-high data rate, secure communication channels, and a lack of interference from electromagnetic (EM) waves, which enable a wide range of applications. Light-emitting diodes (LEDs) have been considered the optimal choice for VLC systems since they can provide excellent illumination performance. However, the quantum confinement Stark effect (QCSE), crystal orientation, carrier lifetime, and recombination factor will influence the modulation bandwidth, and the transmission performance is severely limited. To solve the insufficient modulation bandwidth, micro-LEDs (μ-LEDs) and laser diodes (LDs) are considered as new ideal light sources. Additionally, the development of modulation technology has dramatically increased the transmission capacity of the system. The performance of the VLC system is briefly discussed in this review article, as well as some of its prospective applications in the realms of the industrial Internet of Things (IoT), vehicle communications, and underwater wireless network applications.

In this demonstration, we propose and investigate experimentally a bidirectional wavelength-division-multiplexed (WDM) free space optical communication (FSO) system integrated with fiber access network for wireless traffics. Here, there are four 10 Gbit/s on–off keying (OOK) WDM-FSO signals would propagate through a 25 km single-mode fiber (SMF) transmission and a 6 m free space transmission length for the bidirectional downstream and upstream FSO traffics. Moreover, an accurately simulation of detected powers of FSO wavelength under different free space transmission lengths can be estimated based on the proposed WDM-FSO system architecture. Therefore, according to the experimental and simulated results, the bidirectional WDM-FSO transmission can achieve 1000 m free space transmission length based on the obtained power sensitivity of each FSO signal.

Radio-over-fiber (ROF)-based mobile fronthaul network supporting the baseband unit and simple remote radio head is a promising network architecture for future wireless networks. In this paper, we propose and demonstrate a silicon photonics (SiPh)-based remote radio frontend (RRF) for the mm-wave ROF systems. The proposed SiPh-based RRF consisted of an integrated Mach-Zehnder modulator and a micro-ring modulator, producing a single-sideband 40 GHz millimeter-wave orthogonal-frequency-division-multiplexing ROF signal, which is robust against fiber chromatic dispersion in the mobile fronthaul transmission. The RRF is fabricated using SiPh platform and could be potentially low cost. High split-ratios can be potentially achieved. Data rate of 7.813 Gbit/s per wavelength channel is achieved in the experiment. Numerical analysis is also performed; there are good matches of the simulation and experimental results.

In the paper, we present and demonstrate experimentally a 10 Gbit/s on-off keying (OOK) bidirectional wavelength-division-multiplexing (WDM) free space optical (FSO) communication architecture integrated in fiber network together with 5 m free space transmission length and 25 km fiber link, respectively. To achieve bidirectional FSO link, the all WDM wavelengths can be used simultaneously to serve as the downstream and upstream traffics in the proposed FSO-WDM system. Here, four pairs of line terminations (LTs) and optical wireless units (OWUs) are integrated arbitrarily in fiber access network for confidential and bidirectional FSO connection based on the requirement of practical environment. In the measurement, the relationship of FSO signal performance and detected tolerance are also discussed and analyzed. Moreover, the WDM-FSO transmission can also avoid the Rayleigh backscattering (RB) beat noise in fiber connection.

In this work, we demonstrate an integrated optical baseband, free space optical (FSO) communication and millimeter-wave (MMW) traffics through the present passive optical network (PON) architecture by utilizing single wavelength for broadcasting triple-play services. In the execution, we exploit 10 Gbit/s on-off keying (OOK) modulation on 10 GHz Mach-Zehnder modulator (MZM) to produce the downstream baseband signal. And the 10 Gbit/s baseband signal also can cause FSO traffic within the forward error correction (FEC) target after 25 km fiber and 160 m free space transmissions. Moreover, we can utilize the fiber to the extension (FTTE) scheme to provide the 36.42 GHz MMW with 10 Gbit/s OOK data after 25 km fiber link and 8 km extended fiber transmission.

We propose and design a Long-Short-Term-Memory (LSTM) algorithm to mitigate transmission impairments of 4-level-pulse-amplitude-modulation (PAM4) produced by silicon- microring-modulator (Si-MRM). 160-Gbit/s PAM4 over 1-km single-mode-fiber (SMF) is achieved satisfying the pre-forward-error-correction (FEC) requirement.

We demonstrate using simulation and experiment a 2-client non-orthogonal-multiple-access visible-light-communication (NOMA VLC) network using non-Hermitian-symmetry (NHS) inverse-fast-Fourier-transform (IFFT)/FFT size-efficient orthogonal-frequency-division-multiplexing (OFDM).

In the work, we propose and investigate a real-time optical wireless communication (OWC) system with 1 Gbps on–off keying (OOK) traffic rate for indoor and outdoor transmissions. Here, 1 Gbps OWC traffic with error-free operation can be achieved indoors under the free space transmission length of 500 m based on the simulation and experimental results. In addition, 952, 904, 476 Mbps throughput rates of proposed real-time OWC system are measured outdoors after passing through the wireless transmission lengths of 120, 300 and 500 m, respectively.

We summarized the recent progress of enabling techniques for the optical wireless communication (OWC) and visible light communication (VLC). Besides, we reported two high data-rate laser-diode (LD) based VLC systems. Several application scenarios using VLC were also discussed.

Using solar cell (or photovoltaic cell) for visible light communication (VLC) is attractive. Apart from acting as a VLC receiver (Rx), the solar cell can provide energy harvesting. This can be used in self-powered smart devices, particularly in the emerging “Internet of Things (IoT)” networks. Here, we propose and demonstrate for the first time using pre-distortion pulse-amplitude-modulation (PAM)-4 signal and parallel resistance circuit to enhance the transmission performance of solar cell Rx based VLC. Pre-distortion is a simple non-adaptive equalization technique that can significantly mitigate the slow charging and discharging of the solar cell. The equivalent circuit model of the solar cell and the operation of using parallel resistance to increase the bandwidth of the solar cell are discussed. By using the proposed schemes, the experimental results show that the data rate of the solar cell Rx based VLC can increase from 20 kbit/s to 1.25 Mbit/s (about 60 times) with the bit error-rate (BER) satisfying the 7% forward error correction (FEC) limit.

Light-emitting-diode transmitter and complementary-metal–oxide–semicon-ductor (CMOS) image sensor receiver based visible light communication is a promising scheme for an optical wireless communication. During the demodulation of the rolling shutter pattern obtained from the CMOS image sensor Rx, due to the high signal fluctuation introduced by the uneven light exposure, special thresholding schemes are needed to correctly identify the data logic. In this work, we propose and demonstrate a modified adaptive scheme (MQA) for the demodulation of the rolling shutter pattern. Experimental bit-error-ratio (BER) measurements using different thresholding schemes at different illuminance are analyzed. The results show that the proposed MQA scheme can provide much lower BER, with similar process latencies when compared with other schemes.

Organic photo-detector (OPD) is lightweight and physically flexible. It can transform plastic or glass into smart surfaces. Visible light communication (VLC) is considered as one of the promising technologies for the future wireless communications. VLC combines the advantages of lighting and communication simultaneously. Besides, it can be deployed using existing lighting infrastructure; hence little extra cost is needed to provide this wireless communication. As the OPD has a large optical detection area, it would be interesting to employ the OPD as VLC receiver (Rx). If the OPD can be used in the VLC systems, it can benefit the Internet-of-Thing (IoT) networks by providing efficient human-to-machine and machine-to-machine communications. However, implementing VLC using OPD Rx is challenging. Due to the slow charging and discharging processes of the OPD, the optical-to-electrical response speed is limited. Besides, the OPD requires external bias to be operated. Here, we propose and demonstrate using pre-distortion scheme for pulse-amplitude-modulation (PAM) signal to a self-powered PCBM:P3HT OPD to enhance the VLC transmission performance. The operation of the self-powered PCBM:P3HT OPD is discussed. Both experiments using PAM-2 and PAM-4 (with and without pre-distortion) are evaluated. The performance, requirement and capability limitations of the pre-distortion schemes are also analyzed and discussed by using numerical simulations.

In order to increase transmission capacity, multiplexing schemes in different physical dimensions, including time, frequency, modulation quadrature, polarization, and space, can be employed. In this work, we propose and demonstrate a red color laser-diode (LD) based visible-light-communication (VLC) system using two kinds of digital domain multiplexing schemes, orthogonal-frequency-division-multiplexing (OFDM) and power-domain division-multiplexing (PowDM). The two digital domain multiplexed data can achieve data rates of 1.66 Gbit/s and 6.41 Gbit/s, respectively, providing a total data rate of 8.07 Gbit/s, fulfilling the pre-forward error correction (pre-FEC) bit-error-rate (BER) limit. The measured signal-to-noise ratios (SNRs) are 10.96 dB and 14.45 dB, respectively. Here, similar to OFDM, the PowDM can enhance the total system capacity by allowing acceptable signal spectra overlapping among different power division signals to maximize the bandwidth utilization. An experiment to verify and evaluate the proposed work is performed. The modulation and demodulation of OFDM and PowDM are discussed. The optimum power levels of the individual signals in the PowDM signal are also analyzed.

We propose and demonstrate a 64-Gbit/s four-level pulse-amplitude-modulation transmission by using a limited modulation bandwidth silicon microring modulator (SiMRM) and the Volterra equalization scheme. Severe intersymbol interference caused by both the chromatic dispersion of the optical fiber and the bandwidth limitation of components can be compensated. Besides, several equalization schemes are compared and analyzed in terms of performance and complexity. In addition, the design and characteristics of the SiMRM used in the experiment are also discussed.

The light emitting diode (LED) based visible light communication (VLC) system can provide lighting and communication simultaneously. It has attracted much attenuation recently. As the photovoltaic cell (also known as solar cell) is physically flexible, low cost, and easily available, it could be a good choice for the VLC receiver (Rx). Furthermore, besides acting as the VLC Rx, the solar cell can convert VLC signal into electricity for charging up the Rx devices. Hence, it could be a promising candidate for the future internet-of-thing (IoT) networks. However, using solar cell as VLC Rx is challenging, since the response of the solar cell is highly limited and it will limit the VLC data rate. In this work, we propose and demonstrate for the first time using pre-distortion Manchester coding (MC) signal to enhance the signal performance of solar cell Rx based VLC. The proposed scheme can significantly mitigate the slow response , as well as the direct-current (DC) wandering effect of the solar cell; hence 50 times increase in data rate can be experimentally achieved.

We propose and demonstrate a distortion mitigation of 50-Gbitls PAM-4 signal generated by a silicon-based Mach-Zehnder-modulator (SiMZM) after 20-km single-mode-fiber transmission via deep-neural-network (DNN). The implementation of a 2-layer DNN is discussed.

We propose an electronic label and sensor system using visible light communication (VLC). The downlink signal is transmitted by a white-light light-emitting diode (LED) lamp that can provide lighting, VLC, and energy harvesting for mobile devices. The downlink is received by a solar cell. The uplink can be captured by a surveillance camera image sensor. However, using the camera image sensor as a VLC receiver (Rx) is challenging since the data rate is limited by the frame rate and due to uneven light exposure. The rolling shutter effect of the image sensor can be used to increase the data rate. In this paper, we propose and demonstrate how to demodulate the obtained rolling shutter pattern using a second-order polynomial (SOP) extinction ratio (ER) enhancement scheme, together with iterative and modified quick adaptive thresholding schemes. The ER enhancement scheme can significantly reduce the large ER fluctuation. Experimental results show that by using the proposed SOP ER enhancement scheme, the bit error rate (BER) improvement can be up to two orders of magnitude. We also believe that the proposed electronic label and sensor system may be applicable to Internet-of-Things sensing networks for connecting a number of mobile devices.

We propose and experimentally demonstrate an indoor positioning system which combines identity positioning and the radio frequency carrier allocation technique in order to reduce the signal interference from nearby light-emitting diodes (LEDs) and improve the accuracy of positioning. In addition, the solar cell is used as an optical receiver for the visible light positioning system. Due to the benefits of solar cells such as low-cost, high light sensitivity, and ease in integration with wearable devices, the proposed system could be an energy-efficient and environmentally friendly choice for indoor positioning in the future.

In this paper, we propose using an energy-efficient and low-cost 682-nm vertical-cavity surface-emitting laser (VCSEL) with 1-GHz modulation bandwidth for high-speed wireless visible light communication (VLC). Moreover, by using spectral-efficient orthogonal frequency division multiplexing (OFDM) modulation with bit-and-power-loading algorithm, we successfully demonstrate VCSEL-based transmission at 11.1 Gbps (10.2 Gbps in a raw data rate) over a free-space length of 1.2 m under small bias current of 3.5 mA. Furthermore, decreasing the bias current as low as 2 mA, we can also demonstrate 10.5 Gbps (9.7 Gbps in a raw data rate) OFDM VLC transmission over a 1.2-m free-space link. This proposed VCSEL-based OFDM transmission system could be viewed as a cost-effective and energy-efficient approach for high-speed (> 10 Gbps) laser diode wireless VLC application.

Visible Light Communication (VLC) technology is an emerging technology using visible light modulation that, in the modern world, will mainly facilitate high-speed internet connectivity. VLC provides tremendous advantages compared to conventional radio frequency, such as a higher transmission rate, high bandwidth, low-power consumption, no health hazards, less interference, etc., which make it more prominent in recent days. Due to their outstanding features, including low cost, low power consumption, etc., µ-light-emitting diodes (LEDs) have gained considerable attention for VLC implementation, but mostly for the ability to be used for lighting as well as communications. In this review paper, we will focus mainly on recent developments in VLC applications and various factors affecting the modulation bandwidth of VLC devices. Numerous factors, such as quantum confined stark effect (QCSE), carrier lifetime, carrier recombination time, crystal orientation, etc. affect the modulation bandwidth of LEDs, and more information will be discussed in the following sections. This paper will focus on VLC applications based on LEDs but mainly on semipolar μ-LEDs and μ-LED-based arrays with high bandwidths. Another important application of VLC is underwater optical wireless communication (UOWC), which has drawn a huge interest in marine exploration and underwater connectivity, but still faces some challenges because visible light is being used. In addition, this paper will focus on how the current VLC system modulation bandwidth can be enhanced. Many methods have been introduced, such as decreasing the active layer thickness or effective active area or using doping, but the bandwidth is restricted by the recombination time when the system configuration reaches its limit. Therefore, it is important to find alternative ways such as optimizing the system, using the blue filter or using the equalization technology, which will be addressed later. Overall, this review paper provides a brief overview of the VLC-based system performance and some of its potential prospects.

To avoid the Rayleigh backscattering (RB) beat noise in colorless wavelength division multiplexing (WDM) access architecture, the dual-band modulation diagram is proposed for demonstration. In the study, 11.25 Gbit/s orthogonal frequency division multiplexing (OFDM) wireless downstream and 2.5 Gbit/s remodulated on–off keying (OOK) upstream traffic are achieved by using same wavelength. Moreover, the bit error rate (BER) measurements of wireless downstream and wired upstream wavelengths are also executed and discussed after 20 km fiber connection.

We demonstrate a non-Hermitian symmetry orthogonal frequency division multiplexing (NHS OFDM), known as serial-complex-valued (SCV)-OFDM for the white-light phosphor-based light-emitting-diode (LED) visible light communication (VLC) system. The white-light LED system can provide both VLC and lighting simultaneously. The proposed scheme is based on the fast-Fourier-transform (FFT)/invert-FFT (IFFT) size efficient technique proposed before. The real (Re) and imaginary (Im) parts of the complex-valued OFDM signals are extracted and time-serially multiplexed to achieve NHS. The proposed scheme is simple and only needs a single LED transmitter (Tx) and one receiver (Rx). The encoding and decoding of the proposed SCV-OFDM are also discussed.

A 400-Gbit/s Ethernet (GbE) pulse-amplitude-modulation-4 (PAM-4) over 10-km single-mode-fiber (SMF) transmission direct-detected by an integrated silicon-photonics-receiver satisfying the IEEE P802.3bs requirement; and its feasibility to support 512-Gbit/s were illustrated.

We propose and demonstrate a convergent wireline and wireless access network using time-and-wavelength-division-multiplexed passive optical network (TWDM-PON) architecture. Bidirectional 40-km single-mode-fiber transmissions (including the 60-GHz wireless transmission) satisfying the forward error correction limit are demonstrated, with data rates of ~10 Gb/s per wavelength in the downstream signal and 17.50 Gb/s per wavelength in the upstream signal. To achieve higher data rate, bit-loading orthogonal frequency-division modulation was used. We also analyze the laser-linewidth-induced performance variation to the signal generated by optical beating and the baseband signal.

Using a single optical filter to demultiplex the all-optical orthogonal frequency-division multiplexing (OFDM) system was regarded as cost-effective and simple. Here, an all-optical OFDM signal demultiplexer using sinc transfer function was analyzed. The performance difference for using optical demultiplexers with different transfer functions was also compared and discussed. Within 20 km transmission, the sinc optical filter providing orthogonality between neighbor optical subcarriers can improve the signal performance by reducing the inter-carrier interference. After 20 km transmission, the signal performance degradation may mainly be dominated by dispersion for 10 Gb/s channel capacity; hence the advantage of sinc filter becomes negligible. These analyses provide the idea for how to choose the optical demultiplexer to integrate the whole optical fast Fourier transform circuit and optical sampling circuit into a single filter. This can effectively reduce the system cost and complexity.

Visible light communication based on LED has attracted more and more attention. As the primary function of LED luminaries is optimized for lighting and illumination, it challenges the communication properties of VLC. An investigation based on different in-home illumination conditions using commercially available whitelight LED luminaries to optimize both illumination and communication is highly desirable. In this work, we investigate joint illumination and communication systems to provide an in-home lighting and VLC system. We first focus on the performance constraints set by illumination properties and discuss lighting conditions using different kinds of commercially available luminaries, beam angles, and LED lamp arrangements, and consider reflections off different wall materials. Then we propose and experimentally demonstrate a white-light phosphor-based LED adaptive data rate VLC system. Finally, the achievable data rates of a joint illumination and VLC system are discussed based on the experimental results, and an environment with reduced VLC data rate fluctuation can be achieved.

In this paper, a flexible and reliable 40-Gb/s time and wavelength division multiplexing passive optical network (TWDM-PON) architecture is proposed and demonstrated. Here, a $4\times 10\ \mbox{Gb/s}$ orthogonal frequency-division multiplexing (OFDM) downstream signal is achieved by utilizing four 2.5-GHz directly modulated lasers in the optical line terminal. A reflective optical semiconductor amplifier is utilized in each optical network unit to serve as upstream transmitter (Tx) transmitting 2.5-Gb/s on-off keying (OOK) and 10-Gb/s OFDM upstream traffic, respectively. In addition, the dynamic bandwidth (capacity) allocation and fiber fault protection also can be achieved by applying the new proposed PON architecture with software-defined networking approach.

We demonstrate using bit-loading orthogonal-frequency-division-multiplexing (OFDM) and adaptive Volterra equalization to mitigate the light-emitting-diode (LED) nonlinearity; hence the data rate of LED based visible-light-communication (VLC) can be increased to > 700 Mbit/s.

In this demonstration, we first propose an optimal analogue front end circuit without employing pre-equalization (series peaking) to increase the modulation bandwidth of phosphor-LED in visible light communication (VLC) transmission. And there is no blue filter and post-equalization in the client side. Here, only using optimal adjustment of resistance (R), inductance (L), and capacitance (C) in bias-tee to compensate the impedance matching of phosphor-LED, nearly 32 MHz modulation bandwidth can be accomplished. Therefore, utilizing orthogonal frequency division multiplexed modulation with bit-loading algorithm in VLC system, 185 Mbps data rate can be achieved under a transmission distance of 80 cm.

We demonstrate for the first time a recorded 56-Gb/s transmission in a new type robust and bend-insensitive glass-glass-polymer structured 80- $$\upmu $$ m ultra-large-core multimode fiber (ULCMMF) using simple and single-polarization on-off-keying for Lightpeak. The LCMMF design is presented. Experimental results show that the ULCMMF could be a good choice for consumer applications in the near future.

In this work, we propose and investigate a 115 Gbit/s (4 � 28.75 Gbit/s) downstream and 10 Gbit/s upstream time- and wavelength-division-multiplexing passive optical network (TWDM-PON) together with 11.25 Gbit/s wireless broadcasting signal using multi-band orthogonal-frequency-divisionmultiplexing (OFDM) modulation within 10 GHz bandwidth. Here, to compensate the power fading and chromatic dispersion in the higher frequency, we utilize a � 0.7 chirp parameter Mach–Zehnder modulator (MZM) for the OFDM signal. Hence, negative power penalties of � 0.3 and � 0.4 dB in the downstream and broadcasting wireless signals; and power penalty of 0.3 dB in the upstream signal are measured at the bit error rate (BER) of 3.8 � 10 � 3 after 20 km standard single mode fiber transmission

In this study, we present and demonstrate a 10 Gbit/s on-off keying (OOK) free space optical communication (FSO) system with signal security operation by using polarization-multiplexing method. A single wavelength can be separated two orthogonal polarization FSO signals, which mean the FSOp and FSOs respectively, by using two polarizers with mutually orthogonal polarization directions. And the FSOp and FSOs wavelengths can act as the data and interference channels for FSO connection. When the injected power of FSOs is >−30 dBm, the FSOp signal will be interfered seriously for security protection. In addition, the FSO signal can pass through 25 km fiber link and support 1000 m free space transmission length.

We propose and experimentally demonstrate a 37.3 Gb/s passive optical network using four-band orthogonal-frequency-division-multiplexing (OFDM) channels within 10 GHz bandwidth. Here, the required sampling rate and resolution of digital-to-analog/analog-to-digital (DA/AD) converter are only 5 GS/s and 8 bits to accomplish the 40 Gb/s OFDM downstream rate. Moreover, to reduce the power fading and fiber chromatic dispersion issues, a $$-$$ - 0.7 chirp parameter Mach-Zehnder modulator is used for the four-band OFDM modulation scheme. Downstream negative power penalty of $$-$$ - 0.37 dB can be obtained at the bit error rate of $$3.8\times 10^{-3}$$ 3.8 × 10 - 3 after 20 km standard single mode fiber transmission without dispersion compensation.

Silicon photonics which is compatible with mature complementary metal oxide semiconductor (CMOS) fabrication process has been extensively demonstrated for monolithic integration of photonic and electrical circuits. We show that an integrated silicon Mach-Zehnder modulator (MZM) may be used for advanced modulation formats despite the nonlinear dependence of refractive index change with applied voltage in the free-carrier depletion modulator. We experimentally demonstrated the use of a silicon MZM for direct detection optical orthogonal frequency division multiplexing (DDO-OFDM) modulation with advanced data formats of quadrature phase-shift keying (QPSK), 8 phase-shift keying (8PSK) and 16-quadrature amplitude modulation (16-QAM). The measured bit error rate performance of the back-to-back and 50 km single mode fiber transmission of each format is well below the forward error correction limit.

We propose and demonstrate a new AC-light emitting diode based visible light communication system, in which the message signal is up-converted to 400 kHz frequency band and combine with the 60 Hz AC-power from the outlet. A special design bias-tee circuit is first implemented to combine the message signal and the AC-power for minimizing the signal distortion. Thus, the spectra of both signals are well separated. A special design clock recovery is used to synchronize the AC-power with the message signal; hence the message signal can be correctly applied to the rectified AC-power cycle.

We propose and demonstrate a simple digital post-equalization technique to improve the bandwidth-limitation of light-emitting-diode (LED) visible-light-communication (VLC) channel. The design of finite-impulse-response equalizer according to the channel response is presented to improve the bandwidth limitation of LED VLC channel. Here, no optical blue filter is used. The simulation and experimental results show $$\sim $$ 10 times enhancement of the direct modulation speed of white-light LED VLC system. When compares with the previous demonstration using high-pass equalization circuit constructed by lumped capacitor and resistor, the proposed scheme shows an improvement in signal quality and transmission distance, and a 10 Mbit/s error-free free-space transmission over 1 m can be achieved under the bit error rate of $$< 10^{-9}$$ .

We propose a multi-band OFDM modulation for wireless VLC system together with dynamic bandwidth allocation. In addition, the proposed modulation format also can enhance the maximum VLC traffic rate to 17.8% without using blue filter.

In this investigation, we propose and demonstrate a wavelength-tunable self-seeding 1.2 GHz reflective semiconductor optical amplifier (RSOA)-based transmitter in each optical network unit for colorless wavelength-division-multiplexed passive optical network access. The output wavelength of the proposed RSOA-based laser can be tuned in the whole C-band. Here, we apply an orthogonal frequency division multiplexing (OFDM) modulation with bit-loading algorithm on RSOA laser to modulate 3.5 Gbps data rate directly for upstream traffic . In addition, we employ a 2.5 GHz direct modulation laser in the head-end to generate 10 Gbps 16-QAM OFDM signal for downstream traffic. Therefore, after transmitting through 20 km single-mode fiber, power penalties of 1.4 and 2.8 dB are observed for downstream and upstream traffics, respectively, under the forward error correction threshold [bit error rate = 3.8 × 10−3].

According to the present passive optical network (PON) standard, the fiber transmission lengths are from 500 m to 20 km between the optical line terminal (OLT) and different optical network units (ONUs). It will result in difference power losses (DPloss) from 4 to 5 dB. Hence, we propose to adjust adaptively the output optical power of the upstream laser diode (LD) depending on the different fiber lengths. With the different fiber transmission lengths, we can properly adjust the bias current and modulation index of upstream LD for energy-saving. We characterize and analyze experimentally the relationship of output optical power and modulation amplitude Vamp under different fiber transmissions in PON access. Moreover, due to the adaptive power control of upstream signal, the optical upstream equalization also can be retrieved with power variation of 1.1 dB in this experiment.

In this paper, we propose and investigate a ring-based wavelength-division-multiplexing passive optical network (WDM-PON) providing both Rayleigh backscattering (RB) noise mitigation and fiber-fault protection. The proposed ring-based WDM-PON has a dual-ring architecture to protect and restore any fiber fault. Besides, the ring architecture also can mitigate the RB beat noise, since the RB and the upstream wavelengths are propagating in opposite directions. Here, we discuss and analyze the characteristics of the downstream signals using 10 Gb/s ON-OFF keying (OOK), 10 Gb/s differential phase-shift keying, and 10 Gb/s orthogonal frequency-division multiplexing (OFDM) modulations, respectively. Moreover, we also investigate the upstream traffic using the 2.5 Gb/s OOK and 10 Gb/s OFDM generated by the directly modulated reflective semiconductor optical amplifier-based optical network unit, respectively.

The wavelength division multiplexing-time division multiplexing (WDM-TDM) passive optical network (PON) using reflective semiconductor optical amplifier (RSOA)-based colorless optical networking units (ONUs) is considered as a promising candidate for the realization of fiber-to-the-home (FTTH). And this architecture is actively considered by Industrial Technology Research Institute (ITRI) for the realization of FTTH in Taiwan. However, different fiber distances and optical components would introduce different power budgets to different ONUs in the PON. Besides, due to the aging of optical transmitter (Tx), the power decay of the distributed optical carrier from the central office (CO) could also reduce the injection power into each ONU. The situation will be more severe in the long-reach (LR) PON, which is considered as an option for the future access. In this work, we investigate a WDM-TDM PON using RSOA-based ONU for upstream data rate adjustment depending on different continuous wave (CW) injection powers. Both standard-reach (25 km) and LR (100 km) transmissions are evaluated. Moreover, a detail analysis of the upstream signal bit-error rate (BER) performances at different injection powers, upstream data rates, PON split-ratios under stand-reach and long-reach is presented.

Carrier-distributed long-reach passive optical network (LR-PON) is a promising candidate for future access networks. In this work, we analyze and compare the 4 × 2.5 Gb/s and 4 × 10 Gb/s upstream traffics in a carrier-distributed LR-PON using four wavelength-multiplexed 2.5 Gb/s on–off keying (OOK) and 10 Gb/s optical orthogonal frequency division multiplexing-quadrature amplitude modulation (OFDM-QAM) signals. Four commercial 1.2 GHz bandwidth reflective semiconductor optical amplifiers (RSOAs) are used in each optical networking unit (ONU) for the generation of the upstream signal. Due to the limited bandwidth of the RSOA, only up to 2.5 Gb/s upstream OOK signal can be generated. However, by using the spectral efficient modulation, such as OFDM-QAM, 10 Gb/s data rate can be achieved. 20, 50 and 75 km fiber transmissions are also compared using the two different kinds of modulation respectively.

We propose and demonstrate a bidirectional transmission, hybrid wired and wireless access network based on subcarrier modulation (SCM) techniques. The scheme simultaneously enables the dispersion-tolerant transmission of millimeter (mm)-wave signals for use in wireless access networks, downstream baseband signals for optical wired access networks, and optical continuous-wave (CW) carriers for use in upstream data remodulations. Error-free transmissions through a 25-km length of single mode fiber (SMF) for both the downstream baseband and the remodulated upstream signals are confirmed by bit-error-rate (BER) measurements. The dispersion tolerance of the radio-over-fiber (RoF) signal is assessed using numerical simulations.