Error-free Transmission Research Articles

A Novel Optical Frequency-Hopping Scheme Based on a Flexible Structure for Secure Optical Communications

A novel optical frequency-hopping scheme based on a flexible structure for secure optical communications is proposed and demonstrated. In the proposed scheme, critical users' data are divided into a lot of segments, and these segments are transmitted by different optical wavelengths in time domain. In other words, one channel optical carrier carries different users' data segments. A flexible structure was demonstrated and used in optical frequency-hopping system to simplify the structure and decrease the cost of the security system. In this paper, the viability of a four-wavelength-frequency-hopping secure optical communication system with a 25-Gb/s error-free transmission through a 32-km single-mode fiber and a 8-km dispersion compensation fiber was demonstrated and verified by simulation tools.

Performance Enhancement in Colorless WDM–PON Using SSB-SC

Abstract In this manuscript, an attempt has been made to enhance the performance of colorless wavelength division multiplexed-passive optical network (WDM–PON) system using a combination of dual-drive Mach–Zehnder modulator and single sideband-suppressed carrier (SSB-SC) technique along with splicing. The proposed design makes use of SSB-SC technique for optical line terminal (OLT) as well as for optical network unit (ONU) that is generated by using dual-drive modulator which in turn reduces the expense for complete communication process. Suppressed RF signals with four channels at a bit rate of 10 Gbps for each channel are multiplexed before injecting into fiber span of 25 km at OLT side. Half of the downlink power is consumed for re-modulating the data signal at ONU side. The performance is further improved by using signal splicing method. Due to suppression in the carrier in this technique, there is no carrier Rayleigh scattering problem. The proposed model is compared with the existing one for error-free transmission of signal. The results revealed that the proposed model possess less value of bit error rate with the same value of received optical power as well as channel.

Simultaneous polarization separation and switching for 100-Gbps DP-QPSK signals in backbone networks**Project supported by the National Key Research and Development Program of China (Grant No. 2017YFC0803900) and the National Natural Science Foundation of China (Grant No. 9163801).

We propose a novel scheme of simultaneous polarization separation and switching, based on the orthogonally-polarized four-wave mixing (FWM) effect, for ultra-high-speed polarization multiplexing (Pol-MUX) fiber networks such as 100-Gbps and 400-Gbps backbone networks. We use theoretical and experimental analysis of the vector theory of FWM to successfully achieve polarization separation and all-optical switching by utilizing a 100-Gbps dual polarization-quadrature phase shift keying (DP-QPSK) signal and two orthogonally-polarized pumps. Both of the polarization-separated QPSK signals have clear constellation diagrams, with root mean square (RMS) error vector magnitudes (EVMs) of 14.32% and 14.11% respectively. The wavelengths of idlers can be created at 30 different wavelengths, which are consistent with International Telecommunication Union-Telecommunication (ITU-T) wavelengths, by flexibly changing the wavelength of the pump light. Moreover, the idlers that have distinct wavelengths have power distributed in a range from −10 dBm to −15 dBm, which can support error-free transmission. The power penaltyis 5 dB lower than that of back-to-back (BTB) signal for both the X- and Y-polarization components measured at a bit error ratio (BER) of 3.8×10−3. Our experimental results indicate that this scheme has promising applications in future backbone networks.

Maximizing capacity, flexibility and efficiency in G-PON networks using VCSEL-based OOK and 2/4-PAM formats

ABSTRACTThis work experimentally demonstrates the potential of multi-level pulse amplitude modulation with direct detection to maximize carrier spectral efficiency and double the Gigabit passive optical networks (G-PON) network data rate. Three scenarios have experimentally been exploited. First, a 1310 nm vertical surface-emitting laser (VCSEL) has directly been modulated with a 10 Gbps OOK data. A receiver sensitivity of −19.11 dBm is attained, and a successful error free transmission over 22 km SMF fibre achieved, with a transmission penalty of 0.46 dB. To maximize carrier spectral efficiency, 2/4 PAM modulation formats are adopted respectively. A receiver sensitivity of −14.64 and −11.63 dBm is attained for 2-PAM and 4-PAM formats respectively. However, a 3.21 km fibre transmission introduces a penalty of 0.64 and 3.30 dB for 2-PAM and 4-PAM formarts respectively. 2/4-PAM modulation formats significantly increase the aggregated data rate at different ONUs within the G-PON without expensive optics investment, though at the cost of reduced transmission reach due to the high bitrate attained. We further demonstrate the design of a software defined digital signal processing assisted receiver to recover the 2/4 PAM transmitted signal without employing costly receiver hardware.

Optimised handoff mechanism using RFID tags for a communication-based train control system

In a communication-based train control system, one of the most important aspects is ensuring that a mobile station is connected continuously to the zone controller to ensure continuous and precise transmission of the train's location, speed and other relevant information. Due to the continuous motion of the train handoffs between different APs is necessary to remain connected. This work aims to propose a location-based handoff method which will minimise handoff latency and provide better connections. The location-based handoff mechanism uses the concept of placing RFID tags at predetermined locations. Handoff is triggered at the location where the RFID tag is present and a connection is made to the new AP based on the channel information obtained. The architecture used in the scenario is a WiMAX architecture and connections are maintained with the help of routers contained within the mobile stations. The proposed handoff method provides better handoff latency and error free transmission in a system where precise information transmission is necessary.

Optimised handoff mechanism using RFID tags for a communication-based train control system

In a communication-based train control system, one of the most important aspects is ensuring that a mobile station is connected continuously to the zone controller to ensure continuous and precise transmission of the train's location, speed and other relevant information. Due to the continuous motion of the train handoffs between different APs is necessary to remain connected. This work aims to propose a location-based handoff method which will minimise handoff latency and provide better connections. The location-based handoff mechanism uses the concept of placing RFID tags at predetermined locations. Handoff is triggered at the location where the RFID tag is present and a connection is made to the new AP based on the channel information obtained. The architecture used in the scenario is a WiMAX architecture and connections are maintained with the help of routers contained within the mobile stations. The proposed handoff method provides better handoff latency and error free transmission in a system where precise information transmission is necessary.

Deep Learning Based Single Carrier Communications Over Time-Varying Underwater Acoustic Channel

In recent years, deep learning (DL) techniques have shown great potential in wireless communications. Unlike DL-based receivers for time-invariant or slow time-varying channels, we propose a new DL-based receiver for single carrier communication in time-varying underwater acoustic (UWA) channels. Without the off-line training, the proposed receiver alternately works with online training and test modes for accommodating the time variability of UWA channels. Simulation results show a better detection performance achieved by the proposed DL-based receiver and with a considerable reduction in training overhead compared to the traditional channel-estimate (CE)-based decision feedback equalizer (DFE) in simulation scenarios with a measured sound speed profile. The proposed receiver has also been tested by using the data recorded in an experiment in the South China Sea at a communication range of 8 km. The performance of the receiver is evaluated for various training overheads and noise levels. Experimental results demonstrate that the proposed DL-based receiver can achieve error-free transmission for all 288 burst packets with lower training overhead compared to the traditional receiver with a CE-based DFE.

Time-Frequency Domain Turbo Equalization for Single-Carrier Underwater Acoustic Communications

Single-carrier frequency-domain equalization (SC-FDE) is a promising technique for coherent high-rate underwater acoustic (UWA) communications. In this paper, a time-frequency domain turbo equalization (TFD-TE) scheme is proposed for single-carrier modulation. The TFD-TE scheme is to couple a multi-channel frequency domain equalizer with phase rotation compensation and a low-order single-channel time-domain turbo equalizer. To mitigate the error propagation and further enhance receiver performance, a bidirectional equalizer that combined the soft outputs of a conventional equalizer and a backward equalizer is introduced into the proposed TFD-TE scheme (Bi-TFD-TF). The sparse channel is estimated by the improved proportionate normalized least mean squares (IPNLMS) algorithm block by block. Both the simulated and experimental results show the proposed TFD-TE can effectively improve system performance with acceptable complexity. The proposed TFD-TE scheme is evaluated using communication data collected from the DJK15 lake experiment. For the $1\times 4$ single-input multiple-output (SIMO) communication system using quadrature phase shift keying (QPSK) and 8-phase shift keying (8PSK) modulations, the proposed scheme achieves error-free transmission after a few iterations. Our receiver achieves a maximum raw data rate of 12 kbit/s and a reliable net data rate of 4 kbit/s within 4-kHz bandwidth at a range of 10.8 km. Compared with conventional frequency domain turbo equalization (FD-TE), the proposed TFD-TE scheme can enhance 0.8–1.3 dB in terms of output signal-to-noise ratio (OSNR). The related bi-TFD-TE provides an additional 0.8–1.7-dB OSNR improvements.

An Efficient Encoder-Subcarrier Mapping Method Combined With Polar Code for Visible Light Communication

A spectral efficient light emitting diode (LED)-based visible light communication (VLC) system adopting polar-coded 128 quadrature-amplitude modulations (QAM) orthogonal frequency division multiplexing (OFDM) is experimentally demonstrated. To overcome frequency fading in the VLC system, an encoder-subcarrier mapping method is proposed. The experimental results show that, at a sampling rate of AWG with 150 MSa/s, it can realize error-free transmission with high-spectral efficiency (SE) up to 5.77 bit/s/Hz using the proposed method. Its SE is 1.3 times of the un-coded system adopting 16-QAM. At a sampling rate of 175 MSa/s, its measured Q-factor is 9.86 dB, which improves by 5.12 dB compared to the case without coding.

Experimental Demonstration of Indoor Infrared Optical Wireless Communications With a Silicon Photonic Integrated Circuit

The optical wireless technology has great potential in realizing high-speed wireless communications in indoor applications, and the silicon photonics platform has been widely investigated to provide photonic integrations using advanced CMOS facilities. In this paper, the silicon integration of key beam steering function in high-speed infrared indoor optical wireless communication systems is proposed and investigated. The beam steering function is realized through edge couplers based silicon integrated optical phased array to achieve both wide operation bandwidth and high power efficiency. A 1 × 4 integrated phased array is designed and fabricated, and up to 12.5-Gb/s data transmission using the silicon integrated beam steering device through over 1.4 m free-space distance is experimentally demonstrated. Results show that error-free data transmission can be achieved with limited mobility provided to users, and the power penalty of the silicon integrated device is negligible. The outcomes successfully demonstrate the feasibility of using silicon photonic integrations in indoor optical wireless communication systems to realize compact and low-cost solutions.

High-Speed Visible Light Communication Based on a III-Nitride Series-Biased Micro-LED Array

Visible light communication (VLC) using III-nitride light-emitting diodes (LEDs) offers many advantages such as license-free operation, high spatial diversity and innate security. In particular, micro-LEDs ( $\mu$ LEDs) are strong candidates for VLC due to their high modulation bandwidths. However, the low optical power of a single $\mu$ LED is a key factor limiting VLC performance. In this paper, we report an optimized series-biased $\mu$ LED array to achieve higher optical power while retaining high modulation bandwidth for high-speed VLC. An example array consisting of 3 × 3 40 $\mu$ m-in-diameter $\mu$ LED elements is presented here. At a current density of 3200 A/cm $^2$ in direct-current operation, the optical power and small signal 6-dB electrical modulation bandwidth of a blue-emitting series-biased $\mu$ LED array are over 18.0 mW and 285 MHz, respectively. The data transmission capabilities of this $\mu$ LED array are demonstrated by using on – off keying, pulse-amplitude modulation, and orthogonal frequency division multiplexing modulation formats over free space with the error-free data transmission rates of 1.95, 2.37, and 4.81 Gb/s, respectively.

Achievable-Rate-Enhancing Self-Interference Cancellation for Full-Duplex Communications

Full-duplex has emerged as a promising technology that enables a communication node to transmit and receive at the same time and same frequency band. One limitation of full-duplex is that the self-interference (SI) is very strong. In this paper, an effective SI cancellation scheme operated in the digital domain is proposed. It is facilitated by the property that the SI channel is reciprocal and the transmitted data is known by both the transmitter and the receiver. It converts the strong SI to the inter-symbol interference through a combination of the signals received in successive time slots. This conversion leads to a reduction in the number of independent signal flows but can be partially compensated for by transmitting more bits using spatial modulation and involving more time slots in the SI cancellation, which enhances the achievable rate. To achieve optimal performance, the transmitted symbols at one node need to be artificially rotated. We also derive a closed-form expression for an upper bound on the average bit error rate, and its error-free information transmission capability is investigated. Monte Carlo simulations over Rayleigh fading channels between two nodes are conducted and advantages are revealed.

Impact on the chirp effect of the shaped electrical-driven current of the directly-modulated 1.55μmVCSEL in an optical fiber link

Abstract In this work, the performance of a point-to-point fiber communication system that use a directly modulated (DML) VCSEL have been studied at 2.5, 10, and 40 Gb/s. We have demonstrated that a low-cost error-free transmission is possible by the appropriate choice of the shape of the driving electric pulse, the extinction ratio (ER) and the On-Off Keying (OOK) signal code (Non Return to Zero-NRZ and Return to Zero-RZ). Additionally, a theoretical model is developed to research and simulate the behavior of chirped signal transmission in dispersive media such as an optical fiber. Thus, the VCSEL-DML generated frequency chirp can be handled in order to avoid the effects of the interaction of laser chirp with fiber dispersion. The transmission performance of a 40 Gb/s optical link over Standard Single-Mode Fiber (SSMF) and over Negative Non-Zero Dispersion Shifted Fiber (NZDSF (−) ) is researched by simulation.

Multicore-Fiber Receptacle With Compact Fan-In/Fan-Out Device for SDM Transceiver Applications

We describe a new multicore fiber (MCF) receptacle for space division multiplexing (SDM) based transceiver applications, in which we integrated a compact fiber-bundle type fan-in/fan-out device for directly connecting MCF to LDs and PDs. We design the length of the fan-out fibers taking their bending stress into account to achieve a configuration with a smaller footprint. With the proposed receptacle, we develop a 100 Gb/s SDM transmitter based on a four-channel, 1.3 μm membrane laser array on Si, in which spot-size convertor (SSC) using inverse taper InP and SiON waveguides is integrated. Since the core size of SiON waveguide is much smaller than that of MCF, we utilize different fibers with optimized modal fields at each connection point and introduce thermally-expanded-core (TEC) fusion splicing to realize a low-loss connection between them. We achieve a pluggable connection between the lasers and 125 μm-cladding 4-core MCF in an LC connector. The developed receptacle maintained satisfactory laser characteristics including sufficient output power and clear eye openings for directly modulated 28 Gb/s NRZ signals. We also achieve an error-free transmission at a bit-error rate of less than 10−12 with a 500-m MCF transmission link for all 4 channels with simultaneous 4-channel operation.

VCSEL-based differential modulation technique for high-speed gigabit passive optical networks

ABSTRACTWith the convergence towards 5G, optical networks need to be upgraded to support the emerging data tsunami. This work experimentally demonstrates the first real-time transmission of 20 Gbps over a class 10G 1550 nm vertical cavity surface emitting laser (VCSEL) in the context of on-off-keying (OOK) modulation format, by employing VCSEL differential drive mode technique, for adoption in high-speed gigabit passive optical networks (GPONs). Two OOK data streams each with 10 Gbps are differentially modulated onto a single VCSEL, therefore generating an aggregated data rate of 20 Gbps OOK signal. A receiver sensitivity of -13.36 dBm is experimentally achieved. Through extinction ratio optimization, an error free transmission over 24.7 km single mode fibre is attained, with a transmission penalty of 1.91 dB. Our proposed technique alleviates band-limitation of the VCSEL carrier, and doubles the channel data rate without replacing the transmitter optics.

Low-cost hybrid integrated 4 × 2578 Gb/s CWDM TOSA for 10 km transmission using DFB-LDs and an arrayed waveguide grating multiplexer

We have developed a cost-effective and highly compact 100-Gb/s coarse wavelength division multiplexing (CWDM) transmitter optical subassembly (TOSA) using lens-free hybrid integration. To achieve large alignment tolerances, distributed feedback laser diodes (DFB-LDs) are butt-coupled to a four-channel silica-based planar lightwave circuit (PLC) arrayed waveguide grating, with the silicon sub-mounts and PLC adhesively bonded. Then, a flexible printed circuit is employed to connect the internal DFB-LDs and the exterior of the TOSA package for radiofrequency signal transmission, eliminating the expensive ceramic feed-through. The packaged CWDM TOSA, which is 15.8 mm×7.0 mm×6.0 mm in size, shows a side-mode suppression ratio of >40 dB, a 3 dB bandwidth of >18 GHz, and error-free transmission with an average optical output power of >0 dBm and dynamic extinction ratio of >4.0 dB at 25.78125 Gb/s over a 10 km single-mode fiber for all four lanes.

Low-latency optical process-level network based on all-optical edge nodes for sample value service in substations

We describe a low-latency optical process-level network (OPLN) scheme based on all-optical edge nodes for sample value (SV) service in substations. The edge nodes we present and demonstrate consist of optical splitters and a wavelength division multiplexer, enabling the proposed scheme to realize optical intrabay physical-layer multicasting and interbay signal gathering. A scalability model for the OPLN and a latency model of the intrabay transmission subsystem are established. Simulation results show that 1 × 32 optical splitters can be used in the all-optical edge nodes with error-free transmission and that the end-to-end latency for the intrabay transmission of SV flows can be reduced by 46.6% compared with an Ethernet switch under the 100BASE protocol. A prototype of the all-optical edge node is developed and tested, achieving ultralow latency (less than 500 ns) and good compatibility with terminals using an Ethernet interface in a substation. A field-experiment system for SV service, covering eight bays with four all-optical edge nodes, is constructed in a 220-kV substation in Sichuan Province, China. This system achieves low-latency transmission of SV flows without frame loss for more than 10 h of continuous operation.

Joint Rate and Resource Allocation in Hybrid Digital–Analog Transmission Over Fading Channels

In hybrid digital-analog (HDA) systems, resource allocation has been utilized to achieve desired distortion performance. However, existing studies on this issue assume error-free digital transmission, which is not valid for fading channels. With time-varying channel fading, the exact channel state information is not available at the transmitter. Thus, random outage and resulting digital distortion cannot be ignored. Moreover, rate allocation should be considered in resource allocation, since it not only determines the amount of information for digital transmission and that for analog transmission, but also affects the outage probability. Based on above observations, in this paper, we attempt to perform joint rate and resource allocation strategies to optimize system distortion in HDA systems over fading channels. Consider a bandwidth expansion scenario where a memoryless Gaussian source is transmitted in an HDA system with the entropy-constrained scalar quantizer (ECSQ). Firstly, we formulate the joint allocation problem as an expected system distortion minimization problem where both analog and digital distortion are considered. Then, in the limit of low outage probability, we decompose the problem into two coupled sub-problems based on the block coordinate descent method, and propose an iterative gradient algorithm to approach the optimal solution. Furthermore, we extend our work to the multivariate Gaussian source scenario where a two-stage fast algorithm integrating rounding and greedy strategies is proposed to optimize the joint rate and resource allocation problem. Finally, simulation results demonstrate that the proposed algorithms can achieve up to 2.3dB gains in terms of signal-to-distortion ratio over existing schemes under the single Gaussian source scenario, and up to 3.5dB gains under the multivariate Gaussian source scenario.

Pre‐emphasis enabled 50 Gbit/s transmission over 1000 m SMF using a 1060 nm single‐mode VCSEL

A single-mode 1060 nm vertical-cavity surface-emitting laser (VCSEL) and single-mode fibre (SMF) based link with two-tap active pre-emphasis enabling error-free transmission of 50 Gbit/s NRZ-OOK over 1000 m is presented.

Experimental demonstration of 50 Gb/s (2 × 25 Gb/s) TDM/WDM PON over 64-way power split using O-band up/down transmission over 20 km with dynamic bandwidth allocation and SDN control

For the accommodation of mobile, business, and residential service in the same optical distribution network, we experimentally demonstrate 50 Gb/s (25 Gb/s × 2 wavelengths) wireless and wired service converged optical access network with 64-way power split over 20 km of single mode fiber in 1300 nm band. Applying simple Reed-Solomon based forward-error-correction and a cost-effective avalanche photodiode receiver without using an optical amplifier realize the 64-way power split. Accommodating dynamic bandwidth allocation and open interface control with OpenDaylight (ODL) controller via network configuration protocol (NETCONF) interface are demonstrated. Furthermore, error-free packet transmission of 50 Gb/s with low latency and guaranteed bandwidth are successfully demonstrated.