IRZ-Manchester coding for downstream signal modulation in an ONU-source-free WDM-PON

Inverted return-to-zero (IRZ)-Manchester coding is proposed for optical downstream signal using amplitude shift keying (ASK) modulation in an optical network unit (ONU)-source-free wavelength-division-multiplexing passive optical network (WDM-PON), and ASK modulation is used for the optical upstream signal generation using remodulation over the optical downstream signal. With IRZ-Manchester coding, differential phase shift keying (DPSK) modulation can be overlaid on the downstream optical ASK signal for broadcasting services. Our experimental results show that the IRZ-Manchester coded optical ASK downstream signal has no modulation extinction ratio restrictions from the overlaid DPSK modulation, and that the remodulated optical upstream signal has very limited signal crosstalk from the downstream signals. In comparison with the conventional schemes using only Manchester coding or IRZ modulation, the proposed IRZ-Manchester coded modulation scheme shows better performance under different PON upstream and downstream traffic bit rate ratios.     

Investigation on wavelength re-modulated bi-directional passive optical network for different modulation formats

In this paper, the cost effective bi-directional passive optical network architecture with wavelength remodulated scheme is investigated. To realize the cost-effective PON, remodulation scheme is used, in which the downstream optical signal is reused as a carrier for the upstream transmission as it eliminates the need for an extra laser source at optical network units. The performance of proposed passive optical network is analyzed and compared for various modulation formats such as Non Return to Zero (NRZ), Return to Zero (RZ) and On–Off Keying (OOK) with 64 optical networks units (ONUs) at different traffic speed for downlink and uplink, respectively. It has been observed that the most suitable data format for proposed PON network is NRZ. Further the proposed system performance is compared with the current state-of-the-art PON architectures.     

Signal remodulation without power sacrifice for carrier distributed hybrid WDM-TDM PONs using PolSK

Signal remodulation is considered to lower the cost of future WDM-PON by wavelength reuse. We propose and demonstrate a signal remodulation scheme using PolSK modulation in both downstream and upstream signals for “colorless” WDM-PON. High extinction-ratio can be achieved in both downstream and remodulated upstream signals; hence power sacrifice of using residual optical power in downstream signal for the upstream remodulation is eliminated. Split-ratio analysis is performed for the hybrid WDM-TDM architecture. Results show that the proposed scheme could be a potential candidate for next generation wavelength reuse WDM-TDM PON.     

Experimental demonstration of RSOA-based WDM PON with PPM-encoded downstream signals

Pulse position modulation(PPM) is introduced downstream of the reflective semiconductor optical amplifier (RSOA)-based single-fiber full-duplex bidirectional wavelength division multiplex passive optical network(WDM PON) to suppress the interference brought by the remodulation effect in the RSOA, Rayleigh backscattering,and reflection of the connection devices.In addition,because of the powerefficient characteristic of the PPM-encoded signals,the power budget shows clear improvement.As the experimental tests indicate,with～6 dB extinction ratio(ER) in the downstream signal,the receiving sensitivity of the PPM-encoded channel is～2.6 and～3 dB higher than that of the NRZ(Non-return to zero)-encoded channel in the downlink and uplink,respectively.     

Bidirectional WDM-PON architecture using a reflective filter and cyclic AWG

We proposed and demonstrated a bidirectional SCM-WDM PON using a reflective filter and cyclic AWG where up/downlink data could be provided using a single optical source. In the proposed scheme, the signal for downstream was modulated by a single CW laser diode and remodulated in the optical network unit as an upstream, the proposed WDM-PON scheme can offer the SCM signal for broadcasting service. In this paper, 1 Gb/s signals both for up- and downstream were demonstrated in 10 km bidirectional optical fiber link.     

Optical phase remodulation for Rayleigh noise mitigation in 10 Gb/s/channel WDM passive optical networks

We investigate the principles of optical phase remodulation and demonstrate its application in a future-proof10 Gb/s/channel wavelength-division-multiplexed(WDM) passive optical network to realize a colorless optical network unit and bidirectional transmission over a single fiber. The modulation depth of downstream differential phase-shift keying is properly reduced to facilitate phase remodulation and Rayleigh noise mitigation. For both downstream and upstream 10 Gb/s signals, error-free transmission via a 20 km single-mode fiber is demonstrated without dispersion compensation operation.     

A full-duplex radio-over-fiber link with 12-tupling mm-wave generation and wavelength reuse for upstream signal

A full-duplex radio-over-fiber (RoF) link with a novel scheme to generate 60 GHz mm-waves from a 5 GHz RF signal source is investigated. In the RoF downlink, the required frequency of the RF oscillator is reduced greatly. Since the optical carrier is not modulated by downstream data, part of it is reused to carry upstream data and the upstream data is transmitted to the central station using optical single-sideband modulation. In this way, a single wavelength is used for both downstream and upstream transmissions. Based on this scheme, a full-duplex RoF link is built and its transmission performance is analyzed. Theoretical analysis and numerical simulation show that the downstream signal cannot only eliminate code form distortion caused by time shift of the code edges, but also reduce the influence of the fading effect as the 60 GHz DSB optical mm-wave signal is transmitted along the fiber, and the upstream signal is immune to both fading effect and time shift of the code edges.     

Flexible broadcasting and multicasting in 4λ × 10 Gb/s AOPR TWDM PON system

In this letter, we propose a new architecture of Time Wavelength Division Multiplexing Passive Optical Network (TWDM PON) system to support dynamic multi wavelength allocation (DMWA) in both upstream and downstream directions using an integrated semiconductor optical amplifier (SOA) and arrayed waveguide grating (AWG) with multi wavelength select continuous wave (CW) pump probe signal module. The significance of this architecture is the flexible routing function with the capability of multicasting and broadcasting between multiple optical line terminal (OLT) PON port with multiple optical distribution network (ODN) link using a new wavelength tuning free (WTF) OLT transmitter module to eliminate wavelength tuning delay in downstream signal utilizing multicasting Cross Gain Modulation (XGM) wavelength conversion. The experimental results show that 4λ × 10-Gb/s TWDM PON system can be used to connect 4096 users with the conventional fixed wavelength OLT transceivers with 36 dB link loss.     

Performance evaluation of bi-directional passive optical networks in the scenario of triple play service

In this paper, the performance of bi-directional passive optical network (BPON) has been evaluated and compared at different bit rates in the scenario of triple play service. The triple-play service is realized as a combination of data, voice and video signals. This architecture is investigated for symmetrical data traffic for uplink and downlink transmission and its performance is also evaluated in terms of Q-factor and eye height at different transmission distance. The Q-factor results show the acceptable performance at 10 Gbps data rate for downstream and upstream transmission, as it accommodates 128 optical network units (ONUs). Further the proposed system's performance is compared with the current state-of-the-art PON architectures.     

Influence of modulation formats performance of the combined modulation in WDM-PON system

Different modulation modes of DPSK and OOK are separately employed in the upstream and downstream link, after the comparison with different modulation formats in the downstream including the codes of non return-to-zero (NRZ), return-to-zero (RZ) and inverse return-to-zero (IRZ), the symmetric rate of 10 Gbps with 20 km transmission is realized without the dispersion compensation. It can be shown that in the combined modulation mode with the downstream of IRZ code, higher extinction ratio in the downstream and better performance of dispersion tolerance in the upstream could be achieved, enhancing the overall property of the transmission system.     

Adaptive upstream optical power adjustment depending on required power budget in PON access

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 (ΔP_loss) 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.     

Advanced modulation formats for delivery of heterogeneous wired and wireless access networks

It is believed that the integration of wired and wireless access networks (or heterogeneous network) will provide high bandwidth and flexibility for both fixed and mobile users in a single and cost-effective platform. Here, we propose and demonstrate a signal remodulated wired and wireless network with wireless signal broadcast. Dark-return-to-zero (DRZ) and polarization-shift-keying (PolSK) signals are used for the downstream wired and wireless applications respectively. At the remote antenna unit (RAU), the PolSK signal is demodulated to produce the binary-phase-shift-keying (BPSK) signal, which will be used for the wireless broadcast application. Signal remodulation is demonstrated using reflective semiconductor optical amplifier (RSOA) as a colorless reflective modulator in the optical networking unit (ONU)/RAU. The downstream signal is remodulated at the ONU/RAU to produce the non-return-to-zero (NRZ) upstream signal.     

A cost-effective WDM-PON architecture simultaneously supporting wired, wireless and optical VPN services

It is believed that next-generation passive optical networks (PONs) are required to provide flexible and various services to users in a cost-effective way. To address this issue, for the first time, this paper proposes and demonstrates a novel wavelength-division-multiplexed PON (WDM-PON) architecture to simultaneously support three types of services: 1) wireless access traffic, 2) optical virtual passive network (VPN) communications, and 3) conventional wired services. In the optical line terminal (OLT), we use two cascaded Mach-Zehnder modulators (MZMs) on each wavelength channel to generate an optical carrier, and produce the wireless and the downstream traffic using the orthogonal modulation technique. In each optical network unit (ONU), the obtained optical carrier is modulated by a single MZM to provide the VPN and upstream communications. Consequently, the light sources in the ONUs are saved and the system cost is reduced. The feasibility of our proposal is experimentally and numerically verified.     

紫外激光通信中PPM与Turbo联合编码调制研究

为提高紫外激光通信系统中的编码效率和频带利用率，提出采用PPM（pulse position modulation）调制和Turbo编码相结合的技术来提高效率。此方法不仅能提高频带的利用率，也能提高码间抗干扰能力、纠错能力和降低误码率，并对PPM调制模式下的Turbo码译码公式进行了推导，最后利用Matlab软件实现了该技术的仿真，仿真结果表明：在紫外激光通信中采用PPM和Turbo统一调制编码的技术能进一步降低系统的效率和误码率。     

基于H-PPM的可见光通信系统RS编码性能分析

为了改善复杂交通环境下湍流信道的光强闪烁对信号的影响,研究了大气湍流光强闪烁的系统模型,并且针对PPM和DPIM等调制方法存在的问题,提出一种新型的无线光通信调制方法——头脉冲位置调制(head pulse position modulation,H-PPM)。根据湍流信道的特点,推导出基于H-PPM的可见光通信系统未编码时与RS(Reed-Solomon)码纠错后的误时隙率公式。数值仿真曲线证明,当系统误码率为10-10时,RS(15, 7)纠错码可以提高约18 dB的编码增益。由此可得,采取H-PPM调制和RS编码相结合可提高信号的质量,更有利于复杂交通环境下的可见光通信。     

Ring-based PON supporting multiple optical private networks using OCDMA technique

This work is a novel attempt to provide local communications for multiple optical private networks (PNs) within ring-based passive optical network (PON). In order to improve network throughput performance, PNs traffic is decentralized from PON traffic let no extra traffic management into optical line terminal (OLT). To achieve multiple secure optical private networking over ring-based PON layout, optical code division multiple access (OCDMA) technique is applied. This technique leads to interconnect optical network units (ONUs) in the same PN sharing the same codeword while other PNs benefiting from different codewords. This scheme can be used in access networks to establish discrete communications between different sites in an enterprise or a university campus or even a residential accommodation. The proposed network architecture is then set up and its bit error rate performance is experimentally demonstrated. Finally, the network scalability and throughput performance of the proposed scheme are analyzed.     

基于超结构光纤光栅的正交四相光码分多址编/解码器

正交四相序列编码相比于二相序列具有更大的码字容量和更好的互相关特性,因此更适用于光码分多址(OCDMA)无源光接入网.提出并实现了一种基于超结构光纤光栅的正交四相光码分多址编/解码器.该编/解码器采用A族四相序列作为地址码,在制作的过程中仅需一个均匀相位掩模板即可实现编码功能,并且在性能上与传统工艺制作的编码器相当.为了与不同波长信道相匹配,提出了变信道编码技术,仿真结果表明采用该技术的编码器具有更高频谱效率,因此得到更好的编/解码性能.对一个码长63,长度4.1 cm的正交四相编/解码器进行了信息速率为2.5 Gb/s.码片速率为156 Gchip/s的编/解码实验,取得了较好的编/解码效果.     

Full-Duplex Link Providing Alternative Wired and Wireless Broadband Access for the Wavelength-Division Multiplexing Passive Optical Network with a Uniform Converged Signal Format

Abstract

A full-duplex link implementing alternative wired and wireless access for wavelength-division multiplexing passive optical network is proposed with the uniformed three-tone converged optical signal, which provides a wired or wireless downlink access signal alternatively and an uplink optical carrier. The uplink optical carrier reversed by the converged optical signal makes the hybrid optical node unit free from the optical source. The simulation results show that the full-duplex link with a 10-Gb/s 16-quadrature amplitude modulation (16-QAM) downstream and 5 Gb/s binary upstream can provide both wired access with a bit-error rate below 10^?9 and radio-over-fiber-based wireless access with a bit-error rate below 10^?7 over 40 km of fiber without an optical source and optical amplifier in the hybrid optical node unit.     

Index Coding with Multiple Interpretations

The index coding problem consists of a system with a server and multiple receivers with different side information and demand sets, connected by a noiseless broadcast channel. The server knows the side information available to the receivers. The objective is to design an encoding scheme that enables all receivers to decode their demanded messages with a minimum number of transmissions, referred to as an index code length. The problem of finding the minimum length index code that enables all receivers to correct a specific number of errors has also been studied. This work establishes a connection between index coding and error-correcting codes with multiple interpretations from the tree construction of nested cyclic codes. The notion of multiple interpretations using nested codes is as follows: different data packets are independently encoded, and then combined by addition and transmitted as a single codeword, minimizing the number of channel uses and offering error protection. The resulting packet can be decoded and interpreted in different ways, increasing the error correction capability, depending on the amount of side information available at each receiver. Motivating applications are network downlink transmissions, information retrieval from datacenters, cache management, and sensor networks.     

A long-reach WDM passive optical network enabling broadcasting service with centralized light source

We propose a long-reach wavelength-division-multiplexed (WDM) passive optical network (PON) to provide conventional point-to-point (P2P) data and downstream broadcasting service simultaneously by superimposing, for each WDM channel, the differential-phase-shift-keying (DPSK) broadcasting signal with the subcarrier multiplexing (SCM) modulated downstream P2P signal, at the optical line terminal (OLT). In the optical network units (ONUs), by re-modulating part of the downstream signal with a reflective semiconductor optical amplifier (RSOA), we realize color-less ONUs for upstream data transmission. The proposed scheme is numerically verified with a 5 Gb/s downstream P2P signal and broadcasting services, as well as 2.5 Gb/s upstream data through a 60 km bidirectional fiber link. In particular, the influence of the downstream lightwave's optical carrier–subcarrier ratio (OCSR) on the system performance is also investigated.