30-gb/s signal transmission over 40-km directly modulated DFB-laser-based single-mode-fiber links without optical amplification and dispersion compensation

Based on a recently proposed novel optical-signal-modulation technique of adaptively modulated optical orthogonal frequency-division multiplexing (AMOOFDM), numerical simulations of the transmission performance of AMOOFDM signals are undertaken in directly modulated DFB laser (DML)-based single-mode-fiber (SMF) links without optical amplification and dispersion compensation. It is shown that a 30-Gb/s transmission over a 40-km SMF with a loss margin of greater than 4.5 dB is feasible in the aforementioned simple configuration using intensity modulation and direct detection (IMDD). In addition, the DFB-laser frequency chirp and the transmission-link loss are identified to be the key factors limiting the maximum achievable transmission performance of the technique. The first factor is dominant for transmission distances of < 80 km and the second one for transmission distances of > 80 km. It is also observed that fibers of different types demonstrate similar transmission performances, on which fiber nonlinear effects are negligible.     

Effectiveness of the Use of 3-dB Bandwidths of Multimode Fibres for Estimating the Transmission Performance of Adaptively Modulated Optical OFDM Signals Over IMDD Links

Detailed investigations of transmission capacities of adaptively modulated optical orthogonal frequency division multiplexed (AMOOFDM) signals against various multimode fibre (MMF) properties, are undertaken for the first time, based on 28000 statistically constructed impulse responses of optical amplification-free, MMF links using intensity modulation and direct detection. The utilization of 3-dB optical MMF bandwidths is identified to be a simple and accurate approach for estimating, without performing complicated simulations, AMOOFDM transmission capacities over any MMF links. For a link loss- (differential mode delay)- dominant performance region, the estimated signal capacities have very low relative standard deviations of $≪$ 6% ($≪$ 17%), which are independent of AMOOFDM modem parameters. Discussions are also made of practical implementation of the identified approach.      

Maximizing the Transmission Performance of Adaptively Modulated Optical OFDM Signals in Multimode-Fiber Links by Optimizing Analog-to-Digital Converters

Based on a comprehensive theoretical model of a recently proposed novel technique known as adaptively modulated optical orthogonal frequency-division multiplexing (AMOOFDM), investigations are undertaken into the impact of an analog-to-digital converter involved in the AMOOFDM modem on the transmission performance of AMOOFDM signals in unamplified intensity-modulation and direct-detection (IMDD) multimode-flber (MMF)-based links. It is found that signal quantization and clipping effects are significant in determining the maximum achievable transmission performance of the AMOOFDM modem. A minimum quantization bit value of ten and optimum clipping ratio of 13 dB are identified, based on which, the transmission performance is maximized. It is shown that 40-Gb/s- over-220-m and 32-Gb/s-over-300-m IMDD-AMOOFDM signal transmission at 1550 nm with loss margins of about 15 dB is feasible in the installed worst case 62.5-mum MMF links having 3-dB effective bandwidths as small as 150 MHz ldr km. Meanwhile, excellent performance, robustness to fiber types, and variation in launch conditions and signal bit rates is observed. In addition, discussions are presented of the potential of 100-Gb/s AMOOFDM signal transmission over installed MMF links.     

WDM-PON采用SOA实现无色光传输

波分复用无源光网络（WDM-PON）实现了点到点的连接,可为每个用户提供专有波长,被普遍认为是未来宽带接入的代表性技术。WDM-PON中采用的调制器,既要实现＂无色＂调制,又要保证系统性能,以降低成本。为此,在强度调制直接检测单模光纤（IMDD SMF）连接系统中,采用半导体光放大器（SOA）作为强度调制器,分析了调制信号与波长的相关性,提出了实现无色自适应调制光正交频分复用（AMOOFDM）传输的优化工作条件。     

Bidirectional SCM Transmission Using a Noise-Suppressed Fabry–Pérot Laser Diode and a Reflective Semiconductor Optical Amplifier in a WDM/SCM-PON Link

We have proposed and experimentally demonstrated a bidirectional hybrid wavelength-division-multiplexed/subcarrier-multiplexed (SCM)-passive optical network based on a noise-suppressed Fabry-Peacuterot laser diode (FP-LD) and a reflective semiconductor optical amplifier (RSOA). For downlink data transmission, an FP-LD with multiple wavelength characteristics was used, and the mode partition noise of the FP-LD was reduced using a gain-saturated SOA with high-pass filter characteristics. For uplink data transmission, the downlink optical source was reused and remodulated by an SCM method, using an RSOA. A bidirectional SCM link with radio frequencies (RFs) of 2.4 GHz in the downlink and 1.0 GHz in the uplink was implemented. To confirm the validity of the proposed configuration, a 16-quadrature amplitude modulation transmission experiment was performed on a 10-km bidirectional optical access link. The transmission performance was investigated by means of the error vector magnitude and RF spectrum     

Impact of Nonlinear Transfer Function and Imperfect Splitting Ratio of MZM on Optical Up-Conversion Employing Double Sideband With Carrier Suppression Modulation

Generation of optical millimeter-wave (mm-wave) signal using a Mach–Zehnder modulator (MZM) based on double-sideband (DSB), single-sideband (SSB), and double-sideband with carrier suppression (DSBCS) modulation schemes have been demonstrated for various applications, such as broadband wireless signals or optical up-conversion for wavelength-division-multiplexing (WDM) radio-over-fiber (RoF) network, wideband surveillance, spread spectrum, and software-defined radio. Among these schemes, DSBCS modulation offers the best receiver sensitivity, lowest spectral occupancy, the least stringent requirement of electrical bandwidth, and the smallest receiving power penalty after long transmission distance. Nonetheless, the inherent nonlinear E/O (electrical/optical) conversion response of a MZM is such that the signal quality of the optical mm-wave suffers. Fabrication tolerances make a balanced 50/50 splitting ratio of the MZM's y-splitter particularly difficult to achieve. As a result, imbalanced MZMs have a finite extinction ratio (ER) and degrade the optical carrier suppression ratio (OCSR) using DSBCS modulation. In this paper, the effect of the MZM nonlinearity and imbalanced y-splitter on optical mm-wave generation by DSBCS modulation is theoretically and experimentally investigated. A novel approach with better performance and greater cost-effectiveness than dual-electrode MZM (DD-MZM) is presented to realize a DSBCS modulation scheme based on a single-electrode MZM (SD-MZM).      

WDM-Based Passive Optical Network Upstream Transmission at 1.25 Gb/s Using Fabry&#8211;P&#201;rot Laser Diodes Injected With Spectrum-Sliced, Depolarized, Continuous-Wave Supercontinuum Source

We experimentally demonstrate the use of low-cost Fabry–PÉrot laser diodes (FP-LDs) injected with spectrum-sliced beams from our proposed, depolarized, high-power, continuous-wave (CW) supercontinuum (SC) for upstream transmission in a wavelength-division-multiplexed (WDM) passive optical network. A$sim$500-mW CW SC with a$sim$130-nm bandwidth is obtained from a narrowband, amplified spontaneous emission (ASE) seed of a pumped erbium fiber by nonlinear effects such as modulation instability and stimulated Raman scattering in a highly nonlinear optical fiber. Through measurements of relative intensity noise at various wavelengths, it is shown that our spectrum-sliced SC offers the same performance as the spectrum-sliced erbium ASE. Error-free 25-km upstream transmission for six WDM signals generated from the CW SC-injected FP-LDs, is readily achieved at 1.25 Gb/s.     

On Frequency-Doubled Optical Millimeter-Wave Generation Technique Without Carrier Suppression for In-Building Wireless Over Fiber Applications

A novel optical millimeter-wave (mm-wave) generation scheme based on double-sideband phase modulation (DSB-PM) to achieve frequency doubling without suppressing the carrier is proposed. Theoretical analysis shows that the generated 60-GHz optical mm-wave can tolerant ${pm}$ 0.016-nm wavelength drifting with filter bandwidth ranging from 70 to 100 GHz to sustain first to second harmonic suppression ratio of 18 dB. In addition, error-free transmission of 60-GHz mm-wave at 2.5 Gb/s is experimentally demonstrated over a combined distance of 3-m wireless with 21-dBm equivalent isotropically radiated power, and 250-m fiber to best emulate an in-building network environment. Dispersion effect on the frequency-doubled PM optical mm-wave without carrier suppression is also analyzed and experimentally studied by comparing the link performance over single-mode fiber (SMF-28) and dispersion-shifted fiber (DSF), respectively.      

Pulse width modulation for analog fiber-optic communications

The pulse width modulation (PWM) technique has been revisited and analyzed to evaluate its merits for application to analog signal transmission in fiber-optic links. Fourier analysis of the PWM signal reveals that it can be used as a vehicle to launch an analog signal onto optical fiber when a symmetrical natural sampling process is used. The SNR of the modulated signal depends on the timing jitter of the carrier pulses and a wide-band (45 MHz) SNR of 45 dB has been obtained with a commercially available multimode laser transmitter. A linear dynamic range of over 50 dB has been experimentally demonstrated. The full fiber bandwidth can be utilized by using a very high pulse carrier frequency, while a more popular pulse frequency modulation technique provides about a 10-MHz analog signal bandwidth when 1 km of multimode fiber is used in conjunction with a short wavelength (0.87 μm) LED transmitter. Analog transmission capability was experimentally demonstrated by constructing a simple video link using common laboratory equipment. The performance of the video link supports the PWM modulation theory developed here and elsewhere. The experimental results indicated that PWM is potentially very attractive for low-cost broad-band local area network (LAN) application, including future highly interactive offices, hospitals, and automated factory floors.     

Characterization of an optical frequency-shift-keying transmitter based on carrier-suppressed phase modulation

We experimentally characterize an optical frequency-shift-keying transmitter based on optical carrier-suppressed phase modulation. Only one laser source is needed to generate an optical FSK signal. The demonstration of 10-Gb/s FSK signal generation and 50-km transmission verified the improved performance of the proposed transmitter, compared with the previous two-laser schemes. To further reduce the complexity of the transmitter, the phase modulator is omitted and a single MZM modulator is used for both optical carrier-suppression (OCS) and phase modulation. This simplified structure is verified by simulation, implying the feasibility that a FSK transmitter can be constructed with only one laser source and one modulator.     

Linearization of DFB laser diode by external light-injected cross-gain modulation for radio-over-fiber link

A novel linearization technique of distributed-feedback laser diode in analog optical transmitter for radio-over-fiber (RoF) link was proposed. The proposed scheme was based on a light-injection technique using cross-gain modulation effect. According to the proposed idea, a linearized RoF transmitter module was implemented and evaluated. The enhanced performance of carrier-to-noise ratio and spurious-free dynamic range were experimentally demonstrated in a wide range of radio-frequency (RF) applications. The experimental results show that the proposed scheme can be applicable for broadband RF optical transmission applications.     

Optical Performance Monitoring of Phase-Modulated Signals Using Asynchronous Amplitude Histogram Analysis

As optical networks continue to grow towards high capacity and high flexibility, new transmission technologies are being introduced. In order to maintain the quality of signal and control over network in the transparent domains, optical performance monitoring (OPM) systems are becoming a necessity. Phase modulation formats emerge as the solution of choice in transparent domains because of their sensitivity, spectral efficiency, and resilience to optical impairments. In this paper, we demonstrate a flexible OPM method for phase-modulated signals using asynchronous amplitude histogram analysis. We show numerically and experimentally the monitoring of optical signal-to-noise ratio (OSNR), chromatic dispersion (CD), and polarization-mode dispersion (PMD) for differential phase-shift keying (DPSK) and differential quadrature phase-shift keying (DQPSK) signals. The OSNR can be measured within range of 20-35 dB and accumulated chromatic dispersion between 600 and 600 ps/nm. The asynchronous amplitude histogram monitoring method is proved to be a precise and versatile monitoring tool for high-capacity optical networks.     

基于LDPC-OFDM编码调制在无源光网络的研究

将低密度奇偶校验码与正交频分复用相结合的编码调制方式引入到无源光网络中,并通过Optisystem和Matlab进行联合仿真,研究了基于LDPC-OFDM编码调制的PON系统的下行传输性能。结果显示,由LDPC-OFDM编码调制的信号,在无源光网络中可以实现10 Gbit·s-1的下行传输。在误码率均为10-4时,基于LDPC-OFDM编码调制的系统传输性能较未编码传输光有4.2 dB的提升。当信噪比＞2.6 dB时,Gallager构造法较Mackay构造法和BIBD构造法有更好的误码率性能,以及当信噪比＞4.6 dB时,LLR-BP及其改进译码算法能使系统性能得到改善。     

Study of dual-polarization OQAM-OFDM PON with direct detection

An offset quadrature amplitude modulation orthogonal frequency-division multiplexing (OQAM-OFDM) passive optical network (PON) architecture with direct detection is brought up to increase the transmission range and improve the system performance. In optical line terminal (OLT), OQAM-OFDM signals at 40 Gbit/s are transmitted as downstream. At each optical network unit (ONU), the optical OQAM-OFDM signal is demodulated with direct detection. The results show that the transmission distance can exceed 20 km with negligible penalty under the experimental conditions.     

强度调制高速光通信系统传输性能研究

码型调制格式是提高通信传输质量的一项关键技术,针对高速光传输系统中码型调制格式及其传输性能进行理论分析,重点研究了强度调制格式在高速光传输系统中的性能;通过光通信仿真软件搭建强度调制格式的产生装置,得到各种调制格式的光谱,对强度调制格式在系统中抗色散能力和抗非线性能力进行了研究和分析。     

STOLAS: switching technologies for optically labeled signals

GMPLS-based labeled optical burst switching (LOBS) networks are being considered as the next-generation optical Internet. GMPLS includes wavelength switching next to label and fiber (space) switching. We present a new concept of optically labeling bursts of packets suitable for LOBS networks supported by GMPLS. It is based on angle modulation, which enables control information to modulate the phase or frequency of the optical carrier, while payload data are transmitted via intensity modulation (IM). In particular, the optical label is orthogonally modulated, with respect to the payload, using either frequency shift keying or differential phase shift keying. We present a performance analysis of the modulation schemes by means of simulations where the influence of the payload IM extinction ratio and laser linewidth are investigated. In addition, the transmission performance of an IM/FSK combined modulated signal is experimentally validated at 10 Gb/s, demonstrating at the same time an FSK label swapping operation. Finally, a suitable optical label-controlled switch design is proposed that takes advantage of these novel labeling techniques, and efficiently combines widely tunable, fast switching lasers and SOA-MZI wavelength converters with an arrayed waveguide grating router.     

Frequency detuning effects in a loop-back WDM-PON employing gain-saturated RSOAs

We report that, in a loop-back wavelength-division-multiplexed passive optical network link with gain-saturated reflective semiconductor optical amplifiers, the upstream performance is strongly affected not only by the gain saturation but also by the selective spectral filtering caused by the frequency difference between the optical downstream signal and the cascaded filter's passband. We experimentally investigate these effects and propose to use an additional negatively detuned optical filter at an optical network terminal to improve the upstream transmission performance.     

Prechirp technique as a linear dispersion compensation forultrahigh-speed long-span intensity modulation directed detectionoptical communication systems

Prechirp technique, as a linear dispersion compensation for intensity modulation direct detection (IM-DD) optical transmission systems, has been investigated theoretically and experimentally. This technique is based on a predistortion technique in an optical transmitter. Implementation to the ordinary IM-DD optical transmitter, which uses an external intensity modulator, is easily realized merely by adding a small injection current modulation to a semiconductor laser diode, allowable optical transmission fiber dispersion will be more than doubled with this technique, modified prechirp technique, which utilizes a time division superimposing prechirped bit streams, has also been investigated to achieve greater dispersion compensation capability     

Full-duplex radio-over-fiber system with photonics frequency quadruples for optical millimeter-wave generation

We have experimentally investigated two different schemes (schemes A and B) to generate optical millimeter-wave using optical frequency quadrupling with a Mach–Zehnder modulator (MZM), and wavelength reuse for uplink connection in the radio-over-fiber (ROF) systems. For scheme A, only one MZM is used for both the optical millimeter-wave generation and signal modulation. For scheme B, two MZMs are used. In this scheme, one of MZMs is used to generate optical millimeter-wave for frequency quadrupling, and another one is used for signal modulation. In both schemes, at the base station (BS), the optical carrier can be reused to carry upstream data and delivered to the central station (CS). By experimentally comparing the performance of downstream and upstream transmission in two schemes, it can be seen that scheme B can overcome the crosstalk between the upstream and downstream signals, but scheme A cannot. Meanwhile we also show that the millimeter-wave generated in scheme B has better quality and is almost robust to fiber chromatic dispersion.     

Signal extraction with frequency arrangement (SEFA) andsuperimposed subcarrier modulation (SSM) schemes in fiber-orientedwireless access systems

This paper describes technologies for the improvement of the noise and nonlinearity characteristics of wireless access systems based on subcarrier optical transmission. First, the superimposed subcarrier modulation (SSM) technique is proposed to reduce the reflection noise induced by fiber connectors. We experimentally confirmed that the proposed method reduces this noise, and we found the optimum frequency and power of the superimposed subcarrier, SSM design methodology is also presented, taking both noise and nonlinearity into account. Second, signal extraction with frequency arrangement (SEFA) is proposed for increasing the optical modulation index, because the third-order intermodulation distortion (IM3) produced by the optical devices can be ignored. Simulation results show that SEFA greatly improves the transmission performance in terms of both the ratio of desired-to-undesired signal and the receiver sensitivity under Rayleigh fading. Combining the SSM and SEFA is also considered, for use with FP-LDs or DFB-LDs. These technologies will enable cheaper FP-LD implementation in fiber-oriented wireless access systems