Hybrid WDM/SCMA-PON using wavelength-locked fabry-Pe/spl acute/rot laser diodes

We propose a large-capacity hybrid passive optical network (PON) with a wavelength-sharing technique achieved by applying subcarrier multiple access on each single channel of a wavelength-division-multiplexed (WDM) PON. We also use forward-error correction to reduce the effect of optical beat interference noise. We demonstrate three-subchannel sharing in a 100-GHz-spaced WDM-PON to accommodate three times more subscribers simultaneously at a fully dedicated connection rate of 125 Mb/s.     

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     

Increasing acceptable number of signals in subcarrier multipleaccess optical networks in the presence of high optical beatinterference

This paper theoretically and experimentally demonstrates that our proposed method improves the carrier-to-noise ratio (CNR) of subcarriers and significantly increases the number of acceptable optical signals in subcarrier multiple access (SCMA) systems using distributed feedback laser diodes (DFB-LD's) with the same center optical frequency. This method reduces optical beat interference by using the multiplied product of the subcarriers and a low-frequency signal. From the experimental results using 1.3 μm DFB-LD's, the CNR sufficiently satisfies the required level even if the number of optical signals is three. Theoretically, the number of acceptable optical signals increases as LD's with wider optical line-width or with greater chirp coefficient are used. For example, assuming a laser chirp coefficient of 540 MHz/mA, the maximum number of LD's that can be used while still meeting the minimal CNR requirement is 12. This number corresponds to 66 optical beat interferences. Thus, this proposed beat-interference reduction technique is very effective in SCMA systems using DFB-LD's without optical frequency control     

WDMA/subcarrier-FDMA lightwave networks: limitations due to opticalbeat interference

The authors present a general model of optical beat interference, and its contribution of channel outage in a WD-SFDMA (wavelength division-subcarrier frequency division multiple access) network. The probability of channel outage due to optical beat interference is determined from analysis and computer simulation for externally and directly modulated single-mode lasers. These results are used to calculate the ultimate limitation on the throughput and capacity of the network due to beat note interference, for a simple retransmission protocol. It is shown that, as more subcarrier channels are added, network capacity increases sublinearly and eventually saturates     

A self-seeded reflective SOA-based optical network unit for optical beat interference robust WDM/SCM-PON link

We have proposed and experimentally demonstrated a novel optical source configuration that uses a self-seeded reflective semiconductor optical amplifier (RSOA) as an optical network unit (ONU) in a wavelength division multiplexed/subcarrier multiplexing (SCM)-passive optical network (PON). A fiber Bragg grating (FBG) was used to obtain a single longitudinal mode of the RSOA. The proposed ONU configuration is simple, cost-effective, and effective regardless of wavelength allocation. Additionally, it would be robust for optical beat interference (OBI) noise. As the ONU is composed only of an RSOA and FBG, the self-seeded RSOA, due to the strong self-injection caused by the reflection of the FBG, has a broad optical spectrum. A self-homodyne apparatus method was performed in order to demonstrate the robustness of the self-seeded RSOA in OBI. To confirm the validity of the proposed scheme, a 16-quadrature amplitude modulation transmission experiment was performed in a 10-, 20-km optical access link with an SCM frequency of 1 GHz. An error vector magnitude of less than 4% for 2 Msps was successfully obtained through the transmission experiment.     

FM subcarrier fiber optical transmission system design and itsapplication in next-generation wireless access

This paper presents a design method of optical frequency modulation (FM) subcarrier (with super carrier) transmission modem. The nonideal link characteristics, including laser chirping, fiber dispersion, voltage controlled oscillator (VCO) phase noise, relative intensity noise (RIN), and equivalent network model of laser diode of such a system that may bring about signal distortion are discussed first. We then propose a hierarchical methods to establish the system equivalent model. Finally this FM modem is applied to a GSM wireless system, in which multichannel signals are transmitted over fiber between radio port and basestation, and system performance is appraised by its dynamic range. It is found that optical FM subcarrier (with super carrier) transmission technique can improve the system dynamic range, compared with the intensity modulated direct detection (IMDD) method, and this is a economical and efficient method     

Analysis of optical amplifier noise in coherent opticalcommunication systems with optical image rejection receivers

A detailed theoretical analysis of optical amplifier noise in coherent optical communication systems with heterodyne receivers is presented. The analysis quantifies in particular how optical image rejection receiver configurations reduce the influence of optical amplifier noise on system performance. Two types of optical image rejection receivers are investigated: a novel, all-optical configuration and the conventional, microwave-based configuration. The analysis shows that local oscillator-spontaneous emission beat noise (LO-SP), signal-spontaneous emission beat noise (S-SP), and spontaneous-spontaneous beat noise (SP-SP) can all be reduced by 3 dB, thereby doubling the dynamic range of the optical amplifier. A 2.5-dB improvement in dynamic range has been demonstrated experimentally with the all-optical image rejection configuration. The implications of the increased dynamic range thus obtained are also discussed from a systems point of view     

Effect of optical beat interference on the dynamic range of asubcarrier multiple access passive optical network using Fabry-Perotlasers

Fiber-in-the loop systems that use subcarrier multiple access can have error floors from optical beat interference (OBI). We show that, when Fabry-Perot lasers are used, OBI can limit the allowable variation in received power from the lasers in the multiple access system. We demonstrate a 7 dB increase in the allowable power variation by using a very large optical modulation index     

Power penalty assessment in optically preamplified receivers witharbitrary optical filtering and signal-dependent noise dominance

The assessment of the power penalty of optically preamplified receivers with signal-dependent noise (SDN) dominance is often accomplished by neglecting the influence of the optical filtering of the amplified spontaneous emission (ASE) noise on the signal-ASE beat noise. In this paper, it is shown that the optical filtering of the ASE noise can have a strong impact on the signal-ASE beat noise and remarkably affect the power penalty, even for optical filter bandwidths five times wider than the signal bandwidth. A simple expression to analytically evaluate the power penalty due to optical filtering, which describes reasonably well the influence of the optical filter on the signal-ASE beat noise variance, is proposed. The accuracy of the new expression is investigated, in the case of assessment of the optical filter detuning impact on receiver performance and the case of optical filter bandwidth optimization, and its predictions are satisfactory in comparison with rigorous estimates. Two new expressions of power penalty due to extinction ratio and to eye closure are also presented. It is shown that the power penalty due to eye closure depends on the extinction ratio and vice versa. Our results show also that the power penalty due to eye closure is remarkably dependent on the eye closure asymmetry     

Effects of phase noise on subcarrier modulation performance over Malaga turbulence channel

The performance of wireless optical system employing subcarrier phase-shift keying modulation was researched,which was influenced by phase noise of system demodulator under on Malaga atmospheric turbulence channel.Combined Fourier series and MeijerG function properties,the probability density function of instantaneous signal to noise ratio in the Malaga turbulence model was got.The Fourier series of receiving signal phase and the closed form expression of symbol error probability were derived,which were in the wireless optical subcarrier shift keying modulation system.Under different modulation order and light intensity fluctuation variance,the influence of phase noise on the system symbol error rate was analyzed.The numeric results present that the system symbol error rate increases with the light intensity fluctuation variance when the phase noise is lower.When the phase noise is larger,the influence of modulation order is greater than of turbulence intensity to the error-rate floor appearing.And with the increasing of modulation order,the corresponding average signal to noise is lower when symbol error-rate floor appears.     

Reduction of dispersion-induced distortion in SCM transmissionsystems by using predistortion-linearized MQW-EA modulators

The application of low-chirp MQW (multiquantum well)-EA (electro-absorption) modulators to subcarrier multiplexing (SCM) optical transmission systems is studied. The authors show that a third-order predistortion circuit is feasible for compensating the nonlinearity of this type of modulator. The degree of frequency chirping per optical intensity modulation depth of the modulator is theoretically determined to be about 1.4 MHz. A 42-channel AM-SCM signal transmitter with the predistortion circuit realizes both composite second-order distortion (CSO) and composite triple beat distortion (CTB) values under -57 dBc after 200-km-long transmission. The authors confirm dispersion-induced distortion of the MQW-EA modulator is as small as that of the LiNbO₃ modulator. Carrier-to-noise ratios (CNRs) of 45.2 dB for channel 1 and 43.8 dB for channel 42 were measured after 100 km transmission. It is found that the deterioration of a CNR is caused by the cascaded erbium doped fiber amplifiers (EDFAs), Rayleigh backscattered power and the optical phase noise. Theoretical CNRs show that the output power of the modulator should be higher to improve CNR     

ASK digital demodulation scheme for noise immune infrared data communication

A high performance architecture is proposed for the ASK (Amplitude Shift Keying) digital demodulation, which is dedicated to the noise immune wireless infrared data communication. In this architecture, an infrared subcarrier detected by a photodetector is digitized into TTL interface level pulses, and the digitized subcarrier is demodulated by a 1‐bit digital demodulator. To improve the noise immunity against fluorescent lamps, the optical noises from the lamps are analyzed and the behavior of an ASK infrared communication link is modeled under these noises. On the basis of this model, a digital demodulator is synthesized by means of a high level synthesis tool, aiming at implementing an algorithm of discriminating the subcarrier from optical noises. A part of experimental results shows that the ASK receiver realized with the use of this digital demodulator can achieve an error free infrared link even under the intense noises from fluorescent lamps. This revised version was published online in July 2006 with corrections to the Cover Date.     

Suppression of common-mode beat noise from optical amplifiers using a balanced receiver

When a coherent (heterodyne or homodyne), single-mixer type optical receiver is combined with an optical preamplifier or in-line amplifier(s), the S/N is deteriorated severely due to the common-mode (signal-ASE and ASE-ASE) beat noise. When a balanced-type coherent receiver is used, the common-mode beat noise can be suppressed and the ideal, so-called LO-ASE beat-noise limited, S/N ratio is attainable. The authors present a clear experimental demonstration of the suppression of common-mode beat noise by a balanced receiver. The minimum required LO power is determined by the thermal noise or the common-mode rejection ratio (CMRR) of the balanced receiver.<>     

Multiple Virtual Private Networks Over Passive Optical Networks Using RF Subcarrier Multiplexing and Fabry&#8211;P&#201;rot Laser Diodes

An optical layer solution for implementing multiple virtual private networking capabilities over a passive optical network using subcarrier multiplexed (SCM) transmission is proposed and experimentally demonstrated with 60-Mb/s data multiplexed with two radio-frequency subcarriers. The transmission of the SCM data is carried out using Fabry–PÉrot laser diodes. Experimental results and theoretical analysis show that our technique can potentially support high data rate traffic from a large number of simultaneous virtual private networks with minimal penalty resulting from optical beat interference.     

光纤SCM通信系统中的噪声分析

本文首先分析了光纤SCM通信系统中存在的噪声,然后深入讨论了光检测器的散粒噪声及其与光器件工作参数的关系和对载噪比C/N的影响,结论可作为实际系统设计时的依据。     

Low-Cost PMD-Insensitive and Dispersion Tolerant In-Band OSNR Monitor Based on Uncorrelated Beat Noise Measurement

A polarization-mode-dispersion-insensitive and dispersion tolerant in-band optical signal-to-noise-ratio monitor based on uncorrelated beat noise measurement is proposed and demonstrated. The proposed technique uses an optical delay line interferometer in recovering symmetrical signal samples and exploits the benefits of low-speed balanced receivers and digital signal processing in measuring the uncorrelated beat noise.     

Ultimate performance of optical DSB signal-based millimeter-wavefiber-radio system: effect of laser phase noise

It is theoretically shown that the phase noise of laser light source can be automatically eliminated by compensating the differential group delay due to the fiber dispersion between the two sidebands of the optical DSB signal. The bit error rate (BER) measurement of 60 GHz millimeter (mm)-wave subcarrier multiplexed optical double-sideband (DSB) signal transport in dispersion-compensated optical fiber link using fiber Bragg grating (FBG) mill show that the effect of the laser phase noise on the BER is as small as a few % relative to the other additive noise effect, thus realizing almost the ultimate performance     

Noise analysis of an amplified fiber-optic recirculating-ring delayline

We present the first theoretical and experimental noise analysis of a fiber-optic recirculating-ring delay line (RDL) including a doped fiber amplifier to compensate for the roundtrip loss. Both thermal-like sources and laser sources are considered. The output source induced noise (signal-signal beat noise), signal-spontaneous (s-sp) beat noise, and spontaneous-spontaneous (sp-sp) beat noise spectra for a thermal-like source are calculated from the autocorrelation function of the output detector current. It is shown that all three electrical beat noise spectra can be expressed as correlations of the output optical signal and ASE spectra. The source-induced noise will normally be the dominating noise source, but in some applications, the other noise terms also will be of importance. We use our theory to define the maximum number of recirculations in an amplified RDL with a pulsed source, where the fundamental noise floor is determined by the sp-sp beat noise     

Sensitivity improvement of a 2 Gb/s quadrature phase shift keyedsubcarrier multiplexed system by use of an optical preamplifier

A traveling wave semiconductor optical amplifier is used as a receiver preamplifier in a quadrature-phase-shift-keyed subcarrier multiplexed system. The intensity-modulated signal from a 1509-m distributed feedback laser bears two 1-Gb/s data signals on a 5-GHz subcarrier. The receiver preamplifier yields a 9.2-dB sensitivity improvement to -29.2 dBm. The system noise sources are measured. Theoretical and measured bit error rates versus received power are presented     

Tuned optical receivers for microwave subcarrier multiplexedlightwave systems

An analysis of tuned optical-receiver noise performance for microwave subcarrier multiplexed lightwave systems is presented. The effect of correlation between the gate and the drain HEMT noise sources and the design of tuning networks to obtain partial noise cancellation were investigated. Anoptimization algorithm is used to determine the tuning elements values for minimizing noise of 16 dB for a 60-video-channel subcarrier multiplexing (SCM) system, and 12 dB for a 120-channel system, which allows a significant increase in passive optical network distribution capacity. Design results for tuned front-end receivers encompassing the effects of p-i-n, HEMT, and SCM band parameters are presented