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This paper presents investigation of the impact of electro-absorption modulator integrated laser (EML) on performance of multiband-orthogonal frequency-division-multiplexing (MB-OFDM) ultra wideband (UWB) signal over single-mode fiber transmission by theoretical and experimental analysis, considering various parameters, such as fiber length, bias voltage, modulation power, bias current, and temperature of EML. The effect of the EML modulation nonlinearities on the OFDM subcarriers in MB-OFDM UWB over fiber system is investigated considering intermodulation distortion (IMD) and adjacent channel power ratio. It is shown that MB-OFDM UWB over fiber is limited by SNR for small modulation power and EML modulation nonlinearities induced IMD for high modulation power. Fiber transmission length is mainly degraded by EML phase noise converted relative intensity noise and power fading. The developed theory is verified by experiments.

Enabling techniques are studied for broadband and millimetre-wave radio-over-fiber components and systems. The use of substrate integrated circuits and design issues such as fiber chromatic dispersion, nonlinear distortion, modulation efficiency, and millimetre-wave distribution are considered.

We propose a novel photonic millimeter-wave (mm-wave) generation technique using two cascaded Electro-Absorption Modulators (EAMs). The two cascaded EAMs are driven by the same low radio frequency (RF) signal but with certain phase shift to suppress odd-order optical sidebands and enhance second order sidebands to obtain frequency doubling and quadrupling. It is shown that RF modulation voltage, phase shift between the two EAMs, and their bias voltages are the keys to be adjusted to efficiently generate high quality mm-wave signal. Experimental proof of concept is also demonstrated.

The performance of Multiband-Orthogonal Frequency Division Multiplexing (MB-OFDM) Ultra-WideBand (UWB) signal over single mode fiber system using a low cost Electro-Absorption Modulator (EAM) integrated laser (EML) is studied experimentally. Error Vector Magnitude (EVM) measurement is carried out to evaluate the system performance considering the effect of bias voltage, bias current temperature and optical modulation index of the EML, and fiber length. The experiment results showed that by using an EML, the UWB signal transmission over fiber can be cost effectively implemented.

Coherence multiplexing (CM) based Radio-over-Fiber (RoF) system is experimentally investigated for the first time for both single tone RF signal and ultra-wideband orthogonal frequency division multiplexing (UWB-OFDM) signal. The impact of received optical power, linewidth of the optical source, input RF power and fiber length are considered. It is found that the system is seriously limited by beat noise and fiber dispersion.

Linewidth enhancement factor (LEF) of InAs/InP quantum dot (QD) multi-wavelength lasers (MWL) emitting at 1.53 μm are investigated both above and below threshold. Above threshold, LEFs at three different wavelengths around the gain peak by injection locking technique are obtained to be 1.63, 1.37 and 1.59, respectively. Then by Hakki-Paoli method LEF is found to decrease with increased current and shows a value of less than 1 below threshold. These small LEF values have confirmed our InAs/InP QDs are perfect gain materials for laser devices around 1.5 μm.

In this paper, a novel channel model on the relay multi-input and multi-output (MIMO) cooperative communication on the basis of the Geometrically Based Double-Bounce Model (GBDBM) is proposed. The correlation properties of the scattering components in the frequency-nonselective two-ring model are investigated. The closed-form solutions of the space-time cross-correlation function (CCF) in Rician fading MIMO relay channel is presented. The simulation results of CCF are analyzed for various spacing of antenna and moving velocities of the relay node (RN) and the destination node (DN).

The capacity of multiple input multiple output (MIMO) system over wireless channels has been investigated analytically and by simulation over different types of wireless fading channels, such as Rayleigh, Ricain and Nakagami fading channels. This paper paper first investigates the channel capacity of the MIMO channels over the Rayleigh-Lognormal fading channel. The paper derives the analytic expression of channel capacity n of the MIMO Rayleigh-Lognormal fading channel in integral form, gives the Eigenvalue Probability Density Function (PDF) of the MIMO Rayleigh-Lognormal fading channel. Numerical calculation for the channel capacity of MIMO Rayleigh-Lognormal fading channel is explored using two numerical calculation methods, Gaussian-Laguerre numerical integration and Gaussian-Hermite numerical integration.

In this article we discuss a coherent optical heterodyne CPFSK receiver using optimum variable delay demodulation considering the effect of narrow-band IF filtering or intersymbol interference (ISI) caused by it. First we investigate the error probability at the normalized bandwidth of IF filter BT = 1 for a Gaussian IF filter. Numerical results show that the impact of narrow-band IF filtering increases with an increase in normalized IF spectral linewidth ΔvT and a decrease in modulation index h. Second, in order to decrease the impact of ISI, the optimum BT values are determined, which can minimize the error probability for given SNR. If a Gaussian IF filter is used, the optimal BT values are 1.3 for ΔvT = 0.25%, 1.4 for ΔvT = 0.5% at h = 0.5, 1.2 for ΔvT = 0.25%, 1.4 for ΔvT = 0.5% at h = 0.7, and 1.2 for all ΔvT ≤ 0.5% at h = 1. Finally, the performance of an optimal receiver employing optimum Gaussian IF filter is studied. We know that h = 1 is optimum and ΔvT ≤ 0.5% is necessary for 1-dB EB/N0 penalty per bit at BER of 10−9. © 1992 John Wiley & Sons, Inc.

The error probability for a coherent optical heterodyne FSK system with a limiter-discriminator-integrator (LDI) detector is analysed. The analysis includes laser quantum phase noise, the correlated receiver additive white Gaussian noise (AWGN), Gaussian narrow-band IF filtering and intersymbol interference (ISI) caused by it. It is shown that, for 1 dBEb/N0penalty at bit error rate (BER) 10−9, (i) the normalized IF beat spectral linewidth ΔνT⩽0.35% for frequency deviation ratioh=0.5(MSK), and ΔνT⩽0.5% forh=0.7 (the receiver is insensitive to laser quantum phase noise ath=1.0, if ISI is not included.); (ii) if ISI is incorporated, ΔνT⩽0.15% forh=0.5, ΔνT⩽0.5% forh=0.7, both with 3dB bandwidth-bit period product (3.0>BT⩾1.5), and ΔνT⩽0.5% forh=1.0 with BT⩾1.0 ifΔνT⩽0.35% when ISI exists,h=0.7 is optimum;h=1.0 otherwise.

The performance of a coherent optical M-ary continuous-phase frequency-shift-keying (CPFSK) receiver using limiter-discriminator (L-D) detection is investigated. It is shown that L-D detection of CPFSK optical signals offers the best performance for a large normalized IF beat spectral linewidth, Delta nu T. When the modulation index is unity, the receiver is immune to laser phase noise and can produce (M/4) exp (-SNR) symbol error probability, which may be considered as the upper bound if the optimal modulation index is used (SNR is the signal-to-noise ratio per symbol). Optimum modulation indexes are 0.8 and 1 at Delta nu T=1% and Delta nu T=2%, respectively, for M=4, 8, and 16. >

We demonstrate a simple black box model to evaluate both saturated gain and corresponding noise figure. This approach is simple and very suitable for system modeling with satisfied accuracy.

So-called polarization-insensitive optical phase conjugation with four-wave mixing in a dispersion-shifted fiber by the use of two orthogonally polarized pumps is analyzed theoretically. An inherent polarization dependence as a result of polarization-dependent cross talk, asymmetrical depletion of the two pumps and input signal, and polarization-sensitive phase conjugation is identified.

By using two orthogonally-polarized pump beams, an ultrabroad tunable wavelength converter is demonstrated with uniform efficiency and equalized signal-to-noise ratio (SNR) through four-wave mixing (FWM) in an 1500-nm semiconductor optical amplifier (SOA). This device allows the conversion of the input data signal to lower or higher frequencies with nearly-constant conversion efficiency and SNR over a 10.66 THz tuning range. This result is a significant improvement of both the conversion efficien cy and the SNR as compared with the conventional FWM-based wavelength converters. We have also investigated the effect of parameters of both input power and wavelength of pump P 2 on conversion efficiency and SNR of the wavelength-converted signals. Key words: All-optical wavelength conversion; Semiconductor optical amplifiers; Four-wave mixing; Two orthogonally-polarized pump beams. 1. INTRODUCTION The growing demand for voice and data telecommunications, such as high-definition television, multimedia services, and the world-wide web, is driving the use of wavelength division multiplexing (WDM) technologies for greater utilization of the available fiber bandwidth. An important element for implementation of all-optical WDM networking systems is an optical wavelength converter, since it makes possible many useful system functions in the optical domain such as wavelength reuse, dynamic wavelength routing and switching, and optical network reconfigurability [1]. Several mechanisms have been demonstrated for the implementation of all-optical wavelength conversion using semiconductor optical amplifiers (SOAs) [2]. These include cross-gain modulation (XGM) [3], cross-phase modulation (XPM) [4] and four-wave mixing (FWM) [5-6]. The XGM and XPM methods directly exploit the gain or phase modulation produced in the SOA by the injected signal, while the FWM technology is based on the generation of a replica of the data signal through a nonlinear interaction involving the optical signal and pump fields injected in the SOA. The XGM and XPM wavelength converters are simple to implement and offer higher conversion efficiency compared to FWM. However, FWM has the advantage of being transparent to both the modulation format and the bit rate, which are of critical importance when handling anal og or digital signals with speed of hundreds gigabit per second [7]. Data transparency is also offered by different frequency generation (DFG). Demonstrated DFG performance has been improved in r ecent years through use of quasi-phase matching in AlGaAs or LiNbO

Performance of a multiband (MB) orthogonal frequency division multiplexing (OFDM) ultra wideband (UWB) over fiber system is investigated in this paper using an optical double sideband subcarrier modulation that is immune to fiber chromatic dispersion induced RF power fading. It is found that the proposed modulation technique enhances the error vector magnitude (EVM) performance of MB-UWB OFDM and improves the power efficiency by 3 dB compared to optical single sideband subcarrier modulation counterpart.

We present and demonstrate a new optical double-sideband modulation technique that is free of dispersion induced RF power fading. The predicted 3-dB RF power improvement over optical single sideband modulation is experimentally verified.

We investigate spur-free dynamic range improvement of linearized optical single sideband Mach-Zehnder modulator using mixed-polarization. The experimental results agree with the theoretical analysis showing an improvement of more than 7 dB.

We present a numerical analysis of mean relative intensity noise (RIN) transfer in a fiber Raman amplifier (FRA) using multiple-wavelength pumps. For the first time, the RIN transfer is investigated to include pump-to-pump and signal-to-signal RIN transfers, together with the ldquotraditionalrdquo pump, to signal transfer in a multiple-wavelength pumped FRA. We show that for a multiple-wavelength pumped FRA, pump-to-pump and signal-to-signal RIN transfers induce an increase of RIN transfer magnitude. For a multiple-wavelength counter pumped FRA, in additional to the major pump to signal RIN transfer, pump-to-pump RIN transfer is considerable, and signal-to-signal RIN transfer is very small. For a multiple-wavelength co-pumped FRA, both pump-to-pump and signal-to-signal RIN transfers increase RIN transfer magnitude significantly. In addition, for both a co- and counter pumped FRAs, particularly for the co-pumped FRA, the longer wavelength signals experience more RIN transfer than the shorter wavelength signals. Furthermore, the bandwidth of RIN transfer is significantly increased in a multiple-wavelength co-pumped FRA with multiple input signals compared to a single-wavelength co-pumped FRA with an input signal.

We have demonstrated a novel approach to achieve a stable multi-wavelength laser system (MWLS) which is making use of a quantum dot semiconductor optical amplifier (QD SOA) as a highly birefringence material and an optical polarizer at the same time. Both the channel frequency spacing and the central lasing wavelength of the QD MWLS can be accurately set by using the desired-designed QD SOA with the certain operation conditions and by setting the polarization controller properly. The detailed working principles and the experimental results have been reported in this paper. The proposed QD MWLS technology can be used for characterizing the intrinsic properties of the QD semiconductor waveguide materials that could also be used for spectral narrowing of a laser system. We have experimentally confirmed that the QD SOA is highly inhomogeneous gain material as compared with QW SOA., Asia-Pacific Optical Communications (APOC 2008) Conference, 26-30 October 2008, Hangzhou, China, Series: Proceedings of SPIE

We comprehensively investigate three modulation techniques for the generation of millimeter-wave (mm-wave) using optical frequency quadrupling with a dual–electrode Mach-Zehnder modulator (MZM), i.e. Technique-A, Technique-B and Technique-C. For Technique-A, an RF signal drives the two electrodes of the MZM with maximum transmission bias, and this MZM is used for both the mm-wave generation and signal modulation. Technique-B is the same as Technique-A, but 180° phase shift between the two electrodes is applied. Technique-C is the same as Technique-B, but the MZM is only used for the mm-wave generation without signal modulation. It is found that Technique-B and Technique-C are better for frequency quadrupling than frequency doubling, tripling and sextupling. Both theoretical analysis and simulation show that the generated mm-wave suffers from constructive/destructive interaction due to fiber chromatic dispersion in Technique-A. However, the generated mm-wave is almost robust to fiber chromatic dispersion in Technique-B and Technique- C. It is found that Technique-C is the best in the quality of the generated mm-wave, especially when poor optical filtering is used. In addition, we develop a theory for calculation of Q-factor in an mm-wave over fiber system using the three modulation techniques for mm-wave generation. We consider an RF at 7.5 GHz and obtain an mm-wave at 30 GHz as an example, i.e. a frequency quadrupler. We evaluate the generation and distribution in terms of system Q-factor. The impact of RF modulation index, chromatic dispersion, MZM extinction ratio and optical filtering on Q-factor are investigated.

In this work, we propose and investigate a novel technique for the generation of millimeter-wave (mm-wave), i.e. frequency sixuplexing technique. The proposed technique is comprised of two cascaded Mach- Zehnder modulators (MZMs). The first MZM, biased at maximum transmission, is only used for even-order optical harmonic generation, and then a second MZM, biased at minimum transmission, is used for both optical carrier suppression modulation and data signal modulation. As an example, we consider an RF at 10 GHz, which carries the data signal and drives the MZMs; and an mm-wave signal at 60 GHz, i.e. a frequency sixupler, is obtained. It is found that our proposed sixupler leads to an 8-dB higher RF power at 60 GHz and a 6-dB improvement in receiver sensitivity with comparison to the conventional technique, i.e. optical carrier suppression modulation. The generated mm-wave signal is robust to fiber chromatic dispersion. The proposed technique is verified by experiments.

A new mechanism: resonant carrier scattering (RCS) between 2-D wetting layer carriers and 0-D quantum dot carriers is proposed in this paper. The mode competition between ground state (GS) emission and excited state (ES) emission is investigated in quantum dot lasers, where the GS emission is suppressed by ES emission at large injection. The calculations based on the proposed model are in agreement with experiments and successfully explain the phenomenon of GS and ES mode competition in quantum dot lasers.

The system model for differential detection of optical heterodyne DPSK systems is set up, taking into account the effects of the IF filter and its production of ISI, the additive white Gaussian noise in the receiver and the quantum phase noise of lasers as well as the bandwidth-time product (BT). We derive the probability distribution function of noise statistics for BT ≥ 1. The bit error rates (BER) are investigated in the presence of ISI. Numerical results for a 140-Mbit /s system are presented for Gaussian IF filters. It is found that the laser linewidth requirement is the same as the system that does not consider the IF filter effect and the ISI it causes.

We point out that the use of polarization-division multiplexed solitons is only preferable to a copolarized pulse train only if the system is interaction-limited and the polarization-mode dispersion (PMD) is sufficiently weak. If the PMD is stronger, copolarized solitons perform better than polarization-division multiplexed ones. A simple analytical formula for when this occurs is derived.

We have demonstrated a continuum-wave (CW) supercontinuum (SC) fiber light source with over 1000 nm bandwidth based on a low-cost erbium/ytterbium co-doped double-cladding fiber ring cavity laser. Based on the observation to the SC evolvement, we have experimentally analyzed the detailed contributions of several nonlinear effects within highly nonlinear dispersion-shifted fiber (HNLF). Our experimental results have clearly indicated that four-wave mixing (FWM) and stimulated Raman scattering (SRS) play key roles in CW-pumped SC generation. At the same time, self-phase modulation (SPM) mainly contributes to generate new frequency components near the peaks that appear in the form of the spectra broadening while cross-phase modulation (XPM) enhances the broadening of peaks.

We demonstrated an ultra-broadband wavelength converter based on co-polarized dual-pumping four-wave mixing technique in a dispersion-flattened photonic crystal fiber. Over 380-nm wavelength conversion range from 1260 nm to 1640 nm has been achieved. By sweeping the wavelengths of the second pump laser, we have obtained the relationship between the wavelength conversion efficiency and the converted data signals, which are consistant with our theoretical analysis. The OSNR of the converted data signals are up to 30 dB.

We have designed, fabricated and characterized self-assembled InAs/InGaAsP QD-waveguide devices around 1.55 μm. In order to obtain optimal performance, we have investigated several QD-based semiconductor optical amplifiers (SOAs) / lasers with different core geometry and doped profiles. To make the fair comparison between QD-SOA and QW-SOA, InAs/InGaAsP QW-SOAs with the same structure and the doped profiles have been designed and characterized. The experimental results indicate the QD-SOA is much better than QW-SOA in term of optical spectral bandwidth, temperature sensitivity and output power stability. The 3-dB and 10-dB bandwidths of the amplified spontaneous emission (ASE) spectra of the QD-SOA are 150 nm and 300 nm around 1520 nm. By using CW pump and probe signals we have demonstrated a non-degenerated four-wave mixing (ND-FWM) process and the experimental results indicate that the asymmetry of the FWM conversion efficiencies is eliminated by using the QD-SOA. To make use of the inhomogeneous broadening which is one of the specific properties of QD waveguide devices, we have designed and investigated the QD-based multi-wavelength semiconductor laser. A stable multi-wavelength laser output with a 93-channel multi-wavelength laser with maximum channel intensity non-uniformity of 3-dB were demonstrated on the basis of a single InAs/InGaAsP QD F-P cavity chip. All channels were ultra-stable because of the inhomogeneous gain broadening due to statistically distributed sizes and geometries of self-assembled QDs.

Photonic millimeter-wave (mm-wave) generation using optical frequency multiplication (OFM) is considered as a cost-effective solution in radio over fiber (RoF) systems. We comprehensively investigate the generation of mm-waves using high-order harmonic generation with a dual-electrode Mach-Zehnder modulator (DE-MZM) theoretically and experimentally, considering; the DE-MZM bias condition and finite extinction ratio. We consider three bias cases, i.e. maximum transmission bias (MATB), minimum transmission bias (MITB) and quadrature bias (QB). Our analysis shows that MATB is the best for the generation of mm-waves using the fourth order harmonics, and the generated mm-waves are almost immune to fiber dispersion. On the contrary, MITB is the best for the generation of mm-waves using the second or sixth-order harmonics, and the mm-waves generated are almost immune to fiber dispersion, too. Mm-waves generated with the QB always suffer from the impact of fiber dispersion.

We experimentally demonstrated a novel radio-over-fiber (ROF) architecture. In this architecture, two lightwaves were generated by using optical carrier suppression. Only one lightwave carried differential phase-shift-keying (DPSK) modulation downstream signals, and another lightwave carried the upstream OOK signal after it was delivered to the base station. The experiment results show 0.5 dB power penalty for 2.5Gibt/s DPSK downlink signal and penalty free for 2.5Gbit/s uplink data after 20 km fiber transmission.

The concept of substrate integrated circuit (SIC) is applied to the optoelectronic devices. The design and analysis of the new optoelectronic devices, including SIC photodetector and SIC modulator, are presented. The SIC concept can be applied to the isotropic and anisotropic substrate with single or multilayer geometry. Photodetectors and modulators can be integrated with the other microwave devices in the same substrate. Microwave part of the new proposed electro-optic devices are designed and optimized for radio over fiber applications. The travelling wave photodetectors with substrate integrated waveguide (SIW) in multilayered isotropic substrate is integrated. In addition the integration of LiNbO3 Mach-Zehnder traveling wave modulator with SIW in single anisotropic substrate is considered.

This paper reviews various photonic techniques available for the generation of millimeter wave signals, including by direct modulation of lasers, injection locking, beat frequency sources with phase-locked loops, dual wavelength lasers and femtosecond lasers.

This letter presents guidelines of how to design actively mode-locked fiber ring lasers to generate nearly transform-limited soliton pulses. The minimum fiber cavity length and/or dispersion, with which nearly transform-limited soliton pulses can be generated, need to satisfy an additional condition besides two previously known conditions of stability.

This letter presents a detailed investigation of how solitons broaden in the presence of polarization-mode dispersion. For a given amount of polarization-mode dispersion and pulsewidth there exists an optimal choice of group-velocity dispersion, for which solitons are most resistant to the effect of polarization-mode dispersion. We also optimize the soliton power enhancement factor and find that solitons can propagate roughly twice the distance compared to linear pulses in the absence of group-velocity dispersion.

Recent advances in radio-frequency (RF) and millimeter-wave (mmW) photonics are reviewed with emphasis on our research in broadband radio-over-fiber system architectures, photonic generation and processing of RF and mmW signals, and optoelectronic device design for mmW photonics applications. Future system design challenges are also discussed. In particular, the concept of substrate integrated circuits (SICs) is shown to have great potentials in the design of highly integrated mmW circuits as well as traveling-wave optoelectronic devices, which are critical to the development of future RF and mmW photonic systems for broadband wireless access and sensor applications.

A PSpice model for laser diodes packaging was established to simulate its thermal behavior and cooling performance. Some heuristic analysis has been made by this model with concept clarity and simplicity.

A low cost, low-dispersion, and real-time video rate optical delay line with a scanning repetition rate of 16 kHz is proposed and predicted. The path delay is obtained based on an optical double-pass delay in a cavity consisting of market available components.

We present a simplified radio over fiber balanced system that uses only one wavelength, optical modulator and fiber. In this balanced system the upper and lower sidebands produced by subcarrier modulation along with its optical carrier are separated before balanced photodetection. Optical time delays are introduced to one of the sidebands by means of two cascaded tunable nonlinearly chirped fiber Bragg gratings. The first nonlinearly chirped fiber Bragg grating produces relative time delay that has the following relationship τ delay ∝ 1/2f, while the second produces a relative time delay of τ delay ∝ 1/f. The first nonlinearly chirped fiber Bragg grating will have a large enough bandwidth and group velocity dispersion to introduce a relative time delay for the subcarrier and second order distortion, while the second will have the bandwidth and group velocity dispersion to introduce a different relative time delay for the third order distortion. The net effect of the relative time delays is to provide a phase shift of π for the subcarrier, second order distortion currents and a phase shift of 2π for the third order distortion current. Simulated results show a suppression of 2nd and 3rd harmonic distortion of 25.4 dB and 2.6 dB, respectively. In the case of 2 nd and 3 rd intermodulation distortion suppression of 33 dB and 20 dB, respectively have been reported. Simulation also shows that the power penalty improvement is approximately 2.5 dB for bit error rate of 10-9 for subcarrier at 10 and 35 GHz and relative intensity noise is suppressed by 3 dB.

Lumped fiber Raman amplifiers (LFRAs) using highly nonlinear fiber (HNLF) are investigated and compared to using dispersion compensating fiber (DCF). It is shown that both the signal and amplified spontaneous emission induced multiple-path interferences are reduced in HNLF, thus for a same Raman gain a better noise performance of LFRAs using HNLF can be achieved compared to using DCF. It is found that noise figure over the C+L band can be improved by ~6.7 dB for a Raman gain of ~15 dB for a LFRA using HNLF compared to DCF with counter-pumping.

This paper presents an analysis of how to calculate bit error ratio (BER) with physical explanation for optically pre-amplified DPSK receivers using optical Mach-Zehnder interferometer (MZI) demodulation and balanced detection. It is shown that BER calculation method for this kind of receivers is different from the conventional calculation method used widely for IM/DD receivers. An analytical relationship in receiver sensitivity between DPSK receivers using MZI demodulation with balanced detection and IM/DD receivers (or DPSK receivers using MZI demodulation and single-port detection) is given based on the Gaussian noise approximation. Our calculation method correctly predicts the 3-dB improvement of receiver sensitivity by using balanced detection over single-port detection or IM/DD receivers. Furthermore, quantum-limited DPSK receivers with MZI demodulation are also analyzed., 24 pages

Distributed fiber Raman amplifier with incoherent pumping is investigated and the performance is compared to that with the conventional coherent pumping. Increasing the spectral bandwidth of incoherent pumping source will results in reduction of Raman gain linearly and gain ripple exponentially, and degradation of noise figure up to 1 dB, compared to coherent pumping with the same pump power.

We find an accurate probability density function for Monte Carlo sampling of a Gaussian laser beam, which can be used to accurately model light transport in tissue. It is shown that our proposed method is accurate by comparing to the exact solution made by the convolution

C+L-band (1530 nm - 1605 nm) discrete fiber Raman amplifiers (dFRAs) with incoherent pumping are investigated considering gain, noise figure, and pumping efficiency with comparison to coherent pumping. It is shown that dFRAs with two incoherent pumping sources can have a gain flatness of less than 0.7 dB over 75 nm bandwidth. Noise performance of dFRAs with incoherent pumping is similar to coherent pumping. The comparison of C+L-band dFRAs with incoherent co-pumping to incoherent counter-pumping shows that dFRAs with incoherent co-pumping perform better due to not only lower but also flatter noise figure, besides increased pumping efficiency.

This report presents an investigation of composite fiber Raman amplifiers, i.e. a distributed fiber Raman amplifier followed by a discrete fiber Raman amplifier, both with incoherent pumping, compared to conventional coherent pumping. It is shown that a flatter gain and optical signal-to-noise ratio (OSNR) over 100-nm bandwidth can be achieved by using two incoherent counter-pumps, compared to using six coherent counter-pumps. Moreover, it is also found that further flatter gain and flatter OSNR over 100-nm bandwidth can be obtained simultaneously in composite fiber Raman amplifiers with bi-directional pumping. The flatness of both gain and OSNR with a ripple of 1 dB is predicted by using one incoherent co-pump and one incoherent counter-pump.

In this paper, we propose a novel millimeter-wave (mm-wave) band radio over fiber (RoF) system with dense wavelength division multiplexing (DWDM) star architecture. Two lasers with a small wavelength difference, phase locked and polarization-aligned, are allocated at a central station (CS) for connecting the CS and each base station (BS); one laser is used for transmitting light and the other for the remote local oscillator. For the conceptual illustration, we consider a DWDM RoF system with a channel spacing of 12.5 GHz and radio frequency (RF) of ~30-GHz mm-wave band. In the downlink system, a single-side band (SSB) subcarrier is used with low RF imposed onto an optical carrier at the CS, and an mm-wave band RF signal is obtained at each BS using direct photo-detection by the SSB subcarrier beat with the remote oscillator. In the uplink system, the received mm-wave band RF signal at each BS is imposed onto the two optical carriers simultaneously, one optical carrier with the closest SSB subcarrier is optically filtered out and fed into in the uplink transmission fiber without frequency interleaving; the electrical signal with a low intermediate frequency can be photo-detected directly at the CS. Such a RoF system has simple, cost-effective and maintenance reduced BS's, and is immune to laser phase noise in principle.

40 Gb/s signal transmission over up to more than 3000 km standard fiber by use of midway optical phase conjugation is predicted with a power penalty of below 5 dB and an eye closure of below 1 dB. This suggests that optical phase conjugation seems to be a very attractive technique in compensating for signal distortion for high speed long-haul standard fiber transmission systems.

In this letter, we predict transmission over more than 6000 km using standard fiber with the application of mid-way phase-conjugation in a 1.55-/spl mu/m, 10-Gb/s IM/DD system with in-line amplifiers for the power penalty at BER=10/sup -9/, which is less than 6 dB; the system must operate with an average power into the fiber within the range of -5 to 5 dBm. >

A new accurate expression is derived to evaluate input power limits and maximum capacity for an amplitude (or intensity) modulated WDM lightwave system only considering the effect of SRS. The maximum limits of input power and capacity are obtained for such a system.