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We present a numerical simulation study on the effect of the linewidth enhancement factor (α) of semiconductor laser and dispersion management methods of optical fibers on the performance of 40-Gb/s directly-modulated fiber links and their application in WDM systems. The dispersion management methods include the use of non-zero dispersion-shifted fiber (NZ-DSF), dispersion-compensating fiber (DCF), and fiber Bragg grating (FBG). The optimal values of the α-parameter and the best dispersion management method are applied to design and simulate a four-channel × 40-Gb/s WDM fiber system. The obtained results show that the increase in the α-parameter and/or fiber length reduces the performance of both the 40-Gb/s optical link and the WDM system. Regarding the 40-Gb/s optical link, when α = 1, using –NZ-DSF or + NZ-DSF, DCF with SSMF, and FBG with SSMF work to increase the transmission length from 1.6 km of a standard single-mode fiber (SSMF) to 7.2, 26.5, and 40 km, respectively. Whereas at α = 3.5, the maximum transmission length reaches 1.2 km when using SSMF, –NZ-DSF, or + NZ-DSF, while it increases to 13 and 35 km when using DCF with SSMF, and FBG with SSMF, respectively. In the designed WDM system, the use of FBG with SSMF is predicted as the most effective method for dispersion management. The maximum transmission length reaches 25 km when α = 1, but reduces to 12 km when α = 3.5. [ABSTRACT FROM AUTHOR]

To fulfill the demands of high-speed photonic applications, researchers, and engineers have been working to improve the modulation bandwidth (MBW) of semiconductor lasers. We extend our prior work on modeling a vertical-cavity surface-emitting laser (VCSEL) with multiple transverse-coupled-cavities (MTCCs) to evaluate the feasibility of boosting MBW beyond 100 GHz in this study. Because of the strong coupling of slow-light feedback from nearby lateral transverse coupled cavities (TCCs) into the VCSEL cavity, the laser has a high modulation performance. The intensity modulation response of the VCSEL design using one, two, four, and six TCCs is compared. Due to the optical-feedback (OFB) from short TCCs, which achieves 3 dB MBW reaching 170 GHz, photon–photon-resonance (PPR) is projected to occur at ultra-high frequencies beyond 145 GHz. In terms of the Fourier spectrum of the relative intensity noise (RIN), we characterize the noise features of the MTCC-VCSEL in the ultra-high bandwidth domain. [ABSTRACT FROM AUTHOR]

This paper presents a theoretical study on the generation of optical frequency combs (OFCs) using direct modulation of semiconductor laser. Influence of gain suppression on characteristics of the generated OFCs is investigated. The study includes intensive and comprehensive investigations of the temporal and spectral characteristics of the generated OFCs as a function of the gain suppression over a wide range of the bias current. We report on generation of short optical pulses and large numbers of comb lines with low-power flatness under weak gain suppression and/or strong modulation depth when the laser is biased near the threshold. The influence of gain suppression becomes more robust when the laser is biased far above threshold. By adopting the operating parameters, we predict pulses with 60 ps width and 10 comb lines with 2.1 dB flatness when the gain suppression is ignored. Under strong gain suppression, broader pulses (132 ps width) and only five lines with higher flatness of 4.99 dB could be obtained. [ABSTRACT FROM AUTHOR]

This paper presents theoretical evaluation of the digital modulation performance of semiconductor lasers in digital communication systems with gigabit rates. The study is based on numerical integration of the rate equations augmented by a nonreturn-to-zero (NRZ) bit generator. For solitary semiconductor lasers, the performance is evaluated in terms of the eye diagram, turn-on delay jitter (TOJ), and signal-to-noise ratio. In communication systems, the performance is evaluated by the bit error rate (BER) and power penalty induced by the laser noise. Contributions of both the intrinsic fluctuations and bit pattern to the TOJ and BER are assessed. The results show that when the modulation current is low and the semiconductor laser is biased relatively above threshold, the power penalty decreases although the eye diagram is not well open. When the modulation current is high enough, biasing the semiconductor laser far-above threshold achieves both lower power penalty and higher eye-diagram quality. [ABSTRACT FROM AUTHOR]

A theoretical study of the dynamics of semiconductor lasers subjected to pseudorandom digital modulation at gigabit rates is presented. The eye diagram, turn-on jitter (TOJ), and power fluctuations in the modulated laser wave form are analyzed. The study is based on numerical large-signal analysis of the laser rate equations. Influences of the biasing and modulation currents on the eye diagram and TOJ are examined. The degree of eye opening is measured in terms of a Q factor of the laser signal analogous to the Q factor determining the bit-error rate in transmission systems. Influence of optimizing both the sampling and decision times on the signal Q factor is modeled. We show that the most eye opening corresponds to shortening the sampling time associated with lengthening the decision time. We also assess the relative contributions of the laser intrinsic noise and pseudorandom bit pattern to the TOJ. The results show that the bit pattern is the major contributor to the TOJ when the setting time of the relaxation oscillation is longer than the bit slot. [ABSTRACT FROM AUTHOR]

Cites a study which used an infinite order perturbation treatment to analyze the nonliner gain injection semiconductor lasers. Information on semiconductors; Application of the semiclassical density matrix analysis to analyze the lasing phenomena of the semiconductors; In-depth look at the gain coefficients of the semiconductors; Details on the reduction of the infinite gain expansion.

This paper analyzes the relative intensity noise (RIN) associated with intensity modulation (IM) of multilongitudinal mode semiconductor lasers. We considered two states of operation; namely, stable single-mode and multimode hopping that correspond to weak and strong asymmetric gain suppression. The former is typically considered by AlGaAs lasers, whereas the latter is considered by InGaAsP lasers. We introduce comparison of the influence of the modulation parameters on both the total and modal RIN between both lasers. We show that the IM response and 2HD display a peak at the relaxation frequency. The multimode hopping in the InGaAsP laser induces levels of signal distortion much higher than those in the AlGaAs laser in the regime of low modulation frequencies. Under weak modulation, the total and modal RINs of both the lasers vary little from those of the non-modulated lasers. The deep modulation releases the multimode hopping phenomenon in the InGaAsP laser and suppresses the mode-hopping peak in the RIN spectrum. [ABSTRACT FROM AUTHOR]

We demonstrate a compact electro-absorption slow-light modulator laterally-integrated with an 850 nm vertical-cavity surface-emitting laser (VCSEL), which enables highly efficient millimeter-wave modulation. We found a strong leaky travelling wave in the lateral direction between the two cavities via widening the waveguide width with a taper shape. The small signal response of the fabricated device shows a large enhancement of over 55 dB in the modulation amplitude at frequencies beyond 35 GHz; thanks to the photon-photon resonance. A large group index of over 150 in a Bragg reflector waveguide enables the resonance at millimeter wave frequencies for 25 μm long compact modulator. Based on the modeling, we expect a resonant modulation at a higher frequency of 70 GHz. The resonant modulation in a compact slow-light modulator plays a significant key role for high efficient narrow-band modulation in the millimeter wave range far beyond the intrinsic modulation bandwidth of VCSELs. [ABSTRACT FROM AUTHOR]

We introduce modeling and simulation of digital modulation characteristics of high-speed semiconductor laser and evaluates its performance for use in 40 Gbps communication systems. The study is applied for both the return to zero (RZ) and non-return to zero (NRZ) formats of the modulation current. The modulation characteristics include the waveform of the modulated signal, eye diagram, and frequency chirp. The receiver sensitivity and power penalty associated with the increase in the transmission bit rate are evaluated in the back to back configuration of an optical communication system. The results showed that under 40 Gbps modulation, the modulated laser signal is broadened within the modulation bits as a pseudorandom bit-pattern effect. The laser chirp is in the range of 34-72 GHz, which is expected to combine with fiber dispersion, degrading the performance of high-speed fiber communication systems. Under both the NRZ and RZ modulations, the receiver sensitivity of the communication system increases with the increase in the bit rate. Except for the bit rate of 40 Gbps, the receiver sensitivity is larger under the NRZ modulation than under the RZ modulation. The power penalty associated with increase of the bit rate from 2 to 40 Gbps ranges between 2 and 14 dB. [ABSTRACT FROM AUTHOR]

SUMMARY A comprehensive study on semiconductor laser characteristics under gigabit-per-second digital modulation is presented. Comparison of the modulation characteristics under both formats of the return to zero (RZ) and non-return to zero (NRZ) bit formats is introduced. The modulation characteristics include the eye diagram, turn-on jitter (TOJ) and frequency chirp. The study elucidates how the laser modulation performance changes with variation of the modulation bit rate relative to the maximum bit rate and the setting bit rate of the relaxation oscillations. The relative contributions of the intrinsic noise of the laser and the pseudorandom bit-pattern effect to the modulation characteristics are differentiated. The results showed that when the bit rate is higher than the setting bit rate, the eye diagram is partially closed and becomes completely closed when the bit rate increases beyond the maximum bit rate. When the bit rate is higher than 2.25 Gbps, the TOJ values under NRZ modulation are smaller than those under RZ modulation near the threshold level. Under both RZ and NRZ formats, chirp increases with the bit rate with the chirp under the RZ format being higher than that under the NRZ format. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper investigates the direct gigabit modulation characteristics of semiconductor lasers using the return to zero (RZ) and non-return to zero (NRZ) formats. The modulation characteristics include the frequency chirp, eye diagram, and turn-on jitter (TOJ). The differences in the relative contributions of the intrinsic noise of the laser and the pseudorandom bit-pattern effect to the modulation characteristics are presented. We introduce an approximate estimation to the transient properties that control the digital modulation performance, namely, the modulation bit rate and the minimum (setting) bit rate required to yield a modulated laser signal free from the bit pattern effect. The results showed that the frequency chirp increases with the increase of the modulation current under both RZ and NRZ formats, and decreases remarkably with the increase of the bias current. The chirp is higher under the RZ modulation format than under the NRZ format. When the modulation bit rate is higher than the setting bit rate of the relaxation oscillation, the laser exhibits enhanced TOJ and the eye diagram is partially closed. TOJ decreases with the increase of the bias and/or modulation current for both formats of modulation. [ABSTRACT FROM AUTHOR]

Influence of the linewidth-enhancement factor on the output and operations of InGaAs/InP pumping lasers emitting at a wavelength of 980 nm under strong optical feedback is investigated numerically. The investigations are performed based on intensive numerical integration of an improved time-delay rate equations of semiconductor lasers over wide ranges of the linewidth-enhancement factor and optical feedback strength. The results show that the semiconductor laser operates under strong optical feedback in continuous wave and pulsation at small values of the linewidth-enhancement factor. Under large values of the linewidth-enhancement factor, the laser happens to exhibit chaos and pulsation. We predict that semiconductor laser subjected to strong optical feedback exhibits much more stable pulsing operation under higher values of the linewidth-enhancement factor, which indicates that the laser is locked at the external cavity frequency. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper investigates numerically influence of the external-cavity length on the type of the route-to-chaos of semiconductor lasers under external optical feedback. The study is based on numerical solution of a time-delay model of rate equations, and the solutions are employed to construct bifurcation diagrams and to examine the Fourier frequency spectrum of the laser output. The ratio of the relaxation frequency to the external-cavity resonance frequency is employed to measure the influence of the length of the external cavity. The route-to-chaos is period doubling when this frequency ratio is less than unity. The route is sub-harmonic when the frequency ratio increases up to 2.25. When the frequency ratio increases further, the transition to chaos becomes quasi-periodic characterized by the compound-cavity frequency and the relaxation frequency as well as their difference. Copyright © 2009 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: This paper introduces a theoretical study of longitudinal mode competition in semiconductor lasers subject to optical feedback. The study is based on a model of time-delay multimode rate equations taking into account both symmetric and asymmetric suppressions of modal gain. The model is numerically solved and applied to the case of a short-external cavity. Mode competition is characterized along the feedback-induced period-doubling route to chaos as well as under chaotic dynamics. Contributions of symmetric and asymmetric gain suppressions to both mode dynamics and modal operation under OFB are clarified. The results show that under chaotic dynamics, mode competition induces multimode hopping giving rise to asymmetric multimode output spectra. In regimes of continuous-wave operation, mode competition supports single-mode oscillation, and the side-mode suppression ratio improves with the increase of feedback. In the regime of strong feedback, the lasing mode moves to either long- or short-wavelength side in a seemingly random fashion, which is strongly related to asymmetric gain suppression. [Copyright &y& Elsevier]

Abstract: Large-signal analog intensity modulation of semiconductor lasers (SLs) is characterized based on numerical integration of the rate equations. The modulation dynamics are classified into seven types with regular and irregular signals. The classification is made in terms of the time trajectory of the laser intensity, phase portrait, and fast Fourier transform (FFT) spectrum. The operating region of each type is defined in a diagram of the modulation index versus modulation frequency. The accuracy of applying the approximate small-signal analysis to study analog modulation is assessed. The validity of identifying the dynamic types by the large-signal modulation response is examined. The laser emits continuous and regular signals under weak modulation. When the modulation index exceeds one half, the laser emits picosecond-pulses. Under strong modulation with frequencies around the relaxation frequency, both continuous and pulsed signals exhibit period-doubling. [Copyright &y& Elsevier]

This paper demonstrates theoretical characterization of intensity modulation of semiconductor lasers (SL's). The study is based on a small-signal model to solve the laser rate equations taking into account suppression of optical gain. Analytical forms of the small-signal modulation response and modulation bandwidth are derived. Influences of the bias current, modulation index and modulation frequency as well as gain suppression on modulation characteristics are examined. Computer simulation of the model is applied to 1.55-μm InGaAsP lasers. The results show that when the SL is biased far-above threshold, the increase of gain suppression increases both the modulation response and its peak frequency. The modulation bandwidth also increases but the laser damping rate decreases. Quantitative description of the relationships of both modulation bandwidth vs. relaxation frequency and maximum modulation bandwidth vs. nonlinear gain coefficient are presented. [ABSTRACT FROM AUTHOR]

This paper demonstrates numerical analysis of the dynamics and intensity noise of fibre-grating semiconductor lasers (FGSLs). The induced phenomenon of strong optical feedback (OFB) is analysed. The simulations are based on an improved time-delay rate equations model of a single-mode laser that takes into account the multiple round-trips of the lasing field in the fibre cavity. The analyses are performed in terms of the temporal trajectory of the laser intensity, bifurcation diagram and relative intensity noise (RIN). We explore influence of the fibre-cavity length on the dynamics and RIN. The results show that when the fibre cavity is short, the regime of strong OFB is characterized by either continuous-wave (CW) operation or periodic pulsation. The pulsation frequency is locked at the frequency separation of either the compound-cavity modes or the external fibre-cavity modes. The corresponding RIN level is close to or higher than the level of the solitary laser depending on pulse symmetry. When the fibre cavity is long, the laser exhibits unstable dynamics over wider range of OFB. Moreover, the strong-OFB pulsation becomes beating quasi-periodic at the relaxation oscillation frequency and the fibre-cavity mode-separation frequency. Copyright © 2007 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper reports on a numerical approach to model the field fluctuations, spectral lineshape and linewidth in semiconductor lasers. The approach is based on numerical solution of the laser rate equations augmented by Langevin noise sources that account for fluctuations in the lasing field. The paper newly examines contributions of intensity and frequency noises to the spectral characteristics of the lineshape and its linewidth over a wide range of injection current. The model is applied to InGaAsP lasers emitting in a wavelength of 1.5 μm as the most representative light sources in optical communication systems. Accuracy of approximated models of calculating linewidth from low-frequency components of the frequency noise is checked. Effect of non-linear gain suppression on the lineshape is also explored. The spectral lineshape promotes and the linewidth decreases as the laser is injected far from the near-threshold region. The lineshape changes mainly with changes in the frequency noise spectrum while the linewidth is sensitive to variation in the low-frequency levels of both intensity and frequency noises. Copyright © 2004 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper reports on numerical characterization of intensity and frequency fluctuations associated with mode hopping and single-mode jittering in semiconductor lasers. A new numerical approach has been applied that takes into account the suppression effects of gain and the intrinsic fluctuations in both intensities and phases of the oscillating modes. The temporal trajectories of mode intensities are investigated. The fluctuations are characterized in terms of their correlation functions and statistical distributions. The intensity and frequency noise contents of fluctuations are also identified. The obtained characteristics are compared with those of stable single-mode operation (SSMO) in nearly-single-mode lasers. The case of multi-mode hopping in multi-mode lasers is also analyzed. The cross-correlation analyses confirm strong anti-correlations among intensity fluctuations of the hopping and jittering modes. The relative intensity noise (RIN) in both total output and modes are most enhanced under mode hopping, and so is the frequency noise (FN). Although the jittering operation induces lower noise levels in the low-frequency regime, the noise is higher than the quantum level characterizing the SSMO. The cross-correlations among the hopping modes are stronger and the intensity noise levels are higher in the case of two-mode hopping in nearly-single-mode lasers than those in the case of multi-mode hopping in multi-mode lasers. The explored characteristics are compared with the experimental observations. [Copyright &y& Elsevier]

Examines the influence of instantaneous mode competition on the dynamics of semiconductor lasers. Simulations of the multimode rate equations; Generation of the Langevin noise sources; Characteristics of the output spectrum.

Focuses on the numerical modelling of intensity and phase noise in semiconductor lasers. Importance of carrier number noise source; Identification of the frequency spectra of intensity and phase noise; Fluctuation of the photon and carrier numbers.

We report on achieving tuned single mode operation of a multimode semiconductor laser by coupling it to a very-short external cavity with selective feedback. We show that the induced uniform feedback light from the very-short external cavity can induce single-mode oscillation over a broad range of optical feedback. Then by applying selective external to the optimum settings of the single-mode oscillation, we predict tuning of the single-mode output over a wavelength range of ~ 20 nm by detuning the peak wavelength of optical feedback from the central wavelength of the modal gain. The study is based on modeling of the dynamics of multimode semiconductor laser subject to selective optical feedback. The model takes into account mechanisms of both self- and cross-modal gain suppression, and the study is concerned with the very-short external cavity that corresponds to stable continuous-wave (CW) operation. [ABSTRACT FROM AUTHOR]

We analyse mode-competition (MC) noise in sinusoidally modulated laser diodes and assess its contribution to the noise performance of directly modulated fibre links. The noise figure (NF) is used to evaluate the noise performance of the link. The present analyses are based on a multimode rate equation model that takes into account both symmetric and asymmetric suppressions of the cross-modal gain. Variations of the MC relative intensity noise of both the total output and the oscillating modes with modulation conditions are investigated. The obtained results show that regardless of the fact that the non-modulated laser oscillates nearly in single-mode or in two-mode hopping, the modulated laser oscillates in single mode when the signal is continuous, and converts into multimode when the signal is pulsing. The contribution of MC noise to the NF of the link increases with an increase in the modulation depth and with a decrease in the modulation frequency, except when the signal has period doubling. This contribution is negligible under high modulation frequencies when the laser signal is continuous and uniform, and is most enhanced (∼53 dB) under low modulation frequencies when the signal is pulsing and superposed with non-uniform relaxation oscillations. [ABSTRACT FROM AUTHOR]

Presents a study that proposed a multimode simulation model of mode-competition low-frequency noise in semiconductor lasers. Effect of the mode-competition phenomena on the operation of semiconductor lasers; Details of the multimode simulation model; Simulation results.