Large-signal analysis of analog intensity modulation of semiconductor lasers (original) (raw)
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Pramana, 2008
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.
Estimation of Parameters Controlling Direct Modulation of Semiconductor Lasers
IEEE- 26th NATIONAL RADIO SCIENCE CONFERENCE, 2009
This paper presents a theoretical estimation of the parameters controlling direct modulation of semiconductor lasers and their dependence on modulation conditions. The study is based on the rate equation model of the emitted photon number and the number of injected charge carriers within the active region. The rate equations are solved numerically in the time domain to determine the transient parameters, and analytically in the frequency domain to determine the small-signal modulation parameters. The transient properties include, tum-on delay, setting time of the relaxation oscillations, damping rate and frequency of the relaxation oscillations. The small-signal modulation parameters include the small-signal response and the associated modulation bandwidth. The numerical calculations are applied to InOaAsP lasers emitting at 1.55 urn. The obtained results for the considered laser showed that the maximum modulation bandwidth is 11.1 OHz when the current is four times its threshold level. This value is nearly twice the maximum bit rate estimated from the laser transients . The maximum bit rate that results in optical signal modulated by pseudorandom returned to zero (RZ) or nonreturned to zero (NRZ) format and free from the bit- pattern effects exceeds 1 Obis when the modulation current is four times the threshold current.
This paper investigates mode dynamics, operation characteristics and signal distortions associated with sinusoidal modulation of semiconductor lasers. The study is based on intensive integrations of the multimode rate equation model of semiconductor lasers over wide ranges of the modulation frequency and depth. The rate equations take into account both spectral symmetric and asymmetric suppressions of modal gain. The higher harmonic distortions as well as the half harmonic distortion associated with the period doubling effect are investigated. The study is applied to both cases of single-mode and multimode oscillations of the non-modulated laser. The obtained results showed that the modulated signal has six distinct waveforms depending on the modulation conditions; three types have continuous periodic waveforms and the others have periodic pulsing waveforms. The modulated laser is found to oscillate in a single mode under weak modulation where the modulated signal is continuous, whereas the pulsing signals are associated with multimode oscillation. The higher harmonic distortions of single-mode laser are lower than those of two-mode lasers, and become serious at modulation frequencies around the relaxation oscillation frequency. These distortions are highest when the laser output is pulsating and the pulses are superposed by relaxation oscillations.
Analysis of semiconductor laser dynamics under gigabit rate modulation
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 ͑TOJ͒, 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.
EL SEVIER - Beni-Suef University Journal of Basic and Applied Sciences, 2015
We investigate the dynamics and noise of semiconductor lasers (SLs) subject to analog modulation with the frequency plan of the National Television Standards Committee (NTSC) for use in the community access television (CATV) systems. The investigations are done in both the time and frequency domains as important methodologies to upgrade the optical CATV systems. The study is based on the rate equation model of the laser. The modulation dynamics is classified into four distinct types according to the waveform of the modulated signal, and the frequency spectra of the relative intensity noise (RIN) of these types are characterized. We show that the laser emits continuous and regular period signals under weak modulation. When the modulation index exceeds 43%, i.e. the modulation current exceeds the bias level above threshold, the laser emits clipped signals superposed by relaxation oscillation. The increase in the modulation index by about 50% in channels beyond channel #24 makes the laser emitting clipped pulsed signals superposed by relaxation oscillation. The laser attains higher noise levels (~108 dB/Hz) when it emits pulses, whereas the noise is lowest (~170 dB/Hz) when the signal is continuous.
Pulse statistics in single-mode semiconductor lasers modulated at gigahertz rates
Optics Letters, 1991
The statistics of switch-on time, maximum light intensity, and pulse width of single-mode lasers modulated at gigahertz rates are analyzed. Numerical results obtained from noise-driven rate equations are reported. Pulse statistics, and in particular timing jitter, are shown to be rather insensitive to the bias current at this high-speed modulation. In addition, pulse statistics become rather independent of the modulation period when biasing slightly below threshold.
Harmonic balance analysis for semiconductor lasers under large-signal modulation
Optical and Quantum Electronics, 2006
The dynamic characteristics of an edge-emitting laser under large-signal modulation are analyzed in the frequency domain using a harmonic balance method on device level. The simulations reveal the nonlinearities of the carrier dynamics in the quantum well region which strongly influence the optical power in the higher harmonics.
Computer simulation of high frequency modulation of laser diode radiation
Lithuanian Journal of Physics, 2004
Dynamic characteristics in the case of a large signal of partly gain-coupled multiple-quantum-well InGaAsP-InP distributed feedback (GC DFB) laser diodes have been investigated. Simple rate equations for carrier and photon densities were taken. A possibility to simulate the modulation characteristics of GC DFB lasers using these equations has been shown. Chirp and optical power pulses obtained by time-resolved frequency chirp measurements were compared with modelled ones.
Arabian Journal for Science and Engineering, 2014
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