Nonlinear amplitude-detuning characteristic of a CO2 laser with modulated losses

2011

Numerical simulations are used to study the effect of pump current modulation depth on the response of quantum-well GaInAs-GaInAsP heterolasers at different lasing frequencies within the gain band as a function of the excess above threshold. It is shown that the amplitude-frequency characteristics of these laser emitters generally contain two local maxima. The low frequency maximum usually corresponds to a resonance for the 1/2 subharmonic and the high frequency maximum, to the fundamental. As the modulation depth is increased, the fundamental frequency decreases, while the resonance frequency for the 1/2 subharmonic can change monotonically or not. The behavior found here can be used to develop quantum-well heterolasers with specified modulation parameters.

supporting

confidence: 61%

Effect of current modulation depth on the response of single-mode quantum-well heterolasers in the region of 1.5 μm

2011

“…Nonlinear ADCs were earlier investigated mainly for CO 2 lasers (see, e.g., [12,13] and the literature therein). These ADCs did not contain marked indications of the multiresonance structure of the nonlinear response.…”

mentioning

confidence: 99%

Modulation Characteristics of Tunable Quantum-Well Heterolasers at the Radiation Frequency Tuning

2005

621.378.35The influence of the tuning of the radiation frequency of quantum-well heterolasers within the limits of their amplification band on the output laser radiation parameters at different frequencies of pump-current modulation has been numerically simulated using two optical models of an active medium under the assumption that the excess of the invariable component of the pump current over its threshold value at any point of the amplification band is constant. It has been established that the amplitude-detuning characteristics of the lasers studied are linear at high current-modulation frequencies and nonlinear at medium ones. The behavior of the nonlinear spectral response of a laser diode is explained by its multiresonance structure and is mainly determined by the ratio between the pump-current modulation frequency and the maximum resonance frequency of the laser.Introduction. At present, semiconductor lasers determine the advancements made in many fields of science and engineering. However, their radiation parameters should be further improved in accordance with new and specific requirements imposed on them by practice. For this purpose, a number of effects arising in the indicated systems should be investigated in greater detail. In particular, of great interest is the influence of the position of the radiation frequency of a laser within its amplification band on the laser modulation parameters. In this connection, the nonlinear amplitude-detuning characteristics (ADC) of injection quantum-well heterolasers have been theoretically investigated in [1-3]. These characteristics reflect the dependence of the response of a laser and the modulation of its pump current on the laser radiation frequency; however, they were obtained only for certain particular cases. For example, it was suggested that the pump current remained unchanged when the radiation frequency was tuned within the limits of the amplification band. Some conclusions were also made on the basis of data obtained with the use of a single model of an active medium.The present work is devoted to investigating the behavior of the nonlinear ADCs of a laser in the case where the excess of the invariable component of the pump current over its threshold value remains unchanged when the laser radiation frequency is changed. Our investigations were performed with the use of two optical models of an active medium under conditions close to the experimental ones. We also investigated the multiresonance structure of the nonlinear response of quantum-well heterolasers with pump-current modulation in greater detail.Main Equations and Parameters Used. For definiteness, we carried out calculations for quantum-well heterolasers based on GaAs with quantum wells of width 5-15 nm in the active region. The dynamics of generation of a monochromatic radiation of frequency ν st by such systems was described using standard equations for the density of photons in the cavity S and the concentration of nonequilibrium current carriers n [4, 5]:

“…The quantities S m as functions of ν g0 are so-called amplitude-frequency characteristics (AFC). It was found previously [10,12,18] that the principal features of the behavior of nonlinear AFC for B-class lasers are determined by the ratio of frequencies ν m and ν r max (maximum resonant laser frequency within the gain band). For example, for the conditions of Fig.…”

mentioning

confidence: 98%

Influence of changing the forbidden-band gap on radiation frequency sweeping of quantum-well heterolasers

2009

The principal features of changing (sweeping) the "instantaneous" emission frequency of quantum-well heterolasers as functions of the modulation frequency and depth and the constant component of the pump current when tuning the lasing frequency within the gain band are established using numerical modeling. The active medium is described in the framework of a two-band model with similar distributions of levels in subbands of electrons and holes assuming transitions between ground subbands with no k-selection rule. Emission frequency sweeping occurs because of changes in both the index of refraction of the active medium due to a variation in the concentration of non-equilibrium charge carriers and the forbidden-band gap. Emission frequency sweeping does not occur at low frequencies of current modulation that correspond with quasi-stationary lasing regimes. The modulation depth of the output radiation and, therefore, the emission frequency sweeping, also approach zero for the other limiting case of relatively high current modulation frequencies.The sweeping is greatest at intermediate current modulation frequencies. The sweeping value is approximately halved in certain instances by taking into account the change of forbidden-band gap of the semiconductor. In general, the sweeping value is determined by the combined effect of the modulation frequency and depth, the constant component of the pump current, and the spectral position of the laser emission frequency within the gain band.Introduction. Semiconducting lasers with narrow and stable spectral emission lines are required for fiber optic communications, high-resolution spectroscopy, measurement technology, etc. Therefore, so-called dynamic single-frequency (SF) semiconducting lasers that operate stably in single-logitudinal generation mode with high-frequency pump current modulation have been developed [1]. However, the "instantaneous" emission frequency can change even in this regime with current modulation (so-called sweep, chirp, dynamic shift, etc.) [2]. This is explained by a change of the index of refraction n of the active medium and, therefore, the instantaneous longitudinal frequencies of resonator modes and the generated radiation.Studies of the features of emission frequency sweeping are of definite practical interest. For example, certain features of the change of emission frequency in vertical cavity surface-emitting lasers [3,4] and of actively and passively mode-locked semiconducting lasers [5] have been examined. The effect of frequency chirp on the dynamics of recirculation in a closed contour and on an injection laser in high-velocity code modulation has been studied [6,7]. Features of frequency sweeping of emission from heterojunction quantum lasers with pump current modulation have been studied for certain special cases in recently published papers [8,9].Herein we report a systematic study of the features of quantum-well heterolaser sweeping as a function of modulation depth and frequency and the value of the constant component of pump current...