Nonlinear Distortion Analysis of Directly Modulated ... - 연세대학교

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oscillation [21]. This will result in the suppression of the instability induced bythe external perturbation in an optically injected semiconductor laser.Therefore, the effect of nonlinear gain suppression factor on the dynamics ofthe system is to stabilize the system.Next, the differential gain effect is analyzed. Fig. 3-6 reveals the stablelocking range according to the various differential gain values. By comparingthe results, it is observed that when the value of differential gain is reduced,while the other parameters are kept unchanged, the stable locking range isenhanced very much. Clearly, the larger the value of differential gain is, themore unstable the system is. The reason is that a higher differential gain resultsnot only in a higher resonance frequency but also in a reduced damping of therelaxation oscillation [22]. This suggests that a semiconductor laser with ahigher differential gain is much easier to be unstable or unlocking.Fig. 3-7 shows the linewidth enhancement factor dependence in lockingrange. The linewidth enhancement factor is dependent on laser structures verymuch, and affects the asymmetric locking characteristics. If α=0, the stablelocking range becomes symmetric around the zero frequency detuning. In caseof weak injection, which means the injection ratio is less than minus 30 dB,the larger the linewidth enhancement factor is, the narrower the stable lockingrange is. Moreover, it is said that the unstable characteristics such as chaos andperiodic doubling is greatly increased [21]. This is because the linewidthenhancement factor couples the amplitude and phase of the laser field. As canbe seen from the rate equation of the laser system, this coupling contributes tothe nonlinear dynamics of the lasers very much. However, under strong opticalinjection, which means the injection ratio is more than -30 dB, the stable30
locking range is increased and the locking occurs at very high detuning values.This is a very strange phenomenon, and the reason cannot be explained usingthe theory of weak injection case.Finally, the SL bias current effects are considered. Fig. 3-8 is the stablelocking range according to the bias current. As shown in the figure, when thebias current is increased, the stable locking range widens at weak injectioncondition. This phenomenon is explained that when a laser is operated at ahigher injection current level, the coherent optical power stored in the cavity ishigher, thus allowing the laser to be more resistant to the perturbation of theexternally injected optical field [21]. However, in case of strong opticalinjection, the stable locking range is shrunk at high injection current. Thisphenomenon is believed that for equalizing the injection power ratio, theexternal light power should be increased very much and this large externalperturbation causes the nonlinear effects.In this section, the stable locking range is analyzed using intrinsic laserparameters and operation condition such as injection current. The large gainsuppression factor affects the stable laser operation, but the large differentialgain influences the unstable laser operation in injection locking. In addition,the large linewidth enhancement factor shrinks the stable locking range, andthe high injection current widens the stable locking range at weak opticalinjection. The explanation is mainly referred to the S.K. Hwang’s simulationobservation and the simulation results are well fitted to his observation [21].However, the small signal analysis used in this thesis cannot explain entirelythe unstable locking phenomena such as chaos, periodic doubling and selfoscillation.Therefore, for more detail analysis of locking phenomena, the31
Page 1 and 2: Nonlinear Distortion Analysis of Di
Page 3 and 4: ________________ ________________ _
Page 5 and 6: IndexFigure Index ⋅⋅⋅⋅⋅
Page 7 and 8: Figure 3.11 Simulation results of I
Page 9 and 10: AbstractNonlinear Distortion Analys
Page 11 and 12: I. IntroductionIn the past, telecom
Page 13 and 14: solution for increasing the detunin
Page 15 and 16: [8, 9, 10]. This phenomenon occurs
Page 17 and 18: 0Optical Power (dBm)-10-20-30-40-50
Page 19 and 20: is the laser nonlinear transfer fun
Page 21 and 22: (3) Laser nonlinear transfer functi
Page 23: D11= τng2− 2( N00[(1 − 2εP)(
Page 26 and 27: f kn . The order of the IMP corresp
Page 28 and 29: 100-10Amplitude (dB)-20-30-40-50-60
Page 30 and 31: -20Amplitude (dB)-30-40-50-60-70thr
Page 32 and 33: locking to suppress nonlinear disto
Page 34 and 35: By using this system matrix, the sy
Page 36 and 37: Harmonic Power (dBm)0-10-20-7 dBc2
Page 38 and 39: these suppression values are depend
Page 42 and 43: 20Detuning Frequency (GHz)0-20-40-6
Page 44 and 45: nonlinear phenomena simulation shou
Page 46 and 47: Normalize Frequency Response (dB)10
Page 48 and 49: effects.Finally, for verifying the
Page 50 and 51: IMD2 Suppression (dB)15141312111098
Page 52 and 53: -20-30-40-0-60-70-802.70 2.75 .80 2
Page 54 and 55: IV. Nonlinear Distortion Suppressio
Page 56 and 57: -10Optical Power (dBm)-20-30-40-50-
Page 58 and 59: Normalized Main Mode Power (dB)0-10
Page 60 and 61: frequency.Then, reduction of IMD3 i
Page 62 and 63: -10-20Detected RF power (dBm)-30-40
Page 64 and 65: -20RF Power (dBm)-30-40-50-60-70-80
Page 66 and 67: V. SummaryIn analog fiber-optic lin
Page 68 and 69: VI. References[1] W, I, Way, “Bro
Page 70 and 71: quantum-well lasers,” J. Quantum
Page 72: .__________________________________

Nonlinear Distortion Analysis of Directly Modulated ... - 연세대학교

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