L.M. Zhang

Dynamic analysis of radiation and side-mode suppression in a second-order DFB laser using time-domain large-signal traveling wave model

In this paper, we have developed a relatively simple algorithm to calculate the large-signal dynamic response of DFB lasers by solving the time-dependent coupled wave equations directly in the time domain. The spontaneous emission noise, longitudinal variations of carrier (hole burning) and photon densities as well as that of the refractive index are taken into consideration. To demonstrate the power of this straightforward algorithm, the model shows how the side-mode suppression ratio in devices with high /spl kappa/L and a /spl lambda4: phase shift is significantly affected by the radiation in the second-order DFB laser. The time-dependent radiation pattern in grating-coupled surface-emitting lasers is also calculated for the first time. >

Large-signal dynamic model of the DFB laser

A computer model is proposed to analyze the characteristics of distributed feedback (DFB) lasers. The model is based on time-dependent coupled wave equations, with spontaneous emission taken into account. In order to avoid uncertain phase factors in spontaneous emission, a method of converting field equations to power equations in a matrix format before computation is introduced. The steady-state LI curve and transient response to the pulse excitation are calculated in the lambda /4 phase-shifted DFB lasers. The longitudinal variations of the carrier and photon densities as well as of the refractive index are considered in the model. >

Dynamics of monolithic passively mode-locked semiconductor lasers

Monolithic colliding pulse mode-locking (CPM) in semiconductor lasers is compared with self colliding pulse mode-locking (SCPM) through a large signal dynamic computer model which incorporates most of the significant features of semiconductor lasers. These include gain saturation, spontaneous emission, the gain-frequency relation, and the line-width enhancement factor. This new model replicates many of the published experimental results and also gives additional insight into the internal operation of the device. In particular, gain saturation combined with the standing waves created by colliding pulses within the saturable absorber produce a transient gain grating. This is found to have significant effects in locking either the even or the odd modes together in CPM. A performance comparison between CPM and SCPM is completed and some key design parameters of both configurations are explored. >

Semiconductor 1.55 /spl mu/m laser source with gigabit/second integrated electroabsorptive modulator

A 1.55 /spl mu/m laser source with low chirp and high speed can be achieved when a single-mode DFB laser is modulated by an integrated quantum-confined Stark effect electroabsorptive modulator. The dynamic characteristics of such a device are simulated by a time domain, large signal dynamic model. The simulation demonstrates that the frequency chirp has two components: 1) changes of the refractive index induced by variation of the absorption coefficient during the modulation and 2) changes in the lasing frequency caused by changes in the effective residual facet reflection as the external modulator is switched on and off. Optimization by choice of the operating wavelength and coupling coefficient in the lasing section is discussed. >

Chirp reduction using push-pull modulation of three-contact lasers

Low-chirp modulation of three-contact distributed-feedback (DFB) lasers is experimentally demonstrated, using a push-pull modulation scheme. When the laser was modulated with a 2.0-Gb/s pseudorandom bit sequence, the -20-dB linewidth was measured to be 0.055 nm after deconvolving the measurement equipments response. The results are simulated using a large-signal time-domain model that illustrates the mechanisms responsible for the low chirp. The grating structure is shown to have a significant effect on the performance of the device under push-pull modulation.<<ETX>>

Dynamic response of the gain-coupled DFB laser

Large signal dynamic responses of temporal and spectral characteristics for gain-coupled distributed-feedback (DFB) lasers are calculated by a computer model based on power matrix methods. Spontaneous emission, longitudinal effects of spatial hole burning and carrier-induced variations of the coupling coefficient have been taken into account. Both antireflection (AR)-coated and cleaved-facet devices are analyzed for the purely gain-coupled DFB. For partly gain-coupled DFBs, it is found that the dynamic behavior is dependent on the phase of the index and gain coupling. Low chirp operation can be achieved by having index and gain coupling in antiphase. >

Large-signal dynamic behavior of distributed-feedback lasers including lateral effects

The large-signal behavior of DFB lasers is analyzed, including lateral as well as longitudinal variations in carrier density, photon density, and refractive index. The effective index method and other approximations are used to reduce the complex three-dimensional problem to one dimension. The coupled wave and carrier rate equations are then solved in a self-consistent manner. Lateral spatial carrier hole burning and lateral diffusion are found to affect the relaxation oscillation frequency and damping rate of DFB lasers, depending on their detailed structure. The effective time-averaged linewidth enhancement factor is also affected. In symmetric AR-coated /spl lambda//4 phase-shifted lasers the side mode suppression ratio can be deteriorated significantly by lateral spatial hole burning when kL is large. >

Dynamic response of colliding-pulse mode-locked quantum-well lasers

The colliding-pulse mode-locked scheme, using quantum-well semiconductor lasers, has been reported to be useful for the generation of short optical pulses with a high repetition rate. In this paper, the large signal dynamic process of a monolithic colliding-pulse mode-locked laser diode is simulated using a large signal laser model. The refractive index changes induced by variations of the carrier density and the standing wave effect in the saturable absorber have been taken into account in the simulation. >

Dynamics of index coupled DFB lasers with minimal spatial hole burning

Spatial hole burning in quarter-wave phase-shifted DFB lasers can be significantly reduced by spatially varying the coupling coefficient in the longitudinal direction. For such a laser, time dependent spatial hole burning is examined using a large signal dynamic model established earlier. The transient power changes, frequency chirp during gain switching and side mode suppression ratio at steady state are also simulated.<<ETX>>