Guang-Hua Duan

Analysis of the phase-amplitude coupling factor and spectral linewidth of distributed feedback and composite-cavity semiconductor lasers

A Greens function approach to the analysis of semiconductor lasers is formulated in a form suitable for complex cavity structures. Both the spontaneous emission rate and the effective phase-amplitude coupling factor can be accurately evaluated. For distributed-feedback (DFB) lasers, the spontaneous emission rate is strongly dependent on both the facet reflectivities and the grating coupling coefficients. The effective phase-amplitude coupling factor depends on the wavelength detuning from the gain maximum. The calculated linewidth of DFB lasers differs considerably from previous calculated results and gives better agreement with experimental results. For composite-cavity lasers, the frequency dependence of the equivalent reflectivity has a strong impact on the phase-amplitude coupling factor and the spontaneous emission rate. Distributed Bragg reflector (DBR) lasers are investigated as an example of a composite-cavity structure. >

Dynamic and noise properties of tunable multielectrode semiconductor lasers including spatial hole burning and nonlinear gain

A general formalism based on the Greens function method is given for multielectrode semiconductor lasers. The effects of both spatial hole burning and nonlinear gain are included in this formalism. An effective nonlinear gain is introduced by taking into account the influence of the laser structure and the associated distribution of the mode intensity along the cavity length and the frequency and intensity modulation properties of multielectrode semiconductor lasers are studied. A general linewidth expression which includes contributions from spontaneous emission and carrier shot noise is given. It is found that the effective alpha -factor affecting the linewidth is in general different from its counterpart affecting modulation and injection locking properties due to spatial hole burning and nonlinear gain. The linewidth due to various contributions is calculated for both uniform intensity distributed lasers and phase-shifted distributed feedback (DFB) lasers. >

Self-pulsation in multielectrode distributed feedback lasers

Measurements on multielectrode distributed feedback (DFB) lasers without a saturable absorber reveal the existence of a self-pulsation (SP) regime. In this regime, the laser remains in the same single-longitudinal mode with simultaneous intensity and frequency modulation. The laser spectrum is similar to that of a current-modulated single-mode laser. At the up-limit of the SP regime, the behavior between the output power and the injection current becomes bistable. In one branch of the bistable loop, the SP laser presents a very large spectrum without distinguishable peaks, a kind of chaotic state with coherence collapse. A qualitative explanation based on the effective differential gain is given for the origin of SP and associated phenomena in these lasers.<<ETX>>

Modeling and measurement of bistable semiconductor lasers

A theoretical model of bistable semiconductor lasers (BSL) under optical triggering is proposed, which takes into account the amplification and absorption processes in the laser structure. It has been found that the main factor limiting the highspeed operation of BSLs is the carrier lifetime in the absorber. A novel solution has been proposed consisting of bombarding the absorber with a proton beam. This paper presents the first experimental and theoretical results on the transition time and the turn-on jitter of such a BSL with optical triggering. Measurements on bulk and multiple quantum well BSLs revealed the dependence law of transition time and turn-on jitter on the injection currents. It has been found that, for a constant current in one active section, the rise time decreases but the fall time increases with injection current in the other section. An optimal current value can then be found to minimize the overall transition time. The measured turn-on jitter and relaxation oscillation period decrease with increasing injection current, in good agreement with theoretical predictions. 2.5 Gb/s optical triggering with a bit-error-rate less than 10/sup -9/ is demonstrated, for the first time, by using such a BSL without electrical reset. >

Linewidth rebroadening due to nonlinear gain and index induced by carrier heating in strained quantum-well lasers

The carrier heating has been recently recognized as one of the main origins of nonlinear gain, in particular in strained quantum-well lasers. The asymmetry of this effect introduces a nonlinear refractive index. The joint effects of nonlinear gain and nonlinear refractive index that are both due to carrier heating together with the spatial-hole-burning give rise to an increase in the carrier density and in the linewidth enhancement factor. These effects can explain the linewidth rebroadening at high power in phase-shifted single-mode DFB lasers.

Determination of nonlinear gain coefficient of semiconductor lasers from above threshold spontaneous emission measurement

The measurement of spontaneous emission power above threshold has shown a nearly linear increase with biasing current in a 1.55-/spl mu/m InGaAs/InGaAlAs multiple quantum-well laser. Based on this measurement, we propose a novel experimental method to determine the nonlinear gain coefficient. The obtained value is 1.2/spl times/10/sup -17/ cm/sup 3/ for the laser used. This value corresponds reasonably to that obtained by chirp-to-modulated-power ratio method, confirming the validity of this new measurement method.<<ETX>>

Modeling and measurement of spatial-hole-burning supplied to amplitude modulated coupling distributed feedback lasers

This work presents a theoretical and experimental study of the spatial hole burning (SHB) applied to phase-shifted amplitude modulated coupling (AMC) distributed feedback (DFB) lasers. Greens function method is used in our model and a new development of this method allows us to calculate the side-mode power. A transverse model is developed allowing the calculation of the spatially dependent refractive index and coupling coefficient from the designed AMC-DFB laser structures. Modeling results show that the effective index variation, associated with that of the coupling coefficient, plays an important role in affecting the lasers characteristics and has to be balanced to improve single-mode behavior. The SHB is studied experimentally by measuring the spontaneous emission radiated from a transparent window inside the electrode. The results clearly show, for the first time, the existence of a hole in the carrier density distribution due to the /spl lambda//4 phase-shift in a highly coupled laser. Both the measured and the calculated SHB are in agreement. >

Drive current noise induced linewidth in tunable multielectrode lasers

It is shown that drive current noise could lead to an important increase of linewidth and a Gaussian line shape of tunable multielectrode distributed Bragg reflector (DBR) lasers. As an example, the drive current noise induced linewidth (DCNIL) has been measured to be about 120 MHz using a standard DC source through at 50 Omega resistor to drive the Bragg section of a tested DBR laser. For tunable lasers with an electronic tuning efficiency of more than 1 GHz/mA ultralow noise current sources should be used to ensure a negligible DCNIL.<<ETX>>

Strong signal analysis of optical nonlinearities in single-quantum-well and double-heterostructure lasers

Based on the numerical strong signal solution of the density-matrix formalism, the nonlinearities of the gain and the refractive index are discussed for both bulk double-heterostructure (DH) and single-quantum-well (SQW) InGaAs lasers. The results show that for both structures the nonlinear gain is well approximated by the recently proposed analytical expression and the modified two-level system approximation up to a range of photon density discussed herein, and the refractive index could either increase or decrease with the photon density depending on the wavelength detuning from the gain peak. The results of a new analytical expression for nonlinear refractive index is in qualitative agreement with the numerical ones; however, significant quantitative difference occurs between these two model results for high photon density values. Due to the more important nonlinear gain in SQW structures, the linewidth enhancement factor increases more rapidly with increasing photon density in these structures than in DH structures.<<ETX>>

Nonuniform injection current induced unusual chirp behavior of a four-electrode bistable distributed Bragg reflector laser

A complete analysis of the chirp of a four-electrode bistable distributed Bragg reflector laser is given in theory and by experiment. Experimentally, the chirp investigation is realized by a Mach-Zehnder interferometer. In small-signal regime, the modulus and phase of 2/spl beta//m, frequency and amplitude modulation index ratio, is measured for different injection currents and shows an unusual behavior against the modulation frequency. A theoretical model including nonuniform injection current shows the same behavior of 2/spl beta//m against the modulation frequency and proves that the nonuniform carrier distribution inside the cavity is the origin of the specific behavior. The large-signal analysis provides a study of the instantaneous chirp behavior during optical switching. >