Intrinsic Modulation Response Research Articles

Wide-Bandwidth and High-Sensitivity Measurement Technique of Intrinsic Modulation Response of Semiconductor Lasers

Wide-Bandwidth and High-Sensitivity Measurement Technique of Intrinsic Modulation Response of Semiconductor Lasers

Equivalent Circuit Model of High-Performance VCSELs

In this work, a general equivalent circuit model based on the carrier reservoir splitting approach in high-performance multi-mode vertical-cavity surface-emitting lasers (VCSELs) is presented. This model accurately describes the intrinsic dynamic behavior of these VCSELs for the case where the lasing modes do not share a common carrier reservoir. Moreover, this circuit model is derived from advanced multi-mode rate equations that take into account the effect of spatial hole-burning, gain compression, and inhomogeneity in the carrier distribution between the lasing mode ensembles. The validity of the model is confirmed through simulation of the intrinsic modulation response of these lasers.

Advanced VCSEL Technology: Self-Heating and Intrinsic Modulation Response

Experimental data and modeling results are presented for a new type of vertical-cavity surface-emitting laser (VCSEL) that solves numerous problems with oxide VCSELs. In addition, the new oxide-free VCSEL can be scaled to small size. Modeling shows that this small size can dramatically increase the speed of the laser through control of self-heating. Modeling compared with both the oxide and the new oxide-free VCSEL predict intrinsic modulation speed for room temperature approaching 80 GHz, indicating the potential for > 100-Gb/s data speed from directly modulated VCSELs. The modeling is one of if not the first to include self-heating and spectral detuning between the gain and the cavity resonance that results from self-heating. The modeling results accurately accounts for the saturation in modulation speed in very high-speed oxide VCSELs operating at high temperature and accounts for the temperature of differential gain and photon density in limiting speed. Saturation of the photon density is found to limit the ultimate intrinsic speed. Differential gain decreases with increasing temperature but with sufficiently weak temperature dependence that it is not found to limit the VCSEL speed.

Intrinsic Dynamics of Quantum-Dash Lasers

Temperature-dependent intrinsic modulation response of InAs/InAlGaAs quantum-dash lasers was investigated by using pulse optical injection modulation to minimize the effects of parasitics and self-heating. Compared to typical quantum-well lasers, the quantum-dash lasers were found to have comparable differential gain but approximately twice the gain compression factor, probably due to carrier heating by free-carrier absorption, as opposed to stimulated transition. Therefore, the narrower modulation bandwidth of the quantum-dash lasers than that of quantum-well lasers was attributed to their higher gain compression factor. In addition, as expected, quantum-dash lasers with relatively long and uniform dashes exhibit higher temperature stability than quantum-well lasers. However, the lasers with relatively short and nonuniform dashes exhibit stronger temperature dependence, probably due to their higher surface-to-volume ratio and nonuniform dash sizes.

A microwave photonic phase-shifter based on wavelength conversion in a DFB laser

We propose and demonstrate a microwave photonic phase-shifter using a distributed-feedback laser-wavelength converter. Through carrier competition in the laser, information is passed from the input signal to the lasing mode. The frequency response of this conversion mechanism follows the intrinsic modulation response of the laser, which exhibits a large phase change near the relaxation frequency. Through current-control of the relaxation frequency, the phase of the wavelength-converted microwave output can be varied by more than 135deg over a bandwidth of 1.8GHz. We further identify an operating regime that exhibits a large discrete phase shift of 114deg at 3 GHz with negligible change in power

Intrinsic modulation bandwidth of strained GaInP/AlGaInP quantum well lasers

We have investigated the intrinsic modulation response of GaxIn1-xP/AlGaInP quantum well lasers. The differential gain resulting from the measurement of the frequency response, is in good agreement with calculations based on a 6-band kp-theory and direct measurements of the optical gain. We find a maximum value of 3.8×10−16 cm2 for a strongly compressively strained sample, which is less than in InGaAs lasers according to the larger effective masses. The maximum bandwidth we observed is 9.3 GHz at −3 dB. We show that the bandwidth is limited by catastrophic optical damage and not by intrinsic mechanisms.

Strain effect on K factor, differential gain and nonlinear gain coefficient for InGaAs/InGaAsP strained multiquantum well lasers

The strain effect on the K factor, the differential gain and the nonlinear gain coefficient for InGaAs/InGaAsP tensile-strained and compressive-strained multiquantum well (MQW) lasers is experimentally investigated from the intrinsic modulation response. The differential gain increases with an increase in strain for both types of laser. The strain dependence of the nonlinear gain coefficient is not as high as that of the differential gain. Therefore, the K factor for strained MQW lasers mainly results from the differential gain.

High-Speed Dynamics in InP Based Multiple Quantum Well Lasers

In this paper, the problem of low frequency rolloff and limited bandwidth in long wavelength InP based multiple quantum well (MQW) lasers is discussed by investigating the dependence of resonance frequency and the damping factor on the strain, and structural design of the wells and barriers. To explain the small bandwidth, we use a model of the carrier transport effect with two parts of the carrier density, inside and outside of the quantum wells. The dependence of the K factor on the operating temperature is investigated, and the results of this measurement are found to fully support the proposed carrier transport model. The solutions to this carrier transport problem are discussed. Finally, we propose a measurement method of the intrinsic modulation response free from the carrier transport effect.

1.5 μm compressive-strained multiquantum-well 20-wavelength distributed-feedback laser arrays

The wide gain spectrum of compressive-strained multiquantum-well active layers was used to fabricate 20-wavelength distributed-feedback laser arrays. A record wide wavelength span of 131 nm in the 1.5/μm wavelength region was demonstrated. The maximum intrinsic modulation response, measured by a parasitic-free optical modulation technique, reaches 16 GHz.

Parasitic-free modulation of semiconductor lasers

Active-layer photomixing is a technique for modulating semiconductor lasers with nearly perfect immunity to device parasitics. Measurements of the intrinsic modulation response of a laser diode using this technique at temperatures as low as 4.2 K are discussed. From these measurements, the temperature dependence of important dynamical parameters is determined. In addition, this provides a stringent test of the active-layer photomixing technique since parasitic response is degraded, while the intrinsic response is improved for low-temperature operation. At 4.2 K, the ideal intrinsic response is measured for frequencies as high as 15 GHz despite an estimated parasitic corner frequency of 410 MHz. >

Low-temperature measurement of the fundamental frequency response of a semiconductor laser by active-layer photomixing

We use the active-layer photomixing technique to directly modulate the output of a GaAs semiconductor laser operating at temperatures as low as 4.2 K. The technique produces modulation with nearly perfect immunity to device parasitic effects, revealing the laser diode’s intrinsic modulation response. At 4.2 K the parasitic corner frequency is estimated to be 410 MHz, yet the response appears ideal out to 15 GHz. We measure the dynamical parameters governing the response function, the relaxation resonance frequency, and the damping rate, and discuss their low-temperature behavior.

Superluminescent damping of relaxation resonance in the modulation response of GaAs lasers

It is demonstrated experimentally that the intrinsic modulation response of injection lasers can be modified by reducing mirror reflectivities, which leads to suppression of relaxation oscillation resonance and a reduction of nonlinear distortions up to multi-GHz frequencies. A totally flat response with a 3-dB bandwidth of 5 GHz was obtained using antireflection coated buried heterostructure lasers fabricated on a semi-insulating substrate. Harmonic distortions were below 40 dB within the entire 3-dB bandwidth. These results are in accord with theoretical predictions based on an analysis which include the effects of superluminescence in the laser cavity.