Toru Fukushima

High speed quantum-well lasers and carrier transport effects

Carrier transport can significantly affect the high-speed properties of quantum-well lasers. The authors have developed a model and derived analytical expressions for the modulation response, resonance frequency, damping rate, and K factor to include these effects. They show theoretically and experimentally that carrier transport can lead to significant low-frequency parasitic-like rolloff that reduces the modulation response by as much as a factor of six in quantum-well lasers. They also show that, in addition, it leads to a reduction in the effective differential gain and thus the resonance frequency, while the nonlinear gain compression factor remains largely unaffected by it. The authors present the temperature dependence data for the K factor as further evidence for the effects of carrier transport. >

Effects of carrier transport on high‐speed quantum well lasers

We present a model for the dynamic response of quantum well lasers which shows that the carrier transport across the separate confinement heterostructure region and the barriers can be critical in determining the modulation bandwidth. We also show that, depending on the particular quantum well laser structure, a large part of the experimentally measured reduction in modulation bandwidth is due to transport factors.

HIGH-SPEED INGAAS/GAAS STRAINED MULTIPLE QUANTUM WELL LASERS WITH LOW DAMPING

Strained In0.2Ga0.8As/GaAs multiple quantum well polyimide buried ridge waveguide lasers with 3 dB bandwidths of 20 GHz and K factors as low as 0.17 ns have been fabricated. This is the highest bandwidth and the lowest K factor reported to date for quantum well lasers in any material system or for lasers of the ridge waveguide geometry.

Long wavelength high-speed semiconductor lasers with carrier transport effects

Carrier transport has a significant effect on the high-speed characteristics of semiconductor lasers. The authors show theoretically and experimentally that the low frequency rolloff and excess increase of damping due to carrier transport significantly limits the high-speed modulation bandwidth of long wavelength InGaAs(P)-InP quantum-well lasers. The inherent small conduction band offset and small hole diffusion constant of this material are responsible for the severe carrier transport effects. The authors also discuss the optimum design for the high speed modulation of the long wavelength lasers and the advantages of the InGaAlAs-InP material system. >

Effect of strain on the resonant frequency and damping factor in InGaAs/InP multiple quantum well lasers

The intensity noise of strained InxGa1−xAs/InP multiple quantum well (MQW) lasers is measured for three types of strain: tensile strain (x=0.48), no strain (x=0.53), and compressive strain (x=0.65). From a comparison between the measured noise power spectral density and the theoretical one, the resonance frequency and the carrier damping factor of each type of lasers are calculated. Although compressive strained MQW lasers show abot 10% increase in resonance frequency compared to those of tensile strained and unstrained lasers, this increase is smaller than theoretically predicted. Most important, all three types of MQW lasers show about two to three times higher nonlinear gain saturation and lower maximum bandwidth than conventional double‐heterostructure lasers. A solution to reduce this high damping is also discussed.

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.

Temperature dependence of damping in high‐speed quantum‐well lasers

The temperature dependence of damping in quantum‐well lasers has been investigated. The lasers with large K factors at room temperature show a rapid increase of the K factor with temperature. The temperature dependence of the K factor is larger for lasers with wider separate confinement heterostructure region, fewer wells, and narrower quantum‐well width. The carrier transport in quantum‐well structures is responsible for the excess increase of the K factor at high temperatures.

Carrier transport effects in high-speed quantum-well lasers

ABSTRACT Carrier transport can significantly affect the high speed propeities of quantum well lasers. We have &xeloped amodel, and derived analytical expressions for the modulation response, resonance frequency, damping rale and K fftw toinclude these effects. We show theoretically and expenmentally that carrier transport can lead to significan low frequency parasitic-like rolloff that reduces the modulation response by as much as a ftor of six in quantum well 1ars. We also show that, in addition, it leads to a reduction in the effective differential gain and thus the resonance frequency, while thenonlinear gain compression ftor remains largely unaffected by it. In the presence of significant transport effects, we show that the real limit to the maximum possible modulation bandwidth is much lower than the one predicted by the K factor alone. 1. INTRODUCTION Quantum well lasers have been theoretically and experimentally shown to have a larger differential gain than bulklasers1 , but the modulation bandwidths reported in quantum well lasers have only recently been comparable to bulk

High speed semi-insulating GaInAsP laser processing

Semi-insulating (SI) planar buried heterostructure (SIPBH) lasers, designed to minimize device parasitics, have been fabricated for high-speed operation. The I-V characteristics of the Fe-doped SI InP employed for the current blocking layers were examined at elevated temperatures associated with high speed laser operation. It was found that the trap filled voltage, V/sub TF/, decreases linearly with increasing temperature. However, a SI InP layer with a V/sub TF/ at room temperature of 70 V demonstrated current blocking characteristics to temperatures in excess of 150 degrees C.<<ETX>>