Multiquantum-well Active Layer Research Articles

Circular beam emission from 1.3 mu m InGaAsP strained-multiquantum-well lasers

The beam divergence in the vertical direction from a graded index separate confinement heterostructure (GRINSCH) multiquantum-well (MQW) laser has been studied. It is demonstrated both theoretically and experimentally that a circular beam MQW laser can be produced by choosing appropriate thicknesses for the GRINSCH layers, while maintaining other desired laser characteristics. The beam divergence is found to be more affected by the index change induced by injected carriers than by strain in the MQW active layer. Theoretical results are in good agreement with the measurements for 1.3- mu m InGaAsP strained MQW lasers. >

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.

Narrow-linewidth (<200 kHz) operation of 1.5- mu m butt-jointed multiple-quantum-well distributed Bragg reflector laser

Linewidths as narrow as 200 kHz were achieved with a 1.5 mu m butt-jointed multiquantum-well (MQW) distributed Bragg reflector (DBR) laser. A low threshold current of 8 mA and a high output power of 28 mW were also realized, as well as narrow-linewidth operation. The device was fabricated by a five-step metalorganic vapor-phase epitaxy (MOVPE) process. These results were realized by introducing a high-quality MQW active layer, a long DBR region with a very small coupling coefficient, and a butt-jointed region with high coupling efficiency. >

Ultralow chirp and high-speed 1.55 mu m multiquantum well lambda /4-shifted DFB lasers

An ultra-low-chirp, high-speed, 1.55- mu m, multi-quantum-well (MQW), lambda /4-shifted, InGaAsP distributed-feedback (DFB) laser is demonstrated. A record chirp width of 0.4-0.5 nm (20-dB down full width) is achieved at 10-Gb/s direct modulation. This low-chirp single-longitudinal-mode operation is attained by an increase in the quantum size effect in the MQW active layer. >

High-power operation in self-sustained pulsating AlGaAs semiconductor lasers with multiquantum well active layer

Self-sustained pulsating optical power and kink level in AlGaAs semiconductor lasers are remarkably improved by introducing a multiquantum well (MQW) structure in the active layer. Stable fundamental transverse mode operation at output power up to 50 mW and self-sustained pulsation at output power up to 40 mW are obtained simultaneously for MQW lasers with antireflective and high-reflective coatings on the facets. Low-noise characteristics (relative intensity noise of less than 10−13 Hz−1 under 3–4% optical feedback) are obtained in the output power range from 7 to 17 mW in MQW lasers with high-reflective coating on the rear facet. These results suggest that low-noise high-power characteristics can be achieved in self-sustained pulsating lasers with a MQW active layer.

AlGaAs/GaAs lateral current injection multiquantum well (LCI-MQW) laser using impurity-induced disordering

A lateral current injection (LCI) multiquantum-well (MQW) laser having planar structure is proposed and its advantages compared with conventional vertical structure lasers. A LCI-MQW laser has been fabricated by using Si- and Zn-induced disordering of an MQW active layer. It is shown that a threshold current of 27 mA is achieved under pulsed current driven at room temperature and a very low stray capacitance of 0.27 pF is obtained at zero bias voltage.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

InGaAsP distributed feedback multiquantum well laser

The fabrication and performance characteristics of 1.3 μm InGaAsP distributed feedback (DFB) lasers with multiquantum well (MQW) active layers are reported. The lasers are of the double channel planar buried heterostructure type and utilize a second order grating with a periodicity of ∼3900 Å for frequency selective feedback. The lasers have threshold currents in the range 25–35 mA at 30 °C and external differential quantum efficiencies of 0.2 mW/mA/facet at 30 °C. The temperature dependence of threshold current is characterized by a T0 value of 95–100 K. The lasers have been operated to an output power of 19 mW in a single frequency. The measured dynamic linewidth under modulation is a factor of 2 smaller than that for regular double heterostructure lasers. The lower temperature dependence of threshold current and smaller dynamic linewidth make real index guided InGaAsP DFB MQW active layer lasers attractive for many system applications.

Long wavelength InGaAsP (λ∼1.3 μm) modified multiquantum well laser

The fabrication and performance characteristics of InGaAsP (λ∼1.3 μm) double channel planar buried heterostructure lasers with multiquantum well (MQW) active layers are reported. The MQW structure has λg∼1.3 μm InGaAsP active wells and λg∼1.03-μm InGaAsP barrier layers. The lasers have threshold current of ∼20 mA at 30 °C and external differential quantum efficiencies of ∼0.2 mW/mA/facet at 30 °C. The temperature dependence of threshold current is characterized by T0∼100 K both under electrical and optical pumping. The lasers have been operated to 110 °C and up to ∼30 mW/facet at 25 °C. The measured dynamic linewidth under modulation is ∼2 smaller than that for conventional double heterostructure lasers. The lower temperature dependence of threshold current and smaller dynamic linewidth makes real index-guided InGaAsP MQW active layer lasers potentially attractive for many system applications.

Gain measurements in InGaAsP multiquantum well lasers

This letter reports the polarization dependence and temperature dependence of gain spectrum in InGaAsP multiquantum well (MQW) lasers emitting at 13 μm. The gain of the TE mode is larger (by ∼40 cm−1) than that of the TM mode. The peak gain for the TM mode is shifted towards shorter wavelengths from that of the TE mode. This is because both light hole and heavy hole transitions contribute to TE emission whereas the TM emission is principally due to light hole transitions. The large gain difference between the TE and TM mode suggests that the occurrence of stress induced effects (e.g., light-current kinks) may be reduced in MQW active layer lasers. The net gain G is found to vary linearly with the injection current I. The slope dG/dI of the gain-current curve for these MQW lasers decreases with increasing temperature. However, the decrease is considerably smaller than that for conventional InGaAsP double heterostructure lasers. The smaller decrease is consistent with the observed lower temperature dependence of threshold (high T0) of the MQW lasers.

Fabrication and performance characteristics of InGaAsP ridge-guide distributed-feedback multiquantum-well lasers

The fabrication and performance characteristics of InGaAsP ridge-guide distributed-feedback lasers with multiquantum-well active layers are reported. The lasers are 320 μm long and have four active wells (300 A thick). The lasers have threshold current 100 mA at 30°C, external differential quantum efficiency 0.1 mW/mA/facet at 30°C and To 60 K and can be operated in the same DFB mode up to 70°C. The measured frequency chirp is about a factor of 3 smaller than that for conventional double-heterostructure lasers. The smaller chirp should allow larger repeater spacing for high-bit-rate long-distance fibre transmission systems applications.

1.3 μm InGaAsP DCPBH multiquantum-well lasers

We report the fabrication and performance characteristics of InGaAsP double-channel planar buried heterostructure (DCPBH) lasers with multiquantum-well active layers emitting at 1.3 μm. These lasers have threshold currents in the range 40–50 mA at 30°C, external differential quantum efficiencies of ̃50% at 30°C and T0 values ̃160 to 180 K in the temperature range 10–60°C.