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Degradation of GaN-based laser diodes (LDs) is studied using Electroluminescence (EL) and Transmission Electron Microscopy (TEM). The slope efficiency decrease is observed in addition to threshold current increase. Further studies on the optical loss and microstructures of the LDs indicate that the reduction of the slope efficiency is attributed to the increase of optical loss (from 14.2 cm−1 to 24.2 cm−1) and decrease of injection current efficiency induced by the defect generation around the waveguide and cladding layers. Injection current induced blue-shift of the spontaneous EL peak reduced after >3000 hrs operation, which is ascribed to the compensation of Quantum-Confined Stark Effect (QCSE) caused by partial strain relaxation near the active region. [ABSTRACT FROM AUTHOR]

Highlights • Study and analysis is focused on use of Group III-V material. • Discussion on structures, performances, and results related to some important works. • Comparison of some important characteristics of TI-MQW-TL by varying SCH width. • Proposed structure shows better performance than previously reported works. Abstract Transistor Laser has already established as a promising candidate for high speed optical interconnects and optical telecommunication networks. The present work is focused on the performance of multiple quantum wells (MQW) based transistor laser by incorporating tunnel injection phenomenon and it's performance by varying the width of the separate confinement heterostructure layer. The virtual state (VS) is assumed as a path for the movement of injected charge carriers from bulk to nanostructures. We have estimated the various characteristics such as base threshold current, light power output, and optical modulation response by considering various physical parameters such as diffusion time, gain compression factor, optical confinement factor, photon lifetime, tunneling time and diffusion length, as a function of separate confinement hetero-structure (SCH) layer thickness. It is found that with increasing thickness of the SCH layer, base threshold current reduces, the light output power increases, but the optical modulation response remains almost constant, which ensures the potentiality of the proposed structure for high speed opto-electronic transmitter with low power consumption. [ABSTRACT FROM AUTHOR]

Hybrid dc switches have become increasingly prominent due to their low ON-state energy loss and less arc erosion in comparison with conventional semiconductor and mechanical switches. Zero-voltage switching (ZVS) is a common method for realizing a hybrid dc switch. However, a certain amount of contact voltage rather than zero voltage is necessary for commutating the current into the semiconductor devices from the mechanical contacts, which may cause arc generation if the contact voltage exceeds the boiling voltage of the contact material. It has been found that current commutation can be accomplished without arc generation if the current is below a threshold value. It is important to determine and improve the threshold current of arc-less current commutation for suppressing arcing even under the condition of a high current load. In this paper, the effect of some parameters, including the contact diameter (10, 15, and 20 mm), separation speed (0.05–0.3 m/s), and cable inductance in the current commutation path (0.1 and $0.25~\mu \text{H}$) on the threshold current of the arc-less commutation, is investigated by using copper contacts. The results show that a larger contact diameter, slow separation speed, and small commutation cable inductance are good for the improvement of the threshold current of the arc-less commutation. A 200-A current commutation is realized without arc generation, particularly by applying a 20-mm-diameter contact, 0.05-m/s separation speed, and 0.1- $\mu \text{H}$ commutation cable inductance. [ABSTRACT FROM AUTHOR]

The gain spectrum and modulation characteristics of ridge-waveguide laser diodes with InAs/GaAs submonolayer (SML) stacks have been investigated in detail. A comparison between active regions with intentionally altered inhomogeneous broadening is presented. The inhomogeneous broadening is controlled via Sb incorporation into the SML allowing for broader gain bandwidth and 3-D confinement of holes. In that way, the degree of charge-carrier localization can be tuned at a given wavelength. A slight performance loss at a given operation wavelength is observed due to a smaller optical overlap for the intentionally broadened gain medium. Still, bit rates up to 17 GBit/s can be obtained with the prospect for wider wavelength tunability. Multiple stacks of Sb-containing SMLs are suggested to enhance the optical overlap, which eventually allows for widely tunable quantum-dot lasers with larger modulation bandwidth. [ABSTRACT FROM AUTHOR]

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This paper extends Johnson’s classical theory [Johnson, Proc. IRE 43, 684 (1955)] for the threshold of backward-wave oscillation (BWO) in a traveling-wave tube by considering the effects of: 1) small random variations of the circuit phase velocity along the tube axis and 2) end reflections. We find that both the BWO threshold and BWO frequency are minimally affected by random variations of the phase velocity, but we find that the oscillation threshold depends sensitively on the magnitude and phase of the composite reflection coefficients. [ABSTRACT FROM AUTHOR]

In this study, the authors propose a novel technique for generating ultrashort pulses using a semiconductor laser subject to strong optical feedback from short external cavities. The influence of three system parameters, viz. the external cavity length, the injection current and the feedback strength on the characteristics of the ultrashort pulses is numerically investigated. The results show that the pulse width decreases and the pulse peak increases with increase of any of these three parameters. The repetition frequency of the ultrashort pulses decreases with increase of the feedback strength but increases with increase of the injection current. Based on these results, ultrashort pulses with a pulse width of 3.6 ps and a repetition frequency of 2.3 GHz have been achieved when the injection current is four times the threshold current. The pulse width can be further decreased and the repetition frequency can be further increased by appropriately adjusting the external cavity length and feedback strength. The results presented in this study open up a new route for designing ultrashort pulse generators for incorporation in future photonic integrated optical circuits. [ABSTRACT FROM AUTHOR]

The effect of the changing doping concentration on performance of vertical cavity surface emitting laser at different temperatures was investigated. The lasing wavelength is 1.55 μm. The doping concentration was changed from 1016 to 1018 at each doping level; the performance of a multi-quantum-well (MQW) vertical cavity surface emitting laser (VCSEL) was evaluated at temperatures between 273 and 350 K. This article presents the dependency of some VCSEL specifications like threshold current, gain, maximum radiation power, and resonance wavelength to the doping concentration of distributed Bragg reflector (DBR) layers at different temperatures. The results show that when doping concentration decreases at constant temperature, optical gain decreases. The highest gain is achieved at 350 K and 4 x 1017 doping concentration. At constant doping concentration, threshold current increases as temperature increases. The worst case for threshold current was observed, at 1018 doping concentration in the DBR layers at 350 K. It was observed that in a particular doping concentration the resonance wavelength increased as the temperature enhanced and photon energy shows a downward shift. [ABSTRACT FROM AUTHOR]

We investigate unidirectionally emitting quantum cascade microcavity lasers with semicircle-patterned top contacts. We employ novel patterned top contacts while fabricating notched ellipse-shaped cavity lasers. We study experimentally the microcavity-structure-based quantum cascade (QC) laser material with a long infrared wavelength of ~10 μm. Then we characterize microcavity lasers with patterned contacts and compare them with nonpatterned ones and observe a lower operating injection threshold current as a consequence of this relatively straightforward technique, with the unidirectional emission feature being kept. We obtain a maximum light output peak power of 16 mW with unidirectional emission at a far-field divergence angle of ~7° at a full width of half maximum, while the patterned device shows low threshold even in the microcavity laser with a size of 150 μm. Furthermore, we also carry out a reliability test of the QC microcavity lasers with semicircle-patterned top contacts, and the testing results show no sudden failure or severe light-output-power drop during an operating time of thousand hours. [ABSTRACT FROM AUTHOR]

This paper presents temperature dependence of the refractive index, coupling factor, and threshold current in a distributed feedback (DFB) semiconductor laser with different grating amplitudes. It is shown that with increasing the temperature, the threshold current increases and the coupling factor decreases. In addition, the performance of DFB semiconductor lasers was theoretically investigated through deformed concave grating. According to calculation, symmetrical grating structures have the maximum coupling factor, which increases with the period of grating grooves. Finally, concave grating would improve the output power. Analysis in this research was done by simultaneously solving both the coupled wave and rate equations using the transfer matrix. [ABSTRACT FROM AUTHOR]

Directly current-modulated 980-nm vertical-cavity surface-emitting lasers (VCSELs) with oxide-aperture-diameters of 1.5 μm exhibit a small-signal -3 dB modulation bandwidth of 31 GHz and a single-mode light-output-power of 3 mW with a side-mode-suppression-ratio (SMSR) of 49 dB at 25 °C at a forward bias current of 3 mA. At 85 °C, the maximum bandwidth is about 25 GHz, the peak power is about 2 mW, and the SMSR remains 49 dB. The bandwidth for a 5.5-μm oxide-aperturediameter VCSEL reaches 26 and 21 GHz at 25 °C and 85 °C, respectively, with corresponding maximum multi-mode optical output power of about 10 and 6 mW. [ABSTRACT FROM PUBLISHER]

To advance on-chip optical interconnections, membrane distributed-reflector (DR) lasers with low threshold current and high-efficiency operation at one side output were realized. First, a membrane distributed Bragg reflector (DBR) laser with 80-μm-long active section and 50-μm-long DBR section was fabricated to clarify the DBR reflectivity. An external differential quantum efficiency of 35% for the output from the front facet was obtained, and the DBR reflectivity was estimated to be 75%. Next, a membrane DR laser with 61- μm-long distributed feedback section and 50-μm-long DBR section was fabricated. A threshold current of 0.48 mA, external differential quantum efficiency from the front side waveguide of 26%, and light output ratio from the front to the rear sides of 13 were obtained. The lasing spectrum showed a single-mode operation with a side-mode suppression-ratio (SMSR) of 40 dB. Finally, small-signal direct modulation was carried out and a modulation current efficiency factor of 7.9 GHz/mA1/2 and 7 GHz/mA1/2 were, respectively, obtained for the 30-μm-long and 61-μm-long devices. [ABSTRACT FROM PUBLISHER]

Five-element phase-locked arrays of 4.7 μm-emitting quantum cascade lasers are demonstrated which operate either in a near-diffraction-limited (D.L.) beam to 3.6 W peak pulsed power or in a narrow beam (< 3.5 × D.L.) up to 6.1 W peak pulsed power. Devices are fabricated by a two-step MOCVD process and operate predominantly in an in-phase array mode, in agreement with design-simulation studies. Analysis based on the actual device dimensions indicate that near-resonant leaky-wave coupling occurs. Scaling to a larger number of array elements and optimization for resonant operation is expected to lead to further increases in output power while maintaining high beam quality. [ABSTRACT FROM PUBLISHER]