Maciej Bugajski - Academia.edu (original) (raw)

Papers by Maciej Bugajski

In this paper, the study of AlInAs/InGaAs/InP Quantum Cascade Lasers application in Free Space Op... more In this paper, the study of AlInAs/InGaAs/InP Quantum Cascade Lasers application in Free Space Optical data link is performed. Implementation of such FSO link operated in long-wavelength infrared (LWIR: 8-12 μm) will be unique for construction of so-called RF/FSO hybrid communication system. The range of longer wavelengths provides better data transfer performance in the case of severe weather conditions, especially, fog, low haze or air turbulence. In the frame of this work, series of QCLs for application in FSO system were examined. They are characterized by different geometries and constructions towards best performance in optical link systems operated in the wavelength range of 8-12 μm. The preliminary test of QCLs included electrical measurements of pulsed light-current-voltage characteristics and time-resolved spectra. The obtained results made it possible to determine operation point for FSO. Their modulation performances were tested using the laboratory laser drivers. Based ...

Novel In-Plane Semiconductor Lasers XVIII, 2019

The paper focuses on the design, fabrication and characterization of monolithic, coupled cavity t... more The paper focuses on the design, fabrication and characterization of monolithic, coupled cavity two-section quantum cascade lasers. The devices were fabricated by reactive ion etching from InP-based heterostructure designed for emission in 9.x micrometer range. To make the device attractive for sensing applications, the idea of the coupled-cavity device was employed, giving the possibility of single longitudinal mode operation. We have previously presented devices fabricated by means of focused ion beam post-processing. However, FIB etching is challenging and time-consuming. In order to overcome the relatively low throughput of the FIB process, in this work, gaps separating sections were defined by dry etching during the fabrication process. Careful optimization of the dry etching process resulted in very good control of gap geometry. Quality of mirrors formed by RIE did not introduce high scattering loss into the cavity, as the threshold current density was not increased significan...

In conventional LEDs it is diff icult to achieve high quantum efficiencies. High difference betwe... more In conventional LEDs it is diff icult to achieve high quantum efficiencies. High difference between the refractive index of GaAs and the air results in low criti cal angle and extraction eff iciency of the order of 2% for isotropic light source. On the other hand if the light source is placed in side a microcavity the emitted light is coupled to the cavity modes and if the proper design is applied it can be completely extracted [1]. In recent years due to development of the nano-scale semiconductors technologies a number of optoelectronic devices employing microcavity structures were proposed. The most notable examples of such devices are Resonant Cavity Light Emitting Diodes (RC LED) realized in the early nineties [2]. The main advantages of resonant cavity LEDs over conventional devices are higher emission intensities, higher spectral purity and more directional emission patterns. In RC LED the record external quantum eff iciencies in excess of 20% have been reported [1]. All abov...

PRZEGLĄD ELEKTROTECHNICZNY, 2018

IEEE Journal of Selected Topics in Quantum Electronics, 2019

In this work design, fabrication and characterization of mid-infrared AlInAs/InGaAs/InP QCLs tape... more In this work design, fabrication and characterization of mid-infrared AlInAs/InGaAs/InP QCLs taper quantum cascade lasers are presented. In order to increase output power while keeping good beam quality, taper design of resonator was used. We have studied devices emitting at 4.5 µm with different shapes (linear, concave and convex) and angles of taper waveguide section, to optimize the output beam parameters, namely M 2 and brightness. Experimental results demonstrate that convex geometry taper laser with 1.7°taper shows the best performance, the highest output power up to 5 W and the smallest horizontal beam divergence of 5.6°in the fundamental mode. This design is also characterized by the highest brightness.

Applied Physics B, 2018

Tuning the wavelength of emitted radiation is a tremendous feature of quantum cascade lasers whic... more Tuning the wavelength of emitted radiation is a tremendous feature of quantum cascade lasers which enables their use in various applications. Usually, this tuning is executed by the change of the bias current or the temperature. In this paper, it is demonstrated, both experimentally and theoretically, that yet another possibility of tuning laser wavelength offers the change of doping density. For the experimental demonstration, a set of GaAs/AlGaAs devices emitting in the range 9.3-9.7 µ m was MBE grown and processed. For the theoretical analysis, the simulations that employ nonequilibrium Green's function formalism, applied to the single-band effective mass Hamiltonian, are used. The analysis shows that the physical mechanism responsible for wavelength-doping correlation is a linear Stark effect. The range of tuning is limited on both low and high doping side. Both these limits are established and discussed.

Microelectronics Reliability, 2019

In this paper external degradation type of failure of Quantum Cascade Laser is analyzed. The fail... more In this paper external degradation type of failure of Quantum Cascade Laser is analyzed. The failure mode discussed in the work is connected with the damage of the gold, top electrode. We show how fabrication faults translate to degradation of device and monitor temperature distributions as well as electrical characteristics of the device during the process. The aim of this research is to demonstrate how external degradation process develops in case of AlInAs/ InGaAs/InP quantum cascade lasers.

Physica Scripta, 1999

The quantum physics of light is a most fascinating field. Here I present a very personal viewpoin... more The quantum physics of light is a most fascinating field. Here I present a very personal viewpoint, focusing on my own path to quantum entanglement and then on to applications. I have been fascinated by quantum physics ever since I heard about it for the first time in school. The theory struck me immediately for two reasons: (1) its immense mathematical beauty, and (2) the unparalleled precision to which its predictions have been verified again and again. Particularly fascinating for me were the predictions of quantum mechanics for individual particles, individual quantum systems. Surprisingly, the experimental realization of many of these fundamental phenomena has led to novel ideas for applications. Starting from my early experiments with neutrons, I later became interested in quantum entanglement, initially focusing on multi-particle entanglement like GHZ states. This work opened the experimental possibility to do quantum teleportation and quantum hyper-dense coding. The latter became the first entanglement-based quantum experiment breaking a classical limitation. One of the most fascinating phenomena is entanglement swapping, the teleportation of an entangled state. This phenomenon is fundamentally interesting because it can entangle two pairs of particles which do not share any common past. Surprisingly, it also became an important ingredient in a number of applications, including quantum repeaters which will connect future quantum computers with each other. Another application is entanglement-based quantum cryptography where I present some recent long-distance experiments. Entanglement swapping has also been applied in very recent so-called loophole-free tests of Bell's theorem. Within the physics community such loophole-free experiments are perceived as providing nearly definitive proof that local realism is untenable. While, out of principle, local realism can never be excluded entirely, the 2015 achievements narrow down the remaining possibilities for local realistic explanations of the quantum phenomenon of entanglement in a significant way. These experiments may go down in the history books of science. Future experiments will address particularly the freedom-of-choice loophole using cosmic sources of randomness. Such experiments confirm that unconditionally secure quantum cryptography is possible, since quantum cryptography based on Bell's theorem can provide unconditional security. The fact that the experiments were loophole-free proves that an eavesdropper cannot avoid detection in an experiment that correctly follows the protocol. I finally discuss some recent experiments with single-and entangled-photon states in higher dimensions. Such experiments realized quantum entanglement between two photons, each with quantum numbers beyond 10 000 and also simultaneous entanglement of two photons where each carries more than 100 dimensions. Thus they offer the possibility of quantum communication with more than one bit or qubit per photon. The paper concludes discussing Einstein's contributions and viewpoints of quantum mechanics. Even if some of his positions are not supported by recent experiments, he has to be given credit for the fact that his analysis of fundamental issues gave rise to developments which led to a new information technology. Finally, I reflect on some of the lessons learned by the fact that Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Japanese Journal of Applied Physics, 2017

In this paper accurate measurements of temperature distribution on the facet of GaN-based diode l... more In this paper accurate measurements of temperature distribution on the facet of GaN-based diode lasers are presented as well as development of the instrumentation for high-resolution thermal imaging based on thermoreflectance. It is shown that thermoreflectance can be successfully applied to provide information on heat dissipation in these devices. We demonstrate the quantitative measurements of the temperature profiles and highresolution temperature maps on the front facet of nitride lasers and prove that thermoreflectance spectroscopy can be considered as the accurate and fast nondestructive tool for investigation of thermally induced degradation modes of GaN lasers.

Acta Physica Polonica A, 1998

We have studied an enhancement of the oscillator strength for optical transitions near the Fermi ... more We have studied an enhancement of the oscillator strength for optical transitions near the Fermi energy in p-type modulation-doped quantum wells, which, so far, deserved much less attention than analogous n-type systems, because of the complicated valence band structure involved. The relatively wide (L = 150 Å) quantum wells and high doping levels were used, containing more than one occupied subband. The enhancement in the photoluminescence intensity at the Fermi energy resulted from the strong correlation and multiple scattering of holes near the Fermi edge by the localized electrons. .

2016 18th International Conference on Transparent Optical Networks (ICTON), 2016

In this paper, we present the absorption edge of (InAs)6ML/(GaSb)n superlattices, which has been ... more In this paper, we present the absorption edge of (InAs)6ML/(GaSb)n superlattices, which has been determined with the use of the 8-band k·p method. The aim of the work was to develop a numerical tool, which gives the possibility to design InAs/GaSb superlattices for infrared detector structures. Most of works, which were published in this field till now, present the results of electronic states calculations performed with the use of the Empirical Pseudopotential Method (EPM) or Envelope Function Approximation (EFA) method. In this work we report on the results of simulations performed with the use of the 8-band k·p method, in which we have considered strain in a superlattice structure and the effects of heavy and light holes interaction at the interfaces in a superlattice. Calculations have been performed for the structures with asymmetric interfaces (i.e., InSb and GaAs ones). Superlattices grown on GaSb substrates were considered and a temperature of 0K was assumed. Results of simulations are in a good agreement with the results of PL spectra and absorbance measurements, which are presented in the literature. They are also in a good agreement with the results of simulations performed with the use of EPM and EFA methods.

Acta Physica Polonica A, 2002

Pr oceed in gs of t he Co n f er ence \ F rom Qu an t um Op t i cs t o Ph o t on i cs" , Z ak opa... more Pr oceed in gs of t he Co n f er ence \ F rom Qu an t um Op t i cs t o Ph o t on i cs" , Z ak opa n e 200 1

Microelectronics Reliability, 2015

Focused ion beam (FIB) systems have become very useful tools used in the nanotechnology because t... more Focused ion beam (FIB) systems have become very useful tools used in the nanotechnology because they provide easy prototyping or post-processing customization of individual devices. A practical application of such postprocessing is modification of monolithic quantum cascade laser (QCL) to obtain the structure with coupled cavities (CC-QCL), enabling its single mode performance, critical in many QCL applications. In-situ electrical measurements of the test structures showed that the main problem is avoiding a secondary deposition of the milled material. The redeposition can significantly reduce the performance and reliability of lasers. An avoidance of FIB imaging after final FIB cleaning of walls was revealed as an important factor leading to high quality of structures. The paper describes the solution by developing appropriate patterning procedure. This enabled the formation of exemplary single mode CC-QCLs with excellent performance at 9.45 μm wavelength with 30 dB side-mode suppression ratio, operating at room temperature. Performance of obtained single-mode coupled cavity quantum cascade lasers was stable, repeatable and no reliability problems were observed.

SPIE Proceedings, 2012

ABSTRACT We report on the study of the temperature influence on optical and electrical performanc... more ABSTRACT We report on the study of the temperature influence on optical and electrical performance of the mid-IR GaAs/AlGaAs QCLs. The temperature dependence of the threshold current, output power, slope efficiency, wall-plug efficiency, characteristic temperatures T0 and T1, and waveguide losses is investigated. In addition, the influence of different mesa dimensions on the QCL parameters is analyzed. Experimental results clearly indicate that among the examined geometries the 25μm wide mesa devices exhibit the best operational parameters i.e., the highest Tmax and T0, highest wall-plug and slope efficiency, as well as a small temperature increases and the smallest thermal resistivity in the active area. The knowledge of the above parameters is crucial for designing GaAs/AlGaAs-based devices for high temperature operation.ÂÂ¬Â«

In this paper, we present a natural method of finding wavefunctions and energy levels in quantum ... more In this paper, we present a natural method of finding wavefunctions and energy levels in quantum cascade lasers. The envelope function approximation has been successfully used for modelling electronic structure in conventional semiconductor lasers. Although calculations in the case of polarized potential are more complicated than in non-polarized wells, it is still possible to obtain quickly reliable results.

Optical and Quantum Electronics, 2014

In this paper we investigate chip bonding technology of GaAs/AlGaAs quantum cascade lasers (QCLs)... more In this paper we investigate chip bonding technology of GaAs/AlGaAs quantum cascade lasers (QCLs). Its results have strong influence on final performance of devices and are essential for achieving room temperature operation. Various solders were investigated and compared in terms of their thermal resistance and induced stress. The spatially resolved photoluminescence technique has been applied for a device thermal analysis. The soldering quality was also investigated by means of a scanning acoustic microscopy. The particular attention has been paid to Au-Au die bonding, which seems to be a promising alternative to the choice between hard and soft solder bonding of GaAs/AlGaAs QCLs operating from cryogenic temperatures up to room temperatures. A good quality direct Au-Au bonding was achieved for bonding parameters comparable with the ones typical for AuSn eutectic bonding process. High performance room temperature operation of GaAs/AlGaAs QCLs has been achieved with the state-of-the-art parameters.

Physical Review B, 2000

Many-body effects have been optically investigated for modulation-doped quantum wells at high acc... more Many-body effects have been optically investigated for modulation-doped quantum wells at high acceptor densities. The observed band-gap shrinkage, up to Ϸ20 meV, is consistent with calculations based on the Hartree and random-phase approximations including the finite well width effect. A recombination near the Fermi edge with light-hole character is strikingly enhanced at high acceptor densities. An interpretation based on carrier-carrier interaction is proposed. Finally, the exciton is found to be quenched for hole densities higher than Ϸ2ϫ10 12 cm Ϫ2 .

Photonics Letters of Poland, 2013

We present experimental evidence for a mid-infrared frequency comb based on AlGaAs/GaAs quantum c... more We present experimental evidence for a mid-infrared frequency comb based on AlGaAs/GaAs quantum cascade laser. The comb-like emission spectra span over ~50cm-1 at a center wavenumber ~1080cm-1. The measured width of the comb lines is  20MHz. The instability sets in when the intracavity power is sufficiently large. In addition, intersubband transitions feature strong third-order optical nonlinearities  (3) , due to a large matrix element between the upper and lower laser states, allowing a parametric process, due to four-wave mixing. The observed spectral behavior is similar, in many ways, to the Risken-Nummedal-Graham-Haken (RNGH) instability.