arXiv subjects

Mircea Guina

Publications and source records attributed to Mircea Guina.

At least 19 recordsLinked to original sources

arXiv2026

Predictive wavelength tailoring of uniform GaSb-based quantum dots for emission at 1.55 um

A detailed study of emission wavelength tailoring of GaSb-based QDs formed by InGaSb-filling of droplet-etched nanoholes in AlGaSb is presented. The study shows that the emission wavelength can be modified from 1.48 um to the center of the telecom C-band at 1.55 mm by independently varying the QD composition and size. More specifically, the optical transition energy shifts linearly as a function of In-content of the QD material at a rate of -4.4 meV/In-percentage, and with the number of monolayers (ML) of material used for filling the nanoholes, at -2.0 meV/ML. These experimentally observed energy shifts are well predicted by simulations yielding rates of -4.3 meV/In-percentage and -2.1 meV/ML, respectively. For the simulation, a uniform In composition, low intermixing, and microscopically measured QD geometry is considered. Additionally, excellent ensemble QD uniformity, with unprecedented inhomogeneous broadening well-below 7 meV across all samples is demonstrated. Finally, photoluminescence of single-QDs reveals narrow excitonic emission lines of 13.8+/-6.7 ueV and low fine-structure splitting values reaching <10 ueV. These results identify GaSb-based LDE QDs as a tunable telecom platform for scaling quantum-photonic applications over long-haul optical fiber networks.

cond-mat.mes-hall↗

arXiv2026

Low optical loss electrical isolation for multi-section monolithic GaSb-based photonic circuits

Monolithic photonic integrated circuits (PICs) platforms exploiting III-V materials combine passive and active waveguide structures in multi-section optoelectronic device architectures. Their operation requires high electrical isolation between adjacent functional sections without compromising the optical signal. This fundamental requirement is addressed for GaSb-based waveguides, which are known to exhibit high conductivity of p-type layers reducing the electrical isolation capability. To this end, a co-designed electrical-optical isolation strategy based on using deeply etched strip waveguides combined with adiabatic ridge-to-strip waveguide tapers in GaSb-based multiple-quantum-well heterostructures is proposed. While deep etching alone enables isolation resistances of up to 40 k-ohm, it severely degrades optical propagation. By introducing optimized adiabatic tapers, we demonstrate good optical performance as single-mode continuous-wave lasing in a two-section device with integrated absorber, while maintaining an isolation resistance of 17.3 k-ohm; this corresponds to an approximately 17-fold improvement over previously reported GaSb two-section devices. The approach establishes a critical building block for the development of monolithic GaSb-based PICs operating above 2 um.

physics.optics↗

arXiv2026

Infrared photonics for healthcare: A roadmap for proactive and predictive health management

The field of infrared (IR) photonics is currently undergoing remarkable progress, moving rapidly towards practical sensing applications demanded by medical therapy and diagnostics (theranostics). The Developments can be divided into three main categories: (i) novel devices and measurement concepts including advanced updates of classical approaches that push medical sensing into the spotlight; (ii) new demonstrations of photonic integrated circuit (PIC-)based IR devices enabling highly miniaturized sensors for point-of-care application as well as medical and wellness wearables; and (iii) technologically-mature IR demonstrators that enable first medical sensing and treatment applications. This roadmap paper provides a consolidated overview of this highly dynamic and interdisciplinary research field with a focus on the major roadblocks that limit the widespread adoption of IR photonics in large-scale medical diagnostics. Special attention is given to the ambivalence between the molecular-level spectroscopic interpretation and a broader health-state assessment, highlighting the need for a common framework. Additionally, the paper discusses the critical importance of unified measurement standards, calibration protocols, and medical certification processes to ensure the validity of experimental results, reproducibility, and clinical trust, particularly when novel experimental techniques and AI algorithms are involved. Perspectives from major past and current contributors to application-oriented IR photonics will be provided.

physics.app-ph↗

arXiv2026

Time-domain optical coherence tomography at 2 $\mu\mathrm{m}$ using GaSb-based broadband superluminescent diode

We report a time-domain optical coherence tomography (TD-OCT) system operating in the 2 $\mu\mathrm{m}$ spectral region, enabled by a GaSb-based superluminescent diode (SLD). The spectrum emitted by the SLD exhibits a full-width half-maximum (FWHM) of $\sim$80 nm centred near 2.1 $\mu\mathrm{m}$. For OCT operation, stable amplified spontaneous emission with low spectral ripple ($<20\%$) is maintained at drive currents below 150 mA. The SLD is fiber coupled and integrated into a fiber-based Michelson interferometer. In the OCT system, the measured coherence envelope yields an axial resolution of approximately 300 $\mu$m in air and enables depth-resolved imaging of scattering paint-based coating samples. In contrast to OCT implementations at 2 $\mu\mathrm{m}$ wavelength region that commonly rely on supercontinuum sources, the use of GaSb-based SLDs offers a compact practical alternative, leveraging the maturity and scalability of electrically driven semiconductor light sources packaged in a standard "butterfly" module. This report represents the first demonstration of TD-OCT imaging at 2 $\mu\mathrm{m}$ using a GaSb-based SLD source and establishes its suitability for compact and scalable mid-IR OCT instrumentation targeting non-biological, low-water-content materials.

physics.optics↗

arXiv2025

Design of broadband optical gain in GaSb-based waveguide amplifiers with asymmetric quantum wells

A design strategy for achieving broadband optical gain in GaSb-based semiconductor amplifiers operating beyond 2 \mu m is presented. By employing asymmetric GaInSb/AlGaAsSb quantum wells (QWs) of varying thicknesses, a flat and wide gain spectrum is demonstrated. The approach leverages carrier density and transition energy tuning across QWs to access various energy levels at specific current densities. Simulations using "Harold" self-consistent environment predict a full-width at half-maximum (FWHM) gain bandwidth exceeding 340 nm for a structure comprising one 7 nm and three 13 nm-thick QWs. The modelling parameters were validated against experimental data, ensuring a robust framework for designing broadband amplifiers and superluminescent diodes for mid-infrared applications.

physics.optics↗

arXiv2025

Fast Recovery Dynamics of GaSbBi-based SESAMs for high-fluence operation

Modelocked lasers operating at 2-3 um wavelength region are interesting for various spectroscopic applications. To this end, GaSb-based semiconductor saturable absorber mirrors (SESAMs) are developing fast as a practical technology for passive modelocking. Yet, such SESAMs suffer from either too high two-photon absorption or slow absorption recovery dynamics. This study introduces GaSbBi quantum wells (QWs) as a novel platform to ensure a larger material selection for engineering GaSb-based SESAMs with decreased two-photon absorption and ultrafast absorption recovery time. Three GaSbBi QW SESAM designs were fabricated to compare their performance against conventional GaInSb QW SESAMs. The first structure makes use of typical GaSb barriers and exhibits comparable characteristics to the conventional design, including a saturation fluence of 1.09 uJ/cm^2, modulation depth of 1.41%, and a fast interband recovery time of 6.03 ps. The second design incorporated AlAs0.08Sb0.92 barriers, achieving reduced two-photon absorption, though at the cost of higher non-saturable losses due to unintended Bi droplet formation during growth of the AlAs0.08Sb0.92/GaSbBi QW heterostructure. Importantly, it maintained a fast interband recovery time (30 ps), overcoming the slow recovery dynamics exhibited by standard GaInSb QW SESAMs with AlAs0.08Sb0.92 barriers. The third design explored GaSbBi QWs with higher Bi content targeted for longer wavelength operation at 2.3 um, which exhibited fast recovery times and good nonlinear reflectivity characteristics. However, the higher Bi content resulted in elevated non-saturable losses. These results highlight the potential of GaSbBi QWs for SWIR SESAMs, opening the path for further epitaxial optimization to enhance their performance.

physics.optics↗

arXiv2025

Nonlinear Optical Microscopy of Semiconductor Metal-Nanocavities

We use second and third harmonic generation microscopy to investigate the nonlinear optical response of GaAs nanocavities embedded in a gold film and compare them to bare GaAs nanocavities. Our results reveal that the surrounding metallic environment significantly modifies both the intensity and spatial distribution of the nonlinear signals. When the harmonic wavelength is spectrally detuned from the nanocavity resonance, the effects due to the metallic environment start suppressing the SHG contrast. Numerical simulations confirm that at a 1060 nm pump wavelength, the SHG produced at 530 nm is suppressed due to the dominant plasmonic response of gold. Meanwhile, the THG produced at 353 nm, which coincides with the nanocavity resonance, enables high contrast imaging. Furthermore, by shifting the pump to 710 nm, aligning SHG at 356 nm with the nanocavity resonance, we recover strong SHG contrast, demonstrating a pathway to enhanced imaging of metal-semiconductor heterostructures.

physics.optics↗

arXiv2024

External busbars for improving current generation in multijunction solar cells

We report an improved device fabrication process employed in the development of an advanced front contact grid design employing external busbars. The advanced fabrication process results in enhanced solar cell performance measured at one-sun illumination. In this grid configuration the busbar area is located outside the active solar cell and the grid fingers travel across the mesa sidewalls. With this design the solar cell size can be scaled down without limitations as the area of the busbar is not restricting the component size. Thus, the demonstrated design is beneficial especially for micro-concentrator solar cells. In general, this approach minimizes the power losses originating from the grid shadowing and dark area related voltage losses. The performance of the proposed design is validated by fabricating GaInP/GaAs/GaInNAsSb triple-junction solar cells employing the grid design with external busbars. Light-biased current-voltage and electroluminescence characteristics of the cells reveal that an additional contact GaAs etching step prior to front contact metal deposition is needed to ensure good photovoltaic performance with a fill factor of 85% at one-sun illumination. The improvement is attributed to removing the plasma-damaged material layer that can extend to a depth beyond 100 nm, leading to resistive losses.

physics.app-ph↗

arXiv2024

Electronic properties of metamorphic GaSbBi films on GaAs

We report on the electronic, structural, and optical properties of epitaxial GaSbBi films with varying Bi-concentration (up to 7%Bi) grown on semi-insulating GaAs(100) substrates. The 1 $\mu$m thick GaSbBi epilayers exhibit fully relaxed narrow X-ray diffraction peaks and smooth surface morphology comparable to that of high-quality GaSb epilayers on GaAs. Low temperature photoluminescence spectra exhibit band gap shrinkage consistent with Bi alloying. Electrical Hall measurements indicate reduction of hole concentration and no change in the hole mobilities with increasing Bi content for the nominally undoped GaSbBi alloy. The residual hole concentration reduces from $10^{18} cm^{-3}$ level for a reference GaSb sample, to low $10^{17} cm^{-3}$ level with increasing Bi content. Hole mobility values of around $300 cm^{2}/Vs$ are observed independent of the Bi content. These dependencies are attributed to the Bi surfactant effect and Bi-induced defect formation.

cond-mat.mtrl-sci↗

arXiv2024

Micro-transfer printing of GaSb optoelectronics chips for mid-infrared silicon photonics integrated circuits

3D integration of GaSb-based gain chips on a silicon photonics platform using micro-transfer printing is demonstrated for the first time. The release process of GaSb coupons, and their transfer for the demonstration of hybrid GaSb/Silicon-photonics on-chip external cavity lasers is reported. A methodology to evaluate the key features of the gain chip coupons, namely the quality of the etched facets and the facet coating deposited using a wafer-level process, is introduced. The characterization provides insight into the fabrication factors limiting the performance of the gain coupons. The level of performance achieved for the transfer printing process offers a solid landmark for the development of photonics integration technology operating at the 2-3 $\mu$m wavelength range. This is instrumental for the deployment of mid-IR photonic integration technology in emerging applications related to gas and biomarker sensing.

physics.app-ph↗

arXiv2024

InP optical amplifiers with Euler U-bend waveguide geometry for low-loss flip-chip hybrid integration

We report on the development of InP-based semiconductor amplifiers with a U-bend waveguide geometry having the input and output ports on one facet only. This waveguide geometry simplifies the chip alignment during the hybrid integration on silicon photonics platforms ultimately reducing the coupling losses, improving the integration yield, and minimizing the length of the optoelectronic chip. To achieve low loss U-bends with small footprint, we utilize the Euler bend geometry previously demonstrated on silicon and GaAs platforms. We analyze the gain properties of the devices by operating them as laser diodes at room temperature. Low loss U-bend performance with a 0.56 dB for a 50 $\mu$m effective bending radius bend in a single-mode strip InP waveguide is demonstrated. The interface between bend and straight waveguides was studied by comparing deep etched waveguides to a combination of shallow straight waveguides and deep etched bends. The effects of this interface on the device losses, electric properties and spectrum are reported. The implications related to having a bend section on the carrier injection and gain are discussed. Finally, results on the integration trials on silicon-on-insulator platform are presented.

physics.app-ph↗

arXiv2024

Purcell-enhanced single-photon emission from InAs/GaAs quantum dots coupled to broadband cylindrical nanocavities

On-chip emitters that can generate single and entangled photons are essential building blocks for developing photonic quantum information processing technologies in a scalable fashion. Semiconductor quantum dots (QDs) are attractive candidates that emit high-quality quantum states of light on demand, however at a rate limited by their spontaneous radiative lifetime. In this study, we utilize the Purcell effect to demonstrate up to a 38-fold enhancement in the emission rate of InAs QDs by coupling them to metal-clad GaAs nanopillars. These cavities, featuring a sub-wavelength mode volume of 4.5x10-4 ({\lambda}/n)3 and low quality factor of 62, enable Purcell-enhanced single-photon emission across a large bandwidth of 15 nm. The broadband nature of the cavity eliminates the need for implementing tuning mechanisms typically required to achieve QD-cavity resonance, thus relaxing fabrication constraints. Ultimately, this QD-cavity architecture represents a significant stride towards developing solid-state quantum emitters generating near-ideal single-photon states at GHz-level repetition rates.

quant-ph↗

arXiv2024

Telecom wavelength single-photon emission from quasi-resonantly excited InGaSb/AlGaSb quantum dots

Deterministic light sources capable of generating quantum states on-demand at wavelengths compatible with fiber optics and atmospheric transmission windows are essential for practical applications in quantum communication, distributed photonic quantum computing, and quantum metrology. Currently, the technology providing semiconductor quantum emitters with the most promising properties is based on filling droplet-etched nanoholes to form quantum dots (QDs). However, the standard GaAs/AlGaAs material system does not offer telecom window emission. Here, we combine this growth method with antimonide-based materials to demonstrate single-photon emission at 1500 nm from a droplet-etched InGaSb QD. Our device with an antimony-based high refractive index contrast back-reflector designed for cryogenic operation and a solid immersion lens improves photon extraction. QD states are protected by a potential barrier limiting the influx of surrounding carriers, which however prevents revealing excitonic fine structure under nonresonant excitation. In this work, we employ a frequency-tunable continuous wave laser to achieve longitudinal optical (LO) phonon-assisted excitation of the QD ground state and resonant excitation of an excited state. These direct approaches for exciting a single InGaSb QD unlock access to its excitonic fine structure. The typical neutral biexciton-exciton cascade exhibits a negative binding energy of 1.4 meV (2.6 nm) and a fine structure splitting of 24.1+/-0.4 ueV. Furthermore, we obtain spectrally isolated emission from a charged exciton with a multi-photon probability of 5 % with LO phonon-assisted two-color excitation. These results represent a major step towards using this novel antimonide-based QD emitters as deterministic quantum light sources in complex quantum secure networks exploiting the wavelength compatibility with standard telecom fibers.

cond-mat.mes-hall↗

arXiv2023

Multi-type quantum well semiconductor membrane external-cavity surface-emitting lasers (MECSELs) for widely tunable continuous wave operation

Membrane external-cavity surface-emitting lasers (MECSELs) are at the forefront of pushing the performance limits of vertically emitting semiconductor lasers. Their simple idea of using just a very thin (hundreds of nanometers to few microns) gain membrane opens up new possibilities through uniform double side optical pumping and superior heat extraction from the active area. Moreover, these advantages of MECSELs enable more complex band gap engineering possibilities for the active region by the introduction of multiple types of quantum wells (QWs) to a single laser gain structure. In this paper, we present a new design strategy for laser gain structures with several types of QWs. The aim is to achieve broadband gain with relatively high power operation and potentially a flat spectral tuning range. The emphasis in our design is on ensuring sufficient gain over a wide wavelength range, having uniform pump absorption, and restricted carrier mobility between the different quantum wells during laser operation. A full-width half-maximum tuning range of > 70 nm (> 21.7 THz) with more than 125 mW of power through the entire tuning range at room temperature is demonstrated.

physics.optics↗

arXiv2023

Electronic structure of GaSb/AlGaSb quantum dots formed by filling droplet-etched nanoholes

Epitaxially-grown semiconductor quantum dots (QDs) provide an attractive platform for the development of deterministic sources of high-quality quantum states of light. Such non-classical light sources are essential for quantum information processing and quantum communication. QDs emitting in the telecom wavelengths are especially important for ensuring compatibility with optical fiber systems required to implement quantum communication networks. To this end, GaSb QDs fabricated by filling local-droplet etched nanoholes are emerging as a viable approach, yet the electronic properties of such nanostructures have not been studied in detail. In this article, an insight into the electronic structure and carrier dynamics in GaSb/AlGaSb QDs is provided through a systematic experimental analysis of their temperature-dependent photoluminescence behavior. A steady-state rate equation model is used to reveal the relevant energy barriers for thermally activated carrier capture and escape processes. Furthermore, results of detailed theoretical simulations of quantum-confined energy states using the multi-band k.p model and the effective mass method are presented. The purpose of the simulations is to reveal the direct and indirect energy states, carrier wavefunctions, and allowed optical transitions for GaSb QDs with different physical dimensions.

cond-mat.mes-hall↗

arXiv2023

Strain-free GaSb quantum dots as single-photon sources in the telecom S-band

Creating single photons in the telecommunication wavelength range from semiconductor quantum dots (QDs) and interfacing them with spins of electrons or holes has been of high interest in recent years, with research mainly focusing on indium based QDs. However, there is not much data on the optical and spin properties of galliumantimonide (GaSb) QDs, despite it being a physically rich system with an indirect to direct bandgap crossover in the telecom wavelength range. Here, we investigate the (quantum-) optical properties of GaSb quantum dots, which are fabricated by filling droplet-etched nanoholes in an aluminum-galliumantimonide (AlGaSb) matrix. We observe photoluminescence (PL) features from isolated and highly symmetric QDs that exhibit narrow linewidth in the telecom S-band and show an excitonic fine structure splitting of $ΔE=(12.0\pm0.5)μeV$. Moreover, we perform time-resolved measurements of the decay characteristics of an exciton and measure the second-order photon autocorrelation function of the charge complex to $g^{(2)}(0)=0.16\pm0.02$, revealing clear antibunching and thus proving the capability of this material platform to generate non-classical light.

cond-mat.mes-hall↗

arXiv2022

Widely tunable 2 $μ$m hybrid laser using GaSb semiconductor optical amplifiers and Si3N4 photonics integrated reflector

Tunable lasers emitting at a 2-3 $μ$m wavelength range and compatible with photonic integration platforms are of great interest for sensing applications. To this end, combining GaSb-based semiconductor gain chips with Si$_3$N$_4$ photonic integrated circuits offers an attractive platform. Herein, we exploit the low-loss features of Si$_3$N$_4$ waveguides and demonstrate a hybrid laser comprising a GaSb gain chip with an integrated tunable Si$_3$N$_4$ Vernier mirror. At room temperature, the laser exhibited a maximum output power of 15 mW and a tuning range of 80 nm (1937-2017 nm). The low-loss performance of several fundamental Si$_3$N$_4$ building blocks for photonic integrated circuits is also validated. More specifically, the single-mode waveguide exhibit transmission loss as low as 0.15 dB/cm, the 90$^\circ$ bend has 0.008 dB loss, and the 50/50 Y-branch has an insertion loss of 0.075 dB.

physics.optics↗

arXiv2021

Watt-level blue light for precision spectroscopy, laser cooling and trapping of strontium and cadmium atoms

High-power and narrow-linewidth laser light is a vital tool for atomic physics, being used for example in laser cooling and trapping and precision spectroscopy. Here we produce Watt-level laser radiation at 457.49 nm and 460.86 nm of respective relevance for the cooling transitions of cadmium and strontium atoms. This is achieved via the frequency doubling of a kHz-linewidth vertical-external-cavity surface-emitting laser (VECSEL), which is based on a novel gain chip design enabling lasing at > 2 W in the 915-928 nm region. Following an additional doubling stage, spectroscopy of the $^1S_0\to{}^1P_1$ cadmium transition at 228.89 nm is performed on an atomic beam, with all the transitions from all eight natural isotopes observed in a single continuous sweep of more than 4 GHz in the deep ultraviolet. The absolute value of the transition frequency of Cd-114 and the isotope shifts relative to this transition are determined, with values for some of these shifts provided for the first time

physics.atom-ph↗