Scholarly Publications - Electrical and Electronics Engineering

Permanent URI for this collectionhttps://hdl.handle.net/11693/115599

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Open Access
Half-marker codes for deletion channels with applications in DNA storage
(Institute of Electrical and Electronics Engineers, 2025-05-14) Haghighat, Javad; Duman, Tolga Mete
DNA data storage systems face significant challenges, including insertion, deletion, and substitution (IDS) errors. Therefore, designing effective synchronization codes, i.e., codes capable of correcting IDS errors, is essential for DNA storage systems. Marker codes are a favorable choice for this purpose. In this letter, we extend the notion of marker codes by making the following key observation. Since each DNA base is equivalent to a 2-bit storage unit, one bit can be reserved for synchronization, while the other is dedicated to data transmission. Using this observation, we propose a new class of marker codes, which we refer to as half-marker codes. We demonstrate that this extension has the potential to significantly increase the mutual information between the input sequence and the soft outputs of an IDS channel modeling a DNA storage system. Specifically, through examples, we show that when concatenated with an outer error-correcting code, half-marker codes outperform standard marker codes and significantly reduce the end-to-end bit error rate of the system.
Open Access
On the structure of robust controllers and weight selection in the mixed sensitivity minimization
(American Institute of Aeronautics and Astronautics Inc., 2025) Özbay, Hitay; Karagül, A. Erdem; Karadavut, Nagihan; Yurdaer, N. Kübra
In this paper we examine the structure of robust controllers obtained from the mixed sensitivity minimization for a class of mechanical systems consisting of rigid body dynamics, weak flexible modes, and small time delays (or non-minimum phase effects due to non-collocated actuator and sensor). In particular, we study the weight selection in the mixed sensitivity design and illustrate that for certain performance and robustness objectives, the resulting H∞ optimal controller is in the form of a classical PID controller cascaded by a filter suppressing the uncertain flexible modes. Furthermore, we provide a link between this H∞ optimal controller and the conventional three-loop controller/autopilot (3LC) scheme frequently used in aerospace applications. More precisely, the 3LC scheme is shown to be equivalent to a two-degree-of freedom (2DoF) control structure where the H∞ controller is used in the feedback loop and the reference signal is filtered outside the loop.
Open Access
Joint age-state belief is all you need: minimizing AoII via pull-based remote estimation
(Institute of Electrical and Electronics Engineers Inc., 2025) Cosandal, Ismail; Ulukus, Sennur; Akar, Nail
Age of incorrect information (AoII) is a recently proposed freshness and mismatch metric that penalizes an incorrect estimation along with its duration. Therefore, keeping track of AoII requires the knowledge of both the source and estimation processes. In this paper, we consider a time-slotted pull-based remote estimation system under a sampling rate constraint where the information source is a general discrete-time Markov chain (DTMC) process. Moreover, packet transmission times from the source to the monitor are non-zero which disallows the monitor to have perfect information on the actual AoII process at any time. Hence, for this pull-based system, we propose the monitor to maintain a sufficient statistic called belief which stands for the joint distribution of the age and source processes to be obtained from the history of all observations. Using belief, we first propose a maximum a posteriori (MAP) estimator to be used at the monitor as opposed to existing martingale estimators in the literature. Second, we obtain the optimality equations from the belief-MDP (Markov decision process) formulation. Finally, we propose two belief-dependent policies one of which is based on deep reinforcement learning, and the other one is a threshold-based policy based on the instantaneous expected AoII.
Open Access
Remote estimation games with random walk processes: Stackelberg equilibrium
(2024) Dökme, Atahan; Velicheti, Raj Kiriti; Baştopçu, Melih; Başar, Tamer
Remote estimation is a crucial element of real time monitoring of a stochastic process. While most of the existing works have concentrated on obtaining optimal sampling strategies, motivated by malicious attacks on cyber-physical systems, we model sensing under surveillance as a game between an attacker and a defender. This introduces strategic elements to conventional remote estimation problems. Additionally, inspired by increasing detection capabilities, we model an element of information leakage for each player. Parameterizing the game in terms of uncertainty on each side, information leakage, and cost of sampling, we consider the Stackelberg Equilibrium (SE) concept where one of the players acts as the leader and the other one as the follower. By focusing our attention on stationary probabilistic sampling policies, we characterize the SE of this game and provide simulations to show the efficacy of our results.
Open Access
A tutorial on MRI reconstruction: From modern methods to clinical implications
(IEEE Computer Society, 2025-10-03) Çukur, Tolga; Dar, Salman UH; Nezhad, Valiyeh A.; Jun, Yohan; Kim, Tae Hyung; Fujita, Shohei; Bilgiç, Berkin
MRI is an indispensable clinical tool, offering a rich variety of tissue contrasts to support broad diagnostic and research applications. Protocols can incorporate multiple structural, functional, diffusion, spectroscopic, or relaxometry sequences to provide complementary information for differential diagnosis, and to capture multidimensional insights into tissue structure and composition. However, these capabilities come at the cost of prolonged scan times, which reduce patient throughput, increase susceptibility to motion artifacts, and may require trade-offs in image quality or diagnostic scope. Over the last two decades, advances in image reconstruction algorithms-alongside improvements in hardware and pulse sequence design-have made it possible to accelerate acquisitions while preserving diagnostic quality. Central to this progress is the ability to incorporate prior information to regularize the solutions to the reconstruction problem. In this tutorial, we overview the basics of MRI reconstruction and highlight state-of-the-art approaches, beginning with classical methods that rely on explicit hand-crafted priors, and then turning to deep learning methods that leverage a combination of learned and crafted priors to further push the performance envelope. We also explore the translational aspects and eventual clinical implications of these methods. We conclude by discussing future directions to address remaining challenges in MRI reconstruction. The tutorial is accompanied by a Python toolbox (https://github.com/tutorial-MRI-recon/tutorial) to demonstrate select methods discussed in the article.
Open Access
Basal ganglia as an fMRI motor neurofeedback target in Parkinson’s disease
(2025-11-19) Baqapuri, Halim I.; Terneusen, Anneke; Luehrs, Michael; Peters, Judith; Kuijf, Mark; Goebel, Rainer; Linden, David; Çukur, Tolga; Visser-Vandewalle, Veerle; Kocher, Martin; Loução, Ricardo; Jarraya, Bechir; Mana, Josef; Lozano, Andres M.
Parkinson’s disease (PD) is a progressive neurodegenerative disorder characterized by motor impairments. While pharmacological treatments offer symptom alleviation, their long-term effectiveness is insufficient. Deep Brain Stimulation (DBS) is a neurosurgical treatment that targets brain pathways to alleviate motor symptoms in PD. It is a highly invasive procedure and carries associated risks. This prompts investigation of non-invasive alternatives, such as real-time functional Magnetic Resonance Imaging (rt-fMRI) neurofeedback (NF). This work investigates the feasibility of using the basal ganglia, more specifically the putamen, a key structure in the motor network, as a potential NF target region. Two rt-fMRI studies were conducted: (i) Twelve healthy individuals participated in a single-blind, crossover study involving one MRI session targeting the putamen and the supplementary motor area (SMA) in separate runs. (ii) Twelve PD patients followed the same protocol but with three MRI sessions. We investigated whether participants could learn to voluntarily control brain activity through NF training. The PD patients successfully recruited the putamen during NF-reinforced motor imagery, which was also found at trend level in the healthy participants. We found no learning effect and no difference in putamen activation when it was directly targeted versus when the target signals came from the SMA. Overall, widespread cortical and subcortical areas involved in motor control were activated during neurofeedback. This study demonstrates for the first time that PD patients can modulate putamen activity through NF training, supporting its potential as a non-invasive neuromodulation target. This opens opportunities for integrating invasive and non-invasive neuromodulation for PD treatment.
Open Access
Efficient noise calculation in deep learning-based MRI reconstructions
(ML Research Press, 2025-05-01) Dalmaz, Onat; Desai, Arjun D.; Heckel, Reinhard; Çukur, Tolga; Chaudhari, Akshay S.; Hargreaves, Brian
Accelerated MRI reconstruction involves solving an ill-posed inverse problem where noise in acquired data propagates to the reconstructed images. Noise analyses are central to MRI reconstruction for providing an explicit measure of solution fidelity and for guiding the design and deployment of novel reconstruction methods. However, deep learning (DL)-based reconstruction methods have often overlooked noise propagation due to inherent analytical and computational challenges, despite its critical importance. This work proposesa theoretically grounded, memory-efficienttechnique to calculate voxel-wise variance for quantifying uncertainty due to acquisition noise in accelerated MRI reconstructions. Our approach approximates noise covariance using the DL network’s Jacobian, which is intractable to calculate. To circumvent this, we derive an unbiased estimator for the diagonal of this covariance matrix—voxel-wise variance—, and introduce a Jacobian sketching technique to efficiently implement it. We evaluate our method on knee and brain MRI datasets for both data-and physicsdriven networks trained in supervised and unsupervisedmanners. Compared to empirical references obtained via Monte-Carlo simulations, our technique achieves near-equivalent performance while reducing computational and memory demands by an order of magnitude or more. Furthermore, our method is robust across varying input noise levels, acceleration factors, and diverse undersampling schemes, highlighting its broad applicability. Our work reintroduces accurate and efficient noise analysis as a central tenet of reconstruction algorithms, holding promise to reshape how we evaluate and deploy DL-based MRI.
Open Access
Recent advances in GaN-based semiconductor lasers
(Institute of Physics Publishing Ltd., 2025-07-17) Zhao, Chunyu; Tan, Swee Tiam; Demir, Hilmi Volkan
III-nitride semiconductor lasers have made remarkable progress in recent years, particularly thanks to their ability to be tuned from the ultraviolet to the infrared. This comprehensive review explores the latest developments in GaN-based semiconductor lasers, with a specific focus on edge-emitting laser, vertical-cavity surface-emitting laser, photonic crystal or nanocrystal surface-emitting laser, and whispering gallery mode laser diodes. The review delves into each laser type’s distinctive properties and potential applications, evaluating their performance while identifying current challenges. Finally, this review aims to shed light on challenges and prospects in GaN-based laser development.
Open Access
Multi-threshold AoII-optimum sampling policies for continuous-time Markov chain information source
(Institute of Electrical and Electronics Engineers, 2025-07-03) Cosandal, Ismail; Akar, Nail; Ulukus, Sennur
We study push-based sampling and transmission policies for a status update system consisting of a general finitestate continuous-time Markov chain (CTMC) information source with known dynamics, with the goal of minimizing the average age of incorrect information (AoII) defined via a linear time penalty function. The problem setting we investigate involves an exponentially distributed delay channel for transmissions and a constraint on the average sampling rate. We first show that the optimum sampling and transmission policy is a multi-threshold policy, where the thresholds depend on both the estimation value and the state of the original process, and sampling and transmission need to be initiated when the instantaneous AoII exceeds the corresponding threshold, called the estimationand state-aware transmission (ESAT) policy. Subsequently, we formulate the problem of finding the thresholds as a constrained semi-Markov decision process (CSMDP) and the Lagrangian approach. Additionally, we propose two lower complexity suboptimum policies, namely the estimation-aware transmission (EAT) policy, and the single-threshold (ST) policy, for which it is possible to obtain these thresholds for CTMCs with relatively larger number of states. The underlying CSMDP formulation relies on the multi-regime phase-type (MR-PH) distribution which is a generalization of the well-known phase-type distribution, which allows us to obtain the first two moments of time until absorption in a CTMC whose transition rates change with respect to time, in a piece-wise manner. The effectiveness of the proposed ESAT, EAT, and ST sampling and transmission policies are shown through numerical examples, along with comparisons with a baseline scheme that transmits packets according to a Poisson process in out-of-sync periods.
Open Access
Design and simulation of SWIR nBn-InGaAs photodetector with AlGaAs barrier
(EDP Sciences, 2025-09-22) Tok, Çaǧrı; Satılmış, Mert; Keleş, Habibe; Oǧuz, Fikri; Sarı, Hüseyin; Özbay, Ekmel
The article discusses the simulation of an nBn-InGaAs photodetector using Silvaco TCAD at 300 K, focusing on optimizing the barrier performance and reducing the valence band offset. It explores the device’s electrical and optical behaviors, including dark current, photocurrent, and capacitance. The results show a peak responsivity of 0.91 A/W at 1.55 µm and a junction capacitance of 9 pF at −5 V. Adding an anti-reflection coating notably improved the optical performance, highlighting the structure’s potential for efficient infrared photodetection.
Embargo
Electro-optical evaluation of Cu¹⁺ and Cu²⁺ states in copper-doped CdSe colloidal quantum wells
(American Chemical Society, 2026-01-29) Yu, Junhong; Wang, Ke; Han, Yadong; Lian, Zhenzhong; Hou, Songyan; Cao, Chang; Demir, Hilmi Volkan; Jasieniak, Jacek J.; Sharma, Manoj
Resolving the ambiguous oxidation state of copper dopants responsible for the large Stokes-shifted emission in CdSe colloidal quantum wells (CQWs) is critical for harnessing their emerging optoelectronic properties. Employing carrier injection to tune the population distribution between Cu¹⁺/Cu²⁺ centers and in situ monitoring of the copper-related emission (CE), we have revealed that the CE band undergoes blueshifting, intensity quenching, and line width broadening with gradually increased Cu²⁺ states. Time-resolved CE dynamics and intragap absorption further confirm that Cu²⁺ states generate narrow, inefficient emission with minimal Stokes shifts due to trap-mediated Auger recombination, reduced radiative center energy spanning, and Fermi-level shifts. Accordingly, we identify Cu¹⁺ as the dominant species that produces the bright, broad CE band with its hallmark large Stokes shift. This work not only presents mechanistic clarifications but also provides an effective approach to electrically modulate defect emissions in CQWs.
Open Access
Correction to “multifaceted effects of the dielectric component within plasmon-assisted light-emitting structures”
(American Chemical Society, 2025-12-17) Kulakovich, Olga; Muravitskaya, Alina; Ramanenka, Andrei; Efimova, Taisia; Krukov, Vitali; Mutlugun, Evren; Kulak, Anatoly; Demir, Hilmi Volkan; Wang, Zhiming; Gaponenko, Sergey
In the original version of the article, the affiliation of Hilmi Volkan Demir needs following correction. The first affiliation of the author “Department of Electrical-Electronics Engineering, Abdullah Gul University, Kayseri 38080, Turkey” should be replaced by the affiliation “UNAM – Institute of Materials Science and Nanotechnology and The National Nanotechnology Research Center and Department of Electrical and Electronics Engineering, Department of Physics, Bilkent University, Ankara 06800, Turkey”. Therefore, the correct affiliations for H.V.D. are “UNAM – Institute of Materials Science and Nanotechnology and The National Nanotechnology Research Center and Department of Electrical and Electronics Engineering, Department of Physics, Bilkent University, Ankara 06800, Turkey; LUMINOUS! Center of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronic Engineering, School of Physical and Mathematical Sciences, School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore”.
Open Access
A new tool for the simulation of controllers for retarded delay systems
(Elsevier B.V., 2025-06-01) Bonnet, C.; Duy, D. D.; Yeğin, M. O.; Özbay, Hitay
In this paper we illustrate functionalities of a new software tool developed for reliable implementation of all stabilizing controllers for retarded time delay systems. This work is the continuation of our paper in TDS2024, Bonnet et al. (2024); it demonstrates a Matlab/Simulink realization and how users interface with it. The paper also discusses some technical issues in the implementation of the infinite dimensional parts of the controller blocks
Open Access
Acoustic gas sensing with weakly coupled mems resonators
(Institute of Electrical and Electronics Engineers Inc., 2025-03-19) Erkan, Derin; Aslan, Ahmet Arif; Tatar, Erdinç
Most of the current gas sensors are individually developed and limited with the detectable gas species due to their material or wavelength dependent sensing technology. We propose an acoustic gas sensing method that utilizes the weak coupling between specialized MEMS resonators originating from the cavity resonance, for the first time. The method directly captures the cavity resonance with inherently strong SNR and can detect any gas. We achieve >7X sensitivity compared to the previously proposed damping and frequency based measurements. We demonstrate the coupling with cavity/no cavity experiments and show the successful sensor operation up to 95% CO2 concentration.
Open Access
The origin of gate degradation under HTRB operation: Buffer engineering to suppress impact ionization in GaN HEMT
(Institute of Electrical and Electronics Engineers Inc., 2025-12-15) Soydan, Mahmut Can; Joya, Amir Ali; Ghobadi, Amir; Özbay, Ekmel
This study investigates the origin of gate degradation in AlGaN/GaN HEMTs under high-temperature reverse bias (HTRB) conditions and proposes a buffer engineering strategy to mitigate this degradation. Transmission electron microscopy (TEM) analysis reveals the presence of a thin oxide layer between the gate and AlGaN contact. It is found that the holes generated through impact ionization (under high electric fields of HTRB operation), are directed toward the gate due to the intense local electric field under the gate and the field plate overhang, and are accumulated under this energetic barrier. Consequently, these trapped holes cause gate degradation and increased gate leakage. To address this issue, impact ionization, as the initial forcing mechanism of the degradation, is suppressed via thinning the channel GaN (C-GaN) layer. This improvement is attributed to the suppression of the local electric field near the gate region in thin C-GaN HEMTs. Additionally, the impact of C-GaN thinning on breakdown characteristics and RF performance is discussed. Overall, the findings provide insights into the root cause of gate degradation and offer a buffer engineering strategy to minimize gate degradation under deep off-state stress. This approach enhances the reliability of future high-power and high-frequency GaN HEMTs, contributing to their long-term performance in demanding applications.
Open Access
Performance evaluation of small pixel-sized Gd₂O₂S and CsI CMOS x-ray detectors
(SPIE, 2025-04-08) Mart, Yağız; Aslan, Ahmet Arif; Büyükdemirci, Kaan; Lee, Denny; Akin, Tayfun; Camlica, Ahmet; Sabol, John M.; Li, Ke; Abbaszadeh, Shiva
Flat panel x-ray detectors with thin-film transistors (TFT) are widely used in x-ray medical imaging applications. However, indirect x-ray detectors with TFT suffer from an inadequate spatial resolution that is required for some medical imaging procedures, where resolving fine details at its early stage plays a crucial role in successful diagnosis such as breast imaging. Besides, indirect conversion x-ray detectors when incorporated with common types of scintillators, i.e., cesium iodide (CsI) or Gd₂O₂S, can meet the requirements of high fabrication yield and respectively lower costs. As an alternative to TFT read-out circuitry, complementary metal oxide semiconductor (CMOS) presents an attractive alternative, offering lower inherent electrical noise and higher temporal resolution, enabling dynamic imaging at lower x-ray doses. The purpose of this work is to develop small pixel size indirect conversion CMOS x-ray detectors. The CsI-based detector features an active area of 1.1x0.8cm2 and a pixel size of 20μm, while the Gd₂O₂S-based detector has an active area of 1.5x1.5cm2 and a pixel size of 20μm. Both detectors comprise of 1024x1024 pixels with an image depth of 14 bits. However, the active area of the CsI-based detector is less than that of the Gd₂O₂S-based detector. To evaluate the spatial resolution of the detectors, the IEC 62220-1:2003 standard is followed. The modulation transfer function (MTF) of both detectors is examined experimentally by the slanted-edge method using the first two prototype CMOS detectors. The initial results indicate that the point at which the MTF reaches 50% is significantly higher for both indirect CMOS detectors compared to commercial CMOS and TFT detectors utilizing the same scintillators. Specifically, the Gd₂O₂S-based detector achieves 2.6lp/mm, while the CsI-based detector reaches 4.7lp/mm. Also, the preliminary images of the medical stent used for angiography operation obtained with the fabricated detectors demonstrate that the indirect conversion CMOS x-ray detectors can be a reasonable alternative to direct conversion x-ray detectors for some specific imaging operations. In addition to MTF, noise power spectrum (NPS), and detective quantum efficiency (DQE) values are also examined. This study is the first attempt to explore our indirect CMOS x-ray detectors and further studies will be carried out to identify their potential application area in medical imaging procedures.
Open Access
Selenium alloying in CdSeTe colloidal quantum wells as an effective strategy for high efficiency and enhanced stability
(American Chemical Society, 2026-01-02) Gökbayrak, Attila Alkım; Delikanlı, Savaş; Görkan, Taylan; Işık, Furkan; Durmuşoğlu, Emek G; Durgun, Engin; Demir, Hilmi Volkan
CdTe colloidal quantum wells (CQWs) exhibit very low quantum yields (QYs) (<1%) and suffer significant stability challenges unlike their CdSe counterparts, which feature near unity QY and high stability under ambient conditions. Here, we synthesized highly stable CdSeTe CQWs with photoluminescence quantum efficiency (PLQY) reaching 25%, which far exceeds the previously best-reported PLQYs from CdTe CQWs while preserving the PL spectral characteristics (PL peak position and full-width-at-half-maximum (fwhm) of PL emission) similar to those of CdTe CQWs. In these as-synthesized CdSeTe nanoplatelets, a progressive increase in the Se/Te ratio leads to a notable enhancement in their quantum yield, accompanied by extended photoluminescence lifetimes, strongly indicating that higher Se incorporation effectively mitigates nonradiative recombination channels. In addition, we demonstrate that these CdSeTe CQWs are stable under ambient conditions unlike pristine CdTe CQWs through systematic studies with X-ray photoelectron spectroscopy (XPS). Using density functional theory (DFT) calculations we demonstrate that, under oxygen-rich conditions, O atoms weaken Cd–Te bonds and destabilize CdTe nanoplatelets, whereas in Se-alloyed CdSeTe CQWs, oxygen atoms preferentially adsorb onto the surface without penetrating the structure, effectively suppressing bond destabilization, which is consistent with our XPS observations. The enhanced optical properties, stability, and robustness of these CdSeTe-alloyed nanoplatelets offer a practical solution to overcoming the inherent limitations of CdTe CQWs and position them as highly attractive materials for practical use in advanced optoelectronic applications.
Embargo
Lasing from brillouin zone folding guided resonances
(American Chemical Society, 2025-09-25) Chua, Matthew R.; Ding, Lu; Liang, Xiao; Dabard, Corentin; Wang, Wudeng; Akhil, Syed; Durmusoglu, Emek Goksu; Tjiptoharsono, Febiana; Demir, Hilmi Volkan; Paniagua-Domínguez, Ramón; Kuznetsov, Arseniy I.
High-quality factor (Q-factor) nanophotonic cavities are critical components in applications such as lasing and nonlinear optics. However, to obtain out-of-plane lasing emission and a low lasing threshold, the lasing mode must fulfill the contradictory requirement of coupling to the light cone while maintaining a high Q-factor. One relatively unexplored method to design such modes consists of using a Brillouin Zone folding guided resonance (BZF-GR) as the high Q-factor mode for lasing. In such a design, guided modes are “folded” into the light cone via periodic perturbations, allowing fine control of the Q-factor throughout momentum space. In this paper, we experimentally demonstrate the use of such a BZF-GR to achieve vertical emission lasing from a nanophotonic cavity with colloidal quantum dots as a gain medium. The lowest lasing threshold fluence under nanosecond pump is (20.4 ± 0.3) μJ cm–2. When considering the absorption, this value falls to (4.08 ± 0.08) μJ cm–2. This work presents a method of designing lasing modes that may be further developed for use in low-threshold nanoscale lasers.
Open Access
Side-emitting optical fibers of colloidal quantum wells for application in curved-surface lighting and sensing
(American Chemical Society, 2025-03-04) Adelpour, Zahra; Shabani, Farzan; Sadeghi, Mojtaba; Khaligh, Aisan; Rahman, Mahmudur; Karaboğa, Fırat; Ünal, Emre; Ordu, Mustafa; Demir, Hilmi Volkan
As specialized optical fibers, side-emitting optical fibers (SEOFs) are designed to emit light from their sides rather than their ends for possible applications in curved-surface lighting and sensing. In this study, we propose and demonstrate an in situ decoration of SEOFs with colloidal quantum wells (CQWs) for the first time. The proposed method enables the homogeneous distribution of CQWs in the polymeric matrix of the fiber with high side-emission efficiency, which is based on a simple yet effective method of CQW sheet coating. Two different structures of CQWs, a red-emitting CdSe/CdZnS core/shell and a green-emitting CdSe/CdS core/crown, were synthesized and employed in SEOFs. Accordingly, carefully tuned concentrations of CQWs were incorporated within the hollow-core optical fibers, and the side-scattered light from the fibers was systematically characterized and analyzed. The results confirm excellent side-emitting characteristics that are highly dependent on the optical fiber structure and CQW absorption spectrum. The average quantum yield values of 51 ± 5% and 34.5 ± 5% for different concentrations of red and green CQWs relative to their solution form were measured in our experiment, which is associated with polymeric medium, cluster formation, and fiber tower temperature. The findings pave the way for developing high-performance optical fiber devices based on CQW-doped SEOFs capable of efficient and precise light emission targeting a wide variety of applications ranging from three-dimensional curved-surface lighting to sensing.
Open Access
GaN-on-SiC broadband driver amplifier for C- and X-band applications
(John Wiley and Sons Inc, 2025-06-12) Hannan, Abdullah; Aras, Erdem; Gürdal, Armağan; Urfalı, Emirhan; Zafar, Salahuddin; Nawaz, Muhammad Imran; Özbay, Ekmel
A GaN-on-SiC-based broadband driver amplifier operating in the C- and X-bands from 5 to 12 GHz has been demonstrated. The MMIC has a typical small signal gain of 29.7 dB with a ±1.4 dB gain ripple. The input and output return losses are better than 10.5 and 8.8 dB, respectively. The average Psat is approximately 2.65 W with an OIP3 of 37.7 dBm, while the large signal gain is 22 dB. This design is distinguished by its low output power ripple and the low large signal gain fluctuations observed across the full frequency range of interest. Consistent load impedance matching at the output stage for the whole frequency range enabled an output power ripple less than ±1.1 dB and a large signal gain ripple less than ±0.6 dB at 10 dBm input power. This allowed for an output power density of at least 2.68 W/mm across the broad frequency range of 5–12 GHz. The typical power-added efficiency is 26.4%. To the best of the authors' knowledge, this DA design exhibits the best combination of gain, output power density, gain ripple, output power ripple and output return loss in this frequency band.