Browsing by Author "Songur, A.C."

Now showing 1 - 9 of 9

Combining Genetic Algorithm Based Joint Time-Frequency Analysis and Keystone Transform for Isar Image Enhancement
(Institute of Electrical and Electronics Engineers Inc., 2022) Sakin, A.O.; Songur, A.C.; Onat, E.
Translational and rotational motion of maneuvering targets can cause range and cross-range cell migrations, culminating in a highly smeared final inverse synthetic aperture radar (ISAR) picture. To overcome this problem, a method for ISAR high-resolution imaging and motion compensation (MOCOMP) is proposed that combines adaptive joint timefrequency (AJTF) analysis and keystone transform (KT) based on genetic algorithm (GA). In synthetic data processing, the motion characteristics of the target are estimated using the Matching Pursuit (MP) technique with a third-order model of polynomial function. The Gabor-wavelet transform (GWT) is utilized as a JTF tool to generate a corresponding 3D time-range-Doppler cube. Keystone transform as remapping of the time axis is applied and Translational Motion Compensation (TMC), Rotational Motion Compensation (RMC), and KT have all been proved to operate well together. In raw data processing, the high-resolution image is obtained by using an AJTF and KT based on a genetic algorithm sans MP and GWT to compensate for migrations in the range and Doppler axis. © 2022 Institute of Electrical and Electronics Engineers Inc.. All rights reserved.
Demonstration of an Ultra-Sharp Bend in 1d Grating Waveguides Based on Inverse Design
(META Conference, 2023) Sakin, A.O.; Songur, A.C.; Gunes, H.A.; Akcay, B.; Unlu, M.
The design of sharp bends in 1D grating waveguides is a challenging problem as the Bloch mode profiles are being pushed towards the outer sidewall and becoming highly asymmetrical, as a result of the steep and high group velocity dispersion of the 1D grating waveguide. To overcome this problem, we propose a first-of-its-kind ultra-sharp bend design in an extensively corrugated 1D grating waveguide on silicon-on-insulator, based on pixelated metamaterials with an ultra-compact size of 2.1 × 2.2 μm2. © 2023, META Conference. All rights reserved.
Design of Polarization-Sensitive Meta Micro-Reflectors in Bragg Grating Waveguide
(SPIE, 2024) Sakin, A.O.; Akcay, B.; Songur, A.C.; Unlu, M.
Bragg-Grating-Waveguide (BGW) delay lines are commonly used in transmission mode, owing to the significant elevation in group index observed at the edge of the stopband. However, achieving delays often necessitates structures with a larger footprint, such as cascaded or spiral designs, which consume a substantial amount of chip estate. Recent approaches to optimize chip space involve round-trip configurations with reflectors, but these can restrict bandwidth and cause mode conversion. Our study introduces an efficient solution: a meta-reflector for TE0 mode, enabling double delays via a single path, while also employing a step taper in TM0 mode to couple the TM signal into a strip waveguide, within a 1.9 × 2.6 µm2 area. Simulations show that in TE mode, there is a peak attenuation of -0.18 dB within the 1530–1590 nm wavelength spectrum, and in TM mode, the loss reaches -4.73 dB across the 1500–1600 nm band. In the computation of losses, the customary impact of the Bragg grating waveguide was disregarded, with attention concentrated exclusively on the design of the reflector. © 2024 SPIE.
Metamaterial-Assisted Power Division: an Inverse Design Study in 1d Grating Waveguides
(META Conference, 2023) Sakin, A.O.; Akcay, B.; Gunes, H.A.; Songur, A.C.; Unlu, M.
Power dividers are vital components playing a crucial role in facilitating signal merging, routing, and division to ensure the efficient functioning of multi-channel systems in photonic integrated circuits. However, the use of bulky power splitters can occupy a significant amount of space on the chip. Therefore, we propose the utilization of a metamaterial-assisted ultra-low-loss T junction power divider, which integrates an input and two output grating waveguides, with a size of just 2.1 × 2.1 ×m2. © 2023, META Conference. All rights reserved.
Optimized Amplitude Distributions for Grating and Side Lobe Suppression in Optical Phased Array Antennas
(SPIE, 2024) Sakin, A.O.; Akcay, B.; Songur, A.C.; Unlu, M.
Integrated optical phased arrays (OPAs) are important for various applications such as LIDAR, microscopy, wireless communication, and holography. Traditional one-dimensional N-element OPAs with individual phase shifters for varied steering angles often have emitter spacings that exceed half a wavelength, leading to grating lobes. Moreover, using true-time-delay lines with varied numbers of periods for different delays may cause amplitude inconsistencies and further side lobe elevation. The proposed partially apodised (PA) one-dimensional grating waveguide design controls amplitude while conserving the time delay for targeted steering angles, using distributions as Uniform to minimize grating and side lobes. We fabricated a four-element array with insertion losses of -3 dB for the PA version across the 1530-1580 nm wavelength band. © 2024 SPIE.
Periodic Topology Optimization-Based Inverse Design of Slow-Light in Silicon Nitride One-Dimensional Grating Waveguides
(SPIE, 2024) Sakin, A.O.; Akcay, B.; Songur, A.C.; Unlu, M.
Devices engineered for slowing light, utilizing one-dimensional grating waveguides and fabricated from silicon nitride, often necessitate large footprints to secure the required delay, a consequence of the material’s inherently low refractive index. Our approach employs a genetic algorithm to optimize 100×100nm̂2 etchings on a predetermined grating waveguide topology, allowing for either the selective guidance of peak pulse intensity of the output or the augmentation of true time delay within the identical unit length. Within the chosen predetermined topology, the optimal configuration was identified based on the properties of the signal excitation in the time domain. This approach significantly facilitates the application-specific selection of peak intensity decay rate and time delay behavior within a 1D grating waveguide system. © 2024 SPIE.
A Terahertz Lens Antenna Array Design for Beam Steering in Time-Domain
(META Conference, 2023) Songur, A.C.; Sakin, A.O.; Gunes, H.A.; Akcay, B.; Unlu, M.
In this paper, a terahertz switched antenna array allowing beam steering between ±30° in the time-domain for 0.8-2 THz band has been designed. A silicon lens is utilized, which also allows a time-domain steering range between ±30° and is custom-developed as an extended-hemispherical lens, and the elements of the antenna array consist of broadband bowtie antennas. The far-field terahertz radiation has been successfully obtained in terms of time-domain performance criteria. © 2023, META Conference. All rights reserved.
A Terahertz Time-Domain Antenna Array Based on a Parametric Study
(META Conference, 2023) Songur, A.C.; Sakin, A.O.; Akcay, B.; Gunes, H.A.; Unlu, M.
In this paper, the design parameters are examined in detail for the terahertz photoconductive antenna arrays operating in the terahertz frequency region, which is one of the most important band candidates for future communication systems, and a 1x4 wide-band time-domain bowtie antenna array providing 30° steering is designed for 0.8-2 THz band. This study is entirely realized in the time-domain to process the broadband terahertz pulsed signals more efficiently. © 2023, META Conference. All rights reserved.
Ultracompact Tapers & Splitter for Fishbone-Like Grating Waveguides
(META Conference, 2023) Sakin, A.O.; Gunes, H.A.; Akcay, B.; Songur, A.C.; Unlu, M.
The use of fishbone-like grating waveguides (FLGWs) in photonic integrated circuits (PICs) presents a challenge in terms of chip space utilization because it requires incorporating conventional, large components. Therefore, we propose the combination of three key elements - a long adiabatic waveguide taper, a power splitter, and a transition region for FLGWs - using digital metamaterials to allow for the effective utilization of FLGWs that are excited by ultrashort pulses in a compact footprint of only 5 × 14.1 μm2. © 2023, META Conference. All rights reserved.