Abstracts Track 2025

Area 1 - Lasers
Area 2 - Optics
Area 3 - Photonics

Area 1 - Lasers

Nr: 6
Title:

Analysis of the Complex Dynamics of a Photonic Neuron with Dual Feedback.
Authors:

Andrés Aragoneses and John P. Bannon
Abstract: Photonic neurons are neuron-inspired photonic devices that mimic the complex dynamics of biological neurons. A diode laser with external optical feedback generates spikes that resemble those produced by other complex and chaotic systems. These photonic neurons hold significant potential in several advanced technological and scientific domains, particularly in neuromorphic computing, optical communication, sensing, signal processing, and nonlinear dynamics. In complex dynamical systems, noise, feedback, and external forcing shape behavior ranging from regularity to high-dimensional chaos. Multiple feedback sources can significantly modify these dynamics and even suppress output behavior. To explore the impact of competing feedback sources on a stochastic complex dynamical system, we employ a photonic neuron—a diode laser with external optical feedback—to examine and characterize the behavior of a nonlinear oscillator subject to dual feedback. We investigate a broad range of feedback intensities from two external reflectors, performing ordinal analysis and applying recent measures to quantify complexity and uncover underlying symmetries in the complex dynamics. Our findings reveal how the interplay between multiple feedback loops influences the system's stability and complexity, providing new insights into the control and predictability of photonic-based dynamical systems. Notably, we observe that while the dynamical behavior of the photonic neuron changes with the feedback ratio, it maintains underlying dynamical symmetries. The system exhibits two distinct temporal scales with different dynamics but similar temporal symmetries. These insights could be instrumental in identifying the relevance of external signals based on the temporal dynamics of the laser's output power.
Nr: 48
Title:

Weld Width Control Using off-Axis Camera During Laser Welding of Copper
Authors:

Tine Brežan, Jan Žalac, Matjaž Kos and Matija Jezeršek
Abstract: In the face of ever stricter laws on CO2 emissions, electric vehicles (EVs) are replacing fossil fuel-powered transportation. E-mobility therefore represents a way forward for a better environment. Joining of copper-metal components enables the construction of electronic subsystems such as battery modules, cell connectors and power electronics. Due to stringent performance requirements, where even a single faulty weld can cause the entire system to malfunction, the need to produce electric vehicles on a large scale to meet policy targets and the demand for zero-defect production has increased significantly. Laser Welding (LW) is the process of choice for a number of electric vehicle manufacturing applications due to its flexibility, accuracy, speed and automation capabilities. Although the need for precise and defect-free welding is paramount, the production of defect-free EV systems for mass production is a challenge. This is due to the temperature dependence of copper’s material properties as well as its low infrared (IR) absorptivity at room temperature. The need to implement a control system is evident. In this study, we developed an optical feedback control system for laser welding of copper using an off-axis camera to capture images of the welding area. The images were further processed, and the weld width was extracted from the region of interest. A proportional–integral–derivative (PID) controller was used to control the laser power to achieve a weld width control in real time. Using the Ziegler-Nichols method, we tested different proposed PID parameters: “classic”, “some-overshoot” and “no-overshoot”. Additionally, a feed-forward approach was implemented. Fiber laser (Ytterbium, λ=1070±10 nm) was used for welding with laser beam diameter of Φ0.15 mm and welding speeds between 100 and 200 mm/s. Three industry-relevant cases were conducted: (i) holding constant target weld width, (ii) change of target weld width, and (iii) induced power disturbance to test the performance indicators of different PID controllers, such as rise time and accuracy. In case (ii) a feed-forward approach was tested to emphasize its ability to improve controller's response time. By using an optical feedback loop, we can accurately control the weld width with a relative standard deviation of 2% and achieve an overall improvement in the stability of the welding process. In addition, a feed-forward approach improves the response time of a “classic” PID controller by up to 80 % and achieves a response time of 0.02s. The developed system enables responsive and accurate control of laser welding, which plays a major role in improving welding quality and reducing material waste due to defective welds for the growing e-mobility sector. In further studies, the monitoring of weld width enables the prediction and control of other weld characteristics, such as weld depth.

Area 2 - Optics

Nr: 5
Title:

A Proposal for a Photonic Quantum Battery
Authors:

Charles Downing and Muhammed Shoufie Ukhtary
Abstract: We present a theoretical proposal for a quantum energy storage device based upon a pair of coupled optical resonators. By parametrically driving the first optical resonator, which acts as the charger, the second resonator, which acts as the battery, can store a tremendous amount of energy (which in fact scales exponentially with the amplitude of the driving pulse). This useful behaviour occurs because the parametric driving induces squeezing into the quantum system, which manifests as an exceedingly large mean population in the quantum battery. We also discuss the pernicious effects of dissipation, as well as the ergotropic quality of the battery (which measures how much work can be done using the energy stored in the battery) and the prospects for experimental detection in optical architectures.
Nr: 8
Title:

Crystallization of Induce Optical Vortex by Bessel Beams
Authors:

Sahil Sahoo, Andre Yaroshevsky and Yuri Gorodetski
Abstract: Optically driven vortex lattices have unlocked exciting possibilities in the field of optics, playing a crucial role in the formation of vortex structures within ultra-cold atomic Bose-Einstein condensates. These lattices are typically generated through beam interference, with significant advancements being made using multi-beam interference techniques. By employing circularly polarized light and metasurfaces with orthogonal nano-slit pairs and spiral segments, researchers have been able to generate optical vortex lattice fields. These fields are created by combining both geometric and dynamic phases, leading to complex lattice patterns. Further advancements have been achieved through spin-based plasmonic effects involving different geometries, which enhance the formation of optical lattice structures. These techniques direct plasmonic waves toward the center of the geometry, enabling superposition and the creation of intricate patterns. Plasmonic waves emerge from the interaction between electromagnetic (EM) waves and metallic structures at subwavelength scales. This interaction couples EM waves with confined electronic oscillations known as surface plasmon polaritons (SPPs). The near-field intensity distribution of SPPs depends on the polarization state of the incident beam, and by designing a plasmonic cavity with polarization-dependent geometric phases, it is possible to produce a plasmonic vortex Bessel beam. In this study, we demonstrated that a hexagonal array of Bessel beams positioned at each corner produces intricate interference patterns due to plasmonic waves. These interactions lead to the formation of a plasmonic vortex lattice (PVL), which is influenced by the system's topological features and the size of the hexagonal array. As plasmonic waves interfere, vortices emerge, and with the expansion of the array, these vortices gradually merge, ultimately forming the complete PVL. This vortex formation process can be likened to crystallization. While vortex crystallization has been explored in atomic-molecular Bose-Einstein condensates through thermal quenching, the creation of a PVL via plasmonic wave interference is still being actively investigated. Specifically, we examine the crystallization process by drawing an analogy to the nematic crystal order parameter across different array sizes. The step-by-step addition of vortices suggests that they form during the interference process, with changes in array size causing the vortices to shift toward more stable energy configurations. As the system reaches energy stabilization, the PVL is fully formed. Notably, this PVL exhibits significant topological stability, maintaining its structure even when disruptions, such as blocking a single Bessel beam, occur. This resilience highlights the lattice's robust topological integrity.
Nr: 11
Title:

Sequentially Deposition of Ag NPs on Rippled Si Pattern for SERS Application.
Authors:

Tarundeep Kaur Lamba, Sebin Augustine, Mahesh Saini, K.P. Sooraj and Mukesh Ranjan
Abstract: The evolution of self-organized nanoscale ripple patterns on various surfaces, produced by low-energy ion beam sputtering (IBS), has garnered significant interest for their potential use as templates in a range of applications, including plasmonics, nanoelectronics, electronic devices, nano-magnetism, and anti-reflective surface finishes, among others [1-2]. The wavelength of these ripple patterns can be controlled by adjusting the ion beam energy, incidence angle, and fluence, with a range of 20-60 nm for silicon surfaces irradiated by ions with energies below 1 keV. In this study, we focus on the application of these ripple patterns in plasmonics. We employed a novel method of sequential deposition to deposit silver nanoparticles (Ag-NPs) onto the ripple structures. This approach enabled the formation of spherical nanoparticles without the need for annealing, which typically causes the Oswald ripening process and results in larger gaps between the nanoparticles. We observed a significant reduction in LSPR anisotropy, as evident from the reflection spectra. The spectral shift reduced from 209 nm to 54 nm in sequential deposition compared to single-direction deposition. In the context of surface-enhanced Raman spectroscopy (SERS), this method effectively minimized variations in SERS intensity both along and across the ripples, while enhancing the SERS signal for Crystal Violet (CV) dye for the concentration of 10-6 M. Finite-difference time-domain (FDTD) simulations confirmed these findings, demonstrating similar electric field enhancements along and across the ripple patterns for spherical nanoparticles. This study offers valuable insights for advancing various applications in the fields of optics and plasmonics [3]. [1] Saini, Mahesh, et al. "Cold cathode electron emission with ultralow turn-on fields from Au-nanoparticle-decorated self-organized Si nanofacets." Journal of Materials Chemistry C 8.47 (2020): 16880-16895. [2] Giordano, Maria Caterina, et al. "Self-organized tailoring of faceted glass nanowrinkles for organic nanoelectronics." ACS Applied Nano Materials 4.2 (2021): 1940-1950. [3] Lamba, Tarundeep Kaur, et al. "LSPR anisotropy minimization by sequential growth of Ag nanoparticles on nanoripple patterned Si surface for SERS Application." Surfaces and Interfaces 52 (2024): 104852.
Nr: 24
Title:

Characterizing Mode Propagation in PMMA POFs with Intensity Measurements and Phase Retrieval
Authors:

Komal Ojha and Kumar Appaiah
Abstract: Plastic optical fibers (POFs) are well-suited for short-range communication due to their durability and flexibility, especially in terms of resistance to bending. However, their achievable data rates fall short compared to glass fibers, largely because of modal dispersion and inherent signal losses. Previous studies have used both deterministic and probabilistic models, relying on power flow equations to approximate the frequency response, but these models often overlook phase variations occurring during transmission. Measuring phase characteristics typically requires an array of coherent receivers, which is not practical for POF systems. In this study, we employ an imaging-based phase retrieval method to estimate the transfer function of POF links at a wavelength of 650 nm, across different link lengths, to determine data rate limits without needing RF measurements. By leveraging an iterative optimization technique, we precisely identify the mode distribution at the output of the POF and estimate the corresponding data rate limits. Additionally, we demonstrate that the data rates achieved using orthogonal frequency-division multiplexing (OFDM) are in line with the predicted limits.
Nr: 41
Title:

AI-Optimized Development of a Power-Efficient Four-Channel Silicon Nitride MMI WDM for O-Band Data Transfer
Authors:

Dror Malka
Abstract: We present an innovative design for a four-channel multiplexer utilizing multimode interference (MMI) wavelength division multiplexing (WDM) technology, optimized for energy efficiency and a compact footprint. Conventional designs typically use cascaded MMI couplers, resulting in larger footprints of several millimeters, which increases power consumption and complicates integration into photonic chips. Our design overcomes this limitation by employing a single MMI coupler unit made from silicon nitride (Si₃N₄), known for its favorable optical properties, operating within the O-band spectrum. The device efficiently transmits four channels with a wavelength spacing of 20 nm, covering the 1270–1330 nm O-band range. This is achieved after a light propagation distance of just 22.8 µm, significantly reducing the footprint. The multiplexer boasts 70% power efficiency, with insertion losses ranging between 1.24 and 1.67 dB. Moreover, the length and width of the MMI coupler demonstrate good fabrication tolerance, ensuring consistent performance despite manufacturing variations. A key aspect of this design is the optimization achieved through the integration of artificial intelligence (AI), combined with RSoft CAD tools using the beam propagation method (BPM) and finite-difference time-domain (FDTD) simulations, alongside MATLAB code. AI algorithms approximated the optimal configuration of the MMI coupler, enabling us to achieve high performance using only one MMI unit instead of cascading multiple couplers, which dramatically reduced the device’s size and complexity. In addition to minimizing footprint and power consumption, the Si₃N₄ waveguides and tapered input/output structures significantly reduce light reflections at the input, resulting in low back reflection. This enhances signal integrity and ensures reliable data transmission, making the device particularly suited for high-performance applications, such as O-band transceivers in data centers using WDM systems. In conclusion, the compact Si₃N₄-based MMI multiplexer offers high power efficiency, low insertion loss, and reduced back reflection, marking it as a highly suitable solution for next-generation data centers. The AI-driven optimization process further enhances the design by enabling a minimal footprint without compromising performance, presenting a significant advancement in photonic multiplexing technology.
Nr: 56
Title:

Recent Advances in Portable OCT Scanner
Authors:

Tatsuo Shiina
Abstract: In this research, we have so far developed OCT systems for industrial applications using TD-OCT.[1][2] Unlike SS-OCT and SD-OCT, TD-OCT has a higher limitation on measurement speed than them, but it is characterized by its high degree of freedom in OCT configuration design, allowing independent setting of wavelength, measurement resolution, measurement range, etc. Especially for industrial applications, this feature can be utilized since the size and the content of the measurement target vary. In this study, a method that uses a rotation mechanism for mechanical scanning of the optical path length as TD-OCT was implemented to realize highly repeatable and resizable scanning. In addition, the SLD was developed specifically for this OCT, enabling measurement with both operability and stability.[3] It is DC-powered, making it a portable OCT scanner that can be carried around or used as a battery-powered measurement style. TD-OCT measurement directly obtains interference intensity signals along the time axis in the depth direction of the optical axis, and since it does not require signal waveform conversion by FFT like SS/SD-OCT, simple and high-speed waveform processing can be realized, and is used for in-situ diagnosis in the manufacturing process. In addition, optical coefficients such as refractive index and dissipation coefficient of the measurement object can be obtained. By tracking their distribution and changes over time, they are used to provide feedback to the manufacturing process and improve yields.[4] The dynamic range of TD-OCT measurements is 45-50dB, which is narrower than SS/SD-OCT of >100dB. However, it is possible to devise ways to improve the dynamic range, and the sensitivity is comparable to that of medical OCT.[5] In fact, portable OCT scanners, which started development for industrial applications, are now being developed for basic medical applications in ophthalmology, dermatology, and dentistry. In this report, we review the history of portable OCT scanner development prior to the presentations of industrial and basic medical applications (Goto, Jumar, Okaneya), and explain how the current configuration has been developed in response to industrial needs. In addition, the new techniques installed into TD-OCT (high speed, multi-channel probes, long-range, ghost imaging etc.) will be discussed to show its potential [6].
Nr: 60
Title:

Holographic Multiplexing for Rapid Imaging of Sperm Cells
Authors:

Natan T. Shaked
Abstract: In vitro fertilization (IVF) treats infertility with 20-30% success rates only, and half of infertility cases are due to male factors. Currently, individual sperm cell selection in IVF is a very subjective and low throughput process due lack of suitable imaging methods, where human sperm staining is not allowed in human IVF. I will review our latest advances in developing label-free 3D imaging approaches for high-throughput optical acquisition of unstained and dynamic cells via interferometric multiplexing and novel tomographic approaches, according to which several perspective off-axis holograms, each containing another perspective wavefront of the imaged cell, are projected onto the camera at once, enabling 3D refractive-index imaging of live and highly dynamic sperm cells during free swim, with a great potential of increasing IVF success rates. I will also discuss the novel designs of the required interferometric systems, making them affordable for direct clinical use.
Nr: 61
Title:

Complex Unit Cells for BIC and Multimode Lasing in Plasmonic Nanoparticle Arrays
Authors:

Rebecca Heilmann, Grazia Salerno, Kristian Arjas, Javier Cuerda, Kerttu Aronen, Jani-Petri Martikainen, Tommi K. Hakala and Päivi Törmä
Abstract: Lattices of plasmonic nanoparticles have emerged as an effective platform for strong light-matter coupling, lasing, and Bose-Einstein condensation. We experimentally studied lasing in plasmonic nanoparticle arrays with complex unit cells. Such complex unit cells contain more than one particle, up to several tens of particles and lead to new modes in the system. We studied lasing in quadrumers arranged in a square array and found polarization-dependent emission patterns of the real space lasing emission. By theoretical analysis, we found that the lasing mode is a quasi-Bound State in Continuum (BIC) with a highly out-of-plane character [1]. For hexamers arranged in a triangular lattice, we found that, when tuning the scale of the unit cell, the lasing mode changes. The observed lasing modes were quasi-BICs with charges q = -2,-1, and +1. By tuning the unit cell, quality(Q)-factors of the modes in the system depend on the unit cell scaling, and the mode with the highest Q-factor is favoured for lasing [2]. We designed a supercell in a square lattice by leaving part of the lattice sites empty, thus creating a unit cell that contains 80 nanoparticles arranged in an aperiodic pattern. This results in an additional period in the system defined by the size of the supercell. By leaving parts of the array empty, some of the destructive interference is removed and additional dispersive branches emerge. This creates additional band edges that can support lasing. We experimentally demonstrate multimode lasing in such a supercell array and found that the lasing modes are bright modes at the 74th Gamma-point and 106th X-point of the supercell [3]. [1] Heilmann, R., Salerno, G., Cuerda, J., Hakala, T. K., & Torma, P. (2022). Quasi-BIC mode lasing in a quadrumer plasmonic lattice. ACS photonics, 9(1), 224-232. [2] Salerno, G., Heilmann, R., Arjas, K., Aronen, K., Martikainen, J. P., & Törmä, P. (2022). Loss-driven topological transitions in lasing. Physical Review Letters, 129(17), 173901. [3] Heilmann, R., Arjas, K., Hakala, T. K., & Törmä, P. (2023). Multimode lasing in supercell plasmonic nanoparticle arrays. ACS Photonics, 10(11), 3955-3962.
Nr: 72
Title:

3D Object Localization by Local Computational Integral Imaging
Authors:

Yitzhak Yitzhaky
Abstract: Computational integral imaging is a passive imaging technique that can produce information about the depth of objects in the scene by imaging the scene using an array of lenses or cameras that form an array of images slightly shifted from each other. These array of shifted images can be processed and analyzed to produce the depths of the objects in the observed 3D scene. The common method for passive depth estimation is stereo imaging, however, it may require complex measurements for the disparity calculations. Non-passive (i.e., active) imaging for producing depth data employs a source of illumination, as in time-of-flight cameras, however, scene illumination may be undesired or less effective in various cases. The method described here follows our recent study [1], which is an improvement of our previous study [2]. We demonstrate here the use of a camera array with computational integral imaging to efficiently estimate depth locations of objects detected and classified in the two-dimensional (2D) image of the scene. The process starts with a camera array [3] that captures an array of images or videos, termed Elemental Videos, where each image or video observes a slightly different angular perspective of the scene. At each time instance, the array of frames of these videos constitutes the current Elemental Images (EIs), which can also be termed Elemental Frames. Object detection using deep learning-based instance segmentation (via methods as Mask R-CNN or YOLOv8) is applied to a central elemental image in the video, producing regions (bounding boxes) and masks of the detected objects in the 2D image of the 3D scene. Each of the 2D detected objects at the current video frame goes through a local computational integral imaging at its bounding box region, forming a reconstructed depth tube constructed of local depth planes of the 3D scene at the object’s region. Sharpness measurements of these local depth planes can give the depth location of the object (the depth is at the location of the sharpest plane). The object’s depth location, together with its 2D segmentation, gives the object’s 3D localization. [1] M. Kadosh and Y. Yitzhaky, “3D Object Detection via 2D Segmentation-Based Computational Integral Imaging Applied to a Real Video”, Sensors 23 (9), 2023. [2] D. Aloni and Y. Yitzhaky, “Automatic 3D Object Localization and Isolation Using Computational Integral Imaging”, Appl. Opt. 54, 6717, 2015. [3] D. Avraham, G. Samuels, J.-H. Jung, E. Peli and Y. Yitzhaky, “Computational Integral Imaging Based on a Novel Miniature Camera Array”, Optica Publishing Group: Washington, DC, USA, 2022.
Nr: 99
Title:

Towards Finger Tactile Sensors Through Fibre Bragg Gratings
Authors:

Arezoo Sheykhian and Ricardo Oliveira
Abstract: In this work, a tactile force sensor based on fibre Bragg grating (FBG) is designed and introduced. The sensor is composed by two parts: metal casing, and FBG. The metal casing has a small diameter ring shape, namely, to accommodate the size of the fingers contact points. A thin metal sheet is soldered to the ring and an FBG is fixed on two sides of the ring and kept below the metal sheet. A small nut is mounted on top of the metal sheet to direct the force exerted by the finger contact point. The sensor was characterized by placing calibrated weights on top of 3 similar sensor structures disposed at equal distances for equal weight distribution. As the pressure increases, the metal sheet bends and the FBG is strained and red shifts. The sensor response time was ≈ 0.7 s and 1.1 s for the rise and fall time, reaching a pressure sensitivity of 3.7 x 10−6 nm/(N/m2). This work paves the way for the development of a multipoint tactile sensors able to monitor the pressure at the finger contact points, allowing its use in hand rehabilitation programs.
Nr: 16
Title:

A Portable Fluorescence-Based Device for Egg Analysis
Authors:

Panayiota Demosthenous, Antonio Varriale, Alessandro Capo and Marios Sergides
Abstract: In this work, we present the development of a portable fluorescence-based device for the detection and analysis of contaminants in eggs. The work comprised two primary sub-activities: first, the development of a portable device utilized a steady state fluorometer design, and second the identification and characterization of the fluorescence biosensor. The fluorometric configuration comprised three main components: (i) an excitation module with optical filters selected based on the labelling reagents excitation/emission wavelengths, (ii) a holder module featuring single use wells as the sample containers, and (iii) a detector module. Fluorescence is excited by a light source, and the emitted intensity is measured by a photodetector giving an indirect measurement of the analyte contaminated in the egg sample. A combination of convex lenses and a dichroic mirror focuses the excitation beam to the sample and directs the fluorescence emission to the detector, while emission filters minimize noise from background light. The entire system was controlled by an acquisition and control unit from National Instruments via LabVIEW, which handled the light source control, sensor data acquisition, basic data processing, and transmission of the results to a custom online data platform for further data processing and results visualization. The second primary activity constituted the identification and characterization of molecular recognition elements (MREs) to serve as biosensors targeting specific analytes, including Penicillin G, Neomycin, Aflatoxin M1, and Ochratoxin A. Antibodies were used as the MREs, which were characterized by ELISA experiments for their binding capabilities. An enzyme activity-based fluorescent immunoassay was subsequently developed and optimized for one of the suggested analytes, Penicillin G, using both laboratory-prepared and real-world egg matrix samples. Specifically, the fluorescence assay was using the enzymatic activities of the HRP enzyme coupled to the antibody. This type of enzyme is widely used as a signal amplifier in immune-enzymatic methods [Liu L, Chang Y, Lou J, Zhang S, Yi X. Overview on the Development of Alkaline-Phosphatase-Linked Optical Immunoassays. Molecules. 2023 Sep 11;28(18):6565]. For the development of the enzyme immunoassay, Penicillin G was conjugated to a Glutamine-binding protein (GlnBP) recombinant from E. coli, following the EDC/NHC protocol. Surface functionalisation of the sample-well with GlnBP-PenG was then applied. This device demonstrated the ability to perform reliable, fluorescence-based detection of a particular dye CF®568 in egg samples that is related to the real fluorescence assay, marking a significant advancement in portable biosensing technology for food safety applications.
Nr: 44
Title:

Singular Optics Approach for Controllable Beam Structuring, Spectral Broadening and Coherent Beam Recombination
Authors:

Lyubomir Stoyanov, Yinyu Zhang, Gerhard G. Paulus and Alexander Dreischuh
Abstract: Ultra-short laser pulse generation, along with extreme nonlinear processes such as high-harmonic generation, are extensively studied and actively evolving areas in modern photonics. Since their discovery, researchers have been addressing challenges like spectral broadening, filamentation, pulse and beam diagnostics, pulse amplification, and coherent beam recombination. Meanwhile, singular optics is another rapidly advancing field, focused on shaping laser beams by embedding phase singularities within them. A key application that warrants special focus is the spectral broadening of intense femtosecond pulses, essential for their subsequent temporal compression. At high intensities, beams can become unstable (see e.g., [1]), a challenge that can be mitigated by controllably splitting the beam into sub-beams. However, this approach is only viable if there is a reliable method to coherently recombine the sub-beams after spectral broadening, allowing for pulse compression just before they enter the laser-matter interaction zone. In this work we implement known objects from the area of the singular optics, like optical vortex arrays in the fields of ultra-short laser pulses in attempt to solve the problem of splitting and the subsequent coherent recombining. Previous studies [2-4] have shown that in the focal plane of a lens (i.e., in the artificial far field), it is possible to achieve a controllable and reversible break-up of square-shaped [2] and hexagonal optical vortex lattices [3] into an ordered array of well-defined peaks. In this work, we apply this technique to coherently recombine the peaks in the focal region after a nonlinear filamentation process in its vicinity, which results in spectral broadening of the femtosecond laser pulses involved. Experimental results demonstrating the controlled break-up into six peaks, filamentation, and coherent recombination of beams using specific optical vortex lattices in nonlinear media - ambient air and a glass substrate will be presented and discussed. Moreover, the compression of the spectrally broadened pulses in glass down to the Fourier transform limit is demonstrated, offering strong motivation for further optimization. This work was funded by the Bulgarian National Science Fund (project KΠ-06-H78/6) and by the Bulgarian Ministry of Education and Science as a part of National Roadmap for Research Infrastructure, project ELI ERIC BG. REFERENCES [1] A. Braun, G. Korn, X. Liu, D. Du, J. Squier, and G. Mourou, Opt. Lett. 20, 73-75 (1995). [2] L. Stoyanov, G. Maleshkov, M. Zhekova, I. Stefanov, D. N. Neshev, G. G. Paulus and A. Dreischuh, J. Opt. Soc. Am. B, vol. 35, pp. 402-409 (2018). [3] L. Stoyanov, G. Maleshkov, M. Zhekova, I. Stefanov, G. G. Paulus and A. Dreischuh, Journal of Optics, vol. 20, Art. No. 095601 (2018). [4] L. Stoyanov, S. Topuzoski, G. G. Paulus, and A. Dreischuh, European Physical Journal Plus , vol. 138, 702 (2023).
Nr: 97
Title:

Twisted Nematic Liquid Crystals as Components of the One-Way Double Pass Polarimeter to Measure the Birefringent Media
Authors:

Monika Salamaga and Władysław Artur Woźniak
Abstract: Liquid crystal variable retaders (LCVRs) as a consequence of the applied voltage introduce only a phase difference between their linear eigenstates, but do not allow changes in the eigenwaves parameters (azimuth and ellipticity angles). In the case of twisted nematic liquid crystals (TNLCs) due to the application of an external electric field there is not only a change in the phase difference which they introduce, but also in the polarization properties of their elliptic eigenvectors. Therefore, the possibilities of generating a variety of light polarization states are increased. We propose to use TNLCs, which are not very popular in Mueller's polarimetry, in a one-way double pass polarimeter. This is a non-classical polarimetric system design in which the same component module is used to generate (PSG) and then analyze (PSA) the light polarization state at the input and output of the system. Light passes twice through the PSG/PSA and the test medium by reflection from the mirror. In the analyzed cases, the PSG/PSA is constructed from a linear polarizer in combination with one or two TNLCs, and TNLC with LCVR. Important for the stability of the system is the azimuthal orientation of the elements and a suitably selected set of phase differences introduced by TNLCs and LCVRs. The developed numerical PSG/PSA models were optimized to find the optimal settings of the components, and thereby the best set of generators and analyzers, leading to the minimum system condition number. The operation of the optimized polarimetric systems was also verified for its ability to determine information about the parameters of the birefringent medium (azimuth and ellipticity angles, phase difference, amplitude transmission coefficients).
Nr: 98
Title:

Generalized Partial Optical Coherence
Authors:

Andrea Astrid Garcia Guzman
Abstract: Processes of partial coherence in optics are analyzed by proposing a generalized coherence matrix. This matrix is expanded to a 3-dimensional system corresponding to the nature of the optical fields. The structure of the resulting coherence matrix allows the identification of an interaction matrix which carries the information from the mixed states from the optical field, this matrix can be associated with a non-linear second-order differential equation and this resulting equation can be matched to a dynamical system, simulation and experimental results are shown.

Area 3 - Photonics

Nr: 7
Title:

Si CMOS Avalanche Photodiodes Based on Radial Electric Field Distribution
Authors:

Seyed Saman Kohneh Poushi and Horst Zimmermann
Abstract: Detecting low-power optical signals is a key challenge in the field of applied optical sensors. Linear-mode avalanche photodiodes (APDs), with their internal amplification, are highly effective optical detectors for systems that demand sensitive low-light detection, such as optical wireless communication (OWC), light detection and ranging (LIDAR), and imaging sensors. This paper reviews Si CMOS APDs based on a radial electric field distribution, which offer a large sensitive-area-to-total-area ratio while achieving high responsivity and bandwidth in the red and near-infrared range—addressing a common limitation in conventional planar photodiodes used in optical communication systems. In [1], we implemented the field-line crowding concept to design a new APD utilizing a compact n+/n-well structure fabricated in a standard CMOS process without modifications. This design achieves a maximum bandwidth of 1.6 GHz and a responsivity of 32 A/W at a wavelength of 675 nm, operating at 67 V, while maintaining a high sensitive-area-to-total-area ratio. Its scalability, combined with high sensitivity and a large fill factor, makes it ideal for array sensor applications. Further characterization in the near-infrared range, as well as analysis of the effects of various design parameters on performance, is presented in [2]. However, the high operational voltages of these diodes can create integration challenges with electronic circuits in certain CMOS technologies. To address this, in [3], we introduced a novel CMOS-integrated dot avalanche photodiode (APD), delivering comparable performance at significantly lower operating voltages compared to the field-line crowding APD. Furthermore, we propose an n+/p-well multi-dot structure, consisting of an array of individual dots with a shared anode. This innovative design allows for the expansion of the active area without compromising performance, positioning the multi-dot APD as an ideal candidate for applications requiring larger light-sensitive areas. By decoupling the P/N junction from the light-sensitive area, this structure enables the design of a photodiode with a large light-sensitive region and relatively low capacitance. REFERENCES [1] S. S. K. Poushi, B. Goll, K. Schneider-Hornstein, M. Hofbauer, and H. Zimmermann, “CMOS integrated 32 A/W and 1.6 GHz avalanche photodiode based on electric field-line crowding,” IEEE Photonics Technology Letters, vol. 34, no. 18, pp. 945–948, 2022. [2] S. S. K. Poushi, C. Gasser, B. Goll, M. Hofbauer, K. Schneider-Hornstein, and H. Zimmermann, “A near-infrared enhanced field-line crowding based CMOS-integrated avalanche photodiode,” IEEE Photonics Journal, vol. 15, no. 3, pp. 1–9, 2023. [3] S. S. K. Poushi, B. Goll, K. Schneider-Hornstein, M. Hofbauer, and H. Zimmermann, “Area and bandwidth enhancement of an n+/p-well dot avalanche photodiode in 0.35 μm CMOS technology,” Sensors, vol. 23, no. 7, p. 3403-3418, 2023.
Nr: 13
Title:

High Topological Charge Lasing in Quasicrystals
Authors:

Kristian Arjas, Jani Taskinen, Rebecca Heilmann, Grazia Salerno and Päivi Törmä
Abstract: Photonic modes exhibiting a polarization winding akin to a vortex possess an integer topological charge. Lasing with topological charge 1 or 2 can be realized in periodic lattices of up to six-fold rotational symmetry – higher order charges require symmetries not compatible with any two-dimensional Bravais lattice. Here, we experimentally demonstrate lasing with topological charges as high as -5, +7, -17 and +19 in quasicrystals. We discover rich ordered structures of increasing topological charges in the reciprocal space. Our quasicrystal design utilizes group theory in determining electromagnetic field nodes, where lossy plasmonic nanoparticles are positioned to maximize gain. Our results open a new path for fundamental studies of higher-order topological defects, coherent light beams of high topological charge, and realizations of omni-directional, flat-band-like lasing. [1] [1] Arjas, Kristian, Jani Matti Taskinen, Rebecca Heilmann, Grazia Salerno, and Päivi Törmä. "High topological charge lasing in quasicrystals." Nature Communications 15, no. 1 (2024): 9544.
Nr: 55
Title:

Investigation of Nonlinear Optical Properties in Lead-Free Double Perovskites
Authors:

Artur Barbedo, José Clabel Huamán, João Valverde, Leonardo de Boni and Cleber Mendonça
Abstract: The continuous advancement of technologies across various fields, from communication to medicine, is driven by exploring new materials and techniques in nonlinear optics (NLO) [1]. Despite significant progress, NLO materials continue to present challenges and innovation opportunities. Among the materials that have gained prominence in this area are semiconductors, particularly perovskites, which have shown great potential for applications in solar cells and other photonics devices [2]. Their nonlinear properties, particularly third-order nonlinearities, have demonstrated promising results, especially in lead-based halide perovskites [3]. Additionally, due to the high toxicity of lead, developing lead-free perovskites with comparable optoelectronic properties has become essential, with lead-free double perovskites emerging as a promising alternative [4]. This study focuses on the linear and nonlinear optical properties of 〖Cs〗_2 AgIn_0,9 Bi_0,1 Cl_6, a lead-free double perovskite, in its pure form and modified with rare earth ions (Er^(3+)and Eu^(3+)). Emphasis is placed on first-order hyperpolarizability (𝛽), a microscopic property related to macroscopic second-order susceptibility χ^((2)), which is crucial for processes like second harmonic generation (SHG), which is relevant to numerous applications. Hyper-Rayleigh scattering (HRS) was employed for spectral analysis, complemented by additional measurements such as Raman spectroscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD) to examine structural modifications in greater detail and their correlation with HRS. These perovskites show promising nonlinear properties, enhanced by structural octahedral modifications in pure, Er-doped, and Eu-doped samples. Both dopants induce asymmetry and alter bond angles, impacting HRS response uniquely, each contributing distinct variations in HRS intensity and wavelength. Raman analysis further reveals shifts in vibrational modes, confirming changes in local bonding environments. HRS measurements present an increase in 𝛽 magnitude with the modification, underscoring their potential for photonics applications. References [1] B. Cichy, D. Wawrzynczyk, A. Bednarkiewicz, M. Samoc, W. Strek; Third-order nonlinear optical response of CuInS2 quantum dots—Bright probes for near-infrared biodetection. Appl. Phys. Lett. 17 June 2013; 102 (24): 243702. https://doi.org/10.1063/1.4811786 [2] J. Xu, X. Li, J. Xiong, C. Yuan, S. Semin, T. Rasing, X.-H. Bu, Halide Perovskites for Nonlinear Optics. Adv. Mater. 2020, 32, 1806736. https://doi.org/10.1002/adma.201806736 [3] Sousa, C. A.; Bonato, L. G.; Gonçalves, E. S.; Alo, A.; Vale, B. R. C.; Almeida, D. B.; Nogueira, A. F.; Zagonel, L. F.; Padilha, L. A. Addressing the Magnitude of the Nonlinear Refraction Response in Perovskite Nanocrystals. ACS Photon. 2023, 10, 1334– 1340, DOI: 10.1021/acsphotonics.2c01985 [4] Manna, D., Das, T. K., & Yella, A. (2019). Tunable and Stable White Light Emission in Bi3+ Alloyed Cs2AgInCl6 Double Perovskite Nanocrystals. Chemistry of Materials. doi:10.1021/acs.chemmater.9b02973.
Nr: 27
Title:

Single Crystal Barium-Titanate-on-Insulator Optoelectronics
Authors:

Aaron Danner and Soon Thor Lim
Abstract: Barium titanate has a strong Pockels effect, with a bulk r-value exceeding 1300 pm/V. We have grown thin film barium titanate on a low index lattice-matched substrate and achieved r-values approaching bulk values, fabricated low-loss waveguides, interferometers, and ring resonators, and also periodically poled the material. The combination of good transparency, good crystallinity, and strong electro-optic properties make barium titanate an attractive material that could potentially compete with lithium niobate for future applications in chip-based nonlinear optics. Due to the fact, however, that the strong r-values in barium titanate are off-diagonal permittivity components, traditional modulator design schemes like Mach-Zehnder interferometers do not function the same way in this material. In this presentation, unusual optical properties associated with off-diagonal permittivity tensor modulation will be explored.
Nr: 51
Title:

Laser LIPSS: Sub-Resolution Laser Structuring for Organic Lasers
Authors:

Tobias Antrack, Tiange Dong, Frithjof Pietsch, Jakob Lindenthal, Markus Löffler, Bernd Rellinghaus, Johannes Benduhn, Markas Sudzius and Karl Leo
Abstract: Organic materials are promising candidates for developing compact, efficient, and tunable thin-film lasers. Among the various resonator designs, distributed feedback (DFB) structures are particularly appealing due to their potential for integrated and compact laser systems. In this study, we present a novel approach for fabricating DFB resonators using laser-induced periodic surface structures (LIPSS). This method allows us to achieve feature sizes significantly smaller than the wavelength of the structuring laser, offering new possibilities for miniaturization and fabrication flexibility. Our samples consist of laser structured glass substrates with vacuum-deposited Alq₃:DCM as the organic gain medium. Under optical pumping, these structures demonstrate efficient lasing emission. By varying the length of the DFB reflectors and the spacing between individual reflectors, we systematically explore the impact of these parameters on the effective mode volume contributing to lasing. This investigation provides valuable insights into optimizing the DFB design for enhanced lasing performance in organic thin-film lasers. The results highlight the potential of LIPSS-fabricated DFBs for the development of easy to produce organic lasers, paving the way for future applications in photonic devices and integrated laser systems.