Abstracts Track 2023

Area 1 - Optics
Area 2 - Photonics

Area 1 - Optics

Nr: 6
Title:

Scan-Less Fluorescence Lifetime Microscopy Using Dual-Comb Optical Beat
Authors:

Takeshi Yasui
Abstract: When a fluorescent substance is momentarily excited by light, the resulting fluorescence decays with a decay time peculiar to the substance, namely fluorescence lifetime. Fluorescence lifetime microscopy (FLIM) is an image acquisition method that uses this fluorescence lifetime as a contrast. Fluorescence lifetime provides high quantification regardless of various observing conditions, and enables highly sensitive visualization of changes in the surrounding environment of fluorescent molecules. However, most FLIMs are based on point measurement, which requires mechanical scanning of the focus position, limiting high-speed image acquisition. We have developed a dual-comb FLIM that enables scan-less imaging by making full use of a group of dual-comb optical beats and wavelength-to-space conversion [1]. In this method, 2D distribution of fluorescence lifetime is collectively acquired by one-to-one correspondence among optical comb mode frequency, RF comb mode frequency, and image pixel position by dimensional conversion. By interfering two optical combs, each mode of the optical comb is tagged with a unique RF beat frequency. Since the fluorescence is modulated at the same RF frequency as the excitation light, the 2D image can be recovered from the mode-resolved RF spectrum. The obtained amplitude and phase information can correspond to the fluorescence intensity and fluorescence lifetime, and the simultaneous acquisition of fluorescence intensity and lifetime images can be realized without mechanical scanning. Since this method ensures simultaneous measurement of the entire field of view, it not only makes it possible to elucidate the movement of molecules inside living cells in the field of life science, but it also enables multifaceted evaluation using fluorescence intensity and fluorescence lifetime. [1] Takahiko Mizuno, Eiji Hase, Takeo Minamikawa, Yu Tokizane, Ryo Oe, Hidenori Koresawa, Hirotsugu Yamamoto, and Takeshi Yasui, "Full-field fluorescence lifetime dual-comb microscopy using spectral mapping and frequency multiplexing of dual-comb optical beats," Science Advances, Vol. 7, No. 1, art. eabd2102(2021).
Nr: 25
Title:

Four Channel C-Band Using Cascaded MMI on Silicon Nitride Strip Waveguide Technology
Authors:

Dror Malka
Abstract: The vast growing of developments in the optical communication systems over the C-band spectrum requires new and powerful waveguide components that can support high speed light communication with low power losses, large bandwidth and low back reflection losses. Optical demultiplexers are an important part of communication networks and can be implemented with different technology techniques: Y-branch devices, Mach-Zehnder interferometers and Multimode Interference (MMI) couplers. Dense wavelength division multiplexing (DWDM) technology is used to increase the data transfer bitrate by decreasing the spacing between peak wavelengths and as a result more channels can be utilized for a single spectral band. Back reflection losses are a key problem that limits the performances of optical communication systems that work on DWDM technology based on Silicon (Si) MMI waveguides. In order to overcome this problem, we propose a novel design for a 1×4 optical demultiplexer based on the MMI in Silicon-Nitride (SiN) strip waveguide structure that operates at the C-band spectrum. Simulation results show that the proposed device can transmit 4-channels with a 10 nm spacing between them that work in the C-band with a low power loss range of 1.98-2.35 dB, large bandwidth 7.68-8.08 nm, good crosstalk 20.9-23.6 dB. Thanks to the low refractive index of SiN a very low back reflection of 40.57 dB is obtained without using a special angled MMI design which usually required using Si MMI technology. The results also show the promising potential for such a device to be implemented in DWDM technology communications systems to increase the data bitrate. Because of the good flexibility in tolerance range of ±2.5 μm for the MMI coupler lengths, the proposed device design can be fabricated using the fab processes that are available today. The simple design of the device makes it easier to expand the number of channels by cascading multiple MMI couplers and adjusting their geometrical parameters accordingly. Moreover, it is shown that the proposed device has a low back reflection loss ranging between 40-41 dB without using a special angled MMI design and this is because the use of SiN as the core material. Thus, this SiN demultiplexer MMI technology can be utilized to be used in DWDM technique for obtaining high data bitrate alongside with a low back reflection in optical communication systems.
Nr: 41
Title:

A Bidirectional Transmission Distribution Function Study of Cellulose Nanofibrils Films
Authors:

Li Yang, Iryna Gozhyk, Jan Audenaert and Youri Meuret
Abstract: Cellulose nanofibrils (CNF) films possess properties ideal as building blocks and supporting platforms for functional devices in photonics. Light transmittance and Haze are often measured quantities which are the overall representations of the complex light-NCF film interactions including reflections / refractions at the interfaces, scattering and absorption in the film’s bulk, etc. In this work, we studied the detailed light transmission behaviours of CNF films using bidirectional transmission distribution function (BTDF) measurement technique, in addition to the spectral transmittance and Haze. Five sets of NCF films made from NCFs that passed 1-5 times through the homogenization process, having different optical properties, were prepared by RISE. The BTDF data was measured for various incident angles by Saint-Gobain. The BTDF obtained from randomly selected illumination spots on the front and back sides of the CNF films. It shows that the film of one pass (1P) has the widest transmission peak, while the one having 5 passes (5P) the narrowest. This indicates that the low-pass samples have stronger light scattering than the ones of higher number passes. The similarity of the profiles also suggest that the random local curvatures of the samples had no significant influence on the BTDF. The BTDF data were further analysed at KU Leuven. The inverse adding-doubling (IAD) procedure was applied to the BTDF data for 0° angles of incidence, to obtain volume scattering parameters for these samples (i.e. the absorption coefficient, scattering coefficient and scattering phase function parameters). These parameters were then used to predict the BTDF at larger incident angles, 15o, 30 o, 45 o, and 60 o, respectively. Despite some inadequateness of the approach, excluding surface roughness and surface shape, the simulation predictions resulted in fairly good predictions of the transmitted radiant intensity (BTDF) at the skew angles of incidence. At angles of incidence above 45°, the simulation model starts to deviate significantly from the measurements because surface scattering effects become more prominent for such large angles of incidence. This work has received funding from the EMPIR programme through the project JRP 18SIB03 BxDiff.
Nr: 12
Title:

Photo-Induced Complex Waveguiding Structures by Counterpropagating Bessel Beams
Authors:

Marsal Nicolas
Abstract: Optical interconnection technologies are expected to replace electronic systems for improving information processing performance due to their broad bandwidth, high speed, long-distance data transmission and potential reconfigurability. Current optical devices, such as optical fibers, silicon waveguides, and photonic integrated circuits, are limited because those classical optical systems necessarily work with high peak power and are usually bulky, passive, and not reconfigurable. Another widespread approach is based on scalable and reconfigurable optical techniques using nonlinear Kerr or photorefractive (PR) medium. Combining such materials with peculiar beam profiles propagating inside offers a smart optical platform to study complex waveguiding structures with multiple inputs/outputs. Due to their unique profiles and fascinating propagating phenomena, unconventional beams like Airy beams are good candidates for photo-inducing waveguiding structures in for example a photorefractive medium. Bessel beams (BBs) share also similar features with Airy beams, such as diffraction-free, multi-lobes profiles, and self-trapping properties under nonlinear conditions. Thus, several studies on waveguides induction using non-diffracting BBs under weak nonlinearity have been developed [2]. Instead, our recent experimental work unveiled that diffracting BBs propagating under high nonlinear conditions provide more advantages and opportunities for fully controllable waveguiding structures [3]. We analyze here theoretically the waveguiding structures photo-induced by two incoherent counter-propagating Bessel beams (BB) in a biased photorefractive crystal. We demonstrate that the cross-coupling of two BBs enables more adressable channels and better tunability of the forming guiding structures. The truncation parameter of the BB’s, its Bessel order and the misalignment between the two beams are all key parameters for tailoring the characteristics of the photo-induced waveguides such as the number of the outputs, the output intensity levels of each channel and the distance between each output gate. Accordingly, we optimized the different parameters for designing not only a fully tunable Y-couplers but also optical splitters with up to five output gates and even more complex star couplers for all-optical interconnect applications. Finally, we report on the stability behavior of the photo-induced platform. The stability threshold depends on the nonlinearity parameter beyond which the beams display time-periodic, quasi-periodic and turbulent dynamics where spatially localized instabilities can be observed. All these results suggest more opportunities for fully controllable complex waveguiding structures and new all optical solutions for active components in optical telecommunication and innovative ways of performing optical computing based on spatiotemporal chaos. [1] N. Wiersma, N. Marsal, M. Sciamanna, D. Wolfersberger, Opitcs Lett. 39, 5997 (2014). [2] F. Xin, M. Flammini, F. Di Mei, L. Falsi, D. Pierangeli, A. J. Agranat, and E. DelRe, Phys. Rev. Appl. 11, 024011 (2019). [3] Y. Chai, N. Marsal, D. Wolfersberger, Phys.Rev.Appl. 17, 064063 (2022).
Nr: 46
Title:

Optical Microcavity Coupling with Two-Dimensional WS2
Authors:

Jiangrui Qian and Jason Smith
Abstract: Understanding and engineering of light-matter interaction play an important role in advances of science and technology, especially after the invention of the laser. This interaction can be enhanced resonantly when suitable material is placed in a small volume with confined light, which can generate exciton-polaritons, quasi-particles comprising superposition states of photons and excitons in semiconductors, holding promise for devices such as 'threshold-less' lasers. Here we investigate the fabrication of exciton-polariton light source devices using 2D semiconductor materials in optical microcavities. 2D semiconductors such as WS2 monolayers offer large exciton binding energies, making polariton formation possible at room temperature. The CVD-grown WS2 monolayers show a typical photoluminescence peak at 2.01eV with a linewidth of 70 meV. We have built a model and simulated numerically how the 2D WS2 perturbs the photonic modes with a finite-difference time-domain (FDTD) method. Only a redshift is observed when the excitonic signature of the monolayer is eliminated by setting its index to an averaged constant. The characteristic anti-crossing behaviour of coupling occurs only when the frequency dependence of the WS2 is incorporated. Cavity mode profiles are resolved spatially, and an anti-node is engineered at the surface of a mirror. As such, the coupling strength can be maximised with the WS2 at the maximal electric field. The dependence of Rabi splitting on the cavity length agrees with the theoretical analysis and analytical simulation using a transfer matrix method. Smaller RoC and cavity length produce smaller cavity mode volume and thus larger coupling strength. Also, cavities composed of distributed Bragg reflectors (DBRs) and metallic mirrors have been simulated. The strongest coupling, producing a Rabi splitting exceeding 120 meV, is achieved with silver mirrors, which can be explained by the small optical penetration depth. Experimentally, hemispherical features have been fabricated with a focused ion beam to build optical microcavities with small mode volumes. Features with a submicron radius of curvature (RoC) have been successfully milled. We have measured planar cavity transmission spectra (Ag-DBR, Ag-Ag) and observed the periodical evolution of the unperturbed cavity modes when the length is swept over 5 microns. The results agree well with the simulation ones. This demonstrates the consistent tunability of cavity modes over a wide range with a mode kept in resonance with excitons. The smallest longitudinal mode number reaches three in an Ag-Ag planar cavity, with a linewidth of 130 meV. An initial coupling experiment is done using an Ag-DBR cavity. The anti-crossing behaviour emerges when photonic and excitonic modes are continuously detuned towards small cavity lengths. A Rabi splitting of ~ 27 meV has been derived, which is smaller than the lower branch's linewidth, indicating a weak coupling. We have built a MATLAB APP to automate the cavity-sweeping with real-time visualisation, which enhances experimental efficiency and reproducibility. Furthermore, a Gaussian optimiser will be integrated for efficient searching of maximal Rabi splitting based on electronically tuneable cavity parameters. Hence, we propose that the WS2 in metallic optical microcavities can be engineered to form exciton-polaritons with a large Rabi splitting (~120 meV) at room temperature, which is of great technological and scientific interest.
Nr: 49
Title:

Diffraction Effects on Long-Path TD-OCT
Authors:

Tatsuo Shiina
Abstract: In this study, long-path time-domain OCT has been developed to evaluate the concentration and refractive index of mixed solution with a certain volume. Their time change and phase change are focused on the experiment. The system has been improved to measure the concrete solution with the measurement range of up to 100mm with high position resolution of 1 micrometer. It is equivalent to the ability to distinguish the difference or change of refractive index (group index of refraction) of 4 decimal places. When we inserted the different index optical material into a solution, the diffraction-like pattern has been observed on their boundary. In general, the diffraction pattern appears on the front screen through the beam propagation, while the observed diffraction pattern is displayed on B-scan of OCT signals with its point measurement. We analyzed this phenomenon with experiments and theory. When the shield plate is inserted into the solution, its boundary acts as the knife-edge, and diffraction-like pattern of knife-edge was appeared on B-scan of OCT signals. The variation of diffraction patterns is coincided with the ordinal diffraction patterns. When the transparent material, of which refractive index is different with the solution, is inserted into the solution, their boundary causes the Becke line pattern. It is caused by the phase shifts interference due to the differences of refractive index and optical path. We estimate this diffraction pattern to calculate their phase shift with theory. It is well coincided with the experimental results. The diffraction pattern appears on the front screen to be spread from the boundary. The incident beam is fixed, and the diffraction pattern spread in the beam area with the optical intensity vibration. On the other hand, the OCT probe beam has a certain size, and conducts the point measurement. The probe beam or inserted material is scanned in vertical direction against the optical axis. The boundary of the material is scanned in the beam area. The OCT diffraction pattern is appeared on this B-scan, that is, the OCT signal intensity causes interference wave due to the arrangement of the probe beam and material boundary. Depending on the beam divergence and the propagation distance, the diffraction pattern changes its behavior. In this study, we evaluate the diffraction phenomenon with quantitatively and consider them theoretically. These diffraction pattern appears on point measurement in sensing scene. Not only OCT but LiDAR observation cause these phenomena. The longer the observation distance is, the larger the influence of the diffraction pattern is. Positioning, size, and optical property of the target should be correct and considered with this evaluation.

Area 2 - Photonics

Nr: 2
Title:

Second Harmonic Generation in 2D-Embedded Optical Fibers
Authors:

Gia Quyet Ngo, Antony George, Emad Najafidehaghani, Falk Eilenberger, Andrey Turchanin, Malte-Per Siems, Ziyang Gan, Alessandro Tuniz, Sara Khazaee, Ulf Peschel and Markus Schmidt
Abstract: Monolayer transition-metal dichalcogenides [1] (TMDs) possess highly intriguing photonic properties including large optical nonlinearities and unprecedented exciton binding energies. Their sheet nonlinear susceptibility is substantial and in the same order of magnitude as the commonly used nonlinear bulk crystal [2]. Remarkably, TMDs can be grown conformally as monolayer crystals on almost any conventional substrates. However, the minuscule thickness limits the total nonlinear conversion efficiency of such crystals. Hence, directly growing monolayer TMDs on the exposed core optical fiber (ECF) [3] could increase the nonlinear interaction and create novel opportunities in nonlinear light sources, fiber-based sensing, and single-photon sources, to name just a few. Here, we demonstrate TMD-functionalized ECFs as a novel nonlinear photonics platform possessing a large second-order susceptibility and show the enhancement of second-harmonic generation in resonance with excitons. In this work, our hybrid fiber exhibits a quantitative χ(2) value of 44 pm/V and an SHG conversion efficiency of 0.2×10-3 m-2W-1 [4]. This χ(2) value is 44x stronger than the relevant contenders for integrated SHG, for instance, Germanium doped glass. References: [1] K. F. Mak, C. Lee, J. Hone, J. Shan, and T. F. Heinz, “Atomically Thin MoS2: A New Direct-Gap Semiconductor,” Phys. Rev. Lett. 105, 136805 (2010). [2] A. Autere, H. Jussila, Y. Dai, Y. Wang, H. Lipsanen, and Z. Sun, “Nonlinear optics with 2D layered materials,” Advanced Materials 30, 1705963 (2018). [3] G. Q. Ngo, A. George, F. Eilenberger, et al., “Scalable functionalization of optical fibers using atomically thin semiconductors,” Advanced Materials 32, 2003826 (2020). [4] Ngo, Gia Quyet, et al. "In-fibre second-harmonic generation with embedded two-dimensional materials." Nature Photonics (2022): 1-8. https://doi.org/10.1038/s41566-022-01067-y.
Nr: 28
Title:

Plasmonic Coupled Nanogold for DNA Fingerprints Recognition with SERS
Authors:

Vasyl Shvalya
Abstract: Plasmonic substrates brought tremendous analytical progress into optical and spectroscopic sensing applications. Specifically, the nanostructures with prominent light-capturing features and capabilities to generate optically induced localized electric fields due to electron-photon coupling have found their use in biosensing with SERS (Surface-Enhanced Raman scattering) and SEIRA (Surface-Enhanced Infra-Red Absorption) techniques. Among various biologically relevant challenges, DNA/RNA-related research represents a significant interest in nanomedicine, bionanotechnology, vaccine design, and functional gene engineering development. This biological macromolecule is the most important and valuable object for microbiologists because it contains genomic information about bio-creatures.[1] At the moment, a selection of molecular-sensitive techniques for DNA/RNA investigations is relatively limited, among which PCR (polymer chain reaction) based methods rule out the field. Nevertheless, it is challenging to probe with optical approaches like inelastic Raman scattering or SERS (Surface-Enhanced Raman scattering). Regardless of being quite promising, SERS is still under technological, nanoengineering and analytical improvement. Better SERS-sensor functionality hails from well-designed plasmonic nanomaterials, which induce noticeably improved photon scattering efficiency of the analyte because of the strong field confinement effect in the vicinity of the metallic surface.[2] The presented report demonstrates how a nanoplasmonic sensor can be designed with the use of plasma. Through this method, microscaled aggregates composed of AuNPs were obtained from the nebulized ionic gold liquid precursor. A strong coupling between gold nanoparticles leads to a high analytical enhancement factor of about 107, confirmed by numerical Maxwell simulations. Analytically, it allowed us to obtain Raman fingerprints of bacterial DNA fragments (M. luteus and S. aureus, E. coli, J. lividum) at nanograms sample quantities. The collected DNA molecular vibrational features related to nucleobase motions were extracted and used to distinguish the bacterial species consistently by engaging statistical principal component analysis. References [1] Garcia-Rico, E., Alvarez-Puebla, R. A., & Guerrini, L. (2018). Chemical Society Reviews, 47(13), 4909-4923. [2] Shvalya, V., Filipič, G., Zavašnik, J., Abdulhalim, I., & Cvelbar, U. (2020). Applied Physics Reviews, 7(3), 031307.
Nr: 37
Title:

Formation of Relief Optical Gratings in Materials Containing Azobenzenes: Optimization of the Method
Authors:

Maria Raposo, José Loja and Paulo A. Ribeiro
Abstract: The azobenzene molecules have the propriety to suffer isomerization induced by the light at a determined wavelength, where the referred molecules are converted from the trans form, which is energetically the most stable form, to the cis form, absorbing radiation. This photochemical process is responsible by the creation of birrefringence in the medium, allowing the formation of optical relief gratings on thin films or at the surface of the materials that contain azobenzenes in their chemical structure. The use of these materials has application in photonics, namely in the creation of optical memories, sensors and devices for the energy conversion. In this work the creation of relief gratings on thin films of azopolymer poly[1-[4-(3-carboxy-4-hydroxyphenylazo) benzene sulfonamido]- 1,2-ethanediyl, sodium salt] (PAZO), when it is irradiated by an interference pattern was characterized. Different experimental assemblies for creating diffraction patterns were tested in PAZO thin films and the optical gratings were characterized. Results demonstrates that the photolithography technique is the most economical and simple technique for the formation of relief optical grids but needs higher intensity light sources. Michelson interferometry technique with heated samples allows the creation relief grids more quickly. However, it cannot be applied to thicker films since the material may contract and break up. The Michelson interferometry technique with auxiliary laser proved to be the most efficient technique in the formation of optical gratings, obtaining more visible relief gratings and with shorter irradiation times.
Nr: 50
Title:

Optical Wavelength Estimation Using Received Optical Powers
Authors:

Jae Myoung Lee
Abstract: A wavelength is estimated based on optical powers measured through photodetectors in the proposed wavelength estimation system. A conventional optical measurement system consists of an optical source, an optical sensor measuring physical quantities, such as temperature, pressure, strain, etc., and an optical receiver with data processing unit. An optical spectrum analyzer (OSA) has been used as a receiver unit which can show a graph of optical power vs. wavelength for certain range of wavelength. The OSA, however, is high-cost, bulky, and vulnerable to environmental impacts, which is the main reason why the OSA has been mostly used for indoor laboratories. The proposed optical wavelength estimation system can overcome those weaknesses, lowering the cost of the system, realizing small size, and making the system robust to exterior mechanical impacts. In the proposed system, a beam which is reflected from an optical sensor, which is usually fiber Bragg grating (FBG) filter, is divided into two beams. One of them travels to a photodetector without any amplitude change, and the other beam passes through an optical filter which reduces the optical power of it. On the second path, the amount of power reduction depends on the wavelength of the beam. Using two optical powers, we can estimate the transmission rate of the second beam which is tied with the wavelength characteristics of the optical filter. The proposed wavelength estimation scheme can use commercial filters such as FBG filters and extend measuring wavelength range by employing multiple filters. In the proposed wavelength estimation, the wavelength resolution of the proposed scheme can be less than 0.4 nm.