Optical Photons Research Articles

Optical Photon Propagation Characteristics and Thickness Optimization of LaCl3:Ce and LaBr3:Ce Crystal Scintillators for Nuclear Medicine Imaging

The present study focuses on the determination of the optimal crystal thickness of LaCl3:Ce and LaBr3:Ce crystal scintillators for Nuclear Medicine Imaging applications. A theoretical model was applied for the estimation of the optical efficiency of the two single-crystal scintillators in terms of Detector Optical Gain (DOG). The theoretical model was validated against the experimental values of the Absolute Efficiency (AE) of the two crystals, obtained in the energy range 110 kVp–140 kVp. By fitting the theoretical model to these experimental data, the propagation probability per elementary thickness k was determined and DOG was theoretically calculated for crystal thicknesses from 0.005 cm to 2 cm, in the energy range of Nuclear Medicine Imaging. k values for LaCl3:Ce and LaBr3:Ce crystals were significantly higher compared to other single-crystal scintillators. The DOG values of the two crystals may serve as evidence that the LaBr3:Ce crystal exhibits significantly better performance compared to the LaCl3:Ce crystal. With an increase in energy, the optimum thickness increases for both crystals. Additionally, crystal efficiency generally demonstrates a decrease beyond a certain thickness. The aforementioned insights may provide valuable guidance for the design and optimization of crystal scintillators in Nuclear Medicine Imaging systems.

High-efficiency edge couplers enabled by vertically tapering on lithium-niobate photonic chips

In the past decade, photonic integrated circuits (PICs) based on thin-film lithium niobate (TFLN) have made substantial progress in various fields, including optical communication, nonlinear photonics, and quantum optics. A critical component is an efficient edge coupler facilitating the connection between PICs and light sources or detectors. Here, we propose an innovative edge coupler design with a wedge-shaped TFLN waveguide and a silicon oxynitride cladding. Experimental results show a low coupling loss between the TFLN PIC and a 3-μm mode field diameter (MFD) lensed fiber, measuring at 1.52 dB/facet, with theoretical potential for improvement to 0.43 dB/facet. Additionally, the coupling loss between the edge coupler and a UHNA7 fiber with an MFD of 3.2 μm is reduced to 0.92 dB/facet. This design exhibits robust fabrication and alignment tolerances. Notably, the minimum linewidth of the TFLN waveguide of the coupler (600 nm) can be readily achieved using commercially available i-line stepper lithography. This work benefits the development of TFLN integrated devices, such as on-chip electro-optic modulators, frequency combs, and lasers.

The SNR of time-of-flight positron emission tomography data for joint reconstruction of the activity and attenuation images

Objective. Measurement of the time-of-flight (TOF) difference of each coincident pair of photons increases the effective sensitivity of positron emission tomography (PET). Many authors have analyzed the benefit of TOF for quantification and hot spot detection in the reconstructed activity images. However, TOF not only improves the effective sensitivity, it also enables the joint reconstruction of the tracer concentration and attenuation images. This can be used to correct for errors in CT- or MR-derived attenuation maps, or to apply attenuation correction without the help of a second modality. This paper presents an analysis of the effect of TOF on the variance of the jointly reconstructed attenuation and (attenuation corrected) tracer concentration images. Approach. The analysis is performed for PET systems that have a distribution of possibly non-Gaussian TOF-kernels, and includes the conventional Gaussian TOF-kernel as a special case. Non-Gaussian TOF-kernels are often observed in novel detector designs, which make use of two (or more) different mechanisms to convert the incoming 511 keV photon to optical photons. The analytical result is validated with a simple 2D simulation. Main results. We show that if two different TOF-kernels are equivalent for image reconstruction with known attenuation, then they are also equivalent for joint reconstruction of the activity and the attenuation images. The variance increase in the activity, caused by also jointly reconstructing the attenuation image, vanishes when the TOF-resolution approaches perfection. Significance. These results are of interest for PET detector development and for the development of stand-alone PET systems.

Optical photon transport simulations for SiPM based PET scanner

Positrons emitted from radioisotope quickly annihilates to two collinear photons that are captured by the array of scintillator detectors to infer about the origin of radioactivity. Coincidence collection of pair of points from the detector modules makes a line of response, their large number reveals a radioactive region of interest. Most of the medical diagnostic research is conducted with position sensitive imaging device whose performance strongly depends on the optical light collection efficiency. A versatile Lutetium–Yttrium Oxyorthosilicate (LYSO) scintillator is used to mimic the optical photon production and transport processes followed by the light collection with Silicon PhotoMultiplier sensor. Charge spectrum from a 2 × 2 × 10 mm3 single LYSO bar is obtained in GEANT4, and reproduces well the scintillation characteristics of LYSO along with photons incidence angle distribution with a single SiPM pad. This excercise is followed by the simulation performance of two PET modules comprises of 12 × 12 SiPM tile coupled with mesh of LYSO bars. The preliminarly results shows the transverse position resolution (FWHM) as 7.82 mm for a point source. Objective of this study is to search for a cheaper detector solution which will have equivalent imaging performance.

Multiterminal nonreciprocal routing in an optomechanical plaquette via synthetic magnetism

Optomechanical systems with parametric coupling between optical (photon) and mechanical (phonon) modes provide a useful platform to realize various magnetic-free nonreciprocal devices, such as isolators, circulators, and directional amplifiers. However, nonreciprocal router with multiaccess channels has not been extensively studied yet. Here, we propose a nonreciprocal router with one transmitter, one receiver, and two output terminals, based on an optomechanical plaquette composing of two optical modes and two mechanical modes. The time-reversal symmetry of the system is broken via synthetic magnetism induced by driving the two optical modes with phase-correlated laser fields. The prerequisites for nonreciprocal routing are obtained both analytically and numerically, and the robustness of the nonreciprocity is demonstrated numerically. Multiterminal nonreciprocal router in optomechanical plaquette provides a useful quantum node for development of quantum network information security and realization of quantum secure communication.

Lagging propagation phase of spatially structured beams

The structured beams especially with spatially varying phase distribution have attracted tremendous attention in both physics and engineering. Recently, studies have shown that the transverse spatial confinement of optical fields or photons leads to a modification of the group velocity but the phase velocity of propagating structured beams is revealed insufficiently in the experiments. In this work, we provide the theoretical model and experimental observation of propagation phase of structured beams. The analysis suggests that the spatially structured beams with a definite axial component of wavevector kr carry a so called “lagging propagation phase”, which can be considered as a generalized Gouy phase that originally appears within a focal region. Taking the higher-order Bessel beam as an example, the propagation phase difference is demonstrated by mapping to the rotating angle of intensity patterns superposed with different radial and angular phase gradients. Physically, the lagging propagation phase may provide an interpretation for the dynamic evolution of complex structured beams or interfering fringes upon propagation such as the vortex knots or braids. From the application aspect, the lagging propagation phase would facilitate a promising way for structured beams in optical sensing and metrology.

High-speed metasurface modulator using perfectly absorptive bimodal plasmonic resonance

Free-space electro-optic (EO) modulators operating at gigahertz and beyond are attractive for a wide range of emerging applications, including high-speed imaging, free-space optical communication, microwave photonics, and diffractive computing. Here, we experimentally demonstrate a high-speed plasmonic metasurface EO modulator operating in a near-infrared wavelength range with a gigahertz modulation bandwidth. To achieve efficient intensity modulation of reflected light from an ultrathin metasurface layer, we utilize the bimodal plasmonic resonance inside a subwavelength metal–insulator–metal grating, which is precisely tuned to satisfy the critical coupling condition. As a result, perfect absorption of −27 dB (99.8%) and a high quality (Q) factor of 113 are obtained at a resonant wavelength of 1650 nm. By incorporating an EO polymer inside the grating, we achieve a modulation depth of up to 9.5 dB under an applied voltage of ±30 V. The 3-dB modulation bandwidth is confirmed to be 1.25 GHz, which is primarily limited by the undesired contact resistance and the output impedance of the driver. Owing to the high electrical conductivity of metallic gratings and a compact device structure with a minimal parasitic capacitance, the demonstrated device can potentially operate at several tens of gigahertz, which opens up exciting opportunities for ultrahigh-speed active metasurface devices in various applications.

Unified gas-kinetic particle method for frequency-dependent radiation transport

This paper proposes a unified gas-kinetic particle (UGKP) method for the frequency-dependent photon transport process. The photon transport is a typical multiscale process governed by the nonlinear radiative transfer equations (RTE). The flow regime of photon transport varies from the ballistic regime to the diffusive regime with respect to optical depth and photon frequency. The UGKP method is an asymptotic preserving (AP) scheme and a regime adaptive scheme. The teleportation error is significantly reduced, and the computational efficiency is remarkably improved in the diffusive regime. Distinguished from the standard multigroup treatment, the proposed UGKP method solves the frequency space in a non-discretized way. Therefore the Rosseland diffusion system can be precisely preserved in the optically thick regime. Taking advantage of the local integral solution of RTE, the distribution of the emitted photon can be constructed from its macroscopic moments. The Monte Carlo particles in the UGKP method need only be tracked before their first collision events, and a re-sampling process is performed to close the photon distribution for each time step. The high computational cost of calculating excessive scattering events can be saved, especially in the optically thick regime. The proposed UGKP method is implicit and removes the light speed constraint on the time step. The particle tracking approach combining the implicit formulation makes the proposed UGKP method an efficient solution algorithm for frequency-dependent radiative transfer problems. We demonstrate with numerical examples the capability of the proposed multi-frequency UGKP method.

Optomechanical ring resonator for efficient microwave-optical frequency conversion

Phonons traveling in solid-state devices are emerging as a universal excitation for coupling different physical systems. Phonons at microwave frequencies have a similar wavelength to optical photons in solids, enabling optomechanical microwave-optical transduction of classical and quantum signals. It becomes conceivable to build optomechanical integrated circuits (OMIC) that guide both photons and phonons and interconnect photonic and phononic devices. Here, we demonstrate an OMIC including an optomechanical ring resonator (OMR), where co-resonant infrared photons and GHz phonons induce significantly enhanced interconversion. The platform is hybrid, using wide bandgap semiconductor gallium phosphide (GaP) for waveguiding and piezoelectric zinc oxide (ZnO) for phonon generation. The OMR features photonic and phononic quality factors of >1 × 105 and 3.2 × 103, respectively. The optomechanical interconversion between photonic modes achieved an internal conversion efficiency {eta }_{i}=(2.1pm 0.1)% and a total device efficiency {eta }_{{tot}}=0.57{times 10}^{-6} at a low acoustic pump power of 1.6 mW. The efficient conversion in OMICs enables microwave-optical transduction for quantum information and microwave photonics applications.

Micr -Transfer Printing for Efficient 3DHI of 100-300mm Wafers and Glass Panels

This paper presents an analysis of using micro-transfer printing (MTP) for three-dimensional heterogeneous integration (3DHI) of diverse components made using 100mm, 200mm and 300mm wafers with large area glass substrates. Techniques for achieving high throughput and high wafer and substrate utilization, despite their size mis-matches, are described in detail along with MTP’s pros and cons versus alternative wafer-to-wafer and die-to-wafer 3DHI technologies. MTP, a massively parallel pick-and-place process, efficiently transfers large arrays of ultra-thin (<10 micron), small, diverse components (“x-chips”) from one or more source wafers to destination substrates. MTP enables disruptive 3DHI of compound semiconductors, including GaN, GaAs, InP, SiGe and emerging materials, silicon and passive components for wireless and optical communications, power management, sensor, photonics and other analog / mixed signal applications. Since the x-chips are ultra-thin and active side up, standard copper redistribution layer (RDL) technology may be readily used to interconnect the x-chips and destination die, resulting in very short path lengths and, hence, minimum parasitics. ASM AMICRA and X Display Company supply R&D and production MTP manufacturing systems. More than twenty MTP systems are installed worldwide at X-FAB, Micross Components, Tyndall National Institute, Teledyne, the Naval Research Laboratory, the University of Illinois Urbana Champaign, the University of Ghent / imec, UPVfab and undisclosed leading manufacturers.

Influence of H on Sn incorporation in GeSnC alloys grown using molecular beam epitaxy

GeSnC alloys offer a route to direct bandgap semiconductors for CMOS-compatible lasers, but the use of CBr4 as a carbon source was shown to reduce Sn incorporation by 83%–92%. We report on the role of thermally cracked H in increasing Sn incorporation by 6x–9.5x, restoring up to 71% of the lost Sn, and attribute this increase to removal of Br from the growth surface as HBr prior to formation of volatile groups such as SnBr4. Furthermore, as the H flux is increased, Rutherford backscattering spectroscopy reveals a monotonic increase in both Sn and carbon incorporation. X-ray diffraction reveals tensile-strained films that are pseudomorphic with the substrate. Raman spectroscopy suggests substitutional C incorporation; both x-ray photoelectron spectroscopy and Raman suggest a lack of graphitic carbon or its other phases. For the lowest growth temperatures, scanning transmission electron microscopy reveals nanovoids that may account for the low Sn substitutional fraction in those layers. Conversely, the sample grown at high temperatures displayed abrupt interfaces, notably devoid of any voids, tin, or carbon-rich clusters. Finally, the surface roughness decreases with increasing growth temperature. These results show that atomic hydrogen provides a highly promising route to increase both Sn and C to achieve a strongly direct bandgap for optical gain and active silicon photonics.

Gpu-based optical photon simulation for the LHCb RICH 1 detector

We present the investigation of the use of Opticks, a GPU-accelerated optical photon interface with the LHCb detector simulation, to improve computation time of optical photon propagation. The hybrid workflow, combining the particle simulation package Geant4 and Opticks, offloads optical photon propagation to GPUs, thereby accelerating the overall simulation process. The consistency of the results obtained from Geant4 and Opticks simulations is verified with a simplified LHCb RICH1 detector geometry, demonstrating the feasibility of the proposed approach. In addition, the ongoing transition to the NVIDIA OptiX 7 API and re-structuring of Opticks code is discussed within the context of HEP simulation workflows, with caveats explored.

Synthesis and optimization of alkaline earth borate glasses doped with Fe2O3: Significance of BaO/MgO on the physical, structural features and radiation shielding performance

In this study, MgO–BaO–B2O3–Fe2O3 glasses were synthesized using the conventional melt and quench method, and the role of BaO and MgO in dictating their structural, physical, and optical properties was investigated. The fast neutrons, electrons, and heavy charged radiation transmission abilities of the glasses were delineated with the aim of evaluating their capacity to act as radiation insulators. The density of the glasses decreased from 3.40 g/cm3 to 2.89 g/cm3 as the MgO content increased. Also, the obtained optical bandgap increased from 1.90 eV to 2.20 eV with the increase of MgO in the MBBFe glasses. The stopping powers of electrons vary from 1.39 to 11.01 MeVcm2/g, 1.41–11.37 MeVcm2/g, 1.43–11.69 MeVcm2/g, 1.44–11.87 MeVcm2/g and 1.46–12.05 MeVcm2/g for glasses with MgO contents of 0 (MBBFe0), 5 (MBBFe1), 10 (MBBFe2), 12.5 (MBBFe3), and 15 (MBBFe4) mol%, respectively. Generally, the increase in the MgO content of the glasses led to increased mass stopping powers of the protons, alpha particles, and carbon ions. The replacement of BaO with MgO compromised the thermal neutron interaction probabilities of the present glassy specimens. The MBBFe-0 glass had the best thermal neutron interaction cross sections. The fast neutron removal cross-section of the glasses was within the range of 0.1037–0.1070 cm−1 with MBBFe-3 having the highest value and MBBFe-4 the least. The increase in the BaO suppresses photon buildup within the glass system. The MBBFe-glasses displayed good physical and optical properties, photon and neutron shielding abilities, which makes them attractive for diverse shielding and optical functions.

Quantum optical memory for entanglement distribution

Optical photons are powerful carriers of quantum information, which can be delivered in free space by satellites or in fibers on the ground over long distances. Entanglement of quantum states over long distances can empower quantum computing, quantum communications, and quantum sensing. Quantum optical memories are devices designed to store quantum information in the form of stationary excitations, such as atomic coherence, and are capable of coherently mapping these excitations to flying qubits. Quantum memories can effectively store and manipulate quantum states, making them indispensable elements in future long-distance quantum networks. Over the past two decades, quantum optical memories with high fidelities, high efficiencies, long storage times, and promising multiplexing capabilities have been developed, especially at the single-photon level. In this review, we introduce the working principles of commonly used quantum memory protocols and summarize the recent advances in quantum memory demonstrations. We also offer a vision for future quantum optical memory devices that may enable entanglement distribution over long distances.

Microwave‐Optics Entanglement Via Cavity Optomagnomechanics

AbstractMicrowave‐optics entanglement is a vital component for building hybrid quantum networks. Here, a new mechanism for preparing stationary entanglement between microwave and optical cavity fields in a cavity optomagnomechanical system is proposed. It consists of a magnon mode in a ferrimagnetic crystal that couples directly to a microwave cavity mode via the magnetic dipole interaction and indirectly to an optical cavity through the deformation displacement of the crystal. The mechanical displacement is induced by the magnetostrictive force and coupled to the optical cavity via radiation pressure. Both the opto‐ and magnomechanical couplings are dispersive. Magnon–phonon entanglement is created via magnomechanical parametric down‐conversion, which is further distributed to optical and microwave photons via simultaneous optomechanical beamsplitter interaction and electromagnonic state‐swap interaction, yielding stationary microwave‐optics entanglement. The microwave‐optics entanglement is robust against thermal noise, which will find broad potential applications in quantum networks and quantum information processing with hybrid quantum systems.

A-Si EPID Modeling in GATE for Monte Carlo Investigation on the Optical Properties of Gd<sub>2</sub>O<sub>2</sub>S:Tb and Lu<sub>2</sub>SiO<sub>5</sub>:Ce Scintillators

A detailed a-Si Electronic Portal Imaging Device (EPID) was implemented in GATE (Geant4 application for tomographic emission) toolkit for Monte Carlo simulations, employing the standard electromagnetic processes and optical photon processes. The composition of the scintillating material is varied using the conventional terbium-doped gadolinium oxysulfide phosphor (Gd2O2S:Tb) and cerium-doped lutetium oxyorthosilicate (Lu2SiO5:Ce) which is widely used in Positron Emission Tomography (PET) detectors due to its supremacy in aiding the detection of low-energy photons. It was found that the number of optical photons produced is higher when using the Lu2SiO5:Ce scintillator resulting in a slightly better signal-to-noise ratio (SNR). The scattering within the EPID components was also investigated where the majority of the detected secondary particles were created in the scintillator. The results also show that the copper plate layer of the EPID contributes to additional Compton electrons and bremsstrahlung and annihilation photons to the measurements in the scintillator and photodiode layer. The glass substrate, graphite plates, electronic components, and aluminum bottom cover are also found to contribute a huge fraction of backscattered particles to the measurements at the photodiode layer.

Modeling and optimization of scintillating crystal layers for designing a three-layer phoswich Alpha-Beta-Gamma detector

Monitoring the level of radioactive contamination and the type of radiation in the environment is very important for the protection of facilities, employees, and people. Phoswich detector is one of the useful tools to identify different radiations and separate them from each other using different scintillating crystals. However, their design can be very diverse based on the type of particles analyzed and various parameters of scintillating crystals and needs optimization to have maximum efficiency. This work aims to optimize the scintillating crystal layers for the design of the three-layer alpha-beta-gamma phoswich detector based on Monte Carlo radiation transport calculations. The selection of the appropriate model for the type and thickness of each layer is based on the optimization of parameters such as energy accumulation, produced scintillation optical photons, attenuation of optical photons, and scintillation decay time. The results showed that the three scintillating layers of ZnS(Ag), CaF2(Eu), and LYSO(Ce) with optimal thicknesses of 25.01 μm, 3.50 mm, and 2.54 cm, respectively, have more suitable optical outputs for detecting common alpha-beta-gamma radionuclide emitters.

Optical Coupling Efficiency, Photon Loss, and Efficiency Estimates for c-Si PERC Modules Enhanced with Downconverting Films and Nanocomposites

Optical Coupling Efficiency, Photon Loss, and Efficiency Estimates for c-Si PERC Modules Enhanced with Downconverting Films and Nanocomposites

Label-free image scanning microscopy for kHz super-resolution imaging and single particle tracking.

We report the modification of a label-free image scanning microscope (ISM) to perform asynchronous 2D imaging at up to 24kHz while keeping the lateral resolution gain and background rejection of a regular label-free ISM setup. Our method uses a resonant mirror oscillating at 12kHz for one-direction scanning and a chromatic line for instantaneous scanning in the other direction. We adapt optical photon reassignment in this scanning regime to perform fully optical super-resolution imaging. We exploit the kHz imaging capabilities of this confocal imaging system for single nanoparticle tracking down to 20 nm for gold and 50 nm for silica particles as well as imaging freely moving Lactobacillus with improved resolution.

Modeling scanning near-field optical photons scattered from an atomic force microscope for quantum metrology

Scattering scanning near-field optical microscopy (s-SNOM) is a promising technique for overcoming Abbe diffraction limit and substantially enhancing the spatial resolution in spectroscopic imaging. The s-SNOM works by exposing an atomic force microscope (AFM) tip to an optical electromagnetic (EM) field, while the tip is so close to a dielectric sample that the incident beam lies within the near-field regime and displays nonlinear behavior. We suggest replacing the incident EM field by photons generated by a single photon emitter, and propose a theoretical model for the suggested system by employing electric-dipole approximation, image theory, and perturbation theory. The count rate of the scattered photons from the AFM tip is extracted through a single photon detector, which contains information about electrical permittivity of the dielectric material beneath the tip. The permittivity of the sample can be extracted through spectroscopic setups. Our proposed scheme is useful for enhancing the spatial resolution of the modern quantum spectroscopy configurations that utilize entangled single photons.