Prismatic Research Articles

Use of calcite for evaluation of spectral resolution of Raman spectrometers.

Raman microscopes are widely used in various fields and their spectral resolutions differ greatly depending on the system and optical components. Thus, it is important to evaluate the spectral resolution of Raman systems under measurement conditions. Although both atomic emission lines and calcites have been used for the evaluation of spectral resolution and described in some guidelines, calcite is preferable because it contains information on laser width. Calcite is a crystal with a trigonal structure and the peak width of Raman spectra is sensitive to crystallinity, so the peak width of calcite may change depending on its quality. In this study, we examined differences in the peak width of atomic emission lines and calcites as well as laser line. The peak width of calcite at ~ 1086cm-1 was wider than that of laser and atomic emission lines due to contribution of laser width and calcite itself. Among various calcite samples, calcite blocks for optical prisms showed the narrowest peak width (< 1.3cm-1) followed by high-grade reagent calcites (1.35-1.43cm-1) and usual-grade reagent calcites (2.23-2.53cm-1). Although the peak width of calcite slightly changed with temperature (~ 0.2cm-1 between 5°C and 45°C), it was comparable to the differences among high-grade reagent calcites. Thus, calcite is preferable for evaluating spectral resolution of Raman systems but its quality requires attention.

Grating Coupler Design for Low-Cost Fabrication in Amorphous Silicon Photonic Integrated Circuits

Photonic circuits find applications in biomedicine, manufacturing, quantum computing and communications. Photonic waveguides are crucial components, typically having cross-section orders of magnitude inferior when compared with other photonic components (e.g., optical fibers, light sources and photodetectors). Several light-coupling methods exist, consisting of either on-plane (e.g., adiabatic and end-fire coupling) or off-plane methods (e.g., grating and vertical couplers). The grating coupler is a versatile light-transference technique which can be tested at wafer level, not requiring specific fiber terminations or additional optical components, like lenses, polarizers or prisms. This study focuses on fully-etched grating couplers without a bottom reflector, made from hydrogenated amorphous silicon (a-Si:H), deposited over a silica substrate. Different coupler designs were tested, and of these we highlight two: the superimposition of two lithographic masks with different periods and an offset between them to create a random distribution and a technique based on the quadratic refractive-index variation along the device’s length. Results were obtained by 2D-FDTD simulation. The designed grating couplers achieve coupling efficiencies for the TE-like mode over −8 dB (mask overlap) and −3 dB (quadratic variation), at a wavelength of 1550 nm. The coupling scheme considers a 220 nm a-Si:H waveguide and an SMF-28 optical fiber.

Angular Deviations, Lateral Displacements, and Transversal Symmetry Breaking: An Analytical Tutorial

The study of a Gaussian laser beam interacting with an optical prism, both through reflection and transmission, provides a technical tool to examine deviations from the optical path as dictated by geometric optics principles. These deviations encompass alterations in the reflection and refraction angles, as predicted by the reflection and Snell laws, along with lateral displacements in the case of total internal reflection. The analysis of the angular distributions of both the reflected and transmitted beams allows us to understand the underlying causes of these deviations and displacements, and it aids in formulating analytic expressions that are capable of characterizing these optical phenomena. The study also extends to the examination of transverse symmetry breaking, which is a phenomenon observed in the laser beam as it traverses the oblique interface of the prism. It is essential to underscore that this analytical overview does not strive to function as an exhaustive literature review of these optical phenomena. Instead, its primary objective is to provide a comprehensive and self-referential treatment, as well as give universal analytical formulas intended to facilitate experimental validations or applications in various technological contexts.

Using a leaky-wave antenna as an acoustic prism for speech-separation

Leaky-wave antennas (LWA) are an acoustic metamaterial comprised of an array of unit cells. For a 1D line array, the output ranges from 0° to 180° relative to the direction of the axis of the array. The direction of the output is dependent on the frequency of the input; a single frequency input will produce a highly directive output beam at a specific angle. Much like an optic prism, which can be used to split a complex optic wave into its components, a LWA can be used to split a complex input audio wave into its components. This work explores the capabilities of LWA to separate transient signals like human speech into different output directions. This is accomplished by way of an equivalent circuit model of the LWA that enables simulations in both the time and frequency domains. The frequency domain performance of the model is validated against previously published results, and then the transient response is shown to recover these as well once steady-state is reached

A Modified Method for Determining the Optical Indicatrix in Monoclinic Crystals Based on Optical Prisms

A Modified Method for Determining the Optical Indicatrix in Monoclinic Crystals Based on Optical Prisms

Automatic Alignment Method for Controlled Free-Space Excitation of Whispering-Gallery Resonances.

Whispering-gallery mode microresonators have gained wide popularity as experimental platforms for different applications, ranging from biosensing to nonlinear optics. Typically, the resonant modes of dielectric microresonators are stimulated via evanescent wave coupling, facilitated using tapered optical fibers or coupling prisms. However, this method poses serious shortcomings due to fabrication and access-related limitations, which could be elegantly overcome by implementing a free-space coupling approach; although additional alignment procedures are needed in this case. To address this issue, we have developed a new algorithm to excite the microresonator automatically. Here, we show the working mechanism and the preliminary results of our experimental method applied to a home-made silica microsphere, using a visible laser beam with a spatial light modulator and a software control.

Investigation and evaluation of a 3D-printed optical modified cultivation vessel for improved scattered light measurement of biotechnologically relevant organisms.

In the field of bioprocess development miniaturization, parallelization and flexibility play a key role reducing costs and time. To precisely meet these requirements, additive manufacturing (3D-printing) is an ideal technology. 3D-printing enables rapid prototyping and cost-effective fabrication of individually designed devices with complex geometries on demand. For successful bioprocess development, monitoring of process-relevant parameters, such as pH, dissolved oxygen (DO), and biomass, is crucial. Online monitoring is preferred as offline sampling is time-consuming and leads to loss of information. In this study, 3D-printed cultivation vessels with optical prisms are evaluated for the use in upstream processes of different industrially relevant microorganisms and cell lines. It was shown, that the 3D-printed optically modified well (OMW) is of benefit for a wide range of biotechnologically relevant microorganisms and even for mammalian suspension cells. Evaluation tests with Escherichia coli, Bacillus subtilis, Saccharomyces cerevisiae, and Chinese hamster ovary (CHO) cells were performed, providing highly reproducible results. Growth behavior of OMW cultures was comparable to behavior of shake flask (SF) cultivations and the signal to noise ratio in online biomass measurement was shown to be reduced up to 95.8% by using the OMW. Especially the cultivation phases with low turbidity respective optical densities below 1.0rel.AU could be monitored accurately for the first time. Furthermore, it was demonstrated that the 3D-printed optics are transferable to different well geometries and sizes, enabling efficient biomass monitoring for individual requirements with tailor-made 3D-printed cultivation vessels in small scale.

Design of a Large-Format Low-Light Imaging System Based on the RGB Filter Wheel

In order to capture true-color information of distant targets under extremely low light, a large-format low-light imaging system is designed based on an RGB filter wheel. By decomposing the system indicators, this study proposes a method for acquiring low-light true-color images using a large-aperture, low-distortion optical lens combined with an RGB filter wheel capable of multi-line sequential exposure. The optical field segmentation is achieved using a four-panel optical reflective prism, and the images from four high-sensitivity SCOMS detectors are stitched together to form a composite image. The working principle of the system is explained, and the low-light imaging capability is thoroughly evaluated. The dimensions and rotation speed of the filter wheel are then calculated in detail, ensuring accurate synchronization of the filter wheel’s speed and exposure time. The calculation method for the parameters of the four-panel reflective prism structure is investigated, mathematical expressions for the geometric parameters of the prism assembly are provided, and a prism assembly suitable for four-way spectral separation is designed. Based on the research and design results, a large-swath-width, low-light true-color imaging system is developed that is suitable for an environmental illuminance of 0.01 lux. The system achieves a ground pixel resolution of 0.5 m (at an altitude of 5 km) and an effective image resolution of 4 K × 4 K, and is capable of accurately reproducing target color information. Laboratory and field flight tests verified that the large-swath-width images obtained by the imaging system are clear, with high contrast and resolution. After image fusion and spectral registration, the color images exhibit full saturation and high fidelity, meeting the requirements of low-light true-color imaging under airborne conditions. The design methodology of this low-light imaging system can serve as a reference for the development of airborne low-light imaging equipment.

Automatic control method for freeform surface shapes.

Designing freeform optics with high degrees of freedom can improve their optical performances; however, there are high requirements for controlling the surface shapes of such optics. Optical designers need to add constraints to the optimization process and make repeated adjustments to ensure the manufacturability of these shapes; this process is cumbersome and relies heavily on the experience of the designer. In this study, an automatic control method for freeform surface shapes is proposed. By adding an outer loop to the optimization process, the principal curvature and sag departure of the sampling points are gradually controlled during the optimization cycle based on the system requirements and surface evaluation results. The method was implemented in CODE V and successfully applied to a design example in freeform prism optics.

A Reconfigurable Phase-Time Array Transmitter Achieving Keyless Secured Transmission and Multi-Receiver Localization for Low-Latency Joint Communication and Sensing

The vast available spectrum at millimeter-wave (mm-Wave)/terahertz (THz) frequencies is envisioned as a key enabler to solve the ever-increasing data rate needs in crowded urban environments and lead the next wireless technology revolution. To overcome the high path loss present at mm-Wave/THz, highly directional antenna arrays have become ubiquitous. Their future large-scale deployment will naturally create dense wireless sensor networks, which in-turn enable joint communication and sensing. However, the beamforming of high-directivity antenna arrays relies on real-time precise localization between transmitters (TXs) and receivers (RXs) to ensure robustness in dynamic mobile applications. Moreover, traditional digital encryption and decryption at multi-Gbps data rate cause large power and latency overhead, and thus, wireless physical layer security has become a promising solution. In this article, we propose and demonstrate a reconfigurable phase-time array (PTA) TX with prism-like spectral-to-spatial mapping of wideband transmitted signals, which achieves keyless physically secured wireless communication and fast multi-RX localization to enable low-latency joint communication and sensing within the same wireless electronics frontend. The PTA realizes reconfigurable spectral-to-spatial mapping by applying both a phase shift and true time delay (TTD) at each array element. This intentionally creates and exploits the array beam squinting effect, such that different frequency components of a wideband signal are transmitted in different directions, analogous to an optical prism. Therefore, multiple RX nodes can simultaneously determine their angular positions relative to the TX array using their received signals for fast multi-RX localization. Judiciously engineering the prism-like beam squinting in PTA TX can also selectively distort signal transmission to unwanted directions for secured communication without cryptography. Furthermore, the PTA scheme can reconfigure its element-level phase-time delay combinations to attain variable levels of communication security and localization/sensing performance depending on the needs.

P‐4.8: Unidirectional Observable Aero Signage Display Using Dye‐doped Corner Cube Prisms Which Enable to Make Transparent from Back Side

Suppose that you look Arabic numerals on transparent glass windows or in the air. Which does it mean ‘85’ or ‘28’? You end up watching the mirrored images when you view from back side. So let us make the mirrored image invisible. To solve mirrored image problems of an aero signage which means images are floating in the air, our research group has utilized dye‐doped prisms and total internal reflection in optics. You know that water is generally colorless and transparent but the water in a bath tub is little blue. The color changes depending on the depth of water. The deeper, the darker water becomes blue. This is the reason why some color is generated in the dye‐doped material. In 2021, we presented a unidirectional observable display using letterings made by intaglio printings for arranging dye‐doped tiny prisms on a glass window. You can watch these colored letterforms from front and transparent pixels from back. But this 2021 model has a little defect that colors are less vivid because of color generating mechanism by twice reflection in conventional optical prisms using transparent materials for making transparent from back side. In this paper, the authors show an aero signage display using dye‐doped corner cube prisms which can lengthen light paths in the prism by multi‐times reflections to avoid the semi‐transparent problem which means colors are not vivid.

P‐8.9: Aero Signage Display Using Quasi‐Spatial Floating Image Generated by Holographic Optical Elements and Optical Illusion Object Maskings

A floating signage which means optical images are floating in the air is one of the useful ways to attract people's attention. Since 2019, our research group proposed unidirectional observable aerial signage display using thin film layers or dye-doped optical prisms to avoid mirrored imaging problem which means observers end up watching wrong messages or images from back side. In this paper, the authors describe the aero signage using quasi-spatial floating image and how to generate floating images using optical illusion and to control light paths.

Temporal rainbow scattering at boundary-induced time interfaces

Since the dawn of modern optics and electromagnetics, the optical prism is one of the most fascinating optical elements for refracting light. Exploiting its frequency dispersive behavior, a prism is able to refract different frequencies in different directions, realizing polychromatic light rainbows. Recently, thanks to their engineerable electromagnetic response, metamaterials have been exploited for achieving novel refractive scattering processes, going beyond the classical prism effects. In this Letter, we report on a rainbow-like scattering process taking place at the interface of a boundary-induced temporal metamaterial realized by instantaneously opening the boundary conditions of a parallel plate waveguide. Changing abruptly the conductivity of one of the two metallic plates, we demonstrate that an equivalent temporal interface between two different media is realized, and the monochromatic wave propagating into the waveguide gets scattered into a polychromatic rainbow in free space. We derive the relationships between the waveguide mode and the raising rainbow in terms of scattered amplitude and frequencies as a function of the elevation angle with respect to the waveguide axis. We apply the underlying physics to control the temporal rainbow by imposing a principal direction of scattering by design. Full-wave numerical simulations are performed for computing the rainbow temporal scattering and verifying the design guidelines for achieving controlled temporal rainbow scattering.

Simultaneous screening of zebrafish larvae cardiac and respiratory functions: a microfluidic multi-phenotypic approach.

Multi-phenotypic screening of multiple zebrafish larvae plays an important role in enhancing the quality and speed of biological assays. Many microfluidic platforms have been presented for zebrafish phenotypic assays, but multi-organ screening of multiple larvae, from different needed orientations, in a single device that can enable rapid and large-sample testing is yet to be achieved. Here, we propose a multi-phenotypic quadruple-fish microfluidic chip for simultaneous monitoring of heart activity and fin movement of 5-7-day postfertilization zebrafish larvae trapped in the chip. In each experiment, fin movements of four larvae were quantified in the dorsal view in terms of fin beat frequency (FBF). Positioning of four optical prisms next to the traps provided the lateral views of the four larvae and enabled heart rate (HR) monitoring. The device's functionality in chemical testing was validated by assessing the impacts of ethanol on heart and fin activities. Larvae treated with 3% ethanol displayed a significant drop of 13.2 and 35.8% in HR and FBF, respectively. Subsequent tests with cadmium chloride highlighted the novel application of our device for screening the effect of heavy metals on cardiac and respiratory function at the same time. Exposure to 5$\mu$g/l cadmium chloride revealed a significant increase of 8.2% and 39.2% in HR and FBF, respectively. The device can be employed to monitor multi-phenotypic behavioral responses of zebrafish larvae induced by chemical stimuli in various chemical screening assays, in applications such as ecotoxicology and drug discovery.

P‐3.22: One‐way Observable Aero Signage Display Using Optical Prisms Doped with Dye and Pigments Which Enable to Make Transparent from Back Side

Suppose that you look Arabic numerals on transparent glass windows or in the air. Which does it mean ‘85’ or ‘28’? You end up watching the mirrored images when you view from back side. So let us make the mirrored image invisible. This paper shows a one-way observable display for aero signage whose images are floating in the air. To solve mirrored image problems of an aero signage, our research group has utilized dye-doped prisms and total internal reflection in optics. You know that water is generally colorless and transparent but the water in a bath tub is little blue. The color changes depending on the depth of water. The deeper, the darker water becomes blue. This is the reason why some color is generated in the dye-doped material. In 2021, we presented a one-way observable display using letterings made by intaglio printings for arranging dye-doped tiny prisms on a glass window. You can watch these colored letterforms from front and transparent pixels from back. But this 2021 model has a little defect that colors are less vivid because of color generating mechanism using transparent materials for one-way observing. In this paper, the authors show special designed optical prisms which are doped with dye and pigments to avoid the semitransparent problem that means colors are not vivid.

Validation of a set of compact and low-cost Stokes lenses aimed at refractive astigmatism measurement for optometric practice

We describe the construction and characterization of three Stokes lenses that can be used in optometric practice to measure different ranges of refractive astigmatism using subjective routines. The proposed set of Stokes lenses is assembled from Risley prism mounts coming from a Nidek phoropter in which the optical prisms are replaced by three different sets of cylindrical lenses ( ± 0.75, ± 1.25, and ± 1.75 D) coming from a trial lens case to cover a different astigmatism range (1.5, 2.5, and 3.5 D in modulus, respectively). We present the experimental characterization of the three Stokes lenses with the power vector notation and use an automatic lensmeter (Topcon CL-300) for dioptric power measurement. The measured dioptric power profiles are in concordance with the theoretical predictions, and statistical testing reveals no differences between measured and theoretical values for the three lenses, neither in spherical nor in cylindrical components (p ≥ 0.05 for all cases). Bland–Altman plots show very good agreement between measured and theoretical values with limits of agreement below 0.12 D for both M and J components for the three lenses. These Stokes lenses can be easily constructed from regular Risley prism mounts, so they can be used in almost any phoropter model for refractive error compensation.

Integration of a multichannel surface plasmon resonance sensor chip and refractive index matching film array for protein detection in human urine

Most prism-based surface plasmon resonance (SPR) experiments use matching fluid with a similar refractive index to mount the chip on the optical prism. The fluidity of the matching fluid easily affects the transmission of the optical signal. In this paper, an integrated SPR sensor chip comprises a three-layer structure of flow layer, metal layer and refractive index matching layer is demonstrated to address the problems related to consistency and uniformity. The Young's modulus, array spacing, shape and other parameters of the matching film were calculated and optimized. The chip can self-adhere to the optical prism, and effectively avoids the generation of air bubbles. The refractive index detection sensitivity of the integrated SPR sensor chip was 3.4359 × 10−6 RIU (refractive index unit), and the chip stabilization time has been effectively shortened. The integrated SPR sensor chip was also used to detect kappa light chain protein and human serum albumin (HSA) in urine samples. The detection limit of kappa light chain protein was 0.06 μg/mL compared with 18.5 μg/mL by conventional immunoturbidimetry. The integrated SPR sensor chip based on refractive index matching film array has great potential in biomedical detection and other fields, including point-of-care testing (POCT).

Aftereffects to Prism Exposure without Adaptation: A Single Case Study.

Visuo-motor adaptation to optical prisms (Prism Adaptation, PA), displacing the visual scene laterally, is a behavioral method used for the experimental investigation of visuomotor plasticity, and, in clinical settings, for temporarily ameliorating and rehabilitating unilateral spatial neglect. This study investigated the building up of PA, and the presence of the typically occurring subsequent Aftereffects (AEs) in a brain-damaged patient (TMA), suffering from apperceptive agnosia and a right visual half-field defect, with bilateral atrophy of the parieto-occipital cortices, regions involved in PA and AEs. Base-Right prisms and control neutral lenses were used. PA was achieved by repeated pointing movements toward three types of stimuli: visual, auditory, and bimodal audio-visual. The presence and the magnitude of AEs were assessed by proprioceptive, visual, visuo-proprioceptive, and auditory-proprioceptive straight-ahead pointing tasks. The patient’s brain connectivity was investigated by Diffusion Tensor Imaging (DTI). Unlike control participants, TMA did not show any adaptation to prism exposure, but her AEs were largely preserved. These findings indicate that AEs may occur even in the absence of PA, as indexed by the reduction of the pointing error, showing a dissociation between the classical measures of PA and AEs. In the PA process, error reduction, and its feedback, may be less central to the building up of AEs, than the sensorimotor pointing activity per se.

Design and characterization of innovative optical prism for four-degree-of-freedom fast steering mirror active laser compensation system.

In this study, an innovative four-degree-of-freedom (4-DOF) compensation prism is designed for fast steering mirror active laser compensation systems. In addition to improving the disadvantages of the commercially available compensation systems, such as a larger number of components and longer optical paths, the proposed system has further enhanced the shortcoming of high sensitivity to the laser by using double Porro prisms as 4-DOF compensation prisms proposed in a previous study. The prism proposed in this study reduces the sensitivity to the laser while maintaining two translations and two rotations in 4-DOF control characteristic for laser, thereby improving the resolution of the system to control the laser. First, Zemax was used to build the overall system and evaluate the system characteristics. Then, the skew-ray tracing method and homogeneous coordinate transformation matrix were used to build the mathematical model of the compensation prism and analyze the sensitivity of the proposed prism to the laser. Finally, the closed-loop algorithm was established and the system was completely built on the optical table for experiments to compare the results between the laser before and after compensation by the proposed prism. In addition, the resolution of the proposed prism is compared with the double Porro prisms.

Study on the development and integration of 3D-printed optics in small-scale productions of single-use cultivation vessels.

Integrating optical sensors and 3D‐printed optics into single‐use (SU) cultivation vessels for customized, tailor‐made equipment could be a next big step in the bioreactor and screening platform development enabling online bioprocess monitoring. Many different parameters such as pH, oxygen, carbon dioxide and optical density (OD) can be monitored more easily using online measuring instruments compared to offline sampling. Space‐saving integrated sensors in combination with adapted optics such as prisms open up vastly new possibilities to precisely guide light through SU vessels. This study examines how optical prisms can be 3D‐printed with a 3D‐inkjet printer, modified and then evaluated in a custom made optical bench. The prisms are coated or bonded with thin cover glasses. For the examination of reflectance performance and conformity prisms are compared on the basis of measured characteristics of a conventional glass prism. In addition, the most efficient and reproducible prism geometry and modification technique is applied to a customized 3D‐printed cultivation vessel. The vessel is evaluated on a commercial sensor‐platform, a shake flask reader (SFR) vario, to investigate its sensing‐characteristics while monitoring scattered light with the turbidity standard formazine and a cell suspension of Saccharomyces cerevisiae as model organism. It is demonstrated that 3D‐printed prisms can be used in combination with commercial scattered light sensor‐platforms to determine OD of a microbial culture and that a 3D‐printed unibody design with integrated optics in a cultivation vessel is feasible. In the range of OD600 0–1.16 rel.AU a linear correlation between sensor amplitude and offline determined OD can be achieved. Thus, enabling for the first time a measurement of low cell densities with the SFR vario platform. Moreover, sensitivity is also at least three times higher compared to the commonly used method.