Optics, Volume 3, Issue 1 (March 2022) – 11 articles

Transmission spheres used in interferometry are specified by f-number and source wavelength. In this paper, we explore a broadband variable transmission sphere (BVTS) system based on freeform Alvarez lenses that enables variable operation across a broad range of f-numbers and wavelengths. Potential applications and performance tradeoffs are discussed in comparison to conventional spherical transmission spheres. Simulation results are presented for f/15 to f/80 configurations from visible to long-wave infrared sources in a Fizeau interferometer. Simulation results highlight that spherical, coma, and astigmatism impose limits on surface measurement quality. Full article

We introduce a holographic wide angle system that combines the accuracy of a long focal length with the extended field of view of a wide angle lens. To accomplish this, we use a computer-generated hologram (CGH) in front of the lens to diffract light from (a discrete number of) specific angular locations. This method is tested in laboratory conditions, as well as under real-world conditions. This measurement system was developed as a possible tool for real-time movement tracking and control of extended dynamic structures, such as bridges and high-rise buildings. Within that application, the obtained measurement uncertainty is 10 μ$\mathrm{m}$ in object space at 10 $\mathrm{m}$ distance spanning 10 $\mathrm{m}$ width. Full article

Metamaterials, in the form of perfect absorbers, have recently received attention for sensing and light-harvesting applications. The fabrication of such metamaterials involves several process steps and can often lead to nonidealities, which limit the performance of the metamaterial. A novel reciprocal plasmonic metasurface geometry composed of two plasmonic metasurfaces separated by a dielectric spacer was developed and investigated here. This geometry avoids many common fabrication-induced nonidealities by design and is synthesized by a combination of two-photon polymerization and electron-beam-based metallization. Infrared reflection measurements revealed that the reciprocal plasmonic metasurface is very sensitive to ultra-thin, conformal dielectric coatings. This is shown here by using Al₂O₃ grown by atomic layer deposition. It was observed experimentally that incremental conformal coatings of amorphous Al₂O₃ result in a spectral red shift of the absorption band of the reciprocal plasmonic metasurface. The experimental observations were corroborated by finite element model calculations, which also demonstrated a strong sensitivity of the reciprocal plasmonic metasurface geometry to conformal dielectric coatings. These coatings therefore offer the possibility for post-fabrication tuning of the reciprocal plasmonic metasurface resonances, thus rendering this novel geometry as an ideal candidate for narrow-band absorbers, which allow for cost-effective fabrication and tuning. Full article

Waveguide gratings are used for applications such as guided-mode resonance filters and fiber-to-chip couplers. A waveguide grating typically consists of a stack of a single-mode slab waveguide and a grating. The filling factor of the grating with respect to the mode intensity profile can be altered via changing the waveguide’s refractive index. As a result, the propagation length of the mode is slightly sensitive to refractive index changes. Here, we theoretically investigate whether this sensitivity can be increased by using alternative waveguide grating geometries. Using rigorous coupled-wave analysis (RCWA), the filling factors of the modes of waveguide gratings supporting more than one mode are simulated. It is observed that both long propagation lengths and large sensitivities with respect to refractive index changes can be achieved by using the intensity nodes of higher-order modes. Full article

We report the first ever demonstration of a wavelength-locked Alexandrite laser using a volume Bragg grating (VBG) as a wavelength-selective mirror. Output power of 3.3 W with a diffraction limited beam quality of M${}^2=1.1$ was obtained at a lasing wavelength of 762.2 nm and a linewidth (FWHM) of 2.5 GHz. Full article

In this work, we present new experimental evidence of a nonclassical behavior of a multimode Fabry–Perot (FP) semiconductor laser by the measurements of intensity correlation functions. Due to the multimode quantum state occurrence, instead of expected correlations between the intensities of the laser modes (a semiclassical theory), their anticorrelations were revealed. Full article

Burns are an actual problem of modern medicine. Oxidative stress, microcirculation, and hemostasis disorders are important links in the pathogenesis of burn disease. It is shown that these processes are significantly influenced by the point effect of low-intensity (LI) electromagnetic radiation (EMR) of the millimeter (MM) and submillimeter (subMM) ranges. However, the final opinion on the advantages of a particular range has not been formed. We have given a comparative assessment of the results of the effects of various frequency-energy parameters of microwaves on the indicators of adaptive reactions in rats under experimental thermal trauma and viscoelastic properties of blood in the case of burn disease. Full article

Generalizing our prior work on scalar multi-Gaussian (MG) distributed optical fields, we introduce the two-dimensional instantaneous electric-field vector whose components are jointly MG distributed. We then derive the single-point Stokes parameter probability density functions (PDFs) of MG-distributed light having an arbitrary degree and state of polarization. We show, in particular, that the intensity contrast of such a field can be tuned to values smaller or larger than unity. We validate our analysis by generating an example partially polarized MG field with a specified single-point polarization matrix using two different Monte Carlo simulation methods. We then compute the joint PDFs of the instantaneous field components and the Stokes parameter PDFs from the simulated MG fields, while comparing the results of both Monte Carlo methods to the corresponding theory. Lastly, we discuss the strengths, weaknesses, and applicability of both simulation methods in generating MG fields. Full article

Deep Neural Networks (DNNs) are nurturing clinical decision support systems for the detection and accurate modeling of coronary arterial plaques. However, efficient plaque characterization in time-constrained settings is still an open problem. The purpose of this study is to develop a novel automated classification architecture viable for the real-time clinical detection and classification of coronary artery plaques, and secondly, to use the novel dataset of OCT images for data augmentation. Further, the purpose is to validate the efficacy of transfer learning for arterial plaques classification. In this perspective, a novel time-efficient classification architecture based on DNNs is proposed. A new data set consisting of in-vivo patient Optical Coherence Tomography (OCT) images labeled by three trained experts was created and dynamically programmed. Generative Adversarial Networks (GANs) were used for populating the coronary aerial plaques dataset. We removed the fully connected layers, including softmax and the cross-entropy in the GoogleNet framework, and replaced them with the Support Vector Machines (SVMs). Our proposed architecture limits weight up-gradation cycles to only modified layers and computes the global hyper-plane in a timely, competitive fashion. Transfer learning was used for high-level discriminative feature learning. Cross-entropy loss was minimized by using the Adam optimizer for model training. A train validation scheme was used to determine the classification accuracy. Automated plaques differentiation in addition to their detection was found to agree with the clinical findings. Our customized fused classification scheme outperforms the other leading reported works with an overall accuracy of 96.84%, and multiple folds reduced elapsed time demonstrating it as a viable choice for real-time clinical settings. Full article

We report the design simulation of the Raman spectrometer using Zemax optical system design software. The design is based on the Czerny–Turner configuration, which includes an optical system consisting of an entrance slit, two concave mirrors, reflecting type diffraction grating and an image detector. The system’s modeling approach is suggested by introducing the corresponding relationship between detector pixels and wavelength, linear CCD receiving surface length and image surface dimension. The simulations were carried out using the POP (physical optics propagation) algorithm. Spot diagram, relative illumination, irradiance plot, modulation transfer function (MTF), geometric and encircled energy were simulated for designing the Raman spectrometer. The simulation results of the Raman spectrometer using a 527 nm wavelength laser as an excitation light source are presented. The present optical system was designed in sequential mode and a Raman spectrum was observed from 530 nm to 630 nm. The analysis shows that the system’s image efficiency was quite good, predicting that it could build an efficient and cost-effective Raman spectrometer for optical diagnostics. Full article