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Optics, Volume 2, Issue 3 (September 2021) – 6 articles

Cover Story (view full-size image): Intensity-based optical sensing provides a compact and cheaper alternative to traditional spectral-shift-based devices. An array of nanodisks sustaining bound states in the continuum is poorly affected by variations of the optical properties of the environment. However, if a small gap is introduced in the middle of the nanodisks, the bound state in the continuum evolves towards a quasi-bound state in the continuum that is highly sensitive to variations of the environment refractive index. Thus, small refractive index variations result in large variations of transmittivity at a fixed wavelength. View this paper

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8 pages, 955 KiB

Open AccessFeature PaperArticle

High Quality Factor Silicon Membrane Metasurface for Intensity-Based Refractive Index Sensing

by Andrea Tognazzi, Davide Rocco, Marco Gandolfi, Andrea Locatelli, Luca Carletti and Costantino De Angelis

Optics 2021, 2(3), 193-199; https://doi.org/10.3390/opt2030018 - 6 Sep 2021

Cited by 26 | Viewed by 6182

Abstract

We propose a new sensing device based on all-optical nano-objects placed in a suspended periodic array. We demonstrate that the intensity-based sensing mechanism can measure environment refractive index change of the order of

1.8 \times 10^{- 6}

, which is close to [...] Read more.

1.8 \times 10^{- 6}

, which is close to record efficiencies in plasmonic devices. Full article

(This article belongs to the Special Issue Feature Papers in Optics)

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9 pages, 1155 KiB

Open AccessFeature PaperArticle

Toric Intraocular Lens Results Considering Posterior Corneal Astigmatism with Online Calculators: Phacoemulsification vs. Femtosecond

by Joaquín Fernández, Manuel Rodríguez-Vallejo, Noemí Burguera, Patrizia Salvestrini and Nuria Garzón

Optics 2021, 2(3), 184-192; https://doi.org/10.3390/opt2030017 - 3 Sep 2021

Cited by 2 | Viewed by 2905

Abstract

To evaluate the prediction error (PE) obtained in Phacoemulsification (Phaco) or Femtosecond (Femto) surgeries without considering posterior corneal astigmatism correction (non-PCA) versus the correction based on Abulafia-Koch + Medicontur (AK) and Barrett calculators in toric intraocular lens (IOL) power calculation. 58 right eyes were retrospectively retrieved from our database. Two groups formed by 28 and 30 eyes depending on the surgery type, Phaco or Femto respectively, were defined. Astigmatism PE were evaluated considering the approach used for calculation of the implanted IOL power (AK) versus the estimation of PEs in non-PCA and Barrett formula. A doubly-multivariate analysis was conducted to assess the differences between-surgery types, within-methods of calculation, and interaction. Mean centroid PE was significantly different between non-PCA, AK and Barrett approaches (p < 0.0005), and neither differences (p < 0.239) nor interaction (p = 0.672) between Phaco or Femto were found. Post-hoc univariate analysis showed a higher PE for the x-component of the non-PCA method versus AK (0.15 D, p < 0.0005) and non-PCA versus Barrett (0.18 D, p < 0.0005), though no differences were found between AK and Barrett (0.03 D, p = 0.93). Against-the-rule under-correction and with-the-rule overcorrection were found in both arms when PCA was not considered. Both calculators provide comparable clinical results. Full article

(This article belongs to the Special Issue Novel Research on Optometry and Vision Sciences)

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15 pages, 7399 KiB

Open AccessArticle

Micro-Machining of Diamond, Sapphire and Fused Silica Glass Using a Pulsed Nano-Second Nd:YVO₄ Laser

by David G. Waugh and Chris D. Walton

Optics 2021, 2(3), 169-183; https://doi.org/10.3390/opt2030016 - 23 Aug 2021

Cited by 3 | Viewed by 3058

Abstract

Optically transparent materials are being found in an ever-increasing array of technological applications within industries, such as automotive and communications. These industries are beginning to realize the importance of implementing surface engineering techniques to enhance the surface properties of materials. On account of the importance of surface engineering, this paper details the use of a relatively inexpensive diode-pumped solid state (DPSS) Nd:YVO₄ laser to modify the surfaces of fused silica glass, diamond, and sapphire on a micrometre scale. Using threshold fluence analysis, it was identified that, for this particular laser system, the threshold fluence for diamond and sapphire ranged between 10 Jcm⁻² and 35 Jcm⁻² for a laser wavelength of 355 nm, dependent on the cumulative effects arising from the number of incident pulses. Through optical microscopy and scanning electron microscopy, it was found that the quality of processing resulting from the Nd:YVO₄ laser varied with each of the materials. For fused silica glass, considerable cracking and deformation occurred. For sapphire, good quality features were produced, albeit with the formation of debris, indicating the requirement for post-processing to remove the observed debris. The diamond material gave rise to the best quality results, with extremely well defined micrometre features and minimal debris formation, comparative to alternative techniques such as femtosecond laser surface engineering. Full article

(This article belongs to the Special Issue Feature Papers in Optics)

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14 pages, 8199 KiB

Open AccessFeature PaperArticle

Study of Superoscillating Functions Application to Overcome the Diffraction Limit with Suppressed Sidelobes

by Svetlana N. Khonina, Ekaterina D. Ponomareva and Muhammad A. Butt

Optics 2021, 2(3), 155-168; https://doi.org/10.3390/opt2030015 - 20 Aug 2021

Viewed by 3200

Abstract

The problem of overcoming the diffraction limit does not have an unambiguously advantageous solution because of the competing nature of different beams’ parameters, such as the focal spot size, energy efficiency, and sidelobe level. The possibility to overcome the diffraction limit with suppressed sidelobes out of the near-field zone using superoscillating functions was investigated in detail. Superoscillation is a phenomenon in which a superposition of harmonic functions contains higher spatial frequencies than any of the terms in the superposition. Two types of superoscillating one-dimensional signals were considered, and simulation of their propagation in the near diffraction zone based on plane waves expansion was performed. A comparative numerical study showed the possibility of overcoming the diffraction limit with a reduced level of sidelobes at a certain distance outside the zone of evanescent waves. Full article

(This article belongs to the Special Issue Feature Papers in Optics)

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7 pages, 1660 KiB

Open AccessArticle

A Preliminary Investigation on the Photothermal Properties of Luminescent Solar Concentrators

by Yilin Li, Yujian Sun, Yongcao Zhang and Wenji Dong

Optics 2021, 2(3), 148-154; https://doi.org/10.3390/opt2030014 - 5 Aug 2021

Cited by 2 | Viewed by 2963

Abstract

Luminescent solar concentrators (LSCs) are considered promising photovoltaic (PV) devices to circumvent practical issues of applying conventional solar panels to the built environment. However, LSCs suffer from low power conversion efficiencies (PCEs) (typically <2% for devices of over 1 m²), despite numerous efforts having been made to develop novel luminescent materials and optical techniques. In this report, we proposed to utilize photothermal (PT) energy of the LSCs to further improve the PCE. We conducted a preliminary investigation on the PV and PT properties of an LSC with dimensions of 300 mm × 300 mm × 5 mm. The results showed that the PT power (27.05 W) was much higher than the PV power (2.12 W). Further analysis indicated that the PCE could reach 3.41% for a device of 1 m². Full article

(This article belongs to the Special Issue Novel Research on Solar Photothermal Technology: Theory, Design, System and Applications)

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14 pages, 3041 KiB

Open AccessArticle

Biochemical Profiles of In Vivo Oral Mucosa by Using a Portable Raman Spectroscopy System

by Marcelo Saito Nogueira, Victoria Ribeiro, Marianna Pires, Felipe Peralta and Luis Felipe das Chagas e Silva de Carvalho

Optics 2021, 2(3), 134-147; https://doi.org/10.3390/opt2030013 - 16 Jul 2021

Cited by 10 | Viewed by 3429

Abstract

Most oral injuries are diagnosed by histopathological analysis of invasive and time-consuming biopsies. This analysis and conventional clinical observation cannot identify biochemically altered tissues predisposed to malignancy if no microstructural changes are detectable. With this in mind, detailed biochemical characterization of normal tissues and their differentiation features on healthy individuals is important in order to recognize biomolecular changes associated with early tissue predisposition to malignant transformation. Raman spectroscopy is a label-free method for characterization of tissue structure and specific composition. In this study, we used Raman spectroscopy to characterize the biochemistry of in vivo oral tissues of healthy individuals. We investigated this biochemistry based on the vibrational modes related to Raman spectra of four oral subsites (buccal, gingiva, lip and tongue) of ten volunteers as well as with principal component (PC) loadings for the difference between the four types of oral subsites. Therefore, we determined the biochemical characteristics of each type of healthy oral subsite and those corresponding to differentiation of the four types of subsites. In addition, we developed a spectral reference of oral healthy tissues of individuals in the Brazilian population for future diagnosis of early pathological conditions using real-time, noninvasive and label-free techniques such as Raman spectroscopy. Full article

(This article belongs to the Special Issue New Discoveries in Biomedical Optical Imaging and Sensing: From Technologies to Applications)

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