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Open AccessArticle

Simulation-Based Considerations on the Rayleigh Criterion in Super-Resolution Techniques Based on Speckle Interferometry

by

Yasuhiko Arai

and

Tong Chen

Photonics 2023, 10(4), 374; https://doi.org/10.3390/photonics10040374 - 28 Mar 2023

Viewed by 491

Abstract

This study sought to explain the physical phenomenon that eludes the constraints of the Rayleigh criterion in the microstructure observation method using speckle interferometry, for which super-resolution has been experimentally proven; the study was conducted using computer simulations. Separating the light from two [...] Read more.

This study sought to explain the physical phenomenon that eludes the constraints of the Rayleigh criterion in the microstructure observation method using speckle interferometry, for which super-resolution has been experimentally proven; the study was conducted using computer simulations. Separating the light from two light sources in close proximity, which exceeded the Rayleigh criterion under incoherent light, was believed to be impossible. The simulation results, however, showed that when coherent light is used, the separation of two close points is not necessarily impossible if the light phases between the two points are different. Furthermore, the resolution of microstructure observation techniques based on speckle interferometry was discussed. A new interpretation of the Rayleigh criterion in super-resolution techniques based on speckle interferometry was reported. Full article

(This article belongs to the Special Issue Advances in 3OM: Opto-Mechatronics, Opto-Mechanics, and Optical Metrology)

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Open AccessArticle

Ensquared Energy and Optical Centroid Efficiency in Optical Sensors: Part 1, Theory

by

Marija Strojnik

,

Beethoven Bravo-Medina

,

Robert Martin

and

Yaujen Wang

Photonics 2023, 10(3), 254; https://doi.org/10.3390/photonics10030254 - 28 Feb 2023

Viewed by 372

Abstract

High-performance megapixel focal plane arrays with small pixels have been widely used in modern optical remote sensing, astronomical, and surveillance instruments. In the prediction models applied in the traditional instrument performance analysis, the image of a point source is assumed to fall on [...] Read more.

High-performance megapixel focal plane arrays with small pixels have been widely used in modern optical remote sensing, astronomical, and surveillance instruments. In the prediction models applied in the traditional instrument performance analysis, the image of a point source is assumed to fall on the center of a detector pixel. A geometrical image of a point source in the realistic optical system may actually fall on any position on the detector pixel because the sensor’s line of sight includes pointing errors and jitter. This traditional assumption may lead to an optimistic error, estimated at between 10% and 20%. We present the critical factors that impact the performance estimate in a realistic instrument design based on the prediction for the noise-equivalent power (NEP). They are the optical centroid efficiency (OCE) and the ensquared energy, or more precisely, the energy on the rectangular detector pixel (EOD). We performed the simulation studies for imaging with an optical system with and without a generalized rectangular central obscuration. Full article

(This article belongs to the Special Issue Advances in 3OM: Opto-Mechatronics, Opto-Mechanics, and Optical Metrology)

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Open AccessCommunication

Design of a Broadband Fiber Optic Mode Coupler for Multimode Optical Coherence Tomography

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Photonics 2023, 10(2), 162; https://doi.org/10.3390/photonics10020162 - 03 Feb 2023

Viewed by 782

Abstract

In this paper, we propose an optical fiber-based broadband mode coupler for multimode optical coherence tomography (OCT) in the O-band (1.26–1.36 μm). The proposed device uses a tapered few-mode fiber (FMF) to lower the effective mode index of the selected higher-order mode, which [...] Read more.

In this paper, we propose an optical fiber-based broadband mode coupler for multimode optical coherence tomography (OCT) in the O-band (1.26–1.36 μm). The proposed device uses a tapered few-mode fiber (FMF) to lower the effective mode index of the selected higher-order mode, which can be phase matched to the fundamental mode of the single-mode fiber (SMF). The tapered FMF and the SMF are side polished to reduce the core-to-core separation to achieve efficient mode coupling. Key design parameters such as the tapering ratio of the FMF, FMF core to SMF core separation, coupler length, and coupling ratio in the O-band are studied thoroughly. Higher-order modes of the FMF will be effectively coupled from the fundamental mode of SMF in the sample arm of the multimode OCT system. The reflected signals of the higher-order modes from the sample will be separated into several single-mode signals using the same fiber device before interfering with the reference light, which was not possible before. The proposed fiber device will be a key component to efficiently achieve multimode OCT operation with better signal collection efficiency and improved penetration depth for deep tissue imaging. Full article

(This article belongs to the Special Issue Advances in 3OM: Opto-Mechatronics, Opto-Mechanics, and Optical Metrology)

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Open AccessArticle

Deformation Measurement of a SS304 Stainless Steel Sheet Using Digital Image Correlation Method

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Photonics 2022, 9(12), 912; https://doi.org/10.3390/photonics9120912 - 28 Nov 2022

Viewed by 770

Abstract

The digital image correlation (DIC) method is widely used in deformation measurements as it has the advantages of being a non-contact, high precision method that provides full field measurements, and requires simple experimental equipment. Traditionally, the grayscale speckle patterns captured by a monochromatic [...] Read more.

The digital image correlation (DIC) method is widely used in deformation measurements as it has the advantages of being a non-contact, high precision method that provides full field measurements, and requires simple experimental equipment. Traditionally, the grayscale speckle patterns captured by a monochromatic camera are used in the DIC method. With the growing development of consumer color cameras, there is great potential for developing color information in the DIC method. This paper proposes a displacement- and stress–strain-invariant DIC deformation measurement method based on the integer-pixel matching approach for speckle patterns during a tension test. For the integer-pixel matching stage, the load and displacement and stress–strain-invariant histories feature is used to estimate the initial value of the deformation parameters. In addition, this paper proposes a reverse retrieve strategy, instead of a forward search, to reduce the search time. Experiments show that the proposed DIC deformation measurement approach is not only capable of displacement invariance measurement, with robustness and high efficiency, but also that the average accuracy of the stress–strain result can reach 0.1%. Full article

(This article belongs to the Special Issue Advances in 3OM: Opto-Mechatronics, Opto-Mechanics, and Optical Metrology)

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Open AccessArticle

Low-Cost 3D-Printed Electromagnetically Driven Large-Area 1-DOF Optical Scanners

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Photonics 2022, 9(7), 484; https://doi.org/10.3390/photonics9070484 - 11 Jul 2022

Cited by 2 | Viewed by 915

Abstract

In this paper, we demonstrate 3D-printed 1-DOF (one torsional axis; 1 degree of freedom) optical scanners with large mirror areas (up to 20 × 20 mm²). Each device consists of an aluminum-coated square silicon substrate serving as the mirror, two miniature [...] Read more.

In this paper, we demonstrate 3D-printed 1-DOF (one torsional axis; 1 degree of freedom) optical scanners with large mirror areas (up to 20 × 20 mm²). Each device consists of an aluminum-coated square silicon substrate serving as the mirror, two miniature permanent magnets, an electromagnet, and a 3D-printed structure including the mirror frame, torsion springs, and base. One device can reach a static half optical scan angle of 14.8 deg., i.e., a full optical scan angle of 29.6 deg., at 12 VDC; this particular device exhibits a mechanical resonance frequency of 84 Hz. These scanners can be a potential, low-cost alternative to the expensive conventional galvanometer scanners. Full article

(This article belongs to the Special Issue Advances in 3OM: Opto-Mechatronics, Opto-Mechanics, and Optical Metrology)

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Open AccessArticle

Influence of Spatio-Temporal Couplings on Focused Optical Vortices

by

Anda-Maria Talposi

,

Vicentiu Iancu

and

Daniel Ursescu

Photonics 2022, 9(6), 389; https://doi.org/10.3390/photonics9060389 - 30 May 2022

Viewed by 1232

Abstract

Ultra-intense laser pulses with helical phases are of interest in laser-driven charged particle acceleration and related experiments with extreme light. However, such optical vortices can be affected by the presence of residual spatial-temporal couplings. Their field distributions after propagating in free-space and in [...] Read more.

Ultra-intense laser pulses with helical phases are of interest in laser-driven charged particle acceleration and related experiments with extreme light. However, such optical vortices can be affected by the presence of residual spatial-temporal couplings. Their field distributions after propagating in free-space and in the focal plane of an ideal focusing mirror were assessed through numerical modeling, based on the Gaussian decomposition method for a 25 fs pulse with a Supergaussian spatial profile. The wash-out of the central hole in the doughnut-shaped profile in the focal plane corresponds to the rotation of the phase discontinuity. Full article

(This article belongs to the Special Issue Advances in 3OM: Opto-Mechatronics, Opto-Mechanics, and Optical Metrology)

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Open AccessCommunication

In-Situ Depth Measurement of Laser Micromachining

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Photonics 2021, 8(11), 493; https://doi.org/10.3390/photonics8110493 - 04 Nov 2021

Cited by 2 | Viewed by 1260

Abstract

Precision laser micromachining plays an important role in the biomedical, electronics, and material processing industries. During laser drilling, precision depth detection with micrometer-level resolution is required, particularly with blind-hole or heterogeneous structures. We present an optical detection system utilizing an optical confocal structure, [...] Read more.

Precision laser micromachining plays an important role in the biomedical, electronics, and material processing industries. During laser drilling, precision depth detection with micrometer-level resolution is required, particularly with blind-hole or heterogeneous structures. We present an optical detection system utilizing an optical confocal structure, experimentally confirmed to achieve a >95% accuracy for micron-diameter holes that are tens-of-microns deep. This system can be easily integrated into commercial laser micromachining processes, and can be employed in laser drilling and three-dimensional active-feedback laser printing. Full article

(This article belongs to the Special Issue Advances in 3OM: Opto-Mechatronics, Opto-Mechanics, and Optical Metrology)

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Open AccessArticle

Frequency Dependence of a Piezo-Resistive Method for Pressure Measurements of Laser-Induced Shock Waves in Solids

by

Ricardo Gonzalez-Romero

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Marija Strojnik

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Guillermo Garcia-Torales

and

Gilberto Gomez-Rosas

Photonics 2021, 8(4), 120; https://doi.org/10.3390/photonics8040120 - 12 Apr 2021

Cited by 2 | Viewed by 1748

Abstract

A shock wave is a mechanical high-pressure pulse that travels inside a medium with a full width at half-maximum of a few nanoseconds that may be induced with a high-power laser pulse. A piezo-resistive measurement method to determine the shock wave pressure has [...] Read more.

A shock wave is a mechanical high-pressure pulse that travels inside a medium with a full width at half-maximum of a few nanoseconds that may be induced with a high-power laser pulse. A piezo-resistive measurement method to determine the shock wave pressure has been widely employed even though there is inner inaccuracy in the calibration process. We are interested in developing a precise theoretical model of laser material processing for applications in material sciences that includes the frequency dependence of the electronic post processing. We show an approach to determine the correction factor to frequency response at a high frequency of a piezo-resistive experimental setup and the results of the pressure measurements obtained in this experimental setup. The theoretical and experimental work demonstrates the feasibility of piezo-resistive methods to measure a laser-induced shock wave pressure in the nanosecond range. The correction factor of the frequency dependence calibration allows the technique to be applied in different shock wave experiments. Full article

(This article belongs to the Special Issue Advances in 3OM: Opto-Mechatronics, Opto-Mechanics, and Optical Metrology)

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Open AccessArticle

Reflectivity of Cholesteric Liquid Crystals with an Anisotropic Defect Layer Inside

by

Dariusz Grzelczyk

and

Jan Awrejcewicz

Photonics 2020, 7(3), 58; https://doi.org/10.3390/photonics7030058 - 10 Aug 2020

Cited by 1 | Viewed by 2104

Abstract

In this study, first, we numerically investigated the reflectivity of a cholesteric liquid crystal with an anisotropic defect layer inside. To model optical phenomena in the examined system, a 4 × 4 matrix method was employed. The tests were carried out for different [...] Read more.

In this study, first, we numerically investigated the reflectivity of a cholesteric liquid crystal with an anisotropic defect layer inside. To model optical phenomena in the examined system, a 4 × 4 matrix method was employed. The tests were carried out for different thicknesses of the whole system, different thicknesses of the defect layer, as well as different defect layer locations inside the cell. Next, a cholesteric liquid crystal comprising a defect layer and held between two parallel electrical conductors was also considered. In this case, the optical properties of the system could also be adjusted by an external applied electric field. Some interesting simulation results of the reflection coefficient (i.e., the fraction of electromagnetic energy reflected) were obtained, illustrated, and discussed. The simulation results showed a significant influence of both the defect and the external electric field on the selective reflection phenomenon, and the possibility of controlling the shape of the reflection spectrum. Finally, some potential applications of the analyzed optical system were discussed. Full article

(This article belongs to the Special Issue Advances in 3OM: Opto-Mechatronics, Opto-Mechanics, and Optical Metrology)

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