Photonics

Research

8 pages, 3285 KiB

Open AccessEditor’s ChoiceArticle

Generation of over 1000 Diffraction Spots from 2D Graded Photonic Super-Crystals

by Safaa Hassan, Yan Jiang, Khadijah Alnasser, Noah Hurley, Hualiang Zhang, Usha Philipose and Yuankun Lin

Photonics 2020, 7(2), 27; https://doi.org/10.3390/photonics7020027 - 10 Apr 2020

Cited by 4 | Viewed by 3218

Abstract

For the first time, we are able to generate over 1000 diffraction spots from a graded photonic super-crystal with a unit super-cell size of 12a × 12a where a is the lattice constant and hole radii are gradually changed in dual directions. The [...] Read more.

For the first time, we are able to generate over 1000 diffraction spots from a graded photonic super-crystal with a unit super-cell size of 12a × 12a where a is the lattice constant and hole radii are gradually changed in dual directions. The diffraction pattern from the graded photonic super-crystal reveals unique diffraction properties. The first order diffractions of (±1,0) or (0,±1) disappear. Fractional diffraction orders are observed in the diffraction pattern inside a square with vertices of (1,1), (1,−1), (−1,−1) and (−1,−1). The fractional diffraction can be understood from lattices with a period of a. However, a dual-lattice model is considered in order to explain higher-order diffractions. E-field intensity simulations show a coupling and re-distribution among fractional orders of Bloch waves. There are a total of 12 × 12 spots in E-field intensity in the unit supercell corresponding to 12 × 12 fractional diffraction orders in the diffraction pattern and 12 × 12 fractional orders of momentum in the first Brillouin zone in k-space. Full article

(This article belongs to the Special Issue Advanced Optical Materials and Devices)

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9 pages, 4707 KiB

Open AccessArticle

Tuning of Fiber Optic Surface Reflectivity through Graphene Oxide-Based Layer-by-Layer Film Coatings

by Catarina S. Monteiro, Maria Raposo, Paulo A. Ribeiro, Susana O. Silva and Orlando Frazão

Photonics 2020, 7(1), 11; https://doi.org/10.3390/photonics7010011 - 18 Jan 2020

Cited by 6 | Viewed by 3208

Abstract

The use of graphene oxide-based coatings on optical fibers are investigated, aiming to tune the reflectivity of optical fiber surfaces for use in precision sensing devices. Graphene oxide (GO) layers are successfully deposited onto optical fiber ends, either in cleaved or hollow microspheres, [...] Read more.

The use of graphene oxide-based coatings on optical fibers are investigated, aiming to tune the reflectivity of optical fiber surfaces for use in precision sensing devices. Graphene oxide (GO) layers are successfully deposited onto optical fiber ends, either in cleaved or hollow microspheres, by mounting combined bilayers of polyethylenimine (PEI) and GO layers using the Layer-by-Layer (LbL) technique. The reflectivity of optical fibers coated with graphene oxide layers is investigated for the telecom region allowing to both monitor layer growth kinetics and cavity characterization. Tunable reflective surfaces are successfully attained in both cleaved optical fibers and hollow microsphere fiber-based sensors by simply coating them with PEI/GO layers through the LbL film technique. Full article

(This article belongs to the Special Issue Advanced Optical Materials and Devices)

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13 pages, 7466 KiB

Open AccessArticle

Nonlinear Optical Study in a Set of Dibenzylideneacetone Derivatives with Potential for Optical Frequency Conversion

by Francisco A. Santos, Luis M. G. Abegão, Ruben D. Fonseca, Aline M. Alcântara, Cleber R. Mendonça, Márcio A. R. C. Alencar, Marcelo S. Valle, Kenji Kamada, Leonardo De Boni and José J. Rodrigues, Jr.

Photonics 2020, 7(1), 8; https://doi.org/10.3390/photonics7010008 - 9 Jan 2020

Cited by 10 | Viewed by 4088

Abstract

The search for advanced optical materials, in particular, materials with nonlinear optical responses, has, in the last years, experienced substantial growth due to their vast applications in the photonics field. One of those applications is ultra-fast optical frequency conversion, in the optics communications [...] Read more.

The search for advanced optical materials, in particular, materials with nonlinear optical responses, has, in the last years, experienced substantial growth due to their vast applications in the photonics field. One of those applications is ultra-fast optical frequency conversion, in the optics communications field. Organic compounds have emerged as promising candidates for raw materials to develop nonlinear optical devices, such as optical converters, due to their intrinsic ultra-fast electronic responses. Also, the easy tailoring of organic molecular structures makes organic materials much more appealing than the inorganic ones. In this work, we have performed a linear and nonlinear optical characterization of a set of dibenzylideneacetone derivatives. The nonlinear optical responses investigated correspond to second- and third-order nonlinear processes, namely, first electronic molecular hyperpolarizability and two-photon absorption cross-section, respectively. The value of the first electronic molecular hyperpolarizability, up to 52 cm⁴·statvolt⁻¹, could be considered a robust value when compared to the short-sized π-electron backbone length of the studied compounds. Such results suggest that these compounds exhibit the potential to be used as optical frequency converters. Quantum chemical calculations were used to predict the theoretical value of the first molecular hyperpolarizability, as well as to simulate the one- and two-photon absorption spectra for all compounds. Full article

(This article belongs to the Special Issue Advanced Optical Materials and Devices)

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10 pages, 5481 KiB

Open AccessArticle

The Effect of Thickness on the Properties of Laser-Deposited NiBSi-WC Coating on a Cu-Cr-Zr Substrate

by Yury Korobov, Yulia Khudorozhkova, Holger Hillig, Alexander Vopneruk, Aleksandr Kotelnikov, Sergey Burov, Prabu Balu, Alexey Makarov and Alexey Chernov

Photonics 2019, 6(4), 127; https://doi.org/10.3390/photonics6040127 - 13 Dec 2019

Cited by 3 | Viewed by 3264

Abstract

Ni/60WC coatings on copper substrate were placed via laser deposition (LD). A structural study was conducted using electron microscopy and a microhardness evaluation. Two body abrasive wear tests were conducted with a pin-on-plate reciprocating technique. A tool steel X12MF GOST 5960 (C-Cr-Mo-V 1.6-12-0.5-0.2) [...] Read more.

Ni/60WC coatings on copper substrate were placed via laser deposition (LD). A structural study was conducted using electron microscopy and a microhardness evaluation. Two body abrasive wear tests were conducted with a pin-on-plate reciprocating technique. A tool steel X12MF GOST 5960 (C-Cr-Mo-V 1.6-12-0.5-0.2) with a hardness of 63 HRC was used as a counterpart. The following results were obtained: Precipitation of the secondary carbides takes place in the thicker layers. Their hardness is lower than that of the primary carbides in the deposition (2425 HV vs. 2757 HV) because they mix with the matrix material. In the thin layers, precipitation is restricted due to a higher cooling rate. For both LD coatings, the carbide’s hardness increases compared to the initial mono-tungsten carbide (WC)-containing powder (2756 HV vs. 2200 HV). Such a high level of microhardness reflects the combined influence of a low level of thermal destruction of carbides during laser deposition and the formation of a boride-strengthening phase from the matrix powder. The thicker layer showed a higher wear resistance; weight loss was 20% lower. The changes in the thickness of the laser deposited Ni-WC coating altered its structure and wear resistance. Full article

(This article belongs to the Special Issue Advanced Optical Materials and Devices)

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8 pages, 3479 KiB

Open AccessArticle

Ultrafast All-Optical Signal Modulation Induced by Optical Kerr Effect in a Tellurite Photonic Bandgap Fiber

by Tonglei Cheng, Fan Zhang, Shunta Tanaka, Shuguang Li, Xin Yan, Xuenan Zhang, Takenobu Suzuki and Yasutake Ohishi

Photonics 2019, 6(4), 113; https://doi.org/10.3390/photonics6040113 - 29 Oct 2019

Cited by 6 | Viewed by 3465

Abstract

Ultrafast all-optical signal modulation induced by optical Kerr effect (OKE) was demonstrated in an all-solid tellurite photonic bandgap fiber (PBGF) which was designed and fabricated based on TeO₂-Li₂O-WO₃-MoO₃-Nb₂O₅ (TLWMN, high-index rods), TeO [...] Read more.

Ultrafast all-optical signal modulation induced by optical Kerr effect (OKE) was demonstrated in an all-solid tellurite photonic bandgap fiber (PBGF) which was designed and fabricated based on TeO₂-Li₂O-WO₃-MoO₃-Nb₂O₅ (TLWMN, high-index rods), TeO₂-ZnO-Na₂O-La₂O₃ (TZNL, background), and TeO₂-ZnO-Li₂O-K₂O-Al₂O₃-P₂O₅ (TZLKAP, cladding) glasses. At the input of a control pulse with high intensity, OKE occurred in the tellurite PBGF and the transmission bands of the tellurite PBGF shifted. The signal at 1.57 μm transmitting in the fiber core can be ultrafast all-optically modulated by the ultrafast single pulse (200 kW, 200 fs) under OKE, where the modulation speed can reach 50 GHz, faster than some commercial LiNbO₃ modulators. The results in this paper can be applied to multi-monitors, local area network, detectors, multi-sources, etc. Full article

(This article belongs to the Special Issue Advanced Optical Materials and Devices)

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12 pages, 1533 KiB

Open AccessArticle

Ultrafast Hyperspectral Transient Absorption Spectroscopy: Application to Single Layer Graphene

by Felice Gesuele

Photonics 2019, 6(3), 95; https://doi.org/10.3390/photonics6030095 - 29 Aug 2019

Cited by 13 | Viewed by 8746

Abstract

We describe the basic principles and the experimental implementation of the hyperspectral transient absorption technique, based on femtosecond laser sources. In this technique the samples were optically “pumped” using the femtosecond tunable pulse delivered by an Optical Parametric Amplifier, and “probed” for changes [...] Read more.

We describe the basic principles and the experimental implementation of the hyperspectral transient absorption technique, based on femtosecond laser sources. In this technique the samples were optically “pumped” using the femtosecond tunable pulse delivered by an Optical Parametric Amplifier, and “probed” for changes in transmission in a broad spectral range with a “white light” laser-generated supercontinuum. The spectra were collected by a pair of multichannel detectors which allowed retrieval of the absorbance change in a wide spectral range in one time. The use of the supercontinuum probe introduced artifacts in the measured 2D data set which could be corrected with a proper calibration of the chirp. The configuration with crossed polarization for pump and probe pulse extended the spectral measured range above and below the pump energy within the same experiment. We showed the versatility of the technique by applying it to the investigation of the charge carrier dynamics in two-dimensional single layer graphene. Full article

(This article belongs to the Special Issue Advanced Optical Materials and Devices)

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13 pages, 3628 KiB

Open AccessArticle

Generation of Coherent and Spatially Squeezed States of an Electromagnetic Beam in a Planar Inhomogeneous Dielectric Waveguide

by Anna Bogatskaya, Andrey Schegolev, Nikolay Klenov and Alexander Popov

Photonics 2019, 6(3), 84; https://doi.org/10.3390/photonics6030084 - 30 Jul 2019

Cited by 3 | Viewed by 3348

Abstract

We use slow-varying amplitude approximation (SVA) for the wave equation to study both analytically and numerically propagation of an electromagnetic beam in the waveguide structure with parabolic susceptibility spatial dependence. Such a structure is similar to the harmonic oscillator in quantum mechanics. We [...] Read more.

We use slow-varying amplitude approximation (SVA) for the wave equation to study both analytically and numerically propagation of an electromagnetic beam in the waveguide structure with parabolic susceptibility spatial dependence. Such a structure is similar to the harmonic oscillator in quantum mechanics. We analyze this structure as a single mode guide and introduce the notion of number of “photons” in the mode. In particular, we pay special attention to the possibility of effective build-up of the coherent and spatially squeezed vacuum states of the mode that can be of interest for a number of practical applications. The way to provide these types of mode excitation is suggested. Several applications for controlling the mode composition of an electromagnetic wave in the parabolic index-gradient waveguide for various frequency ranges are considered. Full article

(This article belongs to the Special Issue Advanced Optical Materials and Devices)

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17 pages, 7250 KiB

Open AccessArticle

The Theoretical Concept of Polarization Reflectometric Interference Spectroscopy (PRIFS): An Optical Method to Monitor Molecule Adsorption and Nanoparticle Adhesion on the Surface of Thin Films

by László Janovák, Imre Dékány and Dániel Sebők

Photonics 2019, 6(3), 76; https://doi.org/10.3390/photonics6030076 - 30 Jun 2019

Cited by 6 | Viewed by 5207

Abstract

In this paper, we present an improved reflectometric interference spectroscopy (RIfS) sensor principle which is suitable for thin films. The conventional RIfS technique is an appropriate method to detect interfacial interactions at the solid–gas or solid–liquid interface in the case of thin films [...] Read more.

In this paper, we present an improved reflectometric interference spectroscopy (RIfS) sensor principle which is suitable for thin films. The conventional RIfS technique is an appropriate method to detect interfacial interactions at the solid–gas or solid–liquid interface in the case of thin films with a thickness of a few hundred nanometers, but when a significantly lower layer thickness (~100 nm) is required, the method is barely usable. By applying polarized reflected light and monitoring the ratio of the p- and s-polarized components, a characteristic curve can be obtained with one or a few local extreme value(s) with significantly favorable intensity ratios compared to the conventional method. In this work we studied the effect of film thickness, incident angle and the refractive indices of the thin film, the medium and the substrate. As a main result, it was demonstrated that the sensitivity of the PRIfS method is 4–7 times higher than that of the conventional technique near a critical angle. In simulated adsorption experiments, it was determined that the sensitivity of RIfS is around 550 nm/RIU (refractive index unit), while it is 1825 and 3966 nm/RIU for PRIfS in gas and aqueous phase, respectively. Full article

(This article belongs to the Special Issue Advanced Optical Materials and Devices)

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9 pages, 930 KiB

Open AccessArticle

Third-Order Nonlinear Spectrum of GaN under Femtosecond-Pulse Excitation from the Visible to the Near Infrared

by Gustavo F. B. Almeida, Sabrina N. C. Santos, Jonathas P. Siqueira, Jessica Dipold, Tobias Voss and Cleber R. Mendonça

Photonics 2019, 6(2), 69; https://doi.org/10.3390/photonics6020069 - 18 Jun 2019

Cited by 12 | Viewed by 4688

Abstract

Gallium nitride (GaN) has been established as a promising candidate for integrated electro-optic and photonic devices, aiming at applications from optical switching to signal processing. Studies of its optical nonlinearities, however, lack spectral coverage, especially in the telecommunications range. In this study, we [...] Read more.

Gallium nitride (GaN) has been established as a promising candidate for integrated electro-optic and photonic devices, aiming at applications from optical switching to signal processing. Studies of its optical nonlinearities, however, lack spectral coverage, especially in the telecommunications range. In this study, we measured the two-photon absorption coefficient (β) and the nonlinear index of refraction (n₂) of GaN from the visible to the near-infrared by using femtosecond laser pulses. We observed an increase of β from (1.0 ± 0.2) to (2.9 ± 0.6) ×10⁻¹¹ m/W as the photon energy approached the band gap from 1.77 up to 2.25 eV (700–550 nm), while n₂ varied from (90 ± 30) ×10⁻²⁰ up to (265 ± 80) ×10⁻²⁰ m²/W within a broad spectral range, from 0.80 up to 2.25 eV (1550–550 nm). The results were modeled by applying a theory based on the second-order perturbation theory and the Kramers-Kronig relationship for direct-gap semiconductors, which are important for the development of GaN-based nonlinear photonic devices. Full article

(This article belongs to the Special Issue Advanced Optical Materials and Devices)

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12 pages, 4187 KiB

Open AccessArticle

An Optical Power Divider Based on Mode Coupling Using GaN/Al₂O₃ for Underwater Communication †

by Retno Wigajatri Purnamaningsih, Nji Raden Poespawati, Tomy Abuzairi and Elhadj Dogheche

Photonics 2019, 6(2), 63; https://doi.org/10.3390/photonics6020063 - 3 Jun 2019

Cited by 13 | Viewed by 3853

Abstract

This paper details the design of a 1 × 8 optical power divider, using a gallium nitride (GaN) semiconductor on sapphire, which can be applied to underwater optical wireless communication. The design consists of nine parallel rectangular waveguides which are based on mode [...] Read more.

This paper details the design of a 1 × 8 optical power divider, using a gallium nitride (GaN) semiconductor on sapphire, which can be applied to underwater optical wireless communication. The design consists of nine parallel rectangular waveguides which are based on mode coupling phenomena. Analysis of the design was performed using the beam propagation method (BPM). The optimization was conducted using the 3D finite difference (FD)-BPM method with an optical signal input at the wavelength required for maritime application of λ = 0.45 µm. The signal was injected into the central waveguide. The results showed that at a propagation length of 1480 µm the optical power is divided into eight output beams with an excess loss of 0.46 dB and imbalance of 0.51 dB. The proposed design can be further developed and applied in future underwater communication technology. Full article

(This article belongs to the Special Issue Advanced Optical Materials and Devices)

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14 pages, 3748 KiB

Open AccessArticle

Synthesis of Nanostructure In_xGa_1−xN Bulk Alloys and Thin Films for LED Devices

by Abd El-Hady B. Kashyout, Marwa Fathy, Sara Gad, Yehia Badr and Ahmed A. Bishara

Photonics 2019, 6(2), 44; https://doi.org/10.3390/photonics6020044 - 24 Apr 2019

Cited by 7 | Viewed by 3896

Abstract

In this study, we investigated an innovative method for the fabrication of nanostructure bulk alloys and thin films of indium gallium nitride (In_xGa_1−xN) as active, thin films for light-emitting diode (LED) devices using both crystal growth and thermal vacuum [...] Read more.

In this study, we investigated an innovative method for the fabrication of nanostructure bulk alloys and thin films of indium gallium nitride (In_xGa_1−xN) as active, thin films for light-emitting diode (LED) devices using both crystal growth and thermal vacuum evaporation techniques, respectively. These methods resulted in some tangible improvements upon the usual techniques of In_xGa_1−xN systems. A cheap glass substrate was used for the fabrication of the LED devices instead of sapphire. Indium (In) and Gallium (Ga) metals, and ammonia (NH₃) were the precursors for the alloy formation. The alloys were prepared at different growth temperatures with compositions ranging from 0.1 ≤ x ≤ 0.9. In_xGa_1−xN alloys at 0.1 ≤ x ≤ 0.9 had different crystallinities with respect to X-Ray diffraction (XRD) patterns where the energy bandgap that was measured by photoluminescence (PL) fell in the range between 1.3 and 2.5 eV. The bulk alloys were utilized to deposit the thin films onto the glass substrate using thermal vacuum evaporation (TVE). The XRD thin films that were prepared by TVE showed high crystallinity of cubic and hexagonal structures with high homogeneity. Using TVE, the In_xGa_1−xN phase separation of 0.1 ≤ x ≤ 0.9 was eliminated and highly detected by XRD and FESEM. Also, the Raman spectroscopy confirmed the structure that was detected by XRD. The FESEM showed a variance in the grain size of both alloys and thin films. The In_xGa_1−xN LED device with the structure of glass/GaN/n-In_0.1Ga_0.9N:n/In_0.1Ga_0.9N/p-In_0.1Ga_0.9N:Mg was checked by the light emitted by electroluminescence (EL). White light generation is a promising new direction for the fabrication of such devices based on In_xGa_1−xN LED devices with simple and low-cost techniques. Full article

(This article belongs to the Special Issue Advanced Optical Materials and Devices)

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12 pages, 4081 KiB

Open AccessArticle

Epsilon-Near-Zero Absorber by Tamm Plasmon Polariton

by Rashid G. Bikbaev, Stepan Ya. Vetrov and Ivan V. Timofeev

Photonics 2019, 6(1), 28; https://doi.org/10.3390/photonics6010028 - 9 Mar 2019

Cited by 33 | Viewed by 5415

Abstract

Two schemes of excitation of a Tamm plasmon polariton localized at the interface between a photonic crystal and a nanocomposite with near-zero effective permittivity have been investigated in the framework of the temporal coupled-mode theory. The parameters of the structure have been determined, [...] Read more.

Two schemes of excitation of a Tamm plasmon polariton localized at the interface between a photonic crystal and a nanocomposite with near-zero effective permittivity have been investigated in the framework of the temporal coupled-mode theory. The parameters of the structure have been determined, which correspond to the critical coupling of the incident field with a Tamm plasmon polariton and, consequently, ensure the total absorption of the incident radiation by the structure. It has been established that the spectral width of the absorption line depends on the scheme of Tamm plasmon polariton excitation and the parameters of a nanocomposite film. The features of field localization at the Tamm plasmon polariton frequency for different excitation schemes have been examined. It has been demonstrated that such media can be used as narrowband absorbers based on Tamm plasmon polaritons localized at the interface between a photonic crystal and a nanocomposite with near-zero effective permittivity. Full article

(This article belongs to the Special Issue Advanced Optical Materials and Devices)

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12 pages, 6513 KiB

Open AccessEditor’s ChoiceArticle

A Bio-Compatible Fiber Optic pH Sensor Based on a Thin Core Interferometric Technique

by Magnus Engholm, Krister Hammarling, Henrik Andersson, Mats Sandberg and Hans-Erik Nilsson

Photonics 2019, 6(1), 11; https://doi.org/10.3390/photonics6010011 - 30 Jan 2019

Cited by 12 | Viewed by 4816

Abstract

There is an increasing demand for compact, reliable and versatile sensor concepts for pH-level monitoring within several industrial, chemical as well as bio-medical applications. Many pH sensors concepts have been proposed, however, there is still a need for improved sensor solutions with respect [...] Read more.

There is an increasing demand for compact, reliable and versatile sensor concepts for pH-level monitoring within several industrial, chemical as well as bio-medical applications. Many pH sensors concepts have been proposed, however, there is still a need for improved sensor solutions with respect to reliability, durability and miniaturization but also for multiparameter sensing. Here we present a conceptual verification, which includes theoretical simulations as well as experimental evaluation of a fiber optic pH-sensor based on a bio-compatible pH sensitive material not previously used in this context. The fiber optic sensor is based on a Mach-Zehnder interferometric technique, where the pH sensitive material is coated on a short, typically 20-25 mm thin core fiber spliced between two standard single mode fibers. The working principle of the sensor is simulated by using COMSOL Multiphysics. The simulations are used as a guideline for the construction of the sensors that have been experimentally evaluated in different liquids with pH ranging from 1.95 to 11.89. The results are promising, showing the potential for the development of bio-compatible fiber optic pH sensor with short response time, high sensitivity and broad measurement range. The developed sensor concept can find future use in many medical- or bio-chemical applications as well as in environmental monitoring of large areas. Challenges encountered during the sensor development due to variation in the design parameters are discussed. Full article

(This article belongs to the Special Issue Advanced Optical Materials and Devices)

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