Photonics

10 pages, 1584 KiB

Open AccessFeature PaperArticle

Stability Boundaries in Laterally-Coupled Pairs of Semiconductor Lasers

by Martin Vaughan, Hadi Susanto, Nianqiang Li, Ian Henning and Mike Adams

Photonics 2019, 6(2), 74; https://doi.org/10.3390/photonics6020074 - 25 Jun 2019

Cited by 6 | Viewed by 3628

The dynamic behaviour of coupled pairs of semiconductor lasers is studied using normal-mode theory, applied to one-dimensional (slab) and two-dimensional (circular cylindrical) real index confined structures. It is shown that regions of stable behaviour depend not only on pumping rate and laser separation, [...] Read more.

The dynamic behaviour of coupled pairs of semiconductor lasers is studied using normal-mode theory, applied to one-dimensional (slab) and two-dimensional (circular cylindrical) real index confined structures. It is shown that regions of stable behaviour depend not only on pumping rate and laser separation, but also on the degree of guidance in the structures. Comparison of results between normal-mode and coupled-mode theories for these structures leads to the tentative conclusion that the accuracy of the latter is determined by the strength of self-overlap and cross-overlap of the symmetric and antisymmetric normal modes in the two lasers. Full article

(This article belongs to the Special Issue Semiconductor Laser Dynamics: Fundamentals and Applications)

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13 pages, 11248 KiB

Open AccessEditor’s ChoiceArticle

Long-Range, High-Resolution Camera Optical Design for Assisted and Autonomous Driving

by Furkan E. Sahin

Photonics 2019, 6(2), 73; https://doi.org/10.3390/photonics6020073 - 25 Jun 2019

Cited by 18 | Viewed by 27501

Abstract

High-quality cameras are fundamental sensors in assisted and autonomous driving. In particular, long-range forward-facing cameras can provide vital information about the road ahead, including detection and recognition of objects and early hazard warning. These automotive cameras should provide high-resolution images consistently under extreme [...] Read more.

High-quality cameras are fundamental sensors in assisted and autonomous driving. In particular, long-range forward-facing cameras can provide vital information about the road ahead, including detection and recognition of objects and early hazard warning. These automotive cameras should provide high-resolution images consistently under extreme operating conditions of the car for robust operation. This paper aims to introduce the design of fixed-focus, passively athermalized lenses for next-generation automotive cameras. After introducing an overview of essential and desirable features of automotive cameras and state-of-the-art, based on these features, two different camera designs that can achieve traffic sign recognition at 200 m distance are presented. These lenses are designed from scratch, with a unique design approach that starts with a graphical lens material selection tool and arrives at an optimized design with optical design software. Optical system analyses are performed to evaluate the lens designs. The lenses are shown to accomplish high contrast from

- 40

°C to 100 °C and allow for a

4 \times

increase in resolution of automotive cameras. Full article

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10 pages, 2236 KiB

Open AccessArticle

On-Chip Guiding of Higher-Order Orbital Angular Momentum Modes

by In Joon Lee and Sangin Kim

Photonics 2019, 6(2), 72; https://doi.org/10.3390/photonics6020072 - 23 Jun 2019

Cited by 6 | Viewed by 3946

Abstract

Higher-order orbital angular momentum (OAM) mode guiding in a waveguide which is suitable for on-chip integration has been investigated. Based on the relation between the Laguerre-Gaussian mode and the Hermite-Gaussian mode, it has been shown that two degenerate guided modes of π/2l [...] Read more.

Higher-order orbital angular momentum (OAM) mode guiding in a waveguide which is suitable for on-chip integration has been investigated. Based on the relation between the Laguerre-Gaussian mode and the Hermite-Gaussian mode, it has been shown that two degenerate guided modes of π/2l-rotation symmetry can support the l-th order OAM mode. In order to mimic the rotational symmetry, we have proposed the waveguide structure of a cross-shaped core and designed a waveguide that can support OAM modes of ±1 and ±2 topological charges simultaneously at a wavelength of 1550 nm. Purity of the OAM modes guided in the designed waveguide has been assessed by numerically calculating their topological charges from the field distribution, which were close to the theoretical values. We also investigated the guiding of OAM modes of ±3 and ±4 topological charges in our proposed waveguide structure, which revealed the possibility of the separate guiding of those OAM modes with relatively lower purity. Full article

(This article belongs to the Special Issue Optical Angular Momentum in Nanophotonics II)

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Graphical abstract

9 pages, 2458 KiB

Open AccessArticle

Modeling and Analysis of SOI Gratings-Based Opto-Fluidic Biosensor for Lab-on-a-Chip Applications

by Venkatesha Muniswamy, Prasant Kumar Pattnaik and Narayan Krishnaswamy

Photonics 2019, 6(2), 71; https://doi.org/10.3390/photonics6020071 - 20 Jun 2019

Cited by 5 | Viewed by 3465

Abstract

The design, modeling, and analysis of a silicon-on-insulator (SOI) grating coupler integrated with a microfluidic channel for lab-on-a-chip applications are presented. The grating coupler was designed to operate at 1310 nm. The simulated SOI structure consisted of a 220 nm top-Si device layer [...] Read more.

The design, modeling, and analysis of a silicon-on-insulator (SOI) grating coupler integrated with a microfluidic channel for lab-on-a-chip applications are presented. The grating coupler was designed to operate at 1310 nm. The simulated SOI structure consisted of a 220 nm top-Si device layer with an integrated waveguide, grating coupler, and a buried oxide layer of 2 µm. A rectangular microfluidic channel was deposited on the SOI optical grating structure for light and fluid interaction. The fluidic flow through the device was driven by centrifugal and Coriolis forces. The grating structure was designed to achieve a maximum coupling efficiency at the optimized injection angle of the light source. The sensitivity of the grating structure could be analyzed and evaluated using the change in coupled power as a function of the effective refractive index and was found to be 0.928 × 10⁻⁶ RIU. The SOI optical grating structure along with the micro fluidic channel on top could be effectively used as an absorbance-based lab-on-a-chip biosensor. Full article

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13 pages, 4146 KiB

Open AccessArticle

Theoretical Study of a Surface Collinear Holographic Memory

by Soki Hirayama, Ryushi Fujimura, Shinsuke Umegaki, Yoshito Y. Tanaka and Tsutomu Shimura

Photonics 2019, 6(2), 70; https://doi.org/10.3390/photonics6020070 - 19 Jun 2019

Cited by 2 | Viewed by 3938

Abstract

Holographic memory is currently attracting attention as a data storage system capable of achieving a data transfer rate of about 10⁵~10⁶ times that of an optical disc such as Blu-ray disc. In conventional holographic memory, data is generally recorded by [...] Read more.

Holographic memory is currently attracting attention as a data storage system capable of achieving a data transfer rate of about 10⁵~10⁶ times that of an optical disc such as Blu-ray disc. In conventional holographic memory, data is generally recorded by optical writing using volume holograms. However, a volume hologram has the problem not only that it is required to have high mechanical accuracy of a system and low coefficient of thermal expansion of a recording medium, because reconstruction tolerance is extremely low, but also that duplicating time efficiency is poor because whole data cannot be recorded at once. In this paper we proposed surface holographic memory that achieved a high data transfer rate, stable readout performance, and collective duplication by expressing holograms with fine surface asperity. Furthermore, the theoretical formulas of recording and reconstruction processes in the proposed system were derived and the reconstruction characteristics of the hologram were evaluated by numerical simulation. As a result, the proposed method generated reconstructed image readout with sufficient signal for a single page recording. However, the reconstructed image had noise, which was particular to a surface holographic memory. Full article

(This article belongs to the Special Issue Holographic Optical Memory and Related Technologies)

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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 10 | Viewed by 4062

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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9 pages, 1026 KiB

Open AccessEditor’s ChoiceArticle

High Concentration Photovoltaics (HCPV) with Diffractive Secondary Optical Elements

by Furkan E. Sahin and Musa Yılmaz

Photonics 2019, 6(2), 68; https://doi.org/10.3390/photonics6020068 - 12 Jun 2019

Cited by 15 | Viewed by 14754

Abstract

Multi-junction solar cells can be economically viable for terrestrial applications when operated under concentrated illuminations. The optimal design of concentrator optics in high concentration photovoltaics (HCPV) systems is crucial for achieving high energy conversion. At a high geometric concentration, chromatic aberration of the [...] Read more.

Multi-junction solar cells can be economically viable for terrestrial applications when operated under concentrated illuminations. The optimal design of concentrator optics in high concentration photovoltaics (HCPV) systems is crucial for achieving high energy conversion. At a high geometric concentration, chromatic aberration of the primary lens can restrict the optical efficiency and acceptance angle. In order to correct chromatic aberration, multi-material, multi-element refractive elements, hybrid refractive/diffractive elements, or multi-element refractive and diffractive systems can be designed. In this paper, the effect of introducing a diffractive surface in the optical path is analyzed. An example two-stage refractive and diffractive optical system is shown to have an optical efficiency of up to 0.87, and an acceptance angle of up to ±0.55° with a 1600× geometric concentration ratio, which is a significant improvement compared to a single-stage concentrator system with a single material. This optical design can be mass-produced with conventional fabrication methods, thus providing a low-cost alternative to other approaches, and the design approach can be generalized to many other solar concentrator systems with different cell sizes and geometric concentration ratios. Full article

(This article belongs to the Special Issue Nonimaging Optics in Solar Energy)

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15 pages, 4951 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Optoacoustic Calcium Imaging of Deep Brain Activity in an Intracardially Perfused Mouse Brain Model

by Oleksiy Degtyaruk, Benedict Mc Larney, Xosé Luís Deán-Ben, Shy Shoham and Daniel Razansky

Photonics 2019, 6(2), 67; https://doi.org/10.3390/photonics6020067 - 12 Jun 2019

Cited by 10 | Viewed by 4941

Abstract

One main limitation of established neuroimaging methods is the inability to directly visualize large-scale neural dynamics in whole mammalian brains at subsecond speeds. Optoacoustic imaging has advanced in recent years to provide unique advantages for real-time deep-tissue observations, which have been exploited for [...] Read more.

One main limitation of established neuroimaging methods is the inability to directly visualize large-scale neural dynamics in whole mammalian brains at subsecond speeds. Optoacoustic imaging has advanced in recent years to provide unique advantages for real-time deep-tissue observations, which have been exploited for three-dimensional imaging of both cerebral hemodynamic parameters and direct calcium activity in rodents. Due to a lack of suitable calcium indicators excitable in the near-infrared window, optoacoustic imaging of neuronal activity at deep-seated areas of the mammalian brain has been impeded by the strong absorption of blood in the visible range of the light spectrum. To overcome this, we have developed and validated an intracardially perfused mouse brain preparation labelled with genetically encoded calcium indicator GCaMP6f that closely resembles in vivo conditions. By overcoming the limitations of hemoglobin-based light absorption, this new technique was used to observe stimulus-evoked calcium dynamics in the brain at penetration depths and spatio-temporal resolution scales not attainable with existing neuroimaging techniques. Full article

(This article belongs to the Special Issue Neurophotonics – Optics for the Brain)

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27 pages, 2481 KiB

Open AccessReview

A Review of Intrinsic Optical Imaging Serial Blockface Histology (ICI-SBH) for Whole Rodent Brain Imaging

by Joël Lefebvre, Patrick Delafontaine-Martel and Frédéric Lesage

Photonics 2019, 6(2), 66; https://doi.org/10.3390/photonics6020066 - 11 Jun 2019

Cited by 5 | Viewed by 5084

Abstract

In recent years, multiple serial histology techniques were developed to enable whole rodent brain imaging in 3-D. The main driving forces behind the emergence of these imaging techniques were the genome-wide atlas of gene expression in the mouse brain, the pursuit of the [...] Read more.

In recent years, multiple serial histology techniques were developed to enable whole rodent brain imaging in 3-D. The main driving forces behind the emergence of these imaging techniques were the genome-wide atlas of gene expression in the mouse brain, the pursuit of the mouse brain connectome, and the BigBrain project. These projects rely on the use of optical imaging to target neuronal structures with histological stains or fluorescent dyes that are either expressed by transgenic mice or injected at specific locations in the brain. Efforts to adapt the serial histology acquisition scheme to use intrinsic contrast imaging (ICI) were also put forward, thus leveraging the natural contrast of neuronal tissue. This review focuses on these efforts. First, the origin of optical contrast in brain tissue is discussed with emphasis on the various imaging modalities exploiting these contrast mechanisms. Serial blockface histology (SBH) systems using ICI modalities are then reported, followed by a review of some of their applications. These include validation studies and the creation of multimodal brain atlases at a micrometer resolution. The paper concludes with a perspective of future developments, calling for a consolidation of the SBH research and development efforts around the world. The goal would be to offer the neuroscience community a single standardized open-source SBH solution, including optical design, acquisition automation, reconstruction algorithms, and analysis pipelines. Full article

(This article belongs to the Special Issue Neurophotonics – Optics for the Brain)

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17 pages, 4723 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Photonic and Iontronic Sensing in GaInAsP Semiconductor Photonic Crystal Nanolasers

by Toshihiko Baba

Photonics 2019, 6(2), 65; https://doi.org/10.3390/photonics6020065 - 10 Jun 2019

Cited by 10 | Viewed by 4357

Abstract

The GaInAsP semiconductor photonic crystal nanolaser operates at room temperature by photopumping and emits near-infrared light at a wavelength longer than 1.3 μm. Immersion of the nanolaser in a solution causes its laser characteristics to change. Observation of this phenomenon makes it possible [...] Read more.

The GaInAsP semiconductor photonic crystal nanolaser operates at room temperature by photopumping and emits near-infrared light at a wavelength longer than 1.3 μm. Immersion of the nanolaser in a solution causes its laser characteristics to change. Observation of this phenomenon makes it possible to perform biosensing without a fluorescent label or a chromogenic substrate. The most common phenomenon between many photonic sensors is that the resonance wavelength reflects the refractive index of attached media; an index change of 2.5 × 10⁻⁴ in the surrounding liquid can be measured through an emission wavelength shift without stabilization. This effect is applicable to detecting environmental toxins and cell behaviors. The laser emission intensity also reflects the electric charge of surface ions. The intensity varies when an electrolyte or a negatively charged deoxyribonucleic acid (DNA), which is positively or negatively charged in water, is accumulated on the surface. This effect allows us to detect the antigen-antibody reaction of a biomarker protein from only the emission intensity without any kind of spectroscopy. In detecting a small amount of DNA or protein, a wavelength shift also appears from its concentration that is 2–3 orders of magnitude lower than those of the conventional chemical methods, such as the enzyme-linked immuno-solvent assay. It is unlikely that this wavelength behavior at such low concentrations is due to the refractive index of the biomolecules. It is observed that the electric charge of surface ions is induced by various means, including plasma exposure and an electrochemical circuit shifting the wavelength. This suggests that the superhigh sensitivity is also due to the effect of charged ions. Thus, we call this device an iontronic photonic sensor. This paper focuses on such a novel sensing scheme of nanolaser sensor, as an example of resonator-based photonic sensors, in addition to the conventional refractive index sensing. Full article

(This article belongs to the Special Issue Photonic Crystal Laser and Related Optical Devices)

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18 pages, 2552 KiB

Open AccessFeature PaperReview

Statistical Assessment of Open Optical Networks

by Emanuele Virgillito, Alessio Ferrari, Andrea D’Amico and Vittorio Curri

Photonics 2019, 6(2), 64; https://doi.org/10.3390/photonics6020064 - 05 Jun 2019

Cited by 8 | Viewed by 2862

Abstract

In order to cope with the increase of the final user traffic, operators and vendors are pushing towards physical layer aware networking as a way to maximize the network capacity. To this aim, optical networks are becoming more and more open by exposing [...] Read more.

In order to cope with the increase of the final user traffic, operators and vendors are pushing towards physical layer aware networking as a way to maximize the network capacity. To this aim, optical networks are becoming more and more open by exposing physical parameters enabling fast and reliable estimation of the lightpath quality of transmission. This comes in handy not only from the point of view of the planning and managing of the optical paths but also on a more general picture of the whole optical network performance. In this work, the Statistical Network Assessment Process (SNAP) is presented. SNAP is an algorithm allowing for estimating different network metrics such as blocking probability or link saturation, by generating traffic requests on a graph abstraction of the physical layer. Being aware of the physical layer parameters and transceiver technologies enables assessing their impact on high level network figures of merit. Together with a detailed description of the algorithm, we present a comprehensive review of several results on the networking impact of multirate transceivers, flex-grid spectral allocation as a means to finely exploit lightpath capacity and of different Space Division Multiplexing (SDM) solutions. Full article

(This article belongs to the Special Issue Lightwave Communications and Optical Networks)

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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 - 03 Jun 2019

Cited by 11 | Viewed by 3465

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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11 pages, 4689 KiB

Open AccessArticle

Fabrication of Modified Random Phase Masks with Phase Modulation Elements Exhibiting Gaussian Profiles Using Molecular Migration under Photopolymerization

by Akira Emoto, Junya Honda, Kou Suzuki, Takumi Kimoto and Takashi Fukuda

Photonics 2019, 6(2), 62; https://doi.org/10.3390/photonics6020062 - 03 Jun 2019

Cited by 1 | Viewed by 3770

Abstract

Random phase masks are important technical elements for realizing holographic memory systems that enable high density recording. However, the broadly distributed Fourier spectrum often presents a problem because wide recording spots result in reduced total storage capacity for a recording medium. In the [...] Read more.

Random phase masks are important technical elements for realizing holographic memory systems that enable high density recording. However, the broadly distributed Fourier spectrum often presents a problem because wide recording spots result in reduced total storage capacity for a recording medium. In the present study, we propose modified random phase masks with phase modulation elements exhibiting Gaussian profiles to suppress the spread of the recording spot and keep it in a narrow area, based on the reduction of the high-frequency components in a random phase pattern. We confirm the effectiveness of the proposed random phase mask using simulations of a computer-generated binary hologram. However, issues still remain in terms of the fabrication of random phase masks with Gaussian profiles. Therefore, we evaluate the feasibility of fabricating the proposed random phase mask using molecular diffusion under photopolymerization. The results confirm the feasibility of this approach over a relatively wide area for actual fabrication. Full article

(This article belongs to the Special Issue Holographic Optical Memory and Related Technologies)

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17 pages, 4373 KiB

Open AccessArticle

Validation of an Inverse Fitting Method of Diffuse Reflectance Spectroscopy to Quantify Multi-Layered Skin Optical Properties

by Chiao-Yi Wang, Tzu-Chia Kao, Yin-Fu Chen, Wen-Wei Su, Hsin-Jou Shen and Kung-Bin Sung

Photonics 2019, 6(2), 61; https://doi.org/10.3390/photonics6020061 - 30 May 2019

Cited by 13 | Viewed by 4613

Abstract

Skin consists of epidermis and dermis layers that have distinct optical properties. The quantification of skin optical properties is commonly achieved by modeling photon propagation in tissue using Monte Carlo (MC) simulations and iteratively fitting experimentally measured diffuse reflectance spectra. In order to [...] Read more.

Skin consists of epidermis and dermis layers that have distinct optical properties. The quantification of skin optical properties is commonly achieved by modeling photon propagation in tissue using Monte Carlo (MC) simulations and iteratively fitting experimentally measured diffuse reflectance spectra. In order to speed up the inverse fitting process, time-consuming MC simulations have been replaced by artificial neural networks to quickly calculate reflectance spectra given tissue geometric and optical parameters. In this study the skin was modeled to consist of three layers and different scattering properties of the layers were considered. A new inverse fitting procedure was proposed to improve the extraction of chromophore-related information in the skin, including the hemoglobin concentration, oxygen saturation and melanin absorption. The performance of the new inverse fitting procedure was evaluated on 40 sets of simulated spectra. The results showed that the fitting procedure without knowing the epidermis thickness extracted chromophore information with accuracy similar to or better than fitting with known epidermis thickness, which is advantageous for practical applications due to simpler and more cost-effective instruments. In addition, the melanin volume fraction multiplied by the thickness of the melanin-containing epidermis layer was estimated more accurately than the melanin volume fraction itself. This product has the potential to provide a quantitative indicator of melanin absorption in the skin. In-vivo cuff occlusion experiments were conducted and skin optical properties extracted from the experiments were comparable to the results of previously reported in vivo studies. The results of the current study demonstrated the applicability of the proposed method to quantify the optical properties related to major chromophores in the skin, as well as scattering coefficients of the dermis. Therefore, it has the potential to be a useful tool for quantifying skin optical properties in vivo. Full article

(This article belongs to the Special Issue Biomedical Photonics Advances)

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12 pages, 3256 KiB

Open AccessArticle

Multiple-Code Technique for Multi-Rate Transmissions in Optical Packet Switching Networks Based on OCDMA Labels

by Kai-Sheng Chen

Photonics 2019, 6(2), 60; https://doi.org/10.3390/photonics6020060 - 30 May 2019

Cited by 3 | Viewed by 2959

Abstract

Supporting multi-rate transmission is an essential factor in current optical packet switching (OPS) networks. In this paper, the author studied a multi-rate scheme capable of forwarding packets with different signal rates based on label switching. The multiple-code (MC) technique was employed to label [...] Read more.

Supporting multi-rate transmission is an essential factor in current optical packet switching (OPS) networks. In this paper, the author studied a multi-rate scheme capable of forwarding packets with different signal rates based on label switching. The multiple-code (MC) technique was employed to label a packet by conveying its payload bits to multiple optical code-division multiple-access (OCDMA) labels. Spectral-amplitude-coding (SAC), which represents the chips in an OCDMA code as a set of wavelengths, was introduced to remove the multiple-access interference (MAI) from the overlapping among labels. The author tested the system effectiveness by conducting numerical analysis to formulate bit-error probability (BEP) and spectral efficiency (SE). The simulation results showed that the proposed network had a stable BEP performance when switching the packet flows of multiple data-rates. Full article

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8 pages, 1391 KiB

Open AccessArticle

Bias Current of Semiconductor Laser: An Unsafe Key for Secure Chaos Communication

by Daming Wang, Longsheng Wang, Pu Li, Tong Zhao, Zhiwei Jia, Zhensen Gao, Yuanyuan Guo, Yuncai Wang and Anbang Wang

Photonics 2019, 6(2), 59; https://doi.org/10.3390/photonics6020059 - 29 May 2019

Cited by 9 | Viewed by 3083

Abstract

In this study, we have proposed and numerically demonstrated that the bias current of a semiconductor laser cannot be used as a key for optical chaos communication, using external-cavity lasers. This is because the chaotic carrier has a signature of relaxation oscillation, whose [...] Read more.

In this study, we have proposed and numerically demonstrated that the bias current of a semiconductor laser cannot be used as a key for optical chaos communication, using external-cavity lasers. This is because the chaotic carrier has a signature of relaxation oscillation, whose period can be extracted by the first side peak of the carrier’s autocorrelation function. Then, the bias current can be approximately cracked, according to the well-known relationship between the bias current and relaxation period of a solitary laser. Our simulated results have shown that the cracked current eavesdropper could successfully crack an encrypted message, by means of a unidirectional locking injection or a bidirectional coupling. In addition, the cracked bias current was closer to the real value as the bias current increased, meaning that a large bias current brought a big risk to the security. Full article

(This article belongs to the Special Issue Semiconductor Laser Dynamics: Fundamentals and Applications)

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11 pages, 2625 KiB

Open AccessArticle

Nonlinear Dynamics of Exclusive Excited-State Emission Quantum Dot Lasers Under Optical Injection

by Zai-Fu Jiang, Zheng-Mao Wu, Elumalai Jayaprasath, Wen-Yan Yang, Chun-Xia Hu and Guang-Qiong Xia

Photonics 2019, 6(2), 58; https://doi.org/10.3390/photonics6020058 - 27 May 2019

Cited by 12 | Viewed by 3212

Abstract

We numerically investigate the nonlinear dynamic properties of an exclusive excited-state (ES) emission quantum dot (QD) laser under optical injection. The results show that, under suitable injection parameters, the ES-QD laser can exhibit rich nonlinear dynamical behaviors, such as injection locking (IL), period [...] Read more.

We numerically investigate the nonlinear dynamic properties of an exclusive excited-state (ES) emission quantum dot (QD) laser under optical injection. The results show that, under suitable injection parameters, the ES-QD laser can exhibit rich nonlinear dynamical behaviors, such as injection locking (IL), period one (P1), period two (P2), multi-period (MP), and chaotic pulsation (CP). Through mapping these dynamic states in the parameter space of the frequency detuning and the injection coefficient, it can be found that the IL occupies a wide region and the dynamic evolution routes appear in multiple forms. Via permutation entropy (PE) calculation to quantify the complexity of the CP state, the parameter range for acquiring the chaos with high complexity can be determined. Moreover, the influence of the linewidth enhancement factor (LEF) on the dynamical state of the ES-QD laser is analyzed. With the increase of the LEF value, the chaotic area shrinks (expands) in the negative (positive) frequency detuning region, and the IL region gradually shifts towards the negative frequency detuning. Full article

(This article belongs to the Special Issue Semiconductor Laser Dynamics: Fundamentals and Applications)

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11 pages, 1534 KiB

Open AccessArticle

Promote Localized Surface Plasmonic Sensor Performance via Spin-Coating Graphene Flakes over Au Nano-Disk Array

by Raed Alharbi and Mustafa Yavuz

Photonics 2019, 6(2), 57; https://doi.org/10.3390/photonics6020057 - 25 May 2019

Cited by 1 | Viewed by 3220

Abstract

Although localized surface plasmonic resonance (LSPR) sensors have advantages over regular surface plasmonic resonance (SPR) sensors, such as in sensor setup, excitation method, and cost, they suffer from low performance when compared to SPR sensors, which thus limits their commercialization. Among different methods [...] Read more.

Although localized surface plasmonic resonance (LSPR) sensors have advantages over regular surface plasmonic resonance (SPR) sensors, such as in sensor setup, excitation method, and cost, they suffer from low performance when compared to SPR sensors, which thus limits their commercialization. Among different methods applied to promote LSPR sensor performance, metal-two-dimensional (2D) hybrid nanostructure has been shown to be an efficient improvement. However, metal-2D hybrid nanostructures may come in a complex or a simple scheme and the latter is preferred to avoid challenges in fabrication work and to be applicable in mass production. In this work, a new and simple gold-graphene hybrid scheme is proposed and its plasmonic sensing performance is numerically evaluated using the finite different time domain (FDTD) method. The proposed sensor can be fabricated by growing a Au nano-disk (ND) array on a quartz substrate and then spin-coating graphene flakes of different sizes and shapes randomly on top of and between the Au NDs. Very high sensitivity value is achieved with 2262 nm/RIU at a 0.01 refractive index change. The obtained sensitivity value is very competitive in the field of LSPR sensors using metal-2D hybrid nanostructure. This proposed sensor can be utilized in different biosensing applications such as immunosensors, sensing DNA hybridization, and early disease detection, as discussed at the end of this article. Full article

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12 pages, 8488 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Propagation of Cylindrical Vector Laser Beams in Turbid Tissue-Like Scattering Media

by Alexander Doronin, Nicolás Vera, Juan P. Staforelli, Pablo Coelho and Igor Meglinski

Photonics 2019, 6(2), 56; https://doi.org/10.3390/photonics6020056 - 24 May 2019

Cited by 22 | Viewed by 5314

Abstract

We explore the propagation of the cylindrical vector beams (CVB) in turbid tissue-like scattering medium in comparison with the conventional Gaussian laser beam. The study of propagation of CVB and Gaussian laser beams in the medium is performed utilizing the unified electric field [...] Read more.

We explore the propagation of the cylindrical vector beams (CVB) in turbid tissue-like scattering medium in comparison with the conventional Gaussian laser beam. The study of propagation of CVB and Gaussian laser beams in the medium is performed utilizing the unified electric field Monte Carlo model. The implemented Monte Carlo model is a part of a generalized on-line computational tool and utilizes parallel computing, executed on the NVIDIA Graphics Processing Units (GPUs) supporting Compute Unified Device Architecture (CUDA). Using extensive computational studies, we demonstrate that after propagation through the turbid tissue-like scattering medium, the degree of fringe contrast for CVB becomes at least twice higher in comparison to the conventional linearly polarized Gaussian beam. The results of simulations agree with the results of experimental studies. Both experimental and theoretical results suggest that there is a high potential of the application of CVB in the diagnosis of biological tissues. Full article

(This article belongs to the Special Issue Biomedical Photonics Advances)

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8 pages, 8766 KiB

Open AccessArticle

Numerical Simulation of Mid-Infrared Optical Frequency Comb Generation in Chalcogenide As₂S₃ Microbubble Resonators

by Elena A. Anashkina, Maria P. Marisova, Arseny A. Sorokin and Alexey V. Andrianov

Photonics 2019, 6(2), 55; https://doi.org/10.3390/photonics6020055 - 23 May 2019

Cited by 9 | Viewed by 4312

Abstract

Mid-infrared optical frequency comb generation in whispering gallery mode microresonators attracts significant interest. Chalcogenide glass microresonators are good candidates for operating in the mid-infrared range. We present the first theoretical analysis of optical frequency comb generation in As₂S₃ microbubble resonators [...] Read more.

Mid-infrared optical frequency comb generation in whispering gallery mode microresonators attracts significant interest. Chalcogenide glass microresonators are good candidates for operating in the mid-infrared range. We present the first theoretical analysis of optical frequency comb generation in As₂S₃ microbubble resonators in the 3–4 μm range. The regime of dissipative soliton plus dispersive wave generation is simulated numerically in the frame of the Lugiato–Lefever equation. Using microbubble geometry allows controlling of the zero-dispersion wavelength and the obtaining of anomalous dispersion needed for soliton generation at the pump wavelength of 3.5 μm, whereas the zero-dispersion wavelength of the analyzed As₂S₃ glass is ~4.8 μm. It is shown that, for the optimized characteristics of microbubble resonators, optical frequency combs with a spectral width of more than 700 nm (at the level of −30 dB) can be obtained with the low pump power of 10 mW. Full article

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14 pages, 2850 KiB

Open AccessFeature PaperArticle

Photonic Crystal Circular Defect (CirD) Laser

by Yifan Xiong, Hanqiao Ye, Takuma Umeda, Shun Mizoguchi, Masato Morifuji, Hirotake Kajii, Akihiro Maruta and Masahiko Kondow

Photonics 2019, 6(2), 54; https://doi.org/10.3390/photonics6020054 - 20 May 2019

Cited by 19 | Viewed by 3780

Abstract

We describe the design of photonic crystal circular defect (CirD) lasers to construct a compact optical module with a wavelength division multiplexing function for the application of inter-chip or intra-chip optical interconnects. Subsequently, we investigated the characteristics of CirD lasers including the quality [...] Read more.

We describe the design of photonic crystal circular defect (CirD) lasers to construct a compact optical module with a wavelength division multiplexing function for the application of inter-chip or intra-chip optical interconnects. Subsequently, we investigated the characteristics of CirD lasers including the quality factor of the cavity, the lasing threshold, and the modulation speed with a three-dimensional finite-difference time-domain method and two-dimensional rate equations. Finally, we demonstrated the single mode lasing and wavelength tuning behaviors of the CirD lasers using optical pumping technology under room-temperature continuous-wave conditions. Full article

(This article belongs to the Special Issue Photonic Crystal Laser and Related Optical Devices)

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11 pages, 3504 KiB

Open AccessArticle

Efficient Dual-Wavelengths Continuous Mode Lasers by End-Pumping of Series Nd:YVO₄ and Nd:GdVO₄ Crystals and Speckle Reduction Study

by Mahmoud Mohamed, Bin Zhang, Qianli Ma, Josh Kneller and Chang-Qing Xu

Photonics 2019, 6(2), 53; https://doi.org/10.3390/photonics6020053 - 17 May 2019

Cited by 3 | Viewed by 3026

Abstract

In this paper, diode pumped solid state (DPSS) lasers based on end-pumping series

N d : Y V O_{4}

and

N d : G d V O_{4}

crystals were studied. Dual-, tri-, and quad-wavelength emissions were achieved. In the dual-wavelength emission [...] Read more.

In this paper, diode pumped solid state (DPSS) lasers based on end-pumping series

N d : Y V O_{4}

and

N d : G d V O_{4}

crystals were studied. Dual-, tri-, and quad-wavelength emissions were achieved. In the dual-wavelength emission operation, an optical-to-optical efficiency (O-O) of 48.9% and the power instability was 0.4% were obtained. These are the most efficient and compact lasers operating in continuous wave mode reported to date with series crystals. Besides this, the effect of changing power ratio between the output laser powers on speckle reduction was investigated for the first time. In addition, tri and quad wavelength emissions were achieved with a reasonable efficiency simply by optimizing the cavity parameters. Full article

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7 pages, 2606 KiB

Open AccessEditor’s ChoiceLetter

The Role of Electron Transfer in the Nonlinear Response of Ge₂Sb₂Te₅-Mediated Plasmonic Dimers

by Burak Gerislioglu and Arash Ahmadivand

Photonics 2019, 6(2), 52; https://doi.org/10.3390/photonics6020052 - 16 May 2019

Cited by 13 | Viewed by 2835

Abstract

Here, we study the possibility of exquisitely selective harmonic generation based on the concept of charge transfer plasmons (CTPs) in bridged nanoparticle assemblies. By choosing plasmonic dimer nanoantenna, as a fundamental member of the nanocluster family, and bridging the capacitive gap space between [...] Read more.

Here, we study the possibility of exquisitely selective harmonic generation based on the concept of charge transfer plasmons (CTPs) in bridged nanoparticle assemblies. By choosing plasmonic dimer nanoantenna, as a fundamental member of the nanocluster family, and bridging the capacitive gap space between the proximal nanoparticles with an optothermally controllable substance, we judiciously showed that variations in the generation of third harmonic light in the visible regime can be possible by considering distinct states of the functional bridge. To this end, the conductive connection between the nanoparticles is mediated with Ge₂Sb₂Te₅ (GST) with inherently opposite optical and electrical properties below (dielectric, amorphous state) and above 477 °C (conductive, crystalline state). This helped to actively control the transition of charges across the bridge and thereby control the excitation of CTP resonances and provide a switching feature between dipolar and CTP modes. This versatile approach also allowed for production of the intended harmonic signal at different wavelengths depending on the conductivity of the interparticle nanojunction. Full article

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8 pages, 1472 KiB

Open AccessArticle

Gasoline Quality Sensor Based on Tilted Fiber Bragg Gratings

by Stenio Aristilde, Cristiano M. B. Cordeiro and Jonas H. Osório

Photonics 2019, 6(2), 51; https://doi.org/10.3390/photonics6020051 - 14 May 2019

Cited by 14 | Viewed by 3346

Abstract

We report on the study of an intensity-based optical fiber sensor for gasoline quality monitoring. The sensor setup employs two Bragg gratings with different spectral responses to interrogate the optical response of a tilted Bragg grating. The sensor operation is based on the [...] Read more.

We report on the study of an intensity-based optical fiber sensor for gasoline quality monitoring. The sensor setup employs two Bragg gratings with different spectral responses to interrogate the optical response of a tilted Bragg grating. The sensor operation is based on the tilted Bragg grating sensitivity to external refractive index changes, which are translated as power variations by the interrogation scheme. Gasoline–ethanol solutions with concentrations ranging from 0% to 60% ethanol were used to demonstrate the sensor performance. The results allowed to estimate that the sensor is able, within its resolution limit, to detect ethanol concentration variations of 1.5% in gasoline–ethanol solutions and discriminate temperature variations of 0.5 °C. The all-optical sensor setup is compact and robust, making it a competitive alternative for the realization of fuel quality analyses in practical applications. Full article

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8 pages, 2492 KiB

Open AccessArticle

Effects of Photonic Band Structure and Unit Super-Cell Size in Graded Photonic Super-Crystal on Broadband Light Absorption in Silicon

by Safaa Hassan, Khadijah Alnasser, David Lowell and Yuankun Lin

Photonics 2019, 6(2), 50; https://doi.org/10.3390/photonics6020050 - 09 May 2019

Cited by 8 | Viewed by 3179

Abstract

The newly discovered graded photonic super-crystal (GPSC) with a large size of unit cell can have novel optical properties that have not been explored. The unit super-cell in the GPSC can be designed to be large or small and thus the GPSC can [...] Read more.

The newly discovered graded photonic super-crystal (GPSC) with a large size of unit cell can have novel optical properties that have not been explored. The unit super-cell in the GPSC can be designed to be large or small and thus the GPSC can have no photonic band gap or several gaps. The photonic band structures in Si GPSC can help predict the light absorption in Si. Photonic resonance modes help enhance the absorption of light in silicon; however, photonic band gaps decrease the absorption for light with a large incident angle. The Si device patterned in GPSC with a unit super-cell of 6a × 6a (a is a lattice constant in traditional photonic crystal) has a broadband high absorption with strong incident-angular dependence. The device with the unit super-cell of 12a × 12a has relatively low light absorption with weak incident-angle dependence. The Si GPSC with a unit super-cell of 8a × 8a combines both advantages of broadband high absorption and weak dependence of absorption on the incident angle. Full article

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14 pages, 1744 KiB

Open AccessArticle

Investigation of the Effect of Intra-Cavity Propagation Delay in Secure Optical Communication Using Chaotic Semiconductor Lasers

by Elumalai Jayaprasath, Zheng-Mao Wu, Sivaraman Sivaprakasam, Yu-Shuang Hou, Xi Tang, Xiao-Dong Lin, Tao Deng and Guang-Qiong Xia

Photonics 2019, 6(2), 49; https://doi.org/10.3390/photonics6020049 - 09 May 2019

Cited by 5 | Viewed by 3075

Abstract

The influence of intra-cavity propagation delay in message encoding and decoding using chaotic semiconductor lasers is numerically investigated. A message is encoded at the transmitter laser by a chaos shift keying scheme and is decoded at the receiver by comparing its output with [...] Read more.

The influence of intra-cavity propagation delay in message encoding and decoding using chaotic semiconductor lasers is numerically investigated. A message is encoded at the transmitter laser by a chaos shift keying scheme and is decoded at the receiver by comparing its output with the transmitter laser. The requisite intra-cavity propagation delay in achieving synchronization of optical chaos is estimated by cross-correlation analysis between the transmitter and receiver lasers’ output. The effect of intra-cavity propagation delay on the message recovery has been analyzed from the bit error rate performance. It is found that despite the intra-cavity propagation delay magnitude being less, it has an impact on the quality of message recovery. We also examine the dependency of injection rate, frequency detuning, modulation depth and bit rate on intra-cavity propagation delay and associated message recovery quality. We found that the communication performance has been adequately improved after incorporating intra-cavity propagation delay correction in the synchronization system. Full article

(This article belongs to the Special Issue Semiconductor Laser Dynamics: Fundamentals and Applications)

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24 pages, 2713 KiB

Open AccessEditor’s ChoiceReview

Multifunctional Smart Optical Fibers: Materials, Fabrication, and Sensing Applications

by Zhengyong Liu, Zhi Feng Zhang, Hwa-Yaw Tam and Xiaoming Tao

Photonics 2019, 6(2), 48; https://doi.org/10.3390/photonics6020048 - 06 May 2019

Cited by 46 | Viewed by 8322

Abstract

This paper presents a review of the development of optical fibers made of multiple materials, particularly including silica glass, soft glass, polymers, hydrogels, biomaterials, Polydimethylsiloxane (PDMS), and Polyperfluoro-Butenylvinyleth (CYTOP). The properties of the materials are discussed according to their various applications. Typical fabrication [...] Read more.

This paper presents a review of the development of optical fibers made of multiple materials, particularly including silica glass, soft glass, polymers, hydrogels, biomaterials, Polydimethylsiloxane (PDMS), and Polyperfluoro-Butenylvinyleth (CYTOP). The properties of the materials are discussed according to their various applications. Typical fabrication techniques for specialty optical fibers based on these materials are introduced, which are mainly focused on extrusion, drilling, and stacking methods depending on the materials’ thermal properties. Microstructures render multiple functions of optical fibers and bring more flexibility in fiber design and device fabrication. In particular, micro-structured optical fibers made from different types of materials are reviewed. The sensing capability of optical fibers enables smart monitoring. Widely used techniques to develop fiber sensors, i.e., fiber Bragg grating and interferometry, are discussed in terms of sensing principles and fabrication methods. Lastly, sensing applications in oil/gas, optofluidics, and particularly healthcare monitoring using specialty optical fibers are demonstrated. In comparison with conventional silica-glass single-mode fiber, state-of-the-art specialty optical fibers provide promising prospects in sensing applications due to flexible choices in materials and microstructures. Full article

(This article belongs to the Special Issue Polymer Optical Fibre)

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21 pages, 3774 KiB

Open AccessArticle

Design Investigation of 4 × 4 Nonblocking Hybrid Plasmonic Electrooptic Switch

by Maithem S. Jaber, Shelan K. Tawfeeq and Raad S. Fyath

Photonics 2019, 6(2), 47; https://doi.org/10.3390/photonics6020047 - 03 May 2019

Cited by 3 | Viewed by 3426

Abstract

This paper proposes a compact, plasmonic-based 4 × 4 nonblocking switch for optical networks. This device uses six 2 × 2 plasmonic Mach-Zehnder switch (MZS), whose arm waveguide is supported by a JRD1 polymer layer as a high electro-optic coefficient material. The 4 [...] Read more.

This paper proposes a compact, plasmonic-based 4 × 4 nonblocking switch for optical networks. This device uses six 2 × 2 plasmonic Mach-Zehnder switch (MZS), whose arm waveguide is supported by a JRD1 polymer layer as a high electro-optic coefficient material. The 4 × 4 switch is designed in COMSOL environment for 1550 nm wavelength operation. The performance of the proposed switch outperforms those of conventional (nonplasmonic) counterparts. The designed switch yields a compact structure (

500 \times 70 {µ m}^{2}

) having

V_{π} L = 12 V \cdot µ m

, 1.5 THz optical bandwidth, 7.7 dB insertion loss, and −26.5 dB crosstalk. The capability of the switch to route 8 × 40 Gbps WDM signal is demonstrated successfully. Full article

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12 pages, 1528 KiB

Open AccessArticle

Modeling the Output Performance of Al_0.3Ga_0.7As/InP/Ge Triple-Junction Solar Cells for a Venus Orbiter Space Station

by Tony Sumaryada, Panji Fitriansyah, Afgan Sofyan and Heriyanto Syafutra

Photonics 2019, 6(2), 46; https://doi.org/10.3390/photonics6020046 - 27 Apr 2019

Cited by 4 | Viewed by 4262

Abstract

The performance of Al_0.3Ga_0.7As/InP/Ge triple-junction solar cells (TJSC) at the geosynchronous orbit of Venus had been simulated in this paper by assuming that the solar cells were put on a hypothetical Venus orbiter space station. The incoming solar radiation [...] Read more.

The performance of Al_0.3Ga_0.7As/InP/Ge triple-junction solar cells (TJSC) at the geosynchronous orbit of Venus had been simulated in this paper by assuming that the solar cells were put on a hypothetical Venus orbiter space station. The incoming solar radiation on TJSC was calculated by a blackbody radiation formula, while PC1D program simulated the electrical output performance. The results show that the incoming solar intensity at the geosynchronous orbit of Venus is 3000 W/m², while the maximum solar cell efficiency achieved is 38.94%. Considering a similar area of the solar panel as the International Space Station (about 2500 m²), the amount of electricity produced by Venus orbiter space station at the geosynchronous orbit of Venus is 2.92 MW, which is plenty of energy to power the space station for long-term exploration and intensive research on Venus. Full article

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7 pages, 2622 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Exploiting the Nonlinear Dynamics of Optically Injected Semiconductor Lasers for Optical Sensing

by Maria S. Torre and Cristina Masoller

Photonics 2019, 6(2), 45; https://doi.org/10.3390/photonics6020045 - 24 Apr 2019

Cited by 4 | Viewed by 3407

Abstract

Optically injected semiconductor lasers are known to display a rich variety of dynamic behaviours, including the emission of excitable pulses, and of rare giant pulses (often referred to as optical rogue waves). Here, we use a well-known rate equation model to explore the [...] Read more.

Optically injected semiconductor lasers are known to display a rich variety of dynamic behaviours, including the emission of excitable pulses, and of rare giant pulses (often referred to as optical rogue waves). Here, we use a well-known rate equation model to explore the combined effect of excitability and extreme pulse emission, for the detection of variations in the strength of the injected field. We find parameter regions where the laser always responds to a perturbation by emitting an optical pulse whose amplitude is above a pre-defined detection threshold. We characterize the sensing capability of the laser in terms of the amplitude and the duration of the perturbation. Full article

(This article belongs to the Special Issue Semiconductor Laser Dynamics: Fundamentals and Applications)

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