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Photonics
Volume 8
Issue 3
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Photonics, Volume 8, Issue 3 (March 2021) – 26 articles

Cover Story (view full-size image): Non-classical and squeezed radiation is one of the most fascinating and impactful developments in quantum optics, with applications to metrology, quantum information, and the detection of gravity waves, among others. The counterintuitive behavior of electronic transitions, driven strongly by squeezed radiation, ranks among the most unexpected phenomena in radiation–matter interaction. The results in this paper open a window into the landscape of such phenomena, resulting from the interplay between non-linearity and quantum fluctuations, which in view of recent technological developments are within experimental reach. Unique features, such as oscillating photon number distributions emanating from the interplay between phase and squeezing parameter, are but a few of the effects discussed. View this paper
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8 pages, 2084 KiB  
Communication
Transverse Asymmetry of the Index Modulation Profile in Few-Mode Fiber Bragg Grating
by Peihong Guan, Min Tang, Min Cao, Yuean Mi, Mei Liu, Wenhua Ren and Guobin Ren
Photonics 2021, 8(3), 87; https://doi.org/10.3390/photonics8030087 - 23 Mar 2021
Cited by 2 | Viewed by 2410
Abstract
The transverse asymmetry of the index modulation profile in the asymmetric few-mode fiber Bragg grating (FM-FBG) was investigated. The transverse asymmetry of the index modulation profile will lead to mode conversion between modes with the different azimuthal orders, and this asymmetry is characterized [...] Read more.
The transverse asymmetry of the index modulation profile in the asymmetric few-mode fiber Bragg grating (FM-FBG) was investigated. The transverse asymmetry of the index modulation profile will lead to mode conversion between modes with the different azimuthal orders, and this asymmetry is characterized by the attenuation coefficient α. We evaluated that the value of attenuation coefficient α was 0.2 μm−1, and grating amplitude χ was 2.8 × 10−4 for FM-FBG inscribed by UV single-side illumination. We found that the optimized value of α was 0.16 μm−1, at which the maximum mode conversion efficiency of LP01–LP11 can be achieved. The results of this paper provide great potential application in few-mode fiber (FMF) devices and mode division multiplexing (MDM) optical communication. Full article
(This article belongs to the Special Issue Advancements in Fiber Bragg Grating Research)
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26 pages, 2221 KiB  
Article
On the Transmittance of Metallic Superlattices in the Optical Regime and the True Refraction Angle
by Pedro Pereyra
Photonics 2021, 8(3), 86; https://doi.org/10.3390/photonics8030086 - 23 Mar 2021
Cited by 3 | Viewed by 2010
Abstract
Transmission of electromagnetic fields through (dielectric/metallic)n superlattices, for frequencies below the plasma frequency ωp, is a subtle and important topic [...] Read more.
Transmission of electromagnetic fields through (dielectric/metallic)n superlattices, for frequencies below the plasma frequency ωp, is a subtle and important topic that is reviewed and further developed here. Recently, an approach for metallic superlattices based on the theory of finite periodic systems was published. Unlike most, if not all, of the published approaches that are valid in the n→∞ limit, the finite periodic systems approach is valid for any value of n, allows one to determine analytical expressions for scattering amplitudes and dispersion relations. It was shown that, for frequencies below ωp, large metallic-layer thickness, and electromagnetic fields moving along the so-called “true” angle, anomalous results with an apparent parity effect appear. We show here that these results are related to the lack of unitarity and the underlying phenomena of absorption and loss of energy. To solve this problem we present two compatible approaches, both based on the theory of finite periodic systems, which is not only more accurate, but has also the ability to reveal and predict the intra-subband resonances. In the first approach we show that by keeping complex angles, above and below ωp, the principle of flux conservation is fully satisfied. The results above ωp remain the same as in Pereyra (2020). This approach, free of assumptions, where all the information of the scattering process is preserved, gives us insight to improve the formalism where the assumption of electromagnetic fields moving along the real angles is made. In fact, we show that by taking into account the induced currents and the requirement of flux conservation, we end up with an improved approach, with new Fresnel and transmission coefficients, fully compatible with those of the complex-angle approach. The improved approach also allows one to evaluate the magnitude of the induced currents and the absorbed energy, as functions of the frequency and the superlattice parameters. We show that the resonant frequencies of intra-subband plasmons, which may be of interest for applications, in particular for biosensors, can be accurately determined. We also apply the approach for the transmission of electromagnetic wave packets, defined in the optical domain, and show that the predicted space-time positions agree extremely well with the actual positions of the wave packet centroids. Full article
(This article belongs to the Special Issue Advanced Metamaterials and Metadevices)
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6 pages, 432 KiB  
Communication
Coherence Stokes Parameters in the Description of Electromagnetic Coherence
by Tero Setälä, Kimmo Saastamoinen and Ari T. Friberg
Photonics 2021, 8(3), 85; https://doi.org/10.3390/photonics8030085 - 22 Mar 2021
Cited by 7 | Viewed by 3356
Abstract
The two-point counterparts of the traditional Stokes parameters, which are called the coherence Stokes parameters, have recently been extensively used for assessing the coherence properties of random electromagnetic light beams. In this work, we highlight their importance by emphasizing two features associated with [...] Read more.
The two-point counterparts of the traditional Stokes parameters, which are called the coherence Stokes parameters, have recently been extensively used for assessing the coherence properties of random electromagnetic light beams. In this work, we highlight their importance by emphasizing two features associated with them. First, the role of polarization in electromagnetic coherence is significantly elucidated when the coherence Stokes parameters are used. Second, the normalized coherence Stokes parameters should be regarded as the true electromagnetic counterparts of the normalized scalar-field correlation coefficient. Full article
(This article belongs to the Special Issue Structured Light Coherence)
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6 pages, 3575 KiB  
Communication
25 Gb/s Data Transmission Using a Directly Modulated InGaAlAs DBR Laser over 14 nm Wavelength Tuning Range
by Daibing Zhou, Yiming He, Dan Lu, Song Liang, Lingjuan Zhao and Wei Wang
Photonics 2021, 8(3), 84; https://doi.org/10.3390/photonics8030084 - 22 Mar 2021
Cited by 4 | Viewed by 2441
Abstract
With the deployment of the fifth generation of mobile networks (5G), 25 and 100 Gb/s directly modulated lasers and modules will become the mainstream optical transmitters. A directly modulated InGaAlAs/InP distributed Bragg reflector (DBR) laser is fabricated by butt-joint technology. A 25 Gb/s [...] Read more.
With the deployment of the fifth generation of mobile networks (5G), 25 and 100 Gb/s directly modulated lasers and modules will become the mainstream optical transmitters. A directly modulated InGaAlAs/InP distributed Bragg reflector (DBR) laser is fabricated by butt-joint technology. A 25 Gb/s data transmission over a single-mode fiber of up to 10 km is demonstrated, and a wavelength tuning range of 14.28 nm is achieved through injection current tuning of a DBR section and temperature control of a thermoelectric cooler (TEC), which is the best candidate of colorless light sources for wavelength-division-multiplexed passive optical network (WDM-PON) systems. Full article
(This article belongs to the Special Issue Optical Technologies for Data Center Networks)
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29 pages, 1073 KiB  
Article
The Overlap Factor Model of Spin-Polarised Coupled Lasers
by Martin Vaughan, Hadi Susanto, Ian Henning and Mike Adams
Photonics 2021, 8(3), 83; https://doi.org/10.3390/photonics8030083 - 20 Mar 2021
Cited by 1 | Viewed by 2803
Abstract
A general model for the dynamics of arrays of coupled spin-polarised lasers is derived. The general model is able to deal with waveguides of any geometry with any number of supported normal modes. A unique feature of the model is that it allows [...] Read more.
A general model for the dynamics of arrays of coupled spin-polarised lasers is derived. The general model is able to deal with waveguides of any geometry with any number of supported normal modes. A unique feature of the model is that it allows for independent polarisation of the pumping in each laser. The particular geometry is shown to be introduced via ’overlap factors’, which are a generalisation of the optical confinement factor. These factors play an important role in determining the laser dynamics. The model is specialised to the case of a general double-guided structure, which is shown to reduce to both the spin flip model in a single cavity and the coupled mode model for a pair of guides in the appropriate limit. This is applied to the particular case of a circular-guide laser pair, which is analysed and simulated numerically. It is found that increasing the ellipticity of the pumping tends to reduce the region of instability in the plane of pumping strength versus guide separation. Full article
(This article belongs to the Special Issue Nonlinear Dynamics of Semiconductor Lasers and Their Applications)
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13 pages, 18109 KiB  
Article
Propagation of a Modified Complex Lorentz–Gaussian-Correlated Beam in a Marine Atmosphere
by Baoyin Sun, Han Lü, Dan Wu, Fei Wang and Yangjian Cai
Photonics 2021, 8(3), 82; https://doi.org/10.3390/photonics8030082 - 19 Mar 2021
Cited by 9 | Viewed by 2716
Abstract
In this paper, we study the second-order statistics of a modified complex Lorentz–Gaussian-correlated (MCLGC) beam, which is a new type of partially coherent beam capable of producing an Airy-like intensity pattern in the far field, propagation through marine atmospheric turbulence. The propagation formula [...] Read more.
In this paper, we study the second-order statistics of a modified complex Lorentz–Gaussian-correlated (MCLGC) beam, which is a new type of partially coherent beam capable of producing an Airy-like intensity pattern in the far field, propagation through marine atmospheric turbulence. The propagation formula of spectral density is derived by the extended Huygens–Fresnel integral, which could explicitly indicate the interaction of turbulence on the beams’ spectral density under propagation. The influences of the structure constant of the turbulence, initial coherence width and wavelength on the spectral density are investigated in detail through numerical examples. In addition, analytical expressions for the r.m.s beam width, divergence angle and M2 factor of the MCLGC beam in the marine turbulence are also derived with the help of the Wigner distribution function. The results reveal that the beam spreads much faster, and the M2 factor deteriorates severely with the increase of the structure constant and the decrease of the inner scale size, whereas the outer scale size has little effect on these two quantities. Full article
(This article belongs to the Special Issue Structured Light Coherence)
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18 pages, 16845 KiB  
Article
Systematic Performance Comparison of (Duobinary)-PAM-2,4 Signaling under Light and Strong Opto-Electronic Bandwidth Conditions
by Ramón Gutiérrez-Castrejón, Md Ghulam Saber, Md Samiul Alam, Zhenping Xing, Eslam El-Fiky, Daniel E. Ceballos-Herrera, Fabio Cavaliere, Gemma Vall-Llosera, Luca Giorgi, Stephane Lessard, Robert Brunner and David V. Plant
Photonics 2021, 8(3), 81; https://doi.org/10.3390/photonics8030081 - 18 Mar 2021
Cited by 5 | Viewed by 4039
Abstract
We present a systematic comparison of PAM-2 (NRZ), Duobinary-PAM-2, PAM-4, and Duobinary-PAM-4 (duo-quaternary) signaling in the context of short-reach photonic communications systems using a Mach–Zehnder modulator as transmitter. The effect on system performance with a relaxed and constrained system’s opto-electronic bandwidth is analyzed [...] Read more.
We present a systematic comparison of PAM-2 (NRZ), Duobinary-PAM-2, PAM-4, and Duobinary-PAM-4 (duo-quaternary) signaling in the context of short-reach photonic communications systems using a Mach–Zehnder modulator as transmitter. The effect on system performance with a relaxed and constrained system’s opto-electronic bandwidth is analyzed for bit rates ranging from 20 to 116 Gb/s. In contrast to previous analyses, our approach employs the same experimental and simulation conditions for all modulation formats. Consequently, we were able to confidently determine the performance limits of each format for particular values of bit rate, system bandwidth, transmitter chirp, and fiber dispersion. We demonstrate that Duobinary-PAM-4 is a good signaling choice only for bandwidth-limited systems operating at relatively high speed. Otherwise, PAM-4 represents a more sensible choice. Moreover, our analysis put forward the existence of transition points: specific bit rate values where the BER versus bit rate curves for two different formats cross each other. They indicate the bit rate values where, for specific system conditions, switching from one modulation to another guarantees optimum performance. Their existence naturally led to the proposal of a format-selective transceiver, a component that, according to network conditions, operates with the most adequate modulation format. Since all analyzed modulations share similar implementation details, signaling switching is achieved by simply changing the sampling point and threshold count at the receiver, bringing flexibility to IM/DD-based optical networks. Full article
(This article belongs to the Special Issue Advances in Integrated Photonics for Communication and Sensing Applications)
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9 pages, 1939 KiB  
Communication
Automatic Bias Control Technique of Dual-Parallel Mach–Zehnder Modulator Based on Simulated Annealing Algorithm for Quadrupled Signal Generation
by Youngseok Bae, Sunghoon Jang, Sungjun Yoo, Minwoo Yi, Joonhyung Ryoo and Jinwoo Shin
Photonics 2021, 8(3), 80; https://doi.org/10.3390/photonics8030080 - 17 Mar 2021
Cited by 7 | Viewed by 3374
Abstract
The radio frequency (RF) signal generation method using an external modulator is widely used in microwave photonics applications because it has the advantage of being able to generate coherent and stable RF signals with a higher resolution performance compared to the conventional method. [...] Read more.
The radio frequency (RF) signal generation method using an external modulator is widely used in microwave photonics applications because it has the advantage of being able to generate coherent and stable RF signals with a higher resolution performance compared to the conventional method. A Mach–Zehnder modulator is widely used as an external modulator due to its high electro-optic coefficients and low attenuation characteristics but has a critical problem in that its electrical characteristics are changed by external environments such as temperature. In this paper, we considered the stabilization configuration to overcome this problem and propose an automatic bias control technique based on the simulated annealing algorithm of a dual-parallel Mach–Zehnder modulator (DPMZM) for quadruple signal generation. The proposed technique searches for the bias voltages of the modulator in real-time through the temperature test. In addition, the output of the quadrupled signal of the DPMZM is constantly controlled throughout the temperature range. Finally, it is confirmed that signals of a 10 GHz and 22 GHz frequency are generated using the intermediate frequency signals of a 2.5 GHz and 5.5 GHz frequency with the proposed automatic bias control technique, respectively. Full article
(This article belongs to the Special Issue Electro-Optic Modulator)
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9 pages, 3751 KiB  
Communication
Novel Low-Loss Fiber-Chip Edge Coupler for Coupling Standard Single Mode Fibers to Silicon Photonic Wire Waveguides
by Siwei Sun, Ying Chen, Yu Sun, Fengman Liu and Liqiang Cao
Photonics 2021, 8(3), 79; https://doi.org/10.3390/photonics8030079 - 16 Mar 2021
Cited by 13 | Viewed by 6076
Abstract
Fiber-to-chip optical interconnects is a big challenge in silicon photonics application scenarios such as data centers and optical transmission systems. An edge coupler, compared to optical grating, is appealing to in the application of silicon photonics due to the high coupling efficiency between [...] Read more.
Fiber-to-chip optical interconnects is a big challenge in silicon photonics application scenarios such as data centers and optical transmission systems. An edge coupler, compared to optical grating, is appealing to in the application of silicon photonics due to the high coupling efficiency between standard optical fibers (SMF-28) and the sub-micron silicon wire waveguides. In this work, we proposed a novel fiber–chip edge coupler approach with a large mode size for silicon photonic wire waveguides. The edge coupler consists of a multiple structure which was fulfilled by multiple silicon nitride layers embedded in SiO2 upper cladding, curved waveguides and two adiabatic spot size converter (SSC) sections. The multiple structure can allow light directly coupling from large mode size fiber-to-chip coupler, and then the curved waveguides and SSCs transmit the evanescent field to a 220 nm-thick silicon wire waveguide based on the silicon-on-insulator (SOI) platform. The edge coupler, designed for a standard SMF-28 fiber with 8.2 μm mode field diameter (MFD) at a wavelength of 1550 nm, exhibits a mode overlap efficiency exceeding 95% at the chip facet and the overall coupling exceeding 90%. The proposed edge coupler is fully compatible with standard microfabrication processes. Full article
(This article belongs to the Special Issue Optical Technologies for Data Center Networks)
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14 pages, 1744 KiB  
Article
Optical Machine Learning Using Time-Lens Deep Neural NetWorks
by Luhe Zhang, Caiyun Li, Jiangyong He, Yange Liu, Jian Zhao, Huiyi Guo, Longfei Zhu, Mengjie Zhou, Kaiyan Zhu, Congcong Liu and Zhi Wang
Photonics 2021, 8(3), 78; https://doi.org/10.3390/photonics8030078 - 15 Mar 2021
Cited by 8 | Viewed by 5679
Abstract
As a high-throughput data analysis technique, photon time stretching (PTS) is widely used in the monitoring of rare events such as cancer cells, rough waves, and the study of electronic and optical transient dynamics. The PTS technology relies on high-speed data collection, and [...] Read more.
As a high-throughput data analysis technique, photon time stretching (PTS) is widely used in the monitoring of rare events such as cancer cells, rough waves, and the study of electronic and optical transient dynamics. The PTS technology relies on high-speed data collection, and the large amount of data generated poses a challenge to data storage and real-time processing. Therefore, how to use compatible optical methods to filter and process data in advance is particularly important. The time-lens proposed, based on the duality of time and space as an important data processing method derived from PTS, achieves imaging of time signals by controlling the phase information of the timing signals. In this paper, an optical neural network based on the time-lens (TL-ONN) is proposed, which applies the time-lens to the layer algorithm of the neural network to realize the forward transmission of one-dimensional data. The recognition function of this optical neural network for speech information is verified by simulation, and the test recognition accuracy reaches 95.35%. This architecture can be applied to feature extraction and classification, and is expected to be a breakthrough in detecting rare events such as cancer cell identification and screening. Full article
(This article belongs to the Special Issue Advanced Technique and Future Perspective for Next Generation Optical Fiber Communications)
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26 pages, 11248 KiB  
Review
Integrated Components and Solutions for High-Speed Short-Reach Data Transmission
by Lin Jiang, Lianshan Yan, Anlin Yi, Yan Pan, Bo Zhang, Qianggao Hu, Wei Pan and Bin Luo
Photonics 2021, 8(3), 77; https://doi.org/10.3390/photonics8030077 - 14 Mar 2021
Cited by 10 | Viewed by 4604
Abstract
According to different transmission distances, application scenarios of a data center mainly include intra- and inter-data center optical interconnects. The intra-data center optical interconnect is considered as a few kilometers optical interconnect between servers and racks inside a data center, which accounts for [...] Read more.
According to different transmission distances, application scenarios of a data center mainly include intra- and inter-data center optical interconnects. The intra-data center optical interconnect is considered as a few kilometers optical interconnect between servers and racks inside a data center, which accounts for nearly 80% of data traffic of a data center. The other one, inter-data center optical interconnect, is mainly applied in tens of kilometers data transmission among different data centers. Since data exchange in data centers generally occurs between many servers and racks, and a lot of transmitter and receiver components are required, optical interconnects become highly sensitive to component costs. In this paper, we firstly review the development and applications of mainstream transmitter components (e.g., VCSEL, DML, EML, MZM, and monolithic integrated transmitter) and receiver components (e.g., single-end photodetector, Kramers-Kronig receiver, Stokes vector receiver, and monolithic integrated receiver), which have been widely applied in short-reach transmission systems. Then, two types of integrated solutions including simplified detection scheme and transceiver integration scheme are presented in detail. Finally, we summarize and discuss the technological and component options for different transmission distances. We believe that monolithic integrated components, especially transceiver integration, will become a powerful solution for next-generation high-speed short-reach transmission systems. Full article
(This article belongs to the Special Issue Advanced Ultra High Speed Optoelectronic Devices)
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11 pages, 14728 KiB  
Article
Photothermal, Photoelectric, and Photothermoelectric Effects in Bi-Sb Thin Films in the Terahertz Frequency Range at Room Temperature
by Mikhail K. Khodzitsky, Petr S. Demchenko, Dmitry V. Zykov, Anton D. Zaitsev, Elena S. Makarova, Anastasiia S. Tukmakova, Ivan L. Tkhorzhevskiy, Aleksei V. Asach, Anna V. Novotelnova and Natallya S. Kablukova
Photonics 2021, 8(3), 76; https://doi.org/10.3390/photonics8030076 - 12 Mar 2021
Cited by 8 | Viewed by 3352
Abstract
The terahertz frequency range is promising for solving various practically important problems. However, for the terahertz technology development, there is still a problem with the lack of affordable and effective terahertz devices. One of the main tasks is to search for new materials [...] Read more.
The terahertz frequency range is promising for solving various practically important problems. However, for the terahertz technology development, there is still a problem with the lack of affordable and effective terahertz devices. One of the main tasks is to search for new materials with high sensitivity to terahertz radiation at room temperature. Bi1−xSbx thin films with various Sb concentrations seem to be suitable for such conditions. In this paper, the terahertz radiation influence onto the properties of thermoelectric Bi1−xSbx 200 nm films was investigated for the first time. The films were obtained by means of thermal evaporation in vacuum. They were affected by terahertz radiation at the frequency of 0.14 terahertz (THz) in the presence of thermal gradient, electric field or without these influences. The temporal dependencies of photoconductivity, temperature difference and voltage drop were measured. The obtained data demonstrate the possibility for practical use of Bi1−xSbx thin films for THz radiation detection. The results of our work promote the usage of these thermoelectric materials, as well as THz radiation detectors based on them, in various areas of modern THz photonics. Full article
(This article belongs to the Special Issue Frontiers in Terahertz Technology and Applications)
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16 pages, 2849 KiB  
Article
Engineering of TiO2 or ZnO—Graphene Oxide Nanoheterojunctions for Hybrid Solar Cells Devices
by Duarte Carreira, Paulo A. Ribeiro, Maria Raposo and Susana Sério
Photonics 2021, 8(3), 75; https://doi.org/10.3390/photonics8030075 - 12 Mar 2021
Cited by 8 | Viewed by 3739
Abstract
It is currently of huge importance to find alternatives to fossil fuels to produce clean energy and to ensure the energy demands of modern society. In the present work, two types of hybrid solar cell devices were developed and characterized. The photoactive layers [...] Read more.
It is currently of huge importance to find alternatives to fossil fuels to produce clean energy and to ensure the energy demands of modern society. In the present work, two types of hybrid solar cell devices were developed and characterized. The photoactive layers of the hybrid heterojunctions comprise poly (allylamine chloride) (PAH) and graphene oxide (GO) and TiO2 or ZnO films, which were deposited using the layer-by-layer technique and DC-reactive magnetron sputtering, respectively, onto fluorine-doped tin oxide (FTO)-coated glass substrates. Scanning electron microscopy evidenced a homogeneous inorganic layer, the surface morphology of which was dependent on the number of organic bilayers. The electrical characterization pointed out that FTO/(PAH/GO)50/TiO2/Al, FTO/(PAH/GO)30/ZnO/Al, and FTO/(PAH/GO)50/ZnO/Al architectures were the only ones to exhibit a diode behavior, and the last one experienced a decrease in current in a low-humidity environment. The (PAH/GO)20 impedance spectroscopy study further revealed the typical impedance of a parallel RC circuit for a dry environment, whereas in a humid environment, it approached the impedance of a series of three parallel RC circuits, indicating that water and oxygen contribute to other conduction processes. Finally, the achieved devices should be encapsulated to work successfully as solar cells. Full article
(This article belongs to the Special Issue Photonics, Optics and Laser Technology)
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12 pages, 9921 KiB  
Article
Performance Evaluation of Underwater Wireless Optical Communication System by Varying the Environmental Parameters
by Dong-Chang Li, Chia-Chun Chen, Shien-Kuei Liaw, Shofuro Afifah, Jiun-Yu Sung and Chien-Hung Yeh
Photonics 2021, 8(3), 74; https://doi.org/10.3390/photonics8030074 - 11 Mar 2021
Cited by 13 | Viewed by 3795
Abstract
Underwater wireless optical communication (UWOC) has been considered a promising technology for high-speed underwater transmission. Some Gb/s level UWOC systems applying visible light have been demonstrated with a transmission distance of several meters or more. Many of the previous works focus on the [...] Read more.
Underwater wireless optical communication (UWOC) has been considered a promising technology for high-speed underwater transmission. Some Gb/s level UWOC systems applying visible light have been demonstrated with a transmission distance of several meters or more. Many of the previous works focus on the advanced technologies to push the systems’ capacity–distance performance. However, practical environmental factors issue such as flow turbulence and temperature variation are seldom studied through specific statistical/theoretical models. In this paper, a UWOC system using a 450 nm blue light laser source was set up using a 1.5-m water tank with mirrors located on both sides for single or multiple reflections corresponding to different transmission distances. The blue laser was modulated by a 1.25 Gbps NRZ-OOK format with PRBS of 7, 24 or 31, respectively, for system performance comparison. The bit error rate (BER) values were measured in 1.5, 3.0 and 6 m, respectively, for system evaluation. At room temperature, the BER value was down to 10 × 10−8 for a 1.25 Gbps data rate in a 6 m transmission. Then, the UWOC transmission system experiment was carried out under several environmental parameters such as temperature, turbulence, artificial seawater by adding salt to simulate practical application in river or sea. When a submerged motor with an output of 1200 L/h was used as a water flow turbulence source, the impact to BER and transmission quality was negligible. For the temperature change issue, the experiment shows that around the original temperature of 25 °C had the best BER as compared to other temperature ranges from 10 to 50 °C. For artificial seawater issues by adding salt to simulate the real seawater environment. The transmission distance was only 3-m instead of 6 m, mainly due to particle scattering and water disturbance. With the motor pump on, the power penalty was 1 dB at 10 × 10−8 BER when compared to the motor pump off. Full article
(This article belongs to the Special Issue Optical Network and Access Technologies)
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7 pages, 1666 KiB  
Communication
Near- to Far-Field Coupling of Evanescent Waves by Glass Microspheres
by Rayenne Boudoukha, Stephane Perrin, Assia Demagh, Paul Montgomery, Nacer-Eddine Demagh and Sylvain Lecler
Photonics 2021, 8(3), 73; https://doi.org/10.3390/photonics8030073 - 6 Mar 2021
Cited by 19 | Viewed by 3304
Abstract
Through rigorous electromagnetic simulations, the natural coupling of high-spatial-frequency evanescent waves from the near field to the far field by dielectric microspheres is studied in air. The generation of whispering gallery modes inside the microspheres is shown independently of any resonance. In addition, [...] Read more.
Through rigorous electromagnetic simulations, the natural coupling of high-spatial-frequency evanescent waves from the near field to the far field by dielectric microspheres is studied in air. The generation of whispering gallery modes inside the microspheres is shown independently of any resonance. In addition, the conversion mechanism of these evanescent waves into propagating waves is analysed. This latter point leads to key information that allows a better physical understanding of the super-resolution phenomenon in microsphere-assisted microscopy where sub-diffraction-limit revolving power is achieved. Full article
(This article belongs to the Special Issue Photonic Jet: Science and Application)
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13 pages, 634 KiB  
Article
Squeezed Coherent States in Double Optical Resonance
by George Mouloudakis and Peter Lambropoulos
Photonics 2021, 8(3), 72; https://doi.org/10.3390/photonics8030072 - 5 Mar 2021
Cited by 1 | Viewed by 3776
Abstract
In this work, we consider a “Λ-type” three-level system where the first transition is driven by a radiation field initially prepared in a squeezed coherent state, while the second one by a weak probe field. If the squeezed field is sufficiently [...] Read more.
In this work, we consider a “Λ-type” three-level system where the first transition is driven by a radiation field initially prepared in a squeezed coherent state, while the second one by a weak probe field. If the squeezed field is sufficiently strong to cause Stark splitting of the states it connects, such a splitting can be monitored through the population of the probe state, a scheme also known as “double optical resonance”. Our results deviate from the well-studied case of coherent driving indicating that the splitting profile shows great sensitivity to the value of the squeezing parameter, as well as its phase difference from the complex displacement parameter. The theory is cast in terms of the resolvent operator where both the atom and the radiation field are treated quantum mechanically, while the effects of squeezing are obtained by appropriate averaging over the photon number distribution of the squeezed coherent state. Full article
(This article belongs to the Special Issue Quantum Optics in Strong Laser Fields)
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27 pages, 8405 KiB  
Review
A Review on X-ray Excited Emission Decay Dynamics in Inorganic Scintillator Materials
by Vineet Kumar and Zhiping Luo
Photonics 2021, 8(3), 71; https://doi.org/10.3390/photonics8030071 - 4 Mar 2021
Cited by 56 | Viewed by 8275
Abstract
Scintillator materials convert high-energy radiation into photons in the ultraviolet to visible light region for radiation detection. In this review, advances in X-ray emission dynamics of inorganic scintillators are presented, including inorganic halides (alkali-metal halides, alkaline-earth halides, rare-earth halides, oxy-halides, rare-earth oxyorthosilicates, halide [...] Read more.
Scintillator materials convert high-energy radiation into photons in the ultraviolet to visible light region for radiation detection. In this review, advances in X-ray emission dynamics of inorganic scintillators are presented, including inorganic halides (alkali-metal halides, alkaline-earth halides, rare-earth halides, oxy-halides, rare-earth oxyorthosilicates, halide perovskites), oxides (binary oxides, complex oxides, post-transition metal oxides), sulfides, rare-earth doped scintillators, and organic-inorganic hybrid scintillators. The origin of scintillation is strongly correlated to the host material and dopants. Current models are presented describing the scintillation decay lifetime of inorganic materials, with the emphasis on the short-lived scintillation decay component. The whole charge generation and the de-excitation process are analyzed in general, and an essential role of the decay kinetics is the de-excitation process. We highlighted three decay mechanisms in cross luminescence emission, exitonic emission, and dopant-activated emission, respectively. Factors regulating the origin of different luminescence centers controlling the decay process are discussed. Full article
(This article belongs to the Special Issue Advanced Optical Materials and Devices II)
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12 pages, 1774 KiB  
Article
Thermally Stimulated Desorption Optical Fiber-Based Interrogation System: An Analysis of Graphene Oxide Layers’ Stability
by Maria Raposo, Carlota Xavier, Catarina Monteiro, Susana Silva, Orlando Frazão, Paulo Zagalo and Paulo António Ribeiro
Photonics 2021, 8(3), 70; https://doi.org/10.3390/photonics8030070 - 4 Mar 2021
Cited by 1 | Viewed by 2333
Abstract
Thin graphene oxide (GO) film layers are being widely used as sensing layers in different types of electrical and optical sensor devices. GO layers are particularly popular because of their tuned interface reflectivity. The stability of GO layers is fundamental for sensor device [...] Read more.
Thin graphene oxide (GO) film layers are being widely used as sensing layers in different types of electrical and optical sensor devices. GO layers are particularly popular because of their tuned interface reflectivity. The stability of GO layers is fundamental for sensor device reliability, particularly in complex aqueous environments such as wastewater. In this work, the stability of GO layers in layer-by-layer (LbL) films of polyethyleneimine (PEI) and GO was investigated. The results led to the following conclusions: PEI/GO films grow linearly with the number of bilayers as long as the adsorption time is kept constant; the adsorption kinetics of a GO layer follow the behavior of the adsorption of polyelectrolytes; and the interaction associated with the growth of these films is of the ionic type since the desorption activation energy has a value of 119 ± 17 kJ/mol. Therefore, it is possible to conclude that PEI/GO films are suitable for application in optical fiber sensor devices; most importantly, an optical fiber-based interrogation setup can easily be adapted to investigate in situ desorption via a thermally stimulated process. In addition, it is possible to draw inferences about film stability in solution in a fast, reliable way when compared with the traditional ones. Full article
(This article belongs to the Special Issue Photonics, Optics and Laser Technology)
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14 pages, 1411 KiB  
Article
Snoring and Sleep-Related Symptoms: A Novel Non-Invasive 808 nm Wavelength Diode Laser Non-Ablative Outpatient Treatment. A Prospective Pilot-Study on 45 Patients
by Isabelle Fini Storchi, Massimo Frosecchi, Francesca Bovis, Angelina Zekiy, Stefano Benedicenti, Andrea Amaroli and Robert A. Convissar
Photonics 2021, 8(3), 69; https://doi.org/10.3390/photonics8030069 - 3 Mar 2021
Cited by 1 | Viewed by 4348
Abstract
Background: Surgical treatments for snoring and sleep-related symptoms are invasive, may have complications, have inconstant success rates, and may have a significant relapse rate. Methods: We evaluated the effectiveness of a non-surgical, non-invasive outpatient 808 nm diode laser treatment. Forty-five patients with snoring [...] Read more.
Background: Surgical treatments for snoring and sleep-related symptoms are invasive, may have complications, have inconstant success rates, and may have a significant relapse rate. Methods: We evaluated the effectiveness of a non-surgical, non-invasive outpatient 808 nm diode laser treatment. Forty-five patients with snoring and sleep disorders were treated with an Elexxion-Claros® 50W Diode Laser 808-nm using the specific SNORE3 application. The possible presence of obstructive sleep apnea syndrome in patients was diagnosed with Polysomnography. The Epworth sleepiness scale was reported pre- and post-laser treatments. Patients were classified according to both Friedman tongue position and Mallampati classification. During treatment, the pain reported by patients was measured on a visual analogue scale. Results: The following data improved significantly: visual analogue scale for the loudness of snoring, Epworth sleepiness scale, waking up during sleep because of snoring, dreaming during the night, dry mouth on awakening, daytime sleepiness, tiredness on awakening, Mallampati score, Friedman tongue position and degree of oropharynx at nose, oropharynx, hypopharynx, and larynx classification (p < 0.001). A cessation of choking in 89% of the patients and of restless legs syndrome in 83% of the patients (p ≤ 0.005 and p ≤ 0.025) was also noted after the laser treatments. All of the patients who reported suffering from headaches upon waking (10 subjects) reported the complete cessation of this phenomenon after laser therapy. Conclusions: diode laser treatment is a promising procedure not only in reducing the loudness of snoring, but also in raising the global quality of sleep, a statistically significant reduction of AHI, and a cessation of bothersome phenomenon related to apnea. Results were sustainable at one year post-treatment. Full article
(This article belongs to the Section Biophotonics and Biomedical Optics)
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7 pages, 2169 KiB  
Communication
Development of Micron Sized Photonic Devices Based on Deep GaN Etching
by Karim Dogheche, Bandar Alshehri, Galles Patriache and Elhadj Dogheche
Photonics 2021, 8(3), 68; https://doi.org/10.3390/photonics8030068 - 2 Mar 2021
Cited by 4 | Viewed by 3565
Abstract
In order to design and development efficient III-nitride based optoelectronic devices, technological processes require a major effort. We propose here a detailed review focussing on the etching procedure as a key step for enabling high date rate performances. In our reported research activity, [...] Read more.
In order to design and development efficient III-nitride based optoelectronic devices, technological processes require a major effort. We propose here a detailed review focussing on the etching procedure as a key step for enabling high date rate performances. In our reported research activity, dry etching of an InGaN/GaN heterogeneous structure was investigated by using an inductively coupled plasma reactive ion etching (ICP-RIE). We considered different combinations of etch mask (Ni, SiO2, resist), focussing on the optimization of the deep etching process. A GaN mesa process with an etching depth up to 6 µm was performed in Cl2/Ar-based plasmas using ICP reactors for LEDs dimen sions ranging from 5 to 150 µm². Our strategy was directed toward the mesa formation for vertical-type diode applications, where etch depths are relatively large. Etch characteristics were studied as a function of ICP parameters (RF power, chamber pressure, fixed total flow rate). Surface morphology, etch rates and sidewall profiles observed into InGaN/GaN structures were compared under different types of etching masks. For deep etching up to few microns into the GaN template, we state that a Ni or SiO2 mask is more suitable to obtain a good selectivity and vertical etch profiles. The optimized etch rate was about 200nm/min under moderate ICP conditions. We applied these conditions for the fabrication of micro/nano LEDs dedicated to LiFi applications. Full article
(This article belongs to the Special Issue Wide Bandgap Semiconductor Photonic Devices)
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18 pages, 5621 KiB  
Article
Peak-to-Average Power Ratio Reduction of Carrier-Suppressed Optical SSB Modulation: Performance Comparison of Three Methods
by K. I. Amila Sampath, Katsumi Takano and Joji Maeda
Photonics 2021, 8(3), 67; https://doi.org/10.3390/photonics8030067 - 26 Feb 2021
Cited by 6 | Viewed by 3003
Abstract
We compare the performances of three previously proposed methods to reduce the peak-to-average power ratio (PAPR) of the carrier-suppressed optical single-sideband (OSSB-SC) signal. PAPR of OSSB-SC signal becomes high due to the peaky Hilbert-transformed signal which is used for spectral suppression. Nonlinear phase [...] Read more.
We compare the performances of three previously proposed methods to reduce the peak-to-average power ratio (PAPR) of the carrier-suppressed optical single-sideband (OSSB-SC) signal. PAPR of OSSB-SC signal becomes high due to the peaky Hilbert-transformed signal which is used for spectral suppression. Nonlinear phase shifts induced by high PAPR degrade OSSB-SC signal during fiber transmission. Previously, we proposed peak folding, peak clipping, and high-pass Hilbert transform methods to reduce the PAPR of OSSB-SC modulation. In this study, we numerically compare the effectiveness of proposed methods in a 10 Gbit/s non-return-to-zero (NRZ)-coded 100-km single-channel transmission link. Due to the reduced PAPR, peak folding and peak clipping can increase the self-phase modulation (SPM) threshold of the studied system by 2.40 dB and 2.63 dB respectively. The high-pass Hilbert transform method improves the SPM threshold by more than 9 dB. Full article
(This article belongs to the Special Issue Advanced Technique and Future Perspective for Next Generation Optical Fiber Communications)
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8 pages, 1492 KiB  
Communication
Unusual Polarization Relation between Single-Mode Lasing Emission and Excitation Laser from an Evanescent-Wave Pumped Micro-Cavity Laser
by Yuchen Wang, Hongsheng Li, Shu Hu, Heng Li and Chuanxiang Sheng
Photonics 2021, 8(3), 66; https://doi.org/10.3390/photonics8030066 - 26 Feb 2021
Cited by 1 | Viewed by 2191
Abstract
Using a fiber of that is 125 μm in diameter in rhodamine 6G ethanol solution, controllable multi- and single-whispering-gallery-mode (WGM) optofluidic lasers based on evanescent-wave-coupled gain are both available. With multi-mode WGM emission, lasing emission with almost pure TM (transverse magnetic) or almost [...] Read more.
Using a fiber of that is 125 μm in diameter in rhodamine 6G ethanol solution, controllable multi- and single-whispering-gallery-mode (WGM) optofluidic lasers based on evanescent-wave-coupled gain are both available. With multi-mode WGM emission, lasing emission with almost pure TM (transverse magnetic) or almost TE (transverse electric) modes can be obtained when the pump laser has an electric field parallel (perpendicular) to the fiber axis, i.e., the polarization direction of output laser is the same as that of the pump laser. On the other hand, when the laser emission is single-mode, the TE output laser always emerges firstly above lasing threshold, then keeps TE mode while the pump laser’s intensity increases with polarization direction perpendicular to the fiber axis; on the contrary, TE emission will dwindle relatively, while the TM emission emerges and dominates the spectra, when the pump laser’s intensity increases with polarization parallel to the fiber axis. Our work proves that controlling the leakage of the evanescent wave from high-Q microcavities is crucial for both modes of lasing emission and its polarization. Full article
(This article belongs to the Section Lasers, Light Sources and Sensors)
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8 pages, 5246 KiB  
Communication
LIDAR and Beam Steering Tailored by Neuromorphic Metasurfaces Dipped in a Tunable Surrounding Medium
by Giuseppe Emanuele Lio and Antonio Ferraro
Photonics 2021, 8(3), 65; https://doi.org/10.3390/photonics8030065 - 26 Feb 2021
Cited by 27 | Viewed by 4972
Abstract
The control of amplitude, losses and deflection of light with elements of an optical array is of paramount importance for realizing dynamic beam steering for light detection and ranging applications (LIDAR). In this paper, we propose an optical beam steering device, operating at [...] Read more.
The control of amplitude, losses and deflection of light with elements of an optical array is of paramount importance for realizing dynamic beam steering for light detection and ranging applications (LIDAR). In this paper, we propose an optical beam steering device, operating at a wavelength of 1550 nm, based on high index material as molybdenum disulfide (MoS2) where the direction of the light is actively controlled by means of liquid crystal. The metasurface have been designed by a deep machine learning algorithm jointed with an optimizer in order to obtain univocal optical responses. The achieved numerical results represent a promising way for the realization of novel LIDAR for future applications with increase control and precision. Full article
(This article belongs to the Special Issue Active/Reconfigurable Metasurfaces)
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24 pages, 6393 KiB  
Article
Synthesis of Super-Oscillatory Point-Spread Functions with Taylor-Like Tapered Sidelobes for Advanced Optical Super-Resolution Imaging
by Haitang Yang and George V. Eleftheriades
Photonics 2021, 8(3), 64; https://doi.org/10.3390/photonics8030064 - 25 Feb 2021
Cited by 6 | Viewed by 4329
Abstract
Recently, the super-oscillation phenomenon has attracted attention because of its ability to super-resolve unlabelled objects in the far-field. Previous synthesis of super-oscillatory point-spread functions used the Chebyshev patterns where all sidelobes are equal. In this work, an approach is introduced to generate super-oscillatory [...] Read more.
Recently, the super-oscillation phenomenon has attracted attention because of its ability to super-resolve unlabelled objects in the far-field. Previous synthesis of super-oscillatory point-spread functions used the Chebyshev patterns where all sidelobes are equal. In this work, an approach is introduced to generate super-oscillatory Taylor-like point-spread functions that have tapered sidelobes. The proposed method is based on the Schelkunoff’s super-directive antenna theory. This approach enables the super-resolution, the first sidelobe level and the tapering rate of the sidelobes to be controlled. Finally, we present the design of several imaging experiments using a spatial light modulator as an advanced programmable grating to form the Taylor-like super-oscillatory point-spread functions and demonstrate their superiority over the Chebyshev ones in resolving the objects of two apertures and of a mask with the letter E. Full article
(This article belongs to the Special Issue Advances in Complex Media Electromagnetics)
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9 pages, 2643 KiB  
Article
A Design Approach of Optical Phased Array with Low Side Lobe Level and Wide Angle Steering Range
by Xinyu He, Tao Dong, Jingwen He and Yue Xu
Photonics 2021, 8(3), 63; https://doi.org/10.3390/photonics8030063 - 25 Feb 2021
Cited by 12 | Viewed by 3814
Abstract
In this paper, a new design approach of optical phased array (OPA) with low side lobe level (SLL) and wide angle steering range is proposed. This approach consists of two steps. Firstly, a nonuniform antenna array is designed by optimizing the antenna spacing [...] Read more.
In this paper, a new design approach of optical phased array (OPA) with low side lobe level (SLL) and wide angle steering range is proposed. This approach consists of two steps. Firstly, a nonuniform antenna array is designed by optimizing the antenna spacing distribution with particle swarm optimization (PSO). Secondly, on the basis of the optimized antenna spacing distribution, PSO is further used to optimize the phase distribution of the optical antennas when the beam steers for realizing lower SLL. Based on the approach we mentioned, we design a nonuniform OPA which has 1024 optical antennas to achieve the steering range of ±60°. When the beam steering angle is 0°, 20°, 30°, 45° and 60°, the SLL obtained by optimizing phase distribution is −21.35, −18.79, −17.91, −18.46 and −18.51 dB, respectively. This kind of OPA with low SLL and wide angle steering range has broad application prospects in laser communication and lidar system. Full article
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9 pages, 1550 KiB  
Communication
Diffraction Efficiency Characteristics for MEMS-Based Phase-Only Spatial Light Modulator with Nonlinear Phase Distribution
by Remington S. Ketchum and Pierre-Alexandre Blanche
Photonics 2021, 8(3), 62; https://doi.org/10.3390/photonics8030062 - 24 Feb 2021
Cited by 20 | Viewed by 3503
Abstract
Micro-electro mechanical systems (MEMS)-based phase-only spatial light modulators (PLMs) have the potential to overcome the limited speed of liquid crystal on silicon (LCoS) spatial light modulators (SLMs) and operate at speeds faster than 10 kHz. This expands the practicality of PLMs to several [...] Read more.
Micro-electro mechanical systems (MEMS)-based phase-only spatial light modulators (PLMs) have the potential to overcome the limited speed of liquid crystal on silicon (LCoS) spatial light modulators (SLMs) and operate at speeds faster than 10 kHz. This expands the practicality of PLMs to several applications, including communications, sensing, and high-speed displays. The complex structure and fabrication requirements for large, 2D MEMS arrays with vertical actuation have kept MEMS-based PLMs out of the market in favor of LCoS SLMs. Recently, Texas Instruments has adapted its existing DMD technology for fabricating MEMS-based PLMs. Here, we characterize the diffraction efficiency for one of these PLMs and examine the effect of a nonlinear distribution of addressable phase states across a range of wavelengths and illumination angles. Full article
(This article belongs to the Special Issue Holography)
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