Photonics, Volume 5, Issue 3 (September 2018) – 15 articles

We design an asymmetric nonlinear optical nanoantenna composed of a dielectric nanodisc and an adjacent nanobar. The proposed composite structure made of AlGaAs exhibits resonant response at both the fundamental and doubled frequencies. Being driven by the strong magnetic dipole resonance at the pump wavelength and a high-quality mode at the harmonic wavelength, the efficient second-harmonic radiation is generated predominantly along the vertical directions under the normally incident plane-wave excitation. Full article

Quantum-dot (QD) photonic-crystal (PC) surface-emitting laser (SEL) devices with bottom distributed Bragg reflector (DBR) were fabricated based on vertical-cavity SEL structure with top DBR completely removed. Two-dimensional (2D) PCs were deeply etched through QD multilayers to yield strong diffraction coupling. Room-temperature optically pumped lasing emissions at 1194 nm and 1296 nm were demonstrated for two lattice periods of 360 nm and 395 nm, respectively. Two lasing wavelengths separated over 100 nm; however, there were less than two times difference in threshold power densities while slope efficiencies were comparable. The unique spectral gain characteristics of QDs were considered in interpretation of gain-cavity detuning. Moreover, simulation revealed the sub-cavity should be designed so that its resonant wavelength is in phase with lasing wavelength. Full article

This paper proposes a hexagonal photonic crystal fiber (H-PCF) structure with all circular air holes in order to simultaneously achieve ultrahigh birefringence and high nonlinearity. The H-PCF design consists of an asymmetric core region, where one air hole is a reduced diameter and the air hole in its opposite vertex is omitted. The light-guiding properties of the proposed H-PCF structure were studied using the full-vector finite element method (FEM) with a circular perfectly matched layer (PML). The simulation results showed that the proposed H-PCF exhibits an ultrahigh birefringence of 3.87 × 10⁻², a negative dispersion coefficient of −753.2 ps/(nm km), and a nonlinear coefficient of 96.51 W⁻¹ km⁻¹ at an excitation wavelength of 1550 nm. The major advantage of our H-PCF design is that it provides these desirable modal properties without using any non-circular air holes in the core and cladding region, thus making the fiber fabrication process much easier. The ultrahigh birefringence, large negative dispersion, and high nonlinearity of our designed H-PCF make it a very suitable candidate for optical backpropagation applications, which is a scheme for the simultaneous dispersion and nonlinearity compensation of optical-fiber transmission links. Full article

We report on the study of energy-harvesting performance in medium-size (400 cm²) glass-based semitransparent solar concentrators employing edge-mounted photovoltaic modules. Systems using several different types of glazing system architecture and containing embedded diffractive structures are prepared and characterized. The technological approaches to the rapid manufacture of large-area diffractive elements suitable for use in solar window-type concentrators are described. These elements enable the internal deflection and partial trapping of light inside glass-based concentrator windows. We focus on uncovering the potential of pattern-transfer polymer-based soft lithography for enabling both the improved photon collection probability at solar cell surfaces, and the up-scaling of semitransparent solar window dimensions. Results of photovoltaic characterization of several solar concentrators employing different internal glazing-system structure and diffractive elements produced using different technologies are reported and discussed. Full article

Adaptive Sliceable-Bandwidth Variable Transceivers (S-BVTs) are key enablers for future optical networks. In particular, those based on Discrete MultiTone (DMT) modulation and Direct Detection (DD) can be considered a flexible solution suitable to address the cost efficiency requirement of optical metro networks. In this paper, we propose to use a cost-effective S-BVT option/implementation in optical metro networks adopting switching nodes based on Semiconductor Optical Amplifier (SOA) technology. Bit loading (BL) and power loading (PL) algorithms are applied to the Digital Signal Processing (DSP) modules, to maximize the performance and/or the capacity as well as enhance the flexibility and adaptability of the system. Our analysis considers switching nodes based on SOAs with and without filtering elements and fiber spans of 25 km. We present the results up to 100 km, with and without SOA-based nodes. Firstly, we analyze the adaptive BVT transmission using the Margin Adaptive (MA) BL/PL algorithm at a fixed bit rate of 28 Gb/s. The possibility of controlling the SOAs current is a key factor to face the transmission impairments due to the fiber and the filtering elements. We also analyze the system considering Rate Adaptive (RA) transmission at a fixed target Bit Error Rate (BER) of 3.8 × 10⁻³, showing that a maximum capacity above 34 Gb/s can be achieved for a single span of 25 km. Although the cascading of filtering elements still constitutes a limiting factor, we show that an improvement of the net bit rate performance can be obtained thanks to the combined use of BVT and SOA technology at the switching nodes, resulting in a promising approach for designing future optical metro networks. Full article

In the phase-sensitivity-based surface plasmon resonance (SPR) sensing scheme, the highest phase jump usually happens at the darkness or quasi-darkness reflection point, which results in low power for detection. To overcome such a limitation, in this paper, a waveguide-coupled SPR configuration is proposed to work at near-infrared. The coupling between surface plasmon polariton (SPP) mode and photonic waveguide (PWG) mode results in electromagnetically induced transparency (EIT) and asymmetric Fano resonance (FR). Near the resonance, the differential phase between p-polarized and s-polarized incident waves experience drastic variation upon change of the surrounding refractive index. More importantly, since the FR occurs at the resonance slope of SPP mode, the corresponding phase change is accompanied with relatively high reflectivity, which is essential for signal-to-noise ratio (SNR) enhancement and power consumption reduction. Phase sensitivity up to 10⁶ deg/RIU order with a minimum SPR reflectivity higher than 20% is achieved. The proposed scheme provides an alternative approach for high-performance sensing applications using FR. Full article

The spectral properties of a one-dimensional photonic crystal bounded by a resonant absorbing nanocomposite layer with the near-zero permittivity have been studied. The problem of calculating the transmittance, reflectance, and absorptance spectra of such structures at the normal and oblique incidence of light has been solved. It is shown that, depending on the permittivity sign near zero, the nanocomposite is characterized by either metallic or dielectric properties. The possibility of simultaneous formation of the Tamm plasmon polariton at the photonic crystal/metallic nanocomposite interface and the localized state similar to the defect mode with the field intensity maximum inside the dielectric nanocomposite layer is demonstrated. Specific features of field localization at the Tamm plasmon polariton and defect mode frequencies are analyzed. Full article

Data centers are continuously growing in scale and can contain more than one million servers spreading across thousands of racks; requiring a large-scale switching network to provide broadband and reconfigurable interconnections of low latency. Traditional data center network architectures, through the use of electrical packet switches in a multi-tier topology, has fundamental weaknesses such as oversubscription and cabling complexity. Wireless intra-data center interconnection solutions have been proposed to deal with the cabling problem and can simultaneously address the over-provisioning problem by offering efficient topology re-configurability. In this work we introduce a novel free space optical interconnect solution for intra-data center networks that utilizes 2D optical beam steering for the transmitter, and high bandwidth wide-area photodiode arrays for the receiver. This new breed of free space optical interconnects can be developed on a photonic integrated circuit; offering ns switching at sub-μW consumption. The proposed interconnects together with a networking architecture that is suitable for utilizing those devices could support next generation intra-data center networks, fulfilling the requirements of seamless operation, high connectivity, and agility in terms of the reconfiguration time. Full article

We demonstrate a spatial division multiplexing (SDM) network testbed composed of three nodes connected via 19-core multi-core fibers. Each node is capable of joint spatial circuit switching and joint packet switching to support 10 Tb/s spatial circuit super channels and 1 Tb/s line rate spatial packet super channels. The performance of the proposed hybrid network is evaluated, showing successful co-existence of both systems in the same network to provide high capacity and high granularity services. Finally, we demonstrate an optical channel selection associated with the quality of service requirements on the SDM network testbed. Full article

Foveated sight as observed in some raptor eyes is a motivation for artificial imaging systems requiring both wide fields of view as well as specific embedded regions of higher resolution. These foveated optical imaging systems are applicable to many acquisition and tracking tasks and as such are often required to be relatively portable and operate in real-time. Two approaches to achieve foveation have been explored in the past: optical system design and back-end data processing. In this paper, these previous works are compiled and used to build a framework for analyzing and designing practical foveated imaging systems. While each approach (physical control of optical distortion within the lens design process, and post-processing image re-sampling) has its own pros and cons, it is concluded that a combination of both techniques will further spur the development of more versatile, flexible, and adaptable foveated imaging systems in the future. Full article

A silica resonator was demonstrated for random laser generation. The resonator consisted of a conventional microsphere fabricated in an optical fiber tip through electric arc discharge, and modifications to its geometry were carried out to create asymmetry inside the silica structure. The resulting Bunimovich stadium-like microsphere promotes multiple reflections with the boundaries, following the stochastic properties of dynamic billiards. The interference of the multiple scattered beams generates a random signal whose intensity was increased by sputter-coating the microstadium with a gold thin film. The random signal is amplified using an erbium-doped fiber amplifier (EDFA) in a ring cavity configuration with feedback, and lasing is identified as temporal and spectral random variations of the signal between consecutive measurements. Full article

Optical modes bearing optical vortices are important light systems in which to encode information. Optical vortices are robust features of optical beams that do not dissipate upon propagation. Thus, decoding the modal content of a beam is a vital component of the process. In this work, we present a method to decode modal superpositions of light beams that contain optical vortices. We do so using shear interferometry, which presents a simple and effective means of determining the vortex content of a beam, and extract the parameters of the component vortex modes that constitute them. We find that optical modes in a beam are easily determined. Its modal content can be extracted when they are of comparable magnitude. The use of modes of well-defined topological charge, but not well-defined radial-mode content, such as those produced by phase-only encoding, are much easier to diagnose than pure Laguerre–Gauss modes. Full article

The magneto-optic (MO) characteristics and sensing performance of noble metal (Ag, Au, Cu) or transition metal (Fe, Ni, Co) single layers and Ag/Co or Au/Co bilayers have been studied and compared in both the standard plasmonic and MO plasmonic configurations at two different wavelengths (632.8 nm and 785 nm) and in two different sensing media (air and water). The sensing performance is found to be medium-specific and lower in biosensor-relevant water-based media. The sensitivities of MO-SPR sensors is found to be superior to SPR sensors in all cases. This enhancement in sensitivity means the detection limit of this class of transducers can be substantially improved by tuning Au/Co layer thickness, wavelength, and incident angle of optical radiation. The optimized bilayer showed an enhancement in sensitivity by over 30× in air and 9× in water as compared to the conventional Au SPR configuration. Notably, the best performance is 3× above that of MO-SPR sensors coupled to a photonic crystal previously reported in the literature and is found when the ferromagnetic layer is furthest from the sensing medium, as opposed to typical MO-SPR configurations. This proposed structure is attractive for next-generation biosensors. Full article