Photonics — Open Access Journal

The extension of the available spectral range covered by quantum cascade lasers (QCL) would allow one to address new molecular spectroscopy applications, in particular in the long wavelength domain of the mid-infrared. We report in this paper the realization of distributed feedback (DFB) QCLs, made of InAs and AlSb, that demonstrated a continuous wave (CW) and a single mode emission at a wavelength of 17.7 µm, with output powers in the mW range. This is the longest wavelength for DFB QCLs, and for any QCLs or semiconductor lasers in general, operating in a CW at room temperature. Full article

In this paper, we propose, analyze and simulate a new configuration to simulate all-optical combinational logic functions based on Nano-rings insulator-metal-insulator (IMI) plasmonic waveguides. We used Finite Element Method (FEM) to analyze the proposed plasmonic combinational logic functions. The analyzed combinational logic functions are Half-Adder, Full-Adder, Half-Subtractor, and Comparator One-Bit. The operation principle of these combinational logic functions is based on the constructive and destructive interferences between the input signal(s) and control signal. Numerical simulations show that a transmission threshold exists (0.25) which allows all proposed four plasmonic combinational logic functions to be achieved in one structure. As a result, the transmission threshold value measures the performance of the proposed plasmonic combinational logic functions. We use the same structure with the same dimensions at 1550 nm wavelength for all proposed plasmonic combinational logic functions. The proposed all-optical combinational logic functions structure contributes significantly to photonic integrated circuits construction and all-optical signal processing nano-circuits. Full article

Electrically tunable metasurfaces with graphene offer design flexibility to efficiently manipulate and control light. These metasurfaces can be used to generate plasmon-induced reflectance (PIR), which can be tuned by electrostatic doping of the graphene layer. We numerically investigated two designs for tunable PIR devices using the finite difference time-domain (FDTD) method. The first design is based on two rectangular antennas of the same size and a disk; in the second design, two parallel rectangular antennas with different dimensions are used. The PIR-effect was achieved by weak hybridization of two bright modes in both devices and tuned by changing the Fermi level of graphene. A total shift of ∼362 nm was observed in the design with the modulation depth of 53% and a spectral contrast ratio of 76%. These tunable PIR devices can be used for tunable enhanced biosensing and switchable systems. Full article

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

Optical injection locking has been demonstrated as an effective filter for optical communications. These optical filters have advantages over conventional passive filters, as they can be used on active material, allowing them to be monolithically integrated onto an optical circuit. We present an experimental and theoretical study of the optical suppression in injection locked Fabry–Pérot and slotted Fabry–Pérot lasers. We consider both single frequency and optical comb injection. Our model is then used to demonstrate that improving the Q factor of devices increases the suppression obtained when injecting optical combs. We show that increasing the Q factor while fixing the device pump rate relative to threshold causes the locking range of these demultiplexers to asymptotically approach a constant value. Full article

In the last few years, the perfect absorption of light has become an important research topic due to its dramatic impact in photovoltaics, photodetectors, color filters and thermal emitters. While broadband optical absorption is relatively easy to achieve using bulky devices, today there is a strong need and interest in achieving the same effects by employing nanometric structures that are compatible with modern nanophotonic components. In this paper, we propose a general procedure to design broadband nanometer-scale absorbers working in the optical spectrum. The proposed devices, which can be considered an extension to optics of microwave circuit-analog absorbers, consist of several layers containing arrays of elongated nanoparticles, whose dimensions are engineered to control both the absorption level and the operational bandwidth. By combining a surface-impedance homogenization and an equivalent transmission-line formalism, we define a general analytical procedure that can be employed to achieve a final working design. As a relevant example, we show that the proposed approach allows designing an optical absorber exhibiting a 20% fractional bandwidth on a thickness of λ/4 at the central frequency of operation. Full-wave results confirming the effectiveness of the analytical findings, as well as some considerations about the experimental realization of the proposed devices are provided. Full article

Recent interest in the application of mid-infrared (mid-IR) lasers has made the generation of ~3 µm ultrafast pulses a hot topic. Recently, the generation of femtosecond-scale pulses in Er³⁺-doped fluoride fiber lasers has been realized by nonlinear polarization rotation (NPR). However, a numerical study on these fiber lasers has not been reported yet. In this work, the output properties of the NPR passively mode-locked Er³⁺-doped fluoride fiber ring laser in ~3 µm have been numerically investigated based on the coupled Ginzburg–Landu equation. The simulation results indicate that stable uniform solitons (0.75 nJ) with the pulse duration of femtosecond-scale can be generated from this fiber laser. This numerical investigation can provide some reference for developing the high energy femtosecond soliton fiber lasers in the mid-IR. Full article

Germanium/Silicon-Germanium (Ge/SiGe) multiple quantum wells receive great attention for the realization of Si-based optical modulators, photodetectors, and light emitters for short distance optical interconnects on Si chips. Ge quantum wells incorporated between SiGe barriers, allowing a strong electro-absorption mechanism of the quantum-confined Stark effect (QCSE) within telecommunication wavelengths. In this review, we respectively discuss the current state of knowledge and progress of developing optical modulators, photodetectors, and emitters based on Ge/SiGe quantum wells. Key performance parameters, including extinction ratio, optical loss, swing bias voltages, and electric fields, and modulation bandwidth for optical modulators, dark currents, and optical responsivities for photodetectors, and emission characteristics of the structures will be presented. Full article

Billions of U.S. dollars of basic and applied research funding have been invested during the last few years in ideas proposing inverse concepts. The photonics market could not make an exception to this global trend, and thus, several agenda-setting research groups have already started providing sophisticated tools, constrained optimization algorithms, and selective evolution techniques towards this direction. Here, we present an approach of inverse design based on the exhaustive trial-and-testing of the available media and changing the physical dimensions’ range according to the operational wavelength. The proposed technique is applied to the case of an optimal radiation-enhancing cylindrical particle fed by a line source of visible light and gives a two-order increase in the magnitude of the produced signal. Full article

This article reviews recent advances in terahertz science and technology that rely on confining the energy of incident terahertz radiation to small, very sub-wavelength sized regions. We focus on two broad areas of application for such field confinement: metamaterial-based nonlinear terahertz devices and terahertz near-field microscopy and spectroscopy techniques. In particular, we focus on field confinement in: terahertz nonlinear absorbers, metamaterial enhanced nonlinear terahertz spectroscopy, and in sub-wavelength terahertz imaging systems. Full article

In this paper, we propose and investigate the modal characteristics of wedge surface plasmon polariton (SPP) waveguides for guiding surface plasmon waves. The wedge SPP waveguides are composed of a silver layer deposited onto the surface of a wedge-shaped silicon dielectric waveguide. The wedge-shaped silicon dielectric waveguides are explored from the anisotropic wet etching property of single crystal silicon. The wedge SPP waveguides are embedded in a dielectric medium to form the metal–dielectric interface for guiding the surface plasmon waves. The propagation characteristics of the wedge SPP waveguides at the optical telecommunication wavelength of 1.55 μm are evaluated by a numerical simulation. The influence of the physical parameters such as the dimensions of the wedge SPP waveguide and the refractive index of the dielectric medium on the propagation of the surface plasmon wave is investigated. In addition, by comparing the propagation characteristics, we derive the wedge SPP waveguide with the optimal performance. Full article

The temporal distribution of the spectral parametric gain was experimentally investigated when a chirped pump pulse was injected into a photonic crystal fiber. A pump-probe experiment was developed and the important characteristics were measured as the chirp of the pump, the signal pulse, and the gain of the parametric amplifier. We highlight that the amplified spectrum depends strongly on the instantaneous pump wavelength and that the temporal evolution of the wavelength at maximum gain is not monotonic. This behavior is significantly different from the case in which the chirped pump has a constant peak power. This measurement will be very important to efficiently include parametric amplifiers in laser systems delivering ultra-short pulses. Full article

In this paper, we propose a modified design of a hexagonal circular photonic crystal fiber (HC-PCF) which obtains a large negative dispersion and ultrahigh birefringence simultaneously. The optical properties of the proposed HC-PCF were investigated using the finite element method (FEM) incorporated with a circular perfectly matched layer at the boundary. The simulation results showed large negative dispersion of −1044 ps/nm.km and ultrahigh birefringence of 4.321 × 10⁻² at the operating wavelength of 1550 nm for the optimum geometrical parameters. Our proposed HC-PCF exhibited the desirable optical properties without non-circular air holes in the core and cladding region which facilitates the fabrication process. The large negative dispersion of the proposed microstructure over the wide spectral range, i.e., 1350 nm to 1600 nm, and high birefringence make it a suitable candidate for high-speed optical broadband communication and different sensing applications. Full article

In this work, we investigate the resonant characteristics of hexahedral (cubical) inclusions at the plasmonic domain. After an introduction to the notion of superquadric surfaces, i.e., surfaces that model various versions of a rounded cube, we present the main resonant spectrum and the surface distributions for two particular cases of a smooth and a sharp cube in the plasmonic domain. We present a historical comparative overview of the main contributions available since the 1970s. A new categorization scheme of the resonances of a cube is introduced, based on symmetry considerations. The obtained results are compared against several recent works, exposing that the higher-order modes are extremely susceptible to both the choice of sharpness of the cube and the modeling mesh. This work can be readily used as a reference for both historical and contemporary studies of the plasmonic aspects of a cube. Full article

Many photochemical or photobiological applications require the use of high power ultraviolet light sources, such as high-pressure mercury arc lamps. In addition, many photo-induced chemical, biochemical and biological applications require either a combinatorial setting or a parallel assay of multiple samples under the same environmental conditions to ensure reproducibility. To achieve this, alternative, controllable light sources, such as ultraviolet light emitting diodes (UV LEDs) with high power and spatial control are required. Preferably, LEDs are arranged in a suitable standardized 96-well microtiter plate format. We designed such an array and established the methods required for heat management and enabling stable, controllable illumination over time. Full article

A number of new architectures for data centre networks employing reconfigurable, SDN controlled, all-optical networks have been reported in recent years. In most cases, additional capacity was added to the system which unsurprisingly improved performance. In this study, a generalised network model that emulates the behaviour of these types of network was developed but where the total capacity is maintained constant so that system behaviour can be understood. An extensive emulated study is presented which indicates that the reconfiguration of such a network can have a detrimental impact on Transmission Control Protocol (TCP) congestion control mechanisms that can degrade the performance of the system. A number of simple scheduling mechanisms were investigated and the results show that an on-demand scheduling mechanism could deliver a throughput increase of more than ∼50% without any increase in total installed network capacity. These results, therefore, indicate the need to link the network resource management with new datacentre network architectures. Full article

A theoretical model for the responsivity and noise-equivalent power (NEP) of photoconductive antennas (PCAs) as coherent, homodyne THz detectors is presented. The model is validated by comparison to experimental values obtained for two ErAs:InGaAs PCAs. The responsivity and NEP were obtained from the measured rectified current, the current noise floor in the PCAs, and the incoming THz power for the same conditions. Since the THz power measurements are performed with a pyroelectric detector calibrated by the National Metrology Institute of Germany (PTB), the experimentally obtained values are directly traceable to the International System of Units (SI) for the described conditions. The agreement between the presented model and the experimental results is excellent using only one fitting parameter. A very low NEP of 1.8 fW/Hz at 188.8 GHz is obtained at room temperature. Full article

Recent advances in nanofabrication and optical manipulation techniques are making it possible to build arrays of quantum emitters with accurate control over the locations of their individual elements. In analogy with classical antenna arrays, this poses new opportunities for tailoring quantum interference effects by designing the geometry of the array. Here, we investigate the $N^{\mathrm{th}}$-order directional correlation function of the photons emitted by an array of N initially-excited identical quantum emitters, addressing the impact of the appearance of grating lobes. Our analysis reveals that the absence of directivity in the first-order correlation function is contrasted by an enhanced directivity in the $N^{\mathrm{th}}$-order one. This suggests that the emitted light consists of a superposition of directionally entangled photon bunches. Moreover, the photon correlation landscape changes radically with the appearance of grating lobes. In fact, the photons no longer tend to be bunched along the same direction; rather, they are distributed in a set of correlated directions with equal probability. These results clarify basic aspects of light emission from ensembles of quantum emitters. Furthermore, they may find applications in the design of nonclassical light sources. Full article

Multitude applications of photonic devices and technologies for the generation and manipulation of arbitrary and random microwave waveforms, at unprecedented processing speeds, have been proposed in the literature over the past three decades. This class of photonic applications for microwave engineering is known as microwave photonics (MWP). The vast capabilities of MWP have allowed the realization of key functionalities which are either highly complex or simply not possible in the microwave domain alone. Recently, this growing field has adopted the integrated photonics technologies to develop microwave photonic systems with enhanced robustness as well as with a significant reduction of size, cost, weight, and power consumption. In particular, silicon photonics technology is of great interest for this aim as it offers outstanding possibilities for integration of highly-complex active and passive photonic devices, permitting monolithic integration of MWP with high-speed silicon electronics. In this article, we present a review of recent work on MWP functions developed on the silicon platform. We particularly focus on newly reported designs for signal modulation, arbitrary waveform generation, filtering, true-time delay, phase shifting, beam steering, and frequency measurement. Full article