Table of contents

JPhys Photonics is a new open access journal from IOP Publishing reporting high-quality, significant, and original research at the forefront of photonics and optics. The journal will showcase the most exciting research advances and discoveries that constitute today's science and will shape tomorrow's technologies. With a particular focus on interdisciplinary research, JPhys Photonics is designed to support the flow and exchange of knowledge across existing and emerging communities, maximising the reach and impact of published research.

Light-emitting diodes (LEDs) are changing indoor wireless communications. Visible light communications (VLC) that use LEDs as transmitters is an emerging research area and has significant commercial potential. The light emitted from LEDs can simultaneously carry information and provide illumination. Due to the intrinsic characteristics of light, VLC is more secure, more power efficient, and can provide higher network data transmission rates than radio frequency communications. This paper describes state-of-the-art VLC systems including transmitters, receivers, and channel models. Modulation and networking algorithms for physical layer and cross-layer designs are discussed. These algorithms are designed considering practical constraints, such as the bandlimited channel, illumination requirements, and transmitted power limitations. Indoor localization algorithms are proposed, with a particular focus on fingerprinting. In addition, this paper introduces practical applications of VLC in many fields such as national defense, healthcare, robotics, and vehicle-to-vehicle communications. The paper concludes with a discussion of the challenges, opportunities, and future of VLC.

Focused ion beam processing has been applied to fabricate coupled-cavity AlInAs/InGaAs/InP quantum cascade lasers. The evolution of the mode spectrum of the two coupled Fabry–Perot cavities, controlled by the driving currents of both sections leading to single mode operation, has been observed. Theoretical analysis of the observed behavior, supported by extensive numerical modeling is given. The analysis showed that the most efficient single mode operation takes place in the case of relatively close current densities in both sections of coupled-cavity quantum cascade lasers, which assures the overlap of the gain spectra. In such a configuration, fine tuning of the currents allows the favoring of the mode that coincides with gain peaks and suppresses all others.

We present a theoretical framework for nonlinear optics of graphene and other 2D materials in layered structures. We derive a key equation to find the effective electric field and the sheet current density in the 2D material for given incident light beams. Our approach takes into account the effect of the surrounding environment and characterizes its contribution as a structure factor. We apply our approach to two experimental setups, and discuss the structure factors for several nonlinear optical processes including second harmonic generation, third harmonic generation, and parametric frequency conversion. Our systematic study gives a strict extraction method for the nonlinear coefficients, and provides new insights in how layered structures influence the nonlinear signal observed from 2D materials.

We report on the design, fabrication and experimental demonstration of single-crystal diamond (SCD) waveguide devices with integrated grating couplers optimized for 850 nm, 635 nm, and 405 nm wavelengths, respectively. The devices are fabricated on SCD thin films using electron-beam lithography and reactive-ion etching technologies. To reduce the wafer wedge typically present in commercial diamond plates, we introduce a novel tilted-etching technique in the preparation of the thin films. We obtain 60% reduction of the wafer wedge, namely from 300 to 120 nm mm^–1, enabling us to properly fabricate the devices designed for the short to ultra-short wavelengths considered here. Using light in- and out-coupling with 50 μm core tapered fibers, we measure total (input plus output) grating coupling losses of 20.6 dB and 22.7 dB, and waveguide losses of 11 dB mm^–1 and 20.5 dB mm^–1 for the 850 nm and 635 nm wavelength devices, respectively. The 405 nm wavelength devices, tested with a lensed 9 μm core input fiber and with the same tapered output fiber as employed for the other devices, also demonstrate light guidance, and feature total grating coupling and waveguide losses on the order of 33.1 dB and 46.7 dB mm^–1, respectively. These results showcase the possibility of down-scaling grating-coupled SCD devices for VIS-UV operation, and pave the way for exploiting diamond's properties on photonic chips at extremely short wavelengths.

Arrays of nanostructures have emerged as exceptional tools for the manipulation and control of light. Oftentimes, despite the fact that real implementations of nanostructure arrays must be finite, these systems are modeled as perfectly periodic, and therefore infinite. Here, we investigate the legitimacy of this approximation by studying the evolution of the optical response of finite arrays of nanostructures as their number of elements is increased. We find that the number of elements necessary to reach the infinite array limit is determined by the strength of the coupling between them, and that, even when that limit is reached, the individual responses of the elements may still display significant variations. In addition, we show that, when retardation is negligible, the resonance frequency for the infinite array is always redshifted compared to the single particle. However, in the opposite situation, there could be either a blue- or a redshift. We also study the effects of inhomogeneity in size and position of the elements on the optical response of the array. This work advances the understanding of the behavior of finite and infinite arrays of nanostructures, and therefore provides guidance to design applications that utilize these systems.

Injection locking has many applications in telecommunications systems, such as narrowing linewidths, increasing bandwidth and improving filtering. Beyond telecommunications, injection locking is widely used in remote sensing. This is of particular interest for applications in the 2 μm region, where gases such as carbon dioxide, water vapour and methane have identifiable absorption features. In this paper, we demonstrate stable injection locking with slotted Fabry–Perot lasers in the 2 μm wavelength region. Injection locking was observed in both the optical domain and power spectrum; with key features recorded such as injection 'pulling', side-mode suppression and the characteristic quiet region in the electrical domain denoting single-frequency emission and stable locking. The effect of varying the injection ratio was investigated, with a decreased injection ratio corresponding to a reduction in the locking bandwidth. Finally, the lasers were shown to remain injection locked, with no thermal drift, for over 24 h, indicating their suitability for implementation in a real-world telecommunications system.

We report on femtosecond laser writing of single mode optical waveguides in chalcogenide Gallium Lanthanum Sulphide (GLS) glass. A multiscan fabrication process was employed to create waveguides with symmetric single mode guidance and low insertion losses for the first time at 800 nm wavelength, compatible with Ti:Sapphire ultrafast lasers and nonlinear photonics applications. μRaman and x-ray microanalysis were used to elucidate the origin of the laser-induced refractive index change in GLS. We found that the laser irradiation produced a gentle modification of the GLS network, altering the Ga–S and La–S bonds to induce an increase in the refractive index. Nonlinear refractive index measurements of the waveguides were performed by finding the optical switching parameters of a directional coupler, demonstrating that the nonlinear properties were preserved, evidencing that GLS is a promising platform for laser-written integrated nonlinear photonics.

The number of probe particles that is detected on a single pixel of a micrograph is finite, either due to source (low power), detector (low dynamic range) or specimen damage constraints. The sensitivity of an otherwise perfect microscope is then limited by the statistical fluctuations in the number of detected particles. It is thus crucial to strive for the optimal signal-to-noise ratio per detected photon. Here we analytically and numerically compare three different contrast enhancing techniques that are all based on self-imaging cavities: CW cavity enhanced microscopy, cavity ring-down microscopy and multi-pass microscopy. We show that all three schemes can lead to sensitivities beyond those achievable with a single pass.

Femtosecond laser machining offers the potential for high-precision materials processing. However, due to the nonlinear processes inherent when using femtosecond pulses, experimental random noise can result in large variations in the machined quality, and hence methods for closed loop feedback are of interest. Here we demonstrate the application of a neural network (NN), acting as a pattern recognition algorithm, for visual monitoring of the target substrate via a camera that observes the sample during machining. This approach has the advantage that it requires zero knowledge of the underlying physical processes, and hence avoids the need for modelling the complex photon–atom interactions that occur with femtosecond laser machining. The NN was shown to accurately determine the type of material, the laser fluence and the number of pulses, directly from a single image of the sample and within ten milliseconds. This approach provides the potential for real-time feedback for femtosecond laser materials processing.