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The optical losses and the refractive index change of optical planar waveguides formed by MeV ion implantation were correlated with the experimental ion implantation parameters. Direct ion implantation was performed by means of carbon, silicon and copper ion beams impinging on the substrate surface at normal incidence. The ions were accelerated at energies ranging from 3 to 12 MeV with fluences varying from 1 × 1012 to 2 × 1016 ion/cm2, according to the type of implanted ion. The modification of the substrate refractive index due to the ion irradiation‐induced damage was evaluated using the prism coupler method, and the refractive index profiles were determined by means of a reconstruction method using a multilayer structure approximation. The guiding properties of the waveguides were analysed using the fibre‐coupling technique to determine both the optical transmission and transversal modes at 635 nm. The main practical relevance of our research is the obtention of high‐quality waveguides at low current density MeV ion implantation (≤80 nA/cm2) without post‐implantation annealing. [ABSTRACT FROM AUTHOR]

In this work, the authors demonstrate the control of quality factor (Q‐factor) is laterally coupled vertical cavities. A 3 μm‐side‐length square cavity directly connected to a 1.5 μm‐width, 10 μm‐length Fabry–Perot (FP) cavity has been fabricated and measured. Dynamic tuning of the Q‐factor has been successfully observed by bringing the square cavity and FP cavity into resonance. The vertical‐cavity‐based Q‐factor control scheme provides a new choice for the modulation of light and holds potentials for applications associated with optical information processing. [ABSTRACT FROM AUTHOR]

Two‐dimensional (2D) metasurface integrated with strip waveguide in silicon‐on‐insulator (SOI) has been designed to achieve high coupling efficiency for 3.8 μm wavelength. The optimisation in period and radius has been achieved using 3D finite‐difference time‐domain (FDTD). The calculated coupling efficiency in the in‐plane waveguide for the out‐of‐plane surface illumination is over 90% with a bandwidth of 1 μm. The design is consistent with the available lithography using 400 nm thick SOI for mid‐IR applications. Finally, monolithic integration can be achieved using standard multi‐project wafer run. [ABSTRACT FROM AUTHOR]

Synthesis of indium (III) oxide (In2O3) and chromium (Cr)‐doped In2O3 thin film (TF) by spin‐on technique was reported. The device showed the Schottky nature under dark and light illumination condition. The ideality factor of the diode showed an exponential increase with the decrease in temperature. The low ideality factor of ∼4 was calculated at 300 K. The barrier height of the device increased with temperature. The Cr‐doped In2O3 TF device possessed high sensitivity compared with undoped In2O3 TF at −2 V all over the temperature range from 10 to 300 K. The Cr‐doped In2O3 TF‐based device showed extremely high sensitivity toward ultraviolet (320 nm) light as compared with visible light. [ABSTRACT FROM AUTHOR]

In this work, the authors present their recent progress in the development of a platform for the mid‐infrared wavelength range, based on suspended silicon waveguides with subwavelength metamaterial cladding. The platform has some intrinsic advantages, which make it a very promising candidate for sensing applications in the molecular fingerprint region. Specifically, it can cover the full transparency window of silicon (up to a wavelength of 8 μm), only requires one lithographic etch‐step and can be designed for strong light–matter interaction. Design rules, practical aspects of the fabrication process and experimental results of a complete set of elemental building blocks operating at two very different wavelengths, 3.8 and 7.7 μm, are discussed. Propagation losses as low as 0.82 dB/cm at λ0 = 3.8 μm and 3.1 dB/cm at λ0 = 7.7 μm are attained for the interconnecting waveguides. [ABSTRACT FROM AUTHOR]

An inverted lateral taper with one vertical discrete step was designed for a medium confinement silicon nitride waveguide platform in the C‐band, as a chip edge coupler, with a predicted insertion loss of 0.58 dB. The design is supported by an extensive study to evaluate the impact of fabrication process variations on the performance of such a coupler. The device was manufactured and measured, showing an insertion loss of 1.47 dB, which was traced back to fabrication process variations as cross‐checked with simulations. To the authors' knowledge, the reported edge coupler is the shortest and among the best performing found for silicon nitride platforms. [ABSTRACT FROM AUTHOR]

Two principal two‐stage switch architectures (cascaded and parallel), both of which are composed of two identical optical crossbar switches with an extra set of inputs and outputs, are compared in terms of their number of crosspoints, switch control complexities, and key optical performances, such as insertion loss and crosstalk power, through theoretical analysis. The authors begin by briefly introducing a known N × N cascaded optical crossbar switch with N2 /2 crosspoints, where N is the switch size, and present a new functional perspective based on quasi‐bitonic sorting. Subsequently, the authors derive two types of two‐stage parallel optical crossbar switches with reduced crosspoints from a conventional single‐stage parallel crossbar switch with N2 + 2N crosspoints. The first type uses two N /2 × N asymmetric switches in parallel, both of which are embedded in a single N /2 × N /2 crossbar switch. It has (N2 + 2N)/2 crosspoints and suffers from a complex switch control of O (N2). The second type is equivalent to a three‐stage Benes network and exploits bidirectional transmission to reduce the number of switching stages. It requires (N2 + 3N)/2 crosspoints, but has a dramatically reduced switch control complexity of O (N), and significantly improved optical performance. [ABSTRACT FROM AUTHOR]

Holographic lithography has been widely used to the realisation of complex photonic structures such as photonic crystal and quasi‐photonic crystals. Dual‐beam multi‐exposure holographic technique was adopted for the fabrication of 18‐fold and 36‐fold sub‐microscopic rotational symmetric structures; the fabricated photonic quasi‐crystals examined by laser diffraction pattern, optical and scanning electron microscopes. Here, the authors have fabricated photonic quasi‐crystals in photoresist and the structure was transformed into metal, the transferred structure in metal could act as a substrate/or back reflector for the thin film solar cell. Further work on concentration of solar light by photonic quasi‐crystals is progressing. [ABSTRACT FROM AUTHOR]

The authors have developed a new heterogeneous‐integration method for fabricating semiconductor lasers with high modulation efficiency on Si substrates. The method employs the direct bonding of an InP‐based active layer to the SiO2 layer of a thermally oxidised Si substrate (SiO2 /Si substrate), followed by the epitaxial growth of InP to form a buried heterostructure (BH). By using the InP membrane, the authors realise epitaxial growth of an InP on the InP membrane directly bonded to Si without crystal quality degradation. Both a theoretical estimation and photoluminescence measurements revealed that the total laser thickness must be less than the critical thickness determined by the applied thermal strain. The authors confirmed that the crystal quality of the BH is comparable to that fabricated on an InP substrate when using a 250‐nm‐thick InP‐based membrane. A distributed feedback laser fabricated on a SiO2 /Si substrate exhibited continuous‐wave operation up to 100°C and was directly modulated by a 40 Gbit/s non‐return‐to‐zero signal with a bias current of 15 mA. These results indicate that epitaxial growth using a directly bonded InP‐based active layer on a SiO2 /Si substrate allows us to achieve lasers with high modulation efficiency and to use a large‐scale Si wafer as a fabrication platform, resulting in low‐cost fabrication. [ABSTRACT FROM AUTHOR]

A theoretical study of nano‐plasmonic couplers constructed using aluminium arsenide (AlAs) and alumina (Al2 O3) is presented. The analysis has been done using the finite difference time domain technique. The dependence of coupling efficiency on the width of the air layer of silver–air–silver waveguide has been investigated to determine the optimal width of air. Coupling efficiency with the variation in input signal wavelength, reflection coefficient and return loss have been calculated numerically in order to characterise the performance of AlAs and Al2 O3 as nano‐plasmonic couplers. The resonant peaks have also been obtained for both AlAs and Al2 O3. The couplers provide appreciable performance at 1550 nm wavelength and have simple rectangular shape with no tapering which provides advantage in the fabrication process. It also offers broadband operation. [ABSTRACT FROM AUTHOR]

Quantum well laser diodes with low far‐field divergence remain a requirement for many applications such as optical interconnects and data networks, pump sources and next generation holographic red–green–blue displays requiring compact, high power, visible light sources with high spatial and spectral coherence. Many designs exist, but the structure must be easy to grow reproducibly, which has commercial advantages. The authors' low far‐field divergence design widens the vertical mode in such a way as to decrease the far‐field divergence without significantly reducing the confinement factor, thus keeping threshold current lower. In this study, the authors calculate the sensitivity of their design, which has high refractive index mode expansion layers inserted in the cladding, to unintentional variations in layer thickness and composition during growth. They obtain consistency in measured far‐fields for three wafers grown over an interval of a year, with a full‐width‐half‐maximum vertical far‐field divergence of 17° for a narrow design (Design A) and just under 13° for a very narrow design (Design B). They have demonstrated a useful, reproducible design, adding to the range of versatile semiconductor lasers available for every application. [ABSTRACT FROM AUTHOR]

The authors report 1.3‐μm InAs/GaAs quantum‐dot (QD) lasers monolithically grown on a Si substrate by optimising the dislocation filter layers (DFLs). InAlAs/GaAs strained layer superlattices (SLSs) have been presented as DFLs in this study. A distinct improvement in the InAs/GaAs QDs was observed when using InAlAs/GaAs SLSs because of the effective filtering of threading dislocations. Consequently, a laser with a threshold current density of 194 A/cm2 at room temperature and an operating temperature as high as 85°C is successfully demonstrated. These results show the potential for integrating III–V QD materials on a Si platform via InAlAs/GaAs SLSs as DFL. [ABSTRACT FROM AUTHOR]