III-Nitride Semiconductors based Optical Power Splitter Device Design for underwater Application

In this paper, we introduce III-nitrides based 1× 4 optical power splitter for underwater optical communication applications. To the best of our knowledge, this is a first study for the design of multimode interference (MMI) and four-branch taper waveguide based on GaN/sapphire. The microstructure of GaN semiconductor grown by Metalorganic Chemical Vapor Deposition (MOCVD) on (0001) sapphire reported. The numerical experimental is conducted using the 3D FD-BPM method. The results showed that the optical power splitter has an excess loss of 0.013 dB and imbalance of 0.17 dB. The results open the opportunity for the future device using this technology for the underwater application

Design of a 1x4 Optical Power Divider Based on Y-Branch Using III-Nitride Semiconductor

Optical communications are identified as a technology that is able to meet future demands. As a passive component of optical communication, optical power dividers play an essential role. We propose a novel 1x4 optical power divider design, which is a combination of an optical power divider design using a Y-branch and an optical power divider using rectangular waveguides utilizing mode coupling phenomena from our previous researched designs. The 1x4 optical power divider design using three Y-branches and utilizing mode coupling phenomena is described in this work. The design consists of three sections: an input Y-branch, rectangular waveguides, and two output Y-branches. By utilizing mode coupling phenomena with 3 rectangular waveguides, the optical power was transferred from one waveguide to its adjacent, so we obtained a wider splitting angle at the input Y-branch. The design was optimized using the beam propagation method (BPM) at a wavelength for optical communication of λ = 1.55 µm. We optimized various parameters such as the width and thickness of the waveguide, splitting angles, coupling gaps, and coupling lengths by doing numerous experiments. The result shows that the proposed design was successfully split into four outputs with 0.14 dB power imbalance at four output ports and 0.12 dB excess loss through the design. The excess loss and power imbalance at varied wavelengths were also observed. The distribution of excess loss and power imbalance is almost stable through the C-band range (1530-1565 nm). The proposed design shows the possibility of a new wide-angle optical power divider design and demonstrates the development possibilities of optical interconnections at wavelengths of 1530-1565 nm

Light coupling and distribution for Si3N4/SiO2 integrated multichannel single-mode sensing system

We present an efficient and highly alignment-tolerant light coupling and distribution system for a multichannel Si3 N4 /Si O 2 single-mode photonics sensing chip. The design of the input and output couplers and the distribution splitters is discussed. Examples of multichannel data obtained with the system are given

Machine Learning in Confocal Laser Microscopy and Spectroscopy

Confocal laser scanning microscopy (CLSM) is a preferred method for obtaining optical images with submicron resolution. Replacing the pinhole and detector of a CLSM with a digital camera (CCD or CMOS) has the potential to simplify the design and reduce cost. However, the relatively slow speed of a typical camera results in long scans. To address this issue, in the present investigation a microlens array (MLA) was used to split the laser beam into 48 beamlets that are focused onto the sample. In essence, 48 pinhole-detector measurements were performed in parallel. Images obtained from the 48 laser spots were stitched together into a final image.Photoluminescence (PL) spectroscopy is a non-destructive optical method that is widely used to characterize semiconductors. In the PL process, a substance absorbs photons and emits light with longer wavelengths. This paper discusses a method for identifying substances from their PL spectra using machine learning, a technique that is efficient in making classifications. Neural networks were constructed by taking simulated PL spectra as the input and the identity of the substance as the output. Six different semiconductors were chosen as categories: gallium oxide (Ga2O3), zinc oxide (ZnO), gallium nitride (GaN), cadmium sulfide (CdS), tungsten disulfide (WS2) and cesium lead bromide (CsPbBr3). The developed algorithm has a high accuracy (>90%) for assigning a substance to one of these six categories from its PL spectrum.With an XY stage, a CLSM can scan a large area on a sample. Adjusting the height of the objective is necessary which made the laser beam could focus on the sample surface. However, if the surface of the sample is not flat, the laser spot will go in and out of focus, causing bad scanning results. Deep learning especially convolutional neural networks is an efficient way to treat images. It shows its success in the field of object detection, image classification, face recognition, etc. The deep learning techniques were used to design a model that predicts the out-of-focus distance with the image of laser spot. The model can develop to a system that could automatically focusing the CLSM in real time

Electro-optical And All-optical Switching In Multimode Interference Waveguides Incorporating Semiconductor Nanostructures

The application of epitaxially grown, III-V semiconductor-based nanostructures to the development of electro-optical and all-optical switches is investigated through the fabrication and testing of integrated photonic devices designed using multimode interference (MMI) waveguides. The properties and limitations of the materials are explored with respect to the operation of those devices through electrical carrier injection and optical pumping. MMI waveguide geometry was employed as it offered advantages such as a very compact device footprint, low polarization sensitivity, large bandwidth and relaxed fabrication tolerances when compared with conventional single-mode waveguide formats. The first portion of this dissertation focuses on the characterization of the materials and material processing techniques for the monolithic integration of In0.15Ga0.85As/GaAs self-assembled quantum dots (SAQD) and InGaAsP/InGaAsP multiple quantum wells (MQW). Supplemental methods for post-growth bandgap tuning and waveguide formation were developed, including a plasma treatment process which is demonstrated to reliably inhibit thermally induced interdiffusion of Ga and In atoms in In0.15Ga0.85As/GaAs quantum dots. The process is comparable to the existing approach of capping the SAQD wafer with TiO2, while being simpler to implement along-side companion techniques such as impurity free vacancy disordering. Study of plasma-surface interactions in both wafer structures suggests that the effect may be dependent on the composition of the contact layer. The second portion of this work deals with the design, fabrication, and the testing of MMI switches which are used to investigate the limits of electrical current control when employing SAQD as the active core material. A variable power splitter based on a 3-dB MMI coupler is used to analyze the effects of sub-microsecond electrical current pulses in relation to carrier and thermal nonlinearities. Electrical current controlled switching of the variable power splitter and a tunable 2 x 2 MMI coupler is also demonstrated. The third part of this dissertation explores the response of In0.15Ga0.85As/GaAs SAQD waveguide structures to photogenerated carriers. Also presented is a simple, but effective, design modification to the 2 x 2 MMI cross-coupler switch that allows control over the carrier distribution within the MMI waveguide. This technique is combined with selective-area bandgap tuning to demonstrate a compact, working, all-optical MMI based switch

Integrated Inp Photonic Switches

Photonic switches are becoming key components in advanced optical networks because of the large variety of applications that they can perform. One of the key advantages of photonic switches is that they redirect or convert light without having to make any optical to electronic conversions and vice versa, thus allowing networking functions to be lowered into the optical layer. InP-based switches are particularly attractive because of their small size, low electrical power consumption, and compatibility with integration of laser sources, photo-detectors, and electronic components. In this dissertation the development of integrated InP photonic switches using an area-selective zinc diffusion process has been investigated. The zinc diffusion process is implemented using a semi-sealed open-tube diffusion technique. The process has proven to be highly controllable and reproducible by carefully monitoring of the diffusion parameters. Using this technique, isolated p-n junctions exhibiting good I-V characteristics and breakdown voltages greater than 10 V can be selectively defined across a semiconductor wafer. A series of Mach-Zehnder interferometric (MZI) switches/modulators have been designed and fabricated. Monolithic integration of 1x2 and 2x2 MZI switches has been demonstrated. The diffusion process circumvents the need for isolation trenches, and hence optical losses can be significantly reduced. An efficient optical beam steering device based on InGaAsP multiple quantum wells is also demonstrated. The degree of lateral current spreading is easily regulated by controlling the zinc depth, allowing optimization of the injected currents. Beam steering over a 21 microns lateral distance with electrical current values as low as 12.5 mA are demonstrated. Using this principle, a reconfigurable 1x3 switch has been implemented with crosstalk levels better than -17 dB over a 50 nm wavelength range. At these low electrical current levels, uncooled and d.c. bias operation is made feasible. The use of multimode interference (MMI) structures as active devices have also been investigated. These devices operate by selective refractive index perturbation on very specific areas within the MMI structure, and this is again realized using zinc diffusion. Several variants such as a compact MMI modulator that is as short as 350 µm, a robust 2x2 photonic switch and a tunable MMI coupler have been demonstrated

Development of passive ultrafast fiber lasers at telecom wavelengths using indium nitride as saturable absorber

This thesis focuses on the research of new technologies for fabrication of passive ultrafast mode-locked fiber lasers, operating at telecom wavelengths (C-band, 1.53-1.57 μm). For this purpose novel saturable absorbers based on indium nitride (InN) are proposed, which have been deposited using molecular beam epitaxy. This material presents unique properties such as direct band gap energy, high thermal and chemical stability, and high radiation hardness. In this thesis, the InN based structures have been completely characterized, being particularly detailed the optical characterization of both the linear and nonlinear behavior. The developed devices have demonstrated high nonlinear optical effects, with modulation depth over 30%. Moreover, they have proved to support over 100 mJ/cm2, with no sign of apparent optical damage, converting them in promising devices for high energy applications. Also, the design and fabrication of laser resonators have been carried out. For this purpose, optical fiber has been used as active medium, besides the InN-based saturable absorbers for achievement of the mode-locking. The developed lasers deliver ultrashort pulses (200-250 fs) with high peak power (over 40 kW). Furthermore, all the lasers using InN based saturable absorbers have exhibited properties such as polarization independence or self-starting operation. For all the experiments that have been performed along this work, InN can be situated as a promising material for application in the design of ultrafast lasers with emission at telecom wavelengths

Recent Advances and Future Trends in Nanophotonics

Nanophotonics has emerged as a multidisciplinary frontier of science and engineering. Due to its high potential to contribute to breakthroughs in many areas of technology, nanophotonics is capturing the interest of many researchers from different fields. This Special Issue of Applied Sciences on “Recent advances and future trends in nanophotonics” aims to give an overview on the latest developments in nanophotonics and its roles in different application domains. Topics of discussion include, but are not limited to, the exploration of new directions of nanophotonic science and technology that enable technological breakthroughs in high-impact areas mainly regarding diffraction elements, detection, imaging, spectroscopy, optical communications, and computing

Photophysical Properties of Single Photon Emitters in Hexagonal Boron Nitride

The development of photonic based quantum technologies such as quantum encryption and quantum computing is mainly restrained by the quality of single photon emitter. Effects like phonon interaction, emission purity, stability and decoherence are the major issues. So far quantum dots are leading the race in terms of indistinguishability, emission purity and stability but low collection efficiency and operation at cryogenic/low temperature are major roadblocks. Hexagonal-Boron Nitride (hBN) is a 2D material with stable single photon emission even at 800 °C. hBN is an emerging material, attracting interest from a wider research community but information about the identity of the emitting defects is very limited. The aim of this work is to use the experimental techniques to probe the emitter and comment on the possible origins of the emission.Engineering and Physical Sciences Research Council (EPSRC)Engineering and Physical Sciences Research Council (EPSRC