The work presented here demonstrated and analyzed an angled multimode interference (AMMI) waveguide optical switch with a feedback network to reduce the length of the device. The optical power in the MMI different ports was controlled by changing the phase using an optical shifter. The MMI waveguide was symmetrically excited in forward direction, giving a single symmetrical image at the output port. This signal is then split into two equal halves using a Y-junction. Each half is guided in a single mode ring-like waveguide to be coupled to the MMI as feedback sources. According to the phase shift between the two rings, the signal can be switched to one of the output ports. A 25 μm tapered waveguide was used to change the spot size and reduce the optical losses, the tapers width for the inputs and outputs was optimized to be Wt =2.1 μm to fit our 6 μm MMI width. Angled ports were used for backward excitation. The angle between the ports and the MMI at the input was optimized at an angle of 8⁰. The MMI optimized length is 127.1 μm and extinction ratio of the proposed design was 18.2 dB and 16.5 dB for the two outputs ports at an operation wavelength of 1.55 μm.
In this work, we investigated the possibilities and limitations of using the arrayed waveguide grating structure in biosensing applications where the arrayed arms region of the structure has been used as a sensing region to maximize the sensitivity and selectivity of the biosensor. The biosensor design is generic and not specific to certain analyte/gas for sensing but rather based on justifying the principle of operation of the biosensor. Here, the concept of sensing is based on the slight change in the effective index of the sensing arms of the arrayed waveguides that happens due to the direct influence of the presence of analyte/gas on the evanescent field of the sensing optical element. The design of the arrayed waveguide grating is done based on silicon nitride (Si3N4) technology due to its transparency in the very near infrared domain which facilitates the operation of the biosensor in the very near-infrared domain where negligible water (in the case of using water as an analyte) absorption values are achievable. The arrayed waveguides region is designed to allow an upper enclosure containing the analyte flow in a chamber made of polydimethylsiloxane over all arms while preserving the additive phase on each arm. The presence of the analyte with an induced refractive indices leads to altering the output wavelength output ports order in the output free propagation region. The shift of the exit wavelengths from different ports is significant to the change in the effective refractive index and consequently to the change in the analyte contents and concentration.
The fabrication of Silicon nanostructures is still a point of interest to sustain a cheaper, faster, and more effective method. This work represents a comparison approach for the fabrication of SiNWs via modified Nanosphere lithography using polystyrene nanospheres (PS-NS) as templates against the Laser Ablation method. First, the Si type-p (111) wafer was treated with Oxygen/Argon Plasma to switch the wafer to the hydrophilic state to acquire an adequate nondispersive layer of PS-NS. The PS-NS was then dispersed in ethanol with a ratio [1:1]. The monolayer deposition on the wafer was achieved via 3-steps spinning with different rpm. The sizes of the PS-NS were then controlled by dry etching, using deep reactive ion etching (DRIE) for different periods to guide the size of the SiNWs. A silver (Ag) layer was then deposited on the structure to guide the silicon etching process via metal-assisted chemical etching (MACE) to control the length of the fabricated SiNWs. Another approach was to implement metal-assisted plasma etching (MAPE) first a layer of gold (Au) was sputtered on the sample using DC-Sputtering. The surface morphology of the structure has been investigated via field effect scanning electron microscopy (FE-SEM) and atomic force microscopy, while the optical characteristics were investigated via Fourier-transform infrared spectroscopy (FTIR) and photoluminescence (PL)
Over a century ago, the study of blackbody radiation led to the development of quantum mechanics. A blackbody is a perfect absorber, absorbing all the electromagnetic light that illuminates it. There is no radiation passing through it, and none is reflected. Now, “bodies” with high absorption qualities are very important in many disciplines of research and technology. Perfect absorbers, for example, can be utilized as photodetectors, thermal pictures, microbolometers, an d thermal photovoltaic solar energy conversion. The Mid-infrared (MIR) wavelength spectrum has numerous advantages in a variety of applications. One of these uses is chemical and biological detection. In this paper, a metasurface mid -IR absorber based on the fractal technology of a doped silicon geometry resonator to realize wideband cross-fractal formation is introduced. The structure exhibits a broadband absorption within a wide range of IR wavelength spectrum extending from 3 to 9 μm. The structure was based on the Sierpinski carpet where different building blocks were simulated to reach the highest absorption. It is shown that light coupling over a broad wavelength range to the proposed fractal metamaterial absorber structure is due to multiple resonance mechanisms at different wavelengths. The propo sed structure is CMOS-compatible. Moreover, this proposed design opens the door to the development of new silicon -based absorbers for different applications such as energy harvesting and photodetection.
Silicon nitride (SiN) and silicon dioxide (SiO2) are high-index and low-index refraction materials that qualify them for waveguide applications. Here, we present the SiN thin film by studying hydrogen content on the surface of the fabricated thin films. The SiN thin films were deposited via plasma-enhanced chemical vapor deposition (PECVD) on a P-type (111) Silicon wafer with a silicon dioxide layer of 1 micron and resistivity of ~ 100 ohm-cm. Hydrogen bonds are formed on the thin-film surface which causes high propagation loss as both N-H bonds and Si-H bonds lead to absorption in the telecom spectrum. Ammonia-free deposition was utilized using only silane (SiH4) and nitrogen (N2) as precursors gases in PECVD run to reduce the hydrogen content. Process pressure was kept constant at 650 mTorr, varying the (SiH4) concentration, RF power and temperature. The thicknesses of the deposited thin films were kept ~300 nm determined by scanning electron microscopy (SEM). while surface roughness was examined using atomic force microscopy (AFM). The hydrogen bonding content was studied using Raman, Fourier-transform infrared spectroscopy (FTIR) and Photoluminescence.
In this work we provide a numerical simulation for doped silicon nanosphere with a validation using 3D FDTD commercial kit (Lumerical). We have calculated the absorption efficiency of silicon microspheres of different doping concentration based on Mie resonance. Meanwhile, filling the surrounding medium with specific gases which have absorption in the MIR region changes the calculated spectrum. The input parameters for this simulation were the radius of the sphere, the complex refractive index of the sphere’s material and the host gas, and the targeted wavelength range. The absorption spectra were calculated for a silicon microsphere of radius 0.5 microns and different doping concentrations. In each case, the microsphere is surrounded with air and then with Methane. There is no peak shift between the two curves. However, there is an oscillation in the curve of Methane in the wavelength range where the absorption region of Methane lies. Increasing the doping concentration of silicon makes the absorption curve of sphereair shift to the left (blue shifted). This in turn makes this oscillation more visible, especially at doping concentration of 5×1020 cm-3. This can be explained that, increasing the doping concentration makes the silicon sphere more metal alike and increases in turn the surface plasmonic effect. That opens the door for multitude of sensing applications using the concept of Mie resonance.
Tunable finesse optical filters and resonators are required for some applications when the signal-to-noise ratio and spectral resolution are traded-off to optimize the system performance. They can be used as well to control the amount of energy stored inside the resonator that can be used for optical trapping and atomistic studies. In this work we report a tunable finesse optical MEMS filter in deeply-etched SOI technology. The structure is composed of an optical cavity formed between a multilayer dielectric-coated optical fiber and slotted micromirror, attached to a comb-drive actuator. The cavity length between the multilayer Bragg coated fiber and the slotted micromirror is constant, while the slit width is being varied. The slit width is controlled by the applied voltage on the actuator. Changing the slit width modulates the reflectivity of the micromirror; and hence the finesse of the optical cavity. The obtained finesse is tuned by a factor of 5 across the band of 1330 nm and 1550 nm.
In this work we report a novel optical MEMS deeply-etched mirror with metallic coating and vertical slot, where the later allows reflection and transmission by the micromirror. The micromirror as well as fiber grooves are fabricated using deep reactive ion etching technology, where the optical axis is in-plane and the components are self-aligned. The etching depth is 150 μm chosen to improve the micromirror optical throughput. The vertical optical structure is Al metal coated using the shadow mask technique. A fiber-coupled Fabry-Pérot filter is successfully realized using the fabricated structure. Experimental measurements were obtained based on a dielectric-coated optical fiber inserted into a fiber groove facing the slotted micromirror. A versatile performance in terms of the free spectral range and 3-dB bandwidth is achieved.
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