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Layer Structured Materials for Photonics
Published in Tuan Anh Nguyen, Ram K. Gupta, Nanotechnology for Light Pollution Reduction, 2023
Felipe M. de Souza, Ram K. Gupta
An example of Ge–Sb–Te use has been performed by Wu et al. [5] developed an efficient optical switch that presented less than 1 dB of insertion loss for the output ports along with up to 20 dB of switching extinction ratio. The satisfactory performance was attributed to the fast n and extinction coefficient among the two Ge–Sb–Te phases. Another factor for that was due to the patterning of Ge–Sb–Te in a nanoscale below wavelengths, likely improving optical confinement and reduction of mode leakage. On top of that, Ge–Sb–Te was placed at the field maximum of the optical mode. Through that, phase transition was improved, which led to a better switching process and avoidance of optical loss. Within those lines, a 1 × 2 optical switch was assembled based on the phase transition of a Ge–Sb–Te film that was incorporated into a microring resonator. In that sense, when Ge–Sb–Te was in its amorphous phase, there was a resonant signal that coupled with the microring leading to outputs from the drop port. On the other hand, when Ge–Sb–Te was in its crystalline phase, there was a decoupling with the microring leading to outputs from the through port. The scheme for that system is provided in Figure 15.2.
Thermo-Optic Devices
Published in Kenichi Iga, Yasuo Kokubun, Encyclopedic Handbook of Integrated Optics, 2018
Thermo-optic (TO) effects, which are refractive index changes caused by temperature variations in a material, have been used when constructing optical switches. TO switches have been developed for a variety of applications in photonic networks including OADM and OXC systems. These switches are mainly used to provide lightpaths and system protection because the switching speed of passive TO switches is usually only of millisecond order [3]. For these applications, the switches are used inside OXCs to reconfigure them to support new lightpaths. The challenge here is to realize large switches. For protection applications, the switches are used to move the traffic stream from a primary fiber to another fiber should the former fail. Small 2 × 2 switches are usually sufficient for this purpose. In addition to switching time, other important parameters used to characterize the suitability of a switch for optical networking applications are insertion loss, the extinction ratio between on and off states, crosstalk, polarization-dependent loss (PDL), and wavelength dependence, which will be reviewed in some detail. The state of integration of optical switches is considerably less than that of electric switches as illustrated by the fact that a 16 × 16 optical switch is currently considered a large switch.
Optical Switches
Published in Abdul Al-Azzawi, Photonics, 2017
Many optical networks integrate optical switches into their design. Opto-mechanical switches redirect optical signals from one port to another by moving a fibre tube assembly or an optical component, such as a mirror or prism. There are many different types of optical switches incorporated into networks. In practice, most optical switches are still operated mechanically and controlled by an electronic control circuit. Speed is a crucial parameter in network applications, since a high-speed data transmission of tenths of milliseconds is required. In the near future, dynamic optical routing will require much faster switching speeds. More technology exists for optical switches than any other functional component within the optical network. Researchers are developing optical switches to increase the number of outputs, and to reduce size, cost, and switching time. Presently, optical switches include many types, for example: opto-mechanical switches, thermo-optic switches, electro-optic switches, micro-electro-mechanical switches (MEMS), and micro-optomechanical switches (MOMS). New types of optical switches are in the research and development stages.
1×5 Microfluidic optical switch using double drives
Published in Journal of Modern Optics, 2021
Jing Wan, WenZhi Yuan, YiJing Chen, Xu Zhu, MingRui Guo, Peng Xu
The optical switch [1] can selectively turn on and off optical signals or switch from one channel to another. It is one of the key parts of various optical circuits and is often applied in the optical communication network such as remotely reconfigurable add-drop multiplexers, optical protection, optical cross-connections (OXCs), signal detection and sensing. It is also used in the fibre laser [2], optical multiplexer [3], the display device [4] and other optoelectronic systems. Common optical switches are the micro-electromechanical systems (MEMS) switch [5], the electro-optic switch [6] and the thermo-optic switch [7]. The MEMS optical switch has a large volume and poor stability due to movable mechanical components. Other switches usually have large insertion loss and need temperature compensation. There are also other types of optical switches. For example, Zhang et al. [8] demonstrated a microring based 2 × 2 optical switch, which has insertion losses of 0.9 and 2 dB at two exit ports, respectively. Xie et al. [9] reported a tunable optical switch based on epsilon-near-zero metasurface, which has an extinction ratio of 5 dB.
Thermoelectric and optical properties of the SrS graphene by DFT
Published in Philosophical Magazine, 2020
Arash Yari, Arash Boochani, Sahar Rezaee
The imaginary epsilon graph is plotted in Figure 6 for x and z directions with the three mentioned approximations. In the x- and z-axes, the highest and lowest optical gap belongs to BSE and RPA approximations, respectively. The BSE and TDDFT approximations show that the SrS graphene in x and z directins has insulator behaviour, while RPA approximation shows a much smaller gap of about 2 eV. Hence, the calculations show that TDDFT approximation is much closer to the real optical behaviour of the material than the two other approximations, and these two approximations fit better with the bandstructure and DOS diagrams. Along the x-axis, the BSE approximation has a blue shift compared to TDDFT, and the RPA approximation has a redshift. The peaks of the imaginary epsilon curve represent the electron transitions from occupied to unoccupied levels, thus, this transitions occur at the maximum of 5–15 eV along the x-axis with the TDDFT approximation, which is due to the electron transition from the p levels of S to the empty d orbitals of Sr. Along the z-axis, another redshift is observed for RPA, but there is a major difference between RPA and TDDFT diagrams, so that in RPA at the energy 2.5 eV, we repeatedly see peaks and valleys with less slope and less sharpness than the two other approximations, while this approximation contradicts the 2D nature of SrS, because we see dangling bonds in the z direction. We expect the behaviour of the imaginary ε to be serrated, and more sharper, and the peaks take a form more similar to Dirac shape. Thus, the RPA approximation is less realistic than both the BSE and TDDFT approximations. However, at high energies of about (10–20 eV), the TDDFT and BSE approximations behaviour are even more different, as we observe repeating sharp peaks in the BSE approximation after 8 ev until 15 eV, while in the TDDFT approximation, there is a 3 eV gap in the range of 10–13 eV. By looking at the bandstructure diagram, it is found that the TDDFT approximation is more realistic because there is a band gap at the range of 2–11 eV, thus, electron transition in this area is weak. The imaginary epsilon shows that the optical band gap changes with the angle of incident light. Therefore, the optical and electrical responses to the reflected light will be different, and this structure can be used as an optical switch. In the z direction, we see sharp peaks that represent optical instability, while in the x direction, the graphs are flattened and show a higher optical stability.
Correlative studies on the fabrication of poly(styrene-methyl-methacrylate-acrylic acid) colloidal crystal films
Published in Journal of Dispersion Science and Technology, 2019
Hilary I. Ifijen, Esther U. Ikhuoria, Stanley O. Omorogbe
In recent years, Colloidal particles with narrow size distributions have found a wide range of captivating applications in area such as; catalysis, coatings, corrosion protection, medicine, chromatography packing materials, ion-exchange beads, calibration standards, drug delivery and medical diagnostics[1–3] etc. One of the major challenges researchers have faced over the years has been to arrive at optimal reaction conditions for the preparation of reproducible monodispersed polymer colloidal particles for the fabrication of colloidal crystals. As a result of this, several studies have investigated the impact of experimental reaction conditions such as temperature, stirring speed, initiation concentration etc. on the particle sizes and morphology of polymer colloidal suspension prepared via the emulsion polymerization method.[4,5] However, there is limited information on studies involving the synthesis and applications of poly(styrene-methylmethacrylate-acrylic acid) P(St-MMA-AA) microspheres as more elaborate studies have been carried out on homopolymers compared to terpolymers. Of particular interest, is P(St-MMA-AA) which is considered to be a terpolymer because it can be obtained from the polymerization of three different monomers (styrene, methyl methacrylate and acrylic acid). The incorporation of the polar acrylate and carboxylic functional groups into the interstice of the non-polar PS microspheres introduces a certain level of polarity in the P(St-MMA-AA) colloidal microspheres. This also improves the hydrophilic property of the terpolymer latex by strengthening the hydrogen bond connections on the carboxyl functional groups in the surface of the colloidal spheres when compared with the typical PS films.[6] Its unique nature makes it possible to obtain interesting and useful functionalities by assembling their colloidal suspension into periodically structured materials with periodicity, whose length and scale is proportional to visible wavelengths.[7] These types of materials are known as photonic crystals. They have unique properties which give an opportunity for a number of applications such as sensory, filtering, fabrication of optical switches, and other optical devices.[8] Several researchers have investigated the preparation of monodisperse polystyrene (PS) colloidal microspheres with different particle sizes via emulsifier-free emulsion polymerization method by varying certain reaction conditions such as reaction time, ionic strength of the system, initiator concentration and other experimental conditions on the particle sizes of the polystyrene colloidal spheres[5] whereas, this cannot be said for P(St-MMA-AA) latex as less research work has been carried out on this terpolymer compared to PS. Previous studies have assembled series of monodispersed P(St-MMA-AA) colloids having different diameters to obtain colloidal crystals.[9–11] However, the effect of varying experimental reaction conditions on the particle sizes of the prepared terpolymer samples was not investigated.