Optical switching

Focusing and guiding light into semiconductor nano-structures can deliver revolutionary concepts for photonic devices, which offer a practical pathway towards next-generation power-efficient optical networks. In this review, we consider the prospects for photonic switches using semiconductor quantum dots (QDs) and photonic cavities which possess unique properties based on their low dimensionality. The optical nonlinearity of such photonic switches is theoretically analysed by introducing the concept of a field enhancement factor. This approach reveals a drastic improvement in both power-density and speed, which is able to overcome the limitations that have beset conventional photonic switches for decades. In addition, the overall power consumption is reduced due to the atom-like nature of QDs, as well as the nano-scale footprint of photonic cavities. Based on this theoretical perspective, the current state-of-the-art QD/cavity switches are reviewed in terms of various optical nonlinearity phenomena that have been utilized to demonstrate photonic switching. Emerging techniques, enabled by cavity nonlinear effects such as wavelength tuning, Purcell-factor tuning and plasmonic effects, are also discussed.

With the rapidly increasing aggregate bandwidth requirements of data centers there is a growing interest in the insertion of optically interconnected networks with high-radix transparent optical switch fabrics. Silicon photonics is a particularly promising and applicable technology due to its small footprint, CMOS compatibility, high bandwidth density, and the potential for nanosecond scale dynamic connectivity. In this paper we analyze the feasibility of building silicon photonic microring based switch fabrics for data center scale optical interconnection networks. We evaluate the scalability of a microring based switch fabric for WDM signals. Critical parameters including crosstalk, insertion loss and switching speed are analyzed, and their sensitivity with respect to device parameters is examined. We show that optimization of physical layer parameters can reduce crosstalk and increase switch fabric scalability. Our analysis indicates that with current state-of-the-art devices, a high radix 128×128 silicon photonic single chip switch fabric with tolerable power penalty is feasible.  The applicability of silicon photonic microrings for data center switching is further supported via review of microring operations and control demonstrations. The challenges and opportunities for this technology platform are discussed.

The self-imaging property of a homogeneous multi-moded planar optical waveguide has been applied in the design optical couplers based on multimode Interference (MMI). Based on this design, the optical wavelength and dimensions tolerance for MMI-3dB couplers are investigated analytically. They are shown to be inversely proportional to the multimode section width. Among Symmetrical, paired, and general mechanism interference types, the symmetrical one has the highest optical wavelength and dimensions tolerance.

A holographic technique for fabricating an electrically switchable liquid crystal/polymer composite Fresnel lens is reported. A Michelson interferometer is used to produce the required Fresnel pattern, by placing a convex lens into one path of the interferometer. Simplicity of the method and the possibility of fabricating different focal length lenses in a single arrangement are advantages of the method. The performance of the fabricated lens was demonstrated and its electro-optical properties were investigated for its primary focal length.

The current major limiting factor in digital optical computing is a fast, efficient, cascadable optical switch with which to build computers. Candidates are not limited to the well known semiconductors and fabrication methods of electronics. A novel facility to evaluate candidate devices has been constructed. Multiline and tunable femtosecond and picosecond laser systems, as well as frequency mixing systems, are used as light sources. The facility has at least picosecond source capability from 200 nm to 2 micrometers. The switch transfer function is evaluated in a pump probe system with femtosecond and picosecond autocorrelators to measure dispersion, an optical multichannel analyzer to measure absorption, a CCD or pyroelectric camera system to measure mode modification, and a multidetector system to measure switching energy and insertion loss both in absorption and in reflection. The switch or switching array under test is mounted in a six-axis micropositioner system with a 0-20 goniometer; x, y, and z translators; and a tilt goniometer. Initial experiments on nonlinear interface optical switches are encouraging, as the selected broad bandwidth media has strong nonlinearity.

The chevron geometry in the SmC* phase of ferroelectric liquid crystals (FLC) has been a major obstacle in the use of FLC in displays as it results in poor electro-optical performance. The present paper reports a novel method to overcome this problem, by doping a small amount of polymer in the FLC matrix. In addition to the improvement in smectic ordering, polymer doping is also found to be useful in improving the vital electro-optical properties. The various electro-optical parameters like switching time, tilt angle, contrast ratio etc. show improvement in polymer mixed guest host mixture of FLC samples. POLYM. COMPOS., 31:1776–1781, 2010. © 2010 Society of Plastics Engineers.

Security is one of the most important issues in new life saving vehicular network, whereas trust is key component of security in vehicular applications. These applications serve users when components (user, vehicle and RSU) of the network behave in an expected manner in peer to peer vehicular communication. Whenever any component of the network unexpectedly changes their behavior then it would be harmful for other users of the network. In this paper, we are proposed three different trust levels in peer to peer vehicular network. Purpose of proposed trust levels to discuss in detail is the functionality of different component of network which circumvents the attacker and emphasizes the role of trusted users in peer to peer vehicular communication.

In this paper we describe the use of thermo-activated PNIPAM nano-material in optical switching devices. In other publications, the PNIPAM is used either as a carrier for crystalline colloidal array self-assemblies or as micro-particles that serve as pigment bags. In this publication we use a simpler-to-fabricate pure PNIPAM solution in a semi-dilute regime. The PNIPAM devices produced are transparent at

We analyzed the polarization-switching characteristics of a ferroelectric liquid-crystal polarization control device using a double-layer cell structure for free-space optical processing and switching systems. We theoretically derived the optimum arrangement of layered cells for 90° polarization switching. The theory shows that the optimum parameter range for the double-layer cell structure is wider than that for a single-layer cell. We verified our theory by measuring the polarization cross talk of experimental polarization control devices.

Means of steering high power optical beams by means of compact low mass technology suitable for spacecraft and microspacecraft were addressed. Non-mechanical means were sought that permit redirection of the beam over half space in times of the order of 1 microsecond or less. The effort included means for steering of optical pulses as well as continuous optical beams. The large apertures needed in space applications and the interest in structures having minimum mass and volume required attention to thin film structures with rapid switching capability that could produce large group delay in a compact structure. Mechanisms for both group delay and phase delay control were examined. New technology was identified in the form of a novel microresonator based switching element employing photonic band structures. The technology explored appears consistent with extrapolation to high average power, e.g., multi-megawatts. The work examined double clad optical fiber as the amplifying element, bu...

This work characterizes holographic polymer dispersed liquid crystals (HPDLC) composite material based on a new monomer, urethane trimethacrylate, by fabricating switchable diffraction grating. The highest diffraction efficiency achieved was 90.3%. Details of the fabrication and preliminary results of electro-optical switching of the HPDLC diffraction gratings are presented and discussed based on the functionality of the monomer. These experimental results are explained by means of morphological scanning electron microscopy analyses.

Fabrication of an all-optical switchable holographic liquid crystal (LC) Fresnel lens based on azo-dye- doped polymer-dispersed LCs is reported using a Michelson interferometer. It is found that, upon circu- larly polarized photoirradiation, the diffraction efficiency of the fabricated Fresnel lens was increased significantly in a reversible manner. We believe this is due to the anisotropy induced by reorientation of the LC molecules coupled with azo-dye molecule orientation due to trans–cis–trans photoisomeriza- tion, which modulates the refractive index of the LC-rich regions. We also studied the effect of azo dye on the polarization dependency of the fabricated lens.

Extensive testing has been done on nonlinear interface optical switch (NIOS) devices fabricated from laser deposited nonstoichiometric tungsten oxide films. A Fresnel coefficient formalism for evaluating the indices of refraction of the films has been developed. Three cycles of testing involving changing the tungsten-oxygen stoichiometry have not produced extremely large photorefractive effects. It was decided, after using a mathematical model to determine the required incident and reflection angles, to make the next set of NIOS devices from a film deposited on ZnS prisms. ZnS more closely matches the low light intensity index of the films. Preliminary studies of further changes to produce stronger nonlinearity have been performed. Raman spectroscopy showed that these films heated in oxygen organize themselves into octohedra, which are thought to be necessary for the photorefractive effects observed in titanates and niobates. Heating the films in vacuum produces blue films which ESC...

Efficient application of the electro-optic effect in a lithium-niobate-based Mach-Zehnder interferometer to construct universal gates has been demonstrated. The study is carried out by simulating the proposed device with the beam propagation method, and the results are verified using MATLAB. Various parameters influencing the performance of the device (such as speed, latency, and power consumption) also have been taken into account.

The ultrafast response of a high-reflectivity GaAs∕AlAs Bragg mirror to optical pumping is investigated for all-optical switching applications. Both Kerr and free carrier nonlinearities are induced with 100 fs, 780 nm pulses with a fluence of 0.64 and 0.8kJ/m2. The absolute transmission of the mirror at 931 nm increases by a factor of 27 from 0.0024% to 0.065% on a picosecond time scale. These results demonstrate the potential for a high-reflectivity ultrafast switchable mirror for quantum optics and optical communication applications. A design is proposed for a structure to be pumped below the band gaps of the semiconductor mirror materials. Theoretical calculations on this structure show switching ratios up to 2200 corresponding to switching from 0.017% to 37.4% transmission.

An all-optical switching device has been proposed by using self-assembled InAs/GaAs quantum dots (QDs) within a vertical cavity structure for ultrafast optical communications. This device has several desirable properties, such as the ultra-low power consumption, the micrometre size, and the polarization insensitive operation. Due to the threedimensional confined carrier state and the broad size distribution of self-assembled InAs/GaAs QDs, it is crucial to enhance the interaction between QDs and the cavity with appropriately designed 1D periodic structure. Significant QD/cavity nonlinearity is theoretically observed by increasing the GaAs/AlAs pair number of the bottom mirror. By this consideration, we have fabricated vertical-reflection type QD switches with 12 periods of GaAs/Al0.8Ga0.2As for the top mirror and 25 periods for the bottom mirror to give an asymmetric vertical cavity. Optical switching via the QD excited state exhibits a fast switching process with a time constant down to 23 ps, confirming that the fast intersubband relaxation of carriers inside QDs is an effective means to speed up the switching process. A technique by changing the light incident angle realizes wavelength tunability over 30 nm for the QD/cavity switch.