Modulation of coupling in a photonic switch by resonant interference

A novel photonic switch structure is described in which the coupling of light between two fiber waveguides is controlled by the resonant interference of a third waveguide. The switching action is controlled by a small variation of the index of refraction of the control waveguide by the application of either photo-optical (Kerr) techniques or electro-optical (Pockels) techniques. The control waveguide can be either a fiber waveguide or a slab waveguide. The equations for the waveguide coupling were obtained by analytical approximations from coupled-mode theory. A beam-propagation simulation was also used. The results of the two models were compared. Multiple resonant interferences were observed in the case of a slab waveguide.     

Optical nonlinearity in photonic glasses

A brief review on optical nonlinearity in photonic glasses is given. For the third-order, relationship between two-photon absorption and nonlinear refractive-index is considered using a formalism developed for crystalline semiconductors. Stimulated light scattering and super-continuum generation in optical fibers are also introduced. Prominent resonant-type nonlinearity in particle-embedded glasses is described. For the second-order, a variety of poling methods are summarized. Finally, it is pointed out that different photoinduced changes can appear when excited by linear and nonlinear optical processes, and the feature is related with glass structures.     

Acousto-optic photonic crossbar switch. Part I: design

We present the design of a 12 × 12 photonic crossbar interconnection network constructed using a single three-dimensional acousto-optic crystal. Previous crossbars based on bulk acousto-optic cells require multichannel deflectors with one deflector per optical input; in contrast the design presented here angularly multiplexes these independent deflectors into a single-transducer acousto-optic device. A Fourier-optics analysis of an acoustically lossy Bragg deflector is coupled to a momentum-space analysis that permits the derivation of complete design equations for the switch. As a concrete example, the complete design of a 12 × 12 crossbar is presented. Finally, a coupled-mode analysis of the first- and second-order diffractions in the angularly multiplexed Bragg cell reveals the fundamental efficiency bounds of the switching network.     

Analysis of an optically controlled photonic switch

The principle that the coupling of light between two fiber waveguides can be controlled by the resonant interference of a third waveguide has been developed [Attard, Appl. Opt. 37, 2296-2302 (1998)]. Here significant details concerning the operation of a photonic switch are obtained, and a more complete analysis is presented. Multiple-resonant conditions are identified for slab and fiber control waveguides at large indices of refraction. Thus a selection of materials with an appropriate refractive index and a Kerr coefficient is rendered more easily. Furthermore it is shown that the light used to control the index of refraction in the control waveguide does not enter the output of the photonic switch but remains confined to the control waveguide, for either a slab or a multimode fiber control waveguide. Spatial fluctuations of the control light beam in the control waveguide do not affect the operation of the photonic switch. Tolerances have been determined for the spacing between the control waveguide and the photonic coupler and also for the index of refraction of the control waveguide.     

Terahertz wave switch based on silicon photonic crystals

A compact and integrated terahertz (THz) wave photonic crystal switch is proposed in silicon. The switch operates based on a dynamic shift of the photonic bandgap by using an external applied electric field. The plane wave expansion method and the finite-difference time-domain method are used to verify and analyze the characteristics of the proposed THz wave switch. Numerical simulation results show that the THz wave switch has a high extinction ratio of 29.9 dB.     

Compact carrier-injection photonic crystal switch for on-chip communications

Performances and metrics of an electro-optical wavelength switch in silicon?on- insulator technology using a 20 μm long photonic crystal directional coupler structure are theoretically studied using both electrical and finite difference time domain simulations. The possibility of photonic switching through carrier injection using a forward-biased PIN diode configuration is evaluated. It is shown that wavelength routing near λ=1550 nm with optical insertion loss of 1 dB and an electrical cut-off frequency of 60 MHz can be achieved with a bias voltage of 1 V and a dissipated electrical power of 700 μW. Integration of the device could be applied to active routing of light in silicon chips for the realisation of on-chip switching networks.     

Optical smart-pixel-based Clos crossbar switch

We present the design of an optically interconnected Clos crossbar switch that uses three smart-pixel devices. This optical Clos architecture is also well matched to a space-wavelength switch that arbitrarily permutes data streams between wavelength-division multiplexed channels on an array of fibers. We have designed a hybrid complementary metal-oxide semiconductor-self-electro-optic device (CMOS-SEED) crossbar smart-pixel array for use in a 16-channel optical Clos switch. The crossbar devices also have an 8 x 8 array of multiple-quantum-well diodes that can be configured electrically as modulators with eight bit planes of randomly addressable local memory or as receivers with adjustable gain and threshold. We show that the current hybrid-SEED technology should support a 1024-channel Clos switch operating at 500 Mbits/s per channel if pixel power consumption can be reduced.     

Bitapered fiber coupling characteristics between single-mode single-core fiber and single-mode multicore fiber

By splicing and tapering at the fusion point of one-core single-mode fiber and three- or four-core single-mode fiber, an effective bitapered fiber coupling technique is implemented. Based on the beam propagation method, the bitapered coupling characteristics between the one-core fiber and the multicore single-mode fiber are simulated and analyzed. The theoretical prediction is confirmed by the experimental results, and the difference between the simulation and the experimental results is also discussed.     

Optical interleavers based on two-dimensional photonic crystals

An ultrasmall device size optical interleaver based on directional coupler waveguides in two-dimensional photonic crystals (PCs) is proposed. The numerical results show that the proposed PCs waveguide structure could really function as an interleaver with the central wavelength 1550 nm and the channel spacing 0.8 nm (frequency spacing of 100 GHz) of the dense wavelength division multiplexing (DWDM) specification. It can be widely used as the wavelength selective element for multiplexer-demultiplexer to lower or raise channel densities in DWDM optical fiber communication systems.     

Optical signal processing using photonic reservoir computing

As a new approach to recognition and classification problems, photonic reservoir computing has such advantages as parallel information processing, power efficient and high speed. In this paper, a photonic structure has been proposed for reservoir computing which is investigated using a simple, yet, non-partial noisy time series prediction task. This study includes the application of a suitable topology with self-feedbacks in a network of SOA’s – which lends the system a strong memory – and leads to adjusting adequate parameters resulting in perfect recognition accuracy (100%) for noise-free time series, which shows a 3% improvement over previous results. For the classification of noisy time series, the rate of accuracy showed a 4% increase and amounted to 96%. Furthermore, an analytical approach was suggested to solve rate equations which led to a substantial decrease in the simulation time, which is an important parameter in classification of large signals such as speech recognition, and better results came up compared with previous works.     

Optical properties of carbon nanofiber photonic crystals

Carbon nanofibers (CNFs) are used as components of planar photonic crystals. Square and rectangular lattices and random patterns of vertically aligned CNFs were fabricated and their properties studied using ellipsometry. We show that detailed information such as symmetry directions and the band structure of these novel materials can be extracted from considerations of the polarization state in the specular beam. The refractive index of the individual nanofibers was found to be n(CNF) = 4.1.     

Ultracompact photonic coupling splitters twisted by PTT nanowires

We report a series of ultracompact photonic coupling splitters with multi-input/output ports assembled by twisting flexible polymer nanowires, which were fabricated by one-step drawing method from poly(trimethylene terephthalate) (PTT). Experimental demonstration shows that the properties of the splitters are dependent on the operation wavelength and the input branch of the optical signal launched. For a fixed operation wavelength and the input branch, desirable splitting ratio can be tuned by controlling the input/output branching angle. The excess loss of these splitters is less than 1 dB, and the intrinsic loss is less than 0.4 dB. They are desirable for high density photonic integrated circuits (PICs) and nanonetworks, while the twisting technology will be useful in constructing other wire-based photonic devices.     

Optical properties and photonic modes in patterned semiconductor systems

The optical response of a photonic crystal slab, where a dielectric grating is the elementary building block, is computed in the semiclassical framework, and compared with the dispersion curves of the bulk. The formalism adopted for the calculation employs the eigenmodes of a single layer as basis set for electromagnetic field expansion; it allows us to compute photonic crystal slab optical response as well as dispersion curves. Recently, the method was generalized to take into account spatial dispersion effects close to an exciton resonance of the system, and it was possible also to study the transition from dissipative to dispersive regime for a system under Bragg condition. The role of bulk and surface waves in the system is discussed as a function of the layer number N in the range N = 1 ÷ ∞. The “mirror effect”, observed in rectangular self-sustained gratings, due to the interplay among traveling, evanescent and guided waves, is recovered. This effect can be preserved also in the semi-infinite photonic crystal for selected values of the physical parameters. The role of light polarization in 1D and 2D systems is briefly discussed.     

Optical switch from silver nanocomposite thin films

Silver nanoparticles capped with sodium alginate were assembled into thin films by using the layer-by-layer dipping technique. Composite films were built by sequential dipping of a glass slide in either anionic alginate capped nanoparticles or cationic Poly(diallyldimethylammonium chloride) (PDADMAC). The growth of the film was characterized using UV-Vis spectroscopy by monitoring the increase in absorbance at 420 nm which correspond to the silver nanoparticles plasmon band. The final films formed onto glass slides displayed and interesting color shift upon exposure to water or to a less polar solvent such as ethanol. In this research, changes in spectral absorbance of the nanoparticles film were monitored as a function of ethanol content (0, 20, 40, 60, 80 and 100%) in water. The color shift from yellow to red color was explained by the changes in the dielectric constant of the silver nanoparticles surrounding medium which induce a shift in their plasmon band absorbance. These composite thin films displayed fast color change and could therefore be used in sensing application as well as for optical switches.     

Optical properties of three-dimensional magnetic opal photonic crystals

We have studied the optical properties of opal photonic crystals infiltrated with the M_0.35Zn_0.65Fe₂O₄ (M = Ni, Co) ferrites. The crystals consisted of amorphous SiO₂ nanospheres. The visible reflectivity spectra of the crystals were used to determine parameters of their photonic band gap and their refractive index.     

Optical modulator based on coupled photonic crystal cavities

Abstract

We propose and numerically investigate an optical signal modulator based on two-photonic crystal nanobeam cavities coupled through a waveguide. The suggested modulator shifts the resonant frequency over a scalable range. We design a compact optical modulator based on photonic crystal nanobeams cavities that exhibits high stability to manufacturing. Photonic crystal waveguide tuning in the low-intensity region of the resonant mode is demonstrated. The advantages of the suggested approach over the single-resonator optical modulator approaches include the possibilities to shift the modulator frequency over a scalable range that depends on switching energy level and to effectively electrically tune the device in the low-intensity region of the resonant mode.     

Optical properties of a carbon-zirconia quantum-dot photonic crystal

We report the optical properties of a new type of photonic crystal: a transparent fused silica matrix containing quantum dots—nanoparticles of another material. In this study, nanoparticles consist of graphite zones several nanometers in size, stabilized by zirconia. The photonic crystal is prepared by high-temperature annealing (1200°C) of synthetic opal infiltrated with zirconia and a small amount of carbon. We demonstrate selective reflection of visible light from the surface of the quantum-dot crystal under broadband illumination. Such crystals are potentially attractive as narrow-band selective filters that would reflect the exciting light in Raman measurements and might be used to convert short-wavelength broadband radiation to quasi-monochromatic light in the visible range.