Design of a vector-sum integrated microwave photonic phase shifter in silicon-on-insulator waveguides

An orthogonal vector-sum integrated microwave photonic phase shifter (IMWPPS), consisting of mode-order converter multiplexers (MOCMs), a variable optical power splitter (VOPS), an optical switch (OS) and fixed time delay lines (FTDLs), was theoretically demonstrated in a silicon-on-insulator wafer. MOCMs, as a key element of our device, were employed to generate orthogonal vector signals and served as lossless optical combiners. Combining with the thermo-optical VOPS, OS and FTDLs, the microwave phase shift of 0～2π could be achieved by a refractive index variation of 0～15×10(-3) in the millimeter wave band. The corresponding tuning resolution was about 1.64°/°C. This work, for the first time to our knowledge, provides an attractive solution to transferring a vector-sum method based bulk MWPPS into a integrated one, which is very important for large-scale optically controlled phase array antenna.     

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.     

Dual in-plane electronic speckle pattern interferometry system with electro-optical switching and phase shifting

A dual in-plane electronic speckle pattern interferometry (ESPI) system has been developed for in situ measurements. The optical setup is described here. The system uses an electro-optical switch to change between the illumination directions for x and y sensitivity. The ability of the electro-optic device to change the polarization of the laser light forms the basis of this switch. The electro-optic device is a liquid-crystal layer cemented between two optically flat glass plates. An electric field can be set up across the layer by application of a voltage to electrodes. The speckle interferometry system incorporates two additional liquid-crystal devices to facilitate phase shifting, and the overall system is controlled by advanced software, which allows switching between the two perpendicular planes in quasi real time. The fact that there are no moving parts is an advantage in any ESPI system for which mechanical stability is vital.     

Embedded metal-wire nanograting for a multifunctional optical device

In this paper, an embedded metal-wire nanograting was fabricated and used to construct a multifunctional optical device. The basic function of the nanograting is as a broadband polarizing beam splitter. On the top of the nanograting surface, a homogeneity cladding layer was deposited, and metal wires were deposited in the grating trench. This multifunctional optical device based on the artificial material is designed with a very simple structure, but with the functions of a variable optical attenuator, an optical switch, and a variable optical power splitter. The experimental result as a variable optical power splitter is presented.     

Eigenvalue and field equations of three-layered uniaxial fibers and their applications to the characteristics of long-period fiber gratings with applied axial strain

By using the Debye potentials, the exact eigenvalue equations and the corresponding field distributions of the core and cladding modes for three-layered, radially stratified, and dielectric uniaxial optical fibers are derived completely; the modes include TE, TM, and hybrid HE/EH modes. The strain characteristics of long-period fiber gratings' (LPFGs') with applied axial strain are investigated theoretically by studying three-layered uniaxial optical fibers. When uniform axial strain is applied to fiber, the core, and inner and outer cladding become uniaxial crystal optically; that is, the optical axes are parallel to the fiber's axis. Analytic expressions of the strain sensitivities of LPFGs are derived. The analysis reveals that the strain sensitivities of LPFGs based on various cladding modes, including the shift value and direction of the resonance wavelength, differ greatly.     

Bragg fibers with matching layer

The optical properties of Bragg fibers with an intermediate (matching) layer between the core and periodic microstructured cladding have been studied. It is established that the optical losses exhibit a periodic dependence on the thickness of the matching layer, which is related to the presence of resonances and anti-resonances in this layer. It is demonstrated that the transmission spectra of Bragg fibers can be controlled by varying the parameters of the internal (matching) layer of the cladding.     

Towards an optimal model for a bistable nematic liquid crystal display device

Bistable liquid crystal displays offer the potential for considerable power savings compared with conventional (monostable) LCDs. The existence of two stable field-free states that are optically distinct means that contrast can be maintained in a display without an externally applied electric field. An applied field is required only to switch the device from one state to the other, as needed. In this paper we examine a theoretical model of a possible bistable device, originally proposed by Cummings and Richardson (Euro J Appl Math 17:435–463 2006), and explore means by which it may be optimized, in terms of optical contrast, manufacturing considerations, switching field strength, and switching times. The compromises inherent in these conflicting design criteria are discussed.     

Novel all-optical logic gate using an add/drop filter and intensity switch

A novel design of all-optical logic device is proposed. An all-optical logic device system composes of an optical intensity switch and add/drop filter. The intensity switch is formed to switch signal by using the relationship between refraction angle and signal intensity. In operation, two input signals are coupled into one with some coupling loss and attenuation, in which the combination of add/drop with intensity switch produces the optical logic gate. The advantage is that the proposed device can operate the high speed logic function. Moreover, it uses low power consumption. Furthermore, by using the extremely small component, this design can be put into a single chip. Finally, we have successfully produced the all-optical logic gate that can generate the accurate AND and NOT operation results.     

Analysis of a digital microstrip optical switch: a novel method

A time domain analysis of an optically controlled digital microstrip switch for microwave integrated circuits on Si substrates is studied. A new model for high-frequency pulse propagation on a microstrip optical switch for different optical parameters is presented. A frequency-dependent macromodel for a microstrip line with a gap is implemented in Spice 3, taking into consideration high-frequency pulse dispersion, conductor and dielectric losses, metallization thickness, gap length, and different optical parameters such as optical energy, surface recombination velocities, and diffusion of generated carriers. In addition, the developed model has been used to optimize the switching frequency, gap length, level of optical power, and suitable substrate material parameters.     

Impact of signal filling factor for switching in reflective vertical cavity-based fast semiconductor saturable absorbers

A numerical model on reflective vertical cavity-based fast semiconductor (carrier recombination time in ps regime) saturable absorbers (VC-FSSA) is investigated for all-optical high-speed future applications, where the fluctuation of cavity optical length due to thermo-optic effects and cavity heating, and optically induced carrier density change are considered simultaneously with the increase of input signal intensity. The phase-shift due to thermal-optic effects and cavity heating is very important for high-speed device performances. At first, intensity and wavelength bi-stabilities are modelled with the different intensity time filling factor of RZ modulated pump signals and also, with the different input intensities, where the intensity tuning time is considered at few μs. Then the inverse saturation characteristics of reflectivity for the universal logic operations are shown for probe signal with the proper wavelength, which can control the negative effects of optically induced heating effects. These characteristics can be used for the high-speed thermally stable bi-stable optical switch and all-optical logic applications.     

Si nanoclusters coupled to Er ions in a SiO2 matrix for optical amplifiers

In this work we will give an overview of the optical properties of Si nanoclusters coupled to Er³⁺ ions in SiO₂ matrices produced by reactive magnetron co-sputtering. We have divided the work into two separate studies realised on the same samples, which are the result of a thorough optimisation work. The first one have been realised in order to get a clear picture of the interaction mechanism. On the second we will show a quantitative evaluation of the potential performances from a material point of view (determination of the whole optically active Er³⁺ content, excitable by direct or indirect means) and actual performance in a waveguide device (determination of internal gain values).     

Controllable nonlinear effects in a hybrid optomechanical semiconductor microcavity containing a quantum dot and Kerr medium

We theoretically investigate the nonlinear effects in a hybrid quantum optomechanical system consisting of two optically coupled semiconductor microcavities containing a quantum dot and a Kerr nonlinear substrate.The steady-state behaviour of the mean intracavity optical field demonstrates that the system can be used as an all optical switch. We further investigate the spectrum of small fluctuations in the mechanical displacement of the movable distributed Bragg reflectors and observe that normal mode splitting takes place for high Kerr nonlinearity and pump power. In addition, we have shown that steady state of the system exhibits two possible bipartite entanglements by proper tuning of the system parameters. The entanglement results suggest that the proposed system has the potential to be used in quantum communication platform. Our work demonstrates that the Kerr-nonlinearity can effectively control the optical properties of the hybrid system, which can be used to design efficient optical devices.     

Wavelength tuning in optically mode-locked semiconductor fiber ring lasers with linearly chirped fiber Bragg gratings

We demonstrate wavelength tuning in single-wavelength and multiwavelength semiconductor fiber ring lasers that are mode locked with an optically injected control signal. A semiconductor optical amplifier is used to provide gain as well as to function as an optically controlled mode-locking element. Linearly chirped fiber Bragg gratings--single or superimposed--are used to define the lasing wavelengths as well as to provide wavelength tunability and allow for multiwavelength operation. We obtain pulses of tens of picoseconds in duration when we inject a sinusoidal optical control signal into the laser cavity, and we can tune the lasing wavelength(s) over the reflection bandwidth(s) of the grating(s) by simply changing the frequency of the injected control signal.     

Dual-peak long-period fiber gratings with enhanced refractive index sensitivity by finely tailored mode dispersion that uses the light cladding etching technique

We have experimentally investigated the mode dispersion property and refractive index sensitivity of dual-peak long-period fiber gratings (LPGs) that were sensitized by hydrofluoric acid (HF) etching. The nature of the coupled cladding modes close to the dispersion turning point makes the dual-peak LPGs ultrasensitive to cladding property, permitting a fine tailoring of the mode dispersion and index sensitivity by the light cladding etching method using HF acid of only 1% concentration. As an implementation of an optical biosensor, the etched device was used to detect the concentration of hemoglobin protein in a sugar solution, showing a sensitivity as high as 20 nm/1%.     

Optical implementation of the weighted sliced orthogonal nonlinear generalized correlation for nonuniform illumination conditions

Optical pattern recognition under variations of illumination is an important issue. The sliced orthogonal nonlinear generalized (SONG) correlation has been proposed as an optical pattern recognition tool to discriminate with high efficiency between objects. But, at the same time, the SONG correlation is very sensitive to gray-scale image variations. In a previous work, we expanded the definition ofthe SONG correlation to the Weighted SONG (WSONG) correlation to modify the discrimination capability in a controlled way. Here, we propose to use the WSONG when pattern recognition is obtained by means of optical correlation under nonuniform illumination. The calculation of the WSONG correlation requires the summation of many linear correlations between binary images. To implement it optically, we use a time sequential joint transform correlator.     

Reprogrammable optical phase array

A novel reprogrammable optical phase array (ROPA) device is presented as a reconfigurable electro-optic element. One specific application of the ROPA, a 1 x 6 electro-optic space switch, is fully described. Switching angles are within 2 degrees , and switching is achieved through a complementary metal-oxide semiconductor (CMOS) controlled, diffraction based, optical phase array in a bulk BaTiO3 crystal. The crystal is flip-chipped to the CMOS chip, creating a compact fully integrated device. The design, optical simulation, and fabrication of the device are described, and preliminary experimental results are presented.     

Vertical antiresonant reflecting optical waveguide coupler for three-dimensional optical interconnects: optimum design for large tolerance, high coupling efficiency, and short coupling length

A compact antiresonant-reflecting-optical-waveguide-(ARROW-) type vertical coupler for three-dimensional optical interconnects was demonstrated. The coupler consists of stacked ARROW's channeled by the stripe lateral confinement structure, and each waveguide is completely separated by a thin metal film in the separation region. In the coupling region the intermediate cladding of a previous coupler was made of the same material as that of the first cladding or the core. However, we had to overcome the problem that both the high coupling efficiency and the large fabrication tolerance cannot be achieved simultaneously. Thus we incorporated an intermediate cladding made of a material different from that of the core and the first cladding. The refractive index and the thickness of the intermediate cladding were optimally designed to achieve large fabrication tolerance and a short coupling length with a high coupling efficiency. The coupling length was reduced from 4.1 to 0.8 mm, and a high coupling efficiency of 96% was experimentally demonstrated.     

Design and characterization of a liquid-crystal spatial light modulator for a polarization-insensitive optical space switch

We report preliminary results concerning a free-space optical switch between single-mode fibers with a ferroelectric liquid-crystal (FLC) spatial light modulator (SLM). In particular, we show experimentally that such a device can operate in a polarization-insensitive manner. The influence of the geometrical and physical features of the FLC SLM on the overall performance of the optical fiber switch are also discussed.     

La3Ga5SiQ14 single-crystal Q switch used as an electro-optic device

A new kind of electro-optic Q switch is designed by use of a La3Ga5SiQ14 (LGS) crystal. Because the LGS crystal is optically active, the Q switch is based on the consideration that the total rotation angle of the polarization plane is zero, whereas the polarized wave propagates through the Pockels cell back and forth, with the polarization plane gyration and electro-optic effect existing simultaneously. The LGS Q switch is a practical electro-optic device that can be used in medium output energy lasers to partially take the place of deuterated potassium dihydrogen phosphate and lithium niobate Q switches.     

Redox switchable self-assembled monolayers of functional ruthenium(III/II) complexes on optically transparent platinum electrodes

Self-assembled monolayers (SAMs) of functional Ru^II complexes on optically transparent ultrathin Pt films (10-nm nominal thicknesses) have been prepared. We have demonstrated that reversible Ru^III/II redox switching of these SAMs can be achieved by using appropriate oxidizing or reducing agents. Such a switching in molecular properties has been simply detected by transmission spectroscopy with a conventional spectrophotometer following the appearance/disappearance of the optical absorption metal-to-ligand charge-transfer (MLCT) band in the visible region. In light of their potential multifunctional properties, these SAMs on an optically transparent metal electrode are appealing candidates in the perspective of integrated molecular switch nanodevices.