Modified solution-processible fabrication of metallic photonic crystals with template removal

High-temperature annealing and pre-annealing lift-off procedures are employed to improve the solutionproeessible technique for the fabrication of one- （1D） and two-dimensional （2D） metallic photonic crystals （MPCs） based on colloidal gold nanoparticles. This enables the successful fabrication of gold nanowires or nanocylinder array structures with the photoresist template removed completely, which is crucial for the application of MPCs in biosensors and optoelectronic devices. Microscopic measurements show homogeneous 1D and 2D photonic structures with an area as large as 100 mm2. Plasmonic resonance of the gold nanostructures and its coupling with the resonance mode of the planar waveguide underneath the photonic structures are observed, implying the excellent optical properties of this kind of MPCs based on the improved fabrication technique.     

Photonic crystal structures:Beam deflector and beam router

We investigate the optical characteristic,transverse magnetic(TM) and transverse electric(TE) band of twodimensional(2 D) square lattice photonic crystal structure,which is composed of cylindrical air regions positioned at the corners of the square shaped dielectric rods.We obtain the wide photonic bandwidths between TM1–TM2 and TM3–TM4 bands.According to the results,we demonstrate the band gaps close to each other in the TM and TE frequencies for proposed structures.The resulting photonic gaps are formed to be about 8% at the higher frequencies of TE modes(TE4–TE5)and TM modes(TM7–TM8 and TM9–TM10).In addition,we examine isotropically generated structures for light guiding properties and observe that the light is directed in a particular route without using any deflection.We also investigate the self-collimation effect with the designed structure.The obtained results reveal the influences of the radius of cylindrical air holes and the angle between these air holes on absolute and partial photonic band gaps.Moreover,we observe the TM and TE band gaps that overlap.It is thought that the obtained band overlap will provide an easy way to produce the photonic crystals in practical applications like photonic insensitive waveguide.It is also believed that these results can provide the photonic crystal structures to work as a beam deflecting and beam router in integrated optical circuit applications.     

Three-dimensional simulation of Ka-band relativistic Cherenkov source with metal photonic-band-gap structures

This paper presents a three-dimensional particle-in-cell (PIC) simulation of a Ka-band relativistic Cherenkov source with a slow wave structure (SWS) consisting of metal photonic band gap (PBG) structures. In the simulation, a perfect match layer boundary is employed to absorb passing band modes supported by the PBG lattice with an artificial metal boundary. The simulated axial field distributions in the cross section and surface of the SWS demonstrate that the device operates in the vicinity of the π point of a TM01-like mode. The Fourier transformation spectra of the axial fields as functions of time and space show that only a single frequency appears at 36.27 GHz, which is in good agreement with that of the intersection of the dispersion curve with the slow space charge wave generated on the beam. The simulation results demonstrate that the SWS has good mode selectivity.     

Development of MEMS-based micro capacitive tactile probe

In this paper, a micro capacitive sensor with nanometer resolution is presented for ultra-precision measurement of micro components, which is fabricated by the MEMS （micro electromechanical systems） non-silicon technique. Based on the sensor, a micro capacitive tactile probe is constructed by stylus assembly and packaging design for dimension metrology on micro/nano scale, in which a data acquiring system is developed with AD7747. Some measurements of the micro capacitive tactile probe are performed on a nano positioning and measuring machine （NMM）. The measurement results show good linearity and hysteresis with a range of 11.6 μm and resolution of better than 5 nm. Hence, the micro capacitive tactile probe can be integrated on NMM to realize measurement of micro structures with nanometer accuracy.     

A method of designing photonic crystal grating slow-wave circuit for Ribbon--Beam microwave travelling wave amplifiers

A method of designing a photonic crystal grating slow-wave circuit in which the cylinders of the 2D photonic crystals dot on a cross-sectional plane is established by calculating the band structures of the 2D photonic crystals, and the eigenfrequency of the equivalent waveguide grating. For calculating the band structures, the eigenvalue equations of the photonic crystals in the system of photonic crystal grating slow-wave circuit are derived in a special polarization mode. Two examples are taken to show the method. The design result is validated by the scattering parameters of the same circuit. The result indicates that there exists no photonic band gap if the metal gratings do not extend into the photonic crystals; the design of the circuit without the metal gratings extending into the photonic crystals is less flexible than that with the metal gratings extending into the photonic crystals.     

Tunable negative-index photonic crystals using colloidal magnetic fluids

The model of using colloidal magnetic fluid to build tunable negative-index photonic crystal is established. The effective permittivity εe and permeability μe of the two-dimensional photonic crystal are investigated in detail. For transverse magnetic polarization, both εe and μe exhibit a Lorentz-type anomalous dispersion, leading to a region where εe and μe are simultaneously negative. Then, considering a practical case, in which the thickness of photonic crystal is finite, the band structures for odd modes are calculated by the plane wave expansion method and the finite-difference time-domain method. The results suggest that reducing the external magnetic field strength or slab thickness will weaken the periodic modulation strength of the photonic crystal. Simulation results prove that the negative-index can be tuned by varying the external magnetic field strength or the slab thickness. The work presented in this paper gives a guideline for realizing the flat photonic crystal lens with tunable properties at optical frequencies, which may have potential applications in tunable near-field imaging systems.     

Sound propagation in ducts with spatially variant parameters

The one-dimensional theory of sound propagation in ducts isgeneralized and investigated in this paper.It can be assumed that anyduct system consists of two kinds of elementary structures:One is thepiped structure in which the characteristics,such as the acousticalparameter on the interior surface of the wall,the cross-section area andthe aerodynamic parameters of the flow,etc.,will vary continuously andslowly with distance along the axis of the duct.The other is the localstructure with discontinuity in which the characteristics will change abruptly.The acoustical properties of both structures are analysed in generalcases based upon the fundamental equations of aerodynamics,and theirtransmission matrixes are derived and discussed respectively.Two typicalexamples are analysed and discussed.     

Fabrication of Two-Dimensional Photonic Crystals with Controlled Defects by Combination of Holographic Lithography and Two-Photon Polymerization

A new ternary photopolymer system is used in fabricating photonic crystals （PhCs） with controlled defects by combination of single-photon and two-photon photopolymerization. The former process can produce PhCs in one-step recording with a low-power （tens mW） continuous-wave laser at 532nm, while the latter can create desired defects. The preparation of the material, the optical setup and the preliminary experimental results are given. Compared with other methods, this approach is much more accessible and convenient for use of visible light and has advantages of making PhCs in a large scale quickly and economicaJly and introducing any defects exactly, especially for three-dimensional structures.     

Exponentially tapered multi-mode interference couplers

Optical couplers are important components in photonic integrated circuits. The multi-mode interference (MMI) coupler is a good candidate because of its bandwidth, polarization properties, and manufacturing tolerances. A MMI coupler with the exponentially tapered multi-mode waveguide is proposed in order to reduce the scale of the MMI device. Compared with parabolically tapered structure which has been successfully used in the MMI devices, this structure can further reduce the length of devices. Simulation results by the beam propagation method for MMI couplers are given. The effectiveness of this structure for reducing MMI device length is proved.     

Exponentially tapered multi-mode interference couplers

Optical couplers are important components in photonic integrated circuits. The multi-mode interference (MMI) coupler is a good candidate because of its bandwidth, polarization properties, and manufacturing tolerances. A MMI coupler with the exponentially tapered multi-mode waveguide is proposed in order to reduce the scale of the MMI device. Compared with parabolically tapered structure which has been successfully used in the MMI devices, this structure can further reduce the length of devices. Simulation results by the beam propagation method for MMI couplers are given. The effectiveness of this structure for reducing MMI device length is proved.     

Design of differential optical system of in-plane remote displacement measurement

In this paper, an optical system for in-plane remote displacement measurement is brought forward. The remarkable characteristic of this optical system is to use a big aperture lens to focus the waists of two Gauss beams on a scatter which have been expanded and collimated, so good laser Doppler signals and high measurement accuracy are achieved. The experiments prove that the measurement system consisting of this optical system, a lock-in amplifier and a digital filter can be used to measure the in-plane displacement of scatters in distance of 50 m with the relative accuracy of 1%.     

Dispersion characteristics of a slow wave structure with a modified photonic band gap

This paper studies the dispersion characteristics of a modified photonic band-gap slow-wave structure with an open boundary by simulation and experiment.A mode launcher with a wheel radiator and a coupling probe is presented to excite a pure TM 01-like mode.The cold test and simulation results show that the TM 01-like mode is effectively excited and no parasitic modes appear.The dispersion characteristics obtained from the cold test are in good agreement with the calculated results.     

Pseudo working-point control measurement scheme for acoustic sensitivity of interferometric fiber-optic hydrophones

A novel pseudo working-point control measurement scheme for the acoustic sensitivity of interferometric fiber-optic hydrophones is described and demonstrated.The measurement principle is introduced in detail. An experimental system,which interrogates an interferometric fiber-optic hydrophone with this method, is designed.The acoustic pressure phase sensitivity of the fiber-optic hydrophone is measured over the frequency range of 20-2500 Hz.The measured acoustic sensitivity is about-156.5 dB re 1 rad/μPa with a fluctuation lower than±1.2 dB,which is in good agreement with the results obtained by the method of phase generated carrier.The experimental results testify the validity of this new method which has the advantages of no electric elements in the sensing head,the simplicity of signal processing,and wide working bandwidth.     

Electrical characteristics and optoelectronic properties of metal--semiconductor--metal structure with zinc oxide nanowires across Au electrodes

This paper reports on a method of assembling semiconducting ZnO nanowires onto a pair of Au electrodes to construct a metal--semiconductor metal （MSM） structure by dieleetrophoresis and studying on its electrical characteristics by using current-voltage （Ⅰ - Ⅴ） measurements. An electronic model with two back to back Sehottky diodes in series with a semiconductor of nanowires was established to study the electrical transport of the MSM structures. By fitting the measured Ⅰ - Ⅴ characteristics using the proposed model, the parameters of the Schottky contacts and the resistance of nanowires could be acquired. The photoelectric properties of the MSM structures were also investigated by analysing the measurements of the electrical transports under various light intensities. The deduced results demonstrate that ZnO nanowires and their Schottky contacts with Au electrodes both contribute to photosensitivity and the MSM structures with ZnO nanowires are potentially applicable for photonic devices.     

Excitations of optomechanically driven Bose Einstein condensates in a cavity: Photodetection measurements

We present a detailed study to analyze the Dicke quantum phase transition within the thermodynamic limit for an optomechanically driven Bose-Einstein condensate in a cavity. The photodetection-based quantum optical measurements have been performed to study the dynamics and excitations of this optomechanical Dicke system. For this, we discuss the eigenvalue analysis, fluorescence spectrum and the homodyne spectrum of the system. It has been shown that the normal phase is negligibly affected by the mechanical mode of the mirror while it has a significant effect in the superradiant phase. We have observed that the eigenvalues and the spectra both exhibit distinct features that can be identified with the photonic, atomic and phononic branches. In the fluorescence spectra, we further observe an asymmetric coherent energy exchange between the three degrees of freedom of the system in the superradiant phase arising as a result of optomechanical interaction and Bloch-Siegert shift.     

Dynamic behaviour of the icosahedral Al——Pd——Mn quasicrystal with a Griffith crack

The dynamic response of an icosahedral Al--Pd--Mn quasicrystal with a Griffith crack to impact loading is investigated in this paper. The elastohydrodynamic model for the wave propagation and diffusion together with their interaction is adopted. Numerical results of stress, displacement and dynamic stress intensity factors are obtained by using the finite difference method. The effects of wave propagation, diffusion and phonon--phason coupling on the quasicrystal in the dynamic process are discussed in detail, where the phason dynamics is explored particularly.     

Modified Optical Properties of Semiconductor Quantum Dots by Photonic Structures

Specially designed photonic structures, such as photonic crystals, can prevent light from propagating in certain directions with specified frequencies.Such photonic stsuctures exhibit many unique features that are highly desirable for the manufacture of photonic integrated circuits.There has been great interest in controlling light-emitters via photonic structures, which can partially suppress and redirect spontaneous emission.Encapsulating an active material in a well-designed photonic structure can successively reduce the active volume.Because the dimensions of the active volume are reduced to a few micrometers, spontaneous emission control can be achieved, which can provide lasing with improved directional, modal control, and reduced noise.     

Fabrication of two- and three-dimensional periodic submicron structures by holographic lithography with a 635~nm laserand matched photopolymer

2D and 3D submicron periodic structures are first fabricated by red-induced photopolymerization using a common 635 nm semiconductor laser and specially developed red-sensitive polymer material. The principle of this new photo-polymer material fabrication is explained and the absorption spectra of the material are measured. This fabrication technique allows a deeper penetration into volume and larger interference irradiation area which is more than 1 cm². The optical design, theoretical calculations and experimental results including diffraction patterns verifying the formation of periodic structures are presented. Compared with other fabrication technologies using high-power lasers, this approach has greatly reduced the demand for laser apparatus. Therefore, it is much more accessible to most laboratories and potentially usable in holographic fabrication of photonic crystals and devices in micro electro-mechanical systems (MEMS).     

Exciton and donor binding energies in quantum-well wires and quantum dots a fractional-dimensional space approach

A simple method for calculating the free-exciton binding energies in the fractional-dimensional-space model for single-quantum-well structure has been extended to quantum-well wires and quantum dots, in which the real anisotropic system is modelled through an effective isotropic environment with a fractional dimension. In this scheme, the fractional-dimensional parameter is chosen via an analytical procedure and involves no ansatz. We calculated the ground-state binding energies of excitons and donors in quantum-well wires with rectangular cross sections. Our results are found to be in good agreement with previous variational calculations and available experimental measurements. We also discussed the ground-state exciton binding energy changing with different shapes of quantum-well wires,     

The rotational anisotropies in the ferromagnetism/antiferromagnetism 1/ antiferromagnetism 2 exchange bias structures

The rotational anisotropies in the exchange bias structures of ferromagnetism/antiferromagnetism 1/antiferromagnetism 2 are studied in this paper. Based on the model, in which the antiferromagnetism is treated with an Ising mean field theory and the rotational anisotropy is assumed to be related to the field created by the moment induced on the antiferromagnetic layer next to the ferromagnetic layer, we can explain why in experiments for ferromagnetism (FM)/antiferromagntism 1 (AFM1)/antiferromagnetism 2 (AFM2) systems the thickness-dependent rotational anisotropy value is non-monotonic, i.e. it reaches a minimum for this system at a specific thickness of the first antiferromagnetic layer and exhibits oscillatory behaviour. In addition, we find that the temperature-dependent rotational anisotropy value is in good agreement with the experimental result.