热交联型聚氨酯集成双通道电光调制器的制备及其性质的研究

研究了交联型聚氨酯材料集成衰减全反射型双通道聚合物波导电光调制器的制备和性能。这种电光调制器的制备技术非常简单,只要用两个分立的下电极代替单通道调制器中的下电极即可。通过测量器件的调制特性,在832 nm波长下,获得了最大电光系数为24.2 Pm/V,调制带宽约为500 MHz、插入损耗低于1.5 dB。由于器件上下电极的垂直距离为微米级、而通道之间的水平距离为毫米量级的设计,使各通道之间的场不会引起相互交迭,因而未测到各通道间的串扰。另外,热交联型聚合物材料的采用提高了整个器件的热稳定性,在100℃经过800 h后,电光系数仍然保持初值的88%。     

基于单通道反射型电光调制器实现不同路光同时调制的方法

提出了一种利用单通道反射型聚合物电光调制器同时调制不同路光的方法。衰减全反射结构的电光调制器,其每一个衰减全反射(ATR)峰的位置分别对应于一个导波共振模式。实验系统中利用衰减全反射导膜峰作为调制通道,使其每一路光路的入射角分别对应于不同导波共振模式的工作角,就可以实现利用单通道的电光调制器同时调制不同路光。提出了三种实现两路光同时调制的模式,并给出了三种模式的调制结果。结果表明,作为调制通道的导模阶数越低,调制效率越高。在832 nm光波波长下,采用最低阶导模进行调制时可以获得42.9%的调制效率。     

New scheme of two-channel WDM modulation with cascaded attenuated-total-reflection modulators

In this paper, we propose a two-channel WDM modulation system by cascading attenuated-total-reflection (ATR) modulators. This system is free from channel demultiplexing and multiplexing elements. Two independent light signals with 20 nm channel spacing are experimentally demonstrated with modulation crosstalk less than −20 dB between the channels.     

A planar electrooptic beam splitter/modulator with a pair of parallel electrodes

A new planar electrooptic beam splitter with a pair of parallel electrodes is proposed and its characteristics are demonstrated on LiNbO₃. At a voltage up to 80 V and a 9.5 m electrode separation, the two output beams can be scanned over a total angle of 3° in the guide plane. The structure can also be applied to amplitude modulation, requiring 15 V for complete on-off modulation. The device permits convenient fabrication and has a potential to operate at high speeds.     

Effect of dipolar interaction on the magnetization state of chains of rectangular particles located either head-to-tail or side-by-side

Magnetostatic coupling in arrays of closely spaced magnetic elements is becoming an important issue in the path to the fabrication of spintronic devices. Dense chains of rounded-corners rectangular particles (dots) of lateral size 1025 × 450 nm², with interdot spacing variable in the range between 55 and 700 nm, have been patterned by deep UV lithography, followed by the lift-off of two permalloy films of thickness 20 and 40 nm. Magneto-optical Kerr effect (MOKE) and magnetic force microscopy (MFM) experiments, together with micromagnetic simulations, were performed to study the dependence of the magnetization configuration on the dipolar coupling. Both MOKE measurements and MFM images clearly show that, at remanence, the magnetic state of isolated particles of thickness 20 nm takes the form of a distorted single domain (C-state or S-State configurations). Instead, when the particle thickness is double (40 nm), closure states characterized by one, two or three vortices occur at remanence. However, when the 40 nm thick dots are placed in chains along the easy axis (head to tail), as the separation is progressively reduced, the single domain state is stabilized at remanence. On the other hand, when the 40 nm thick particles are placed side by side in chains the effect of dipolar interactions is to favour the nucleation of vortex states. For small inter-element separation, there is only one vortex per particle and it has the same chirality in adjacent particles, due to the dipolar interaction. Different from this, for the 20 nm thick samples and sub-100 nm separation, adjacent particles are single-domain but with antiparallel magnetization in neighbour elements, like in an artificial antiferromagnet.     

Low voltage electro-optic polymer light modulator using attenuated total internal reflection

An improved electro-optic (EO) polymer light modulator based on attenuated-total-internal-reflection (ATR) is demonstrated. The modulator consists of a prism–metal–EO-polymer–metal multilayer structure. An applied electric field across the EO polymer layer electrically modulates the energy coupling efficiency of incoming light into guided wave resonance at fixed angles. Compared with conventional ATR modulators based on surface plasmon resonance, the driving voltage for this modulator has been greatly reduced because of the newly chosen working interior angle. It also offers advantages in terms of insertion loss and aperture size over other techniques for the amplitude modulation of a collimated light beam.     

A flexible carbon nanotube field emitter fabricated on a polymer substrate by a laser separation method

The fabrication of a sparsely networked carbon nanotube (CNT) thin film on a polycarbonate substrate as the conductor electrode and the emitting cathode by a newly proposed laser separation method is reported. Based on this approach, numerous surface protruding tube tips can be structured straightforwardly, which results in favorable field-emission characteristics. A flexible field emitter with a low turn-on voltage of 1.0 V/μm can be obtained. This method also demonstrates the abilities for fabricating a film with precision patterns and varying CNT concentrations as well as the flexibility of direct film formation on a curved surface. Moreover, all fabrication steps are executed in the ambient environment and at room temperature.     

Optimization and fabrication of a planar thermoelectric generator for a high-performance solar thermoelectric generator

A planar thermoelectric generator (TEG) could be used as an energy harvester for wireless sensor networks (WSNs). Its planar configuration offers the advantages of miniaturization and low-cost fabrication. Herein, we report the fabrication of a device based on a co-evaporated thick film of Bi–Te. Before fabrication we studied quantitative optimization dimensions for the planar TEG via finite element method (FEM) simulations. The planar TEG was also used in a high-performance solar thermoelectric generator (STEG) that concentrated heat from solar radiation via a solar absorber to generate a temperature difference (ΔT) between two thermoelectric and electrode junctions. When exposed to a solar simulator, the STEG produced a ΔT of about 6 °C and generated 2.3 μW of power. The demonstrated high flexibility and mechanical stability of this device suggests applications in wearable electronics.     

A novel optical picosecond-duration NRZ-to-RZ format converter with simultaneous wavelength multicasting using a single-stage Mach–Zehnder modulator

We propose a novel and simple scheme to achieve NRZ-to-RZ format conversion and simultaneous wavelength multicasting based on a single-stage dual-arm electro-optic Mach–Zehnder modulator (MZM) and a short single mode fiber (SMF). The format conversion and wavelength multicast process are achieved by chirp compensation under the condition of generation of optical flat frequency comb. 40 Gb/s NRZ-to-RZ conversion with one-to-five multiple-wavelength channel multicasting and transmission of the NRZ and the converted signals over 200 km dispersion-managed fiber-link are successfully demonstrated by numerical simulation. Research results show that 40 Gb/s 2 ps RZ signal with wavelength-preserving can be obtained after format conversion. The converted RZ signal presents good transmission performance and can easily be multiplexed to 160 Gb/s using optical time division multiplexing (OTDM) technology. All the multicast channels can be error free after 50 km transmission. Besides, the conversion operation can also greatly reduce the timing jitter of the degraded NRZ signal due to the retiming function of the proposed scheme.     

Electrical studies on ionic liquid-based gel polymer electrolyte for its application in EDLCs

Ionic liquid-based gel polymer electrolyte (GPE) has been synthesized using standard solution cast technique. Different weight percent of ionic liquid, 1-Butyl-3-methylimidazolium chloride (BMIMCl) and liquid electrolyte, ethylene carbonate (EC)–propylene carbonate (PC)–tetra ethyl ammonium tetra fluoro borate (TEABF₄) was incorporated in polymer, poly(vinylidene fluoride-co-hexafluoro propylene (PVdF-HFP) to obtain mechanically stable gel polymer electrolyte film (GPE) having maximum conductivity of ~10⁻³ S cm⁻¹ at room temperature, which is acceptable from device fabrication point of view. Potential window and ionic transference number has been obtained to examine the potential limit and ionic characteristics of optimized GPE system. Temperature dependence behavior of electrical conductivity curve follows Arrhenius nature in the temperature range of 303–373 K. Pattern of dielectric constant and its loss as a function of frequency and temperature have been studied and is being explained on the basis of electrode interfacial polarization effect. Frequency-dependent conductivity spectra obey the Jonscher’s power law. Further, optimized composition of GPE has been tested successfully for its application in supercapacitor fabrication with activated charcoal as an electrode material. Maximum specific capacitance of 118.6 mF cm⁻² equivalent to single electrode specific capacitance of 61.7 F g⁻¹ have been observed for the optimized GPE film.

     

Electrohydrodynamic force produced by a corona discharge between a wire active electrode and several cylinder electrodes – Application to electric propulsion

Low-speed electric propulsion systems for long-duration near-space travels by using solar energy could be based on the electrohydrodynamic force produced inside a corona discharge. This paper is a contribution to a better understanding of these types of thrusters, in order to enhance the produced thrust and their electromechanical effectiveness. Three different simple designs are experimentally studied and compared. The first one is composed of a wire active electrode and a single cylinder grounded one. For the second three-electrode design, the single grounded cylinder is replaced by two cylinders. Finally, the last design is composed of an active wire supplied by a positive voltage, two grounded electrodes and two others cylinders at a negative voltage. On one hand, results show that the use of two grounded electrode instead of a single one results in an increase of the discharge current. Moreover, whatever the electrode gap d, the current-to-thrust conversion is more effective with the three-electrode design. It changes from 31 to 58 N/A (+87%), from 74 to 85 N/A (+15%), and from 104 to 120 N/A (+15%), for electrode gaps d = 10, 20 and 30 mm, respectively. The thruster effectiveness θ is improved by 2 mN/W. On the other hand, the use of two collecting electrodes supplied by a negative high voltage does not result in an effectiveness enhancement because the power consumption is significantly increased.     

Control of a turbulent flow separated at mid-chord along an airfoil with DBD plasma actuators

The goal of the present experimental study is to investigate the ability of surface DBD plasma actuators to delay flow separation along the suction side of a NACA0015 airfoil. Three single surface DBD actuators that can operate separately are mounted on the suction side of the profile, at 18%, 27% and 37% of the chord length. The boundary layer is transitioned by a tripper to be sure that the flow control is not due to the laminar-to-turbulent transition. The angle of attack is equal to 11.5° and the free-stream velocity to U₀ = 40 m/s, resulting in a chord-based Reynolds number of Re_c = 1.33 × 10⁶. The flow is studied with a high-resolution PIV system. In such conditions, the baseline flow separation occurs at 50% of chord. Then, the different single DBD have been switched on separately, in order to investigate the actuator location effect. One highlights that the DBD located at x_c/c = 18% is more effective than the two others ones, with a separation delay up to 64% of chord. When the three DBDs operate simultaneously, the separation point moves progressively toward the trailing edge when the high voltage is increased, up to 76% of chord at 20 kV. Finally, the effect of the actuation frequency on the control authority has been investigated, by varying the value of the operating frequency and by burst-modulation. For frequencies equal to 50 Hz and 500 Hz (reduced frequency F⁺ = 0.31 and 3.1), the separation has been delayed at 76 and 80% of chord, respectively.     

Microfiber Mach-Zehnder interferometer embedded in low index polymer

Microfiber Mach Zehnder Interferometer (MMZI) is demonstrated by micromanipulating an optical microfiber drawn from a single mode fiber (SMF) using a flame brushing technique. The MMZI shows good interference fringes with an extinction ratio of 13 dB and a free spectral range (FSR) of 0.52 nm at 1530 nm. The MMZI is then embedded in a polymer with the refractive index of 1.36 to increase the stability and robustnes of the device. It is found that the transmission spectrum of the packaged MMZI is changed by the polymer, which increases the FSR to 0.83 nm. The degradation in transmission loss and extinction ratio are attributed to the disturbance at the coupling area during the packaging. Compared with waveguide based mach zehnder interferometer, the proposed MMZI is favoured due to easy fabrication, compact size, and easy integration with the fiber system.     

DWDM VSB modulation-format optical transmission: Effects of optical filtering and electrical equalization

The transmission of 40 Gb/s wavelength multiplexed channels under vestigial single side band modulation format is transmitted over long haul optically amplified fiber systems. Bit-error-rate (BER) of 10⁻¹² or better can be achieved across all channels. Optical filters are designed with asymmetric roll-off bands. Simulations of the transmission performance, BER versus receiver sensitivity are demonstrated with wavelength channel spacing of 20–40 GHz. An optical filter, whose passband is 28 GHz and 20 dB cut-off band, performs best for 40 Gb/s bit rate due to optimum filtering and minimum noise contribution. Furthermore the single-sideband property of VSB format can assist linear equalization by electronic processing. The transmission performance is accurately evaluated based on the eye opening using a fast statistical method based on an equivalent Gaussian probability density distribution (pdf) which is derived from multiple peaks pdf of distorted eye diagram.     

Nanosecond polymer Mach-Zehnder interferometer electro-optic modulator using optimized micro-strip line electrode

A Mach-Zehnder interferometer (MZI) electro-optic (EO) modulator based on micro-strip line (MSL) electrode and guest-host EO polymer DR1/SU-8 is experimentally demonstrated. For achieving high response speed, electrode structure is especially optimized and fabrication technology is seriously controlled. The final characteristic impedance of electrode is about 49.4 Ω, and the difference between microwave index (1.5616) and lightwave index (1.6006) is also minimized. At 1,550 nm, the insertion loss and extinction ratio are 12 and 16 dB, respectively, and under switching operation, the rise time and fall time are 16.3 and 16.7 ns, respectively. A long-term monitoring over 2000 hours at room temperature (25 °C) is performed on switching response, and a novel mathematical modeling on response time variation is established using logistic function. The rise time and fall time are observed to change from the initial value of ~16 ns to the stable value of ~28 ns within 300 and 2000 hours, respectively. The device exhibits nanosecond response time by virtue of impedance-matched electrode, small index mismatch and serious control on fabrication process.     

Lyot filter based multiwavelength fiber ring laser actively mode-locked at 10 GHz using an electroabsorption modulator

A multiwavelength fiber ring laser comprising of a Lyot filter and hybrid gain medium is presented. A wavelength channel spacing of 100 GHz is achieved by appropriate tuning of the Lyot filter length. Four wavelength channels are simultaneously mode-locked at 10 GHz using an electroabsorption modulator. We highlight how the intra-cavity modulator can affect the stability of the mode-locked laser spectrum when used in conjunction with a Lyot filter. We show that, due its reduced polarization sensitivity, an electroabsorption modulator significantly improves the stability of the mode-locked laser spectrum when compared to using a Mach-Zehnder modulator.     

Simulative investigation of nonlinear distortion in single- and two-tone RoF systems using direct- and external-modulation techniques

In this paper, we investigated a Radio-over-Fiber (RoF) system consisting of two different system set-ups using direct- and external-laser modulation techniques to study frequency response. Further, second- and third-harmonic generations of single- and two-tone RoF systems have been studied. In this work, we also measured the electric Rf power of two receiving channels and BER at received optical power at different modulating Rf frequencies up to 20 GHz using EDFA or SOA amplifiers. The results have been compared for the electric Rf power of receiving channels obtained using a sin² Mach Zehnder modulator and a linear modulator, and an improvement in the received Rf power with linear modulator in comparison with the sin² modulator is observed.     

Multi-channel light modulation based on the attenuation total reflection

Multi-channel light modulation, which is based on the attenuated total reflection (ATR) configuration, is proposed in this paper. The device consists of a prism and a polymer optical waveguide. Guided modes which give rise to the resonance dips in the ATR spectrum are employed to act as the modulation channels. Double channel's modulation with the same modulation signal has been demonstrated in the proposed device.     

Nano-composite LiMnPO4 as new insertion electrode for electrochemical supercapacitors

Nano-composite olivine LiMnPO₄ (nC-LMP) was found to exhibit facile pseudo-capacitive characteristics in aqueous as well as non-aqueous electrolytes. We demonstrated employing nC-LMP as positive electrode in hybrid electrochemical capacitors namely Li-Ion hybrid capacitors (LIC). Adapting a simple CVD technique, nano-crystallites of LiMnPO₄ were coated with carbon monolayers of ∼2 nm thick to circumvent its poor intrinsic electronic conductivity. The novelty is that the single crystallites were intimately covered with carbon ring and networked to the neighboring crystallites via the continuous carbon wire-like connectivity as revealed from HRTEM analysis. Single electrode faradic capacitance of 3025 Fg⁻¹ (versus standard calomel reference electrode) was deduced for carbon coated LMP, the highest reported hitherto in Li⁺ aqueous electrolytes. Employing nC-LMP as working electrode versus an activated carbon (AC), we obtained a high specific energy of 28.8 Wh kg⁻¹ with appreciable stability in aqueous electrolytes whereas in nonaqueous electrolyte there is an obvious increase in energy density (35 Wh kg⁻¹) due to wider potential window. That is, a full cell version of LIC, AC|Li⁺|LMP, was fabricated and demonstrated its facile cycling characteristics via removal/insertion of Li⁺ within nC-LMP (positive electrode) and the electrosorption of Li⁺ into mesoporous carbon (AC) (negative electrode). Such cells ensured a typical battery-like charging and EDLC-like discharging characteristics of LIC type electrochemical capacitors (ECs) which are desired to enhance safety and energy densities.