Ribamidil as a modulator of the toxic effect of 5-fluorouracil

The in vitro experiments on CaOv cells demonstrated that ribamidyl (ribavirine) (Rb) enhances the intracellular pool of pyrimidine precursors of DNA. This was the basis for studies of its modifying effect on the antitumour activity of antimetabolites. In experiments with intact hybrid mice F1 (CBA+C57B1) the five times administration of ribavirine increase sharply the toxicity of 5-FU. The data should be taken into consideration when combining Rb with antimetabolites in clinical practice.     

Bidirectional fibre-optical transmission using a multiple-quantum-well (MQW) modulator/detector

We demonstrate a simple architecture for bidirectional optical fibre transmission which uses an MQW device as both modulator and photodetector. We achieved transmission of 50 Mbit/s and 600 Mbit/s in both directions over one 3.34 km-long single-mode fibre at 860 nm wavelength. Coherent Rayleigh interference was found to be a limiting factor in single-source bidirectional systems.     

用于卫星双向时间传递系统的调制器设计

设计开发了一种用于卫星双向时间传递(TWSTT) 系统的调制器,详细介绍了该调制器 的内部结构和相关算法。采用FPGA和DDS进行硬件实现,并完成系统的仿真测试。该调制器 的中频输出频率为70 MHz,峰值输出功率为-15 dBm。     

The effect of fabrication parameters on a ridge Mach-Zehnder interferometric (MZI) modulator

A study of Mach-Zehnder interferometer (MZI) modulators using unetched and etched Ti:LiNbO/sub 3/ waveguides has been made. A full vectorial finite-element-based mode solver was used, followed by a finite element-based solution of the Laplace equation to calculate the electrooptic effect and, subsequently, the half-wave voltage, V/sub /spl pi// The optical loss due to the metal electrodes was also found using the H-field finite-element method (FEM) incorporating the perturbation method. The microwave effective index, n/sub m/, and the characteristic impedance of the metal electrodes, Z/sub c/, were also found for a number of electrode thicknesses and ridge heights. A semivectorial finite-element beam propagation method (SVFEBPM) was used to estimate the radiation loss for the curved input and output (I/O) waveguides of the MZI. The device characteristics were then studied by making changes to a number of fabrication parameters, of which the two most important were found to be the etch depth of the ridge and the thickness of the SiO/sub 2/ buffer layer.     

Ge_xSi_（1－_x）等离子体色散效应及电光调制器

在研究了Ｓｉ的等离子体色散效应之后，我们预计ＧｅｘＳｉ１－ｘ也会有这一效应。理论分析和实践的结果都表明ＧｅｘＳｉ１－ｘ具有比Ｓｉ更强的等离子体色散效应。     

Microwave reflection properties of a rotating corrugated metallicplate used as a reflection modulator

The performance of a simple microwave modulating retro-reflector based on a rotating corrugated metallic plate is analyzed theoretically and compared with laboratory measurements. Fields within the corrugations are described by waveguide modes and free-space fields by Floquet modes. The periodicity of the grooves is represented through the reciprocal lattice corresponding to the periodic structure. The accuracy of the calculation is analyzed as a function of the number of modes used to describe the electromagnetic field. Graphs are given for the design of a modulator for any wavelength     

Low-frequency model of the microwave frequency (phase) detector with amplitude modulator and shift oscillator

A low-frequency model of the microwave frequency (phase) detector with amplitude modulator and shift oscillator has been studied theoretically and experimentally. The results of experiment indicate that such FM (PM) detector can be also used in the HF band of radio frequencies.     

Noninvasive pulse modulator concept for nonradiative dielectric(NRD) waveguide

The nonradiative dielectric (NRD) waveguide has been identified as a promising candidate for use at millimetre-wave frequencies. To realise this promise NRD waveguide must support the design of the necessary active and passive components for the realisation of systems and subsystems. The authors describe the principle of a novel modulator for use with NRD waveguide and present preliminary results     

Characteristics of a delta modulator

Additional results from a previously described computer simulation of an adaptive delta modulator are presented and interpreted, and their relevance to a proposed upper bound on delta-modulator performance is indicated.     

Analysis of a delayed delta modulator

While delta modulation (DM) simply compares the current predictive estimate of the input with the current sample, delayed delta modulation (DDM) also compares with the upcoming sample so as to detect and anticipate slope overloading. Since this future sample must be available before the present output is determined and the estimate updated, delay is introduced at the encoding. The performance of DDM with perfect integration and step-function reconstruction is analyzed for each of three random input signals. In every case, the stochastic stability of the system is established. For a discrete time, independent and identically distributed input, the (limiting) joint distribution of input and output is derived, and the (asymptotic) mean-square sample point error mse(SP) is computed when the input is Gaussian. For a Wiener input, the joint distribution of the sample point and prediction errors is derived, and mse(SP) and the time-averaged mse (mse(TA)) are computed. For a stationary first-order Gauss-Markov input, the joint distribution of input and output is derived and mse(SP) and mse(TA) computed. Graphs of the mse's illustrate the improvement attainable by using DDM instead of DM. With optimal setting of parameters, mse(SP) (mse(TA)) is reduced about15percent (35percent).     

Analysis of a digital PSK modulator

This is a time and frequency domain study of an exclusive-OR gate used as a digital modulator. The output spectrum obtained has been partitioned into the desired PSK waveform, and the undesired part to be removed by the following filter. A simpler scheme of PSK generation has also been briefly discussed.     

On the effects of a spacecraft subcarrier unbalanced modulator

This paper presents mathematical models with associated analysis of the deleterious effects which a spacecraft's subcarrier unbalanced modulator has on the performance of a phase-modulated residual carrier communications link. The undesired spectral components produced by the phase and amplitude imbalances in the subcarrier modulator can cause (1) potential interference to the carrier tracking and (2) degradation in the telemetry bit signal-to-noise ratio (SNR). A suitable model for the unbalanced modulator is developed and the threshold levels of undesired components that fall into the carrier tracking loop are determined. The distribution of the carrier phase error caused by the additive White Gaussian noise (AWGN) and undesired component at the residual RF carrier is derived for the limiting cases. Further, this paper analyses the telemetry bit signal-to-noise ratio degradations due to undesirable spectral components as well as the carrier tracking phase error induced by phase and amplitude imbalances. Numerical results which indicate the sensitivity of the carrier tracking loop and the telemetry symbol-error rate (SER) to various parameters of the models are also provided as a tool in the design of the subcarrier balanced modulator.     

中红外波段高速硅基电光调制器设计与优化（特邀）

作为中红外波段中最接近O波段和C波段的波段,2 μm波段区域逐渐引起人们的广泛关注。主要对2 μm波段的马赫-增德尔型调制器进行优化设计和仿真,根据2 μm波长下光模场分布的特点,选用具有340 nm厚度顶层硅的SOI衬底,结合实际工艺中240 nm硅刻蚀深度,得到宽度为600 nm以及平板层厚度为100 nm的最优脊波导结构。通过优化掺杂浓度和掺杂区位置获得综合性能最优的调制器器件,在4 V反向偏压下器件光损耗为5.17 dB/cm,调制效率为2.86 V·cm,静态消光比为23.8 dB,3dB EO带宽为27.1 GHz。同时,与220 nm厚度顶层硅器件相比较,器件的综合性能更为优越。研究内容为后续器件实际制作提供了依据,也为后续2 μm波段光收发集成模块所需调制器设计提供了新的方向。     

Bias pulse modulator for a high power Kα band (26–40 GHz) impact oscillator

A pulse, modulator for driving K_α band IMPATT diodes is described, which facilitates chirp control and optimization of oscillator performance by current pulse shaping. Peak powers in excess of 20Watts have been achieved, with a pulse duration of 250ns and 0.1% duty cycle.     

The GaAs MESFET as a pulse regenerator, amplifier, and laser modulator in the Gbit/s range

Using GaAs MESFET's under switching conditions, the regeneration and amplification of fast pulses and the modulation of semiconductor lasers in the Gbit/s speed range is performed. Sharpening factors of 3 at output pulse rise times of nearly 50 ps and voltage amplification factors of 2 at 50 /spl Omega/ are attained for output pulses up to 100 mA. The regeneration is caused by the clamping at the input port of the MESFET and by the nonlinear transconductance characteristic. In the pulse modulation mode, the laser diode is directly controlled by the MESFET. The switching behavior of the driver stage is calculated using the equivalent circuit of the laser diode and of the MESFET. This evaluation reveals that the maximum pulse rate is limited by the laser diode.     

Experimental and theoretical studies of a novel hetero-nipireflection modulator

A novel GaAs/Al_0.35Ga_0.65As hetero-nipi all-optical reflection modulator has been investigated, both theoretically and experimentally. The modulation is found to be dominated by the refractive index changes that occur in the quantum wells as a result of optically induced electric field changes via the quantum-confined Stark effect. Good agreement is found between the theoretical and experimental behavior, with a maximum absolute experimental modulation of 11% and a maximum contrast ratio of 4.4:1 being observed at room temperature at optical pump densities of only 1.9 mW/cm². A numerical model of the device is developed, which predicts large reflectivity modulations of greater than 53% with a contrast ratio of 25:1 in optimized device structures     

Broad-band linearization of a Mach-Zehnder electrooptic modulator

Analog optical-link dynamic range in excess of 75 dB in a 1-MHz band has been achieved using specially designed electrooptic modulators that minimize one or more orders of harmonic and intermodulation distortion. To date, however, such “linearized” modulators have only enabled improved link dynamic ranges at frequencies below 1 GHz. Additionally, linearization across more than an octave bandwidth has required precise balancing of the signal voltage levels on multiple electrodes in a custom modulator, which represents a significant implementation challenge. In this paper, a link linearization technique that uses a standard Mach-Zehnder lithium-niobate modulator with only one RF and one dc-bias electrode to achieve broad-band linearization is discussed, resulting in a dynamic range of 74 dB in 1 MHz across greater than an octave bandwidth (800-2500 MHz). Instead of balancing the voltages on two RF electrodes, the modulator in this new link architecture simultaneously modulates optical carriers at two wavelengths, and it is the ratio of these optical carrier powers that is adjusted for optimum distortion canceling. The paper concludes by describing a second analogous link architecture in which it is the ratio of optical power at two modulated polarizations that is adjusted in order to achieve broad-band linearization     

Nonlinear analysis of a balanced diode modulator

Equations describing the performance of a balanced diode modulator are solved by an iterative process and the fast Fourier transform is used to obtain the spectrum of the output. The analysis provides an interesting example of the extension, to large-signal applications, of the method of solution recently described for quasilinear systems.     

Arsenic deposition as a precursor layer on silicon (211) and (311) surfaces

We investigate the properties of arsenic (As) covered Si(211) and Si(311) surfaces by analyzing data from x-ray photoelectron spectroscopy (XPS) and low-energy electron diffraction (LEED) images. We then create a model using total surface energy calculations. It was found that both Si(211) and Si(311) had 0.68±0.08 surface As coverage. Si(211) had 0.28±0.04 Te coverage and Si(311) had 0.24±0.04 Te coverage. The Si(211) surface replaces the terrace and trench Si atoms with As for a lower surface energy, while the Si edge atoms form dimers. The Si(311) surface replaces all terrace atoms and adsorbs an As dimer every other edge site. These configurations imply an improvement in the mean migration path from the bare silicon surface by allowing the impinging atoms for the next epitaxial layer, tellurium (Te), to bind at every other pair of edge atoms, and not the step terrace sites. This would ensure a nonpolar, B-face growth.