Residual chirp in integrated-optic modulators

The authors have analyzed and measured the dispersion effects of residual chirp arising from asymmetry in field overlap in Mach-Zehnder structures. A clear influence of chirp was seen at 7 Gb/s and a propagation length of 75-km nondispersion shifted fiber at λ=1.55 μm. It is shown that a MZ-modulator with field overlap in one arm only and operated in the blue-shift mode is the best choice for single coplanar stripline (CPS) electrode MZ-modulators in this case. Calculations have shown good agreement with measured results. This indicates that a simple model for fiber mode propagation have shown good agreement with measured results. This can be used together with a FFT-algorithm for calculating the effect of residual chirp from external modulators in multigigabit dispersive fiber-optic systems     

A dual SQUID linearization concept using a phase modulation scheme

A critical control system evaluation is presented of basic flux-locked loop systems. The development of a new superconducting quantum interference device (SQUID) linearization method is then described, where no magnetic flux feedback is necessary to cancel the applied flux. It is shown that a dual SQUID configuration will be able to produce a true phase modulation system that is easily demodulated with a phase-locked loop. The theoretical performance of the proposed configuration is verified by simulations, and the performance and limitations are discussed in detail. It is shown that small dc correction voltages at the output of the SQUID's significantly decrease output noise, as is the case with an increase in SQUID dc bias currents. An optional feedback system is also described for optimal performance of the dual SQUID configuration     

New methods for adaptation of quadrature modulators anddemodulators in amplifier linearization circuits

Imperfections in analog quadrature modulators (QMs) and demodulators-gain and phase imbalance and DC offset-have a devastating effect on amplifier linearization circuits. Correction circuits have a simple structure, but their parameters must be adjusted adaptively. This paper introduces two new methods for such an adaptation. The first is based on a training sequence consisting of a tone at one or more amplitudes, and the second needs no training sequence at all. They are faster and more robust than previously published methods     

A novel integrated-optic WDM cross-connect for wide area all optical networks

The authors propose a novel design for an integrated-optic wavelength-division-multiplexing (WDM) cross-connect that can be used in routing network applications at various wavelengths. The device is based on integrating a two-dimensional array of Bragg diffraction cells at cross points of input/output (I/O) coplanar waveguides. The wavelength tuning of the individual Bragg cells can be chosen to produce a WDM cross-connect with any number of required I/O interconnections. These cross-connects have proved extremely useful in the design and deployment of wide-area/nationwide all-optical networks.<>     

OFDR diagnostics for fibre and integrated-optic systems

Optical frequency-domain reflectometry (OFDR) shows promise as a diagnostic tool for high-resolution ranging in fibre/integrated-optic systems, and in high-resolution distributed fibre-optic sensors. We discuss some signal processing aspects of this technology, potential performance and application.     

A folded-type integrated-optic spectrum analyzer using butt-coupled chirped grating lenses

A folded-type integrated-optic spectrum analyzer (IOSA) using reflection-type chirped grating lenses butt-coupled to a LiNbO3waveguide Bragg cell is presented. The lenses can be easily fabricated by the well-established planar process, and the IOSA has good performance as well as a reduced device length. The spectrum analyzer function of 4.0 MHz resolution in 95-345 MHz RF frequency range is demonstrated.     

一种模拟预失真自适应线性化方法

针对射频功率放大器的非线性问题,提出一种基于两个复量多项式的模拟预失真电路,并根据射频功率放大器的响应用LMS(最小均方)算法自适应优化多项式的系数,从而使功率放大器的线性性能达到最佳。该预失真器的优点是电路简单,运算量少,适用于宽带通信。基于双频信号和WCDMA(宽带码分多址)信号对该预失真器进行了仿真测试。实验结果表明,该预失真线性化方法对交调失真分量抑制效果明显,ACPR(邻信道功率比)可改善至56.1dB,对功率放大器的非线性具有良好的补偿效果。     

Novel type of broadband travelling-wave integrated-optic modulator

We propose and analyse a novel type of baseband travelling-wave integrated-optic modulator which has a broadened baseband response compared with corresponding modulators of conventional design. Numerical calculations are reported for this novel structure, and a comparison of figures of merit for the novel modulator and conventional types is given.     

Novel LiNbO3 integrated-optic component for coherent optical heterodyne detection

A novel LiNbO3 integrated-optic device capable of performing the optical signal processing functions of optical combining, frequency translation and polarisation control required for coherent optical detection is described. The operating characteristics of the device are reported and its use in coherent optical heterodyne detection described.     

热敏电阻温度计大范围线性化的新方法

本文提出一种新的对数函数来实现热敏电阻温度计的线性化,介绍所提出的方案的理论研究。文中讨论实现这种对数函数的电路结构,既新颖又简单。所述方案能够在大的动态范围内实现温度—电压变换,而且输出与环境温度的波动无关。电路测试结果证实了理论研究所得出的结论。     

A new dithering method for sigma-delta modulators

A new dithering method to remove limit-cycles in Sigma-Delta modulators is presented. With this new method, the sequence length of a Pseudo-Noise generated dither is matched to the digital decimation filter. This causes the frequency spikes of the dither to coincide with the notches of the filter which results in total elimination of the applied dither power. In contrast to existing dithering techniques, matched dithering will not introduce additional inband noise. Compared to existing dithering techniques, the required dither amplitudes are relatively small (5%–30% FS) and may decrease with increasing oversampling ratio. Matched dithering proves to be very powerful for instrumentation applications.     

一种适用于间接学习结构的功率放大器线性化算法

针对目前基于间接学习结构(indirect learning architecture, ILA)的线性化算法对于功率放大器的非线性补偿效果较差、频谱失真改善效果不明显的缺点,提出了一种基于功率检测模块的交替迭代算法。该算法利用数据窗截取ILA中后失真器反馈回来的数据流并通过功率检测模块计算其功率大小,筛选出功率最大的信号数据流,根据迭代次数,使得其输出在大功率信号流与随机信号流之间相互切换并送至后失真模块进行训练. 预失真模块和后失真模块均采用记忆多项式模型. 采用峰均比为9 dB的LTE信号通过在线测试平台RF WebLab对真实GaN功放进行仿真,结果表明,新提出算法的带外抑制效果相对于传统的顺序数据流处理算法与大功率数据流处理算法分别优化了5 dB与2.5 dB左右,其平均归一化均方误差也分别优化了1 dB与0.6 dB左右.     

Four-channel integrated-optic wavelength demultiplexer with weakpolarization dependence

A planar four-channel wavelength demultiplexer with weak polarization dependence is proposed and demonstrated. This demultiplexer is based on an optical-phased array. An experimental device with dimensions 4.5×3.2 mm² was designed and fabricated, using conventional (high-quality) optical lithography. The demultiplexer operates in the wavelength range 776.5-781.2 nm, with a channel spacing of 1.55 nm. Insertion loss was 0.6 dB for the central channels and 1.2 dB for the outer channels for transverse-electric (TE) polarization, excluding 1.3-dB waveguide propagation loss. Crosstalk values measured 15.4-29.7 dB for the TE and 13.4-22.2 dB for the transverse-magnetic (TM) polarization     

A time-domain noise-coupling technique for continuous-time sigma-delta modulators

In this paper, a time-domain noise-coupling technique based on the pulse width modulation is proposed. The time-domain quantization error is digitally extracted and shaped by an asynchronous digital filter. This digitally filtered quantization error is applied to the quantizer input to increase the modulator’s noise-shaping order. By using this technique in continuous-time sigma-delta modulators, the modulator’s shaping property is significantly enhanced. Comparative analytical calculations and simulation results are presented to estimate the performance of modulators employing the proposed quantizer. System-level simulation results reveal a (L + 2)th order noise-shaping capability of the proposed modulator while it employs only L analog integrators. The effects of main circuit non-idealities in the modulator’s performance are analytically investigated and confirmed by the simulation results.     

Modeling modulators for A/D signal conversion

The performance of an SDM is reported to decline by various factors produced during the design and fabrication process. Namely, the nonideal factors are: the limit of the operational amplifier (op-amp) output swing, the finite DC gain of the op-amp, op-amp slew rate, the integrator gain error by mismatching of the capacitor and nonideality of the internal multibit quantizer. In this article we report not only modeling results of the ideal second-order SDM with a multibit quantizer, but also evaluate its performance according to bit number and OSR. In addition, we determine the maximum error limit of the SDM after investigating the influence of the nonideal factors on the performance of the SDM     

Harmonic and intermodulation performance of active integrated-optic waveguides

An empirical formula is developed for the static input/output optical characteristic of the active integrated-optic waveguide. Using this formula, closed-form analytical expressions, in terms of the ordinary Bessel functions, are obtained for the output optical components resulting from a modulated multisinusoidal optical input. Using these expressions the effect of the wavelength of the light input, the guide width, the modulation depth and the optical power for transperancy on the harmonic and intermodulation performance of the active integrated-optic waveguide can be studied.     

A modified model and linearization method for solid state power amplifier

For successful implementation of a multi-standard receiver, a reconfigurable receiver architecture and a reconfigurable component design technique are essential. In this paper, an adaptable receiver architecture and a reconfigurable RF design technique using a switchable passive network are proposed. To verify the proposed design technique, the reconfigurable mixer and QVCO are designed using a flexible matching network and flexible LC tank, respectively. The measurement results of each component well prove the usefulness of the switchable passive network. Y.-K. Jang is now working for Samsung Electronics, Kiheung, Korea.     

通用可编程多量子阱空间光调制器驱动电路

A universal programmable multi-quantum-well（MQW） spatial light modulator（SLM） driving circuit is developed.With a twice scanning, it can generate programmable signals to drive a non-linear MQW SLM by using a software preprocessing unit.By adjusting the switching network of the driving circuit, this circuit can reduce the switching noise and improve the output precision.The chip test results show that the driving voltage can swing from 0 to VDD, and its resolution could be close to 256 with a pixel area of only 65 × 65 μm2.