Output Power Spectrum Research Articles

Optical Fiber Systems Are Convectively Unstable

We theoretically and experimentally evidence that fiber systems are convective systems since their nonlocal inherent properties, such as the dispersion and Raman effects, break the reflection symmetry. Theoretical analysis and numerical simulations carried out for a fiber ring cavity demonstrate that the third-order dispersion term leads to the appearance of convective and absolute instabilities. Their signature is an asymmetry in the output power spectrum. Using this criterion, experimental evidence of convective instabilities is given in a fiber cavity pumped by a pulsed laser.

Broadband Interference Suppression Performance of Minimum Redundancy Arrays

The broadband interference suppression performance of the minimum redundancy array (MRA) used in the linearly constrained minimum variance (LCMV) beamformer is studied in this paper. The ideal continuous-time, infinite-length filter instead of the realistic finite-order digital filter is assumed in the array processor. The expressions of the power spectrum of the beamformer output in different scenarios are derived to compute the mean output power. Several original properties of the performance of the MRA compared with that of the uniform linear array (ULA) are obtained by mathematical proofs and numerical studies.

UWB Chaotic-OOK 통신을 위한 송신기 설계

본 논문에서는 TSMC 0.18 um CMOS 공정을 사용하여 UWB Chaotic-OOK(On-Off Keying) 통신을 위한 송신기를 설계하였다. 송신기는 Quasi-chaotic 신호 발생기, OOK 변조기, 구동 증폭기로 구성되어 있다. 일반적으로 아날로그 피드백을 사용하는 chaotic 신호 발생기는 공정 변화에 대한 취약점이 있어 이를 개선하기 위하여 디지털 피드백 구조의 Quasi-chaotic 신호 발생기를 사용하였다 또한, OOK 변조를 위해 T형 구조의 변조기와 단일 출력 신호를 얻기 위한 차동 입력 단일 출력 구동 증폭기를 설계하였다. 측정 결과, 요구되는 spectrum mask를 만족시키는 출력을 얻었으며, 데이터 20 Kbps, 200 Kbps, 2 Mbps, 10 Mbps에 따른 OOK 변조 테스트를 통해 출력 신호를 확인하여 UWB chaotic-OOk 송신기로 사용 가능함을 확인하였다. Chaotic OOK modulation method can be used in LDR(Low Data Rate) UWB systems. In this paper, UWB chaotic-OOK transmitter system is designed and verified using TSMC 0.18 um CMOS process. A transmitter system is composed of Quasi-chaotic signal generator, OOK Modulator, and driving amplifier. The traditional chaotic signal generators using analog feedback method is weak to process variation. In order to solve this problem, a quasi-chaotic signal generator using digital feedback technique is get wide band signal and OOK Modulator using T-type switching structure is used to enhance the isolation characteristic. A driving amplifier has differential to single structure to avoid an external balun for low cost communication. The measured output power spectrum of the transmitter meet the FCC regulation and the result of the modulation test at data rate of 20 Kbps, 200 Kbps, 2 Mbps, and 10 Mbps is conformed to LDR UWB system. It is shown that the transmitter in this paper can be used for the UWB chaotic-OOK system.

자동차용 모듈화 도어의 동특성 분석에 관한 연구

This study presents the design improvement process for door module. Its objective evades the resonance generated at module plate due to the operation of window regulator motor. For this study, the design improvement process is composed of experimental methods having three steps. First step is modal analysis at door assembly status for acquisition of dynamic characteristics which are modal frequency and damping. Second step is a vibration experiment to get the test mode considered an efficiency of window regulator motor. Last step is a vibration measurement by the form of array on module plate. A vibration measurement of array form can be got to three analysis results which are a transfer path of vibration using cross correlation function, a vibration map using OA level and a contribution by frequency band using coherent output power spectrum on module plate. These results are applied to SDM(structural dynamic modification) for design improvement to get around the resonance on module plate by the excitation of window regulator motor.

Considering even-order terms in stochastic nonlinear system modeling with respect to broadband data communication

Abstract. As a tradeoff between efficiency and costs \\mbox{modern} communication systems contain a variety of components that can at least be considered weakly nonlinear. A critical element in evaluating the degree of nonlinearity of any underlying nonlinear system is the amount of undesired signal strength or signal power this system is introducing outside the transmission bandwidth. This phenomenon called spectral regrowth or spectral broadening is subject to stringent restrictions mainly imposed by the given specifications of the particular communication standard. Consequently, achieving the highest possible efficiency without exceeding the linearity requirements is one of the main tasks in system design. Starting from this challenging engineering problem there grows a certain need for specialized tools that are capable of predicting linearity and efficiency of the underlying design. Besides a multitude of methods aiming at the prediction of spectral regrowth a statistical approach in modeling and analyzing nonlinear systems offers the advantage of short processing times due to closed form mathematical expressions in terms of input and output power spectra and is therefore further examined throughout this article.

Analytical expression of output power spectra of spin-transfer nano-oscillators

Analytical expressions of the output power spectra are derived for spin-transfer nano-oscillators, by using the phase-noise theories, which have been developed for electronic oscillators. The output spectra, which are proportional to the power spectra of transverse component of magnetization, are calculated under the thermal fluctuation with a small amplitude approximation.

Transition from a Strong to a Weak Coherence Resonance in Phase Neuron Models

We study the dynamical response to noise in the one-dimensional type-I phase neuron model with a parameter α (0 ≤ α ≤ 1) tuning the degree of multiplication in the noise. For α = 0, the phase model is just the Adler equation, while it becomes the canonical type-I theta model for α = 1. For the subthreshold case, the effect of noise on the oscillating characteristics is investigated by increasing α from 0. A characteristic correlation time τc has a maximum at some optimal noise intensity D∗, independently of α. However, the phase model exhibits spectrally a coherent or incoherent response to noise, depending on the value of α. For α = 0, a spectrally coherent response to noise occurs in the Adler equation (i.e., noise-induced peaks appear in the output power spectrum) and is maximized near D∗. Thus, the Adler equation exhibits a “strong” coherence resonance (i.e., a maximal correlation occurs along with a spectral coherence resonance). However, as α increases and passes a threshold value α∗, such a spectrally coherent response ceases because the noise-induced peaks disappear from the output power spectrum for α > α∗. Thus, the phase model for α > α∗ exhibits a “weak” coherence resonance (i.e., a maximal correlation occurs without any spectral coherence).

Coherence Resonance in Coupled Theta Neurons

We study the temporal coherence resonance (CR) of a local neuron in an excitatory network of globally coupled canonical type-I theta neurons. For the (isolated) single case, a subthreshold theta neuron exhibits a maximal correlation without any spectral coherence at some optimal noise intensity (i.e., occurrence of maximal correlation without any appearance of peaks in the output power spectrum). This kind of “weak” CR is in contrast to “strong” CR (i.e., occurrence of maximal correlation along with the spectral CR) occurring in the type-II excitable neuron. For the coupled case, each local neuron may be driven by a temporally coherent synaptic current occurring due to spatial coherence between neural spikings. Consequently, a strong CR may occur through the appearance of peaks in the local output power spectrum.

Physics-Based Analysis and Simulation of Phase Noise in Oscillators

A technology computer-aided design framework that can predict the phase noise spectrum of an oscillator using nonlinear perturbation analysis is developed. The device-circuit mixed-mode simulation technique based upon the shooting-Newton method is exploited to evaluate the periodic steady-state solution of the oscillator. The influence of noise sources inside the devices on the phase deviation is calculated in an efficient and accurate way using the perturbation projection vector. The period jitter and the output power spectrum can be easily obtained in this framework. As an application, the output power spectrum of a CMOS LC voltage-controlled oscillator is calculated

Using white light during photodynamic therapy: visualization only or treatment?

Photodynamic therapy (PDT) involves selective uptake and retention of a photosensitizer in a tumor, followed by irradiation with light (usually a 630 nm diode laser), initiating tumor necrosis through formation of oxidized products or singlet oxygen. Successful PDT of early cancers of the esophagus and of Barrett's esophagus with severe dysplasia has been reported. However, side effects (edema, stricture, etc.) and treatment failure have been observed. This study aims to evaluate the possible photodynamic effect induced by illumination from the endoscope on the PDT effect, since a photon emitted to see the lesion can potentially be a photon to treat it! Two fiber endoscopes (Olympus GIFPQ20 and Pentax FG34X) and one videoendoscope (Olympus GIFQ140) were evaluated. Output power, irradiance and emission spectrum were measured. Using the molar extinction coefficient of Photofrin and optical coefficients of the esophagus, the relative photodynamic reaction yield, determined as a function of depth, was compared with that obtained with a 630 nm diode laser. The irradiance at 1 and 2 cm was, respectively, 18.4 and 4.6 mW/cm (Pentax FG34X), 10.6 and 2.65 mW/cm (Olympus GIFPQ20), and 2.7 and 3.2 mW/cm (Olympus GIFQ140). The highest irradiance could lead to a relative photodynamic reaction yield at the surface of the esophagus similar to (Olympus GIFPQ20) or greater than (Pentax FG34X) that obtained using a diode laser alone. Our results could explain side effects sometimes observed when performing PDT. 'Endoscopic' illumination, however, could also represent an interesting alternative to the 630 nm diode laser. When using white light, superficial efficacy of PDT could be reinforced and transmural necrosis leading to perforation or stenoses reduced, since there is less red light in depth compared with a diode laser.

Theoretical and numerical analysis of superluminescent diodes

The authors present a set of simple analytical expressions for the design of superluminescent diodes (SLDs). To validate the analytical model, numerical simulations by a comprehensive mixed frequency-domain-time-domain traveling-wave model are performed. Through a comparison between them, guidelines for design optimization of SLDs are also discussed. In particular, the authors focus on the effects of the design parameters (e.g., cavity length and active region cross-sectional area) and operating condition (i.e., bias current) on the performance of SLDs (e.g., output power spectrum and power-bandwidth product). The good agreement between the analytical and numerical results demonstrates that the power-bandwidth product of SLDs can be enhanced by increasing the cavity length, reducing the active region cross-sectional area, and raising the operating current. It is shown that the dilution of carrier density along with the modal loss is the main factor that limits the cavity length.

Modeling nonlinear distortion of ultra wideband signals at X-band

Nonlinear distortion in the adjacent channels of an X-band amplifier driven by an ultra-wideband digitally-modulated carrier is analyzed. Statistical properties of the input signal with a complex power series-based behavioral model of the amplifier are used to calculate the output power spectrum. Comparisons are made between measured and predicted adjacent channel power rejection for the X-band monolithic microwave integrated circuit.

Generalized analysis of subcarrier multiplexing in dispersive fiber-optic links using Mach-Zehnder external modulator

A new exact analytical model is presented to analyze the dispersive transmission in subcarrier multiplexing (SCM) fiber-optic links using dual-drive Mach-Zehnder external modulator (DD-MZM). The model is very general and can be applied to almost all operating conditions of DD-MZM, such as bias point, drive level, phase shift, and modulation index difference between DD-MZM drives. The model results in simple, new, and closed-form expressions for output power spectrum, permitting an accurate and fast analysis of such links. Two special cases, double sideband (DSB) and single-sideband (SSB) modulation, are studied in detail. Some important system parameters, such as 1-dB compression point, the input third-order intercept point (IIP3), and the system capacity, are derived for the first time. Measured results for system capacity and intermodulation products of different orders match very well with the calculated results.

Quantum trajectory analysis for electrical detection of single-electron spin resonance

A Monte Carlo simulation on the basis of quantum trajectory approach is carried out for the measurement dynamics of a single electron spin resonance. The measured electron, which is confined in either a quantum dot or a defect trap, is tunnel-coupled to a side reservoir and continuously monitored by a mesoscopic detector. The simulation not only recovers the observed telegraphic signal of detector current, but also predicts unique features in the output power spectrum which are associated with electron dynamics in different regimes.

Clad-pumped Er3+/Yb3+-codoped short pulse fiber laser with high average power output exceeding 2W

A clad-pumped short pulse Er3+/Yb3+-codoped fiber laser based on master oscillator and power amplifier (MOPA) structure, integrating the performances of broad-band tunable wavelength, uniform output power spectrum, high repetition rate and high average power to together, is proposed and demonstrated. Combining the cavity parameter optimization of the fiber master oscillator and power fiber amplifier with gain saturation characteristic of erbium-doped fiber, we achieved a lasing output with uniform output power and continuously tunable wavelength in the range from 1535 to 1530nm (i.e. 35nm band width). The maximum output power fluctuation is no more than 0.5 dBm, the average power is about 2 W, pulse repetition rate is greater than 10 GHz and pulse width is less than 30 ps in the whole tunable wavelength band width. Furthermore, the laser has advantages of good performance, simple all-fiber structure and convenient operation.

High-power multi-mode laser to single-mode pump conversion

A novel pump-sharing module for multi-channel amplifiers based on integration of high-power multimode semiconductor lasers and planar waveguide circuits is proposed. The feedback-free modules are designed for optimum coupling, throughput and power uniformity on silicon using BPM method and fabricated via the sol–gel process of photo patternable precursors. Modal properties of the multimode lasers are considered by studying spectrum and spatial distribution of laser output power at different temperatures. Employing an 1500mW 980nm multimode laser (TE polarized), via lens and Butt coupling up to 1250mW of laser output is coupled into the multimode channel waveguides, which are tapered and branched to four single mode waveguides. The measured pump power from splitter outputs, randomly polarized, exceeds 600mW. At constant temperatures ranging from 22°C to 30°C, the pump-sharing modules exhibit good stability with a power uniformity of <0.5dB over hours.

Planck-LFI 44 GHz back end module

This work describes the principle of operation, assembly and performance of one branch of the 44 GHz back end module (BEM) for the Planck low frequency instrument (LFI). This subsystem constitutes a fully representative branch of the qualification-model version (QM). It includes waveguide to microstrip transition, GaAs pseudomorphic high electron mobility transistor (PHEMT) low noise amplifiers (LNA), bandpass filter, square-law detector and dc amplifier. The fundamentals of the design of the RF part are described and all of the components have been tested individually before integration. Using single tone and wideband noise stimuli, the output voltage has been measured for several input powers, in order to obtain the sensitivity factor of the complete BEM. The effective bandwidth and the equivalent noise temperature have been calculated from the measurements, taking into account the frequency dependence on the noise source and the BEM. Finally, the low frequency output power spectrum has been obtained and a maximum 1/f knee frequency around 200 Hz has been measured with a 3 dB output signal video bandwidth above 50 KHz.

An exact analytical model for dispersive transmission in microwave fiber-optic links using Mach-Zehnder external modulator

A new exact analytical model is presented to analyze the dispersive transmission in microwave fiber-optic links using a dual-drive Mach-Zehnder external modulator (DD-MZM). The model is very general and can be applied to almost all operating conditions of DD-MZM, such as bias point, drive level, phase shift, and modulation index difference between DD-MZM drives. The model results in simple new closed-form expressions for output power spectrum, permitting an accurate and fast analysis of such links. Expressions for two special cases, double sideband and single sideband modulation, are included, together with a novel presentation of some new results on power fading of fundamental and second harmonic.

A method for elimination of alternative noise by digital control of an analog Laguerre filter in biopotential measurements

The biological electrical signals measured on the surface of the body, such as electroencephalograms, electromyograms, and electroretinograms, contain strong AC noise from the commercial power supply. Even if a differential amplifier with a high discrimination ratio is used, it is often difficult, depending on the measurement environment, to completely eliminate AC noise. This paper considers a method for AC noise elimination in which an analog Laguerre filter is inserted on the negative input side of the differential preamplifier, and digital control is applied to the filter. An algorithm is constructed in which the transfer function of the Laguerre filter is designed so that AC noise with the known frequency and its harmonic components are minimized, based only on the output power spectrum, without using the tap output of the filter. A system was constructed and its application to biological electrical signals such as electroencephalograms and electroretinograms was attempted. © 2005 Wiley Periodicals, Inc. Syst Comp Jpn, 36(14): 1–10, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.20429

Investigation of dynamical pump control for backward-pumped fiber Raman amplifiers

For a broadband backward-pumped distributed fiber Raman amplifier (B-DFRA) operated in long-haul transmission system with massive signal channels, not only the average level but also the tilt of the output power spectrum will vary due to the variation of signal-to-signal Raman scattering. So, when the signal channel number or channel power varies, dynamical control of both the average level and tilt of the on–off gain is necessary. In this paper, an approximate two-dimensional linear expression for the individual pump power at each pump wavelengths versus the average on–off gain level and tilt was derived based on the theoretical analysis and numerical simulation. The method to pre-determine the control constants based on measured data was also introduced. By using this linear relation, output power spectrum clamping over C+L band (1529.1–1602.7 nm) was demonstrated experimentally for a single 100 km B-DFRA and a 6×100 km cascaded hybrid Raman/erbium-doped fiber amplifiers with up to five pump-wavelengths on standard single mode fiber. The average clamping error was less than 0.32 dB for single span and 0.5 dB for 6 spans.