Electrical Filter Research Articles

Multiplexed reflectometric fiber optic frequency-modulated continuous-wave interferometric displacement sensor

A practical double-sensor multiplexed fiber optic displacement sensor is reported. The sensor is based on the principles of optical frequency-modulated continuous-wave (FMCW) interference and frequency-division multiplexing. The beat signals from the individual sensors are assigned in the frequency domain and separated with different electrical bandpass filters. The displacements of the targets can be determined simultaneously by detecting the phase shifts of the corresponding beat signals. The cross talks between the individual sensors are analyzed algebraically and with a phasor diagram. An accuracy of 0.05 µm in a dynamic range of 1000 µm is achieved.

The ELPI Response and Data Reduction II: Properties of Kernels and Data Inversion

The first part of this article reports the analytical form of the Electrical Low Pressure Impactor (ELPI) kernel functions. In this latter part, the numerical quality of ELPI response matrices is studied and an example of an inversion algorithm is given. The ELPI assemblies with and without an electrical filter stage and with smooth or sintered impaction plates are studied and compared with basic impactor kernels and the kernels for the calculation of the aerosol mass distribution. It is shown that the ELPI assembly with the electrical filter stage and smooth impaction plates should be the best choice for the inversion of data if no bounce occurs. The comparison to a mass impactor shows that the devices are on par in data inversion. The inversion ELPI data is studied with a Bayesian algorithm assuming a bimodal lognormal size distribution of the aerosol. The algorithm includes a novel procedure for obtaining an initial guess of the distribution parameters. To our knowledge, it is also the first algorithm ...

Evaluation of Transparent Optical Network Performance in Presence of Incoherent Homodyne Crosstalk

A simple method to evaluate the performance of transparent optical networks (TON) that takes into account the incoherent homodyne crosstalk, signal distortion, inter-symbol interference (ISI), amplified spontaneous emission (ASE) noise, and arbitrary optical and electrical filters is proposed. This method combines the effect of the incoherent homodyne crosstalk with an exhaustive Gaussian approximation for the influence of ASE noise, signal distortion, and ISI. It is shown that the incoherent homodyne crosstalk penalty depends on the ASE noise accumulated in the TON, ISI, and extinction ratio. The proposed method estimates are compared with experimental results published by other authors. Good agreement is observed for one, two, and four incoherent homodyne crosstalk signals, revealing that the proposed method provides accurate estimates even when the methods based on a Gaussian approximation for the incoherent homodyne crosstalk fail. The proposed method is used to assess the performance of a TON composed by optical add-drop multiplexers based on arrayed waveguide gratings. Results reveal that incoherent homodyne crosstalk, ASE noise, and ISI impair the TON performance and, therefore, none can be neglected in the TON design.

Tunable Microelectromechanical Filters that Exploit Parametric Resonance

Abstract Background: This paper describes an analytical study of a bandpass filter that is based on the dynamic response of electrostatically-driven MEMS oscillators. Method of Approach: Unlike most mechanical and electrical filters that rely on direct linear resonance for filtering, the MEM filter presented in this work employs parametric resonance. Results: While the use of parametric resonance improves some filtering characteristics, the introduction of parametric instabilities into the system does present some complications with regard to filtering. Conclusions: The aforementioned complications can be largely overcome by implementing a pair of MEM oscillators with tuning schemes and some processing logic to produce a highly effective bandpass filter.

Self-starting picosecond optical pulse source using stimulated Brillouin scattering in an optical fiber

We demonstrate a regeneratively mode-locked optical pulse source at about 10 GHz using an optoelectronic oscillator constructed with an electro-absorption modulator integrated distributed feedback laser diode. The 10 GHz RF component is derived from the interaction between the pump wave and the backscattered, frequency-downshifted Stokes wave resulted from stimulated Brillouin scattering in an optical fiber. The component serves as a modulation source for the 1556 nm laser diode without the need for any electrical or optical RF filter to perform the frequency extraction. Dispersion-compensated fiber, dispersion-shifted fiber, and standard single-mode fiber have been used respectively to generate optical pulses at variable repetition rates.

Performance Monitoring in Optical Networks Using Asynchronously Acquired Samples With Nonideal Sampling Systems and Intersymbol Interference

This paper presents a study on the influence of nonideal sampling in asynchronous Q-factor monitoring. An overestimation of the Q-factor of signals impaired with optical noise may occur if the averaging effects due to nonideal sampling affect only the noise component of the monitored signal. It is shown that this problem can be rectified using a correction factor, dependent only on the receiver parameters. This allows reasonable Q-factor estimates using sampling systems with aperture times close to the monitored signal bit period. Nonideal sampling may also affect the signal component of the monitored signal. For such cases, a novel and accurate technique is presented to estimate the Q factor using asynchronous histograms, which takes into account changes in the shape of the monitored signal due to averaging effects. Numerical simulations are used to evaluate the proposed technique achieving Q-factor estimates within a 14% error margin, independently of the sampling aperture for the considered range. Distortion affecting the signal due to the transmission system can also be handled by the new technique presented in this paper. It is verified that the impact of intersymbol interference due to chromatic dispersion or electrical filtering in the receiver on the performance of the system is well reflected by the estimated Q factor.

Chromatic Dispersion Tolerance of New Duobinary Transmitters Based on Two Intensity Modulators Without Using Electrical Low-Pass Filters

This paper describes an investigation of the effect of the extinction ratio and the chirp parameter of the first intensity modulator on the transmission performance of a proposed duobinary transmitter based on two intensity modulators without using electrical low-pass filters. This modulation scheme can generate duobinary signals using only two-level electrical signals without the conversion process to three-level electrical signals using electrical low-pass filters. The simulation results suggest that the appropriate chirp and extinction ratio of the first intensity modulator provide larger dispersion tolerance, compared with the conventional duobinary transmitter. The duobinary transmitter based on two intensity modulators can increase the dispersion tolerance without using electrical low-pass filters.

Electrically Band-Limited CSRZ-DPSK Signal With a Simple Transmitter Configuration and Reduced Linear Crosstalk in High Spectral Efficiency DWDM Systems

In this letter, we propose a novel transmitter configuration for generating electrically band-limited (EB) carrier-suppressed return-to-zero (CSRZ) differential phase-shift-keyed (DPSK) signals, which requires only a single-stage Mach-Zehnder modulator in conjunction with an electrical band-limiting low-pass filter and electrical mixer. The proposed scheme is cost-effective due to the simple configuration. In addition, when applied to dense wavelength-division-multiplexing systems with high spectral efficiency, the EB-CSRZ-DPSK signal exhibits reduced linear crosstalk, increased dispersion tolerance, and no additional nonlinearity penalty in comparison to the conventional CSRZ-DPSK signal.

Experimental Evaluation of an Open-Loop All-Optical Chaotic Communication System

An experimental investigation of the performance of an open-loop optical chaotic communication system has been carried out under different optical injection conditions. The most popular message encoding techniques have been considered, tested and compared at gigabit rates and for different levels of optical injection to the receiver, by bit-error-rate (BER) measurements. Different low-pass electrical filters have been implemented for the various message bit-rates tested, in order to employ the most appropriate one for message decoding. The best performance of all the examined encryption methods for messages of 1.5 Gb/s bit-rate emerged for the chaos modulation encryption method and was characterized by Q-factor values up to 5.1, after synchronizing in the strong injection regime, while the corresponding BER of the decoded message was as low as 7/spl middot/10/sup -5/. In order to confirm the secure encryption of the message, BER measurements are also performed for the chaotic carrier into which the message is encrypted.

Gaussian approach to the performance assessment of optical multiplexer/demultiplexer concatenation in transparent optical networks

A Gaussian approach (GA) with two equivalent optical filters, one for the noise and the other for the signal, is proposed for analytically evaluating the transparent optical network (TON) performance for arbitrary TON topologies, optical multiplexers/demultiplexers and electrical filters. This GA helps in identifying, in a fast computational way, the different mechanisms that contribute to TON performance degradation. The accuracy of estimates obtained through the GA is assessed in comparison with an exact method. In the case of no laser misalignment, the estimates given by the GA are very accurate, with maximum discrepancies of 0.5 dB observed for infinite extinction ratio. With extinction ratio reduction, the accuracy of GA estimates is further improved. With laser misalignment, for an extinction ratio of 10, the GA estimates are reasonably accurate, and for infinite extinction ratio, the accuracy is slightly reduced, but TON Q-factor behaviour is well assessed by the GA. Only for optical filters with large bandwidth and some laser misalignment, can GA estimates diverge, with discrepancies not exceeding 2.6 dB in the range of parameters investigated.

Filters and Components With Inductance Cancellation

Electrical filters are important for attenuating electrical ripple, eliminating electromagnetic interference (EMI) and susceptibility, improving power quality, and minimizing electromagnetic signature. Capacitors are critical elements in such filters, and filter performance is strongly influenced by the capacitor parasitics. This paper introduces a new design technique that overcomes the capacitor parasitic inductance that limits filter performance at high frequencies. Coupled magnetic windings are employed to effectively cancel the parasitic inductance of capacitors, and to add inductance in filter branches where it is desired. The underlying basis of the new technique is treated in detail, and its application to the design of both discrete filters and integrated LC filter components is described. Numerous experimental results demonstrating the high performance of the approach in both discrete filters and integrated filter elements are provided.

Noise Suppression Using Dispersion Decreasing Fibers for RZ Transmission Systems

A new technique is proposed for noise suppression in return-to-zero systems. The nonlinear propagation in dispersion decreasing fiber (DDF) combined with narrow-band optical and/or electrical filters suppresses noise superposed on signal. As a result, Q-factor is improved by about 2.5 dB as compared to the case without DDF.

Impact of Chromatic and Polarization-Mode Dispersions on DPSK Systems Using Interferometric Demodulation and Direct Detection

We study the impact of chromatic dispersion (CD) and first-order polarization-mode dispersion (PMD) on systems using binary differential phase-shift keying (2-DPSK) or quaternary DPSK (4-DPSK) with nonreturn-to-zero (NRZ) or return-to-zero (RZ) formats. These signals are received using optical preamplification, interferometric demodulation, and direct detection. We consider the linear propagation regime and compute optical power penalties at fixed bit-error ratio (BER). In order to evaluate the BER precisely taking account amplifier noise, arbitrary pulse shapes, arbitrary optical and electrical filtering, CD, and PMD, we introduce a novel model for DPSK systems and compute the BER using a method recently proposed by Forestieri for on-off keying (OOK) systems. We show that when properly applied, the method yields highly accurate results for DPSK systems. We have found that when either the NRZ or RZ format is used, 2-DPSK exhibits lower power penalties than OOK in the presence of CD and first-order PMD. RZ-2-DPSK, as compared with NRZ-2-DPSK, incurs smaller penalties due to PMD, but offers no advantage in terms of CD. 4-DPSK, as it has twice the symbol duration of OOK or 2-DPSK for a given bit rate, incurs much lower CD and PMD power penalties than either of these techniques. RZ-4-DPSK is especially promising, as it offers CD and PMD penalties significantly smaller than all other techniques, including NRZ-4-DPSK.

Reducing the Toxicity of Diesel Exhausts with Electrical Filters

Reducing the Toxicity of Diesel Exhausts with Electrical Filters

Impact of Modulation Format and Filtering on the Calculation of Amplified Spontaneous Emission Noise Penalty

We report a generalized analytical model for computing amplified spontaneous emission (ASE) noise in optically amplified systems. Our new model analytically takes into account both the pulse shape associated with different modulation formats as well as the exact transfer functions of the optical and electrical filters. We compare our model against fully numerical simulations and show excellent agreement for all cases.

319 鉄道車輪/レール系騒音の車上設置型デバイスによるアクティブ消音制御の基礎的研究(能動的騒音制御,OS-20:サイレント工学)

The concept of the active sound cancellation control of the railway wheel/rail noises by the On-vehicle-type devices is presented. And the apparatus of randomly exciting 60kg rail by the electromagnetic shaker which is enclosed with the panel system simulating the floor/side wall of the railway car was constructed. Further, one unit of the devices which realizes in principle the sound cancellation control of the see-through space was manufactured and the parabola-microphone and actuating speaker was installed on it in addition to the controller consisting of the analog electrical band-pass filter circuit group. And it was verified that the sound cancellation control effects are observed actually for the both cases of a speaker and the randomly excited rail system which were regarded as the primary sound sources.

Modified duobinary polarization-shift keying transmission scheme

A new version of duobinary polarization-shift keying scheme is proposed. The relocation of the duobinary filter at the receiver side and the optimization of both transmitter and receiver electrical filters offer a receiver sensitivity improvement while maintaining chromatic dispersion tolerance. The main reason for this sensitivity enhancement is the reduction of the timing jitter and the noise narrow filtering provided. Moreover, the system is more tolerant against fiber nonlinear effects.

New Rigorous Model for Rx ISI Effects in WDM Systems

We present a model for Rx ISI effects using a new and completely general and rigorous dynamic Rx model formulation aiming at 10-40 Gbit/s WDM system design applications. The signal shaping part of an electrical filter is modelled in the optical domain using the filter impulse response to modify the signal vector and the covariance matrix. In this way inter-symbol-interference (ISI) effects from any type of electrical filter - specified by the filter impulse response - can be described. The formulation leads to a Hermitian form of the covariance matrix, thus allowing a straightforward analytical formulation of the moment generating function (MGF) which in turn specifies the bit-error-ratio (BER). Numerical examples for a 10 Gbit/s pre-amplified Rx shows that the ISI leads to (up to) several dB's degradation in sensitivity. Thus it is imperative to account for the Rx ISI effect in rigorous and accurate form in any general WDM transmission model.

A detector for monitoring the onset of cavitation during therapy-levelmeasurements of ultrasonic power

Acoustic cavitation occurring in the water path between a transducer and the targetof a radiation force balance can provide a significant source of error during measurements ofultrasonic power. These problems can be particularly acute at physiotherapy levels (>1 W),and low frequencies (⩽ 1 MHz). The cavitating bubbles can absorb and scatter incidentultrasound, leading to an underestimate in the measured power. For these reasons, InternationalSpecification standards demand the use of degassed water. This imposes requirements that mayactually be difficult to meet, for example, in the case of hospitals. Also, initially degassedwater will rapidly re-gas, increasing the likelihood of cavitation occurring. For these reasons,NPL has developed a device that monitors acoustic emissions generated by bubble activity, fordetecting the onset of cavitation during power measurements. A commercially available needlehydrophone is used to detect these emissions. The acoustic signals are then monitored using aCavitation Detector (CD) unit, comprising an analogue electrical filter that may be tuned todetect frequency components generated by cavitating bubbles, and which provides anindication of when the measured level exceeds a pre-defined threshold. This paper describesstudies to establish a suitable detection scheme, the principles of operation of the CD unit, andthe performance tests carried out with a range of propagation media.

An Advanced Direct Detection Receiver Model

An advanced receiver model for the optically amplified communication system (based on EDFA, Raman or hybrid Raman/EDF amplifiers) is proposed. It is independent on modulation scheme, pulse shape, type of electrical filter and type of optical filter. The channel is modeled as a stationary additive noise channel with memory (intersymbol interference-ISI), with the noise at its arbitrary statistics. The validity of the model is verified by Monte Carlo simulations for different modulation schemes like non return to zero (NRZ), return to zero (RZ), chirped return to zero (CRZ) and carrier suppressed return to zero (CSRZ) with respect to the amplifier spontaneous emission (ASE) noise. An excellent agreement is obtained for the all considered schemes.