Electrical Filter Research Articles

A general and rigorous WDM receiver model targeting 10-40-Gb/s channel bit rates

We present a general and rigorously formulated dynamic receiver model aiming at 10-40-Gb/s wavelength division multiplexing (WDM) system design applications. A demultiplexing (DEMUX) characteristic with periodic transfer function has been treated in detail and it has been indicated how the model should be adjusted to take into consideration a general type of noise spectral density (NSD). The bit error ratio (BER) is evaluated accounting for the influence of non-Gaussian detected amplified spontaneous emission (ASE) noise, noise correlation between stochastic noise samples in the receiver, the gain and effective noise figure variation with wavelength of optical amplifiers, channel crosstalk, and intersymbol interference (ISI) effects caused by nonideal signal modulation, fiber dispersion, fiber nonlinearities, optical MUX, and DEMUX filtering and the impulse response of the electrical low-pass filter in the receiver. Also, the influence of shot and thermal noise is taken into account. Numerical results for the BER are presented considering a realistic 16-channel 10-Gb/s WDM system operating in the C-band using normal transmission fibers and including cascaded erbium-doped fiber amplifiers (EDFAs) with dispersion compensating fibers.

Gaussian approach for performance evaluation of optically preamplified receivers with arbitrary optical and electrical filters

A Gaussian approach (GA), which takes into account the influence of arbitrary optical and electrical filters, is proposed to analytically evaluate the performance of optically preamplified receivers. This GA also takes into account the effects of waveform distortion in the signal and in the signal-amplified spontaneous emission beat noise. Exact expressions for the mean and variance of the current at the decision circuit input are derived, which explicitly present the dependence on the optical and electrical filter transfer functions and take into account the presence or absence of a polariser. This GA is computationally much faster and simpler than more rigorous methods and the accuracy of its sensitivity estimates is investigated for different optical and electrical filters. It is shown that the GA predicts the optimal optical filter bandwidth very reasonably. Discrepancies below 1.2 dB are found between its sensitivity estimates and rigorous estimates. The assessment of the optical filter detuning impact on the receiver sensitivity is also investigated with this GA. Discrepancies less than 1 dB are found between the GA estimates and rigorous estimates. The GA sensitivity estimate's accuracy is also investigated in the presence of intersymbol interference (ISI) and very accurate predictions are obtained by the GA for significant ISI.

Transmission performance of 10-Gb/s optical duobinary transmission systems considering adjustable chirp of nonideal LiNbO/sub 3/ Mach-Zehnder modulators due to applied voltage ratio and filter bandwidth

We investigate interplay between the residual and applied chirp of optical duobinary modulated signals in order to improve transmission performance. To find the best performance for 10-Gb/s optical duobinary transmission systems, we consider the residual chirp accompanying from the finite extinction ratio, the applied chirp adjusted by the applied voltage ratio (the chirp parameter) between two electrodes of LiNbO/sub 3/ modulators, and the bandwidth of electrical low-pass filters used in duobinary transmitters. The simulation results suggest that nearly zero chirp during the mark ('1') period and large peak chirp at the middle of the space ('0') provide the best transmission performance. This zero chirp around marks and high peak chirp at the middle of each space can be controlled by the applied voltage ratio between two electrodes of modulator and the filter bandwidth, respectively.

A novel analytical approach to the evaluation of the impact of fiber parametric gain on the bit error rate

We present in this paper a novel accurate method to analyze the performance of an optical link where the amplified spontaneous emission noise, enhanced by a fiber nonlinear phenomenon called parametric gain, is the limiting factor. Our method allows us to compute the exact error probability given a generic noise spectral density at the input of a direct detection optical receiver, using arbitrary optical and electrical filters. We compare our results with those predicted using the standard Gaussian technique (based on the Q factor), showing that this approximation may lead to significant errors. Our method is then used to evaluate the impact of parametric gain on a realistic long-haul multiwavelength link operating at 10 Gb/s, showing both the system limitation imposed by this phenomenon and the inaccuracy of the Q factor method.

Dew Point Hygrometers for Irrigation Scheduling in Fine-Textured Soils

The competition for water in irrigated agriculture with other water users has increased demand for accurate determination of soil water status for efficient irrigation. There has been much interest in measuring topsoil hydraulic properties, including soil matric potential (SMP), as a tool for irrigation scheduling. Currently, many methods are available to measure SMP, including tensiometers, electrical resistance units, heat dissipation, and filter paper techniques. However, their acceptance is limited because of limitations in different applications (i.e., soil type, measurement range, accuracy, etc.). Soil hygrometers may be better-suited instruments to measure SMP when they are used in fine-textured soils (i.e., clay). The objectives of this experiment were: (1) to determine the mean SMP in topsoil (0-0.30 m) at the onset of irrigation, resulting in maximum corn (Zea mays> L.) grain yield using the dew point soil hygrometer; (2) to relate these SMP values to the full profile (0-0.90 m) available water (AW) to determine the optimum value of SMP for scheduling irrigations for summer-grown corn under a Mediterranean climate; and (3) to determine the number of soil samples required for a valid representation of SMP measured with a dew point hygrometer under field conditions. An experiment with three irrigation treatments (S1, S2, and S3) was conducted on a clay soil (47% clay). Three irrigation treatments were based on replenishing the 0.90 m root zone to the field capacity when the soil water dropped to 75% (S1), 50% (S2), and 25% (S3) of available water holding capacity (AWHC). A dryland treatment (S4) was also included. The mean SMPs for topsoil at the onset of irrigation were -303, -406, and -635 kPa for S1, S2, and S3 treatments, with grain yields of 5333, 6058, and 4570 kg/ha, respectively. The dryland treatment resulted in the minimum yield of 740 kg/ha. Results showed that the mean SMP value of -406 kPa can be a reliable point to apply irrigations for corn grown in this soil. The relationship between 0-0.30 m depth SMP versus full profile (crop root zone) AW was found to be: SMP = 2150 - 4.35AW (r2 = 0.80, n = 47, SMP in kPa, AW in mm). This equation can be used to estimate full profile AW using 0-0.30 m depth SMP. For this soil and no-rainfall condition, monitoring one layer (topsoil) SMP can be used to estimate full profile AW. Results also showed that 28 ± 8 or 20 ± 5 soil samples are needed to obtain ± -10 kPa precision of SMP measurements for the maximum yielding treatment (S2) at 95% and 90% confidence levels, respectively. For these soil conditions, the dew point soil hygrometer is a well-suited device that can be used to measure SMP for irrigation scheduling. It is sensitive and consistent, and easy to calibrate and use.

Performance evaluation of prechirped RZ and CS-RZ formats in high-speed transmission systems with dispersion management

This paper describes the transmission performance of prechirped return-to-zero (RZ) and prechirped carrier-suppressed return-to-zero (CS-RZ) signals over a periodically dispersion-compensated transmission line. We analyze the transmission characteristics of both formats, taking account the transmitter configuration expected, in which pulse chirping is generated by using both a phase modulator and a linear dispersion compensating device. We also discuss the dependence of the transmission characteristics on phase modulation, pre- and postcompensating dispersion, and receiver optical and electrical filter widths. We show that, in single-channel transmission, phase modulation effectively reduces the intrachannel nonlinear interaction and improves the transmission performance. Next, we discuss the transmission characteristics of chirped RZ and chirped CS-RZ signals in dense wavelength division multiplexed (DWDM) signal transmission. In 100-GHz spaced 40-Gb/s-per-channel systems, it is shown that the phase modulation must be carefully optimized in order to minimize the linear crosstalk and waveform distortion induced by the intra- and interchannel nonlinear interaction in the transmission fiber.

Optimum filter bandwidths for optically preamplified NRZ receivers

We present a comprehensive treatment of optically preamplified direct detection receivers for non-return-to-zero (NRZ) and return-to-zero (RZ) on/off keying modulation, taking into account the influence of different (N)RZ optical pulse shapes, specified at the receiver input, and filter transfer functions; optical Fabry-Perot filters (FPFs) and Bragg gratings as well as electrical fifth-order Bessel and first-order RC low-pass filters are considered. We determine optimum optical and electrical filter bandwidths and analyze the impact of bandwidth deviations on receiver sensitivity. Optimum receiver performance relies on a balance between noise and intersymbol interference (ISI) for NRZ transmission, while for RZ reception detection noise has to be traded against filter-induced signal energy rejection. Both for NRZ and 33% duty cycle RZ, optical filter bandwidths of around twice the data rate are found to be optimum. Receivers using RZ coding are shown to closely approach the quantum limit, and thus to outperform NRZ-based systems by several decibels. We further analyze the impact of important degrading effects on receiver sensitivity and optimum receiver bandwidths, including receiver noise, finite extinction ratio, chirp, and optical carrier frequency (or optical filter center frequency) fluctuations.

Comparison of PMD-compensation techniques at 10 Gbit/s using an optical first-order compensator and electrical transversal filter

We present, for what is believed to be the first time, a direct comparison of two basically differently working polarization mode dispersion compensation techniques, the first-order compensator working in optical domain and an adjustable transversal filter working in electrical domain. Based on numerical simulations we show the efficiency of both equalizers in presence of first- and higher order PMD applying a transmission at 10 Gbit/s. Furthermore we show the applicability of spectral filtering for penalty signal extraction in presence of higher order PMD and give an overview of adaptive blind channel equalization.

Learning to discriminate reduced-channel /bɑ/–/wɑ/ syllables in normal-hearing adults

Acoustic information delivered to individuals with cochlear implants differs in many ways from the same information delivered via a normally functioning cochlea. One difference is that the number of frequencies that can be distinguished is sharply reduced in implanted listeners. This results in poor frequency selectivity where only sounds that fall into different frequency bands are distinguishable (all other things being equal). Shannon [Science 270, 303–304 (1995)] used an electrical filtering and rectification system to simulate this aspect of cochlear implant function in normal-hearing listeners. In the present study software filtering was combined with envelope-shaped-noise (ESN) processing to accomplish the same end. The immediate goal was to examine the efficacy of a simple technique in training listeners to distinguish between reduced-channel versions of syllables. The stimuli tested were synthetically produced /bɑ/ and /wɑ/ syllables, identical in every aspect except for their onset duration. These syllables were filtered into eight frequency bands and ESN processed. Following this they were once-again filtered at the same frequencies to create reduced-channel versions of the original syllables. The resulting stimuli were presented to 16 normal-hearing adult subjects in behavioral and electrophysiological tasks. Results demonstrated that the training rapidly improved listeners’ abilities to identify reduced-channel /bɑ/ and /wɑ/.

Classical measurements of sound

From the 1500s the study of sound involved acoustics and vibrations. Early theoreticians tried to experimentally justify their analytical models. Many vibrating devices were available to generate acoustic waves but few means were available to quantify these sources and sound propagation. The human ear was the only means of amplitude measurement and spectral analysis. The development of electrical and electromechanical technology allowed great advancements in the measurement of sound. Bell’s telephone transmitter/receiver and Flemming’s valve brought great strides in quantifying sound. The capacitor microphone brought high accuracy. The advent of the oscilloscope and electrical filters provided analysis of complex sounds. This level of technology served the field well until the advent of the computer age.

Error Rate Analysis of Optical Receivers with Fabry-Perot Optical Filter and Equalizing Postdetection Filtering

A complete analytic solution in form of the moment-generating function is presented for the statistical distribution of the decision variable of an on-off system with a Fabry-Perot optical filter. The results include ASE noise, photodetector shot noise and dark current together with thermal noise in the decision circuit. The influence of intersymbol interference is incorporated into the analysis and the optimal bandwidth of the optical filter is determined. It is shown that an equalizing electrical postdetection filter may make a significant improvement in performance. The analysis is extended to cover receivers with an arbitrary optical filter and arbitrary postdetection filtering by making use of a Gaussian approximation.

Polarization mode dispersion compensation at 10, 20, and 40 Gb/s with various optical equalizers

Polarization mode dispersion (PMD), especially in old fibers, is considered harmful for installation and upgrading of trunk lines. An optical PMD equalizer should have several or many differential group delay (DGD) sections with polarization transformers in between which can endlessly transform any input polarization into a principal state of the following DGD section. The sections must practically have fixed DGDs unless there is only one section. The small-signal baseband transfer function for PMD, higher order PMD, and the necessary number of sections as well as their control by the output signals of an electrical filter bank in the receiver are also discussed in this context. Several PMD equalizers have been realized and successfully tested in transmission systems with bit rates of 10, 20, and 40 Gb/s. The systems operated stably with well-opened eye diagrams for DGDs ranging between 0 and 1.7 bit durations. Best performance is obtained from a distributed PMD equalizer with one piece of polarization-maintaining fiber twisted by 64 stepper motors. The principle can also be realized in LiNbO/sub 3/.

Intensity correlations in filtered phase-diffusing light

Light undergoing phase diffusion displays a Lorentzian line shape: Here, electrical filtering techniques are used to examine the correlations among different spectral regions under this line shape. The experiment involves delayed self-heterodyne measurements of the output from a single-mode semiconductor laser. Two filters are tuned to isolate the signal contributions from opposite wings of the spectrum, and the transmitted intensities are shown to be strongly correlated in some regimes and strongly anticorrelated in others.

A Correlation Study Among Various CSS Testers

A correlation study is performed on three types of contact start/stop (CSS) testers: a spin-stand tester, a drive tester with an aluminum strain arm, and a drive tester with a brass strain arm. The measured stiction values are different, up to 78% for the same type of head/media combination on these three types of testers. It is found that strain arm resonant frequency, electrical filter, and system dynamics are the major factors for different stiction values. For a drive motor with back-cogging, the back-cogging acceleration also affects the measured stiction value. If these effects are considered properly, good correlation is obtained among various types of CSS testers. Presented at the 53rd Annual Meeting in Detroit, Michigan May 17–21, 1998

Effect of temperature on electrical resonance in leopard frog saccular hair cells.

Leopard frog saccular hair cells exhibit an electrical resonance in response to a depolarizing stimulus that has been proposed to contribute to the tuning properties of the frog sacculus by acting as an electrical band-pass filter. With the whole cell patch-clamp technique, we have investigated the effect of temperature on electrical resonances in isolated saccular hair cells, and we have described the effects of temperature on the currents and channel kinetics underlying electrical resonance. A hair cell's onset resonant frequency in response to a constant depolarizing current pulse increases linearly with temperature at a rate of 11 Hz/1 degrees C, exhibiting a mean Q10 of 1.7 between 15 and 35 degrees C. However, offset resonant frequencies continue to double every 10 degrees C, exhibiting a mean Q10 of 2.1. If steady-state voltage during the stimulus is held constant, all oscillatory frequencies increase with a mean Q10 of 2.1. The average level of steady-state depolarization during a +150-pA depolarizing current pulse decreases with increasing temperature (-6 mV from 15 to 25 degrees C). This temperature-dependent reduction of the steady-state membrane potential causes a shift in the voltage-dependent channel kinetics to slower rates, thus reducing the apparent Q10 for onset resonant frequencies. The peak outward tail current and net steady-state outward current, which is the sum of a voltage-dependent inward calcium current (ICa) and an outward calcium-dependent potassium current (IK(Ca)), increase with temperature, exhibiting a mean Q10 of 1.7 between 15 and 25 degrees C. The activation rate (T1/2) of the outward current exhibits a mean Q10 of 2.3 between 15 and 25 degrees C, while the deactivation rate (taurel) exhibits a mean Q10 of 2.9 over the same temperature range. These results support previous models of the molecular determination of resonant frequency, which have proposed that a combination of IK(Ca) channel kinetics and the overall magnitude of the outward current are primarily responsible for determining the resonant frequency of an isolated hair cell. The robust temperature sensitivity of the hair cell receptor potential contrasts sharply with the temperature-insensitive tuning properties of in vivo saccular nerve fiber recordings. Possible explanations for this discrepancy are discussed.

WDM transmission system performance: influence of non-Gaussian detected ASE noise and periodic DEMUX characteristic

This paper presents the first unified wavelength division multiplexing (WDM) transmission model for systems incorporating cascaded optical amplifiers and a realistic demultiplexing (DEMUX) characteristic with periodic transfer function. The bit error ratio (BER) is evaluated accounting in rigorous form for the influence of non-Gaussian detected amplified spontaneous emission (ASE) noise, noise correlation between stochastic noise samples in the receiver, the bandwidth of the electrical receiver noise filter, the gain tilt and effective noise figure of optical amplifiers (with as well as without optical ASE noise filtering), channel crosstalk, signal extinction ratio and a one-or two-stage DEMUX implementation. The model is compared to the Gaussian receiver model in realistic design cases providing important information as to the validity of the Gaussian model. Practical design results indicate the link budget dependence on the DEMUX design and the ASE noise filtering.

A miniaturized artificial mastoid using a skull simulator.

A miniaturized artificial mastoid of size and weight that allow calibration and measurement of bone conduction hearing aids in a conventional audiometric soundproof box has been developed. Its level of mechanical impedance corresponds to the standard IEC 373 (1990) within the frequency range 250 Hz to 8 kHz. The miniaturized artificial mastoid consists of three parts: coupler, skull simulator (TU-1000), and an external electrical correction filter. The coupler is a highly damped mass-spring system designed to give the miniaturized artificial mastoid mechanical impedance in accordance with the standard IEC 373 (1990). It was found that the miniaturized artificial mastoid yielded results that are in correspondence with results obtained with the Brüel & Kjaer type 4930 artificial mastoid for frequencies above 450 Hz. Thus, at these frequencies, the miniaturized artificial mastoid can be used for audiometer calibration as well as measurement of bone conduction hearing aids.

On the relationship between chromatic dispersion and transmitter filter response in duobinary optical communication systems

It is shown through numerical simulation that limiting the spectral occupancy of a duobinary optical signal, which can be achieved by an appropriate choice of electrical transmitter filter response, is necessary in order to receive a benefit from duobinary transmission in single-mode optical communication systems. It is explained why such band limiting gives an improvement in dispersion immunity, and why ideal duobinary signaling is ineffective. The results are in good agreement with published experimental work.

Electrical filters made of polymer materials

Polymer composite material based on polypropylene (PCMP) which can changes metal in constructions of electric filters worked out. The material have high electric and heat conduction, configuration stability on exposure loads and temperature, chemical endurance, adaptability to manufacture. The properties of PCMP increase the service life and efficiency of electric filters operation. Volt - ampere characteristics of electric filters with electrodes from lead and PCMP are president in paper. Method of achievement high electric conduction of material, constructions, advantages of using of PCMP in comparison with metal are described.

Electrical filtering strategies to compensate waveform distortion in optically amplified IM/DD systems

Postdetection filtering strategies are investigated as a means of compensating the waveform distortion caused by the combined effect of chromatic dispersion and self-phase-modulation in intensity modulated, direct detection (IM/DD) systems. A design lechnique based on realisable filter models and a rigorous performance evaluation is introduced. In addition, a method of finding the theoretical optimum filter is given, providing a measure of the achievable system performance and the efficacy of the various filtering strategies. It is shown that the optimised postdetection filtering is effective in reducing the system power penalty, and the relative merits of different filters are quantified. The optimised filters are also shown to be tolerant to various system impairments, such as noise, timing jitter and perturbation of filter parameters.