Optimum Filter Bandwidth Research Articles

A 10-Gbit/s EML link using detuned narrowband optical filtering

In this paper, the effects of asymmetric narrowband optical filtering are investigated in a 10-Gbit/s optical communication link using integrated electro-absorption modulated lasers (EML). We investigate the effect of EML chirp on link performance as well as the optimal filter bandwidth and wavelength detuning. We show that both the phase response and the spectral narrowing of the filter will enable a longer distance transmission by interacting with the EML transient chirp and compensating for the fiber chromatic dispersion. Experimentally, an 8.75-GHz filter is shown to improve the link distance by 40 km from 65 to 105 km, when transmitting over standard single mode fiber.

Spectrally sliced transmission with burst mode operation

The bit error rate performance of on-off keyed spectrally sliced burst mode receivers in the presence of dispersion is analysed for the first time. The treatment includes realistic excess noise statistics plus the effects of pulse distortion and intersymbol interference resulting from the dispersion. Numerical answers are obtained using the saddlepoint approximation, known to be both computationally efficient and accurate. The variation in power penalty with fibre path length, using the optimum optical filter bandwidth, is determined in addition to the impact of burst mode preamble lengths. The optimum ratio between the fibre path length and the distance for the root mean square width of spectrally sliced pulse to double is found to be between 0.75 and 0.76. Although the optical power penalty is found to be greater than in the case of a laser-based burst mode system, operation close to this optimum ratio reduces it to <1 dB for preambles of 4 bits or more.

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.

Optical preamplifier receiver for spectrum-sliced WDM

Spectrum-slicing provides a low-cost alternative to the use of multiple coherent lasers for wavelength division multiplexing (WDM) applications by utilizing spectral slices of a single broadband noise source for creating the multichannel system. In this paper we analyze the performance of both p-i-n and optical preamplifier receivers for spectrum-sliced WDM using actual noise distributions, and the results are compared with those using the Gaussian approximation. This extends prior results of Marcuse for the detection of deterministic signals in the presence of optical amplifier and receiver noise. Although the methodology is similar, the results are considerably different when the signal is itself noise-like. For the case of noise-like signals, it is shown that when an optical preamplifier receiver is used, there exists an optimum filter bandwidth which minimizes the detection sensitivity for a given error probability. Moreover the evaluated detection sensitivity, in photons/bit, represents an order of magnitude (>10 dB) improvement over conventional detection techniques that employ p-i-n receivers. The Gaussian approximation is shown to be overly conservative when dealing with small ratios of the receiver optical to electrical bandwidth, for both p-i-n and preamplifier receivers.

Sensitivity of optically preamplified DPSK receivers with Fabry-Perot filters

The error-rate performance of a DPSK lightwave receiver having an optical amplifier followed by a Fabry-Perot filter and delay-line demodulator is analyzed. Receivers with sampling and with integrate-and-dump threshold comparison are compared to the well-known result for a matched optical filter. The Fabry-Perot filter decreases the sensitivity at 10/sup -9/ error-rate from 20 to 24.5 photons/b with optimum optical filter bandwidth and postdetection integration time.

M-ary CPFSK-DPD with L-diversity maximum ratio combining in Rician fast-fading channels

We derive a formula for the bit error probability (BEP) of M-ary continuous phase frequency shift keying with differential phase detection and maximum ratio combining diversity in Rician fast-fading channels. We assume that transmitter and receiver filters distort the signal and limit the noise. We compute the BEP as a function of energy-to-noise ratio per bit (E/sub b//N/sub 0/) and other system and channel parameters: Rician factor K=0, 6 dB, 10, /spl infin/; number of diversity channels L=1, 2, 3; Doppler frequency shift f/sub D/T=0, 0.01, 0.02; Butterworth filters in transmitter and receiver of order N/sub T/=3 and N/sub R/=4; optimal sampling time and filter bandwidth. In all cases the BEP is significantly reduced by diversity.

Error-rate performance of optical amplifierswith Fabry-Perot filters

The error-rate performance of an ON-OFF keyed lightwave receiver having an optical amplifier followed by a Fabry-Perot filter is analysed. Receivers with sampling and with integrate-and-dump threshold comparison are compared with the well known result for a matched optical filter. The Fabry-Perot filter decreases the sensitivity at 10/sup -9/error rate from 76 to 89 photon/bit (peak) with optimum optical filter bandwidth and postdetection integration time. >

Digital signal processing of Decca Navigator radionavigation signals

New techniques are described for digital signal processing of Decca Navigator radionavigation signals. A simulator (a computer program) is used to investigate the effects of different digital filter characteristics of the accuracy of phase measurements and to find an optimum filter bandwidth. The performance of the optimum filter in the presence of noise and other sources of error is investigated. Methods are presented for compensating for initial errors and drift in the clock frequency of the system, and for synchronising to the pattern of transmissions.

Multichannel coherent FSK transmission at 622 Mbit/s with synchronous intra-bit sinusoidal polarisation spreading

The feasibility of polarisation insensitive multichannel coherent FSK transmission with synchronous intra-bit sinusoidal polarisation spreading has been experimentally demonstrated at 622 Mbit/s for the first time, complying with a front-end bandwidth of 3.2 GHz. Results evidenced an optimum IF filter bandwidth of four times the bit rate, and a minimum channel spacing of 11 GHz.

Theoretical analysis of phase diversity optical homodyne receiver with FSK demodulation

A detailed analysis of optical coherent phase diversity single-filtered and dual-filtered frequency-shift keying (FSK) receivers corrupted by shot and phase noise is presented. With delay and cross-product detection, the effect of various parameters, including bandwidths of filters, delay time, frequency deviation and noises, are investigated. The tolerance of phase noise is quite large, when small time delay in the demodulator and appropriately large frequency deviation is selected. It is also shown that there exists an optimal bandwidth for the first filter in the dual-filtered FSK receiver. For a total linewidth equal to half of the bit rate, the power penalty incurred (at BER=10/sup -9/) is 1.92 dB when the modulation index is 4, provided that an optimal filter bandwidth and a frequency deviation-delay product of 0.25 are used.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Theory of direct-detection lightwave receivers using optical amplifiers

A simple theory is presented for analyzing the sensitivity and bit-error rate (BER) performance of direct-detection lightwave receivers using optical amplifiers. The analysis provides closed-form expressions for the BER and receiver sensitivity, and includes the impact of phase noise. Furthermore, the proposed theory predicts the optimum filter bandwidth values required for linewidths of practical interest (up to 100% of the bit rate). For the special case of zero linewidth, the average signal energy predicted by this work is 42.3 photons/b at BER=10/sup -9/. This result is within 0.47 dB of the sensitivity predicted by more accurate techniques. >

Techniques for the determination of left ventricular mass by signal-averaged electrocardiography

The standard ECG correlates poorly with LV mass. The SAECG precisely measures myocardial energy and may allow more exact noninvasive assessment of LV mass. A commercially available system (Corazonix Predictor I) was tested for its ability to reproduce and measure known input energy in square wave and QRS waveforms, using frequency bandwidths different from those used for late potential analysis. A test group of 15 patients was studied to determine optimum filter type and bandwidth for comparison of SAECG energy measurement versus LV mass as determined by echocardiography (Penn conversion) and LV hypertrophy via standard ECG criteria. The best means of energy measurement were maximum and total RMS voltage and the integral of the area under the QRS curve. Optimum correlation with echocardiography was seen with a bidirectional bandpass filter of 5 to 250 Hz applied either to the vector sum of the three orthogonal leads or to the Z lead alone ( r values 0.61 to 0.73), which was equal to or superior to standard ECG LV hypertrophy determinants. A second group of 20 patients was studied prospectively to confirm these findings, which yielded similar results. Conclusion: (1) the SAECG when appropriately modified serves as a rapid noninvasive assessment of LV mass. (2) These modifications must examine the entire duration and energy spectrum of the surface ECG and not just the region of late potentials. (3) Very low frequencies (below 5 Hz) must be excluded to eliminate the energy present due to DC offset voltage.

Perceived contrast and stimulus size: Experiment and simulation

Perceived contrast functions were determined for three different Gabor patch sizes using magnitude estimation and verified by contrast matching. While thresholds show a significant decrease with decreasing patch size, perceived contrasts are equal and independent of patch size for contrasts above 0.06. Contrast matching was also used to study the apparent contrast of two other spatially limited stimuli; the sum of two orthogonal 4 c/deg sine waves multiplied by a gaussian envelope and the sum of spatially adjacent positive and negative gaussians. Models of contrast perception, based on tuned Gabor spatial filters, were formulated and tested for agreement with our experimental data. A model that pools filter responses across spatial frequencies and orientations was found to be more in agreement with our data than a model that simply uses the response of a single, maximally excited, mechanism to mediate contrast perception. Optimum filter bandwidth was found to be about 1.1 octaves.

Simple Expression for Interchannel and Intersymbol Interference Degradation in MSK Systems with Application to Systems with Gaussian Filters

In this paper, we derive a simple expression for the degradation in signal-to-noise ratio caused by intersymbol and adjacent channel interference in MSK systems for which the total response is nonnegative and the response is such that only two intersymbol and one adjacent channel terms are dominant. An MSK system with Gaussian filters in transmitter and receiver satisfy this condition. The resulting expression is simple because we simultaneously maximize the signal value from the main channel (by selecting the sampling time) and the degradation caused by the signals in the interfering channels. For such systems we derive the relation between the optimal filter bandwidth and channel frequency separation. Numerical results are presented for the case of Gaussian filters in both transmitter and receiver or receiver only and either one or two adjacent interfering channels.

Spectral Filters for Digital Fibre-optic Communication Systems

With a proper choice of the spectral filter to be used with an LED fibre-optic digital communication link, a substantial increase in information pulse rate can be achieved, when the system is bandwidth limited due to material dispersion. The optimum filter bandwidth depends on the fibre length, attenuation, dispersion and on the LED optical power. A 60 Afilter would increase the maximum pulse rate from 150 to 800 Mb/s for a 1 km length of fibre with attenuation of 8·6 dB/km and coupled optical power of 100 μ W. A power reduction penalty of about 13 dB results.

Noncoherent Pseudonoise Code Tracking Performance of Spread Spectrum Receivers

The optimum design and performance of two noncoherent PN tracking loop configurations, namely, the delay-locked loop and tau-dither loop, are described. In particular, the bandlimiting effects of the bandpass arm filters are considered by demonstrating that for a fixed data rate and data signal-to-noise ratio, there exists an optimum filter bandwidth in the sense of minimizing the loop's tracking jitter. Both the linear and nonlinear loop analyses are presented and the region of validity of the former relative to the latter is indicated. In addition, numerical results are given for several filter types. For example, assuming ideal bandpass arm filters, it is shown that the tau-dither loop requires approximately 1 dB more signal-to-noise ratio than the delay-locked loop for equal rms tracking jitters.

Optimum Performance of Suppressed Carrier Receivers with Costas Loop Tracking

The performance of suppressed carrier receivers with Costas loop tracking is optimized by proper choice of loop arm filter bandwidth. In particular, it is shown that for a variety of passive arm filter types, there exists, for a given data rate and data signal-signal-to-noise ratio, an optimum filter bandwidth in the sense of minimizing the loop's squaring loss. For the linear theory case, this is equivalent to minimizing the loop's tracking jitter. When symbol synchronization is known, it is shown that by replacing the passive arm filters with active filters, i.e., integrate-and-dump circuits, one can achieve an improvement in carrier-to-noise ratio of as much as 4 to 6 dB depending on the passive arm filter type used for comparison and the value of data signal-to-noise ratio (SNR).

Nonideal Photoelectron Counting

Expressions are obtained for the probability of error of a binary intensity-modulated direct-detection optical communication system consisting of an ideal photodetector followed by a nonideal photoelectron counter, in this case an RC low-pass filter. Calculation of probability of error requires the determination of the output statistics of the nonideal counter. Numerical techniques are used to evaluate the expression for probability of error and optimum thresholds as a function of signal level. The optimum filter bandwidth required to simulate an ideal counter is also evaluated numerically. Results indicate that, for the particular case considered, the nonideal receiver requires an additional 1 dB of signal power to achieve performance equivalent to the ideal receiver.

Linear scale-factor error and optimum filter bandwidth for correlation accuracy

Theoretical results are presented for the effect of linear scale factor on the alignment accuracy of two 1-dimensional random signals. For the low-signal/noise-ratio Gaussian correlation function, the optimum resolution is obtained as T|e|/√6, where T is the map length and e is the fractional scale-factor error.

Optimum Bandwidth of a Low-Pass Filter for Detection of a Pulse in Nonstationary Noise

The two-dimensional spectrum is used to compute the optimum low-pass filter bandwidth for the detection of a pulse in noise having an exponential variation of the spectrum level. A simple equation for the two dimensional spectrum of the input is derived. The resulting equations are used to compute curves showing the time variation of the optimum filter bandwidth and the variation of the output signal-to-noise ratio.