Butterworth filter

About: Butterworth filter is a research topic. Over the lifetime, 6187 publications have been published within this topic receiving 69070 citations.

Second-order all-fiber comb filter based on polarization-diversity loop configuration

Abstract: By concatenating three birefringence loops in series, a second-order all-fiber comb filter based on a polarization-diversity loop configuration is newly proposed. The proposed filter consists of one polarization beam splitter, polarization-maintaining fibers, and two halfwave plates. The effect of a second-order structure of polarization-maintaining fiber loops on a bandwidth of the filter passband was theoretically analyzed and experimentally demonstrated. Transmission output of the second-order filter (flat-top and narrow-band transmission spectra) could be obtained by adjusting two half-wave plates. 1 and 3 dB bandwidths of the proposed filter in flat-top and narrow-band operations were greater by approximately 102.9 and 44.3 % and smaller by approximately 47.9 and 47.1 % than those of a conventional Sagnac birefringence filter, respectively.

Subband all-pass filter architectures with applications to dispersion and dispersion-slope compensation and continuously variable delay lines

Abstract: A new optical filter architecture is proposed that employs optical subband and all-pass filters but circumvents the typical tradeoff between passband width and peak delay inherent to all-pass filters. A filter design for a dispersion compensator with a tuning range of /spl plusmn/1000 ps/nm and 95-GHz passband width on a 100-GHz grid is presented. Compared with a cascade architecture, a lower core-to-cladding index contrast for planar waveguide ring resonator implementations can be used, and lower filter losses are achieved, since the signal propagates through fewer all-pass filter stages for the same dispersion. A continuously variable delay line is designed with more than 90% bandwidth utilization. For a ten-stage all-pass filter with 25-GHz free spectral range (FSR) in a double-pass configuration, a 1000-ps continuous tuning range can be achieved. Finally, a dispersion-slope compensator design is presented with a change in dispersion of 700 ps/nm over a wavelength range determined by the filter FSR-to-channel-spacing ratio.

Implications of low-pass filtering on power spectra and autocorrelation functions of turbulent velocity signals

Abstract: Filtering either through the electronics of an instrument or through digital procedure is performed routinely on geophysical data. When velocity fluctuations are measured in turbulent flows using electromagnetic current meters (ECMs), a builtin lowpass Butterworth filter of order n usually attenuates fluctuations at high frequencies. However, the effects of this filter may not be acknowledged in turbulence studies, thus impeding comparisons between data collected with different ECMs. This paper explores the implications of the filters on the characteristics of velocity signals, mainly on variance, power spectra, and correlation analyses. Variance losses resulting from filtering can be important but will vary with the order n of the Butterworth filter, decreasing as n increases. Knowing the filter response, it is possible to reconstruct the original signal spectrum to evaluate the effect of filtering on variance and to allow comparisons between data collected with different instruments. The autocorrelation function also is affected by filtering which increases the value of the coefficients in the first lags, resulting in an overestimation of the integral length scale of coherent structures. These important effects add to those related to size and shape differences in ECM sensors and must be taken into account in comparative studies.

Antenna duplexer with divided and grounded transmission line

Abstract: An antenna duplexer has a first filter and a second filter coupled to respective signal terminals and to a common node. The common node is coupled to an antenna terminal. The first filter has a higher-frequency passband than the second filter. A transmission-line circuit, inserted between the first filter and the common node, increases the impedance of the first filter in its lower stopband. The transmission-line circuit includes an internal node, a first transmission line coupling the internal node to the common node, a second transmission line coupling the internal node to the first filter, and a grounding circuit such as a capacitor coupling the internal node to ground. The grounding circuit further enhances the lower stopband impedance of the first filter.

A micromechanical bandpass filter with adjustable bandwidth and bidirectional control of centre frequency

Abstract: This paper introduces a tunable, narrow-band, micromechanical filter whose bandwidth and centre frequency can be adjusted independently. The filter is made of two micro-resonators that are electrostatically coupled using a middle electrode. A low coupling strength results in nearly constant bandwidth while one tunes the centre frequency bi-directionally by applying a DC voltage to the coupling electrode. On the other hand, the bandwidth of the filter is independently modified by applying axial stress to one of the resonators, without affecting the signal attenuation through the filter. Analytic and numerical models for the behaviour of the filter are also presented. Test devices with a centre frequency of about 300 kHz were fabricated in a standard micromachining process. Experimental results support the design principle and validity of the proposed models.