Sharp Passband Research Articles

Novel Continuously Tunable Microwave Photonic Bandpass Filter

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A new technique for tuning the passband frequency of a microwave photonic bandpass filter is presented. It is based on controlling the polarization state of the signal in an amplified recirculating delay line loop with a polarizer at the output. A fixed wavelength laser can be used as an optical source. The filter has a sharp passband, which can be tuned continuously while maintaining the same passband width. Experimental results demonstrate continuous tuning capability of the high-resolution bandpass filter. </para>

Tri-Band Bandpass Filter With Sharp Passband Skirts Designed Using Tri-Section SIRs

This letter presents a second-order tri-band bandpass filter (BPF) designed using tri-section stepped-impedance resonators (TSSIRs). The impedance ratios of the TSSIRs were computed using the formulas expressed as functions of the passband center frequencies, which are located at 1.57, 2.45, and 3.5 GHz. A cross-coupled configuration was arranged to sharpen the passband skirts. The newly designed tri-band BPF was verified by circuit implementation and very good agreement between the simulated and measured results was observed.

Wavelength-adjustment-free optical low coherence interferometry for high-resolution and highly accurate optical network analysis of arrayed-waveguide gratings

The core technique for the highly accurate network analysis of arrayed-waveguide gratings (AWGs) with optical low coherence interferometry at 1.5 μm involves propagating a 1.3 μm laser light through the interferometer where the AWG is installed in one of two arms. By combining a DFB LD that has a fixed wavelength of 1.3 μm with a balanced detection scheme in the system, we achieved a high phase-error-measurement accuracy of 0.01 radians when the LD light was attenuated by 68 dB by the sharp AWG passband. We no longer need to adjust the laser wavelength to the AWG passband peak.

A new compact microstrip bandpass filter using triangular open-loop resonators and folded-line DGS

A novel microstrip BPF designed using triangular open-loop resonators and a folded-line-shaped defected ground structure (DGS) is proposed. By appropriately choosing the tapping positions of the resonator's feed lines, the created transmission zeros can be properly located so as to improve the skirt rejection. Also, with the addition of the newly designed folded-line DGS, the skirt rejection at the upper passband edge can be increased. The results demonstrate that such a filter design can achieve a compact circuit size and a sharp passband skirt, while retaining the insertion loss at a relatively lower level. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 43–47, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21255

Integrated band demultiplexer using waveguide grating routers

We present a novel band demultiplexer design for planar lightwave circuits. It consists of two perfectly sampled waveguide grating routers connected by sets of equal-path-length waveguides separated on one side. Its advantages are compactness, sharp passband corners, and a lack of chromatic dispersion.

Electronic band-structure engineering of GaAs/Al xGa 1−xAs quantum well superlattices with substructures

We report a theoretical investigation on the band structures of electrons in both infinite and finite semiconductor quantum well/barrier superlattices with each unit cell containing alternately two types of materials. When the unit cell of a superlattice, made of GaAs and Al xGa 1−xAs, is further divided into four and six sublayers of these two materials, narrower passbands and/or broad stopbands can be obtained for electrons with energy slightly larger than the potential barrier. When a finite superlattice has two different periods and each unit cell contains six sublayers of alternating GaAs and Al xGa 1−xAs, very sharp passbands can be obtained for electron energy right below and above the potential barrier. The results may be used to build a high-Q electron energy filter.

Real-time plasma rotation diagnostic for measuring small Doppler shifts

A noninvasive velocity measurement has been developed for use in high-temperature plasma confinement devices, having particular use where multi-kilohertz measurement of plasma rotation is needed. The most interesting aspect of the technique is that the Doppler shift is determined from the ratio of the light intensity from two detectors rather than by resolving the emission line with a spectrometer. One detector views the plasma through an interference filter whose passband has a negative slope, and the other channel views the identical volume of plasma through a positive-slope filter. The signal ratio varies as the line is shifted across the passbands, but is not sensitive to changes in plasma emission. For interference filters with linear passbands, that is, constant slopes, the ratio is not sensitive to ion temperature, and the shifted wavelength reduces to a simple function of the signal ratio, the channels’ relative responsivity, and the two filters’ transmission curves. Filters with sharp passband slopes (100%–200% per nm) and ≈0.1% deviation from linearity have been fabricated. For an uncertainty in the signal ratio of ±1%, the expected error in the wavelength shift is ±0.001 nm (Δvφ≈±1 km/s).

Tunable microstrip bandpass filters with two transmission zeros

This paper presents an analytical technique for positioning the locations of two transmission zeros for a microstrip bandpass filter. In addition, this paper discusses how the tapping positions of asymmetric feed lines affect the coupling between resonators. The bandpass filter uses two resonators with two transmission zeros to obtain lower insertion loss than a conventional cross-coupled microstrip filter. Also, by using four resonators, the bandpass filter has better out-of-band rejection than the conventional cross-coupled microstrip filter. The filter designs using four cascaded resonators provide a sharp passband that can be tuned using a piezoelectric transducer to change the effective dielectric constant. The filters demonstrate high selectivity, compact size, and can be used in many wireless communication systems.

Acoustic band-gap engineering using finite-size layered structures of multiple periodicity

The transmission coefficient of a layered structure made of glass and water was calculated using transfer matrix method and also measured as a function of frequency. It was found that acoustic band gaps can be created using only 3–4 cells of a two-phase layered structure. By introducing two or more periods into the layered structure, very sharp passbands and very broad stopbands can be engineered for acoustic waves. Such acoustic band-gap materials could be used for making high-quality acoustic filters, acoustic mirrors and vibration insulation devices in selective frequency range.

WDM filter modules in compact, low-cost plasticpackages for byte-wide multimode fibre ribbon cable data links

WDM filter modules are presented for multimode fibre ribbon cables which employ a simple package and provide low crosstalk and sharp passband edges, suitable for 10 nm channel spacing. These devices exhibit low insertion loss (1.6 dB average) and good wavelength uniformity (/spl plusmn/0.8 nm).

Microwave optical filters using in-fiber Bragg grating arrays

A novel multitap optical transversal signal processor based on wavelength multiplexed Bragg grating arrays is presented. This structure enables the realization of a large number of taps for obtaining sharp bandpass filtering with high resolution and also enables arbitrary tap weight profiles to be obtained. Results on a 4-GHz, 29-tap filter demonstrates a sharp bandpass filter response, and windowing techniques on the tap profiles are demonstrated to enhance the sidelobe suppression characteristics.

Numerical analysis of nonlinear optical fiber couplers with a gaussian mode field distribution

AbstractNonlinear coupling characteristics taking account of evanescent field overlap were evaluated numerically by assuming a Gaussian field distribution for the mode field in nonlinear directional couplers (NLDC). The nonlinear coefficients Q3 to Q5 were found to be Q3 = 3.7 × 10−12 cm−1, Q4 = Q5 = 0 for the plane wave approximation used in Jensen's paper [1], with a core radius of 4 μm, a core spacing of 5 μm, a core refractive index of 1.455, and a nonlinear refractive index of 1.1 × 10−12 esu; and the wavelength of the incident light was 1.06 μm. On the other hand, in the case of the Gaussian field approximation, Q3 = 2.5 × 10−12 cm−1, Q4 = 2.2 × 10−14 cm−1, and Q5 = 7.3 × 10−14 cm−1 were obtained, indicating that these values cannot be ignored. The full coupling period is increased by increasing the core spacing, and the full coupling period is decreased by using a longer wavelength. Further, from the dependence of nonlinear coupling characteristics on optical wavelength, it is confirmed that wavelength selective characteristics with a sharp bandpass filtering can be realized in NLDC.

Imaging in the far‐red with electronic light microscopy: Requirements and limitations

The acquisition of simultaneous dual confocal images with red and far-red light has both advantages (e.g. lower autofluorescence) and limitations. An understanding of these requisites is necessary to acquire high-quality images and to avoid the misinterpretation of experimental data. The poor detection of far-red light mandates a high optical transfer efficiency for the system, thus the transmittance of the objective lens and its axial and lateral chromatic aberration in the far-red are important factors for consideration. This technical note is an attempt to 'demystify' the process of filter set design for confocal microscopy by discussing the considerations that went into the construction of a filter set for use with the reagents cyanine 3.18 (Cy3) and cyanine 5.18 (Cy5), and thus to encourage users to look beyond the multi-purpose designs available commercially. The 568-nm laser line exciting Cy3 is at its emission maximum, which limits the collectable Cy3 fluorescence. High-transmission optical filters with sharp band pass cutoffs are thus desirable for maximum light throughout. Light path mirror efficiency rapidly degrades above 700 nm, but the loss of this portion of the Cy5 emission spectrum is acceptable since the fluorophore is very bright, and these very long wavelengths are also likely to introduce aberration. While resolution is decreased with far-red light, there is also greater penetration and less scattering, and it is thus possible to obtain high-quality images from deeper within the specimen.(ABSTRACT TRUNCATED AT 250 WORDS)

High-temperature superconductor antennas: Utilization of low rf losses and of nonlinear effects

The low radio frequency (r.f.) losses in epitaxial HTS thin films allow the realization of novel antenna structures which have to be excluded in conventional antenna techniques with normal conductors because of the highly reduced radiation efficiency. Thus, the design of miniaturized but nevertheless highly efficient antennas down to a lower limit determined by both the required order of radiation pattern and the frequency bandwidth becomes possible. For a bandwidth of more than about 1%, a considerable margin for a size reduction below the “critical size” is restricted to the case of electrically small antennas and of superdirective antennas with a relatively low order of the radiation pattern, e.g. antennas with a beam of less than 15 dB maximum gain. If the size approaches the lower limit, the antennas show a sharp bandpass frequency response. This is demonstrated by means of experimental results for a novel HTS meander antenna. These bandpass characteristics can be utilized in compact multiport antenna systems in order to decouple subantennas for adjacent frequency bands. Besides the low losses in HTS's, their nonlinear properties can be used in order to realize current-controlled HTS switches for antenna systems.

A varactor-tuned active microwave bandpass filter

Traditionally, microwave filters have been implemented as passive networks of waveguide, transmission-line, or discrete lumped elements. More recently, microwave active filters have also been realized. A microwave high Q-active bandpass filter is presented. using a varactor diode for tuning, and an active component giving a substantial increase in Q of the resonant sections of filter. High-Q filter elements offer low-filter insertion loss and also yield sharp passband corners, which cannot be achieved by lossy filter and amplifier combination.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

New formulae for switch ed‐capacitor band pass filters

The governing equations for switched‐capacitor band pass filters are greatly simplified into a new set of much simpler equations, with no approximation involved. For sharp band pass filters with narrow bandwidths, we expand the new set, cancel out many leading terms, and get a set of new formulae. Based on these formulae, we obtain and tabulate numerical design data for sharp 4th to 8th order Butterworth band pass filters, including values for the required resistors. The application of switched‐capacitor filters MF5 and MF10 is then greatly expanded to cover sharp and very sharp band pass filters.

High-Level Psychophysical Tuning Curves

Simultaneous-masked psychophysical tuning curves were obtained from normal-hearing listeners using low-level (20-25 dB SPL) probe tones in quiet and high-level (60 dB SPL) probe tones, both in quiet and in the presence of a broad-band background noise. The background noise was introduced to eliminate combination tones or combination bands and other off-frequency listening cues that exist at high levels. Tuning curves were obtained using pure-tone maskers and 100-Hz-wide narrow-band noise maskers for probe tones at 1000 and 4000 Hz. High-level tuning curves for pure-tone maskers demonstrated large discontinuities or "notches" on the low-frequency sides of the tuning curves. Broad-band background noise eliminated those notches, indicating that the notches were due to the detection of off-frequency listening cues at combination-tone frequencies. High-level tuning curves for 100-Hz-wide narrow-band maskers also demonstrated notches on the low-frequency sides. Those notches were eliminated with broad-band background noise, which indicates that combination bands strongly influenced the shapes of high-level tuning curves obtained with narrow-band maskers. The influence of combination bands was dependent upon test frequency. At 1000 Hz, combination bands had very little influence on the shapes of high-level tuning curves. At 4000 Hz, where the masker bandwidth was substantially less than the critical bandwidth, combination bands strongly affected the low-frequency sides of the tuning curves. In 2 subjects tested at a probe frequency of 2000 Hz with 100-Hz-wide masking bands, combination bands also influenced the low-frequency sides of high-level tuning curves. The presence of combination-tone or combination-band cues essentially steepened the low-frequency slopes of tuning curves, resulting in sharper estimates of tuning. Comparisons of tuning curves obtained with pure-tone maskers and narrow-band maskers, in the same listeners, revealed that pure-tone maskers were more effective than narrow-band maskers when the masker frequencies were in the tail region of the tuning curve. The results of these experiments support the notion that tuning in the normal auditory system broadens notably with stimulus level, once off-frequency listening cues such as combination tones or combination bands are eliminated. The low-level simultaneously masked tuning curve demonstrates a sharp bandpass tuning characteristic, whereas the high-level simultaneously masked tuning curve in background noise demonstrates a broad low-pass tuning characteristic.(ABSTRACT TRUNCATED AT 400 WORDS)

Bandpass and bandstop recursive filters with low sensitivity

In a sharp cutoff bandpass or bandstop recursive digital filter, the poles and zeros are expected to be clustered around the band edges, and in close proximity of the unit circle in the z-plane. Implementation of such filters with low sensitivity could be achieved by cascading second-order sections, with appropriate low sensitivity structures chosen for individual sections depending on the locations of the poles. An alternative approach for design and implementation of band-pass/bandstop filter with low sensitivity is shown to be based on transformation of sensitivity characteristics of a low sensitivity structure to appropriate angular regions on the unit circle. A fourth-order section of such a filter is realized with a level of sensitivity which is the same as that of the prototype second-order low-pass filter section realized with low sensitivity and with reduced number of multiplications. A few transformations along with their respective structures for transforming a prototype low-pass filter are given.

Masking by tone bursts of changing frequency

AbstractMost of the common sounds in our daily life change their frequencies transiently, and it is important in engineering applications such as voice recognition and instrument tone discrimination to find a correspondence between the physical properties of these sounds of changing frequency and human perception. This paper reports on the experimental study of masking by tone bursts of changing frequency as an effort toward clarifying such dynamic auditory perception. First, using artificial formant stimuli the masking patterns for continuous tones were measured with the formant frequency changed discontinuously. The results showed masking overshoot at the formant transition and forward and backward masking phenomena, which suggests a characteristic extraction of the voice formant transition in the auditory system. Next, using various combinations of artificial formant and “bridge” tones as the masker, the masking patterns for continuous tones mixed with the masker at various phases were measured. As a result it became clear that the resultant pattern is not a simple addition of individual maskings by the component tones and shows relatively sharp bandpass filter characteristics in the critical band of the auditory system. This suggests the existence of a special processing mechanism for compound consonants in the auditory system.

Design of recursive digital filters for the selection or rejection of a particular velocity in seismic signals

In this paper a new type of “velocity-selecting/rejecting filter” which passes or stops a particular event in a seismic signal is proposed. The velocity-selecting filter is based on a time-space band-pass filter with sharp passband for a particular direction, and similarly, the velocity-rejecting filter is based on a time-space band-stop filter. A technique for designing such filters, in terms of an infinite-impulse-response (IIR) filter, is presented, in which a rotated version of separable filter is used. Finally, numerical examples are included to illustrate the design theory.