Dispersive 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.

Phylogenetic relationships of mid-oceanic ridge and continental lineages of Lasaea spp. (Mollusca: Bivalvia) in the northeastern Atlantic

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 213:165-175 (2001) - doi:10.3354/meps213165 Phylogenetic relationships of mid-oceanic ridge and continental lineages of Lasaea spp. (Mollusca: Bivalvia) in the northeastern Atlantic Diarmaid Ó Foighil1,*, Robert Jennings1,**, Joong-Ki Park1, D. Andrew Merriwether2 1Museum of Zoology and Department of Biology, University of Michigan, Ann Arbor, Michigan 48109-1079, USA 2Departments of Anthropology and Biology, University of Michigan, Ann Arbor, Michigan 48109-1382, USA *E-mail: diarmaid@umich.edu **Present address: Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA ABSTRACT: Direct-developing lineages of the genus Lasaea are common constituents of both oceanic island and continental rocky shore crevice faunas in the eastern North Atlantic. We utilized mitochondrial gene sequence variation to flesh out the phylogenetic relationships of individuals sampled from 2 Macaronesian archipelagos (Azores, Madeira) and from downstream continental (Iberian) sites. There was no evidence for colonization of the islands by upstream western North Atlantic congeners. Of 5 Lasaea clades detected in Iberia, 1 was also present on Madeira, whereas 4 of the 5 had representatives on the Azores. Madeira did not share haplotypes with the other sampling locations. In contrast, the Azorean and Iberian samples shared multiple haplotypes and our phylogenetic tree topologies were consistent with a minimum of 6 inferred migration events across the >1400 km oceanic expanse separating these 2 regional populations. Three of the putative migration events involved a predominantly island clade whose topology was consistent with colonization by ancestral continental lineages, extensive island cladogenesis, and secondary downstream migrations back to the mainland. The remaining 3 inferred migration events were distributed across the tips of the phylogenetic trees, a topology consistent with evolutionarily recent migrations against the prevailing current fields. Our results indicate that the pattern of easterly surface flow in the study area may generate differentially effective dispersal filters downstream of the Azorean and Madeiran archipelagos. Evidence for countercurrent migration in marine populations should be assessed in light of the totality of surface-flow patterns in the study system, not merely the prevailing one. KEY WORDS: Biogeography · 16S rDNA · Azores · Madeira · Oceanic island Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 213. Online publication date: April 04, 2001 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2001 Inter-Research.

Dispersion-induced power penalty in fiber-Bragg-grating WDM filter cascades using optically preamplified and nonpreamplified receivers

In wavelength-division-multiplexed optical networks, signals pass through cascades of multiplexing/demultiplexing channel filters present in the network access nodes. We describe experimental measurements and numerical simulations of the signal power penalty at 10 Gbps due to dispersion slope in such a cascade of fiber-Bragg-grating filters. The dispersion penalty of the cascade limits the allowed frequency detunings of the signal laser and channel filters. We observe that optically-preamplified receivers show a significantly larger dispersion penalty than nonpreamplified receivers, with a simple relation between the two penalties. This penalty difference should exist for any signal impairment that degrades optical signal extinction such as dispersive filter or fiber transmission and optical channel bandwidth narrowing.

Amplitude and phase control of ultrashort pulses by use of an acousto-optic programmable dispersive filter: pulse compression and shaping

We demonstrate experimentally that an arbitrary phase and amplitude profile can be applied to an ultrashort pulse by use of an acousto-optic programmable dispersive filter (AOPDF). Our filter has a large group-delay range that extends over 3 ps and a 30% diffraction efficiency over 150 THz. Experiments were conducted on a kilohertz chirped-pulse amplification laser chain capable of generating 30-fs pulses without additional pulse shaping. Compensating for gain narrowing and residual phase errors with an AOPDF in place of the stretcher results in 17-fs transform-limited pulses. Arbitrary shaping of these 17-fs pulses is also demonstrated in both the temporal and the spectral domains.

High signal-to-noise detection of rotational Raman scattering through refluorescent and dispersive atomic filters

We introduce new methods for capturing rotational Raman scattering that simultaneously suppress background scattering and have exceedingly high spectral dispersion at low wavenumbers. These methods are based on resonant absorption and refractive index dispersion of atomic vapor, and take advantage of the availability of tunable lasers. Three different configurations are presented. The first is an atomic notch transmission filter which is based on refluorescence from an optically thick atomic vapor cell. This configuration is demonstrated in air using mercury vapor at 254 nm. The second configuration is an atomic resonance prism cell which is demonstrated in CO2 using mercury vapor, again at 254 nm. The third configuration is a density gradient atomic vapor cell which uses rubidium vapor at 780 nm. In the last two configurations, the atomic cell simultaneously blocks the elastic scattering while spatially dispersing the rotational Raman lines. In each case, a tunable Ti : sapphire laser was employed as an illuminating source. Copyright ” 2000 John Wiley & Sons, Ltd.

Arbitrary dispersion control of ultrashort optical pulses with acoustic waves

Acousto-optic programmable dispersive filters (AOPDF) can compensate in real time for large amounts of group-delay dispersion. This feature can be used in chirped-pulse amplification femtosecond laser chains to compensate adaptively for dispersion. An analytical expression relating the group delay at the output of the AOPDF to the input acoustic signal is obtained with coupled-wave theory in the case of collinear and quasi-collinear bulk acousto-optic interactions and also in the case of planar waveguides and optical fibers. With this relation, the acoustic signal that will induce an arbitrary group-delay variation with frequency can be easily obtained. Numerical simulations are shown to support the principle of arbitrary group-delay control with an AOPDF.

Effect of dispersed filter particles on the strength behavior of composites

An attempt is made to find a solution by which the effect of neighboring filler particles on the strength of composites could be indirectly estimated. The stresses in composites with a great amount of filler are calculated. Composites based on epoxy-resin binder are tested. A comparison of different models shows that the modified Kerner model reflects only the tendency for the compression strength to change with the degree of filling. The relations between the compression strength and the degree of filling are better described by models allowing for constraint of the plastic deformations of the matrix. However, in this case, the effect of the neighboring particles is not properly taken into account.

How Habitat Edges Change Species Interactions.

Traditionally, ecologists interested in habitat edges have focused on edge-related gradients in patterns of species richness or abiotic variables. Here, however, we take a different perspective, attempting to synthesize recent empirical results concerning the effects of habitat edges on population dynamics with contemporary theoretical developments to outline the ways in which species interactions, and the dynamics of the communities in which they are embedded, can be changed by habitat edges. We find a striking convergence between empirical notions of a patch's core area and analytical results from partial differential equation models. A review of both empirical and theoretical studies suggests four general classes of mechanisms through which habitat edges can have similar impacts on dissimilar types of species interactions. Specifically, we focus on edges' roles as dispersal barriers or filters, edges' influences on mortality, edges' involvement in spatial subsidies (in which dispersers' intrapatch impacts are maintained by their activities in other habitats), and edges' roles as generators of novel interactions. For each class of edge-mediated effects, we provide examples of how one can use spatial modeling to address the relevant questions on these topics, which together form a key link between community dynamics and landscape structure.

Temperature properties of Na dispersive Faraday optical filter at D 1 and D 2 line

In this paper, investigations of a Na-atom dispersive Faraday optical filter that has been used in a narrow-band lidar of daytime operation are reported. We have constructed a Na Faraday optical filter and measured its transmission characteristics under the conditions of two different probe light beams from a CW laser and pulse Na fluorescent light, respectively. The analyses of temperature characteristics of the Na Faraday optical filter are given.

Dispersion filter for spectral and spatial resolution of pure rotational Raman scattering

A new filtering technique for Raman spectroscopy utilizes atomic vapor to suppress strong elastic and Rayleigh scattering while simultaneously resolving individual rotational Raman lines. Filtered images capture high-resolution spectral information in one dimension and spatial resolution in the other dimension. The filter is based on resonance enhanced dispersion, where the index of refraction varies dramatically. In a simple prism geometry the vapor disperses incident radiation according to frequency. A mercury-vapor-based dispersion filter has been fabricated, modeled, and demonstrated to capture pure rotational Raman scattering from CO(2).

Infrared filters and analyzers of the composition of substances based on them

Results of investigations on designing band dispersion and dispersion-interference filters for the 4–30 μm IR range and cutoff filters for the 50–300 μm region are presented. Analyzers of the composition of a substance that are designed on the basis of band IR filters and analysis procedures are described.

Comments on "On the relationship between chromatic dispersion and transmitter filter response in duobinary optical communication systems" [and Reply

For original paper see ibid., vol. 9, p 1005-7 (1997). A new interpretation has been recently proposed in the spectral domain to explain the good performance obtained by certain AM-PSK duobinary signals. However, we show in this comment that many counter-examples to this interpretation suggested by a previous time-domain theory can be found.

Optimal dispersion of optical filters for WDM systems

The phase response of optical filters determines their dispersive properties and impacts wavelength-division multiplexing (WDM) system performance. We present a general analysis of the phase response of optical filters used in WDM systems and suggest ways to minimize the detrimental dispersive effects of these filters. Some filters are found to be inherently linear phase filters and in principle are dispersionless. We also show that some filters may be realized for the phase correction of dispersive filters. Experimental system results demonstrate the negative effects of filter dispersion on system performance.

Acousto-optic programmable dispersive filter for adaptive compensation of group delay time dispersion in laser systems

It is demonstrated in this communication that using an acousto-optic interaction in an anisotropic birefringent medium it is possible to produce a chirped optical signal reproducing an original acoustic signal. This acoustic signal can then be used to generate a pre-distorted optical signal at the input of a laser chain to compensate for group delay time dispersions within the chain. The first experiments achieved with such a device are reported.

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.

Daytime mesopause temperature measurements with a sodium-vapor dispersive Faraday filter in a lidar receiver

Using a dispersive Faraday bandpass filter, we have upgraded our Na temperature lidar to be capable of 24-h operation. Along with a transmitting telescope to reduce the laser beam divergence to 0.2 mrad, the initial use of this unique narrow-band filter in a lidar receiver allowed us to reduce the detected daytime sky background to a level previously encountered at night, making routine daytime temperature measurements in the mesopause region a reality. The implementation, characterization, and results of what we believe are the first daytime mesopause temperature measurements are reported.

Use of dispersion filters for acoustooptical determination of gase concentration

Use of dispersion filters for acoustooptical determination of gase concentration

All-fiber dispersive transmission filters based on fiber grating reflectors

A novel, low-insertion-loss transmission f ilter with the implementation of linearly chirped fiber Bragg grating reflectors and polarization-splitting fiber fusion couplers is reported. Pulse chirping, chromatic dispersion compensation, and pulse compression are demonstrated. Cascading of dispersive filters, including application to a low-loss pulse stretchery/recompressor of femtosecond pulses, is also demonstrated.

Generation of transform-limited optical pulses at 10 GHz using an electroabsorption modulator and a chirped fibre Bragg grating

Transform-limited pulses of 5–6 ps have been generated at 10 GHz using an electroabsorption modulator in conjunction with a dispersive transmission filter based on a chirped fibre Bragg grating. This method is compact, controllable and incorporates minimal fibre lengths.

Unidirectionality in dispersive SAW transducers

Low loss SAW filters can be built making use of unidirectionality and selfmatching of dispersive transducers. The origin of unidirectionality lies in internal reflections between electrodes. The calculated loss level may be as low as 0.08 dB in down chirp double dispersive IDT filters.