Discrete Reflections Research Articles

40 Gb/s Operation of SOA-REAM in Single-Feeder WDM-PON [Invited

The integrated semiconductor optical amplifier (SOA) with a reflective electro-absorption modulator (REAM) is a promising candidate for the colorless optical network unit in a wavelength-division-multiplexed passive optical network (WDM-PON), due to its low chirp and wide bandwidth. However, 40 Gb/s operation of REAMs (bandwidth ≤ 20 GHz) still encounters severe intersymbol interference. Furthermore, Rayleigh backscattering (RB) and discrete reflections cause strong beat noise in WDM-PONs with single-fiber loopback configuration. In this paper, we present two novel techniques based on electrical equalization for a 40-Gb/s single-feeder WDM-PON based on SOA-REAM. The first method is to employ partial-response (PR) signaling and a noise predictive maximum likelihood (NPML) equalizer at the upstream receiver. The other one combines correlative level (CL) pre-coding with partial-response maximum likelihood (PRML) equalization. We experimentally demonstrate a 40-Gb/s uplink of 20 km using a 20-GHz SOA-REAM in a WDM-PON by both PR-NPML and CL-PRML. The results also verify the superiority of PR-NPML over the previously reported equalizers. Moreover, compared with PR-NPML, CL-PRML further improves the system performance. Experiments prove that the tolerance to beat noise and the receiver sensitivity are enhanced by 4 dB and 0.8 dB, respectively, at a bit error ratio of 2×10−4.

Detecting the angle of arrival of discrete echoes by measuring polar energy time curves in a contemporary church

In order to deal with speech intelligibility concerns from the main sound system at a contemporary church, the authors executed measurements in the main assembly hall to detect late arriving reflections at various positions in the audience and on the stage. By implementing Polar Energy Time Curves (PETC) at each measurement location, discrete reflections were identified by time arrival and also, more critically, by angle of arrival. The advantage of calculating the PETCs on site during the measurement session was that the authors could physically pinpoint the sources of discrete echoes by using a laser positioned at the center of the microphone armature used to take the measurements. This gave the authors immediate feedback to diagnose reflections and help select additional measurement positions within the room. With this information, the authors were able to identify room surfaces that contributed significantly to the late arriving echoes and specify appropriate sound absorptive treatments for these surfaces.

Attenuation of Wave Reflection by Wave Entrapment Creates a “Horizon Effect” in the Human Aorta

Wave reflection is thought to be important in the augmentation of blood pressure. However, identification of distal reflections sites remains unclear. One possible explanation for this is that wave reflection is predominately determined by an amalgamation of multiple proximal small reflections rather than large discrete reflections originating from the distal peripheries. In 19 subjects (age, 35-73 years), sensor-tipped intra-arterial wires were used to measure pressure and Doppler velocity at 10-cm intervals along the aorta, starting at the aortic root. Incident and reflected waves were identified and timings and magnitudes quantified using wave intensity analysis. Mean wave speed increased along the length of the aorta (proximal, 6.8±0.9 m/s; distal, 10.7±1.5 m/s). The incident wave was tracked moving along the aorta, taking 55±4 ms to travel from the aortic root to the distal aorta. However, the timing to the refection site distance did not differ between proximal and distal aortic measurement sites (proximal aorta, 48±5 ms versus distal aorta, 42±4 ms; P=0.3). We performed a second analysis using aortic waveforms in a nonlinear model of pulse-wave propagation. This demonstrated very similar results to those observed in vivo and also an exponential attenuation in reflection magnitude. There is no single dominant refection site in or near the distal aorta. Rather, there are multiple reflection sites along the aorta, for which the contributions are attenuated with distance. We hypothesize that rereflection of reflected waves leads to wave entrapment, preventing distal waves being seen in the proximal aorta.

Multipath interference test method using synthesized chirped signal from directly modulated DFB-LD with digital-signal-processing technique

We propose a method of testing transmission fiber lines and distributed amplifiers. Multipath interference (MPI) is detected as a beat spectrum between a multipath signal and a direct signal using a synthesized chirped test signal with lightwave frequencies of f(1) and f(2) periodically emitted from a distributed feedback laser diode (DFB-LD). This chirped test pulse is generated using a directly modulated DFB-LD with a drive signal calculated using a digital signal processing technique (DSP). A receiver consisting of a photodiode and an electrical spectrum analyzer (ESA) detects a baseband power spectrum peak appearing at the frequency of the test signal frequency deviation (f(1)-f(2)) as a beat spectrum of self-heterodyne detection. Multipath interference is converted from the spectrum peak power. This method improved the minimum detectable MPI to as low as -78 dB. We discuss the detailed design and performance of the proposed test method, including a DFB-LD drive signal calculation algorithm with DSP for synthesis of the chirped test signal and experiments on single-mode fibers with discrete reflections.

Improving performance of MLSE in RSOA-based WDM-PON by partial response signaling

High data-rate upstream transmission in wavelength division multiplexed passive optical network (WDM-PON) based on reflective semiconductor optical amplifier (RSOA) is limited by severe inter-symbol interference (ISI), owing to low-bandwidth transmitter and fiber dispersion. To overcome the limitations in RSOA-based WDM-PON, we propose a novel receiver based on partial response maximum likelihood (PRML) equalization which combines the use of partial response (PR) signaling with maximum likelihood sequence estimation (MLSE). MLSE has been long considered as the optimal reception technique to overcome various types of impairment in optical transmission such as dispersions. It is demonstrated in this paper that PRML surpasses standard MLSE in ISI and reflection suppression with reduced complexity for RSOA-based WDM-PON system. 150 km unidirectional distance is demonstrated for 10 Gb/s uplink, while bidirectional uplinks up to 50 km and 20 km are achieved for data rate of 10 Gb/s and 20 Gb/s respectively, in WDM-PON using PRML. Furthermore, the impacts of discrete reflections on various equalization techniques are investigated, where PRML also shows superiority over MLSE.

On the acoustics of operating rooms.

Designing modern operating rooms to meet al.l design criteria can be a challenge. Creating a sterile, well‐lit, temperature and humidity appropriate environment for medical operations typically takes precedence over the acoustics of the operating room. The sterile, washable operating room surfaces are commonly hard and reflective, offering little sound absorption. These surface finishes result in strong discrete reflections, increased background noise, and reduced speech intelligibility. Code mandated energy efficiency and ventilation requirements coupled with the owner‐driven desire for economical mechanical systems can result in excessive HVAC noise, adding to background noise levels. Yet, speech intelligibility and speech privacy levels are expected to be superb to minimize errors due to miscommunication and to prevent the unintentional spread of confidential patient information. The acoustical challenge is to design operating rooms to control noise and to enhance room acoustics without affecting the performance of other systems. Speech intelligibility and impulse response measurements from modern hospital operating rooms and design strategies will be discussed.

Application of Hot-Pressed Ge-Crystal Monochromators for Reactor-Based Neutron Beam Experiments

A renewed Ge-crystal monochromator was installed in a neutron spectrometer at JRR-3. The beam size at the sample position is vertically about 1.5 times as large as before, while the neutron luminosity is unchanged. Well-collimated, monochromatic beams with quite different incident energy ( E i ) are available through a slight rotation in the monochromator-crystal angle by making use of discrete Bragg reflections of Ge. The ability of inelastic-neutron-scattering measurements is examined through observation of magnetic Brillouin scattering with extremely high resolution and with a supplementary use of two E i s.

Discovery of new MWW family zeolite EMM-10: Identification of EMM-10P as the missing MWW precursor with disordered layers

We the report discovery of zeolite EMM-10, a new member of the MWW family, and its layered zeolite precursor, EMM-10P. The latter is closely related to the layered precursor MCM-22P but its layers are stacked without vertical alignment. The layers are believed to be twisted off-register or otherwise disordered in-plane but still hydrogen bonded through silanols. The proposed structural disorder is concluded from the X-ray powder diffraction pattern, which is very similar to that of MCM-22P but lacks the discrete interlayer reflections, especially (1 0 1) and (1 0 2). EMM-10P complements the series of three distinct, as-synthesized MWW materials, viz: MCM-22P, MCM-49 and MCM-56, all differing in packing of the MCM-22 monolayers. The EMM-10P precursor was synthesized using a diquaternary ammonium template while the preceding three materials were obtained with hexamethyleneimine as the structure directing agent. Upon calcination EMM-10P partially converts to an ordered MWW structure but, to a large extent, the stacking disorder persists while the layers fuse together. Basic characterization including sorption, electron diffraction, electron microscopy, NMR, and swellability with surfactants, reveals properties similar to MCM-22. EMM-10, therefore, represents a further extension of the already uniquely diverse MCM-22 zeolite family, and corresponds to an anticipated structure variation. It has also broader fundamental implications, illustrating the growing contribution of disordered structures among zeolites and the need for better characterization tools and methods.

On time‐dependent properties of room responses to characterize scattering and diffusion.

The process of diffusing or mixing sound in a room is of both theoretical and practical significance in room‐acoustics. Simplified statistical models are often used to describe its overall behavior, but these models are not valid in general, especially in the early part of a room response. The geometry and scattering properties of the room determine the sound field and affect the validity of statistical assumptions. Several authors have proposed a theoretical time when the field can be considered sufficiently mixed or homogeneous, the transition between discrete reflections and the reverberant field. Since the time‐evolution of the room response is dictated by the room, estimation of this time limit and other temporal characteristics affords the extraction of geometrical and scattering properties from a measured room impulse response. This paper investigates time‐dependent properties of measured room impulse responses in order to characterize the scattering properties of rooms.

Counting reflections in measured acoustic impulse response functions.

A novel method of counting reflections and reflection density has been developed. The method is borrowed from non‐linear studies of fractal systems where time delayed versions of a signal are plotted against each other. In this case, the sound pressure p(t) of an impulse response function is plotted against its time derivative, dp(t)/dt. Each resulting circle represents a reflection. The results are, in effect, a dynamic version of (a normally steady state) Lissajous figure. Measured reflection counts are much lower than would be expected from theoretical predictions, primarily in the hundreds rather than thousands. A new method for estimating the temporal border between discrete and diffuse reflections is also presented.

Analysis of the Discretization Error at Material Interfaces in Staggered Grids

We address the problem of modeling discontinuities at material interfaces and we propose an intuitive model to discuss the origin of spurious discrete reflections. We restrict ourselves to the 1-D analysis and we consider perfectly matched layers as a case study. The approach, based on an approximation, leads to a closed form expression to quantitatively evaluate the performance of perfectly matched layers. Furthermore, the algorithms are presented in details for reproducibility.

Reverberation-Chamber Test Environment for Outdoor Urban Wireless Propagation Studies

We introduce a test environment to replicate the well-known clustering of reflections in power delay profiles arising from late-time delays and reflections. Urban wireless propagation environments are known to exhibit such clustering. The test setup combines discrete reflections generated by a fading simulator with the continuous distribution of reflections created in a reverberation chamber. We describe measurements made in an urban environment in Denver, CO, that illustrate these multiple distributions of reflections. Our comparison of measurements made in the urban environment to those made in the new test environment shows good agreement.

Effects of Reflection in RSOA-Based WDM PON Utilizing Remodulation Technique

We investigate the effects of the discrete reflection on the performances of upstream and downstream signals in the wavelength-division-multiplexed passive optical network (WDM PON) implemented in a single-fiber loopback configuration using the reflective semiconductor optical amplifiers (RSOAs). We first analyze the optical beat interference (OBI) noise caused by the discrete reflection, and clarify the relation between the reflection tolerance and the network's operating conditions such as the RSOA gain, the link loss, and the location of the reflection point, etc. The results show that the impact of the reflection can be expressed by using the effective crosstalk level. We then measured the reflection tolerance of the RSOA-based WDM PON, in which the downstream signal operating at 1.25 Gb/s is remodulated by the RSOA at the subscriber's site for the transmission of 155-Mb/s upstream signal. The reflection tolerances are measured to be in the range of -42 to - 35ndB for the downstream signals and -29 to -19ndB for the upstream signals, depending on the RSOA gain. These small reflection tolerances are caused by the fact that the reflected light is re-amplified by the RSOA. We also show that the dependence of the reflection tolerance on the RSOA gain can be explained by using the effective crosstalk level. These results are used to evaluate the impacts of the unwanted discrete reflections on the RSOA-based WDM PON.

Multichannel Room Impulse Response Generation With Coherence Control

A method is proposed by which an arbitrary number of room impulse responses (RIRs) is generated from one input RIR. The method works by convolving the input RIR with a multitude of filters, one for each desired output RIR. The filters are designed in such a way that the coherence between all possible pairs of output RIRs feature assignable frequency-dependent values. An application example is given where the values for the coherence are given by the diffuse field coherence functions for the microphones in a five-element microphone array. The limitations in terms of achieving the desired coherence values exactly and avoiding spectral coloration are also discussed. The proposed method is most suitable for the part of the RIR that does not contain strong discrete reflections.

Tilted lamellae in an affinely deformed 3D macrolattice and elliptical features in small‐angle scattering

AbstractLamellar reflections in small‐angle X‐ray and neutron scattering patterns of uniaxially drawn semicrystalline polymers appear to fall on elliptical or hyperbolic arcs. We attribute this to a 3D lattice of tilted lamellae, a macrolattice. Affine deformation of this lattice, such as during uniaxial draw, moves and spreads the reflections along elliptical arcs, and nonaffine deformation, such as during rolling, moves and spreads the reflections along an arc that deviates from an ellipse. Discrete reflections are the product of two functions: the elliptical trace that is the Fourier transform of the affinely deformed lattice and the radial streak that is the Fourier transform of the individual lamella in the reciprocal space. Four‐point patterns are obtained if the lamellar‐surface normal is tilted away from the fiber‐axis, and two‐point patterns if it is not. This model is used to discuss the transformation between four‐ and two‐point patterns and other changes in lamellar morphology that occur during drawing and annealing of oriented semicrystalline polymers. The deformation of the macrolattice of crystalline lamellae, need not be correlated to the tilt of the lamellae. The tilt of the lamellae is shown to be important. It reflects the cross‐sectional area mismatch at the lamellar surface between crystalline stems and amorphous chains segments, and this indicates the internal strain in the interfibrillar amorphous regions. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1277–1286, 2006

Investigation of a high Tc piezoelectric system: (1−x)Bi(Mg1/2Ti1/2)O3–(x)PbTiO3

(1−x) Bi(Mg 1/2 Ti 1/2 ) O 3 –x PbTiO 3 polycrystalline ceramics were investigated for potential as high-temperature piezoelectric materials. A morphotropic phase boundary (MPB) between tetragonal (T) and rhombohedral (R) ferroelectric (FE) phases, which exhibited enhanced piezoelectric activity and a ferroelectric–paraelectric phase transition at 478 °C was observed at x≈0.37. Electron diffraction patterns (x⩽0.37) contained discrete superlattice reflections at 12{hkl} positions arising from antiphase rotations of the O octahedra, consistent with R3c space group symmetry. These reflections were diffuse at the MPB (x=0.38) and absent in the T phase (x=0.5). In the unpoled state, FE R (x=0.35) ceramics revealed a polar microdomain structure whereas the T phase (x=0.5) contained classic {110} twin domain boundaries. However, poled R samples underwent a field-induced transformation to an aligned domain structure with {110} twin boundaries similar to those in the T phase. Correlations are made between structure and properties for these piezoelectric materials.

Bi-directional coupling between two coupled transmission lines

Coupled mode theory including backward coupling is employed to investigate the bi-directional coupling mechanism in two symmetrical coupled microstrip transmission lines. Analytical scattering parameter expressions for the case of matched terminations are presented. Reflections and near-end crosstalk is attributed to the combined effects of distributed backward coupling and interference between discrete reflections caused by termination mismatches at two ends.

Diffusion and Auditorium Acoustics

The prominence of diffusion in auditorium acoustics is commonly acknowledged in the literature, but neither objective measure nor subjective description indicates how it should be defined. Since we know the early sound plays an important part in the subjective success of a concert hall, several acoustical parameters for acoustical design such as EDT, tI, C80, G80, LFE, IACCE, etc. were developed in relation to the early reflections. A sound field composed of a few discrete reflections is of course non-diffuse even in a hall with plenty of surface diffusers. These diffusers may be relevant to the late reverberant sound field, which contributes to the acoustical quality of a hall and will be considered as dependent on the degree of diffusion. Compared with RT60, EDT is a better indication of perceived reverberance, and the quality of reverberant sound may not be that significant to the hall acoustics. Although the early studies of spatial impression focused on the importance of reverberant sound, recent investigations reveal that late-arriving sound from the side of the listener is more important for creating a strong sense of listener envelopment (LEV). Hence the question is: “Is diffusion over-emphasized?” After an overview on this subject, the author suggests several issues to be clarified through further investigations.

Reverberation and the Franssen effect

The Franssen effect, in which the location of a sudden-onset (transient) tone can occlude the location of a contralateral slow-onset (steady-state) tone, has been previously shown to occur only in a reverberant space. The nature of the reverberation required—how much and what kind—for the effect to occur has yet to be determined. To explore the role of reverberation in the Franssen effect, listeners were asked to identify the location(s) of transient/steady-state pure tones with frequencies ranging from 250–4000 Hz in a variety of real and virtual contexts: (a) limited (single reflective panel) reverberant enclosure; (b) discrete reflections in an anechoic room; (c) mannequin recordings of a reverberant enclosure presented over headphones; (d) impulse-response filtered signals presented over headphones; and (e) simulated 3-D reverberation via consumer-grade software. Results indicate that the Franssen effect can be a simple, effective means to judge the verisimilitude of a virtual environment. [Work supported by NIDCD.]

Measurement of 3-D directional characteristics of reverberant sound fields using a spherical microphone array

A new measurement system has been used to analyze directional characteristics of reverberant sound fields in several small- and medium-sized rooms. The system employs a pair of 32-element spherical microphone arrays to obtain the room impulse response in each of 60 steering directions. The two different-sized arrays are used to cover the frequency range from 300–3300 Hz with an angular (directional) resolution of about 28 degrees. An analysis of these directional room impulse responses enables the variation of arriving sound energy with (3-D) direction and time to be studied. Specifically, the isotropy of the sound field at the receiving position can be assessed at any time instant, or over any time range desired. Directions from which significant or insignificant proportions of sound energy arrive are identifiable. Furthermore, the time and direction of incidence of the direct sound and discrete early reflections can be identified. This can be of use in localizing sources, finding reflections, and in decomposing the sound field into arriving components.