Receiver Bandwidth Research Articles

A study of the feasibility and reproducibility of measuring blood perfusion in the kidney using MRI without a contrast agent

s from the Irish Association of Physicists in Medicine 6th Annual Scientific Meeting Diagnostic Parallel Session A study of the feasibility and reproducibility of measuring blood perfusion in the kidney using MRI without a contrast agent Andrew J. Fagan, Susie Clarke, James F. Meaney. National Centre for Advanced Medical Imaging (CAMI), St. James’s Hospital/ School of Medicine, Trinity College Dublin Introduction: MRI contrast agents are contra-indicated for patients with impaired renal function, and hence there is considerable interest in developing a non-contrast agent techniquewhich can quantify blood perfusion, for example in transplant patients. Pseudo-continuous arterial spin labelling (pCASL) is a new technique which has recently been recommended for use in cerebral perfusion studies; however, its use in the torso/ abdomen regions is severely compounded by artefacts arising from respiratory motion andmagnetic susceptibility inhomogeneities. This study aimed to optimise and assess the reproducibility of pCASL for renal perfusion. Methodology: 15 healthy controls were scanned using a 3T Philips scanner. A high spatial resolution pCASL sequence was optimised through careful tailoring of all acquisition parameters. 16 label/control image pairs were acquired in all cases, with the labelling plane positioned perpendicular to the aorta above the kidneys, and the image plane orientated coronallyoblique. Breath-hold acquisitions were used tominimise respiratorymotion, and B-spline image registration was performed on all images prior to fitting to the standard pCASL perfusion model. Results: Image SNR of 56 ± 3 was achieved in images with: voxel resolution = 2.5 × 2.5 × 6 mm3, receiver bandwidth = 3037 Hz, label duration = 1500 ms, label delay = 1500 ms. Excellent contrast was achieved between medulla and cortex regions, with measured perfusion values of 293 ± 44 and 139 ± 20ml/100 g/min respectively. Excellent intraand intersession reproducibility was noted. Conclusions: It is possible to perform sensitive and reproducible measurements of blood perfusion in the kidney using the pCASL technique, with a spatial resolution sufficiently high to allow for separation of medulla from cortical regions. How to estimate the dose from a dental CT or CBCT scan Anthony Reynolds. IDT Ireland, Kinsale, Co. Cork Cone beam computed tomography (CBCT) scanners are now widely used in dentistry. Under current legislation, dental practitioners must balance the benefit to the patient against the radiation risk. Calculating exact values of dose (and hence risk) is time-consuming and requires specialist knowledge. Thiswork showsa simplemethodof estimating thedosewith sufficient accuracy for the task at hand. We estimate the effective dose from parameters stored in the DICOM header or displayed on the CT or CBCT screen. Database technology interpolates missing or incomplete data, and database tables can be refined as more information becomes available. Most modern equipment displays the Dose Length Product (DLP) or Dose Area Product (DAP). Published data can be used when machines do not provide this information. Multiplying the DLP (expressed in mGy.cm) by 2 for the maxilla or 3 for the mandible gives a rough estimate of the effective dose in microSieverts, within the context of an adult dental CT or CBCT scan. Results are accurate to within a factor of 2, which is sufficient for decisions regarding patientmanagement. Trade-offs between dose and image quality can be complex, and are not always well understood. Selecting a smaller voxel sizemay improve the resolution, at the expense of greater noise, and operators may compensate by increasing the mAs. The additional patient detriment must be justified on the basis of increased diagnostic information. Providing amethod (however rough) of estimating the dose empowers dental practitioners to make an informed decision. Assessment of colour Doppler sensitivity of a range of early pregnancy ultrasound systems Browne JE a, Cournane S b, Fagan AJ c. a School of Physics & Medical Ultrasound Physics & Technology Group, IEO, FOCAS Institute, Dublin Institute of Technology; b Medical Physics and Bioengineering, St James’s Hospital, Ireland; c Centre for Advanced Medical Imaging, St James’s Hospital & Trinity College

Matched‐filter properties of linear‐frequency‐modulation radar signal reflected from a phase‐switched screen

The phase-switched screen (PSS) imposes phase modulation onto the radar-reflected signal so that its energy is redistributed into sidebands that lie outside the receiver pass-band. However, when illuminated by a wideband linear frequency modulation (LFM) radar, the modulated reflected signal may still occupy the radar pass-band if the LFM signal bandwidth is greater than the modulating frequency. Previous research about the reflectivity performance of a PSS against LFM radar illumination focuses mainly on the frequency spectrum characteristics. In this study, an investigation has been carried out to determine the matched-filter properties of an LFM radar signal modulated by a PSS. Theoretical analyses and simulation results have proven that even though the radar receiver bandwidth has been corrupted to aliasing by component of the reflected signal, the PSS is shown to be equally effective in shielding a target and additionally provide a multiple-decoy capability.

A View-Level Rate Distortion Model for Multi-View/3D Video

Multi-view/3D video is currently available in games, entertainment, education, security, and surveillance applications . Since the amount of data in multi-view/3D increases proportionally with the number of cameras, and due to different bandwidth and playback capabilities of receivers, appropriate compression of multi-view/3D video to produce the correct bitrate while maintaining smooth video quality is crucial, a task that is mostly performed by the rate control module of the encoder. There are many existing rate control algorithms for single-view and multi-view video coding considering the specific features or aspects of these videos. In this paper, we introduce a novel view-level rate distortion (RD) model. We use a systematic methodology to derive this RD model by investigating the impact of multi-view/3D video characteristics on the bitrate of a compressed video. Our proposed RD model considers the concepts of intra-view and inter-view disparity as an effective feature of multi-view/3D video to estimate the overall bitrate of each view more accurately. Evaluation results indicate that our proposed view-level RD model outperforms existing linear models by a factor of 3 and can predict the rate of each view with relatively high precision and a low estimation error of 12% on average.

Experimental demonstration of correlation detection with limited receiver bandwidth in Nyquist OTDM scheme

Experimental demonstration of correlation detection with limited receiver bandwidth in Nyquist OTDM scheme

Compact InP-Based DFB-EAM Enabling PAM-4 112 Gb/s Transmission Over 2 km

We demonstrate a 56-GBd pulse-amplitude modulation-4 compact InP transmitter module integrating a distributed feedback laser and an electro-absorption modulator, which exhibits 50-GHz bandwidth, >13-dB extinction ratio and up to 1.5-mW output power. Successful amplifier-free 112-Gb/s transmission is performed over 2 km using low complexity three-taps equalization. We also study the tradeoff between receiver bandwidth, equalizer length and performance, and show successful signal recovery with bandwidths as low as 18 GHz when increasing the equalizer length.

100-Gb/s DD-MB-OFDM Metro Network With 11-Gb/s Granularity and 2.85-GHz Receiver

An ultra-dense 100-Gb/s multi-band orthogonal frequency division multiplexing (MB-OFDM) system employing virtual-carrier-assisted direct-detection and a 2.85-GHz receiver bandwidth is demonstrated experimentally. Nine OFDM bands with a band spacing of 6 GHz and a band capacity of 11 Gb/s are employed. The proposed system enables single-band extraction with low-complexity, provides high granularity, flexibility, and scalability, and is proposed for metropolitan (metro) networks. The experiments show that the transmission of the 100-Gb/s MB-OFDM signal comprising the nine-bands along metro networks reaching 150 km is successfully accomplished with bit error ratio levels below the forward error correction threshold. Reduced penalty relative to back-to-back operation is observed for optical power levels launched into each fiber span in the range between 0 and 4 dBm.

Advances in Metal Artifact Reduction Techniques for Periprosthetic Soft Tissue Imaging.

Artifact from metallic orthopedic prosthesis is caused by inhomogeneity in the B0 magnetic field, particularly in the frequency encoding direction. This results in signal voids, signal pileup, and geometric distortion. Advances in reducing this artifact allow us to assess the complications of joint replacement and improve imaging of nearby tissues such as within the pelvis. Selection of titanium implants and lower field strength MR units provide optimal conditions for artifact reduction. Conventional sequences can be optimized by using inversion recovery sequences, large matrices, high receiver bandwidths, and thin slices. Optimizing these parameters comes with a penalty in terms of signal-to-noise ratio or increased acquisition times. Successful artifact reduction depends on the strength of the frequency encoding gradients. Newer dedicated artifact reduction sequences include view-angle-tilting and a selection of multispectral techniques including multiacquisition variable-resonance image combination (MAVRIC) and slice encoding for metal artifact correction (SEMAC). Many of these are being used in combination. The multispectral sequences acquire three-dimensional data at very narrow frequencies and use of phase encoding for spatial localization. Planar images can then be reconstructed with very little susceptibility artifact.

Optical Code-Division Multiplexing (OCDM) Networks Adopting Code-Shift Keying/Overlapping PPM Signaling: Proposal and Performance Analysis

Optical code-division multiplexing (OCDM) systems use short pulses compared with bit-duration to achieve high transmission rate. The use of short pulses poses several problems as a result of group velocity dispersion (GVD), intersymbol interference (ISI) (due to avalanche photodiode (APD) buildup time), and receivers limited bandwidth. In this paper, an OCDM system employing code-shift keying (CSK) and overlapping pulse-position modulation (OPPM) signaling is proposed and theoretically investigated. By using CSK while maintaining same data rate, the chip duration can be increased to counteract the GVD effect in 2D OCDM systems. Moreover, by increasing the chip duration, the chip rate is decreased and the stringent requirement on receiver bandwidth is relaxed. In addition, using overlapping property in OPPM allows for further chip duration increase. We consider using correlation receivers with hard-limiters and APDs at the receiver side. The bit error probability (BEP) of the proposed system is derived taking into account the impacts of APD noise, thermal noise, GVD, ISI, and multiple-access interference (MAI). A performance comparison between OOK-, PPM-, OPPM-OCDM and the proposed system is carried out. Our results reveal that the use of CSK/OPPM-OCDM with data rate constraint allows the reduction of MAI, GVD and ISI effects with improved spectral efficiency.

Recent developments in radar altimetry over land and their application to the CryoSat -2 mission

Altimeters are active microwave instruments for the accurate measurement of vertical distances (between the spacecraft and the altimeter footprint). The technology determines the two-way delay of the radar pulse echo from the Earth’s surface to a very high precision (to less than a nanosecond). The instrument is also able to measure the power and the shape of the reflected radar pulses. Since the first dedicated altimeter was launched on the Seasat platform in 1978, satellite altimetry has experienced incredible and continuous development as new sensors have been designed and have become operational. The accuracy in range measurements gradually reached values that have produced an extraordinary increase in our knowledge of many aspects of ocean and ice dynamics and variability. Mainly, the evolution of the altimeter transmitter is marked by improvements in pulse compression techniques that have substantially reduced peak power requirements, as reported in [1] and [2], for example. The altimeter missions considered in this paper operate at Ku-band. The choice of frequency is constrained by both the system and the operational requirements. Since a narrow transmitted pulse is required to achieve reasonable range precision, high-frequency operation supports both the large receiver bandwidth and the narrow antenna beamwidth requirements. The upper limit on the operational frequency is constrained by atmospheric attenuation effects that significantly degrade the performance of the altimeter for frequencies > 18 GHz. In some altimetric missions, such as Topex, the radar altimeter instrument includes a C-band transmitter so that ionospheric propagation delays can be accurately measured. Generally, the two-frequency system produces subdecimeter range precision so that very small variations (particularly in the ocean surface) can be detected.

Optimum Linewidth of Spectrum-Sliced Incoherent Light Source Using a Gain-Saturated Semiconductor Optical Amplifier

We investigate the optimum linewidth of the spectrum-sliced incoherent light (SSIL) source using a gain-saturated semiconductor optical amplifier (SOA) for the maximum capacity and longest transmission distance. For this purpose, we carry out experimental and simulation studies on the transmission performance of a 10-Gb/s on–off keying signal generated by using the SSIL source over a wide range of the SSIL linewidth. We find out that there are two windows of the linewidth for the high-speed operation of the SSIL source: ultra-narrow (i.e., linewidth $\ll$ receiver bandwidth) and very wide (i.e., linewidth $\gg$ receiver bandwidth). However, when the linewidth of the SSIL source is very wide, the 10-Gb/s signal generated by using this SSIL suffers severely from fiber chromatic dispersion and optical filtering. The simulation results are confirmed by experimental data measured by using an ultranarrow fiber Fabry–Perot filter (bandwidth = 700 MHz) and a bandwidth-tunable optical filter (bandwidth = 20 ∼ 53 GHz). Thus, we can conclude that the optimum linewidth of SSIL for capacity and transmission distance is ultranarrow. We also present a couple of drawbacks of the ultranarrow SSIL source, compared to the conventional wide-linewidth SSIL one, such as a large spectrum-slicing loss, a large SOA input power required for the suppression of excess intensity noise inherent in the incoherent light source, and the susceptibility to in-band crosstalk.

Real‐time imbalance compensator for wideband receiver applications

To increase the bandwidth of a wideband receiver for surveillance applications, an in-phase/quadrature-phase (I/Q) channel-based receiver is a potential approach. However, the image caused by an imperfect coupler prevents the I/Q channel-based receiver from becoming a reality. Air Force Research Laboratory developed an imbalance compensation method covering two Nyquist zones. In this study, the authors present its implementation with a field-programmable gate array board. Experimental results demonstrate the effectiveness of the proposed imbalance compensation algorithm and its feasibility.

Body MR Imaging: Artifacts, k-Space, and Solutions.

Body magnetic resonance (MR) imaging is challenging because of the complex interaction of multiple factors, including motion arising from respiration and bowel peristalsis, susceptibility effects secondary to bowel gas, and the need to cover a large field of view. The combination of these factors makes body MR imaging more prone to artifacts, compared with imaging of other anatomic regions. Understanding the basic MR physics underlying artifacts is crucial to recognizing the trade-offs involved in mitigating artifacts and improving image quality. Artifacts can be classified into three main groups: (a) artifacts related to magnetic field imperfections, including the static magnetic field, the radiofrequency (RF) field, and gradient fields; (b) artifacts related to motion; and (c) artifacts arising from methods used to sample the MR signal. Static magnetic field homogeneity is essential for many MR techniques, such as fat saturation and balanced steady-state free precession. Susceptibility effects become more pronounced at higher field strengths and can be ameliorated by using spin-echo sequences when possible, increasing the receiver bandwidth, and aligning the phase-encoding gradient with the strongest susceptibility gradients, among other strategies. Nonuniformities in the RF transmit field, including dielectric effects, can be minimized by applying dielectric pads or imaging at lower field strength. Motion artifacts can be overcome through respiratory synchronization, alternative k-space sampling schemes, and parallel imaging. Aliasing and truncation artifacts derive from limitations in digital sampling of the MR signal and can be rectified by adjusting the sampling parameters. Understanding the causes of artifacts and their possible solutions will enable practitioners of body MR imaging to meet the challenges of novel pulse sequence design, parallel imaging, and increasing field strength.

A High-Speed CMOS Integrated Optical Receiver With an Under-Damped TIA

We present a CMOS integrated optical receiver having under-damped transimpedance amplifier (TIA) and CMOS avalanche photodetector (APD) realized in 65-nm CMOS technology. The under-damped TIA compensates the bandwidth limitation of CMOS APD and provides enhanced receiver bandwidth performance with reduced power consumption and better sensitivity compared with previously reported techniques. We successfully demonstrate 10-Gb/s $2^{31}-1$ PRBS and 12.5-Gb/s $2^{7}-1$ PRBS operation with the bit-error rate less than $10^{-12}$ at the incident optical power of −6 and −2 dBm, respectively. The receiver has core size of 0.24 mm $\times 0.1$ mm and power consumption excluding output buffer of $\sim 13.7$ mW with 1.2 V supply voltage.

Optimized protocols for cardiac magnetic resonance imaging in patients with thoracic metallic implants.

Cardiac magnetic resonance (MR) imaging is a valuable tool in congenital heart disease; however patients frequently have metal devices in the chest from the treatment of their disease that complicate imaging. Methods are needed to improve imaging around metal implants near the heart. Basic sequence parameter manipulations have the potential to minimize artifact while limiting effects on image resolution and quality. Our objective was to design cine and static cardiac imaging sequences to minimize metal artifact while maintaining image quality. Using systematic variation of standard imaging parameters on a fluid-filled phantom containing commonly used metal cardiac devices, we developed optimized sequences for steady-state free precession (SSFP), gradient recalled echo (GRE) cine imaging, and turbo spin-echo (TSE) black-blood imaging. We imaged 17 consecutive patients undergoing routine cardiac MR with 25 metal implants of various origins using both standard and optimized imaging protocols for a given slice position. We rated images for quality and metal artifact size by measuring metal artifact in two orthogonal planes within the image. All metal artifacts were reduced with optimized imaging. The average metal artifact reduction for the optimized SSFP cine was 1.5+/-1.8mm, and for the optimized GRE cine the reduction was 4.6+/-4.5mm (P < 0.05). Quality ratings favored the optimized GRE cine. Similarly, the average metal artifact reduction for the optimized TSE images was 1.6+/-1.7mm (P < 0.05), and quality ratings favored the optimized TSE imaging. Imaging sequences tailored to minimize metal artifact are easily created by modifying basic sequence parameters, and images are superior to standard imaging sequences in both quality and artifact size. Specifically, for optimized cine imaging a GRE sequence should be used with settings that favor short echo time, i.e. flow compensation off, weak asymmetrical echo and a relatively high receiver bandwidth. For static black-blood imaging, a TSE sequence should be used with fat saturation turned off and high receiver bandwidth.

TH-CD-207-12: A Phantom Study of MR Geometric Distortion and Its Orientation Dependency On a 1.5T MR-Simulator

Purpose: Gradient non-linearity and B0 inhomogeneity introduce system-dependent MR image distortion that violates geometry fidelity required for radiotherapy. In addition, gradient non-linearity induced distortion can be acquisition orientation dependent, while this effect has rarely been investigated. This study aimed to quantitatively assess 3D geometric distortion of MR images acquired in different orientations with a dedicated 1.5T wide-bore (70cm diameter) MR-simulator, using a customized geometry accuracy phantom. Methods: A polyurethane phantom (WxLxH=55×55×37.5cm3) was constructed with 4276 spherical markers (6mm diameter, MR/CT visible) arranged on a 3D grid (25mm isotropic-interval). Phantom reference images were acquired on a CT-simulator. Axial, coronal and sagittal MR images were individually acquired with 3D fast-spoiled-gradient-echo sequence (TR/TE=5.8/2.5ms, FOV=50cm, isotropic voxel size=1.3mm, flip angle=60o, NEX=4, receiver bandwidth=62.5kHz, with 3D geometric correction) within a single scan. Centroid positional deviations between MR images and CT reference were computed using a customized MatLab script to build a 3D displacement map for distortion quantification. Results: Marker displacements of axial, coronal and sagittal acquisitions (mean±SD) were 2.46±2.66mm, 2.13±2.32mm and 2.48±3.18mm respectively. The minimum diameter-spherical-volume (DSV) that reported 1mm maximum/mean displacements on axial, coronal and sagittal images were 72mm/288mm, 72mm/244mm and 150mm/316mm respectively. Thus, sagittal acquisition provided the largest DSV that had a geometric accuracy comparable to a CT-simulator under the AAPM-TG66 requirement (distortion induced displacement<1mm). Conclusion: We rigorously examined the acquisition orientation dependent geometric distortion of a wide-bore MR-simulator with a geometry accuracy phantom. The DSVs with 1mm maximum/mean displacements of the sagittal acquisition were notably larger than the others, implying the importance of considering acquisition orientation in clinical applications. Because of the relatively small DSV, MR geometric fidelity for large FOV applications has yet to be further improved. In vivo study is further needed to investigate subject-dependent distortion due to tissue susceptibility and chemical shift.

Magnetic resonance imaging of an equine fracture model containing stainless steel metal implants.

Post operative imaging in subjects with orthopaedic implants is challenging across all modalities. Magnetic resonance imaging (MRI) is preferred to assess human post operative musculoskeletal complications, as soft tissue and bones are evaluated without using ionising radiation. However, with conventional MRI pulse sequences, metal creates susceptibility artefact that distorts anatomy. Assessment of the post operative equine patient is arguably more challenging due to the volume of metal present, and MRI is often not performed in horses with implants. Novel pulse sequences such as multiacquisition variable resonance image combination (MAVRIC) now provide improved visibility in the vicinity of surgical-grade implants and offer an option for imaging horses with metal implants. To compare conspicuity of regional anatomy in an equine fracture-repair model using MAVRIC, narrow receiver bandwidth (NBW) fast spin echo (FSE), and wide receiver bandwidth (WBW) FSE sequences. Nonrandomised in vitro experiment. MAVRIC, NBW FSE and WBW FSE were performed on 9 cadaveric distal limbs with fractures and stainless steel implants in the third metacarpal bone and proximal phalanx. Objective measures of artefact reduction were performed by calculating the total artefact area in each transverse image as a percentage of the total anatomic area. The number of transverse images in which fracture lines were visible was tabulated for each sequence. Regional soft tissue conspicuity was assessed subjectively. Overall anatomic delineation was improved using MAVRIC compared with NBW FSE; delineation of structures closest to the metal implants was improved using MAVRIC compared with WBW FSE and NBW FSE. Total artefact area was the highest for NBW FSE and lowest for MAVRIC; the total number of transverse slices with a visible fracture line was highest in MAVRIC and lowest in NBW FSE. MAVRIC and WBW FSE are feasible additions to minimise artefact around implants.

Time and frequency synchronisation in all‐optical orthogonal frequency division multiplexing systems

In all-optical orthogonal frequency division multiplexing (AO-OFDM) systems, symbol time misalignment (STM) and subcarrier frequency offset (ScFO) result in intercarrier-interference and intersymbol interference, leading to degradation of bit error rate (BER) performance. In this study, an analytical study of the impacts of STM and ScFO on AO-OFDM system performance is conducted. In the presence of STM and ScFO, AO-OFDM system performance is evaluated with the number of subcarriers (N SC), cyclic prefix requirements and receiver bandwidth (BWRX ). For AO-OFDM system without CP, results show that the STM gives higher BER than the ScFO. To keep the BER below 10 − 3 in AO-OFDM systems with on-off keying-modulated three optical subcarriers and homodyne detection with BWRX = 30 GHz, the maximum acceptable relative deviations for the STM and the ScFO are 11 and 14%, respectively.

The effect of free-breathing on left ventricular rotational mechanics in normal subjects and patients with duchenne muscular dystrophy

Reyhan et al. Journal of Cardiovascular Magnetic Resonance 2015, 17(Suppl 1):Q22 http://www.jcmr-online.com/content/17/S1/Q22 WALKING POSTER PRESENTATION Open Access The effect of free-breathing on left ventricular rotational mechanics in normal subjects and patients with duchenne muscular dystrophy Meral Reyhan 2,3 , Zhe Wang 2,1* , Hyun J Kim 2 , Nancy Halnon 4 , Paul J Finn 2 , Daniel B Ennis 2,1 From 18th Annual SCMR Scientific Sessions Nice, France. 4-7 February 2015 Background Patients with Duchenne Muscular Dystrophy (DMD) develop respiratory impairment and signs and symptoms of cardiac involvement at an early age. Quantitative mea- sures of cardiac function from MRI tagging can be used to stage disease progression and monitor the response to therapy. Traditional cardiac MRI exams, however, require repeated breath holding, which places a notable burden on patients with DMD and can impart intrathoracic pressure changes that alter cardiac function. The effect of free- breathing on quantitative measure of left ventricular (LV) rotational mechanics for DMD patients is incompletely understood. Objective: To evaluate differences in LV rota- tional mechanics acquired during breath holding (BH), free-breathing with averaging (AVG), and free-breathing with respiratory bellows gating (BEL). Methods 16 healthy volunteers (1 female, 27.8±3.9 years) and 5 DMD patients (all male, 11.3±3.7 years) were scanned on a 3.0T Siemens Scanner with BH, AVG and BEL. ORI-SPAMM (Reyhan. M et. al. JMRI 2014;39(2):339- 345) was used to acquire short-axis images at the base and apex of the heart. 280-330x280-330mm field-of- view, 6mm slice thickness, 192x192 acquisition matrix, 395 Hz/pixel receiver bandwidth, TE/TR =2.33-2.39/ 4.71-4.83 ms, 8 phase encode lines per segment, 12° imaging flip angle, 8 mm tag spacing, GRAPPA 2. LV Figure 1 Mean LV twist of (A) healthy volunteers and (B) patients with DMD for breath-held (BH, solid), free-breathing with averaging (AVG, dashed), and bellows gated (BEL, dash-dotted) methods. BH LV twist is generally higher compared to AVG or BEL, especially at its peak. Radiological Sciences, University of California Los Angeles, Los Angeles, CA, USA © 2015 Reyhan et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver (http:// creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

Performance Analysis of DWDM System with Optical Amplifiers in Cascade Considering the Effect of Crosstalk

In this paper, an analytical approach is presented to evaluate the performance of DWDM system with intensity modulation direct detection (IM/DD) due to the effects of amplified spontaneous emission (ASE) noise of optical amplifier, optical receiver noises and crosstalk. And a system has been proposed with an optimum number of amplifiers with higher gain and an improved optical receiver has been proposed. We have investigated the effects of optical amplifiers and optical receiver in the presence of crosstalk on the overall performance; in particular, Signal-to-Noise Ratio (SNR) and Bit-Error-Rate (BER) performance of a DWDM system. The system performances are evaluated for varying different amplifier gains, number of optical amplifiers, hop length, number of hops, receiver bandwidth and receiver gain considering the relationship between crosstalk and the number of wavelengths channel spacing. It is found that, the performance is highly degraded due to crosstalk and noises. As a result the system suffers significant power penalty at a given BER.

Real-time coherent detection of phase modulated ultrashort pulses after time-to-space conversion and spatial demultiplexing.

Phase modulated sub-picosecond pulses are converted by a time-to-space processor to quasi-monochromatic spatial beams that are spatially demultiplexed and coherently detected in real-time. The time-to-space processor, based on sum-frequency generation (SFG), serves as a serial-to-parallel converter, reducing the temporal bandwidth of the ultrashort pulse to match the bandwidth of optoelectronic receivers. As the SFG process is phase preserving, we demonstrate homodyne coherent detection of phase modulated temporal pulses by mixing the demultiplexed SFG beam with a narrow linewidth local oscillator (LO) resulting in single-shot phase detection of the converted pulses at a balanced detector. Positively and negatively phase-modulated signal pulses are individually detected and LO shot noise limited operation is achieved. This demonstration of real-time demultiplexing followed by single-shot full-field detection of individual pulses, highlights the potential of time-to-space conversion for ultrahigh bit rate optical communications and data processing applications.