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Moss D.J.,University of Sydney | Morandotti R.,INRS EMT | Gaeta A.L.,Cornell University | Lipson M.,Cornell University
Nature Photonics | Year: 2013

Nonlinear photonic chips can generate and process signals all-optically with far superior performance to that possible electronically-particularly with respect to speed. Although silicon-on-insulator has been the leading platform for nonlinear optics, its high two-photon absorption at telecommunication wavelengths poses a fundamental limitation. We review recent progress in non-silicon CMOS-compatible platforms for nonlinear optics, with a focus on Si3N4 and Hydex®. These material systems have opened up many new capabilities such as on-chip optical frequency comb generation and ultrafast optical pulse generation and measurement. We highlight their potential future impact as well as the challenges to achieving practical solutions for many key applications. © 2013 Macmillan Publishers Limited.

Shalaby M.,INRS EMT | Peccianti M.,CNR Institute for Complex Systems | Ozturk Y.,INRS EMT | Ozturk Y.,Ege University | Morandotti R.,INRS EMT
Nature Communications | Year: 2013

A Faraday isolator is an electromagnetic non-reciprocal device, a key element in photonics. It is required to shield electromagnetic sources against the effect of back-reflected light, as well as to limit the detrimental effect of back-propagating spontaneous emissions. A common isolator variant, the circulator, is widely used to obtain a complete separation between forward-and backward-propagating waves, thus enabling the realization of a desired transfer function in reflection only. Here we demonstrate a non-reciprocal terahertz Faraday isolator, operating on a bandwidth exceeding one decade of frequency, a necessary requirement to achieve isolation with the (few-cycle) pulses generated by broadband sources. The exploited medium allows a broadband rotation, up to 194/T, obtained using a SrFe 12 O 19 terahertz-transparent permanent magnet. This in turn enables the design of a stand-alone complete terahertz isolator without resorting to an external magnetic field bias, as opposed to all the optical isolators realized so far. © 2013 Macmillan Publishers Limited. All rights reserved.

Driben R.,Tel Aviv University | Driben R.,University of Paderborn | Hu Y.,INRS EMT | Chen Z.,San Francisco State University | And 2 more authors.
Optics Letters | Year: 2013

By means of direct simulations and theoretical analysis, we study the nonlinear propagation of truncated Airy pulses in an optical fiber exhibiting both anomalous second-order and strong positive third-order dispersions (TOD). It is found that the Airy pulse first reaches a finite-size focal area as determined by the relative strength of the two dispersion terms, and then undergoes an inversion transformation such that it continues to travel with an opposite acceleration. The system notably features tight focusing if the TOD is a dominant factor. These effects are partially reduced by Kerr nonlinearity. © 2013 Optical Society of America.

Razzari L.,INRS EMT | Razzari L.,University of Pavia | Duchesne D.,INRS EMT | Ferrera M.,INRS EMT | And 5 more authors.
Nature Photonics | Year: 2010

Integrated multiple-wavelength laser sources, critical for important applications such as high-precision broadband sensing and spectroscopy, molecular fingerprinting, optical clocks and attosecond physics, have recently been demonstrated in silica and single-crystal microtoroid resonators using parametric gain. However, for applications in telecommunications and optical interconnects, analogous devices compatible with a fully integrated platform do not yet exist. Here, we report a fully integrated, CMOS-compatible, multiple-wavelength source. We achieve optical hyper-parametric oscillation in a high-index silica-glass microring resonator with a differential slope efficiency above threshold of 7.4% for a single oscillating mode, a continuous-wave threshold power as low as 54mW, and a controllable range of frequency spacing from 200GHz to more than 6THz. The low loss, design flexibility and CMOS compatibility of this device will enable the creation of multiple-wavelength sources for telecommunications, computing, sensing, metrology and other areas. © 2010 Macmillan Publishers Limited. All rights reserved.

Djerafi T.,INRS EMT | Wu K.,Ecole Polytechnique de Montréal
IEEE Transactions on Antennas and Propagation | Year: 2012

This communication presents a low-cost 77-GHz switched-beam slot antenna array driven by a Butler matrix. In the proposed configuration, four broadband couplers are combined and crossovers are effectively avoided. In this case, the overall circuit and beamforming network losses are considerably reduced. A 4$\,\times\,$4 planar SIW Butler matrix is designed and demonstrated for integrated beamforming network applications, which exhibits about 7 degrees phase error and $\pm {0.75}~{\rm dB}$ coupling imbalance over 11% bandwidth. This experimentally prototyped matrix is integrated with a four-array slot antenna on the same substrate. An alternating displacement of the slots in subsequent radiating waveguides is proposed to save the arrangement of the input ports and to achieve broadband performances. Measured radiation patterns are in good agreement with simulated counterparts over the proposed 77-GHz frequency range. © 1963-2012 IEEE.

Szczecinski L.,INRS EMT
IEEE Transactions on Communications | Year: 2012

In this work we analyze the problem of correction of the reliability metrics (L-values) in bit-interleaved coded modulation (BICM) receivers. First, we propose a method for finding the linear correction factors that minimize the probability of error of a maximum likelihood decoder that uses the corrected L-values. To this end, we use the efficient approximation of the pairwise error probability in the domain of the cumulant generating functions (CGF) of the L-values and conclude that the optimal correction factors are equal to the twice of value of the saddlepoint of the CGF. Next, a simple extension of the proposed method to the non-linear correction is presented. We provide numerical examples demonstrating improvements attainable with the proposed method comparing it to the competitive solutions. © 2012 IEEE.

Tehranchi A.,University of Montréal | Morandotti R.,INRS EMT | Kashyap R.,University of Montréal
Optics Express | Year: 2011

High-efficiency ultra-broadband wavelength converters based on double-pass quasi-phase-matched cascaded sum and difference frequency generation including engineered chirped gratings in lossy lithium niobate waveguides are numerically investigated and compared to the single-pass counterparts, assuming a large twin-pump wavelength difference of 75 nm. Instead of uniform gratings, few-section chirped gratings with the same length, but with a small constant period change among sections with uniform gratings, are proposed to flatten the response and increase the mean efficiency by finding the common critical period shift and minimum number of sections for both single-pass and double-pass schemes whilst for the latter the efficiency is remarkably higher in a low-loss waveguide. It is also verified that for the same waveguide length and power, the efficiency enhancement expected due to the use of the double-pass scheme instead of the single-pass one, is finally lost if the waveguide loss increases above a certain value. For the double-pass scheme, the criteria for the design of the low-loss waveguide length, and the assignment of power in the pumps to achieve the desired efficiency, bandwidth and ripple are presented for the optimum 3-section chirped-gratings-based devices. Efficient conversions with flattop bandwidths > 84 nm for lengths < 3 cm can be obtained. © 2011 Optical Society of America.

Masmoudi A.,INRS EMT | Bellili F.,INRS EMT | Affes S.,INRS EMT | Stephenne A.,INRS EMT
IEEE Transactions on Signal Processing | Year: 2013

In this paper, we present a new implementation of the maximum likelihood criterion for the estimation of the time delays in a multipath environment and then extend it to the estimation of the time difference of arrival when the transmitted signal is unknown. The new technique implements the concept of importance sampling (IS) to find the global maximum of the compressed likelihood function in a modest computational manner. It thereby avoids traditional complex multidimensional grid search or initialization- dependent iterative methods. Indeed, one of themost interesting features is that it transforms the multi-dimensional search inherent to multipath propagation into a much simpler one-dimensional optimization problem in the delays dimension. Moreover, it guarantees convergence to the global maximum, contrarily to the popular iterative implementation of the maximum likelihood criterion by the well known expectation maximization (EM) algorithm. Comparisons with some other methods such as the EM algorithm, MUSIC and accelerated random search (ARS) demonstrates the superiority of the proposed IS-based multipath delay estimator in terms of estimation performance and complexity. © 2012 IEEE.

Bellili F.,INRS EMT | Methenni A.,INRS EMT | Affes S.,INRS EMT
IEEE Transactions on Signal Processing | Year: 2014

In this contribution, we derive for the first time the closed-form expressions for the Cramér-Rao lower bounds (CRLBs) of the signal-to-noise ratio (SNR) estimates from BPSK-, MSK- and square-QAM modulated signals over turbo-coded transmissions. These CRLBs, relatively easy to derive from BPSK, MSK and QPSK transmissions, become extremely challenging with higher-order square-QAM-modulated signals. In the latter, by exploiting the structure of the Gray mapping, we are able to factorize the likelihood function thereby linearizing all the derivation steps for the Fisher information matrix (FIM) elements. We also propose another approach that allows the evaluation of the considered bounds using extensive Monte Carlo computer simulations. The analytical CRLBs coincide exactly with their empirical counterparts validating thereby our new analytical expressions. Numerical results suggest that the CLRBs for code-aided (CA) SNR estimates range between the CRLBs for non-data-aided (NDA) SNR estimates and those for data-aided (DA) ones, thereby highlighting the expected potential in SNR estimation improvement from the coding gain. Indeed, the CA CRLBs improve by decreasing the overall coding rate due to enhanced decoding capabilities. However they do increase with the modulation order for a given code rate. Finally, the derived bounds are also valid for LDPC coded systems and they can be evaluated when the latter are decoded using the turbo principal. © 1991-2012 IEEE.

Larouche N.,INRS EMT | Stansfield B.L.,INRS EMT
Carbon | Year: 2010

Raman scattering is known to be a unique characterization tool for carbon-based materials such as graphite, diamond, graphene and nanostructured carbons. In this article, we propose a new parameter for estimating the crystallinity of nanostructured carbons. This new parameter estimates the length of the curved graphene planes. To take into account the effect of curvature, the importance of the second-order band at about 2700 cm-1 is emphasized. Using this new parameter, we propose a classification of different nanostructured carbons. The relevance of this new parameter for characterizing nanostructured carbons is confirmed by transmission electron microscopy. © 2009 Elsevier Ltd. All rights reserved.