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In this paper I present a generic model that describes the lasing characteristics of continuous-wave circular and racetrack-shaped ring Raman lasers based on micro- and nano-scale silicon waveguides, including their lasing directionality and polarization behavior. This model explicitly takes into account the effective Raman gain values for forward and backward lasing, the Raman amplification in the bus waveguide, and the spatial gain variations for different polarization states in the ring structure. I show numerically that ring lasers based on micro-scale waveguides generate unidirectional lasing in either the forward or backward direction because of an asymmetry in nonlinear losses at near-infrared telecommunication wavelengths, whereas those based on nanowires yield only backward lasing due to a non-reciprocity in effective gain. Furthermore, the model indicates that backward lasing can yield a significantly higher lasing output at the bus waveguide facets than lasing in the forward direction. Finally, considering a TE-polarized pump input for a (100) grown silicon ring Raman laser, I demonstrate numerically that the polarization state of the lasing radiation strongly depends on whether micro-scale or nano-scale waveguides are used.

We discuss two novel nonlinear photonic functionalities of silicon nanowire waveguides. First, we address the Raman gain non-reciprocity that results from the tight light confinement in these waveguide structures, and investigate what consequences this non-reciprocal effect has for Raman lasing in silicon nanowire rings. Secondly, we show that when using silicon nanowire rings for four-wave mixing experiments, one can establish quasi-phase-matching for the four-wave mixing process, simply by properly choosing the radius of the nanowire ring. We also compare this novel quasi-phase-matching approach to phase matching based on dispersion engineering.

We report the first demonstration of resonant-grating-based laser wavelength tuning in the mid-infrared spectral domain and with Littrow mounting of the grating. We show for a mid-infrared Cr:ZnSe laser that this tuning technique is much more wavelength selective than prism-based tuning, while inducing very low cavity losses (around 2%), which are at least two times smaller than in the case of a standard metal grating. Furthermore, the resonant grating allows tuning the Cr:ZnSe laser over as much as 400 nm around a center wavelength of 2.38 mu m. This shows the potential of employing Littrow-mounted resonant diffraction gratings for controlling and tuning the emission wavelength of lasers emitting in the mid-infrared spectral domain and other wavelength regions. (C) 2011 by Astro Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA

The prospect for low pump-power Raman amplification in silicon waveguides has recently been boosted by theoretical studies discussing the enhancement of nonlinear phenomena in slow-light structures. In principle, the slowing down of either the pump or the signal beam is equivalent in terms of Raman gain, but in the presence of losses, we show that they play different roles in determining the net signal gain. We also investigate the impact of the mode profile in realistic slow-light waveguides on the total gain, an effect that is usually neglected in the context of stimulated Raman scattering. By taking representative losses and mode shapes into account, we provide a realistic estimation of the achievable performance of slow-light photonic crystal waveguides. Publisher PDF

We propose an efficient wavelength conversion scheme that is based on either Raman-resonant four-wave mixing or non-resonant Kerr-induced four-wave mixing in a silicon nanowire ring, and that does not require dispersion engineering of the nanowire. We rely on the spatial variation of the Raman and Kerr susceptibilities around the ring to quasi-phase match the wavelength conversion processes for TE polarized fields. The flexibility of this quasi-phase-matching scheme can lead to wavelength conversion efficiencies from -26.7 dB to values larger than 0 dB, and in certain circumstances makes it possible to outperform conventional phase-matched conversion in a dispersion-engineered silicon ring by factors exceeding 6 dB.

In this work we designed and made a photonic crystal structure with a photonic band gap around 532 nm wavelength. The structure was to be made from two commercially available glasses. Both should have similar temperature coefficients (alpha), also melting and softening temperatures should be as close as possible in order to thermally process both glasses together. In addition the refractive indexes of chosen glasses should be as different as possible in order to facilitate a wide band gap. The pair of glasses that met those requirements is LLF1 and SF6 produced by Schott. For those two glasses we performed a series of computer simulations using MIT MPB software. After checking various structures the widest band gap for the 532 nm wavelength was found for the hexagonal structure of high dielectric constant rods in low index material with a linear fill factor of 0.12 and a lattice constant 3.75 μm. This structure was manufactured using the stack and draw method. The measurements of the final structure made by ESM show that it is regular, with diffusion between glasses at the manageable level. This assures that manufacture process is repeatable.

Background: Patients with inflammatory bowel disease (IBD) display immunoreactivity to self-antigens and microbial antigens. We used a protein microarray approach to identify novel autoantigens in IBD. Methods: ProtoArray Human Protein Microarray v4.0 containing 8268 human proteins from Invitrogen (La Jolla, CA) was used. Results: Twenty-five IBD patients and five healthy controls were screened for candidate autoantigens. For 256 antigens, IBD patients had a higher seroreactivity than controls. Twenty antigens were selected for further evaluation in a larger cohort (60 ulcerative colitis [UC] patients, 60 Crohn's disease [CD] patients, 60 healthy controls, and 60 gastrointestinal-diseased controls) by means of a customized protein microarray. Out of these 20 antigens, one antigen, family with sequence similarity 84 member A (FAM84A), was identified as a target antigen in IBD. Antibodies to FAM84A were significantly more prevalent in IBD patients (19%) than in gastrointestinal-diseased controls (1.7%) (P = 0.0008) and healthy controls (5%) (P = 0.01). Anti-FAM84A antibodies were found in 26.6% of UC patients and in 11.7% of CD patients. FAM84A was confirmed as target antigen in IBD by means of Western blotting in a large independent cohort (100 UC patients, 106 CD patients, 102 healthy controls, and 100 gastrointestinal-diseased controls). Antibodies to FAM84A were significantly more prevalent in IBD patients (20%) than in gastrointestinal-diseased controls (5%) (P = 0.0004) and healthy controls (0%) (P < 0.0001). Anti-FAM84A antibodies were found in 18% of UC patients and in 22% of CD patients. Conclusions: We identified FAM84A as a novel autoantigen in IBD. (Inflamm Bowel Dis 2011;)

Background: Patients with inflammatory bowel disease (IBD) carry autoantibodies such as perinuclear antineutrophil cytoplasmic antibodies. The aim of the current study was to further characterize the immune reactivity in IBD. Methods: We used an immunoproteomic approach with extracts from granulocytes and serum from ulcerative colitis (UC) patients and controls to identify target antigens. By means of Western blot analysis, we screened 60 UC and 60 Crohn's disease (CD) patients, 60 diseased, and 60 healthy controls for the antibodies. We performed gene array experiments on RNA extracted from colonic mucosal biopsies from 42 IBD patients and six controls. Results: We identified aldolase A, phosphoglycerate mutase, alpha-enolase, triose-phosphate isomerase, and malate dehydrogenase as target antigens in IBD. Seroreactivity to at least one of these five antigens was detected in 53.3% of UC patients, 38.3% of CD patients, and 8.3% of controls. Seroreactivity to at least two antigens was detected in 16.7% of UC patients, 11.7% of CD patients, and none of the controls. Gene array experiments showed a significant upregulation of aldolase A, phosphoglycerate mutase, alpha-enolase, and pyruvate kinase mRNA in biopsies from IBD patients, but not controls. UC and CD patients also showed enhanced expression of hypoxia-inducible factor-1, a transcription factor that induces expression of glycolytic enzymes. Conclusions: IBD patients show strong seroreactivity toward enzymes involved in the glycolysis. IBD patients also have increased colonic mRNA expression of glycolytic enzymes, which is triggered by hypoxia through the transcription factor HIF-1. Inflamm Bowel Dis 2011

Introduction Over the past several decades there has been growing interest in the development of devices for optical wavelength conversion. In Raman converters, a long-wavelength Stokes input is in the presence of a pump transformed into a short-wavelength anti-Stokes output via a Raman-resonant third-order nonlinear process called coherent anti-Stokes Raman scattering (CARS) [1]. In Kerr-based parametric converters, a signal input is in the presence of a pump converted to an idler output via the third-order nonlinear process of non-resonant four-wave-mixing (FWM) [2]. Both types of conversion can occur in silicon waveguides, and as such have great potential for application in optical communication systems.

We present a Mach-Zehnder interferometer to characterize semiconductor microlenses in transmission. We therefore make use of a wavelength of 1550nm with the possibility of expansion towards the IR spectrum. In this paper, the concept of our interferometer as well as the set-up is explained. We demonstrate the working principle and measurements on fused silica and silicon microlenses and benchmark the experimental results with measurement data obtained with well established micro-optics instrumentation tools.

In this invited paper, we first discuss different submicron- and nanoscale structures that have been introduced over the past few years to enhance the Raman scattering efficiency in two important materials, namely silicon and hydrogen gas. Next, we explain how the heat dissipation in silicon- and hydrogen-based Raman lasers and amplifiers could be intrinsically reduced by the use of coherent anti-Stokes Raman scattering (CARS). We conclude by numerically demonstrating that with this CARS-based heat mitigation technique the heat generation in these Raman devices could be suppressed with at least 30%.

We propose a silicon ring Raman converter in which the spatial variation of the Raman gain along the ring for TE polarization is used to quasi-phase-match the CARS process. If in addition the pump, Stokes, and anti-Stokes waves involved in the CARS interaction are resonantly enhanced by the ring structure, the Stokes-to-anti-Stokes conversion efficiency can be increased by at least four orders of magnitude over that of one-dimensional perfectly phase-matched silicon Raman converters, and can reach values larger than unity with relatively low input pump intensities. These improvements in conversion performance could substantially expand the practical applicability of the CARS process for optical wavelength conversion.

We present our latest findings on the nature and behavior of CARS in active Raman devices, such as Raman converters and Raman lasers, which operate at exact Raman resonance. We demonstrate that the CARS mechanism in these devices actually comprises two opposite and competing interactions, which respectively create and annihilate phonons in the Raman-active medium. Furthermore, we show that both the phase mismatch of the CARS process and the level of pump depletion determine which of these two interactions takes place along the fields' propagation path in the Raman devices. Finally, we compare this CARS model with the model used by the CARS spectroscopy community, and explain that the difference between both models is mainly due to the fact that "CARS" in the context of Raman devices refers to Ramanresonant four-wave mixing, whereas "CARS" in the context of spectroscopy often denotes a two-step Raman interaction.

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Patients who have inflammatory bowel diseases (IBD) express strong antibody responses to a variety of epitopes. A number of (auto)antibodies have been described in patients who have Crohn's disease or ulcerative colitis. These markers reflect a loss of tolerance toward bacterial and fungal flora and have been studied for their clinical value in IBD patients. However, currently, they have no place in the diagnostic work up. Their real promise may lie in their use as surrogate markers of complicated aggressive disease as shown in various retrospective studies, but prospective data are lacking.

In this paper, we present a model that fully describes the quasi-stationary behavior of coherent anti-Stokes Raman scattering (CARS) in an anti-Stokes Raman converter operating at exact Raman resonance. We demonstrate that the CARS mechanism actually comprises two opposite and competing interactions, which respectively create and annihilate phonons in the Raman medium. Furthermore, we show that both the phase mismatch of the CARS four-wave mixing process and the level of pump depletion determine which of these two interactions takes place along the converter path length. In addition, we demonstrate that our CARS model is fully in line with seemingly contradictory findings in Raman conversion experiments. Finally, we discuss the fundamental differences between our CARS interpretation and the CARS models presented earlier.

We present a novel technique that intrinsically mitigates the quantum-defect heating in Raman lasers. The basic principle of this so-called "coherent anti-Stokes Raman scattering (CARS)-based heat mitigation" is to suppress the phonon creation in the Raman medium by increasing the number of out-coupled anti-Stokes photons with respect to the number of out-coupled Stokes photons. We demonstrate with the aid of numerical simulations that for a hydrogen and a silicon Raman laser, CARS-based heat mitigation efficiencies of at least 30% and 35%, respectively, can be obtained.

We present different methods to enhance the effectiveness of CARS-based heat mitigation, a novel approach for reducing the quantum-defect heating in Raman lasers. More specifically, we discuss the influence of the CARS-related phase mismatch and of backward Raman scattering on our CARS-based heat mitigation technique and explain how these heat-mitigation-affecting factors should be managed to enhance the effectiveness of our technique. To illustrate the feasibility of obtaining efficient CARS-based heat mitigation, we discuss to what extent the described effectiveness-enhancing methods can be applied to near- and mid-infrared silicon-based Raman lasers. Finally, we numerically demonstrate that for near-infrared silicon-based Raman lasers a heat mitigation efficiency of 15% can be obtained, whereas the corresponding efficiency for their mid-infrared counterparts can be as high as 35%.

In this paper we present an original technique, to mitigate the heat dissipation in Raman lasers. The lasing mechanism of a Raman laser is stimulated Stokes Raman scattering (SSRS), where a pump photon is converted into a lower energy Stokes photon and a phonon or heat, the so-called quantum-defect heating. We have theoretically demonstrated that, in the case of phase matching, CARS converts a pump photon and a Stokes photon into a pump photon and an anti-Stokes photon, while extracting quantum-defect heating from very different from the most common interpretation of CARS. By using these "novel" photon and phonon balances of CARS, one finds that the quantum-defect heating in a Raman laser will decrease if the ratio of the number of anti-Stokes photons to the number of Stokes photons, coupled out of the Raman laser, is increased. The latter forms the basic principle of our intrinsic heat mitigation technique. Besides introducing this concept, we have also developed several methods to enhance the heat mitigation efficiency. Finally, by using our Raman laser modeling formalism, we have numerically demonstrated for a mid-infrared silicon Raman laser that our technique can reduce the quantum-defect heating as much as 35 percent.

Power performance of a compact, broadly tunable, continuous-wave (cw) Cr2+:ZnSe laser pumped by a thulium fiber laser at 1800 nm was investigated. In the lasing experiments, a Cr2+:ZnSe sample with a small-signal differential absorption coefficient of 11 cm(-1) and a fluorescence lifetime of 4.6 mu s was used. An astigmatically compensated x-cavity with 15% output coupler produced as high as 640 mW of output power at 2480 nm with 2.5 W of incident pump power. Resonator losses were investigated using three different methods, and an in-depth analysis of the results was performed. The stimulated emission cross section values determined from laser threshold data and fluorescence measurements were in good agreement with each other. Finally, broad, continuous tuning of the laser was demonstrated between 2240 and 2900 nm by using an intracavity Brewster-cut MgF2 prism and a single set of optics., European Union 6th Framework program; Scientific and Technical Research Council of Turkey (Scientific and Technological Research Council of Turkey (TÜBİTAK)); Scientific and Technological Research Council of Turkey (TÜBİTAK) in the framework of the BAYG program

well plates. BMDC were treated with media alone, E. coli LPS (1 μg/mL) or murine CpG (20 μM) for 24 hours, after which culture supernatant was harvested for cytokine ELISA. BMDC were stained for cell surface markers of activation and analyzed by flow cytometry. Results: LPS treated FVB.mdr1a-/BMDC cultures had greater amounts of IL-12 (679±149 vs. 488±73, pg/mL) but similar levels of TNF-α compared to FVB.WT. FVB.mdr1a-/BMDC cultured with CpG also produced more IL-12 (98±28 pg/mL vs. non-detectable) and TNFα (418±91 vs. 207±40, pg/mL). The percentage and absolute number of CD11c+CD11b+ cells were greater in CpG treated FVB.mdr1a-/BMDC. The levels of BMDC activation as determined as being CD11c+ CD80+ and CD11c+ CD80+, were greater in the LPS and CpG treated FVB.mdra1-/BMDC. Conclusions: TLR4 and TLR9 ligand treatment results in a greater activation of BMDC from FVB.mdra1-/-. Since these TLRs are present in the intracellular compartment the absence of p-glycoprotein (an ATP-dependent pump) to expel LPS or CpG from intestinal dendritic cells could contribute to the mechanism of colitis in FVB.mdra1-/mice.

We present a novel technique that intrinsically mitigates the quantum-defect heating in Raman lasers. The basic principle of this so-called "coherent anti-Stokes Raman scattering (CARS)-based heat mitigation" is to suppress the phonon creation in the Raman medium by increasing the number of out-coupled anti-Stokes photons with respect to the number of out-coupled Stokes photons. We demonstrate with the aid of numerical simulations that for a hydrogen and a silicon Raman laser, CARS-based heat mitigation efficiencies of at least 30% and 35%, respectively, can be obtained.

In this invited paper, we will first discuss the recent research progress regarding silicon-on-insulator (SOI) Raman wavelength converters, the working principle of which is based on the four-wave mixing process of coherent anti-Stokes Raman scattering (CARS). Next, we will present our research results on other aspects of CARS in SOI waveguides. First, starting from the basic formalism for CARS we will show that, in contrast to what most scientists believe, CARS exchanges energy with the Raman medium in which it takes place and is even able to extract energy (i.e. extract phonons) from it. Furthermore, we will introduce a novel CARS-based approach to reduce the heat dissipation in Raman lasers due to the quantum defect between pump and lasing photons, and we will numerically demonstrate that with this "CARS-based heat mitigation technique" the quantum-defect heating in SOI waveguide Raman lasers could be reduced with as much as 35%.

We present a novel approach to intrinsically mitigate the heat dissipated in Raman lasers due to the pump-Stokes quantum defect. We explain the principle of this so-called "Coherent Anti-Stokes Raman Scattering (CARS)-based heat mitigation", which is based on decreasing the amount of phonons created in the Raman medium by increasing the ratio of the number of anti-Stokes photons to the number of Stokes photons coupled out of a Raman laser. To illustrate the potentialities of this optical cooling technique, we numerically demonstrate that for mid-infrared silicon-based Raman lasers the heat dissipation can be reduced with at least 35% by the use of CARS-based heat mitigation.

We present the first modeling results for the Stokes and anti-Stokes output of a mid-infrared continuous-wave silicon-based Raman laser. These emission characteristics are generated by the use of an iterative resonator model, the loss terms of which we adapted for the case of silicon-based Raman lasers operating in the mid-infrared spectral domain. These loss terms contain besides linear losses also the three-photon absorption losses that occur in this type of lasers. We discuss the behavior of this three-photon absorption mechanism and its influence on both the Stokes and anti-Stokes output. Finally, we compare these emission characteristics with the corresponding simulation results for a near-infrared silicon-based Raman laser in which linear losses, two-photon absorption losses and free carrier absorption losses occur.

We present a CARS-based heat mitigation technique that intrinsically reduces the quantum-defect heating in Raman lasers by increasing the number of out-coupled anti-Stokes phtons with respect to the number of out-coupled Stokes photons. Numerical simulations predict heat mitigation efficiencies of as much as 35%.

The energy consumption per transmitted bit is becoming a crucial figure of merit for communication channels. In this paper, we study the design trade-offs in photodetectors, utilizing the energy per bit as a benchmark. We propose a generic model for a photodetector that takes optical and electrical properties into account. Using our formalism, we show how the parasitic capacitance of photodetectors can drastically alter the parameter values that lead to the optimal design. Given certain energy-per-bit and bandwidth requirements, is it possible that a photodetector optimized for the energy per bit would be noise limited. We identify different noise sources and model them in the simplest useful approximation in order to calculate this noise limit. Finally, we apply our theory to a practical case study for an integrated plasmonic photodetector, showing that energies per bit below 100 attojoules are feasible despite metallic losses and within noise limitations without the introduction of an optical cavity or voltage amplifying receiver circuits.

We present a generic approach to determine the phase mismatch for any optical nonlinear process. When applying this approach, which is based on the evaluation of local phase changes, to Raman-and Kerr-based four-wave mixing in silicon waveguides, we obtain an expression for the phase mismatch which is more accurate as compared to the conventional definition; and which contains additional contributions due to the dispersion of the four-wave-mixing processes. Furthermore, starting from the general propagation equations for the involved pump, Stokes and anti-Stokes waves, we investigate the impact of this four-wave-mixing dispersion in silicon waveguides and examine how it is influenced by changing the frequency difference between the pump and Stokes input waves. We show by means of numerical simulations that, by detuning this frequency difference slightly away from Raman resonance, the four-wave-mixing conversion efficiency can be more than doubled, but can also lead to a decrease in efficiency of more than 10 dB. We also discuss how the pump-Stokes frequency difference that is optimal for wavelength conversion varies with the length of the silicon waveguides and with their dispersion characteristics. Finally, starting from the newly introduced phase mismatch formula we simplify the set of propagation equations such that they are less computationally intensive to solve while still giving accurate estimates of the optimal pump-Stokes frequency difference and the corresponding wavelength conversion efficiency. (C) 2011 Optical Society of America

We describe a compact, broadly tunable, continuous-wave (cw) Cr2+:ZnSe laser pumped by a thulium fiber laser at 1800 nm. In the experiments, a polycrystalline ZnSe sample with a chromium concentration of 9.5 × 1018 cm−3 was used. Free-running laser output was around 2500 nm. Output couplers with transmissions of 3%, 6%, and 15% were used to characterize the power performance of the laser. Best power performance was obtained with a 15% transmitting output coupler. In this case, as high as 640 mW of output power was obtained with 2.5 W of pump power at a wavelength of 2480 nm. The stimulated emission cross-section values determined from laser threshold data and emission measurements were in good agreement. Finally, broad, continuous tuning of the laser was demonstrated between 2240 and 2900 nm by using an intracavity Brewster cut MgF2 prism and a single set of optics.

Power performance of a compact, broadly tunable, continuous-wave (cw) Cr2+:ZnSe laser pumped by a thulium fiber laser at 1800 nm was investigated. In the lasing experiments, a Cr2+:ZnSe sample with a small-signal differential absorption coefficient of 11 cm(-1) and a fluorescence lifetime of 4.6 mu s was used. An astigmatically compensated x-cavity with 15% output coupler produced as high as 640 mW of output power at 2480 nm with 2.5 W of incident pump power. Resonator losses were investigated using three different methods, and an in-depth analysis of the results was performed. The stimulated emission cross section values determined from laser threshold data and fluorescence measurements were in good agreement with each other. Finally, broad, continuous tuning of the laser was demonstrated between 2240 and 2900 nm by using an intracavity Brewster-cut MgF2 prism and a single set of optics.

We present a novel approach for measuring nonlinear coefficients in fibers with significant pulse broadening. We perform a proof-of-concept demonstration for 200-m-long polarization-maintaining and single-mode fibers pumped at 1060 nm with ps pulses.

We present a novel numerical model that allows determining the Stokes and anti-Stokes emission characteristics of a continuous-wave silicon-based Raman laser. This so-called iterative resonator model evaluates for every half roundtrip time the longitudinal distribution of the intra-cavity pump, Stokes and anti-Stokes fields propagating in forward and backward directions, while taking into account the two-photon absorption losses and free carrier absorption losses occurring in the silicon laser medium. Furthermore, we demonstrate that our model exhibits important advantages in comparison with the power distribution model used for silicon-based Raman lasers. Finally, we present the first numerical simulation results for a silicon-based Raman laser emitting both Stokes and anti-Stokes photons.

The prospect for low pump-power Raman amplification in silicon waveguides has recently been boosted by theoretical studies discussing the enhancement of nonlinear phenomena in slow-light structures. In principle, the slowing down of either the pump or the signal beam is equivalent in terms of Raman gain, but in the presence of losses, we show that they play different roles in determining the net signal gain. We also investigate the impact of the mode profile in realistic slow-light waveguides on the total gain, an effect that is usually neglected in the context of stimulated Raman scattering. By taking representative losses and mode shapes into account, we provide a realistic estimation of the achievable performance of slow-light photonic crystal waveguides.

We present a novel numerical model describing the continuous-wave operation of Raman lasers. This so-called 'iterative resonator model' calculates how the forward- and backward-propagating Stokes and anti-Stokes electric fields inside the Raman laser cavity grow at the expense of the intra-cavity pump fields. We show that the iterative resonator model exhibits important advantages in comparison with the rate equation model used for e.g. hydrogen-based Raman lasers.

In this paper, we numerically demonstrate the promise of silicon microdisks for Raman Stokes/anti-Stokes wavelength conversion. We design a silicon microdisk suitable for Raman wavelength conversion with ldquoautomaticrdquo quasi-phase matching. We show that with this design and with a 2.5% incoupling efficiency for the pump and Stokes input, we can theoretically achieve wavelength conversion efficiencies up to 3.2 dB at input pump powers as low as 7.8 mW. Regarding fabrication tolerances of the design, we find that small deviations from the optimal cross coupling coefficient and from the condition for ldquoautomaticrdquo quasi-phase matching are allowed without deteriorating the wavelength conversion efficiency.

Nonlinear four-wave-mixing (FWM) interactions enable a wide variety of photonic functionalities, including wavelength conversion, all-optical switching, signal regeneration, and generation of entangled photons. To achieve efficient FWM interactions the waves either have to be phase-matched, or a quasi-phase-matching (QPM) scheme has to be realized. However, these techniques conventionally require light-guiding media with specific characteristics. We propose a more general QPM scheme for enabling efficient FWM interactions in the presence of a large phase-mismatch. The scheme is based on increasing the distance over which there is FWM gain, while simultaneously decreasing the distance over which there is FWM loss. This is achieved by adiabatically alternating between two phase-mismatch values along the propagation path. We discuss in detail how such phase-mismatch switching (PMS) can be employed to achieve QPM of a FWM process, what the requirements are for optimal FWM efficiency, and how the scheme is impacted by nonlinear dispersion as well as optical losses. Additionally, we describe how QPM by PMS can be implemented with a silicon-on-insulator strip waveguide of which the width is adiabatically varied between two values along the propagation path. By means of numerical simulations, we show that such a waveguide can enhance the wavelength conversion by 20 dB after 1 cm compared to a corresponding constant-width waveguide. For a pump wavelength of 1550 nm, PMS enables efficient conversion (> -21 dB) around a target signal wavelength situated anywhere in the entire near-infrared wavelength domain of 1300-1900 nm.

We perform a perturbative calculation of the third order optical conductivities of doped graphene, using approximations valid around the Dirac points and neglecting effects due to scattering and electron-electron interactions. In this limit analytic formulas can be constructed for the conductivities. We discuss in detail the results for third harmonic generation, the Kerr effect and two-photon carrier injection, parametric frequency conversion, and two-color coherent current injection. We find a complicated dependence on the chemical potential and photon energies. The linear dispersion causes resonances over a wide range of photon energies, and it is possible to obtain large optical nonlinearities by tuning the chemical potential.

The mitigation of quantum-defect heating in Raman lasers by the use of coherent anti-Stokes Raman scattering (CARS) is numerically demonstrated for two silicon-based waveguide Raman lasers pumped at a near-infrared (near-IR) wavelength around 1.5 mu m and at a mid-infrared (mid-IR) wavelength around 2.7 mu m, respectively. We show that, for the mid-IR laser, the CARS-based heat-mitigation technique attains an efficiency of 35%, whereas the corresponding efficiency for the near-IR laser without taking into account the two-photon-absorption-induced heat equals 15 %. The discrepancy between these two values finds its origin in the fact that for the mid-IR laser (quasi-) perfect phase matching for the CARS process can be obtained more easily, and the loss of anti-Stokes photons due to stimulated anti-Stokes Raman scattering (SARS) can be reduced more efficiently. Furthermore, we discuss two important practical aspects of Raman lasers with CARS-based heat mitigation, and we find that this category of Raman lasers could be used as dual-wavelength sources emitting codirectional Stokes and anti-Stokes beams of comparable power.

In this invited paper, we first address the differences between the uses of coherent anti-Stokes Raman scattering (CARS) as light generating mechanism in Raman devices and as optical analysis tool in spectroscopy. Next, with respect to the light generating functionality of CARS, we briefly review the latest progress on CARS-based Raman wavelength converters in silicon-on-insulator (SOI) technology and explain a new approach for boosting the efficiency of these converters. Finally, we show that the CARS process is also able to extract heat from a Raman-active medium and that therefore CARS can be used for reducing the heat dissipation in SOI-based Raman lasers.

We present the design of a photonic crystal-based multilayer structure that allows to experimentally demonstrate, using attenuated total reflectance experiments, the existence of the predicted transverse electric (TE) polarized excitation in graphene. We show that this mode can be excited in a single layer of graphene, even at room temperature. Furthermore, we prove that the observed mode in the reflection spectra corresponds to the TE- polarized graphene excitation and not the Bloch Surface Wave of the photonic crystal experiencing graphene- induced loss. Finally, we point out that adding an extra layer of dielectric material on top of the structure would ensure the unambiguous identification of the TE graphene mode even in the presence of fabrication errors.

Numerical calculations based on finite-difference time-domain (FDTD) simulations for metallic nanostructures in a broad optical spectrum require an accurate modeling of the permittivity of dispersive materials. In this paper, we present the algorithms behind B-CALM (Belgium-CAlifornia Light Machine), an open-source 3D-FDTD solver simultaneously operating on multiple Graphical Processing Units (GPUs) and efficiently utilizing multi-pole dispersion models while hiding latency in inter-GPU memory transfers. Our architecture shows a reduction in computing times for multi-pole dispersion models and an almost linear speed-up with respect to the amount of used GPUs. We benchmark B-CALM by computing the absorption efficiency of a metallic nanosphere in a broad spectral range with a six-pole Lorentz model and compare it with Mie theory and with a widely used Central Processing Unit (CPU)-based FDTD simulator.