Metal-semiconductor-metal ion-implanted Si waveguide photodetectors for C-band operation

Metal-semiconductor-metal Si waveguide photodetectors are demonstrated with responsivities of greater than 0.5 A/W at a wavelength of 1550 nm for a device length of 1mm. Sub-bandgap absorption in the Si waveguide is achieved by creating divacancy lattice defects via Si+ ion implantation. The modal absorption coefficient of the ion-implanted Si waveguide is measured to be ≈185 dB/cm, resulting in a detector responsivity of ≈0.51 A/W at a 50V bias. The frequency response of a typical 1mm-length detector is measured to be 2.6 GHz, with simulations showing that a frequency response of 9.8 GHz is achievable with an optimized contact configuration and bias voltage of 15V. Due to the ease with which these devices can be fabricated, and their potential for high performance, these detectors are suitable for various applications in Si-based photonic integrated circuits

Pulse compression in adiabatically tapered silicon photonic wires

We present a comprehensive analysis of pulse compression in adiabatically tapered silicon photonic wire waveguides (Si-PhWWGs), both at telecom (λ ∼ 1.55 μm) and mid-IR (λ ≳ 2.1 μm) wavelengths. Our theoretical and computational study is based on a rigorous model that describes the coupled dynamics of the optical field and photogenerated free carriers, as well as the influence of the physical and geometrical parameters of the Si-PhWWGs on these dynamics. We consider both the soliton and non-soliton pulse propagation regimes, rendering the conclusions of this study relevant to a broad range of experimental settings and practical applications. In particular, we show that by engineering the linear and nonlinear optical properties of Si-PhWWGs through adiabatically varying their width, one can achieve more than 10× pulse compression in millimeter-long waveguides. The inter-dependence between the pulse characteristics and compression efficiency is also discussed. © 2014 Optical Society of America

Quasi-phase-matched four-wave-mixing of optical pulses in periodically modulated silicon photonic wires

We demonstrate enhanced conversion efficiency (CE) and parametric amplification of optical pulses via quasiphase- matched four-wave-mixing (FWM) in long-period Bragg waveguides made of silicon. Our study is based on a rigorous theoretical model that describes optical pulse dynamics in a periodically, adiabatically modulated silicon photonic waveguide and a comprehensive set of numerical simulations of pulse interaction in such gratings. More specifically, our theoretical model takes into account all of the relevant linear and nonlinear optical effects, including free-carriers generation, two-photon absorption, and self-phase modulation, as well as modal frequency dispersion up to the fourth-order. Due to its relevance to practical applications, a key issue investigated in our work is the dependence of the efficiency of the FWM process on the waveguide parameters and the operating wavelength. In particular, our analysis suggests that by varying the waveguide width by just a few tens of nanometers the wavelengths of the phase-matched waves can be shifted by hundreds of nanometers. Our numerical simulations show also that, in the anomalous group-velocity dispersion regime, a CE enhancement of more than 20 dB, as compared to the case of a waveguide with constant width, can be easily achieved. © 2014 SPIE

Generation and collision of optical similaritons in dispersion-engineered silicon photonic nanowires

We present a comprehensive study of generation and collision of optical similaritons in sub-micron silicon photonic wire waveguides. Our analysis of optical pulse dynamics in such wave guiding devices is based on a rigorous theoretical model that incorporates all of the relevant linear and nonlinear optical effects, including modal dispersion, free-carrier dispersion and absorption, self-phase modulation, two-photon absorption, frequency dispersion of the optical nonlinearity, and the free-carrier dynamics. In addition to the particular characteristics of the generation of optical similaritons in silicon photonic wires, we also investigate the dependence of the efficiency of this optical process on the physical parameters and temporal profile of the input pulse. The collision of optical similaritons that propagate both in the normal and anomalous dispersion regime is also analyzed. Guided by the target applications of our study, we considered two technologically relevant spectral regions, namely, telecom and mid-IR frequency domains. © 2013 SPIE

Ar+-Implanted Si-Waveguide Photodiodes for Mid-Infrared Detection

Complementary metal-oxide-semiconductor (CMOS)-compatible Ar+-implanted Si-waveguide p-i-n photodetectors operating in the mid-infrared (2.2 to 2.3 µm wavelengths) are demonstrated at room temperature. Responsivities exceeding 21 mA/W are measured at a 5 V reverse bias with an estimated internal quantum efficiency of 3.1%–3.7%. The dark current is found to vary from a few nanoamps down to less than 11 pA after post-implantation annealing at 350 °C. Linearity is demonstrated over four orders of magnitude, confirming a single-photon absorption process. The devices demonstrate a higher thermal processing budget than similar Si+-implanted devices and achieve higher responsivity after annealing up to 350 °C

The Role of Provenance for the Projected Growth of Juvenile European Beech under Climate Change

European beech is one of the most common tree species in Europe and is generally suggested to play even more of a prominent role in forestry in the future. It seems to have the potential to partially replace Norway spruce, as it is less sensitive to expected warmer and drier conditions. It is, however, not well known in which regions these new plantings would be particularly favourable and if specific provenances may be better adapted to the new conditions than others. Therefore, we estimated the potential early height growth under climate conditions in 2040–2060 for 20 beech provenances across a region covering the Czech Republic and Slovakia. This Central European region is expected to experience considerably drier and warmer conditions in the future. For this exercise, we implemented a new neural network model developed from height growth information obtained from the open-access BeechCOSTe52 database. The simulations are driven by past and future climate data obtained from the WorldClim database of historical climate data and future climate projections. Simulations revealed that provenances originating from drier regions performed on average significantly better than those from regions with good water supply. Moreover, provenances originating from drier regions had a particularly large advantage in the relatively arid regions of Central Czechia and Southern Slovakia. We can also confirm that all provenances showed a high phenotypic plasticity of height growth across the whole investigated region

Full recovery of a 13-year-old boy with pediatric Ramsay Hunt syndrome using a shorter course of aciclovir and steroid at lower doses: a case report

<p>Abstract</p> <p>Introduction</p> <p>Reports on children with Ramsay Hunt syndrome are limited in the literature, resulting in uncertainty regarding the clinical manifestations and outcome of this syndrome. Treatment for Ramsay Hunt syndrome is usually with antivirals, although there is no evidence for beneficial effect on the outcome of Ramsay Hunt syndrome in adults (insufficient data on children exists). Here, we report a case of Ramsay Hunt syndrome occurring in a child who inadvertently received a lower dose of aciclovir and steroid administered for shorter than is usual. Our patient made a full recovery.</p> <p>Case presentation</p> <p>A 13-year-old African boy presented to our out-patients department with an inability to move the right side of his face for one week. He had previously been seen by the doctor on call, who prescribed aciclovir 200 mg three times per day and prednisone 20 mg once daily, both orally for five days, with a working diagnosis of Bell's palsy. After commencement of aciclovir-prednisone, while at home, our patient had headache, malaise, altered taste, vomiting after feeds, a ringing sound in his right ear as well as earache and ear itchiness. Additionally, he developed numerous fluid-filled pimples on his right ear. On presentation, a physical examination revealed a right-sided lower motor neuron facial nerve palsy and a healing rash on the right pinna. On direct questioning, our patient admitted having had chicken pox about three months previously. Based on the history and physical examination, Ramsay Hunt syndrome was diagnosed. Our patient was lost to follow-up until 11 months after the onset of illness; at this time, his facial nerve function was normal.</p> <p>Conclusions</p> <p>This case report documents the clinical manifestations and outcome of pediatric Ramsay Hunt syndrome; a condition with few case reports in the literature. In addition, our patient made a full recovery despite inadvertently receiving a lower dose of aciclovir and steroid administered for shorter than is usual.</p