164 research outputs found

    Ultra-narrow (sub-MHz) linewidth emission from discrete mode laser diodes

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    A class of laser which exhibits ultra-narrow sub MHz linewidth emission necessary for numerous applications in optical communications and sensors is described. The spectral performance of commercial discrete mode (DM) and distributed feedback (DFB) lasers is compared. The devices used in this work are asymmetrically coated ridge waveguide Fabry Perot lasers which incorporated etched slot features and emitting around lambda = 1.55 mum. The active region of the devices consisted of a strained compensated InAlGaAs MQW structure

    Designing aerobic exercise interventions for stroke rehabilitation

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    More than 405,000 Canadians are currently living with the life-altering effects of stroke. Cardiorespiratory fitness is characteristically low after stroke and has negative consequences for functional recovery, cardiovascular risk, and quality of life in this population. Although scientific evidence supports incorporating moderate-intensity aerobic exercise during stroke recovery, these findings have not translated into clinical care where patients are very sedentary and cardiorespiratory fitness levels remain in the “very poor” category. Among the challenges to incorporating aerobic exercise include a lack of access to the specialized equipment needed to accommodate stroke-related impairments. Also, hemiparesis can limit stroke survivors’ ability to sustain the workloads needed to reach moderate levels of aerobic intensity. Accordingly, the current thesis aimed to develop exercise strategies that can overcome these barriers. The first study investigated whether incorporating task-oriented activities typically offered during stroke rehabilitation into circuits that pair more metabolically demanding tasks with less demanding ones is an acceptable method to sustain moderate-intensity aerobic workloads over a single session. The second study evaluated the feasibility and preliminary effects of the task-oriented circuit-training protocol compared to treadmill aerobic exercise over a 10-week intervention period among 40 chronic hemiparetic stroke survivors. The final study investigated the safety and feasibility of pairing treadmill walking exercise with moderate normobaric hypoxia as a means to increase the cardiovascular strain of submaximal exercise among stroke survivors. The task-oriented circuit training protocol was associated with at least moderateintensity aerobic workloads over a single session and, compared to treadmill aerobic exercise, similar proportions of participants were able to maintain the exercise criteria over a 10-week intervention period. One participant reported mild symptoms of nausea during treadmill walking under conditions of moderate normobaric hypoxia. No other adverse events were observed, and participants maintained constant absolute workloads during exercise in normobaric hypoxia, which was associated with a 10% increase in relative effort. The task-oriented circuit training protocol is a promising strategy to provide moderate-intensity aerobic exercise training stimulus without specialized equipment. Initial data also supports simulated altitude exposure as a safe and feasible method to increase the cardiovascular stress of submaximal exercise among chronic hemiparetic stroke survivors

    Low sensitivity to optical feedback and optical injection of discrete mode lasers

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    In this paper, we demonstrate the low sensitivity to both external optical feedback and external optical injection of a new type of extremely low cost single-mode lasers, called "discrete mode" (DM) lasers. The DM lasers are obtained from ridge waveguide Fabry Perot (FP) lasers, in which the effective refractive index of the lasing mode has been perturbed. These lasers exhibit a low sensitivity to external optical feedback since the coherence collapse threshold is around 5 dB higher in comparison to a commercial DFB laser

    Discrete mode lasers for applications in access networks

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    Fast development of the modern telecommunication networks such as fiber-to-the-home or radio-over-fiber systems require an inexpensive yet reliable optical transmitter for electro-optic conversion. Such devices should be able to generate stable, single moded optical signals suitable for athermal operation. Discrete Mode Lasers (DMLs) are able to fulfill all the above-mentioned requirements with the added benefit of low sensitivity to optical feedback. DMLs are essentially Fabry-Perot lasers in which the refractive index is modified by introducing perturbations along very small sections of the laser cavity. These modifications result in a single mode laser output with a very narrow linewidth (order of 400 kHz). In this paper, we demonstrate how a DML can outperform the commonly used/commercially available DFB lasers in terms of linewidth, sensitivity to optical feedback and transmission performance in the presence of feedback

    Cost efficient narrow linewidth laser transmitter for coherent detection

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    Authors present a cost efficient narrow linewidth laser transmitter for future coherent detection systems. The spectral purity of the laser allows the phase modulation of data signals at bit rates as low as 155 Mb/s

    A novel two-section tunable discrete mode Fabry-PÉrot laser exhibiting nanosecond wavelength switching

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    A novel widely tunable laser diode is proposed and demonstrated. Mode selection occurs by etching perturbing slots into the laser ridge. A two-section device is realized with different slot patterns in each section allowing Vernier tuning. The laser operates at 1.3 mum and achieves a maximum output power of 10 mW. A discontinuous tuning range of 30 nm was achieved with a side mode suppression greater than 30 dB. Wavelength switching times of approximately 1.5 ns between a number of wavelength channels separated by 7 nm have been demonstrated

    Fabrication and measurement of a photonic crystal waveguide integrated with a semiconductor optical amplifier

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    A III-V semiconductor photonic crystal (PhC) waveguide is integrated into a semiconductor optical amplifier (SOA); this has the potential to reshape pulses that are distorted and chirped on propagation through the SOA. The PhC waveguide is modeled using the three-dimensional (3D) finite difference time domain (FDTD) method initially for the ideal case of infinite depth holes, and this shows a ministop band close to 1600 nm. The PhC waveguide is then fabricated into a commercial SOA using focused ion beam etching. The optical power measured at the output of the PhC-SOA waveguide shows evidence of a ministop band but with a small stopband depth. More realistic 3D FDTD modeling including effects of finite hole depth and vertical layer structure is then shown to give much better agreement with measured results. Finally predictions are made for the performance of a membrane structure

    Discrete mode laser diodes with ultra narrow linewidth emission <3kHz

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    Ex-facet, free-running ultra-low linewidth (<3 kHz), single mode laser emission is demonstrated using low cost, regrowth-free ridge waveguide discrete mode Fabry-Perot laser diode chips

    Uniquely D-colourable digraphs with large girth

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    Let C and D be digraphs. A mapping f:V(D)→V(C)f:V(D)\to V(C) is a C-colouring if for every arc uvuv of D, either f(u)f(v)f(u)f(v) is an arc of C or f(u)=f(v)f(u)=f(v), and the preimage of every vertex of C induces an acyclic subdigraph in D. We say that D is C-colourable if it admits a C-colouring and that D is uniquely C-colourable if it is surjectively C-colourable and any two C-colourings of D differ by an automorphism of C. We prove that if a digraph D is not C-colourable, then there exist digraphs of arbitrarily large girth that are D-colourable but not C-colourable. Moreover, for every digraph D that is uniquely D-colourable, there exists a uniquely D-colourable digraph of arbitrarily large girth. In particular, this implies that for every rational number r≄1r\geq 1, there are uniquely circularly r-colourable digraphs with arbitrarily large girth.Comment: 21 pages, 0 figures To be published in Canadian Journal of Mathematic

    A Bout of High Intensity Interval Training Lengthened Nerve Conduction Latency to the Non-exercised Affected Limb in Chronic Stroke

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    Objective: Evaluate intensity-dependent effects of a single bout of high intensity interval training (HIIT) compared to moderate intensity constant-load exercise (MICE) on corticospinal excitability (CSE) and effects on upper limb performance in chronic stroke.Design: Randomized cross-over trial.Setting: Research laboratory in a tertiary rehabilitation hospital.Participants: Convenience sample of 12 chronic stroke survivors.Outcome measures: Bilateral CSE measures of intracortical inhibition and facilitation, motor thresholds, and motor evoked potential (MEP) latency using transcranial magnetic stimulation. Upper limb functional measures of dexterity (Box and Blocks Test) and strength (pinch and grip strength).Results: Twelve (10 males; 62.50 ± 9.0 years old) chronic stroke (26.70 ± 23.0 months) survivors with moderate level of residual impairment participated. MEP latency from the ipsilesional hemisphere was lengthened after HIIT (pre: 24.27 ± 1.8 ms, and post: 25.04 ± 1.8 ms, p = 0.01) but not MICE (pre: 25.49 ± 1.10 ms, and post: 25.28 ± 1.0 ms, p = 0.44). There were no significant changes in motor thresholds, intracortical inhibition or facilitation. Pinch strength of the affected hand decreased after MICE (pre: 8.96 ± 1.9 kg vs. post: 8.40 ± 2.0 kg, p = 0.02) but not after HIIT (pre: 8.83 ± 2.0 kg vs. post: 8.65 ± 2.2 kg, p = 0.29). Regardless of type of aerobic exercise, higher total energy expenditure was associated with greater increases in pinch strength in the affected hand after exercise (R2 = 0.31, p = 0.04) and decreases in pinch strength of the less affected hand (R2 = 0.26 p = 0.02).Conclusion: A single bout of HIIT resulted in lengthened nerve conduction latency in the affected hand that was not engaged in the exercise. Longer latency could be related to the cross-over effects of fatiguing exercise or to reduced hand spasticity. Somewhat counterintuitively, pinch strength of the affected hand decreased after MICE but not HIIT. Regardless of the structure of exercise, higher energy expended was associated with pinch strength gains in the affected hand and strength losses in the less affected hand. Since aerobic exercise has acute effects on MEP latency and hand strength, it could be paired with upper limb training to potentiate beneficial effects
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