Nonlinear Dynamics of Interband Cascade Laser Subjected to Optical Feedback

We present a theoretical study of the nonlinear dynamics of a long external cavity delayed optical feedback-induced interband cascade laser (ICL). Using the modified Lang–Kobayashi equations, we numerically investigate the effects of some key parameters on the first Hopf bifurcation point of ICL with optical feedback, such as the delay time (τf), pump current (I), linewidth enhancement factor (LEF), stage number (m) and feedback strength (fext). It is found that compared with τf, I, LEF and m have a significant effect on the stability of the ICL. Additionally, our results show that an ICL with few stage numbers subjected to external cavity optical feedback is more susceptible to exhibiting chaos. The chaos bandwidth dependences on m, I and fext are investigated, and 8 GHz bandwidth mid-infrared chaos is observed.

Culture conditions effect properties of the Na+/K+-ATPase pump current in hiPSC cardiomyocytes

Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): BMBF Background Cardiomyocytes derived from human induced pluripotent stem cells (hiPSC) provide an opportunity to study human cardiac physiology and pathophysiology or to use for cardiac repair as well as for cardiovascular drug testing. Suitability for these purposes requires generating hiPSC cardiomyocytes that share typical electrophysiological properties of adult human cardiomyocytes. In the human heart the Na+/K+-ATPase pump current plays a major role in the regulation of contractile force and electrical stability. So far there are no data about Na+/K+-ATPase pump current function in hiPSC cardiomyocytes available. Purpose We compared the properties of Na+/K+-ATPase pump current in hiPSC cardiomyocytes from conventional monolayers (ML) culture to three-dimensional engineered heart tissue (EHT). Methods HiPSC cardiomyocytes differentiated from in-house control hiPSC cell line C25 were dissociated from ML and EHT culture. Na+/K+-ATPase pump current was recorded by whole-cell patch clamp technique at 37°C. The holding potential was -40 mV to inactivate sodium current. Current was measured in the absence of K+ and after adding 5.4 mM potassium chloride (KCL). Na+/K+-ATPase pump current was defined as the ouabain (10 µM) sensitive current. Voltage-dependency of Na+/K+-ATPase pump was determined using rectangular voltage pulses (increasing from -120 mV to +60 mV). Results Outwardly directed Na+/K+-ATPase pump could be recorded at -40 mV when KCL was added to the bath solution (5.4 mM). Currents were larger in EHT than in ML (0.8 ± 0.08 pA/pF n = 16 ML vs. 1.29 ± 0.13 pA/pF n = 28 EHT; p < 0.05). The K+-induced outward current was abolished by ouabain. The K+- and ouabain-sensitive current densities were similar in size (0.84 ± 0.11 pA/pF n = 16 ML vs. 1.12 ± 0.11 pA/pF n = 28 EHT for ouabain), indicating the measured K+-induced current was Na+/K+-ATPase pump current. Increasing extracellular K+-concentration in a stepwise manner (0,25 mM, 0,5 mM, 1 mM, 2 mM, 5,4 mM and 10 mM) showed a concentration-dependent relationship to Na+/K+-ATPase pump current with throughout higher current densities in EHT compared to ML (sensitivity to K+ not different). Na+/K+-ATPase pump current showed expected voltage-dependency with +0.23 ± 0.13 pA/pF at -120 mV and +0.89 ± 0.16 pA/pF at +60 mV (n= 18) in ML and with +0.71 ± 0.17 pA/pF at -120 mV and +1.2 ± 0.2 pA/pF at +60 mV (n= 24) in EHT. Conclusion HiPSC cardiomyocytes possess Na+/K+-ATPase pump current. Current density is in the range of human cardiomyocytes in EHT but substantially smaller in ML. 3D culturing may be needed to develop the physiological properties of Na+/K+-ATPase pump current.

Investigations with all optical sequential circuit at higher data rate

All optical signal processing is one of the growing area, finds relevance where fast computing speed is one of the vital concern. Optical sequential logic system is the backbone of the ultrafast processing network. Accordingly, this article explores proposed optical sequential schemes for the JK and T-type optical flip flop’s investigation at higher data rate. The outputs have been verified for the JK and T-type flip flops. Numerical simulations showed ER of 11.6 and 10 dB for the executed designs. Design have been investigated for variation in pump current, data rate (10–100 Gbps), peak power, bias voltage yielded the optimal performance with ER of over 12 dB. This schematic is simple excludes expensive optoelectronic translation and outcomes are well helpful for the design of complex sequential logic operations.

Исследование динамики выходной оптической мощности полупроводниковых лазеров (1070 nm) с маломодовым латеральным волноводом мезаполосковой конструкции при сверхвысоких токах накачки

At ultrahigh levels of pulsed current pumping, the characteristics of semiconductor lasers based on an asymmetric heterostructure with a broadened lateral waveguide of a mesa-stripe design are studied. A peak power of 5.1 W is demonstrated at a pump current amplitude of 10 A. Three types of spatial dynamics of laser radiation are determined: the first one is a slow (~ 200 ns) intensity profile variation along the lateral near field at initial level of pump currents; the second one is a presence of fast (~ 10 ns) processes of mode competition at moderate pump currents; the third one is a chaotic temporal behavior of the output power at maximum pump currents.

Рабочие характеристики полупроводниковых лазеров на квантовых ямах в зависимости от ширины волноводной области

Operating characteristics of semiconductor quantum well (QW) lasers are theoretically studied in terms of the thickness of the waveguide region [optical confinement layer (OCL)]. We calculate the maximum modal gain, optical confinement factor (in QW, OCL, and cladding layers), threshold current density, electron and hole densities (in QW and OCL), internal optical loss (in QW, OCL, and cladding layers), internal differential quantum efficiency, stimulated and spontaneous recombination currents, and output optical power of the laser as functions of the OCL thickness. It is shown that up to the pump current density 50 kA/cm2 the output power of the considered lasers depends only slightly on the OCL thickness in the range of thicknesses 1.5–2.8 m. This result is important for designing high brightness lasers as broadened waveguides are used in such lasers to attain low beam divergence. At high pump current densities, the output power is shown to have a maximum as a function of the OCL thickness.

Monensin-Induced Increase in Intracellular Na+ Induces Changes in Na+ and Ca2+ Currents and Regulates Na+-K+ and Na+-Ca2+ Transport in Cardiomyocytes

<b><i>Background/Aims:</i></b> Monensin, an Na ionophore, increases intracellular Na ([Na]i). Alteration of [Na]i influences ion transport through the sarcolemmal membrane. So far, the effects of monensin on ventricular myocytes have not been examined in detail. The main objective of this study was to elucidate the mechanism via which monensin-evoked increases in [Na]i affect the membrane potential and currents in ventricular myocytes of guinea pigs. Methods: Membrane potentials and currents were measured using the whole-cell patch-clamp technique in single myocytes. The concentration of intracellular Ca ([Ca]i) was evaluated by measuring fluorescence intensity of Fluo-4. Results: Monensin (10⁻⁵M) shortened the action potential duration (APD) and reduced the amplitude of the plateau phase. In addition, monensin decreased the sodium current (I_Na) and shifted the inactivation curve to the hyperpolarized direction. Moreover, it decreased the L-type calcium current (I_Ca). However, this effect was attenuated by increasing the buffering capacity of [Ca]i. The Na-Ca exchange current (I_Na-Ca) was activated particularly in the reverse mode. Na-K pump current (I_Na-K) was also activated. Notably, the inward rectifying K current (I_K1) was not affected, and the change in the delayed outward K current (I_K) was not evident. Conclusion: These results suggest that the monensin-induced shortened APD and reduced amplitude of the plateau phase are primarily due to the decrease in the I_Ca, the activation of the reverse mode of I_Na-Ca, and the increased I_Na-K, and second due to the decreased I_Na. The I_K and the I_K1 may not be associated with the abovementioned changes induced by monensin. The elevation of [Na]i can exert multiple influences on electrophysiological phenomena in cardiac myocytes.

Targeting Cardiac Myocyte Na + -K + Pump Function With β3 Adrenergic Agonist in Rabbit Model of Severe Congestive Heart Failure

Background: Abnormally high cytosolic Na + concentrations in advanced heart failure impair myocardial contractility. Stimulation of the membrane Na + -K + pump should lower Na + concentrations, and the β3 adrenoceptor (β3 AR) mediates pump stimulation in myocytes. We examined if β3 AR-selective agonists given in vivo increase myocyte Na + -K + pump activity and reverse organ congestion in severe heart failure (HF). Methods: Indices for HF were lung-, heart-, and liver: body weight ratios and ascites after circumflex coronary artery ligation in rabbits. Na + -K + pump current, I p , was measured in voltage-clamped myocytes from noninfarct myocardium. Rabbits were treated with the β3 AR agonists CL316,243 or ASP9531, starting 2 weeks after coronary ligation. Results: Coronary ligation caused ascites in most rabbits, significantly increased lung-, heart-, and liver: body weight ratios, and decreased I p relative to that for 10 sham-operated rabbits. Treatment with CL316,243 for 3 days significantly reduced lung-, heart-, and liver: body weight ratios and prevalence of ascites in 8 rabbits with HF relative to indices for 13 untreated rabbits with HF. It also increased I p significantly to levels of myocytes from sham-operated rabbits. Treatment with ASP9531 for 14 days significantly reduced indices of organ congestion in 6 rabbits with HF relative to indices of 6 untreated rabbits, and it eliminated ascites. β3 AR agonists did not significantly change heart rates or blood pressures. Conclusions: Parallel β3 AR agonists-induced reversal of Na + -K + pump inhibition and indices of congestion suggest pump inhibition is a useful target for treatment with β3 AR agonists in congestive HF.