This paper presents a theoretical and experimental study of nonlinear effects in distributed Bragg reflector (DBR)type tunable lasers, which are responsible for asymmetric spectral or power characteristics, and for hysteresis phenomena. We propose an optimized DBR semiconductor optical amplifier design that suppresses these effects, making the control simpler and more reliable, while maintaining the same performances as a DBR (16 nm tuning, 40 dB side mode suppression ratio, 20 mW coupled output power). Aiming to reach C-band tuning range with only one Bragg current control and reduced nonlinear effects, a new double Bragg DBR laser is proposed.Index Terms-Four-wave mixing (FWM), monolithically integrated sources, semiconductor tunable lasers.

Quantum point contacts (QPCs), defined by surface gate technology, are increasingly featuring as basic building blocks of more sophisticated geometries such as coupled dot, single electron, and coherent wave devices. For many of its potential roles the electron density within the QPC needs to be known accurately as a function of the voltage applied to the split gates that define the QPC within the two-dimensional electron gas. A common characterization technique extracts the density from the positions of the conductance plateaus that result from the depopulation of edge states as the gate voltage is swept at high magnetic fields. We study the high current breakdown of these plateaus and investigate the nonlinear current–voltage characteristics for both split gate and continuous gate geometries. We demonstrate that the breakdown is not centred around the plateaus and that, unlike the breakdown of the quantum Hall effect, a forward propagation mechanism needs to be considered and indeed is the dominant process.