Christos Simos

Dual-wavelength mode-locked quantum-dot laser, via ground and excited state transitions: Experimental and theoretical investigation

We report a dual-wavelength passive mode locking regime where picosecond pulses are generated from both ground (lambda = 1263 nm) and excited state transitions (lambda = 1180 nm), in a GaAs-based monolithic two-section quantum-dot laser. Moreover, these results are reproduced by numerical simulations which provide a better insight on the dual-wavelength mode-locked operation.

Two-Section Quantum-Dot Mode-Locked Lasers Under Optical Feedback: Pulse Broadening and Harmonic Operation

In this paper, we numerically investigate the role of gain and absorber dynamics on the operation of monolithic two-section mode-locked quantum-dot lasers under optical feedback. The analysis is carried out by means of a time-domain traveling wave model for propagation in the gain and absorbing sections. The obtained results indicate that in devices with slow dynamics, pulse duration tends to increase significantly with feedback. On the contrary, devices with fast dynamics exhibit an operation that depends primarily on the external cavity length.

Pulse width narrowing due to dual ground state emission in quantum dot passively mode locked lasers

We present an experimental investigation of the emission properties of a multisection InGaAs quantum dot passively mode locked laser under dual waveband emission from the ground state (GS). A mode locking regime directly related to the GS splitting has been depicted. It is related to significant pulse width decrease with increasing injection current under dual peak emission from the GS, leading to generation of pulses with increased peak power with respect to the usual device operation.

Effect of optical feedback to the ground and excited state emission of a passively mode locked quantum dot laser

We present an experimental study on the effect of optical feedback in both ground and excited emission of a GaAs quantum dot passively mode locked laser. The experimental setup consisted of a long external cavity with variable cavity length and feedback level ranging from –50 to –20dB. The obtained experimental results show dependence of the emission properties on the cavity length regarding both the ground and excited state. In addition a strong tolerance of the laser operation to feedback at the excited state operation regime is observed.

Dual ground-state pulse generation from a passively mode-locked InAs/InGaAs quantum dot laser

In this paper, we present experimental results related to tunable dual wavelength passive mode locking of two independent ground state sub-bands in a multi section InAs/InGaAs quantum dot laser. The emission of these sub-bands is related to gain suppression at the center of the ground state emission, whereas their wavelength separation is tunable with injection current. Through the mechanism of passive mode locking two independent pulses were obtained, with typical pulse width in the order of 17 ps.

Numerical Analysis of Passively Mode-Locked Quantum-Dot Lasers With Absorber Section at the Low-Reflectivity Output Facet

In this paper, we present a theoretical study on the optimization of passively mode-locked quantum dot lasers based on an alternative cavity design. In particular, we investigate a geometry in which the saturable absorber is located near the low reflection facet of the chip (output facet). The investigation is carried out by means of a time-domain traveling wave numerical model for quantum-dot active medium for both the gain and absorbing sections. The analysis shows superior performance in terms of pulsewidth and peak power of devices based on the new geometry compared to devices based on the conventional geometry, where the saturable absorber is placed near the high reflectivity facet. The optimization relies on the enhanced bleaching of the saturable absorber when the latter is located near the output facet, which prevents the generation of colliding or self-colliding pulse effects.

Tapered InAs/InGaAs quantum dot semiconductor optical amplifier design for enhanced gain and beam quality

In this Letter, a design for a tapered InAs/InGaAs quantum dot semiconductor optical amplifier is proposed and experimentally evaluated. The amplifiers geometry was optimized in order to reduce gain saturation effects and improve gain efficiency and beam quality. The experimental measurements confirm that the proposed amplifier allows for an elevated optical gain in the saturation regime, whereas a five-fold increase in the coupling efficiency to a standard single mode optical fiber is observed, due to the improvement in the beam quality factor M² of the emitted beam.

Effect of the number of quantum dot layers and dual state emission on the performance of InAs/InGaAs passively mode-locked lasers

In this paper, a series of quantum-dot passively mode-locked Fabry-Perot lasers has been experimentally investigated. The devices vary in terms of number of quantum dot layers, thus allowing the extraction of guidelines regarding the impact of this parameter on the quality of mode locking. Although, theoretical estimations imply that the increase of the quantum dot layers can enhance the emitted optical power but degrade mode-locking stability, the experimental evaluation proved that the existence of dual wavelength emission can affect this trend and allow better performance from devices that do not exhibit excited state emission.

Chaotic emission and tunable self-sustained pulsations in a two-section Fabry–Perot quantum dot laser

We present an experimental study on the intrinsic instabilities of a two electrode InAs/InGaAs Fabry–Perot quantum dot laser in the absence of optical feedback. By individually controlling the current injected in each electrode, different regimes of operation are allowed including tunable self-sustained pulsations and coherence collapse resulting to possible chaotic emission. The origin of these effects does not resign in the presence of optical feedback but is associated to the carrier dynamics of the quantum dot device. A numerical analysis on the time traces collected from the device reveals high complexity output in terms of correlation dimension.

Compact optical displacement sensing by detection of microwave signals generated from a monolithic passively mode-locked laser under feedback

A monolithic passively mode-locked laser is proposed as a compact optical sensor for displacements and vibrations of a reflecting object. The sensing principle relies on the change of the laser repetition frequency that is induced by optical feedback from the object under measurement. It has been previously observed that, when a semiconductor passively mode locked laser receives a sufficient level of optical feedback from an external reflecting surface it exhibits a repetition frequency that is no more determined by the mode-locking rule of the free-running operation but is imposed by the length of the external cavity. Therefore measurement of the resulting laser repetition frequency under self-injection permits the accurate and straightforward determination of the relative position of the reflecting object. The system has an inherent wireless capability since the repetition rate of the laser can be wirelessly detected by means of a simple antenna which captures the microwave signal generated by the saturable absorber and is emitted through the wiring of the laser. The sensor setup is very simple as it requires few optical components besides the laser itself. Furthermore, the deduction of the relative position of the reflecting object is straightforward and does not require any processing of the detected signal. The proposed sensor has a theoretical sub-wavelength resolution and its performance depends on the RF linewidth of the laser and the resolution of the repetition frequency measurement. Other physical parameters that induce phase changes of the external cavity could also be quantified.