External control of semiconductor nanostructure lasers

Novel semiconductor nanostructure laser diodes such as quantum-dot and quantum-dash are key optoelectronic candidates for many applications such as data transmitters in ultra fast optical communications. This is mainly due to their unique carrier dynamics compared to conventional quantum-well lasers that enables their potential for high differential gain and modified linewidth enhancement factor. However, there are known intrinsic limitations associated with semiconductor laser dynamics that can hinder the performance including the mode stability, spectral linewidth, and direct modulation capabilities. One possible method to overcome these limitations is through the use of external control techniques. The electrical and/or optical external perturbations can be implemented to improve the parameters associated with the intrinsic lasers dynamics, such as threshold gain, damping rate, spectral linewidth, and mode selectivity. In this dissertation, studies on the impact of external control techniques through optical injection-locking, optical feedback and asymmetric current bias control on the overall performance of the nanostructure lasers were conducted in order to understand the associated intrinsic device limitations and to develop strategies for controlling the underlying dynamics to improve laser performance. In turn, the findings of this work can act as a guideline for making high performance nanostructure lasers for future ultra fast data transmitters in long-haul optical communication systems, and some can provide an insight into making a compact and low-cost terahertz optical source for future implementation in monolithic millimeter-wave integrated circuits.\u2

Nieuwe concepten voor golflengte-afstembare laserdiodes voor toekomstige telecommunicatienetwerken = New concepts of wavelength tunable laser diodes for future telecom networks

Widely tunable semiconductor laser diodes with tuning ranges of several tens of nanometers are considered key components in optical telecommunication networks and sensor applications. Those widely tunable lasers can help telecom operators worldwide to respond to the increasing bandwidth demand at a low price, while ntroducing new functionality and higher flexibility in the network. The primary goal of this doctoral research was to evelop and experimentally investigate new types of widely tunable laser diodes that have the same qualities as (non-tunable) DFB lasers, i.e. high output power and high side-mode suppression, and are widely tunable, easily controllable and easily manufacturable. Two new types of widely tunable laser diodes were developed and experimentally investigated during this doctoral research. Both concepts satisfy all the telecom specifications and they have a promising dynamic behavior. Both designs are worthy competitors with other transmitters for optical telecom networks

Self-pulsation dynamics in narrow stripe semiconductor lasers

In this paper, we address the physical origin of self-pulsation in narrow stripe edge emitting semiconductor lasers. We present both experimental time-averaged polarization-resolved near-field measurements performed with a charged-coupled device camera and picosecond time resolved near-field measurements performed with a streak camera. These results demonstrate dynamic spatial-hole burning during pulse formation and evolution. We conclude from these experimental results that the dominant process which drives the self-pulsation in this type of laser diode is carrier induced effective refractive index change induced by the spatial-hole burning

Semiconductor ring lasers for all-optical signal processing

Since the late 1980s there has been a strong interest in exploiting optical bistablity for all-optical signal processing. In this scenario, a novel and promising building block is the semiconductor ring laser (SRL) that exhibits bistability between the counter-propagating cavity modes. This thesis reports on the design, fabrication and characterisation of 1550 nm lasing wavelength SRLs that are intended for applications as all-optical flip-flops and logic elements. Substantial optimisation of SRL design and processing technology is carried out in order to promote unidirectional bistable operation and allow high yield. Fabricated, large size, 150 um - 200 um radius SRLs, show robust unidirectional bistable operation with 30 - 35 dB directional extinction ratio (DER) between the counter-propagating modes, from near threshold up to 5 - 6 times threshold current bias. A significant advantage of the optimised technology is that 98% of the devices per chip show continuous wave (cw) and room temperature lasing with an average 2 - 3mA threshold current dispersion. Switch-on and switch-off times as short as 60 ps and 30 ps were measured, respectively, and reliable 10 Gbit/s flip-flop (FF) operation with external triggering optical pulses was achieved with these devices. Temporal measurements and calculations show that the switching speed of the free running SRL is limited by the carrier lifetime. A monostable device consisting of a SRL and an integrated distributed feedback laser (DFB) source is also presented, and this holding beam (HB) configuration is used to demonstrate all-optical NOT operation with data rates up to 2.5 Gbit/s. Dry etch chemistries for realizing 3.2 - 4.5 um deep waveguides, which show minimal bending losses, are developed and evaluated in order to enable dense integration of SRL devices. In addition, compact, milliwatt output power racetrack shaped cavity designs with radii as small as 10 um are presented. These devices exhibit minimal intra-cavity back-reflections by employing bi-level etching couplers and adiabatic straight to curved waveguide convertors. Finally, these developments provide a more than 150 times footprint reduction compared to large radius devices, whilst also preserving the robust unidirectional operation of their relatives with slightly lower, 20 - 30 dB DER