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Nanostructure Injected Lasers for Ultra-High Frequency Applications

Final Report Summary - NINFA (Nanostructure Injected Lasers for Ultra-High Frequency Applications)

The Marie Curie project 'Nanostructure injected lasers for ultra-high frequency applications' (NINFA) combines quantum laser technology and ultra-high frequency (UHF) techniques for novel applications in disparate fields from data communications to spectroscopy and sensing.
This project focuses on advanced semiconductor lasers built with quantum-dot and quantum-dash active regions. Such devices offer many potential advantages in comparison to traditional quantum-well laser sources. These include enhanced temperature operation, lower energy requirements and increased frequency performance. These features make them ideal for use in high frequency applications in disparate fields from data communications to security, spectroscopy and sensing. However, full exploitation requires increasing the frequency response of such devices into the microwave, millimetre-wave and Terahertz (THz) ranges.

This project proposed a very ambitious long-term objective: the development of a completely tuneable Ultra High Frequency oscillator with operation from the microwave, millimetre-wave and the THz frequency range using nanostructure lasers. This approach uses therefore simple photonic components offering great promise for miniaturization and integration into photonic circuits. The scientific team of NINFA has successfully achieved this ground-breaking milestone offering exciting prospects for novel future applications of quantum lasers in high frequency applications. Moreover, specific emphasis was given in this project to devices operating at the important telecom wavelengths of 1310 and 1550 nm, the most commonly used wavelengths in long-haul optical communication systems over silica optical fibres. This permitted our approach to be totally compatible with optical telecommunication networks for its future use in data communication applications, optical wireless and radio-over-fibre networks.

The scientific team of NINFA has investigated in great detail the effects of external optical injection in different types of nanostructure lasers including 1550nm-Fabry-Perot (FP) QDash and 1310nm-Distributed-Feedback (DFB) QD lasers. Our analyses have contributed significantly to enhance the basic understanding of fundamental physical phenomena in these advanced laser sources. These included first the experimental observation of different patterns of nonlinear switching and optical bistability in a 1550nm-QDash FP laser. Also, we reported the first observation of two-wavelength switching and bistability in a 1310nm-QD DFB laser. Additionally, we have also studied in detail the optical injection locking properties and nonlinear dynamics arising in this type of lasers when subject to external optical injection. The team provided complete stability maps for 1310nm-QD DFB lasers describing the regions of injection locking, where the emission frequency of the QD laser is locked to that of the externally injected signal, as well as the different non-linear behaviours appearing outside the locking range.

Specifically, for the case of a 1310nm-QD DFB laser, the experimental findings were indeed very different to those previously reported in traditional Quantum Well laser sources. In fact, outside the locking range only the so-called period 1 dynamics were observed. These are characterized by periodic oscillations at a constant frequency, whose value depends on the injection conditions (injection strength and frequency detuning) and which happens to fall within the microwave spectral range. Such a system is therefore ideal for the generation of continuously tuneable microwave signals. Moreover, for the case of the investigated QD DFB laser, the whole stability map can be actually used for signal generation purposes since there are no undesired gaps due to regions of unwanted complex dynamics (such as chaos).

Elucidation of these behaviours demonstrated the suitability of a quantum dot laser for the generation of tuneable microwave signals. Following this line of inquiry, the team delivered for the first time a quantum-dot laser based microwave signal generation system allowing complete and continuous tuneability over five octaves: from below 1 gigahertz (GHz) to over 40 GHz. Moreover, such a system was totally compatible with fibre-optic telecommunication technologies for use in optical wireless networks.

Furthermore, we have described a novel mechanism for tuneable dual mode-lasing operation in a 1310nm-QD DFB. Our experimental findings revealed that the frequency separation between the existing two lasing lines can be controlled and tuned within the millimetre-wave (30-300 GHz) and THz (300 GHz to 3 THz) frequency ranges. Following this line of work this project has led to the description of a novel technique to generate tuneable millimetre-wave and THz signals with frequencies ranging from 119 to 954 GHz. Such an extension in the frequency range of nanostructure lasers poises them indeed at the frontiers of imaging, spectroscopy and security applications.

Additionally, the team of NINFA has successfully demonstrated the possibility to simultaneously generate microwave and millimetre-wave signals using a 1310nm QD DFB laser. The frequencies of both high frequency signals could be controlled and tune within specific windows. Also, new forms of high frequency nonlinear switching and bistability have been experimentally observed. These recent findings offer great promise for novel practical uses of nanostructure lasers in Ultra High Frequency applications, not only from the signal generation point of view, but also from the perspective of frequency conversion and amplitude modulation-to-frequency modulation format conversion.

NINFA has presented its results in high-impact peer-reviewed scientific journals and conferences and has already filed its first patent application. Quantum laser technology holds great promise for superior performance and NINFA is unlocking the potential and paving the way to exciting new devices and applications.