The purpose of this project is to create a new generation of integrated mechanical micro-resonators for high-selectivity and sensitivity gas photoacoustic detection (sub-ppm concentrations), in a very compact, robust, portable system. In photoacoustic spectroscopy, measurement is performed by a microphone or mechanical resonator, using the acoustic pressure generated by the local warming caused by optical absorption. Mechanical resonators installed in the gas chamber provide high sensitivities, but they are not specifically developed for this application. The NOMADE project aims to develop micro-resonators specially designed for this application. A significant gain on the detection performances is expected. This new technology will allow placing the laser next to the micro-resonator, eliminating the need for any optical element. This compactness allows totally rethinking gas sensors, which can now be understood as a modular element easy to integrate in a more complex system.

Information technology requires more and more high-performing devices for information encoding and processing. In this regard the use of optical solitons as information bits appears promising, especially if implemented in fast, compact and cheap devices as semiconductor lasers. In particular, "light-bullets" (LB), where the light would be localized in the three dimensions of space, are expected to lead to disruptive performances in terms of bit rate, resilience and agility. The aim of this project is to conceive, to realize and to operate semiconductor laser devices for the generation and control of spatiotemporal solitons, also called “light bullets” (LB). LB will be implemented in Vertical External-Cavity Surface Emitting semiconductor devices mounted in an external cavity configuration (VECSEL) closed by a saturable absorber mirror (SESAM). Devices fabrication will be developed in the frame of this project to match the parameters requirements for LB existence. Once LS will be obtained and characterized, their application to information processing will be addressed by targeting a three-dimensional all-optical buffer. LB have been chased in conservative systems since the pioneer work by Silberberg at the beginning of ’90. The propagation of an optical pulse in a medium where diffraction and anomalous group dispersion are both compensated by a non-linearity is strongly unstable and, despite the efforts made, it is impossible to avoid the pulse to collapse or to spread. The originality of our approach to LB consists in implementing them in dissipative system, where LB will appear as stable solutions for a wide set of initial conditions and control parameters. In addition, when the system is strongly dissipative, LB can be individually addressed by an external (optical) perturbation and used as information bits. More precisely, LB we are aiming at in this project are spatio-temporal “Localized Structures” (LS). LS have been observed in the transverse section (spatial LS) and in the longitudinal direction (temporal LS) of optical resonators. Several experiments have disclosed the potential of LS for information processing, especially when implemented in fast and scalable media as semiconductor resonators. LB we will obtain will lead to three-dimensional buffering of data inside the VECSEL external cavity. If the transverse section of the device allows creating an array of NXN spatial bits and the longitudinal cavity allows for storing M bits, one may handle MXNXN bits in a single device by using LB as information bits. The temporal bit rate is accordingly increased by a factor given by NXN with respect to single-transverse mode resonators. The performances obtained in past experiments in semiconductor lasers lead to an estimation of 5 Kbit sequences stored in the cavity and a writing/reading bit rate of 100 GS/s. Beyond information processing, LB are very interesting for other applications where picoseconds laser pulses are required at an arbitrary low repetition rate and at an arbitrary pattern sequence (time-resolved spectroscopy, optical code division multiple access communication networks and LIDAR). The possibility of integrating metasurfaces onto the VECSEL or onto the SESAM will induce vorticity to each light bullet, thus enabling the creation of an array of optical tweezers for parallel manipulation of biological nano-objects. The use of semiconductor lasers for supporting LB is an important aspect of our project. If implementation of LB in semiconductor lasers enhances their attractiveness for applications, the conception and manufacturing of devices able to sustain these structures is challenging and a large part of the project will be devoted to devices optimisation.

The combination of the Silicon technology with III-V semiconductors is expected to have a major impact for the realization of high-volume / low-cost integrated circuits. Photonic chips based on the already mature Silicon photonics capabilities together with integrated III-V lasers or photodetectors will soon be the foreground for optical-interconnects or lab-on-chip sensors. While heterogeneous integration - where the III-V device or material is bonded to the Si circuit - already showed promising results, a more direct integration scheme is highly desirable in order to improve the yield, the integration density and to decrease the cost of devices. In this context, the monolithic integration by epitaxial growth of high-quality III-V heterostructures directly on Si has been intensively pursued in the past decade. The main challenge remains a drastic reduction of the threading dislocation density (TDD). These line defects are created at the III-V/Si interface due to the large lattice-mismatch and propagate through the epilayers, severely degrading the device performance and lifetime. Despite a considerable amount of work over the past years, TDDs in the range of 1E9 to 1E10 /cm2 are still generally present after growth of about 1 µm of III-V material. We propose to explore a radically new design and growth strategy with the main objective to reduce TDDs down to below 1E5 /cm2. The groundbreaking concept in this project is to initiate in a controlled manner the interaction between on the one hand threading dislocations and, on the other hand, other types of extended defects such as anti-phase boundaries or misfit dislocation arrays at interfaces between specially designed interlayers. These interlayers can be inserted directly at the III-V/Si interface or inside the III-V buffer layer and should act as sink for the threading defects. To this end, MBE growth strategies and new structure designs will be proposed by the French group thanks to an extensive study by advanced transmission electron microscopy techniques of dedicated samples carried out by the German group. The progress made on the TDD reduction will be assessed by the fabrication and testing of lasers demonstrating the impact of the proposed project. The III-V material used here will be GaSb, which can readily serve as a starting point for many optoelectronic devices in the mid- to far-infrared. Even so, the filter design rules derived on the basis of detailed microstructure analysis as well as the growth techniques developed throughout the project are expected to be applicable to other compound semiconductor families and have consequently a major impact on a wide range of applications from data/tele-communication to sensing among others. Furthermore, the developed methodology of dynamic microscopy in three dimensions is in itself an important step towards a complete and efficient determination of the structure-function relationship which can be applied to many materials combinations.

This project aims at developping nanostructured spectral filters made of semiconductors, contrary to usual materials (metal and dielectrics). We will address the LWIR spectral range. We follow two goals: - we will demonstrate monolithic integration of the filters on T2SL photodetectors - we will demonstrate the ability to realize dynamic spectral filtering thanks to electrical actuation. The target is the scan of several hundreds-wide spectral range, with a maximum voltage of 5V. To reach these goals, we will rely on semiconductors such as GaSb and heavily doped InAs (HDS - heavily doped semiconductor). Thanks to heavy doping, InAs will have "metallic" properties in the spectral range of interest. This HDS can be thus used instead of metals in usual nanostructured filters architectures. Furthermore, T2SL photodetectors are also made of InAs, GaSb and other material with the same lattice parameter. Thus, the monolitic integration of the filter on the photodetectors is possible. Then, we will study a mechanism of tunability based on the move of the free carriers in the HDS, when voltage is applied to the component. The concentration of these carriers will then be higher in the vicinity of a barrier, and refractive index will there be modified. If the barrier is properly placed in the nanostructured component, the resonant conditions will lead to a modification of filtering wavelength. Four components will be fabricated and each of them will be designed, fabricated and characterized. These components are: - nanostructured spectral filter made of semiconductors : this will validate the conception experimentaly - a LWIR photodiode with a nanostructured spectral filter on it : this will validate the monolitic integration - a component without nanostructures which will allow to validate experimentaly the barrier - a tunable nanostructured spectral filter grown on photodetector, which is the final goal of the project The work will be divided into three parts: - conception (electromagnetism to design nanostructures and electronics to design the barrier) - nanofabrication of components in clean-room - characterisation (experimental validation of the optical functions) We believe that these components will be building blocks for the next generation of multispectral imaging system with high frequency acquisition. These building blocks will break the traditionnal compromise between spatial and spectral resolution. Besides, the concept of tunability with barrier could be used in other applications, such as nanostructured thermal sources. Two laboratories will be part of the consortium : (1) ONERA, leader, where conception of nanostructures will be done and also electro-optical characterization of components ; (2) Montpellier University, where epitaxial growth, most of fabrication process and conception of barrier will be done. We underline the fact that promising experimental and theoretical results have been obtained by our teams these last months. These results have not been published yet, but a summary is described in the proposal.

Context – THz waves (1-10 THz) are non-ionizing radiation that can potentially find applications in a variety of domains. The most promising at this time are THz imaging and spectroscopy. Quantum cascade lasers (QCL) have emerged as one of the rare compact and powerful THz sources that potentially suit such applications. They can operate at 50/80K with compact Stirling coolers systems or at liquid nitrogen temperature. Beside the available optical power which is an important parameter, what is really limiting the widespread commercial success of THz QCLs is the lack of frequency tunability. Objectives – The goal of the project TERASEL is to develop a highly tunable THz Quantum Cascade Vertical External Cavity Surface Emitting Laser (QC-VECSEL). It will consist of an active medium made of an electrically pumped semiconductor/metal microstructures, providing a reflective gain thanks to THz intersubband transitions. The laser will be frequency tunable thanks to the use of a frequency-selective adjustable external mirror. We target the 2.5-4.5 THz range, with operating temperatures in the 50-80K range and CW output powers larger than 10 mW. An additional objective of the project will be to demonstrate a free-space optical amplifier for THz waves which currently does not exist. Such a device would be useful for extending the practical frequency range of TDS systems above 2 THz or for broadband amplification of THz pulses from mode-locked QCLs. Team – The consortium consists of 3 complementary research groups which are major national and international actors in the domain of QCLs: IES (molecular beam epitaxy of QCLs), C2N (THz photonic microstructure and devices) and LPA (TDS, pulsed QCL, dynamic gain). Relevance – The concept of THz QC-VECSEL is novel, original and very promising. This idea has been recently shown by a USA research team at UCLA. Our proposal builds on this extremely recent development and aims at contributing to this emerging field with state of the art results thanks to an early start and the mobilization of a complimentary and expert consortium. The project innovates in at least 3 aspects: first, we aim at demonstrating a practical THz VECSEL with large frequency tunability (10%); second, we aim at improving considerably the output power performance of the tuneable laser compared to the state-of-the-art; third, we plan to use the envisioned devices as amplifiers of THz pulses from TDS systems and MOPA for mode-locked QCLs. An additional important point is the timeliness of this proposal relative to this emerging hot topic, but also relative to the national structuration of the research in the field. For the first time, the complete fabrication chain (quantum and optical design, growth, characterizations) is available in France, thanks to the state of the art growth of THz QCLs at IES. An important objective of this project is therefore to rapidly capitalize on this situation by demonstrating advances with strong applicative potential.