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We overview recent advances in the research on spatiotemporal beam shaping in nonlinear multimode optical fibers. An intense light beam coupled to a graded index (GRIN) highly multimode fiber undergoes a series of complex nonlinear processes when its power grows larger. Among them, the lowest threshold effect is the Kerr-induced beam self-cleaning, that redistributes most of the beam energy into a robust bell-shaped beam close to the fundamental mode. At higher powers a series of spectral sidebands is generated, thanks to the phase matching induced by the long period grating due to the periodic self-imaging of the beam and the Kerr effect. Subsequently a broadband and spectrally flat supercontinuum is generated, extending from the visible to the mid-infrared.

Imaging arrays of direct detectors in the 0.5-5 THz range are being experimentally developed. Terahertz active imaging with amplitude-modulated quantum cascade lasers emitting at 2.5 and 4.4 THz performed by using an antenna-coupled superconducting microbolometer. We then present two room-temperature terahertz detector technologies compatible with monolithic arrays: i) GaAs Schottky diodes with air-bridge sub-micron anodes; ii) high electron mobility transistors with sub-micron Schottky gate. Performances, requirements and fabrication costs of the different detector technologies are compared.

A terahertz quantum cascade laser has been realized from an isotropic disordered hyperuniform design. Such a system presents a photonic band-gap although it is characterized by an efficient depletion of the long range order. Hyperuniform patterns allow greater versatility in engineering band gaps in comparison to standard photonic-crystal materials. Bidimensional hyperuniform patterns were simulated for hexagonal tiles composed of high refractive index disks merged in a low dielectric constant polymeric matrix. Based on this design, quantum cascade lasers were fabricated by standard photolithography, metal evaporation, lift-off and dry-etching techniques in a half-stack bound to continuum active region emitting around 2.9 THz.

We acknowledge support from the EPSRC (ADF, Fellowships No. EP/I004602/1 and No. EP/J004200/1) and KAUST (AF, Grant No. CRG-1-2012-FRA-005). We show here theoretically and experimentally how chaotic Photonic Crystal resonators can be used for en- ergy harvesting applications and the demonstration of fundamental theories, like the onset of superradiance in quantum systems. Publisher PDF

In our development of a field deployable infrared isotope ratio spectrometer (IR2) for compound specific isotope analysis (CSIA), the IR2‘s accuracy and stability have reached a stage that small fractionation in reference gas pulses generated as standard are observed easily and repeatedly. Such fine fractionation is often difficult to observe in regular Isotope Ratio Mass Spectrometer (IRMS) due to instrument drift on the order of 10s of minutes. After careful design of reference pulse sequences and long period of data collection, such fractionations are also verified in a commercial continuous flow CSIA-IRMS. Implications of the fractionation and observation process are discussed.

There have been limited choices of optical materials in the Mid-Infrared for polarization control and subsequent isolation. We show several combinations of existing materials and optics that could realize polarization control and isolation for quantum cascade lasers in the MIR. Improvements in signal to noise ratio in MIR laser spectroscopy, as well as saturated absorption spectroscopy utilizing the isolation achieved, will be discussed.

A field deployable Compound Specific Isotope Analyzer (CSIA) coupled with capillary chromatogrpahy based on Quantum Cascade (QC) lasers and Hollow Waveguide (HWG) with precision and chemical resolution matching mature Mass Spectroscopy has been achieved in our laboratory. The system could realize 0.3 per mil accuracy for ^(12)C/^(13)C for a Gas Chromatography (GC) peak lasting as short as 5 seconds with carbon molar concentration in the GC peak less than 0.5%. Spectroscopic advantages of HWG when working with QC lasers, i.e. single mode transmission, noiseless measurement and small sample volume, are compared with traditional free space and multipass spectroscopy methods.

International audience; We will present a brief overview of the interest in subwavelength gratings for spectral filtering in the mid-infrared wavelength range. Guided-mode, plasmonic and dipolar resonances will be considered. We will particularly focus on components fabricated in our laboratories, achieving band-pass or cut-band filtering. Optical characterization will be shown, revealing resonances with high quality factors. Multispectral camera has been realized by integrating our components into a cooled infrared focal plane array.

Engineered substrates such as large diameter (100mm) GaSb wafers need to be ready years in advance of any major shift in DoD and commercial technology, and typically before much of the rest of the materials and equipment for fabricating next generation devices. Antimony based III-V semiconductors are of significant interest for advanced applications in optoelectronics, high speed transistors, microwave devices, and photovoltaics. GaSb demand is increasing due to its lattice parameter matching of various ternary and quaternary III-V compounds, as their bandgaps can be engineered to cover a wide spectral range. For these stealth and spaced based applications, larger format IRFPAs benefit clearly from next generation starting substrates. In this study, we have manufactured and tested 100mm GaSb substrates. This paper describes the characterization process that provides the best possible GaSb material for advanced IRFPA and SLS epi growth. The analysis of substrate by AFM surface roughness, particles, haze, GaSb oxide character and desorption using XPS, flatness measurements, and SLS based epitaxy quality are shown. By implementing subtle changes in our substrate processing, we show that a Sb-oxide rich surface is routinely provided for rapid desorption. Post-MBE CBIRD structures on the 100mm ULD GaSb were examined and reveals a high intensity, 6.6nm periodicity, low (15.48 arcsec) FWHM peak distribution that suggests low surface strain and excellent lattice matching. The Ra for GaSb is a consistent ~0.2-4nm, with average batch wafer warp of ~4 μm to provide a clean, flat GaSb template critical for next generation epi growth.

To improve the Mid-Infrared (IR) chemical sensing capabilities in liquids and gases, a polymer based waveguide that has 100% interaction with Quantum Cascade (QC) laser field is proposed and demonstrated. The waveguide has thickness down to 10s nanometers so that chemical diffusion and preconcentration could happen very fast; the path length is increased from several microns to over centimeters due to the high spectral and diffraction brightness of QC lasers. Efficient prism coupling into whispering gallery resonators’ coated with submicron polymers and planar slab polymer waveguide are demonstrated, high signal to noise ratio is obtained and potential applications discussed.

We show that QC laser could improve capillary Gas Chromatography Infrared spectroscopy resolution significantly, i.e. both Doppler limited and Doppler free resolution could be achieved. To achieve these goals, we report our latest efforts in characterizing the tuning and noise properties of Quantum Cascade (QC) lasers; novel schemes on modulation to gain largest tuning range as well as on stabilizing and locking the QC lasers are proposed, and results presented.

International audience; Mid-infrared spectroscopy has gained significant importance in recent years as a detection technique for substances that absorb in this spectral region. Traditionally, a spectroscopic system consists of bulky equipment which is difficult to handle and incurs high cost. An integrated spectroscopic system would eliminate these disadvantages. GaSb-based active opto-electronic devices allow realizing mid-infrared light sources and detectors in the 2-3 mu m wavelength range for such integrated systems. Silicon photonics, based on Silicon-on-Insulator (SOI) waveguide circuits, on the other hand, is a well established technology based on high refractive index contrast waveguides, enabling ultra-compact passive integrated photonic circuits. Moreover, SOI waveguide circuit processing is compatible with CMOS processes. Hence, the integration of GaSb-based active devices onto SOI passive waveguide circuits potentially allows highly compact spectroscopic systems with a large degree of freedom in passive device design to improve the system performance. This approach has a high potential for several applications, e. g. an implantable glucose level monitor and gas sensing devices. In this paper, we report our work on the integration of GaSb-based epitaxy onto SOI waveguide circuits. The heterogeneous integration is based on an epitaxial layer transfer process using the polymer divinylsiloxane-benzocyclobutene (DVS-BCB) as a bonding agent. The process is performed by transferring the epitaxial layer to an SOI waveguide circuit wafer through a die-to-wafer bonding process. With this approach, a bonding layer of 150 nm thickness is easily achievable. We also report our results on the integration of waveguide-based GaSb p-i-n photodetectors coupled to SOI waveguide circuits using evanescent coupling, which show a responsivity higher than 0.4A/W. The design of active and passive structures and the overall fabrication process will also be discussed.

An amplifier design for broadband Mid-IR buried-hetero (BH) structure epitaxial laser is presented, and external cavity design based on this amplifier is described. Spectroscopy results characterizing such single frequency lasers are demonstrated with whispering gallery mode CaF2 disc/ball, saturated absorption in hollow waveguide and direct chemical analysis in water.

Photonic crystal structures have been used to improve modal properties of broad area semiconductor lasers in recent years. It has been demonstrated that the width of single-mode semiconductor laser can be increased by at least two orders of magnitude using the transverse Bragg reflection of two dimensional periodic nanostructures. In this talk, we will describe a photonic crystal structure to obtain the single mode operation of large-area, edge-emitting semiconductor lasers. Pulsed and CW operation of electrically pumped, single-mode photonic crystal broad area lasers (100μm wide and 550μm long) with single-lobe, diffraction-limited far-fields are experimentally demonstrated at room temperature. A wavelength tuning sensitivity 80 times smaller than a conventional DFB laser is also achieved for the photonic crystal Bragg laser.

Excitation of the whispering gallery modes (WGM) of a CaF_2 ball resonator is demonstrated at 4.5 micron with a pulsed Quantum Cascade laser. A prism coupling scheme for mid-infrared is described. Future applications of WGM resonators as hyphenated inline chromatography sensors are discussed.

Semiconductor nanostructures, such as quantum wells and quantum dots, are well known, and some have been incorporated in applications. Here we propose a new general approach to make use of polar optical phonons in quantum wells for terahertz (THz) devices. As the first example, we show the coupling of phonon and intersubband transition leading to Fano resonance in photocurrent spectra. We investigate the phenomenon experimentally in specially designed GaAs/AlGaAs quantum well infrared photodetectors. Finally, we discuss the future research and potentials., SPIE OPTO: Integrated Optoelectronic Devices, 24 January 2009, San Jose, CA, USA, Series: Proceedings of SPIE; no. 7222

We describe the performance of submicron microdisk and photonic crystal lasers fabricated within InGaP/InGaAlP quantum well material. The smallest lasers, with diameters of approximately 600 nm, feature ultra-small mode volumes and exhibit single mode operation at low threshold powers. Their small cavity volumes of approximately 0.03 μm 3 for microdisk lasers and 0.01 μm 3 for photonic crystal lasers enable them to be used as spectroscopic sources. Here we demonstrate the fabrication and characterization of visible, monolithically fabricated, submicron mode volume lasers.

GaSb/AlSb/InAs is an attractive system for making low noise avalanche photodetectors (APD) due to possible resonant enhancement of hole impact ionization in Al_xGa_(1-x)Sb and potential enhancement of electron impact ionization in GaSb/AlSb superlattices. We have employed molecular beam epitaxy (MBE) to fabricate device structures so that these effects could be further explored. The devices were grown on GaSb substrates and incorporated a p^-n^+ one sided abrupt junction. The p^- multiplication region consisted of either bulk Al_(0.04)Ga_(0.96)Sb or 10 periods of alternating, 300 angstrom thick GaSb and AlSb layers. A short period, selectively doped InAs/AlSb superlattice was used as the n^+ layer. Dark current suppression in these devices was found to be largely dependent on the InAs/AlSb superlattice configuration and the resulting band offset at the p^-n^+ heterojunction. Notably, for devices with a 0.6 micrometer Al_(0.04)Ga_(0.96)Sb multiplication region and an optimized InAs/AlSb superlattice, an avalanche break down voltage of 13 V was observed. The dark current density for this device was 6 A/cm^2 at a multiplication factor of 10. Devices with GaSb/AlSb superlattice multiplication regions exhibited a higher breakdown voltage (18.5 V) and a lower dark current density (0.4 A/cm^2) at comparable gain. Impact ionization rates in Al_(0.04)Ga_(0.96)Sb were studied by using 781 nm and 1645 nm laser light. The results were consistent with enhancement of hole impact ionization in Al_(0.04)Ga_(0.96)Sb.