N. Laurand

Colloidal quantum dot random laser

We report random laser action in a system where optical amplification is provided by colloidal quantum dots (CQDs). This system is obtained by depositing from solution CdSe/ZnS core-shell CQDs into rough micron-scale grooves fabricated on the surface of a glass substrate. The combination of CQD random packing and of disordered structures in the glass groove enables gain and multiple scattering. Upon optical excitation, random laser action is triggered in the system above a 25-mJ/cm2 threshold. Single-shot spectra were recorded to study the emission spectral characteristics and the results show the stability of the laser mode positions and the dominance of the modes close to the material gain maximum.

Flexible blue-emitting encapsulated organic semiconductor DFB laser.

Mechanically flexible distributed feedback (DFB) lasers are fabricated by a low-cost approach using soft-lithography from a holographic master grating. The gain material is a star-shaped oligofluorene providing laser emission from 425 to 442 nm with a soft pump threshold at 14.4 μJ/cm (2.7 kW/cm). Encapsulation of the devices enables stable operation in ambient atmosphere at a 1/e degradation energy dosage of 53 J/cm.

Nanoscale-accuracy transfer printing of ultra-thin AlInGaN light-emitting diodes onto mechanically flexible substrates

The transfer printing of 2 μm-thick aluminum indium gallium nitride (AlInGaN) micron-size light-emitting diodes with 150 nm (±14 nm) minimum spacing is reported. The thin AlInGaN structures were assembled onto mechanically flexible polyethyleneterephthalate/polydimethylsiloxane substrates in a representative 16 × 16 array format using a modified dip-pen nano-patterning system. Devices in the array were positioned using a pre-calculated set of coordinates to demonstrate an automated transfer printing process. Individual printed array elements showed blue emission centered at 486 nm with a forward-directed optical output power up to 80 μW (355 mW/cm2) when operated at a current density of 20 A/cm2.

Long-wavelength monolithic GaInNAs vertical-cavity optical amplifiers

We report on the continuous-wave amplification characteristics of an optically pumped 1.3-/spl mu/m multiple-quantum-well GaInNAs-GaAs vertical-cavity semiconductor optical amplifier (VCSOA). The VCSOA structure was monolithically grown by molecular beam epitaxy and operated in reflection mode in a fiber-coupled system. The maximum on-chip gain attained, limited by the onset of laser action, was 15.6 dB at 196 mW of 980-nm pump power. For a chip gain of 10.4 dB, the optical bandwidth was 10.8 GHz and the saturation output power was -9 dBm. By varying the pump laser power, a maximum extinction ratio of 22.3 dB was obtained. Temperature-controlled tuneable operation of the device is also presented and demonstration of 9 dB of chip gain obtained over 9.5 nm with an optical bandwidth of 12 GHz is reported.

Microlensed microchip VECSEL

We report a 1.055-mum microchip VECSEL array which uses a microlens-patterned diamond both as a heatspreader and as an array of concave output mirrors. This configuration, which is suitable for laser array operation, is here exploited to perform a systematic study of a set of microchip lasers with the same semiconductor structure but different cavity properties. The transverse mode selection of individual VECSELs is found to depend on the mode-matching conditions and on the microlens aperture size. Mode-matched single-device emission in the fundamental mode (M2~1.1) with pump-limited output power of 70 mW is demonstrated.

Wavelength-tunable colloidal quantum dot laser on ultra-thin flexible glass

A mechanically flexible and wavelength-tunable laser with an ultra-thin glass membrane as substrate is demonstrated. The optically pumped hybrid device has a distributed feedback cavity that combines a colloidal quantum dot gain film with a grating-patterned polymeric underlayer, all on a 30-μm thick glass sheet. The total thickness of the structure is only 75 μm. The hybrid laser has an average threshold fluence of 450 ± 80 μJ/cm2 (for 5-ns excitation pulses) at an emitting wavelength of 607 nm. Mechanically bending the thin-glass substrate enables continuous tuning of the laser emission wavelength over an 18-nm range, from 600 nm to 618 nm. The correlation between the wavelength tunability and the mechanical properties of the thin laser structure is verified theoretically and experimentally.

Colloidal quantum dot nanocomposites for visible wavelength conversion of modulated optical signals

We report on the steady-state and optical modulation characteristics of a luminescence down-converting colloidal quantum dot/polyimide nanocomposite system suitable for integration with gallium nitride optoelectronics. The approach provides solution-processable and environmentally stable composite materials whose optical conversion and intrinsic modulation properties were evaluated at wavelengths from 535 to 624 nm. A nanocomposite for white-light generation upon excitation and mixing with 450-nm light was also obtained by blending colloidal quantum dots of different sizes in the same matrix. The forward external quantum efficiencies of the resulting nanocomposites were found to depend on the wavelength and can be as high as 33%. Optical modulation bandwidth above 25 MHz, which is an order of magnitude higher than for typical phosphor-based color-converters for GaN LEDs, and wavelength-converted data with an open-eye diagram at 25 Mb/s are demonstrated under external gallium nitride light-emitting diode excitation. These modulation characteristics are correlated with carrier lifetimes. This work provides guideline parameters and creates a possible path to integrated hybrid visible light sources for scientific and communications applications.

Flexible distributed-feedback colloidal quantum dot laser

By fabricating a submicron-scale gratingstructure on a bendable polymer substrate, we demonstrate a flexible distributed-feedback colloidal quantum dot laser. This laser uses cadmium selenide/zinc sulfide core-shell nanostructures, operating in transverse electric polarized multiple-modes, and has a typical threshold pump fluence of ∼4 mJ/cm2.

An oligofluorene truxene based distributed feedback laser for biosensing applications

The first example of an all-organic oligofluorene truxene based distributed feedback laser for the detection of a specific protein-small molecule interaction is reported. The protein avidin was detected down to 1 μg mL(-1) using our biotin-labelled biosensor platform. This interaction was both selective and reversible when biotin was replaced with desthiobiotin. Avidin detection was not perturbed by Bovine Serum Albumin up to 50,000 μg mL(-1). Our biosensor offers a new detection platform that is both highly sensitive, modular and potentially re-usable.

Highly-photostable and mechanically flexible all-organic semiconductor lasers

Two formats of all-organic distributed-feedback lasers with improved photostability, respectively called nanocomposite and encapsulated lasers, are reported. These lasers are compatible with mechanically-flexible platforms and were entirely fabricated using soft-lithography and spin-coating techniques. The gain elements in both types of lasers were monodisperse π-conjugated star-shaped macromolecules (oligofluorene truxene, T3). In the nanocomposites lasers, these elements were incorporated into a transparent polyimide matrix, while in the encapsulated devices a neat layer of T3 was overcoated with Poly(vinyl alcohol) (PVA). The T3-nanocomposite devices demonstrated a 1/e degradation energy dosage up to ~27.0 ± 6.5 J/cm2 with a threshold fluence of 115 ± 10 µJ/cm2. This represents a 3-fold improvement in operation lifetime under ambient conditions compared to the equivalent laser made with neat organic films, albeit with a 1.6-time increase in threshold. The PVA-encapsulated lasers showed the best overall performance: a 40-time improvement in the operation lifetime and crucially no-trade-off on the threshold, with respectively a degradation energy dosage of ~280 ± 20 J/cm2 and a threshold fluence of 36 ± 8 µJ/cm2.