Development of high-speed directly-modulated DFB and DBR lasers with surface gratings

The conventional distributed feedback and distributed Bragg reflector edge-emitting lasers employ buried gratings, which require two or more epitaxial growth steps. By using lateral corrugations of the ridge-waveguide as surface gratings the epitaxial overgrowth is avoided, reducing the fabrication complexity, increasing the yield and reducing the fabrication cost. The surface gratings are applicable to different materials, including Al-containing ones and can be easily integrated in complex device structures and photonic circuits. Single-contact and multiple contact edge-emitting lasers with laterally-corrugated ridge waveguide gratings have been developed both on GaAs and InP substrates with the aim to exploit the photon-photon resonance in order to extend their direct modulation bandwidth. The paper reports on the characteristics of such surface-grating-based lasers emitting both at 1.3 and 1.55 μm and presents the photon-photon resonance extended small-signal modulation bandwidth (> 20 GHz) achieved with a 1.6 mm long single-contact device under direct modulation. Similarly structured devices, with shorter cavity lengths are expected to exceed 40 GHz smallsignal modulation bandwidth under direct modulatio

Use of microcutting for high throughput electrode patterning on a flexible substrate

The use of printing technologies is promising for low-cost manufacturing of flexible, light-weight and large-area electronics, such as electronic paper or solar cells. Here, we demonstrate a microcutting technique and methods to fabricate cutting blades for the patterning of metal structure on a polymer substrate. Microcutting is done using a hot embossing and nanoimprinting techniques. The metallic fine patterns obtained by using stamps fabricated using different techniques are compared. Combination of microcutting and our recently proposed dielectric alignment opens up a novel platform for a variety of applications, such as the fabrication of metal crossover or organic field effect transistors as well as contact resistance measurement of metal-semiconductor junctions.acceptedVersionacceptedVersionPeer reviewe

GaSb diode lasers tunable around 2.6 μm using silicon photonics resonators or external diffractive gratings

We report two tunable diode laser configurations emitting around 2.6 μm, where the gain is provided by a high-gain GaSb-based reflective semiconductor optical amplifier. The lasers are driven in pulsed mode at 20 °C, with a pulse width of 1 μs and 10% duty cycle to minimize heating effects. To demonstrate the broad tuning and high output power capability of the gain chip, an external cavity diode laser configuration based on using a ruled diffraction grating in a Littrow configuration is demonstrated. The laser shows a wide tuning range of 154 nm and a maximum average output power on the order of 10 mW at 2.63 μm, corresponding to a peak power of 100 mW. For a more compact and robust integrated configuration, we consider an extended-cavity laser design where the feedback is provided by a silicon photonics chip acting as a reflector. In particular, the integrated tuning mechanism is based on utilizing the Vernier effect between two thermally tunable micro-ring resonators. In this case, a tuning range of around 70 nm is demonstrated in a compact architecture, with an average power of 1 mW, corresponding to a peak power of 10 mW.publishedVersionPeer reviewe

Ion irradiation induced nitrogen mobility in a GaInNAs quantum well laser

Changes in the optical properties in GaInNAs/GaAs quantum wells after alpha particle bombardment followed by low temperature annealing are reported. Both blue and red shifts of the lasing wavelength are observed under different annealing conditions. This differs from the usually observed blue shift which is found after high-temperature post-grown annealing. Competing processes that result in the lasing wavelength shifts are energetic considerations which act to increase the number of Ga-N and In-As bonds (maximize the cohesive energy), minimizing the strain of the system which increases the number of In-N and Ga-As bonds (large-ion-small-ion links), maximizing the number of N located at lattice sites effective at shrinking the band-gap and moving the N position within the quantum well. For the case of high-temperature post-grown annealing the increase of Ga-As and In-N bonding wins, resulting in the blue shift observed. The wavelength shifts are discussed in terms of these competing mechanisms. © 2008 IOP Publishing Ltd

Inhomogeneities in the nonlinear tensorial responses of arrays of gold nanodots

We use second- and third-harmonic-generation microscopy to address the tensorial nonlinear responses of individual particles in an array of cylindrical gold nanodots. The responses in both orders exhibit widely-variable, polarization-dependent differences between individual nanodots and thereby indicate tensorial inhomogeneities in the sample. The result provides clear evidence that the second-order response, which is forbidden by symmetry for ideal particles, must arise from small-scale, symmetry-breaking features. A similar result for the third-order response, which is allowed for ideal particles, suggests that both nonlinear responses are dominated by strong variations in field localization around the small-scale features differing among individual nanodots.Peer reviewe

Double-asymmetric-structure 1.5 μ m high power laser diodes

Abstract Design considerations for high pulsed power and brightness 1.5 μm laser emitters for laser radar applications, based on comprehensive semi-analytical theory, are presented. A strongly asymmetric waveguide design with a bulk active layer positioned very near the p-emitter interface is chosen to minimize the current-induced losses at high power while maintaining a single, broad transverse mode. Moderate to high doping of the n-side of the Optical Confinement Layer and high p-doping of the p-cladding layer are used to reduce the residual current-induced losses and the electric resistance of the structure. For pulsed room-temperature operation, short laser resonators are found to be advantageous. First experimental results are presented. An as-cleaved sample with a stripe width of 90 μm and a resonator 2 mm long exhibits an output power of about 18 W at a pumping current amplitude of 80 A, with 1 mm long resonators showing higher power output. Further improvements are predicted by structure optimization as well as increase in internal quantum efficiency and thermal performance

High power 1.5 μm pulsed laser diode with asymmetric waveguide and active layer near p-cladding

Abstract We report first experimental results on a high-power pulsed semiconductor laser operating in the eye-safe spectral range (wavelength around 1.5 μm) with an asymmetric waveguide structure. The laser has a bulk active layer positioned very close to the p-cladding in order to eliminate current-induced nonuniform carrier accumulation in the p-side of the waveguide and the associated carrier losses. Moderate doping of the n-side of the waveguide is used to strongly suppress nonuniform carrier accumulation within this part of the waveguide. Highly p-doped InP p-cladding facilitates low series resistance. An as-cleaved sample with a stripe width of 90 μm exhibits an output power of about 18 W at a pumping current amplitude of 80 A. Theoretical calculations, validated by comparison to experiment, suggest that the performance of lasers of this type can be improved further by optimization of the waveguide thickness and doping as well as improvement of injection efficiency

High-power 1.5μm laser diodes for LIDAR applications

Abstract We report on the development of high peak power laser diodes emitting in the 1.5μm wavelength band for eye-safe LIDAR applications. Different techniques for wavelength locking to and operation with a narrow emission spectrum are discussed. Furthermore, we review the strategies to increase the beam brightness. Recent progress in new epitaxial layer designs enabling high peak powers is also discussed. Finally, we discuss the performance of the laser diodes in terms of improvements they render possible for high-performance LIDAR systems