N. C. Frateschi

Effects of Ga+ milling on InGaAsP quantum well laser with mirrors milled by focused ion beam

InGaAsP/InP quantum well ridge waveguide lasers were fabricated for the evaluation of Ga+ focused ion beam milling of mirrors. Electrical and optical properties were investigated. A 7% increment in the threshold current, a 17% reduction in the external quantum efficiency, and a 15 nm blueshift in the emission spectrum were observed after milling as compared to the as-cleaved facet result. Annealing in inert atmosphere partially reverts these effects, resulting in a 4% increment in the threshold current, an 11% reduction in the external efficiency, and a 13 nm blueshift with the as-cleaved result. The current-voltage behavior after milling and annealing shows a very small increase in leakage current, indicating that optical damage is the main effect of the milling process.

Low-roughness active microdisk resonators fabricated by focused ion beam

The authors present a new approach for the fabrication of active microdisk resonators using focused ion beam (FIB) followed by selective wet-chemical etching. This efficient technique enables the placement of the devices at any region of a sample and facilitates prototyping of monolithical integration. Also, it allows the production of very smooth walls required by the resonators. High-quality resonators with an active region based on high-gain InGaAsP∕InP quantum wells are demonstrated using this technique. Emission in the C-band at whispering-gallery modes is observed.

Evidences of the simultaneous presence of bow-tie and diamond scars in rare-earth doped amorphous silicon microstadium resonators

Microdisks and microstadium resonators were fabricated on erbium doped amorphous hydrogenated silicon (a‐Si:H⟨Er⟩) layers sandwiched in air and native SiO2 on Si substrates. Annealing condition is optimized to allow large emission at 1550nm for samples with erbium concentrations as high as 1.02×1020atoms∕cm3. Near field scanning optical microscopy shows evidence of the simultaneous presence of bow-tie and diamond scars. These modes indicate the high quality of the resonators and the potentiality for achieving amorphous silicon microcavity lasers.

Electrical isolation and transparency in ion-irradiated p-InGaP/GaAs/InGaAs structures

He+-ion irradiation was applied for electrical isolation of p-In0.49Ga0.51P in InGaP/GaAs/InGaAs structures. Sheet resistance of approximately 1×106 Ω/□ was achieved with doses above 1×1013 cm−2 at 100 keV. Thermal stability of isolation was maintained for annealing temperatures up to 500u2009°C. Photoluminescence results show that InGaP transparency to InGaAs/GaAs quantum-well emission is closely related to sheet resistance changes in the irradiated structure.

Enhanced side-mode suppression in chaotic stadium microcavity lasers

We report an enhanced side-mode suppression in Bunimovich stadium lasers with strained InGaAs/InGaP quantum well (QW) active regions. This is realized with spatially selective carrier injection along a particular periodic orbit of the stadium. The selectivity is achieved using He+3 ion implantation. Up to 21 dB enhancement in side-mode suppression is observed for a 40×20u2002μm2 stadium with interband transition between the first excited quantum well level. The improvement in side-mode suppression is apparently a consequence of coherent beating between orbits leading to a Vernier effect. A simple model corroborate with this hypothesis.

Electrical and optical effects of He+ ion irradiation in InGaP/GaAs/InGaAs lasers

Abstract Effects of He + ion irradiation in InGaP/GaAs multilayered laser structures with 7 nm InGaAs quantum wells (QWs) have been investigated. Two versions of the ion irradiation were performed: (I) into the complete structure, and (II) into the structure after a removing the p ++ -GaAs contact layer. In case I, two-energy He + ion implantation includes a 20 keV irradiation for an isolation of p ++ -GaAs and a 170 keV irradiation for the isolation of the p-InGaP cladding layer. In case II, a one-energy (100 keV) implantation is used. Front-side photoluminescence studies show an appearance of the QW emission peak at 9260 A in ion irradiated structures. This transparency effect was attributed to a reduction in a free-carrier absorption in the InGaP layers.

Photonic molecules for application in silicon-on-insulator optical sensors

Optical sensors based on integrated photonics have experienced impressive advancements in the past few decades and represent one of the main sensing solutions in many areas including environmental sensing and medical diagnostics. In this context, optical microcavities are extensively employed as refractive index (RI) sensors, providing sharp optical resonances that allow the detection of very small variations in the surrounding RI. With increased sensitivity, however, the device is subjected to environmental perturbations that can also change the RI, such as temperature variations, and therefore compromise their reliability. In this work, we present the concept and experimental realization of a photonic sensor based on coupled microcavities or Photonic Molecules (PM) in which only one cavity is exposed to the sensing solution, allowing a differential measurement of the RI change. The device consists of an exposed 5-μm radius microdisk resonator coupled to an external clad microring resonator fabricated on silicon-on-insulator (SOI) platform. This design allows good sensitivity (26 nm/RIU) for transverse electrical mode (TE-mode) in a compact footprint (40 × 40 μm2), representing a good solution for real-life applications in which measurement conditions are not easily controllable.

Mode pattern dependence on the eccentricity of microstadium resonators

Microdisk and microstadium resonators based on InGaAsP multiquantum-well laser structures were fabricated by focused ion beam employing Ga+ ion milling and polishing followed by selective chemical etching. Stadia with very good morphology and with different eccentricities were fabricated for the study of optical mode selection. Light emission was investigated by infrared microscopy and spectroscopy. The measured emission pattern and the spectra agree well with a simple model based on the summation over periodic orbits or scar modes. The dependence of the scar mode emission with the resonator eccentricity was modeled based on the difference between photon lifetime and orbital round-trip time. The mode selection dependence with the surrounding index of refraction is suggested for chemical sensing applications.

Continuous and Pulsed THz generation with molecular gas lasers and photoconductive antennas gated by femtosecond pulses

TeraHertz waves, associated with the far-infrared region of the electromagnetic spectrum, are gaining increasing interest in the past years due to promising applications in imaging, spectroscopy, and even communications. Here we report THz generation based on two systems: 1) continuous-wave (cw) laser generation in molecular gas lasers, and 2) short pulse generation in photoconductive antennas, gated by femtosecond near-infrared Ti:sapphire lasers. With the first system, we have generated tens of monochromatic CW laser lines over the last years, extending roughly from 40 microns to several hundred microns. This is done by optical pumping of gas lasers based on polar molecules such as methanol and its isotopes. In the second system, under development, pulsed THz radiation is generated by a photoconductive antenna built in a semi-insulating GaAs substrate excited by femtosecond pulses from a near-infrared (800 nm) Ti:sapphire laser.

Effects of facet head-on light ion-irradiation in InGaP/GaAs/InGaAs quantum well lasers

Summary form only given. We present results on the reduction in free-carrier absorption for n-InGaP material with He/sup +/ ion irradiation. Threshold doses for isolation above 1/spl times/10/sup 13/ cm/sup -2/ at 100 keV are obtained. Transparency through 1 /spl mu/m of n-InGaP material is examined by photoluminescence. We find a twofold increase in quantum well emission photoluminescence intensity after irradiation. Also, damage to the quantum well is investigated as a function of irradiation energy and quantum well depth. Finally, we investigate irradiation effects on the field intensity and temperature distribution at the facets. Evidence of enhancement in cladding layer transparency to the laser emission is observed on the irradiated facet. Therefore, less facet heating and degradation is expected with the head-on irradiation treatment.