V. Bardinal

Fabrication and characterization of microlens arrays using a cantilever-based spotter

We present a quantitative study on the fabrication of microlenses using a low-cost polymer dispending technique. Our method is based on the use of a silicon micro-cantilever robotized spotter system. We first give a detailed description of the technique. In a second part, the fabricated microlenses are fully characterized by means of SEM (Scanning Electron Microscope), AFM (Atomic Force Microscopy) non contact optical profilometry and Mach-Zehnder interferometry. Diameters in the range [25-130mum] are obtained with an average surface roughness of 2.02nm. Curvature radii, focal lengths as well as aberrations are also measured for the first time: the fabricated microlenses present focal lengths in the range [55-181mum] and exhibit high optical quality only limited by diffraction behaviour with RMS aberration lower than lambda/14.

IN SITU MEASUREMENT OF ALAS AND GAAS REFRACTIVE INDEX DISPERSION AT EPITAXIAL GROWTH TEMPERATURE

In situ molecular beam epitaxy control of III–V optoelectronic device growth has been achieved by dynamic optical reflectometry with tunable excitation wavelength, through the use of a titanium:sapphire laser light source. This new multiwavelength reflectometry method was used to determine the values of the AlAs and GaAs refractive indices at growth temperature (600 °C). Index dispersion between 760 and 960 nm is presented and found to be in good agreement with the existing models.

Miniaturized Scanning Near-Field Microscope Sensor Based on Optical Feedback Inside a Single-Mode Oxide-Confined Vertical-Cavity Surface-Emitting Laser

We propose and demonstrate an original concept of a near-field sensor using the optical feedback properties of a vertical cavity surface-emitting laser (VCSEL) as the detection principle. This is based on the monitoring perturbation induced in the laser cavity by the backscattered light coming from the specimen. Test images confirm the efficiency of the proposed scanning near-field optical microscopy (SNOM) and a solution for the integration of the proposed architecture is given.

Collective Micro-Optics Technologies for VCSEL Photonic Integration

We describe the main recent technological approaches that associate micro-optical elements to VCSELs in order to control their output beam and to improve their photonic integration. These approaches imply either a hybrid assembly or a direct integration technique. They are compared with regards to their tolerance to alignment errors and to their ease of implementation onto arrays of devices at a wafer level. In particular, we detail the integration techniques we have developed for self-aligned polymer microlens fabrication for beam collimation and short distance beam focusing. Finally, designs to achieve active micro-optics or to exploit novel nanophotonic effects are discussed.

Four‐wave mixing in bulk GaAs microcavities at room temperature

We studied pico‐ and femtosecond degenerate four‐wave mixing in bulk GaAs Fabry–Perot microcavities at room temperature. For wavelengths below the GaAs band edge, a cavity with a finesse of approximately 20 yields an enhancement of the diffracted signal by more than two orders of magnitude as compared to a cavityless GaAs layer of the same thickness (685 nm). The cavity‐enhanced nonlinearity of the interband transition results in a diffraction efficiency η≊0.5% for 150 pJ pulses with a duration of 900 fs at 878 nm, being 400 times larger than that for the bare GaAs reference sample.

Fabrication of polymer-based optical microsystem arrays suited for the active focusing of vertical laser diodes

We present a low-cost fabrication technique of a polymer-based micro-optical-electrical-mechanical systems (MOEMS) suited for the dynamic focusing of VCSELs (vertical-cavity surface-emitting lasers). A simple method based on an SU(8) double exposure is proposed for the collective integration of small footprint transparent suspended membrane arrays on vertical laser diodes. We demonstrate that this kind of MOEMS can provide under thermal actuation a vertical displacement of around 0.2 ?m W?1?over a maximal range of 8??m. As a wide range of initial gaps between the membrane and the laser source can be chosen, this approach opens new insights into the dynamic control of the VCSEL beam waist position as well as for tunable VCSEL fabrication.

Experimental demonstration of oxide-mode influence in a dual-purpose oxide-confined vertical-cavity surface-emitting laser/resonant detector

We report on design, fabrication, and characterization of a vertical-cavity surface-emitting laser (VCSEL) used as a resonant-cavity-enhanced detector for dual-purpose application. The geometry of this oxide-confined VCSEL takes advantage of the properties of the buried oxide layer to allow both single-mode laser emission and detection on a large surface. Here, we demonstrate the presence and the influence of oxide modes in the optical sensitivity spectrum of the device through spatially localized detection measurements. The wavelength of these modes has been correlated to the dip on the reflectivity spectrum measured at the same area of the device surface.

Subnanosecond density dynamics of the electrondashhole plasma in GaAs/AlAs microcavities

Abstract We study the time-resolved reflectivity spectra of distributed Fabry-Perot (DFP) cavities following a picosecond laser excitation. The structures, which are composed of two GaAs/AlAs Bragg reflectors enclosing a central GaAs layer, exhibit a sharp reflectivity minimum slightly below the GaAs band gap. Due to the photogeneration of carriers in the central zone, we observe a red shift of 5–6 nm of the reflectivity minimum on a subnanosecond time scale. This effect enables one to deduce the plasma density from the spectra analysis. This method still works at low plasma density, i.e., for nondegerated plasma, when the standard luminescence method fails. The reflectivity of a photoexcited DFP is calculated by combining the absorption and index theory in the presence of thermalized carriers with a many-layer description of the structures (Abeles formalism). We trace the relaxation kinetics of the plasma density in the central zone of the microcavity and conclude the stimulated emission in the microcavity.

Photo-chemical study and optical properties of microtips self- written on vertical laser diodes using NIR photo-polymerization

Near infra-red (NIR) self-guided photo-polymerization is investigated in the context of micro-optics photo-fabrication on VCSELs (Vertical-Cavity Surface Emitting Lasers). We present the optimized process we have developed to allow for a collective fabrication on III-V devices wafers under real-time optical monitoring. The influence of photo-chemical parameters on final micro-elements dimensions is studied for two types of single mode 760 nm VCSELs. The difference of the resulting tip shape between the two lasers is due to the strong differences of their emissions, as they are nicely reproduced by the computed near-field profiles. The tip shapes are also compared to those produced by the light emitted by an optical fiber and differences with VCSEL tips are discussed. Also the VCSEL characteristics with fabricated tips are discussed and found in good agreement with optical modeling.

Liquid crystal-based tunable photodetector operating in the telecom C-band

Liquid crystal (LC) microcells monolithically integrated on the surface of InGaAs based photodiodes (PDs) are demonstrated. These LC microcells acting as tunable Fabry-Perot filters exhibit a wavelength tunability of more than 100 nm around 1550 nm with less than 10V applied voltage. Using a tunable laser operating in the S and C bands, photocurrent measurements are performed. On a 70 nm tuning range covered with a driving voltage lower than 7V, the average sensitivity for the PD is 0.4 A/W and the spectral linewidth of the LC filter remains constant, showing a FWHM of 1.5 nm. Finally, the emission spectrum from an Er-doped fiber is acquired by using this tunable PD as a micro-spectrometer.