Jean-Baptiste Doucet

A microtip self-written on a vertical-cavity surface-emitting laser by photopolymerization

We present the integration of a self-aligned microtip on a vertical-cavity surface-emitting laser (VCSEL) by near infrared photopolymerization. This one-step fabrication process is triggered by the laser source itself. It is based on the use of photopolymers sensitive at the lasing wavelength and can be applied to VCSEL devices after their process fabrication. We have characterized the fabricated microtips and shown that they focus laser light at few micrometers from the device. The applications of this simple method may concern VCSEL beam shaping as well as the fabrication of microprobes for near-field optical microscopy.

3D optimization of a polymer MOEMS for active focusing of VCSEL beam

We report on the optimized design of a polymer-based actuator that can be directly integrated on a VCSEL for vertical beam scanning. Its operation principle is based on the vertical displacement of a SU-8 membrane including a polymer microlens. Under an applied thermal gradient, the membrane is shifted vertically due to thermal expansion in the actuation arms induced by Joule effect. This leads to a modification of microlens position and thus to a vertical scan of the laser beam. Membrane vertical displacements as high as 8μm for only 3V applied were recently experimentally obtained. To explain these performances, we developed a comprehensive tri-dimensional thermo-mechanical model that takes into account SU-8 material properties and precise MOEMS geometry. Out-of-plane mechanical coefficients and thermal conductivity were thus integrated in our 3D model (COMSOL Multiphysics). Vertical displacements extracted from these data for different actuation powers were successfully compared to experimental values, validating this modelling tool. Thereby, it was exploited to increase MOEMS electrothermal performance by a factor higher than 5.

A miniaturized VCSEL-based system for optical sensing in a microfluidic channel

We report on design and fabrication of a VCSEL-based Micro-Optical-Electrical-Mechanical-System (MOEMS) suited for portable optical biosensors. It is based on a tunable polymer microlens directly integrated on the surface of the VCSEL laser device. We demonstrate that this method leads to a VCSEL focusing at a working distance of ~300μm suitable for optical analysis in a microfluidic channel. Moreover, as the microlens can be vertically moved up to 8μm with an applied power of only 43 mW (3V), a dynamic scan of the laser spot is possible over 100μm. This integrated approach opens new insights for the use of VCSEL arrays in miniaturized optical sensors.

Study of SU-8 reliability in wet thermal ambient for application to polymer micro-optics on VCSELs

We present experimental data on the reliability of SU-8 polymer when used as a core material for the integration of microlenses on vertical-cavity surface-emitting lasers (VCSELs). The respective effects of a hot and humid environment on structural, mechanical and optical properties of this epoxy resist are investigated. High aspect-ratio SU-8 micropillars are found to keep a good surface morphology and a stable optical transmission, as well as a good adherence on the wafer. Thermal cycling is also studied to check material stability under electro-thermal actuation in SU-8 micro-opto-electro-mechanical system (MOEMS). These results are of great importance for the collective integration of low-cost SU-8-based passive or active microlens arrays onto VCSELs wafers for optical interconnects and optical sensing applications.

Polymer optical MEMS integrated on VCSELs for biosensing

We present our recent advances on design and fabrication of polymer optical MEMS that can be directly integrated on VCSELs arrays for dynamic beam focusing. These studies open new insights for the fabrication of compact optical sensors that require a real-time scan of laser beam position.

Liquid crystal based tunable PIN-photodiodes for detection around 1.55-µm

In this work, we report InGaAs based photodiodes integrating liquid crystal (LC) microcells resonant microcavity on their surface. The LC microcavities monolithically integrated on the photodiodes act as a wavelength selective filter for the device. Photodetection measurements performed with a tunable laser operating in the telecom S and C bands demonstrated a wavelength sweep for the photodiode from 1480 nm to 1560 nm limited by the tuning range of the laser. This spectral window is covered with a LC driving voltage of 7V only, corresponding to extremely low power consumption. The average sensitivity over the whole spectral range is 0.4 A/W, slightly lower than 0.6 A/W for similar photodiodes that do not integrate such a LC tunable filter. The quality of the filter integrated onto the surfaces of the photodiodes is constant over a large tuning range (70 nm), showing a FWHM of 1.5 nm.

Soft mold NanoImprint Lithography: a versatile tool for sub-wavelength grating applications

Due to its independency to the substrate used, Soft mold NanoImprint Lithography (S-NIL) is a technique of great interest nin particular for the fabrication of optical devices. We demonstrate a mature pathway for the fabrication of optical filters nfrom the conception to the optical characterization. Those filters can be fabricated on large surfaces (up to 600 diameter nwafers) with high conformity on various substrates. Quality of the transfer will be discussed throughout the process and noptical performances compared to those obtained with classical techniques. In this paper we fabricated tunable spectral nfilters with a grating periodicity down to 260 nm and imprint surfaces up to 600. Physical conformity of the gratings will be ndiscussed in terms of long-range stitching obtained on 600 Si hard mold, dimensional shrinkage during thermal NanoImprint non Zeonor(R) soft mold and conformity towards patterned hard mold throughout the process.

Soft mold NanoImprint Lithography: A versatile tool for sub-wavelength grating applications

Due to its independency to the substrate used, Soft mold NanoImprint Lithography (S-NIL) is a technique of great interest in particular for the fabrication of optical devices. We demonstrate a mature pathway for the fabrication of optical filters from the conception to the optical characterization. Those filters can be fabricated on large surfaces (up to 6″ diameter wafers) with high conformity on various substrates. Quality of the transfer will be discussed throughout the process and optical performances compared to those obtained with classical techniques. In this paper we fabricated tunable spectral filters with a grating periodicity down to 260xa0nm and imprint surfaces up to 6″. Physical conformity of the gratings will be discussed in terms of long-range stitching obtained on 6″ Si hard mold, dimensional shrinkage during thermal NanoImprint on Zeonor® soft mold and conformity towards patterned hard mold throughout the process.

1D crossed gratings for narrow band polarization insensitive reflective filtering

We present experimental characterizations of 1D crossed Guided Mode Resonant Filters (GMRFs) in the near infrared fabricated by nanoimprint lithography. We will show that subwavelength gratings up to 4″ diameter can be fabricated using such techniques. We compare the performances of the GMRFs to the performances of Fabry-Perot filters and discuss the sensitivity to fabrication inhomogeneity of these components.

Tunable graded cavity resonator integrated grating filters

We demonstrated Graded Cavity Resonator Integrated Grating Filters (G-CRIGFs) that are narrowband spectral reflectors, spectrally tunable over more than 40 nm around 850 nm using a spatial gradient. A simple analytical model is introduced and validated experimentally to determine spectral performance of G-CRIGFs from the spectral properties of a standard Cavity Resonator Integrated Grating Filter (CRIGF).