Polymer micro-optics and VCSEL-based MOEMS

VCSELs are now strategic light sources for optical communications as well as for instrumentation or sensing applications. Despite a limited far-field beam divergence, these sources have more and more to be associated with micro-optical components to enhance their performances or to increase their integration in systems.

Microlens fabrication

We have developed a new deposition technique based on a microcantilever-based spotter to fabricate polymer microlenses arrays. Spherical microlenses with high  optical quality were demonstrated using a home-made thermocurable epoxy polymer (collaboration TONA-IR-VUB). Microlenses sizes achievable with this novel method have been shown to be well suited for VCSEL beam collimation.

VCSELs collimation with integrated microlenses

We have fabricated self-aligned microtips on VCSEL devices using novel near infra-red photopolymers sensitive to the laser wavelength. (NIR Optics project : collaboration with IS2M Mulhouse and LNIO Troyes). This approach is totally compatible with a post-processing process. Using this method, a focusing effect has been observed on a lens self-formed on a singlemode VCSEL operating at 760nm. Potential applications concern the development of novel types of optical probes for near-field optics or high density optical data storage.

(left) Fabrication principle (Right) SEM image of a polymer microtip self-written at the centre of a singlemode VCSEL by NIR self- photopolymerization [Appl. Phys. Lett. 96, 2010]

Polymer MOEMS for tunable lens integration on VCSELs

We have developed a low-cost polymer-based technique for the fabrication of a Micro-Optical-Electrical-Mechanical Systems (MOEMS) in view of dynamic focusing of VCSEL beam.
A simple method based on a SU-8 double exposure is proposed for the collective integration of small footprint transparent suspended membranes on vertical laser diodes arrays.  A complete optimization of the full circular membrane has been led thanks to a thermo-mechanical simulation tool (COMSOL). Our study shows that a 2.7 µm vertical displacement is possible with an applied thermal gradient of 100°C. This value is suited for a significant active beam vertical tuning given by optical modelling (coll. FOTON)
We recently demonstrated that this kind of MOEMS can be thermally actuated with a vertical displacement of ~0.2 µm/W over a maximal range of 8 µm. As a wide range of initial gaps between the membrane and the laser source can be chosen, this approach opens new insights for dynamic control of VCSEL beam waist position and for tunable VCSELs fabrication. [B. Reig et al, Journal of Micromechanics and Microengineering, 2012]