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International audience; In this work, the thermo-optical properties of nematic liquid crystals are investigated through localized reflectance spectra measurements performed on a tunable LC-filter. The final aim is to insert such LC in the cavity of a tunable VCSEL device, in which local self-heating due to optical or electrical pumping must be taken into account. We demonstrate that, whereas standard LC E7 is not suited for real device operation, the maximal operating temperature of QYDPLC-36 LC is 95°C, with a birefringence at 1.55 μm higher than 0.18 at 60°C.

International audience; In this work we investigate a tunable 850nm laser based on a hybrid combination of a liquid crystal micro-cell and a half GaAs VCSEL. The target application is optical coherence tomography. The inherent tolerances of the hybrid technology, the presence of metals in the cavity and the need for a pure extraordinary mode lasing make challenging the optical design of this laser. Hence, VELM, a full 3D and vectorial VCSEL optical solver, is utilized to understand loss mechanisms and provide an optimized design.

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.

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.

Beam control of VCSELs (Vertical Cavity Surface Emitting Lasers) is a key topic to integrate these laser diodes in microsystems for instrumentation or biomedical application [1]. We report here on a simple method to control dynamically the beam shape of VCSELs devices. Our approach is based on an electro-thermal actuator including a polymer membrane, a heating electrode and a polymer microlens (fig.1 a). The operation principle is the following: the laser beam waist position can be tune thanks to the membrane vertical displacement induced by varying the applied current. Optical and thermo-mechanical optimizations of membrane geometry have been carried out. These studies point out that a vertical deflection of 2µm should be obtained with a thermal gradient of 100°C [2], leading to a corresponding waist displacement of few hundred microns.

Nowadays, there are two types of sensors to detect the low luminous flux, PMT (PhotoMultiplier Tube) and Geiger-APD (Geiger Avalanche PhotoDiode). The Geiger-APD is a component on Silicon that was developed in the early 90s to detect very low light flux, as is currently the PMT. The main advantages of these devices on the PMT are a very high sensitivity to light (single photon), a very high time resolution (

This paper reports on a generic approach for the development of polysilicon diodes on glass wafers for thermal sensing and control applications. The capabilities of polysilicon diodes as thermal sensors are demonstrated on glass wafers with good thermal sensitivities about 40mV/oC. A simple experimental set-up has been developed to evaluate the potentialities of these devices in microfluidics operating conditions. First encouraging results of temperature detection are presented.

A new VCSEL design is proposed to combine emission and detection, based on a standard mesa process. Lateral guided optical signal is detected through a Schottky contact. Temperature, time-response and geometry-dependent characterizations are presented.

In this paper, we present results on modelling, fabrication and characterization of oxide-confined VCSELs for short-distance alternative emission and photodetection at 820 nm. In the present designed single-cavity GaAs-based device, the buried oxide layer is not only used to obtain a single mode laser beam but also to enable decoupling between a small surface emission, limited by the aperture and a large surface detection, limited by the internal diameter of the top electrodes. The selective wet etching was found to improve simultaneously the detection sensitivity and the differential quantum efficiency without damaging the active surface.

The thermal resistance of power devices is determined by means of a 3D heat dissipation modeling. In particular, we have evaluated the thermal resistance of Heterojunction Bipolar Transistors (HBTs) in which GaAs substrate is replaced by a substrate exhibiting a higher thermal conductivity like Diamond, Aluminium Nitride or Silicon. Thus, through use of the electrothermal model we can predict an increase of about 50 percent of the RF power at 10 GHz and at the compression point when the power device is transferred onto a diamond substrate. The different techniques we are performing to transfer the HBT active layers onto host substrates are described.