Michel Garrigues

Broadband and compact 2-D photonic crystal reflectors with controllable polarization dependence

Two-dimensional (2-D) compact photonic crystal reflectors on suspended InP membranes were studied under normal incidence. We report the first experimental demonstration of 2-D broadband reflectors (experimental stopband superior to 200 nm, theoretical stopband of 350 nm). They are based on the coupling of free space waves with two slow Bloch modes of the crystal. Moreover, they present a very strong sensitivity of the polarization dependence, when modifying their geometry. A compact (50/spl times/50 /spl mu/m/sup 2/) demonstrator was realized and characterized, behaving either as a broadband reflector or as a broadband transmitter, depending on the polarization of the incident wave. Experimental results are in good agreement with numerical simulations.

Highly selective and compact tunable MOEMS photonic crystal Fabry-Perot filter

The authors report a compact and highly selective tunable filter using a Fabry-Perot resonator combining a bottom micromachined 3-pair-InP/air-gap Bragg reflector with a top photonic crystal slab mirror. It is based on the coupling between radiated vertical cavity modes and waveguided modes of the photonic crystal. The full-width at half maximum (FWHM) of the resonance, as measured by microreflectivity experiments, is close to 1.5nm (around 1.55 microm). The presence of the photonic crystal slab mirror results in a very compact resonator, with a limited number of layers. The demonstrator was tuned over a 20nm range for a 4V tuning voltage, the FWHM being kept below 2.5nm. Bending of membranes is a critical issue, and better results (FWHM=0.5nm) should be obtained on the same structure if this technological point is fixed.

InP-based MOEMS and related topics

Potential applications of InP and related compound semiconductors for the realization of micro-opto-electro-mechanical systems are presented. Specific features and advantages of InP and related material based micromachining show that the optical capabilities of InP-air based microcavities can be considerably enhanced.

Tunable high-finesse InP/air MOEMS filter

We have fabricated Fabry-Pe/spl acute/rot tunable filters based on a multi-air-gap/InP suspended structure. High spectral selectivity is achieved by displacing the resonant cavity into the high index material rather than in air. This configuration reduces the lateral losses of the cavity. The filters feature a bidirectional electrostatic actuation. A spectral linewidth better than 0.15 nm over a tuning range of 40 nm is experimentally demonstrated.

III-V Semiconductor based MOEMS devices for optical telecommunications

The general objective of this presentation is to demonstrate the potential of micro-opto-electro-mechanical system (MOEMS) devices based on III-V semiconductor materials, with special emphasis on applications for telecommunications. Unlike more classical MOEMS devices, such as shutters, rotating mirrors, etc., which utilize the concept of geometrical optics, the III-V semiconductor MOEMS structures presented here through the manipulation of optical interferences. The basic building block consists of a multi-air-gap/suspended-membrane structure which can be micro-machined using multi-layered III-V semiconductor based heterostructures. This building block is very generic in that it can be designed in a variety of ways allowing for the production of a wide range of optical functions. Devices such as tunable filters for WDM systems, tunable photodetectors, and tunable VCSEL, which are based on this generic building block, will be presented.

Paramorphic Growth: A New Approach in Mismatched Heteroepitaxy to Prepare Fully Relaxed Materials

We propose paramorphic growth as a new approach for growing thick, ideally relaxed, epitaxial layers on mismatched substrates. First, a thin seed layer, originally grown pseudomorphically strained on a mismatched substrate coated with a sacrificial layer, is separated by chemical etching from its original substrate and subsequently deposited on the final substrate after being elastically relaxed. Consequently, thick layers, lattice matched to the cubic-relaxed seed layer, can be grown epitaxially without the introduction of any structural defects. The validity of this approach is demonstrated by growing fully relaxed In0.65Ga0.35As thick layers on 300×300 µm2 platforms deposited on an InP substrate, using molecular beam epitaxy.

Fabrication of ultrathin and highly flexible InP-based membranes for microoptoelectromechanical systems at 1.55 /spl mu/m

In this letter, tunable microcavities have been fabricated to evaluate their tunability in dependence on the membrane thickness. The membrane thickness has been decreased from 615 nm down to a record thickness of 123 nm yielding in a maximum mechanical tunability of 15.15 nm/V/sup 2/. Furthermore, a three-period /spl lambda//4 InP/air-gap high reflective mirror (R > 99.8% at 1.55 /spl mu/m) with a record wide stopband of more than 1100 nm has been fabricated. These results are achieved thanks to specific metal-organic vapor-phase epitaxy growth parameters.

Optical and mechanical design of an InP-based tunable detector for gas-sensing applications

It has been shown that it is possible to produce highly selective and continuously tunable filters based on InP material using surface micro-machining. One interesting issue for this kind of device is NIR absorption spectroscopy for gas analysis. In this work, we present the design of a Resonant Cavity Enhanced tunable photodiode for operation around 1.6 micrometer near the C-H stretching frequency for organic molecules such as benzene. For this type of application, the required performances are a large tunability, a high selectivity, a weak temperature dependence and a constant absorption level over the tuning range. To meet these requirements the micro-system must be optimized from the optical and mechanical point of view. The RCE photodiode structure is composed of an air/InP bottom Bragg mirror and a dielectric top Bragg mirror. The cavity includes an air-gap and the InP layer containing a p.i.n. photodiode with absorption in a few strained InGaAs Quantum Wells (QWs). Tuning is obtained by actuating electrostatically the air micro-cavity thickness. A prospective device meeting the optical requirements has been designed. It is based on an absorption region composed of three InGaAS QWs conveniently located in the cavity standing wave pattern in order to optimize the resonant absorption over the tuning range. Optical simulation shows that an absorption level greater than 50% can be achieved. The temperature dependence of the resonance wavelength can be kept below 0.08 nm/(Delta) T(C degrees) at room temperature. The mechanical properties of the micromachined structure has been investigated using finite element analysis.

An indium phosphide-based near-infrared MOEMS microspectrometer for agri-food and environmental monitoring

The general aim of this project is to realize optical microsystems for NIR spectroscopy (1.5 μm to 2 μm) using the InP/InGaAs material system. We have designed an integrated microspectrometer based on a long-wavelength strained InGaAs quantum well RCE photodiode combined with a wavelength tunability function (MEMS concept). The weak absorption of the QWs is enhanced by embedding the quantum wells into a micromachined tunable vertical resonator that consists of multiple InP/air-gap alternate layers that form both the DBR reflectors and the electrostatically tunable air-gap cavity. The devices are fabricated using a specific MOEMS process based on selective wet etching of an InP/InGaAs epitaxial layer stack grown by MOVPE. The small size and low cost of these microsystems pave the way to promising industrial applications, such as non-invasive biological analysis, on-line industrial process analysis and hyperspectral imaging. The paper focuses on critical design and process issues in order to accommodate residual stresses in the suspended membranes while preserving a suitable tuning range. We present a specific design optimized for the monitoring of sugar concentration in water. The selected spectral range for this analysis is comprised between 1650 nm and 1750 nm.

A phase-matching and pseudoresonance-enhanced design for tunable micromachined photodetectors

A novel optical design is provided for developing tunable, active microoptoelectromechanical system (MOEMS) devices. The active layer is placed outside and on the top of an asymmetric Fabry-Perot resonant cavity and the selectivity is obtained by controlling the relative phase of the incident and reflected waves, a mechanism which we call the phase-matching and pseudoresonance-enhancement (PMPRE). We propose a practical design for a tunable MOEMS photodetector based on this PMPRE principle.