DUV photolithography, as the major process of nanofabrication, typically requires high volumes of toxic chemicals within resist formulation, solvent and developer. In this context, alternative chemistries to current petroleum-derived photoresists are proposed to reduce environmental impacts. Chitosan represents a bio-sourced resist allowing water-based patterning processes free of organic solvent and alkali-based developers, by substitution with a green solvent (deionized (DI) water). This paper present last stepwise process in the patterning integration with a chitosan-based resist. Preliminary results using a 300 mm pilot line scale at CEA-Leti demonstrate patterns resolution down to 800 nm along with plasma etch transfer into Si substrate. Finally, the environmental impact through life cycle analysis (LCA) of the whole process based on chitosan resist is assessed and compared to conventional solvent-based processes.
Biopolymers represent natural, renewable and abundant materials. Their use is steadily growing in various areas (food, health, building …) but, in lithography, despite some works, resists, solvents and developers are still oil-based and hazardous chemicals. In this work, we replaced synthetic resist by chitosan, a natural, abundant and hydrophilic polysaccharide. High resolution sub-micron patterns were obtained through chitosan films as water developable, chemically unmodified, positive tone mask resist for an eco-friendly electron beam and deep-UV (193 nm) lithography process. Sub-micron patterns were also successfully obtained using a 248 nm photomasker thanks to the addition of biosourced photoactivator, riboflavin. Patterns were then transferred by plasma etching into silica even for high resolution patterns.
The seminal work of R.B. Wood (1902), who discovered anomalies in the reflection spectra of sub-wavelength metallic gratings, triggered the field of plasmonics, where ultra-thin metallic sheets laterally structured on a sub-wavelength scale, so called metallic meta-surface, are under operation. The goal of the field has extended considerably in the last decades and has aimed at arbitrary control over the amplitude, phase and polarization… of light waves at the sub-wavelength scale. All-dielectric meta-surfaces consisting in nano-structured thin films of high index dielectric material, are attracting much attention, owing to their capability to achieve the same goal as their metallic counterpart, yet with an enhanced efficiency (especially for the manipulation of strong optical resonances), being freed from significant energy dissipation as encountered in metallic nano-structures. All dielectric meta-surfaces have been around for quite a while, but were named differently (photonic crystal dielectric membranes or high index contrast gratings). Unless rare exceptions, the literature reports on structures with non-broken vertical symmetry. In the present contribution we emphasize that breaking the vertical symmetry of all-dielectric meta-surfaces provides a widely enhanced degree of freedom for the control of spatial routes and spectral characteristics of light, which depends, to an essential extent, on the local density of photonic states in the thin nano-structured dielectric film. As an enlightening illustration, we concentrate on a dielectric meta-surface formed by two super-imposed identical evanescently coupled gratings, with adjustable gap distance and lateral alignment. We show that this remarkably simple meta-surface can provide any local density of photonic states from zero (Dirac cone) to infinity (ultra-flat zero curvature dispersion characteristics), as well as any constant density over an adjustable spectral range. Exemplifying applications will illustrate the great potential of this new approach.
Surface addressable Photonic Crystal Membranes (PCM) are 1D or 2D photonic crystals formed in a slab waveguides where Bloch modes located above the light line are exploited. These modes are responsible for resonances in the reflection spectrum whose bandwidth can be adjusted at will. These resonances result from the coupling between a guided mode of the membrane and a free-space mode through the pattern of the photonic crystal. If broadband, these structures represent an ideal mirror to form compact vertical microcavity with 3D confinement of photons and polarization selectivity. Among numerous devices, low threshold VCSELs with remarkable and tunable modal properties have been demonstrated. Narrow band PCMs (or high Q resonators) have also been extensively used for surface addressable optoelectronic devices where an active material is embedded into the membrane, leading to the demonstration of low threshold surface emitting lasers, nonlinear bistables, optical traps...
In this presentation, we will describe the main physical rules which govern the lifetime of photons in these resonant modes. More specifically, it will be emphasized that the Q factor of the PCM is determined, to the first order, by the integral overlap between the electromagnetic field distributions of the guided and free space modes and of the dielectric periodic perturbation which is applied to the homogeneous membrane to get the photonic crystal. It turns out that the symmetries of these distributions are of prime importance for the strength of the resonance. It will be shown that, by molding in-plane or vertical symmetries of Bloch modes, spectrally and spatially selective light absorbers or emitters can be designed. First proof of concept devices will be also presented.
In this presentation we emphasize that, within the variety of parameters usable for the design of HCGs, the transverse (vertical) symmetry properties of HCGs provide a power-full joystick for the dispersion engineering of guided mode resonances. We concentrate on asymmetric HCGs designed to accommodate guided mode resonances with ultra-flat zero-curvature dispersion characteristics (or photons with ultra-heavy effective mass), as well as with Dirac cone shaped linear dispersion characteristics. Examples of the great potential of this family of asymmetric HCGs will include the development of a platform for polaritonic devices and the production of micro-lasers particularly suited for hybrid III-V / silicon heterogeneous photonic integration, along CMOS compatible technological schemes.
Selective etching of pre-stressed multi-layered structures releases intrinsic stresses creating flexible macroscopic shapes (rolls, spirals, tubes…). Combining mechanical and photonic concepts, we develop an experimental approach by controlling material composition, mask design and etching process in order to obtain prescribed macroscopic 3D hollow optical micro-cavities. New photonic microstructures are proposed for an efficient light trapping in low index media. Cylindrical hollow cavities formed by bending a photonic crystal membrane are designed. Using numerical simulations, strong confinement of photons is demonstrated for very open resonators. The resulting strong light matter interaction can be exploited in optical devices comprising an active material embedded in a low index matrix like polymer or even gaz.
KEYWORDS: Solar energy, Waveguides, Dispersion, Atmospheric modeling, Photonic crystals, Nanophotonics, Wave propagation, Nanotechnology, Solar cells, Control systems
The comprehension and manipulation of the spectral characteristics of photonic structures is of great interest for a vast bunch of applications, in particular for energy efficiency. In this paper we focus on a perturbation model capable of providing insight and control on the resonances that are supported by high index contrast gratings.
The mid-infrared (mid-IR, wavelength range between 2 and 10 μm) is of great interest for a huge range of applications
such as medical and environment sensors, security, defense and astronomy. I will give a broad overview of the different
activities recently launched in INL Lyon, in close collaboration with several French and Australian institutions, under
the umbrella of “Mid-IR integrated photonics” with a particular focus on novel integrated sources for the Mid-IR
including hybrid III-V semiconductors on SiGe sources, thermal sources and nonlinear sources.
Recently, we developed a new family of 3D photonic hollow resonators which theoretically allow tight confinement
of light in a fluid (gaz or liquid): the photon cages. These new resonators could be ideal for sensing applications
since they not only localize the electromagnetic energy in a small mode volume but also enforce maximal overlap
between this localized field and the environment (i.e. a potential volume of nano-particles). In this work, we will
present numerical and experimental studies of the interaction of a photon cage optical mode with nano-emitters. For
this, PbS quantum dot emitters in a PDMS host matrix have been introduced in photon cages designed to have
optimal confinement properties when containing a PDMS-based active medium. Photoluminescence measurements
have been performed and the presence of quantum dot emitters in the photon cages has been demonstrated.
We propose a new approach for the 3D control of light in real 3D optical micro-resonators that can be assimilated
to 'cages', where photons are efficiently trapped. The main attractive feature of this photon cages lies in their
ability to result in a considerable enhancement of the electromagnetic field in the central part of the cage,
that is in the air region, opening the way to new sensing or trapping of nanoparticles in fluidic (gas or liquid)
ambiances. Fabrication of three dimensional structures consists in exploiting the process of elastic relaxation of
patterns formed in pre-stressed multi-layer structures. The final shape of these objects can be predetermined
by the distribution of the deformations in the various semiconductor layers, imposed during their epitaxial
growth, before their freestanding from the substrate by selective etching. We will present the basic concepts
and fabrication we exploit to confine photons in air using spherical structures based on progressive relaxation
of pre-stressed InGaP/InAsP bilayer films. It is worthwhile to notice that the formed microstructures exhibit
patterns with dimensions compatible with optical operation in the visible/NIR wavelength range.
We present the design and the fabrication of a dual-wavelength micro-photonic resonator combining a photonic crystal
membrane (PCM) and a vertical Fabry Perot (FP) cavity where the former is embedded in the latter. A strong optical
coupling between a PCM Γ-point Bloch mode and a FP mode at the same frequency can be used to provide a dual-wavelength
device with a frequency difference which is analysed in terms of modes overlapping. We propose and
demonstrate a process flow that can be used to provide such a device. Optical reflectivity characterisation is presented
for a monolithic device and photoluminescence dual-wavelength spontaneous emission is demonstrated in an extended
vertical cavity. Finally the dual-mode laser emission stability is examined with numerical Monte Carlo simulation.
We propose a novel concept of dual-wavelength microlaser based on the association of a Photonic crystal membrane and
a Fabry-Perot vertical cavity. The goal is to fabricate a surface addressable compact microlaser exhibiting stimulated
emission for two optical modes with about 1THz frequency difference.
We report on design, simulation and fabrication of ultimate and compact 3D close-geometries optical microcavities.
These are based on the extension of the so-called 2.5D nanophotonic approach where a quasi 3D control of the photons
has been soon demonstrated by our group. A tight control of photons, spectrally and spatially, in a small air region
inside a circular regular pattern of high index material-based nanopillars is demonstrated when adjusting the number of
pillars, their diameters and the diameter of the pillar-circle. Bottom-up approach based on InP nanowires grown by
molecular beam epitaxy and top-down approach based on high aspect ratio anisotropic etching have been developed for
fabricating these optical microcavities.
We propose a new approach to realise surface addressable active photonic crystal devices. High Q-factor and low optical
volume can be achieved combining lateral control of the mode size by a local modulation of the planar photonic crystal
parameters, and vertical confinement assisted by a Bragg reflector. The low Q-factor of a 1D PC band edge mode can be
increased up to 40000, while the optical mode volume is limited at the wavelength scale. Experimental results on laser
operation achieved using this strategy in the case of an InP-based PC membrane bonded onto a Si/SiO2 Bragg reflector
will be presented.
Vertical Fabry Perot cavities (VFPCs) have enabled the realization of devices of great interest, like filters,
photodetectors, VCSELs. In traditional VFPCs, the optical feedback is provided by two distributed Bragg Mirrors
(DBRs). However, DBRs present two major drawbacks: they are generally rather thick mirrors, and they do not allow for
a very high control on the lateral losses of the VFPC. We propose the use of a novel type of mirror, the photonic crystal
slab mirror (PCM) which is able to overcome these limitations. In fact, we demonstrate that PCMs are ultra-thin single-layer
mirrors that exhibit a very high reflectivity, and that allow also for a very tight control of the lateral velocity of
photons, by a convenient engineering of the PCM Bloch modes. This concept will lead to the realization of ultra-compact
and highly resonant VFPCs, interesting for VCSELs, non-linear optics-based devices, imaging, highly sensitive
detectors, or 3D optical communication routing.
Compact photonic crystal mirrors (PCM) formed in suspended InP membranes are theoretically and experimentally
studied under normal incidence. They are based on the coupling of free space waves with slow Bloch modes of the
crystal. These mirrors provide high-efficiency and broadband reflectivity (stop-band superior to 400nm), when involving
two slow Bloch modes of the crystal. They allow also for an accurate control of the polarization.
These PCMs can be used in new photonic devices, where they replace DBR mirrors. The authors report on the
demonstration of a compact and highly selective (Q>1000) tunable filter at 1.55&mgr;m, using a Fabry-Perot resonator
combining a bottom micromachined 3-pair-InP/air-gap Bragg reflector with a top InP/air PCM. Micromechanical tuning
of the device via electrostatic actuation is also demonstrated over a 20nm range for a maximum 4V tuning voltage. The
active version of this device is also considered: a PCM-VCSEL is studied, combining a solid 40 quarter wavelength
InP/InGaAlAs DBR with a top PCM. First experimental results show a high Q-factor (around 2000) compatible with a
laser regime. We finally demonstrate in this paper a vertical-cavity Fabry-Perot filter with ultimate compactness,
associating two PCMs.
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.
We describe the design and fabrication of novel Fabry-Perot tunable filters based on a deformable structure composed of surface micromachined indium phosphide (InP) / Air Distributed Bragg Reflectors (DBRs). As compared to conventional designs, superior spectral selectivity has been achieved by displacing the resonant cavity into the high index material (InP) rather than in air. This configuration is expected to reduce significantly the lateral losses of the cavity. The filters feature also a novel doping structure for bi-directional electrostatic actuation. We present simulations
and experimental results that demonstrate the effectiveness of this high index cavity concept for improving the selectivity of small dimension tunable MOEMS filters. The devices are fabricated using a multiple InP-air-gap MOEMS technology based on the sacrificial etching of an InP / InGaAs stack A spectral linewidth better than 0.15 nm over a tuning range of 40 nm is experimentally demonstrated. Design improvements for doubling the tuning range are also proposed.
1D and 2D compact photonic crystal reflectors on suspended InP membranes are theoretically and experimentally studied under normal incidence. They are based on the coupling of free space waves with slow Bloch modes of the crystal. We first present monomodal 1D photonic crystal reflectors. Then, we focus on multimodal 1D reflectors, which involve two slow Bloch modes of the crystal, and thus present broadband high-efficiency characteristics. 2D broadband reflectors were also investigated. They allow for an accurate control on the polarization dependence of the reflection. A compact (50 μm x 50 μm) 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 stop-band superior to 200nm, theoretical stop-band of 350nm). These photonic crystal slabs can be used in new photonic devices as reflectors, where they can replace multilayer Bragg mirrors. 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 μm). 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.
In this paper we describe a new class of tunable interferometric MOEMS devices able to perform tunable wavelength selective beam steering. These GEMOEMS (Grating Enhanced Micro Opto Electro Mechanical Systems) devices comprise a diffraction grating etched on top of a selective and tunable vertical interferometric MOEMS filter. The underlying filter reflects the transmitted orders with controllable amplitude and phase so that they interfere with the reflected orders and modulate the diffraction efficiency distribution into these reflected orders. Our first demonstrator is a 1X2 optical switch designed for operation over the C-band (1530-1560 nm). The diffraction efficiency in the reflected orders is controlled by changing the distance from the grating to a Bragg mirror via an electrostatic actuation of the suspended grating membrane. The devices are fabricated using a multiple InP-air-gap MOEMS technology based on the sacrificial etching of an InP / InGaAs stack. The grating is realized using an electron-beam lithography step. The simulated performances on the C-band show low insertion loss (less than 0.3dB), low ripple (0.15dB), reasonable cross-talk (-15dB), and an estimated switching time around 10μs. These characteristics make such an optical switch a solid contender of a rotating mirror, with the advantage of a much faster response. In this presentation, we introduce the general physical principles of GEMOEMS and describe the design, simulation, fabrication and preliminary experimental results for a simplified 1x2 optical switch. We also propose other prospective devices such as add-drop filters.
Photonic devices based on 2D PCs have so far been principally targeted at operation in a wave-guided configuration and at providing the basic building blocks for Photonic Integration. The problem of optical losses, which are considered as hindering the operation of 2D photonic integrated circuits based on 2D PC, can be approached from a completely different perspective: instead of attempting to confine the light entirely within waveguide structures, the 2D structures can be deliberately opened to the third space dimension by controlling the coupling between wave-guided and radiation modes. It is shown in this paper that interaction of radiative and guided modes through a photonic crystal, especially under conditions where the later correspond to extrema of the dispersion characteristics of the photonic crystal, results in resonance phenomena which can be used practically for the development of new classes of devices, e.g. combining photonic crystal and MOEMS (Micro Opto Electro Mechanical Systems) structures.
We present here the general trends for designing and fabricating PC-MOEMS structures and first experimental results on demonstrators which are now under investigations in our group.
The general objective of this presentation is to demonstrate the great potential of InP-membrane photonic devices, with a special emphasis on applications for Optical Communications. Various classes of devices will be presented, which are based on MOEMS (Micro-Opto-Electro-Mechanical) structures, or 2 dimensional (2D)photonic crystals (PC) or a combination of both, according to a '2.5-dimensional' approach, which should broaden considerably the combinations of functionality beyond those presently contemplated with the two first classes. For the MOEMS devices, the basic building block consists in a multi-air-gap/suspended-membrane structure, which can be micro-machined using multi-layered III-V semiconductor based heterostructures : tunable filters will be presented for illustration. For PC devices, the basic building block consists in an InP (and related material) membrane including a 2D PC formed by a lattice of holes : the membrane is either suspended in air or bonded onto low index material, e.g. silica on silicon substrate, in the prospect of heterogeneous integration with silicon based microelectronics. Examples of devices will be presented, specifically micro-lasers based on 2D PC micro-cavities as well as on 2D in plane Bloch modes (2D Distributed-Feed-Back micro-laser). For the '2.5-dimensional' photonic structures, it will be shown that the multi-layer membrane approach, where individual layers or combinations of layers may be structured across to form a 2D PC, is naturally suitable for this purpose. Examples of devices will be presented (2D PC surface emitting micro-sources, switching devices combining vertical MOEMS multi-layer membrane structures and 2D PC).
In this paper, we present a new concept of tunable active Micro-Opto-Electro-Mechanical System (MOEMS) microdevice for specific applications in the 1.3-2.5 micrometers wavelength range such as near infrared spectroscopy or optical telecommunications. The proposed optical structure can be used for the realization of tunable wavelength selective devices (photodetectors or emitters). The device uses a radically new optical design which separates the detector (or emitter) from the filter but place it on top of the filter. As compared to the existing micro-mechanical tunable devices, this concept does present two main advantages such as the improvement of the optical spectral response (forward and backward traveling of the optical waves through the active part) and relaxation of the technological constraints for fabrication (planar monolithic integration of the active component with post-process micromachining). We present here the design, the optical simulations and the fabrication procedure of a first demonstrator consisting in an optically pumped wavelength selective and tunable light emitting diode. The gain active region comprises InAs quantum wires designed for light emission aro7und 1500 nm. The MOEM structure is made of InP/air gap layers. We have obtained an increase of the spontaneous emission by a factor of about 40 and tuning range about 60 nm for actuation voltages up to 15 V.
We report on the combination of the well established 1.55 micrometers monolithic VCSEL's concept with the Micro-Opto-Electro- Mechanical System (MOEMS) technological breakthrough in order to develop a novel tunable laser device for wavelength division multiplexing optical systems. Technological issures are presented for fabricating surface micromachined InP-based tunable VCSELs.
The general objective of this presentation is to demonstrate the potential of Micro-Opto-Electro-Mechanical (MEOMS) devices based on III-V semiconductor materials, with a special emphasis on applications for Telecommunications. Unlike more classical MOEMS devices, such as shutters, rotating mirrors, etc..., which utilize the concept of geometrical optics, III-V semiconductor MOEMS structures presented here operate via the manipulation of optical interferences. The basic building block consists in a multi-air-gap/suspended membrane structure which can be micromachined using multi-layered III-V semiconductor based heterostructures. This building block is very generic in that it can be designed in a variety of manners allowing for the production of a wide range of optical functions. As a matter of fact the wavelength dependence of the transmittance or of the reflectance depends strongly on the number, the thickness and the successive air- gap/semiconductor pairs, and, given the high index contrast between air and semiconductor, a wide choice of spectral responses can be obtained with very few of them. In addition, a wide choice of electro-opto-mechanical modulations of the spectral responses can be produced by moving vertically, via electrostatic actuation, one or several suspended membranes independently. One single device can be designed in order to achieve one or several functions. Such devices as tunable filters for WDM systems, tunable photodetectors, tunable VCSEL, which are based on this generic building block, will be presented.
Micromachined planar spiral inductors and transformers have been largely proposed for RF applications, using MEMS processes. Q-factors and self-resonant frequencies have been significantly increased by suspending such structures. However, thermal and mechanical properties are somewhat compromised. In this paper, a complete analysis of such parameters is presented through extensive finite element method (FEM) simulations. Partially released structure is proposed to avoid these troubles.
The state of the art of III-V semiconductor based MOEMS is presented with a special emphasis on InP and related materials. It is shown that the MOEMS technology can enhance considerably the capabilities of optical micro-cavities, which are considered as a major component for optical signal processing and light generation. Illustrations of the potential of III-V MOEMS are given in the fields of optical telecommunications. Design and fabrication of highly selective and widely tunable optical filters for wavelength division multiplexing systems are presented. These devices are monolithic and are based on surface micro-machining technology. They combine a variety of very attractive properties such as low control power, low insertion loss, tunability, small bandwidth no polarization dependence, simple fiber coupling, no memory effects and reasonable tuning speed. Fiber to fiber transmission characterizations of packaged filters are presented, including bit error rate measurements. Future prospects implying the use of multi-air-gap MOEMS structures as a basic building-block for a wide variety of routing photonic devices are proposed.
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.
We report here micro-transmission measurements of a highly selective and a widely tunable optical filter at 1.55 micrometers . This filter is formed by a (lambda) /2 air cavity sandwiched between two 3.5 alternances InP-air Bragg mirrors. Reflectors and air cavity are fabricated by selective micro- machining of InGaAs sacrificial layers. Measurements have shown a very large wavelength tuning of 108nm for only 4.7V and a filter linewidth of 0.6 nm. Such performances have been possible because of the high reflectivity, large bandwidth and good optical confinement of the InP-air Bragg mirrors.
We demonstrate NIR (1.8 micrometer - 2.3 micrometer) resonant photo-detectors based on inter-band (Ecl- Ehhl) absorption in strain compensated, indium rich, InGaAs quantum wells (QW). Extremely low room temperature dark current densities are achieved by reduction of the active layer thickness combined with low defect density of the pseudomorphic strain compensated QWs. The weak absorption of the QW is enhanced by embedding the quantum well into a vertical resonant cavity. We present the experimental results for a demonstrator designed for a wavelength of 2 micrometer. The device, based on a single In0.83Ga0.17As quantum well and tensile strained barriers for strain compensation, exhibits a selectivity of 9 nm and 18% quantum efficiency. InP/InGaAs and Si/SiO2 material systems are used for the bottom and top distributed Bragg reflectors (DBR) of the cavity, with 20 pairs and 2 pairs respectively. The semiconductor structure is grown by MOCVD. The top Si/SiO2 DBR is deposited after fabrication of p-i-n planar photodiodes. Typical dark current densities are lower than 10-7 A/cm2 at -2 V bias. Conditions for extension of the operating wavelength up to 2.3 micrometer have been obtained experimentally using InAs/GaAs superlattice deposition to increase the thickness of the strained QW. A prospective tunable detector based on an actuable micro-machined air cavity and air/InP bottom DBR is proposed.
InP-based microstructuring optimization is presented in order to develop the fabrication of highly selective and widely tunable optical filter for WDM applications. Technological constraints such as etching selectivity, etching anisotropy, sticking phenomena and residual stress are listed and their respective practical solutions are demonstrated. Opto-electro-mechanical simulations combined with this technological 'know how' have yielded to the fabrication of 8 air gaps InP-based microstructures suitable for production of optical filter demonstrators.
We present an exact numerical technique for analyzing Bragg reflectors. Bragg reflectors can be used as narrow-band distributed feedback reflectors that reflect at the center of the grating stopband and transmit at frequencies to either side. THese reflectors can be sued as highly selective pass-band filters. These reflectors can be also used as highly selective pass-band filters. Our structure that is realized by the LEAME consists of microcavities inserted in a waveguide suspended in air. These cavities ar air voids placed periodically in a high-refractive index semiconductor material. Recently Zhang et al. realized a broad-band Bragg reflector by placing a 1D array of air holes in a dielectric waveguide without taking into account the power loss in their simulation. Power loss due to radiation at abrupt discontinuities limits the performance of these microcavities.Unlike the other analytical methods no physical approximations are made throughout the entire analysis, so it may be used to analyze any periodic dielectric structure regardless of the geometry or strong discontinuities. Our exact technique uses the local normal modes of the structure to form a transfer matrix for the whole structure. For this reason our method can be used to evaluate exactly the transmitted, reflected and radiated power. We will present later the result of the numerical simulations for a Bragg reflector with few steps.
The design and the fabrication of vertical InP-based micro- opto-electro-mechanical devices are reported. These are based on micromachined III-V semiconductor structures realized by selective removal of adapted sacrificial layers in order to produce Fabry-Perot resonant microcavity. Continuous wavelength running of 50nm around 1.55 micrometers for a 15 volt bias actuation has been demonstrated. Resonant peak full width at half maximum of about 10 nm at 1.5 micrometers has been performed on a InP/air gap multilayered interferometric filter. The integration of absorbing layers inside the cavity will allow us to realize resonant cavity enhanced photonic devices with thinner, and therefore faster, photodetector structures with high quantum efficiencies.
We have studied actuable suspended beams that form vertical optical resonant cavities. They are fabricated by sacrificial layers etching techniques on InP. They can be used as tunable optical filters for telecommunication applications. In this paper, we report optical characterizations of those devices. We have used micro reflectivity and optical profilometer measurements to make those characterizations. We have developed a micro- reflectivity experimental setup which uses the confocal principle. We have shown the deformation of the suspended beams and the variation of the reflectivity response induced by electrostatic actuation of the devices.
Microoptoelectromechanical (MOEMS) systems with InP based micromechanics are proposed for devices with wide tuning ranges in the optical wavelengths where InP optoelectronics are normally used. To evaluate if these InP based micromechanical structures may be strong enough the mechanical strengths of surface micromachined epitaxial InP micro beams are evaluated. Reactive ion etching (RIE) with CH4:H2:H2Ar is used to structure the beams. A sacrificial InGaAs layer is below the InP microstructures and selectively etched by HCl:H2O2:H2O in ratios 1:1:10 to release the InP beams. Sublimation of tert-butanol is used to dry the micro structures. The RIE conditions are shown to be of large importance, since the induced surface defects are here the dominant reasons for fracture. Bending strength values up to 3.1 GPa were measured, i.e. much higher than for the strongest construction steel. Weibull statistics show that it is possible to make micromachines for typical MOEMS applications with acceptable loss in yield due to fracture probability, i.e. with a fracture probability of 0.0001 for 100 MPa maximum bending stress.
GaAs is for many people regarded as being too difficult and expensive for a sensor or actuator application. It is a fact that GaAs is not cheap in comparison with silicon and also cannot currently be produced with as high purity and few crystalline defects as Si. Therefore, it is preferable to use GaAs where and when one can take advantage of the good properties that it possesses. Possible applications could be where high working-temperature, high frequency, integrated optoelectronics or piezoelectricity are demanded. As for silicon, gallium arsenide based microsystems should be manufactured on industrial production lines, with an additional post-processing for microsystem specific structures. Thus, using the same approach applied to silicon, CMP investigates gallium arsenide micromachining techniques using the Philips Microwave Limeil HEMT and the Vitesse MESFET foundry processes. This paper treats the advantages and disadvantages of gallium arsenide as a micromechanical material in comparison with silicon and quartz. The MESFET and HEMT compatible micromachining will also be detailed.
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