This papers reports on the integration of pixelated multispectral filters on a COTS CMOS detector CMV4000 from CMOSIS. This paper covers several aspects: from de filter conception, to its characterization before and after its integration on the detector. Studies on demosaicing and inter-pixel crosstalk correction will also be presented. The last domain covered by this paper is a space assessment carried out on some assembly in order to check any weakness concerning space environment particularities.
The short wave infrared (SWIR) spectral band is an emerging domain thanks to its large potential. Close to VISible/Near Infrared wavelengths, SWIR images interpretation is made easier for the users. In this spectral region, new opportunities can be found in several fields of applications such as defense and security (night vision, active imaging), space (earth observation), transport (automotive safety), or industry (nondestructive process control, food and plastic sorting). In the frame of this paper, two different developments of the InGaAs technology addressing emerging fields of SWIR imaging are described: pixel pitch reduction and multi-spectral imaging. In pixel pitch reduction the obvious objective is to increase the imaging resolution without jeopardizing system cost. Multi-spectral resolution deals, on the other hand, with interposition of pixelated filters in the optical path right onto SWIR focal plane arrays (FPA) to enable a real time spectral analysis of recorded SWIR images.
The launch of ESA EUCLID mission is foreseen in 36020. The goal of the mission is to understand the nature of the dark energy and to map the geometry of the dark matter. The EUCLID telescope will be equipped with two instruments working in the visible range (VIS) and in the IR range (NISP) to investigate the distance-redshift relationship and the evolution of cosmic structures. The NISP (Near Infrared Spectro-Photometer) will operate in the near-IR spectral range (0.9-2μm) with two observing modes: the photometric mode for the acquisition of images with broadband filters, and the spectroscopic mode for the acquisition of slitless dispersed images on the detectors. NISP is then using four low resolution grisms to acquire spectroscopic image in different orientations to better distinguish the spectra observed and to cover two spectral ranges: 1250-1850nm range, and 920-1300nm range. Since 2010, Laboratoire d’Astrophysique de Marseille is working on the development and the test of the NISP grisms, that are complex optical components. The grism combines four main optical functions: a grism function done by the grating on the prism hypotenuse, a spectral filter done by a multilayer filter deposited on the first face of the prism, a focus function done by the curved filter face of the prism and a spectral wavefront correction done by the grating which grooves paths are nor parallel, neither straight. The NISP instrument is now entering in the integration phase of the proto flight model of the instrument. Therefore, the NISP grism flight models have been manufactured and delivered to the grism wheel assembly for integration by end of 2017. In this paper, we present the optical performance and characteristics of the four EUCLID NISP grisms flight models that have been developed and manufactured by four different industrial partners then integrated and tested by LAM. We focus on the performance obtained on the optical performance of the component; wavefront error of the components, the spectral transmission and groove profiles. The test results analysis show that the grisms flight models for NISP are well within specifications with an efficiency better than 70% on the spectral bandpass and a wavefront error on surfaces better than 30nm RMS. The results on the component show a good control of the manufacturing and integration process despite the difficulties at the beginning of the project to manufacture these components.
In order to study the dark universe (energy and matter), EUCLID space mission will collect near infrared spectra and images of millions of galaxies. This massive measurement survey requires a slitless spectroscopic channel including GRISMs (for “Grating pRISMs”) in NISP (Near Infrared SpectroPhotometer). Very special technical specifications are required for the grating manufacturing: large aperture, low groove frequency and blaze angle, line curvature. In addition, it has to withstand space environment. Therefore, in the frame of a R&D project funded by the CNES, we developed bulk silica gratings in close collaboration with the French company SILIOS Technologies. SILIOS delivered two resin-free blazed gratings with curved lines engraved directly into the fused silica substrate of 80mm and 108mm useful aperture. At LAM, we measured very high optical performances of these prototypes: <80% transmitted efficiency, <30nm RMS wavefront error, groove shape and roughness very close to theory and uniform over the useful aperture. In this paper, we give specifications of these gratings, we describe the manufacturing process developed by SILIOS Technologies, we present briefly optical setups and models allowing optical performances verifications at LAM and we show very encouraging results obtained on the two gratings.
A GRISM, made of a grating on a prism, allow combining image and spectroscopy of the same field of view with the
same optical system and detector, thus simplify instrument concept. New GRISM designs impose technical
specifications difficult to reach with classical grating manufacturing processes: large useful aperture (>100mm), low
groove frequency (<30g/mm), small blaze angle (<3°) and, last but not least, line curvature allowing wavefront
corrections. In addition, gratings are commonly made of resin which may not be suitable to withstand the extreme space
environment. Therefore, in the frame of a R&D project financed by the CNES, SILIOS Technologies developed a new
resin-free grating manufacturing process and realized a first 80mm diameter prototype optically tested at LAM. We
present detailed specifications of this resin-free grating, the manufacturing process, optical setups and models for optical
performance verification and very encouraging results obtained on the first 80mm diameter grating prototype: >80%
transmitted efficiency, <30nm RMS wavefront error, groove shape and roughness very close to theory and uniform over
the useful aperture.
Photoacoustics is a hybrid imaging modality that is based on the detection of acoustic waves generated by absorption of pulsed light by tissue chromophors. In current research, this technique uses large and costly photoacoustic systems with a low frame rate imaging. To open the door for widespread clinical use, a compact, cost effective and fast system is required. In this paper we report on the development of a small compact handset pulsed laser probe which will be connected to a portable ultrasound system for real-time photoacoustic imaging and ultrasound imaging. The probe integrates diode lasers driven by an electrical driver developed for very short high power pulses. It uses specifically developed highly efficient diode stacks with high frequency repetition rate up to 10 kHz, emitting at 800nm wavelength. The emitted beam is collimated and shaped with compact micro optics beam shaping system delivering a homogenized rectangular laser beam intensity distribution. The laser block is integrated with an ultrasound transducer in an ergonomically designed handset probe. This handset is a building block enabling for a low cost high frame rate photoacoustic and ultrasound imaging system. The probe was used with a modified ultrasound scanner and was tested by imaging a tissue mimicking phantom.
Our approach consists in finding the eigenmodes and the complex eigenfrequencies of structures using
a finite element method (FEM), that allows us to study mono- or bi-periodic gratings with a maximum
versatility : complex shaped patterns, with anisotropic and graded index material, under oblique incidence
and arbitrary polarization. In order to validate our method, we illustrate an example of a four layer
dielectric slab, and compare the results with a specific method that we have called tetrachotomy, which
gives us numerically the poles of the reflection coefficient (which corresponds to the eigenfrequencies of
the structure). To illustrate our method, we show the eigenvalues of one- and two-dimensional gratings.
Stellar coronagraphs using circular phase masks are promising concepts dedicated to the image suppression of an
observed bright star in order to enhance the substellar mass companions present in its vicinity, typically 2 λ/D
angular separation. These concepts include a focal plane phase mask which introduces a phase delay on a part
of the stellar image. With an adequate choice of the mask parameters (thickness, diameter), the light going
through the mask and the light going outside the mask will interfere destructively inside the geometric pupil in
the following pupil plane. The light rejected outside this re-imaged pupil will be blocked by a Lyot stop.
Typically, the mask physical size is about λF, where F denotes the f-number of the optical system, and the mask
thickness depends on the required phase shifting. The contrast provided by these concepts is highly related to
the quality of thickness profile of the phase mask and therefore, severe manufacturing tolerances are necessary to
reach the theoretical performance of the corresponding coronagraphic system. In 2007, we designed a Roddier
& Roddier phase mask with a 65 μm diameter and ordered it to GEPI of Paris Observatory which manufactured
it using ion etching process. A roughness of 0.8 nm rms and a transition width of 1% of the mask diameter were
measured with a profilometer for this mask showing the good quality of the mask (N'Diaye et al. 2010).
We pursue our efforts to design and manufacture high quality masks in collaboration with the firm SILIOS. Several
tests of manufacturing procedures are currently realized to reach the best trade-off between mask roughness and
mask transition width. These values, measured in our laboratory with a profilometer, allow us to determine the
best configuration for fabrication. In addition, by knowing the mask profile, we can estimate theoretically the
performance that can be reached.
The unavoidable absorption of thin films used in antireflective coatings forms a permanent bottleneck in the
development of optics for high power laser applications. A valid alternative would be the micro-structuring of the optics
surface, realizing a diffraction grating which emulates the functioning of an Anti-Reflection thin film layer. Due to the
absence of film material, this diffractive structure would not contribute to the overall absorption of the optics. This paper
investigates the practical limits of this strategy, applied to zinc selenide as low absorption infrared substrate material.
Multi-beam laser interference lithography (MB-LIL) is a rapid and cost-effective maskless optical lithography technique
to parallelly pattern periodic or quasi- periodic micro/nano-structured material over large areas more than square
centimetres. An interference pattern between two or more coherent laser beams is set up and recorded in a recording
material of substrate. This interference pattern consists of a periodic series of geometries representing intensity minima
and maxima. The patterns that can be formed depend on the number and configuration of laser beams. This review
introduces the development and application of MB-LIL system for fabrication of micro/nano-structured material. At first,
it surveys various types of MB-LIL methods by classifying different beam configurations. Then the paper shows some
application results for fabrication 2D/3D micro/nano structure arrays by means of interference patterns with multi-exposed
or directly ablation technique. The patterend micro/nano-structure arrays include crossed diffraction grating
array in photoresist, 3D pattern in polymetric photonic crystals, and magnetic nanoarrays in thin film. Finally, an
innovative four-beam LIL system is introduced, which is being developed within the EC-granted project DELILA.
This paper presents a theoretical analysis of formation of 4-beam laser interference patterns for nanolithography.
Parameters of 4-beam interference patterns including the pattern amplitude, period, orientation and uniformity were
discussed. Analytical expressions were obtained for the spatial distribution of radiation of the interfering beams as a
function of their amplitudes, phases, angles of incidence on the sample, and polarization planes with computer
simulation and experimental results.
Laser damage studies are made on a phase mirror used for laser beam shaping in high power laser applications.
The phase mirror is composed of a glass substrate with defined patterns to encode a phase, on top of which a
multilayer mirror is deposited. We describe in this paper the LIDT obtained (at 1064nm, 6ns) and the laser
damage test procedure, adapted to the geometry, that has been used. A morphologic analysis of the damage
sites is made with Nomarski and Atomic Force Microscopy, to obtain information on the damage initiation and
its localization on the structured component. The results are completed with simulations of the electric field
within the multilayer by using a wave propagation computer code. We obtain localization and values of the light
intensification occurring in the structure, that we correlate to experimental measurements.
The Multi-Atmospheric Phase screens and Stars (MAPS) instrument is a powerful tool that has been developed in the framework of the ESO Multi-conjugate Adaptive optics Demonstrator project (MAD). It allows emulating a 3D evolving Paranal-like atmosphere as well as up to 12 sources in a 2 arc minutes field of view, as seen at a Nasmyth focus of one of the VLT. It will be used to perform advanced laboratory tests on MAD before its shipment to Chile. In this paper we present the opto-mechanical design of MAPS. This one simulates the characteristics of the VLT focus and achieves a high Strehl Ratio over the whole Field of View in the visible as well as in the infrared. A curved entrance plate crowded with fibers emulates various stars configurations including real sky asterisms. In order to simulate the atmosphere, three rotating Phase Screens are placed in the beam and conjugated with different altitudes. Those are glass plates dig in their surface in a way that the beam passing through is distorted as it would be by an atmospheric turbulent layer. In this poster we also present the process of research that lead to the choice of a reliable technique to imprint the aberrations into the screens, their properties and expected performance.
The I3O technology based on Titanium ion implantation in silica is proposed for the fabrication of passive compact PLC devices. It is demonstrated that the guided field can be easily tailored to fit standard fibers or can be compatible with the use of bent waveguides having a small radius of curvature.
Refractive index gratings made by titanium ion implantation are studied. Computations using the rigorous differential method and otpical measurements show that our gratings implanted in SiO2 substrates have a diffraction efficiency of typically 2 percent in the 1st order. We propose to insert such grating in multilayer dielectric Fabry-Perot cavities in order to enhance the free space diffraction efficiency. Computations are performed by taking into account the index profile of the implanted zone. The best structure is obtained by optimizing the thickness of the implanted silica layer which is embedded between two mirrors. We study the dependence of optical properties of the structure with respect to various characteristic parameters such as the index profile, the multilayer design, the filling factor of the grating and the incident angle. To demonstrate the feasibility of such components, we focus our attention on an implanted grating embedded in a Fabry-Perot cavity whose mirrors have five dielectric layers. This component reaches a theoretical efficiency of 10 percent in the 1st order. First experimental results are presented.
The consequences of Ti implantation in silica glasses and Ta2O5 layer are studied. It is shown that the optical losses can be low with a variation of the refractive index which can be well controlled. Results on rectangular waveguides and Y junctions are given. Erbium implanted Ta2O5 layers exhibit a luminescent behavior both in the green and in the infra-red. The emission diagram of the coating can be controlled with a multilayer structure.
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