Microlenses, and especially microlens arrays (MLA), are commonly used as stand-alone optical components, for beam homogenization and shaping. Or integrated as wafer-level optics (WLO), either on top of light sources for beam shaping, or on top of light or image sensors as light concentrators. Many techniques are available to originate the microlens shape: laser ablation, grayscale lithography, two photon absorption, etc. One common way is to pattern photoresist pillars by photolithography and to melt (reflow) them. We report new advances in thermal reflow mastering addressing its intrinsic limitations and expanding the design capabilities of reflow-based MLAs.
Plug and play fiber coupling at the wafer-scale is highly relevant to interconnect photonic integrated circuits (PICs), switches and multiplexer for short to long range communication, as well as chiplets in new chip design with optical interconnects. A new solution is presented being compact, low-loss, and in plane, adaptable to a wide range of fibers. It is based on beam-shaping reflecting elements monolithically fabricated with integrated comp like fiber alignment structures. Successful assembly of a 12-fiber ribbon is demonstrated with excess losses as low as 0.35 dB. The processes and methods are highly homogeneous and scalable.
The need for free-form micro-optics (FFMO) is constantly growing in well-established business segments including flatpanel displays, solid-state illumination, thin-film solutions for security/anti-counterfeiting applications, AR/VR wearables, and automotive headlights. However, the high access barriers to pre-commercial production capabilities prevent companies, especially SMEs, from exploiting the FFMO technology in commercial products and hinder further innovation. To lower the barrier to access FMOA technology, CSEM and their partners have established the PHABULOuS Pilot Line. PHABULOuS offers a unique one-stop shop for all requests for prototyping and manufacturing of free-form microoptics services, from pilot to full-scale production. To mature the FMOA technology, the Pilot Line members have developed high precision origination techniques complemented by industry-fit, high-throughput up-scaling technologies for the cost-effective production of large-area FFMO. At the core of these technologies is Step & Repeat UV imprinting. The method has been successfully demonstrated in the PHABULOuS project for high precision upscaling of rigid small masters to flexible tools with 600 x 300 mm2 dimensions using a standard UV-NIL stepper modified for this purpose. Since there is currently no commercial Step & Repeat machine on the market able to replicate free-form micro-structures on large area with the required precision, CSEM has developed a high precision S&R UV-replication platform designed specifically to this purpose. Combined with the expertise in design and optical simulation, origination, and electroforming, the newly developed Step&Repeat capabilities at CSEM will strengthen the PHABULOuS Pilot Line offerings.
In next generation space and ground-based instrumentation for Earth and Universe Observation, new instrument concepts include often non planar gratings. Their realization is complex and costly. We propose a new technology for designing and realizing convex blazed gratings for high throughput spectrographs. For this purpose, the requirements are driven by a Digital-Micromirror-Device-based (DMD) MOS instrument we are developing, called BATMAN. The two-arm instrument is providing in parallel imaging and spectroscopic capabilities. The objects/field selector is a 2048 x 1080 micromirrors DMD, placed at the focal plane of the telescope; it is used as a programmable multi-slit mask at the entrance of the spectrograph. The compact Offner-type spectrograph design contains a low density convex grating to disperse light. For optimization of the spectrograph efficiency, this convex grating must be blazed. A blazed reflective grating has been designed with a period of 3300 nm and a blaze angle of 5.04°, and fabricated into convex substrates with 225 mm radius of curvature and a footprint diameter of 63.5 mm. The blaze is optimized for the center wavelength of 580 nm within the spectral range of 400 – 800 nm. Such grating has been fabricated by using lithography, angular Ar ion etching, transfer of the blazed grating from a flat surface onto a convex substrate with a flexible stamp, etched into the substrate by RIE etching. and finally coated with a silver-based layer. With a final 7° blaze angle over the whole surface, efficiency close to 90% on the 1st diffraction order at 700nm has been obtained, measured on BATMAN spectroscopic arm. An optimized device with the exact required blaze angle would reach the same efficiency and be centered on the mid of 400-800nm wavelength band: its realization is on-going. The wavefront error of the diffracted beam will also be optimized. The grating brings a significant contribution in the total amount of straylight at instrument level. Their straylight level remains a critical issue, and its reduction by specific and controlled implementation of improvements in manufacturing process is a challenge to tackle. Straylight measurement has been done and shows a BRDF cosθ values of 10-8 sr-1 on the optical surface and 10-7 sr-1 on the structured features. This new type of non-planar reflective gratings will be the key component for future high throughput spectrographs in space missions
Microlenses, and especially microlens arrays (MLA), are commonly used as stand-alone optical components, for beam homogenization and shaping. Or integrated as wafer-level optics (WLO), either on top of light sources for beam shaping (e.g., on micro-LED or vertical-cavity surface-emitting laser – VCSEL), or on top of light or image sensors as light concentrators. In the latter case, each microlens of the MLA, also known in the photography domain as On-Chip Lens (OCL), redirects the light to the active volume of the pixel located underneath. This increases the external quantum efficiency (EQE) by increasing the pixel effective fill-factor, especially for front-illuminated image sensors and their limited fill-factors. We report various MLA optimizations and the concentration factors achieved when addressing challenges encountered with advanced photon detectors such as single-photon avalanche diodes (SPAD) or silicon photon multiplier (SiPM). For example: substrate size and type (wafer, bare or packaged die), optical transmission range from NUV to NIR, microlens geometrical parameter space (diameters from micrometers to millimeters) and stability to temperature, vibrations and irradiation (UV, gamma and proton).
Freeform micro-optical arrays (FMOAs) can overcome some limitations of rotationally symmetric optical components. The manufacturability assessment for FMOA designs containing many freeform elements is demanding. We present computer-aided design (CAD) tools that analyze FMOA designs for manufacturing constraints. They 1) extract the height (Sag) and 2) local slope while highlighting areas beyond manufacturing limits, 3) extract the minimum tool radius and 4) convert CADs into ray traceable solids using NURBS for performance comparison of the actual micro-structure to the design. Critical parameters can be identified early, reducing time-consuming and costly adjustments later.
Microlenses replicated on front-illuminated single-photon avalanche diodes (SPAD) or back-illuminated CMOS image sensor are found to be stable to temperature variations, exposure to humidity, mechanical shocks and vibrations, as well as irradiation by gamma rays (for space applications). They highly improve the effective fill-factor, on front-illuminated SPAD-based image sensors, and the parasitic light sensitivity on a back-illuminated CMOS image sensor. Their broad transmission spectrum from NUV to NIR, combined with the wide geometrical space available to fabricate microlenses on various active substrates (wafer or die down to 2×2 mm2), make them suitable to a wide range of quantum photonics applications.
Quantum sensing devices such as atomic clocks enable unmatched precision in various area of metrology. Initially bulky laboratory devices, it is of great interest to miniaturize them to lower their energy consumption and deploy them in many embedded and mobile systems. To allow a dramatic cost reduction and miniaturization, CSEM developed and tested with success miniature atomic clocks based on wafer-level processes. On top of the control electronics and the atomic vapor cells, the optical design, the optical components and their assembly have been fully redesigned to be wafer-level fabricated. To achieve low aspect ratio and integrated optical management, thin glass planar waveguides have been implemented allowing to transport and beam shape the interrogating beam going from and to the atomic vapor gas cell. This proved a much simpler wafer scale assembly process, a monolithic construction less prone to single component alignment issues and provide much more compact atomic clocks
In next generation space and ground-based instrumentation for Earth and Universe Observation, new instrument concepts include often non planar gratings. Their realization is complex and costly. We propose a new technology for designing and realizing convex blazed gratings for high throughput spectrographs. For this purpose, the requirements are driven by a Digital-Micromirror-Device-based (DMD) MOS instrument we are developing, called BATMAN. The two-arm instrument is providing in parallel imaging and spectroscopic capabilities. The objects/field selector is a 2048 x 1080 micromirrors DMD, placed at the focal plane of the telescope; it is used as a programmable multi-slit mask at the entrance of the spectrograph. The compact Offner-type spectrograph design contains a low density convex grating to disperse light. For optimization of the spectrograph efficiency, this convex grating must be blazed. A blazed reflective grating has been designed with a period of 3300 nm and a blaze angle of 5.04°, and fabricated into convex substrates with 225 mm radius of curvature and a footprint diameter of 63.5 mm. The blaze is optimized for the center wavelength of 580 nm within the spectral range of 400 – 800 nm. Such grating has been fabricated by using lithography, angular Ar ion etching, transfer of the blazed grating from a flat surface onto a convex substrate with a flexible stamp, etched into the substrate by RIE etching. and finally coated with a silver-based layer. With a final 7° blaze angle over the whole surface, efficiency close to 90% on the 1st diffraction order at 700nm has been obtained, measured on BATMAN spectroscopic arm. An optimized device with the exact required blaze angle would reach the same efficiency and be centered on the mid of 400-800nm wavelength band: its realization is on-going. The wavefront error of the diffracted beam will also be optimized. The grating brings a significant contribution in the total amount of straylight at instrument level. Their straylight level remains a critical issue, and its reduction by specific and controlled implementation of improvements in manufacturing process is a challenge to tackle. Straylight measurement has been done and shows a BRDF cosq values of 10-8 sr-1 on the optical surface and 10-7 sr-1 on the structured features. This new type of non-planar reflective gratings will be the key component for future high throughput spectrographs in space missions.
Photonics integration continues to be a main driver for innovation in multiple aspects, including wafer-scale integration, new materials, sub-micron alignment of components and protection from harsh environment. We show cost-effective fabrication technologies of micro-optical components by UV wafer-scale replication into chemically stable polymers. Furthermore, for simplified fiber coupling and packaging, a novel 90° optical interconnect is presented, integrated with self-alignment structures. Replicated, space compliant microlenses on packaged CMOS imagers show improved light sensitivity by a factor 1.8. A laser based, low stress bonding process is explored to generate wafer-scale hermetic enclosures for harsh environment applications ranging from space to implants.
Regular arrays of quasi-micro-beads have been fabricated via a modified microlens array fabrication process. Thanks to surface energy modification and control, microlens have been obtained with shapes being significantly more than hemispherical, realizing regular arrays of quasi-micro-beads. This fabrication method is the only reported technique - to the best of our knowledge - enabling the massive parallelization of super-resolution imaging via nanojet thanks to the regularity of the array. Results of super-resolution imaging using these arrays will be reported and discussed.
The recent new development of Meta Resonant Waveguide-Gratings (RWG) allows adapting the unique optical properties of Resonant Waveguide-Grating away from the specular reflection and direct transmission, in which they were confined in the last 35 years. Exploiting Wood's second type of anomalies, the so-called resonance anomalies in meta-devices based-on horizontal guided-mode resonances (GMR) create excellent transparency out of the resonance condition. Meta RWG can be engineered to exhibit highly selective and tunable optical properties to realize as examples monochromatic diffraction gratings, monochromatic metalenses and meta-couplers, while their nanostructures are made very compact and with flat aspect-ratio.
Examples of new optical combiners implementation for augmented and mixed reality will be presented. A roadmap for future developments will be sketched as well as their advantages and limitations, for which they will be compared to surface relief grating, volume holograms and visible-light metasurfaces.
The author will focus on the implementation of Meta-RWG in augmented and mixed reality systems addressing the many challenges of such see-through near-eye display system, such as large field of view, large eye-box with a sufficient eye-relief distance, high transparency, high compactness and low-weight, high pixel angular resolution as well as a mitigated vergence accommodation conflict or a non single/fix focal plane architecture.
Resonant waveguide gratings (RWGs) are thin-film structures, where coupled modes interfere with the diffracted incoming wave and produce strong angular and spectral filtering. The combination of two finite-length and impedance matched RWGs allows the creation of a passive beam steering element, which is compatible with up-scalable fabrication processes. Here, we propose a design method to create large patterns of such elements able to filter, steer, and focus the light from one point source to another. The method is based on ellipsoidal mirrors to choose a system of confocal prolate spheroids where the two focal points are the source point and observation point, respectively. It allows finding the proper orientation and position of each RWG element of the pattern, such that the phase is constructively preserved at the observation point. The design techniques presented here could be implemented in a variety of systems, where large-scale patterns are needed, such as optical security, multifocal or monochromatic lenses, biosensors, and see-through optical combiners for near-eye displays.
A novel thin-film single-layer structure based on resonant waveguide gratings (RWGs) allows to engineer selective color filtering and steering of white light. The unit cell of the structure consists of two adjacent finite-length and cross-talking RWGs, where the former acts as in-coupler and the latter acts as out-coupler. The structure is made by only one nano-imprint lithography replication and one thin film layer deposition, making it fully compatible with up-scalable fabrication processes. We characterize a fabricated optical security element designed to work with the flash and the camera of a smartphone in off-axis light steering configuration, where the pattern is revealed only by placing the smartphone in the proper position. Widespread applications are foreseen in a variety of fields, such as multifocal or monochromatic lenses, solar cells, biosensors, security devices and seethrough optical combiners for near-eye displays.
Plasmonics involves the interaction of light with metallic structures at the nanoscale, which enables in particular the generation of strong reflection and absorption effects in the visible and near infrared range. The fabrication of plasmonic nanostructures using ultra-violet (UV) imprint and thin metallic coatings is reported. Wafer-scale fabrication and process compatibility with cost-efficient roll-to-roll production are demonstrated, which paves the road towards an industrial implementation. The color, phase, polarization and direction of the transmitted light are controlled by tuning the process parameters and the symmetry of the nanostructures. A family of devices is presented, for which the potential for sensing, filtering, anticounterfeiting and optical security is evaluated.
We present an innovative disposable endoscope based on extra flat flexible polymer slabs used as multimode
waveguides. The waveguides are compatible with low-cost roll-to-roll production technologies and can be easily
customized by patterning, coating and printing techniques according to the specifications of the target application. In
order to couple the light (i.e. the illumination beam and the imaging beam) in and out of the waveguide, diffractive
subwavelength gratings are used. These nano-scale optical structures enable an efficient and controlled light trapping by
total internal reflection, thus minimizing the distortion effects generated by the rough edges. Nano-patterning is obtained
using established techniques (i.e. hot embossing and/or UV casting) that are compatible with industrial roll-to-roll
production lines or plastic injection molding.
Unique features of these innovative endoscopes are i) the achievable very thin form that can be reduced to thicknesses
below 200 μm, ii) the ability to record lateral images with respect to the endoscope direction, iii) the ability to image
samples (e.g. tissues, tiny objects) in direct contact with the polymer slab, with a minimum imaging distance equal to
zero, and iv) the access to high volume fabrication techniques that can enable the production of low-cost disposable
endoscopes.
A possible device implementation is demonstrated and tested, which consists of a flat line-scanning endoscope enabling
the acquisition of 1D images in monochromatic illumination and the reconstruction of 2D images by scanning. Images
taken with such a disposable endoscope are discussed and the related technological constraints such as manufacturing
tolerances, image distortion, scattered light and signal to noise ratio are further described. Finally, advantages and
disadvantages with respect to other endoscopic techniques will be discussed, thus demonstrating the potential of this
innovative approach for endoscopic applications in very confined volumes.
Metallic nanostructures interact strongly with light through surface plasmon modes and many application fields
have been proposed during the past decade, including light harvesting, sensing and structural colors. However,
their implementation for the industry requires the development of up scalable and cost effective manufacturing
processes. The fabrication at wafer scale of plasmonic nanostructures and metamaterials using nano imprint
lithography is reported. After structuring, the evaporation of various plasmonic materials are performed with a
tilt angle with respect to the substrate, which increases the light interactions with the different metallic layers as
well as enlarges the design possibilities. A step and repeat process is used to increase further the area of nanostructured
surface. The measured optical properties of the fabricated structures show a very good agreement
compared to numerical calculations using the rigorous coupled wave analysis. These numerical calculations together
which structural characterization, increase the process control and enable the design of the nanostructures
for specific applications. In particular, nanostructures with a shape similar to split ring resonators and which
support high order plasmonic modes showing Fano resonances are shown to be promising for sensing applications.
The structures were designed in such a way to have a strong spectral response in the blue/green region of the
visible spectrum. Examples of refractive index sensors and stretch sensors were finally discussed.
The fabrication by nanoimprint lithography of large-area plasmonic and photonic sensing platforms is reported. The plasmonic nanostructures have the shape of split–ring resonators and support both electric dipole and quadrupole modes. They carry the spectral signature of Fano resonances. Their near-field and far-field optical properties are investigated with an analytical model together with numerical calculations. Fano-resonant systems combine strong nanoscale light confinement with a narrow spectral line width, which makes them very promising for biochemical sensing and immunoassays. On the other hand, chemical sensors based on resonant gratings are obtained by patterning a sol-gel material, evaporating a high refractive index semiconductor and coating with a chemically sensitive dye layer. By exposition to a liquid or an invisible gas such as ammonium, the change in absorption is detected optically. An analytical model is introduced to explain the enhancement of the signal by the resonant grating, which can be detected with the naked eye from a color change of the reflected light.
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