Browsing by Subject "Microlenses"

Now showing 1 - 3 of 3

Open Access
High-efficiency low-crosstalk dielectric metasurfaces of mid-wave infrared focal plane arrays
(American Institute of Physics Inc., 2017) Akın, O.; Demir, Hilmi Volkan
High-resolution compact-size focal plane arrays (FPAs) suffer the fundamental geometrical tradeoff between the optical resolution (pixel size miniaturization) and the optical crosstalk (spillover of neighboring pixel focusing). For FPAs, our previously reported metallic metasurfaces reached an unprecedented level of crosstalk suppression. However, practical utilization of these metallic microlens arrays has proved to be intrinsically limited due to the low device efficiency (of the order of 0.10) resulting from the fundamental absorption losses of metals and their cross-polarization scheme. Exceeding this limit, here we show highly efficient microlens designs enabled by dielectric metasurfaces for mid-wave infrared (MWIR) operation. These dielectric MWIR FPAs allow for a substantially high device efficiency over 0.80 without compromising the optical crosstalk performance. Systematically studying dielectric nanoantennas of silicon nanodisks that do not dictate the cross-polarization scheme using full-wave solutions, we found that the optical crosstalk is suppressed to low levels ≤ 3.0% while sustaining the high efficiency. A figure-of-merit (FoM) defined for the device performance as the focusing efficiency per optical crosstalk times the f-number achieves 84, which is superior to all other types of MWIR FPAs reported to date, all falling below a maximum FoM of 70. These findings indicate that the proposed approach can pave the way for the practical usage of metasurface microlens arrays in MWIR.
Open Access
Metasurface microlens focal plane arrays and mirrors
(2017-01) Akın, Onur
Lenses, mirrors and focal plane arrays (FPAs) are among the key components a ecting the functionality, performance and cost of electro-optical (EO) systems. Conventional lenses rely on phase accumulation mechanism for bending wavefront of light. This mechanism and the scarcity of transparent materials result in high-complexity, high-cost and bulky EO systems. Conventional mirrors, on the other hand, are limited by the electromagnetic properties of metals and cannot be used in certain EO systems. Also, conventional FPAs su er the fundamental tradeo between the optical resolution and optical crosstalk. Metasurfaces, relying on the concept of abrupt phase shifts, can be used to build a new class of optical components. However, for realizing metasurfaces, optical resonators should cover a full 0-to-2 phase shift response with close to uniform amplitude response. In this thesis, to develop these metasurface optical components, nanoantennas that act as unit cell optical resonators were designed and modeled. A design methodology for building and optimizing these metasurfaces using the designed nanoantennas was developed. After obtaining the metasurfaces, we successfully addressed the problems of optical crosstalk in mid-wavelength infrared (MWIR) FPAs and weak eld localization in mirror contacts. Full-wave simulations con rmed major crosstalk suppression of the microlens arrays to achieve 1% optical crosstalk in the proposed metasurface FPAs, which outperforms all other types of MWIR FPAs reported to date. However, due to intrinsic absorption losses in metals, the resulting device e ciency was low ( 10%). To solve this problem, metallic nanoantennas were replaced by dielectric nanoantennas and the focusing e ciency was dramatically increased to 80%. This is the rst account of high-e ciency low-crosstalk metasurface MWIR FPAs. Full-wave simulations also con rmed the strong eld localization of metasurface mirrors that can impose a phase shift response close to 0 . The ndings of this thesis indicate that metasurface FPAs and mirrors are highly promising for future EO systems.
Open Access
Optical reconstruction of transparent objects with phase-only SLMs
(Optical Society of American (OSA), 2013) Stoykova, E.; Yaraş F.; Yontem, A.Ö.; Kang H.; Onural L.; Hamel P.; Delacrétaz, Y.; Bergoënd I.; Arfire, C.; Depeursinge, C.
Three approaches for visualization of transparent micro-objects from holographic data using phase-only SLMs are described. The objects are silicon micro-lenses captured in the near infrared by means of digital holographic microscopy and a simulated weakly refracting 3D object with size in the micrometer range. In the first method, profilometric/tomographic data are retrieved from captured holograms and converted into a 3D point cloud which allows for computer generation of multi-view phase holograms using Rayleigh-Sommerfeld formulation. In the second method, the microlens is computationally placed in front of a textured object to simulate the image of the textured data as seen through the lens. In the third method, direct optical reconstruction of the micrometer object through a digital lens by modifying the phase with the Gerchberg-Saxton algorithm is achieved. © 2013 Optical Society of America.