Wavefront measurement

This study investigated the relationship between high-order aberrations (HOAs) and accommodative dysfunctions by analyzing their changes with accommodation. Understanding this relationship is important for understanding the mechanisms underlying these conditions. Sixtythree subjects were divided into five groups: control, infacility of accommodation (INFA), excess of accommodation (EA), insufficiency of accommodation (INSA), and symptomatic without dysfunction (SWD). Variations in root-mean-square (RMS) of the 3rd, 4th, 5th, and 6th orders and HOAs, and fluctuations of RMS HOAs, were measured using a Shack-Hartmann aberrometer at different accommodative stimuli and during residual accommodation after their removal, in the following order: 0.00 D, 1.00 D, 0.00 D, 2.45 D, 0.00 D, 4.73 D and 0.00 D. The SWD group showed a significant increase in RMS HOAs during accommodation and residual accommodation. In contrast, the EA group showed an improvement in the ocular optical quality at higher stimuli. Different patterns of changes in the 3rd, 4th, 5th, and 6th orders were observed across all groups, and fluctuations of RMS HOAs increased significantly in the SWD group during accommodation and residual accommodation. These distinct patterns of aberration changes in different accommodative dysfunctions suggest a potential link between their underlying mechanisms, providing insights that may aid their earlier diagnosis and improved management.

When a news item is first published (the first wave of news), it spreads rapidly but with limited reach, analogous to a short wavelength. As the dissemination continues (the second wave of news), the speed of propagation decreases, but the reach (wavelength) increases, covering a broader audience. This study aims to draw an analogy between the propagation of water waves generated by a dropped object and the dissemination of news within communication and broadcasting systems. This study presents a conceptual framework that draws an analogy between the physical propagation of water waves and the dissemination of news within communication and broadcasting systems. By comparing the initial rapid spread of information to high-speed, short-wavelength waves and the subsequent slower, broader dissemination to longer-wavelength waves, the study highlights the dynamic and layered nature of information flow. The formation of waves in water serves as an effective analogy for the propagation of news in media and communication systems. When a news item is published, it resembles the formation of waves, where the first wave represents rapid propagation with a short wavelength, while subsequent waves propagate more slowly but with longer wavelengths. This analogy between wave propagation in water and the dissemination of news offers a novel conceptual lens for understanding patterns of information diffusion. By applying physical principles such as wave speed, wavelength, and dispersion to communication dynamics, we can gain deeper insights into the mechanisms by which news propagates through various phases. While this model provides a compelling theoretical framework, further research is needed to validate its applicability through empirical analysis and to explore its implications for media theory, communication strategy, and public information flow.

Wireless power transfer between an external electromagnetic (EM) source and implanted dipoles into human body can be greatly assisted by employing a matching part atop of the skin. Two different approaches are proposed: one incorporating lossless layers that minimize the reflections and another dealing with active metasurfaces that boost the transmissivity. Obviously, the performance is higher in the latter scenario since gain media are involved; however, even with passive layers, significant enhancement in the coupling between the two radiators is achieved. These coupling scores exhibit substantial robustness under the condition of misaligned dipoles, a feature that renders them suitable to operate under experimental imperfections. The proposed concept has been experimentally demonstrated at bluetooth frequencies leading to strong enhancement of power transmission, even when the radiation patterns of the two antennas are heavily misaligned. Accordingly, the reported designs can be utilized in biomedical setups that call for fast and reliable wireless communication: from healthcare monitoring and biosensing to real-time drug delivery and bioimaging. INDEX TERMS Biomedical communication, Electromagnetic coupling, Implants, Metasurfaces, Wireless power transfer.

A novel approach based on the two-channel moiré deflectometry has been used to measure both wave-front and transverse component of the Poynting vector of an optical vortex beam. Generated vortex beam by the q-plate, an inhomogeneous liquid crystal cell, has been analyzed with such technique. The measured topological charge of generated beams are in an excellent agreement with theoretical prediction.

An approach based on the two-channel moiré deflectometry has been used to measure both wavefront and transverse component of the Poynting vector of an optical vortex beam. Generated vortex beam by the q-plate, an inhomogeneous liquid crystal cell, has been analyzed with such technique. The measured topological charge of generated beams are in an excellent agreement with theoretical prediction.

Background: This study aimed to compare objective refractive errors and keratometry measurements obtained using the Nidek OPD-Scan II aberrometer/topographer and Topcon KR 8900 autorefractokeratometer. Methods: The right eye medical records of 176 patients aged 18-35 years who were admitted to our clinic as refractive surgery candidates were tested for refractive status and keratometry measurements with a Nidek OPD-Scan II aberrometer/topographer and a standard table-top autorefractokeratometer (Topcon KR 8900) before and after the induction of cycloplegia. Patients who had undergone any eye surgery and had hereditary, ectatic, or acquired corneal pathology were excluded. Refractive data were compared as spheres, cylinders, spherical equivalents, and power vectors before and after the induction of cycloplegia. Flat and steep keratometry (K1-K2) readings were recorded in diopters (D) and axis degrees, respectively, for each eye. Results: The spherical, cylindrical, spherical equivalence, J0-J45 vector values and K1-K2 readings (D, axis) between the two devices were statistically significant before and after the induction of cycloplegia (p<0.05). Bland-Altman analysis identified mean differences (95%CI of limits of agreement) of 0.77 (-0,57 to 2,11) in sphere, 0.74 (-0,54 to 2,01) in spherical equivalent,-0,07 (-0,41 to 0,26) in J0 vector, 0,06 (-0,31 to 0,43) in J45 vector,-0,16 (-0,66 to 0,33) in K1,-0,23 (-0,79 to 0,33) in K2 values before induction of cycloplegia. Conclusion: The refractive and keratometry results of the Nidek OPD Scan II system and Topcon KR 8900 standard table-top autorefractokeratometer are not interchangeable in healthy adult population before and after induction of cycloplegia.

We report on the optical design of an infrared (0.85-1.8 µm) pyramid wavefront sensor (IRPWFS) that is designed for the 6.5m MMT telescope adaptive optics system using the latest developments in low-noise infrared avalanche photodiode arrays. The comparison between the pyramid and the double-roof prism based wavefront sensors and the evaluation of their micro pupils' quality are presented. Our analysis shows the use of two double-roof prisms with achromatic materials produces the competitive performance when compared to the traditional pyramid prism, which is difficult to manufacture. The final micro pupils on the image plane have the residual errors of pupil position, chromatism, and distortion within 1/10 pixel over the 2×2 arcsecond field of view, which meet the original design goals.

Purpose:  To show the feasibility of modified point‐diffraction interferometry for the qualitative analysis and accurate quantification of phase aberrations of eye lenses in vitro.Method:  Optical aberrations of crystalline lenses in vitro were evaluated by means of a point‐diffraction interferometer modified to increase its dynamic range.Results:  Analysis of the Zernike polynomials, , which contribute significantly to the wavefront aberration of two representative crystalline lenses (a mammalian and a fish lens) is presented. In the mammalian case, the in vitro experiments were performed for pig lenses. It is shown that spherical aberration, astigmatism, coma, and trefoil of different radial orders, n, are the only modes contributing significantly to wavefront aberration, i.e., aberrations with azimuthal frequencies, m, greater that three can be regarded as noise. In the case of fish lenses (sea bream), we show that the technique allows quantification of the deviation from the sph...

While developing deformable mirrors for adaptive optics, and while studying scintillation, we also tested the method of curvature sensing and different variants of it. By very carefully adjusting the optics we were able to discern variations on the scale of one nanometer. The limited dynamic range of the detectors and various optical artifacts caused systematic and random errors of 5-8 percent. Calibration of the measurements turned out to be a difficult issue as well. One of the main problems with non-atmospheric measurements was vignetting. We suspect that strong atmospheric scintillation might cause similar problems in curvature sensing, because of light scattered outside the measurement aperture, leading to errors in the estimated wave front phase. We looked into measuring turbulence along the optical path, by comparing field data of both Hartmann-Shack and intensity sensors collected under similar conditions. It seems that some of the turbulence can be tracked back to its range, but this is still being tested. If so, it might be possible to ~orrect it using multi-conjugate optics and reduce significantly scintillation effects. Scintillation can also be removed artificially by correcting a scaled-up version of the turbulence at a scaled-down conjugate distance and vice versa.

It is often if interest to measure the centroid of a light intensity pattern in order to deduce physical properties. Examples are the Hartmann-Shack sensor, which measures the wavefront slopes, and position sensors. We investigate whether amplitude changes of the incoming electromagnetic field can affect the location of the centroid and we show that the effect is strongly dependent on the relative size of the diffraction pattern in relation to the lenslet size. We show that if the phase varies slowly in space, and the focal spot size relative to the centroid integration area approaches zero-this variation does not affect the centroid. This is a consequence of symmetry properties of the Fresnel operator. We then show that when the focal width is not infinitely small, changes in the field amplitude can exacerbate distortion of the centroid results.

Wavefront shaping is increasingly being used in modern microscopy to obtain high-resolution images deep inside inhomogeneous media. Wavefront shaping methods typically rely on the presence of a “guide star” to find the optimal wavefront to mitigate the scattering of light. However, the use of guide stars poses severe limitations. Notably, only objects in the close vicinity of the guide star can be imaged. Here, we introduce a guide-star-free wavefront shaping method in which the optimal wavefront is computed using a digital model of the sample. The refractive index model of the sample, that serves as the input for the computation, is constructed in situ by the microscope itself. In a proof of principle imaging experiment, we demonstrate a large improvement in the two-photon fluorescence signal through a diffuse medium, outperforming state-of-the-art wavefront shaping by a factor of two in imaging depth.

Light scattering in biological tissue significantly limits the accessible depth for localized optical interrogation and deep-tissue optical imaging. This challenge can be overcome by exploiting the time-reversal property of optical phase conjugation (OPC) to reverse multiple scattering events or suppress turbidity. However, in living tissue, scatterers are highly movable and the movement can disrupt time-reversal symmetry when there is a latency in the OPC playback. In this paper, we show that the motion-induced degradation of the OPC turbidity-suppression effect through a dynamic scattering medium shares the same decorrelation time constant as that determined from speckle intensity autocorrelation - a popular conventional measure of scatterer movement. We investigated this decorrelation characteristic time through a 1.5-mm-thick dorsal skin flap of a living mouse and found that it ranges from 50 ms to 2.5 s depending on the level of immobilization. This study provides information o...

A technique for the design of conformal metasurfaces with two spatially disconnected space wave ports connected by a surface wave is presented. The passive and lossless metasurface absorbs the incident plane wave at port 1, converts it perfectly into a surface wave which transports the energy along an arbitrarily shaped/curved metasurface to port 2, then reradiates the captured power as a radiated field with control over its amplitude and phase. Since the incident field is seen to disappear at the input port and reappear at a spatially dislocated port as a new formed beam, the field can be said to have teleported. The metasurface consists of a single, conformal, spatially variant, impedance sheet supported by a conformal grounded dielectric substrate of the same shape. It is modeled using integral equations. The impedances of the sheet are optimized using the adjoint variable method to achieve the perfect teleporting operation from a passive and lossless metasurface. Possible applications include channel optimization for cellular networks, inexpensive power harvesting, sensing, around-the-corner radar, and cloaking.

Focused and controllable optical delivery beyond the optical diffusion limit in biological tissue has been desired for long yet considered challenging. Digital optical phase conjugation (DOPC) has been proven promising to tackle this challenge. Its broad applications, however, have been hindered by the system's complexity and rigorous requirements, such as the optical beam quality, the pixel match between the wavefront sensor and wavefront modulator, as well as the flatness of the modulator's active region. In this paper, we present a plain yet reliable DOPC setup with an embedded four-phase, non-iterative approach that can rapidly compensate for the wavefront modulator's surface curvature, together with a non-phase-shifting in-line holography method for optical phase conjugation in the absence of an electro-optic modulator (EOM). In experiment, with the proposed setup the peak-to-background ratio (PBR) of optical focusing through a standard ground glass in experiment can be improved from 460 up to 23,000, while the full width at half maximum (FWHM) of the focal spot can be reduced from 50 down to 10 μm. The focusing efficiency, as measured by the value of PBR, reaches nearly 56.5% of the theoretical value. Such a plain yet efficient implementation, if further engineered, may potentially boost DOPC suitable for broader applications.

Strongly aberrated wavefronts lead to inaccuracies and nonlinearities in holography-based modal wavefront sensing (HMWS). In this contribution, a low-resolution Shack-Hartmann sensor (LRSHS) is incorporated into HMWS via a compact holographic design to extend the dynamic range of HMWS. A static binary-phase computer-generated hologram is employed to generate the desired patterns for Shack-Hartmann sensing and HMWS. The low-order aberration modes dominating the wavefront error are first sensed with the LRSHS and corrected by the wavefront modulator. The system then switches to HMWS to obtain better sensor sensitivity and accuracy. Simulated as well as experimental results are shown for validating the proposed method.

A new method for designing holographic optical elements is presented. The method is based on matching the grating-spacing profile of the recording light interference pattern to the desired grating-spacing profile. We show that for designing near-field holograms, in which the optical images involved are close to the hologram aperture, the grating-matching technique is superior to the well-established aberrationbalancing method introduced by Latta ͓Appl. Opt. 10, 609 ͑1971͔͒.

The modulated pyramid wavefront sensor is known for its high sensitivity and adjustable dynamic range. The need for mechanically moving parts in a modulated pyramid wavefront sensor can be overcome by using the recently proposed digital pyramid wavefront sensor. In this paper, a digital multi-faceted pyramid wavefront sensor is demonstrated with the use of a reflecting phase-only spatial light modulator. The four-pupil digital pyramid wavefront sensor with 4-facets is extended to 6 and 8-facets. It is noted from the experiments performed under identical low-noise conditions that the performance of the wavefront sensor in terms of the root mean square wavefront error remains nearly the same in cases of four, six and eight pupil configurations. Under the circumstances elucidated here, the results of simulations indicate that in the presence of scatter noise, the pyramid wavefront sensor with greater number of pupils could lead to an improvement over the standard four-pupil pyramid wavefront sensor. Noise from scattering makes the choice of optimal modulation radius critical while sensing in open-loop adaptive optics systems.

This article presents results on the scattering and absorption behavior of lossy impedanceboundary spheres and cubes. The albedo (the ratio between the scattering and extinction cross sections) of these scatterers turns out to be a very insightful quantity in this respect. The strongly nonlinear dependence of albedo on the size of the objects is illustrated and compared with the albedo of dissipative penetrable spheres. The shape of the object seems to have surprisingly little effect on the albedo. Furthermore, the effect of losses on the resonance behavior of small impedance-boundary spheres is analyzed, leading to the observation that the dipolar mode vanishes from the albedo spectrum, while higher order multipoles remain visible. This resembles a similar phenomenon earlier shown to appear in connection with small plasmonic scatterers.

The use of a large apex-angle axicon for common-path interferometric wavefront sensing is proposed. The approach is a variant of point-diffraction interferometry bearing similarities to pyramidal wavefront sensing. A theoretical basis for wavefront sensing with an axicon is developed, and the outcomes of numerical simulations are compared to experimental results obtained with spherical and cylindrical ophthalmic trial lenses. It is confirmed that the axicon can be used for wavefront sensing, although its refraction may ultimately complicate and limit its operational range.

The Large Synoptic Survey Telescope (LSST) will use an active optics system (AOS) to maintain alignment and surface figure on its three large mirrors. Corrective actions fed to the LSST AOS are determined from information derived from four curvature wavefront sensors located at the corners of the focal plane. Each wavefront sensor is a split detector such that the halves are 1 mm on either side of focus. In this paper, we describe the extensions to published curvature wavefront sensing algorithms needed to address challenges presented by the LSST, namely the large central obscuration, the fast f/1.23 beam, off-axis pupil distortions, and vignetting at the sensor locations. We also describe corrections needed for the split sensors and the effects from the angular separation of different stars providing the intrafocal and extrafocal images. Lastly, we present simulations that demonstrate convergence, linearity, and negligible noise when compared to atmospheric effects when the algorit...

Acquiring full control over a large number of diffraction orders can be strongly attractive in the case of realizing multifunctional devices such as multichannel reflectors. Recently, the concept of metagrating has been introduced, which enables obtaining the desired diffraction pattern through a sparse periodic array of engineered scatterers. In this Letter, for the first time, to the best of our knowledge, a tunable all-graphene multichannel meta-reflector is proposed for operating at terahertz (THz) frequencies. In the supercell level, the designed metagrating is composed of three graphene ribbons of different controllable chemical potentials which can be regarded as a five-channel THz meta-reflector. By choosing proper distribution of DC voltages feeding the ribbons, our design can realize different intriguing functionalities such as anomalous reflection, retroreflection, and three-channel power splitting within a single shared aperture and with high efficiency. This Letter pave...

We report on the current state of surface slope metrology on deformable mirrors for soft x-rays at the Advanced Light Source (ALS). While we are developing techniques for in situ at-wavelength tuning, we are refining methods of ex situ visible-light optical metrology to achieve sub-100-nrad accuracy. This paper reports on laboratory studies, measurements and tuning of a deformable test-KB mirror prior to its use. The test mirror was bent to a much different optical configuration than its original design, achieving a 0.38 micro-radian residual slope error. Modeling shows that in some cases, by including the image conjugate distance as an additional free parameter in the alignment, along with the two force couples, fourth-order tangential shape errors (the so-called bird shape) can be reduced or eliminated.

We demonstrate aberration-free dynamic focusing with a low-cost 19-channel continuous-surface micromachined membrane deformable mirror ͑MMDM͒. A lookup table of the optimum control voltages for various focal lengths is obtained with an adaptive optics algorithm. Diffraction-limited imaging resolution is achieved owing to the capablility of the MMDM for aberration compensation. The measured speed of the MMDM supports dynamic focusing operations at several hundred hertz. Our dynamic focusing approach is shown to function with either monochromatic or broadband optical sources.

The process of Zernike mode detection with a Shack-Hartmann wavefront sensor is computationally extensive. A holographic modal wavefront sensor has therefore evolved to process the data optically by use of the concept of equal and opposite phase bias. Recently, a multiplexed computer-generated hologram (CGH) technique was developed in which the output is in the form of bright dots that specify the presence and strength of a specific Zernike mode. We propose a wavefront sensor using the concept of phase biasing in the latter technique such that the output is a pair of bright dots for each mode to be sensed. A normalized difference signal between the intensities of the two dots is proportional to the amplitude of the sensed Zernike mode. In our method the number of holograms to be multiplexed is decreased, thereby reducing the modal cross talk significantly. We validated the proposed method through simulation studies for several cases. The simulation results demonstrate simultaneous wavefront detection of lower-order Zernike modes with a resolution better than λ=50 for the wide measurement range of AE3:5λ with much reduced cross talk at high speed.

A fast holographic wavefront sensor is proposed using a computer-generated hologram (CGH). This CGH is a multiplexed hologram of different Zernike mode-amplitude combinations, and is designed in such a manner as to get the corresponding spots on the detector according to the presence and strength of a particular aberration. Interference between the aberrated wavefront (with a single mode-amplitude combination) and the Fourier transform of an image with single bright pixel (defined as dot image) is numerically calculated for one hologram. Different mode-amplitude combination and corresponding different positions of bright pixels (dots) are taken to compute various holograms and then all the holograms are multiplexed to get the final hologram. When the aberrated wavefront with a particular mode-amplitude combination is incident onto the multiplexed hologram, the corresponding dot is generated in the Fourier plane. A lens performs the Fourier transform in optical domain and provides the instant detection of amplitude of the respective Zernike mode. The main advantage of the scheme is to avoid the need of any computations, which makes it really fast. The simulation results are presented with the cross-talk analysis for few Zernike terms.

Optical proximity correction (OPC) is one of the most widely used Resolution Enhancement Techniques (RET) in mask designs. Conventional OPC is often designed for a set of nominal imaging parameters without giving sufficient attention to the process variations caused by aspherical wavefront leaving the exit pupil of the lithography system. As a result, the mask designed may deliver poor performance with process variations. In this paper, we first describe how a general point spread function (PSF) with wave aberration can degrade the output pattern quality, and then show how the wave aberration function can be incorporated into an inverse imaging framework for robust input mask pattern design against aberrations. A level-set-based time-dependent model can then be applied to solve it with appropriate finite difference schemes. The optimal mask gives more robust performance against either one specific type of aberration or a combination of different types of aberrations.

We present a novel method for the development of a micro lenslets hexagonal array. We use gradient index (GRIN) micro lenses where the variation of the refraction index is achieved with a structure of nanorods made of 2 types of glasses. To develop the GRIN micro lens array, we used a modified stack-and-draw technology which was originally applied for the fabrication of photonic crystal fibers. This approach results in a completely flat element that is easy to integrate with other optical components and can be effectively used in high refractive index medium as liquids. As a proof-of-concept of the method we present a hexagonal array of 469 GRIN micro lenses with a diameter of 20 µm each and 100% fill factor. The GRIN lens array is further used to build a Shack-Hartmann detector for measuring wavefront distortion. A 50 lens/mm sampling density is achieved.

Steering the incoming photonic power toward unusual directions, not predicted by Snell's laws of reflection and refraction, is a fundamental operation behind numerous wavefront engineering applications. In this study, strong anomalous transmission is reported to all-dielectric electrically thin structures comprising only two materials in alternating rectangular posts. These binary metagratings have been thoroughly optimized to support almost perfect negative refraction by suppressing all the rest of diffraction orders; such an effect is found to be very robust with respect to oscillation frequency, incident beam angle, and structural defects. In this way, easy-to-fabricate setups working at different colors of the visible spectrum are determined and may be directly incorporated in various optical integrated systems from lenses and beamformers to field enhancers and power splitters.

A general technique for synthesizing both planar and conformal beamforming metasurfaces is presented that utilizes full-wave modeling techniques and rapid optimization methods. The synthesized metasurfaces consist of a patterned metallic cladding supported by a finite-size grounded dielectric substrate. The metasurfaces are modeled using integral equations which accurately account for mutual coupling and the metasurface's finite dimensions. The synthesis technique consists of three phases: a direct solve phase to obtain an initial metasurface design with complex-valued impedances satisfying the desired far-field beam specifications, a subsequent optimization phase that converts the complex-valued impedances to purely reactive ones, and a final patterning phase to realize the purely reactive impedances as a patterned metallic cladding. The optimization phase introduces surface waves which facilitate passivity. The metasurface is optimized using gradient descent with a semi-analytic gradient obtained using the adjoint variable method. Three examples are presented: a low-profile directly-fed metasurface antenna with near perfect aperture efficiency, a scanned-beam reflectarray design with controlled sidelobes, and a conformal metasurface reflectarray. The far-field and near-field performance of the metasurfaces are verified and the bandwidth and loss tolerance of the metasurfaces are investigated. INDEX TERMS Metasurface, beamforming, conformal, adjoint variable method.

The use of a large apex-angle axicon for common-path interferometric wavefront sensing is proposed. The approach is a variant of point-diffraction interferometry bearing similarities to pyramidal wavefront sensing. A theoretical basis for wavefront sensing with an axicon is developed, and the outcomes of numerical simulations are compared to experimental results obtained with spherical and cylindrical ophthalmic trial lenses. It is confirmed that the axicon can be used for wavefront sensing, although its refraction may ultimately complicate and limit its operational range.

The modulated pyramid wavefront sensor is known for its high sensitivity and adjustable dynamic range. The need for mechanically moving parts in a modulated pyramid wavefront sensor can be overcome by using the recently proposed digital pyramid wavefront sensor. In this paper, a digital multi-faceted pyramid wavefront sensor is demonstrated with the use of a reflecting phase-only spatial light modulator. The four-pupil digital pyramid wavefront sensor with 4-facets is extended to 6 and 8-facets. It is noted from the experiments performed under identical low-noise conditions that the performance of the wavefront sensor in terms of the root mean square wavefront error remains nearly the same in cases of four, six and eight pupil configurations. Under the circumstances elucidated here, the results of simulations indicate that in the presence of scatter noise, the pyramid wavefront sensor with greater number of pupils could lead to an improvement over the standard four-pupil pyramid wavefront sensor. Noise from scattering makes the choice of optimal modulation radius critical while sensing in open-loop adaptive optics systems.

A metallic ring based, diode-integrated, low-profile, power-dependent, reflective metasurface working from 3 GHz to 3.6 GHz is proposed in this letter. Unlike the previous study which shifts a band up and down to change the impedance of the surface, the triggering of the diodes directly transforms the structure from a surface wave supportive state to a self-induced bandgap topology if exposed to high power RF illumination. We demonstrate the concept by conducting the EM-circuit cosimulation and measurements for a 6 by 8 unit 2D prototype. Near field scan experiments verify that the proposed topology works in two distinct states, the ON and OFF state, and high-power measurements prove that the reflection varies with the incident signal power. The highest 10 dB decrement in transmission occurs at 3.3 GHz with 52 dBm illumination. This structure can be used to protect sensitive devices from large signals while otherwise supporting a communication channel for small signals.

A metallic ring based, diode-integrated, low-profile, power-dependent, reflective metasurface working from 3 GHz to 3.6 GHz is proposed in this letter. Unlike the previous study which shifts a band up and down to change the impedance of the surface, the triggering of the diodes directly transforms the structure from a surface wave supportive state to a self-induced bandgap topology if exposed to high power RF illumination. We demonstrate the concept by conducting the EM-circuit cosimulation and measurements for a 6 by 8 unit 2D prototype. Near field scan experiments verify that the proposed topology works in two distinct states, the ON and OFF state, and high-power measurements prove that the reflection varies with the incident signal power. The highest 10 dB decrement in transmission occurs at 3.3 GHz with 52 dBm illumination. This structure can be used to protect sensitive devices from large signals while otherwise supporting a communication channel for small signals.

Steering the incoming photonic power toward unusual directions, not predicted by Snell's laws of reflection and refraction, is a fundamental operation behind numerous wavefront engineering applications. In this study, strong anomalous transmission is reported to all-dielectric electrically thin structures comprising only two materials in alternating rectangular posts. These binary metagratings have been thoroughly optimized to support almost perfect negative refraction by suppressing all the rest of diffraction orders; such an effect is found to be very robust with respect to oscillation frequency, incident beam angle, and structural defects. In this way, easy-to-fabricate setups working at different colors of the visible spectrum are determined and may be directly incorporated in various optical integrated systems from lenses and beamformers to field enhancers and power splitters.

In this paper we present the theoretical considerations and the design evolution of a proof-of-concept intelligent metasurface, which can be used as a tunable microwave absorber, as well as a wavefront manipulation and polarization conversion device in reflection. We outline the design evolution and all considerations taken into account, from the selection of patch shape, unit cell size, and substrate, to the topology of the structure that realizes the desired tunability. The presented design conforms to fabrication restrictions and is co-designed to work with an integrated circuit chip for providing tunable complex loads to the metasurface, using a commercially available semiconductor process. The proposed structure can perform multiple tunable functionalities by appropriately biasing the integrated circuit chip: Perfect absorption for a wide range of incidence angles of both linear polarization states, accommodating a spectral range in the vicinity of 5 GHz, as well as wavefront c...

We present the concept and electromagnetic aspects of HyperSurFaces (HSFs), artificial, ultrathin structures with software controlled electromagnetic properties. The HSFs key unit is the metasurface, a plane with designed subwavelength features whose electromagnetic response can be tuned via voltage-controlled continuously-tunable electrical elements that provide local control of the surface impedance and advanced functionalities, such as tunable perfect absorption or wavefront manipulation. A nanonetwork of controllers enables software defined HSFs control related to the emerging Internet of Things paradigm.

Accurate bidirectional measurements are performed at PTB using UVmicroscopy. For this purpose, edge detection algorithms based on the rigorous calculation of the optical imaging problem are employed. Hence, all the parameters of the imaging system and the object must be considered due to their specific impact on the image formation. In order to further improve the model-based edge detection the small but inevitable optical aberrations of the imaging optics must be included into the simulations. For the determination of the aberrations, microscopic images of state-of-the-art line gratings (shapes verified by AFM) are measured in the focus and several afocal planes of the microscope. This procedure is similar to a phase retrieval method with the only difference that usually idealized pinholes are measured there. A particle swarm optimisation (PSO) method is developed to determine the aberration of the used microscope in terms of Zernike polynomials. Therefore, the particles of the PSO...

Accurate bidirectional measurements are performed at PTB using UVmicroscopy. For this purpose, edge detection algorithms based on the rigorous calculation of the optical imaging problem are employed. Hence, all the parameters of the imaging system and the object must be considered due to their specific impact on the image formation. In order to further improve the model-based edge detection the small but inevitable optical aberrations of the imaging optics must be included into the simulations. For the determination of the aberrations, microscopic images of state-of-the-art line gratings (shapes verified by AFM) are measured in the focus and several afocal planes of the microscope. This procedure is similar to a phase retrieval method with the only difference that usually idealized pinholes are measured there. A particle swarm optimisation (PSO) method is developed to determine the aberration of the used microscope in terms of Zernike polynomials. Therefore, the particles of the PSO...

We have constructed a 1m-diameter, holographically corrected membrane mirror telescope for optical imaging. Several thousand waves of surface error were removed using a corrective hologram, resulting in near diffraction-limited performance. A detailed discussion of the mirror, the corrective process and the performance of the final telescope are included.

This paper reports the design and fabrication of transmission holographic optical elements (HOEs) for clock distribution. First, we have studied and fabricated a multi-focus doublet HOE. The aberrations due to the wavelength shift between recording (= 488 nm) and reconstruction (= 780 nm) have been minimized by an appropriate recording and readout geometry. The diffraction efficiency has been optimized by a copying technique. Second, we have investigated the near-field internal reflection (TIR) holographic recording technique to solve the problems of miniaturization. With this method, we have recorded a lOOxlOO lenlet array with focal lengths of f =400 jim.

In this paper we propose and experimentally demonstrate information transfer through free-space using a laser beam encoded with multiple orthogonal aberration modes in its phase profile. We use Zernike polynomials which forms a complete set of basis functions to represent the aberration modes. The user information is encoded as amplitudes of multiple Zernike modes whose linear combination is used to define the wavefront of the laser beam in the transmission station. It therefore requires a single phase modulating device since the multiplexing is done digitally providing flexibility over the number and type of modes used. The receiving station uses a wavefront sensor that gives a direct measure of all the aberration modes from a single measurement which is decoded to retrieve the user information. The transmission mechanism enables the use of multiple modes and multiple strengths of each mode to encode the user information and external perturbation compensation, utilizing the completeness of the orthogonal modes.

We present the concept and electromagnetic aspects of HyperSurFaces (HSFs), artificial, ultrathin structures with software controlled electromagnetic properties. The HSFs key unit is the metasurface, a plane with designed subwavelength features whose electromagnetic response can be tuned via voltage-controlled continuously-tunable electrical elements that provide local control of the surface impedance and advanced functionalities, such as tunable perfect absorption or wavefront manipulation. A nanonetwork of controllers enables software defined HSFs control related to the emerging Internet of Things paradigm.

In recent years, metasurfaces have shown extremely powerful abilities for manipulation of electromagnetic waves. However, the local electromagnetic response of conventional metasurfaces yields to an intrinsic performance limitation in terms of efficiency, minimizing their implementation in real-life applications. The efficiency of reconfigurable metasurfaces further decreases because of the high density of meta-atoms, reaching 74 meta-atoms per λ 2 area, incorporating lossy tunable elements. To address these problems, we implement strong electromagnetic non-local features in a sparse metasurface composed of electronically reconfigurable meta-atoms. As a proof-of-concept demonstration, a dynamic sparse metasurface having as few as 8 meta-atoms per λ 2 area is experimentally realized in the microwave domain to control wavefronts in both near-field and far-field regions for focusing and beam-forming, respectively. The proposed metasurface with its sparsity not only facilitates design and fabrication, but also opens the door to high-efficiency real-time reprogrammable functionalities in beam manipulations, wireless power transfer and imaging holography.

In this paper we propose and experimentally demonstrate information transfer through free-space using a laser beam encoded with multiple orthogonal aberration modes in its phase profile. We use Zernike polynomials which forms a complete set of basis functions to represent the aberration modes. The user information is encoded as amplitudes of multiple Zernike modes whose linear combination is used to define the wavefront of the laser beam in the transmission station. It therefore requires a single phase modulating device since the multiplexing is done digitally providing flexibility over the number and type of modes used. The receiving station uses a wavefront sensor that gives a direct measure of all the aberration modes from a single measurement which is decoded to retrieve the user information. The transmission mechanism enables the use of multiple modes and multiple strengths of each mode to encode the user information and external perturbation compensation, utilizing the complet...

The recording of data in multiple layers, rather than a single layer, permits a significant increase in the capacity of optical data storage devices. However, focusing to the different layers introduces different amounts of depth-dependent aberrations. Variable aberration correction is therefore necessary to maintain diffraction-limited operation. We demonstrate the use of adaptive optics to predict and correct these aberrations for both the recording and read-out of such media.

We have developed a two-dimensional Shack-Hartman wavefront sensor that uses binary optic lenslet arrays to directly measure the wavefront slope (phase gradient) and amplitude of the laser beam. This sensor uses an array of lenslets that dissects the beam into a number ofsamples. The focal spot location of each of these lenslets (measured by a CCD camera) is related to the incoming wavefront slope over the lenslet. By integrating these measurements over the laser aperture, the wavefront or phase distribution can be determined. Since the power focused by each lenslet is also easily determined, this allows a complete measurement of the intensity and phase distribution of the laser beam. firthermore, all the information is obtained in a single measurement. Knowing the complete scalar field of the beam allows the detailed prediction of the actual beam's characteristics along its propagation path. In particular, the space-beamwidth product, @, can be obtained in a single measurement. The intensity and phase information can be used in concert with information about other elements in the optical tiain to predict the beam size, shape, phase and other characteristics anywhere in the optical train. We present preliminary measurements of an Ar+ laser beam and associated @ calculations.