Optical Plane Research Articles

High precision wavefront control in point spread function engineering for single emitter localization.

Point spread function (PSF) engineering is used in single emitter localization to measure the emitter position in 3D and possibly other parameters such as the emission color or dipole orientation as well. Advanced PSF models such as spline fits to experimental PSFs or the vectorial PSF model can be used in the corresponding localization algorithms in order to model the intricate spot shape and deformations correctly. The complexity of the optical architecture and fit model makes PSF engineering approaches particularly sensitive to optical aberrations. Here, we present a calibration and alignment protocol for fluorescence microscopes equipped with a spatial light modulator (SLM) with the goal of establishing a wavefront error well below the diffraction limit for optimum application of complex engineered PSFs. We achieve high-precision wavefront control, to a level below 20 mλ wavefront aberration over a 30 minute time window after the calibration procedure, using a separate light path for calibrating the pixel-to-pixel variations of the SLM, and alignment of the SLM with respect to the optical axis and Fourier plane within 3 μm (x/y) and 100 μm (z) error. Aberrations are retrieved from a fit of the vectorial PSF model to a bead z-stack and compensated with a residual wavefront error comparable to the error of the SLM calibration step. This well-calibrated and corrected setup makes it possible to create complex '3D+λ' PSFs that fit very well to the vectorial PSF model. Proof-of-principle bead experiments show precisions below 10 nm in x, y, and λ, and below 20 nm in z over an axial range of 1 μm with 2000 signal photons and 12 background photons.

Restoration of IP Networks by Using a Hybrid Interacting Mechanism Between Layer 2 & 3 in the Networks Over OA&M

The Internet generation infrastructure is growing and moving towards a consistency model of high-speed nodes interconnected by optical core networks. Therefore, the interaction between IP and optical network layers, specifically, the routing and signalling aspects, are maturing and they can lead to enhance the services and network performance. At the same time, a consensus has emerged in the industry on utilizing IP-based protocols for the optical control plane. This paper defines a new technique for IP over Optical networks (interacting between bottom layers), considering both the IP-based control plane for optical networks as well as IP-optical network interactions (together referred to as “IP over optical networks”). In this paper, a new technique is proposed that reduces recovery time by making an interoperation between the data link layer (layer 2) with the network layer (layer 3). The proposed technique enables layer 2 with layer 3 to make a hybrid mechanism that improves the recovery time in the network through two cases (1st-Detection and 2nd-Rerouting). The technique involves detecting failure in less time through layer 2 and rerouting traffic through an alternative path between source and destination by using a new algorithm in layer 3 to deliver data packets without the need to wait for the routing protocol to update the network topology and compute the routing table. In case of the network recovery, layer 2 has demonstrated its capability to detect failure extremely quickly shown through the immediate detection of the loss of signals for the link or node. The recovery mechanism, i.e., the rerouting mechanism, which leads the node, switches the data packets through an adjacent node to its destination via the life node. The latter is created by the proposed mechanism before the occurrence of the failure. The aim of this mechanism is to avoid loss of packets, improve QoS and improve recovery time as we have shown in the results shown below.

LeMMINGs – I. The eMERLIN legacy survey of nearby galaxies. 1.5-GHz parsec-scale radio structures and cores

We present the first data release of high-resolution ($\leq0.2$ arcsec) 1.5-GHz radio images of 103 nearby galaxies from the Palomar sample, observed with the eMERLIN array, as part of the LeMMINGs survey. This sample includes galaxies which are active (LINER and Seyfert) and quiescent (HII galaxies and Absorption line galaxies, ALG), which are reclassified based upon revised emission-line diagrams. We detect radio emission $\gtrsim$ 0.2 mJy for 47/103 galaxies (22/34 for LINERS, 4/4 for Seyferts, 16/51 for HII galaxies and 5/14 for ALGs) with radio sizes typically of $\lesssim$100 pc. We identify the radio core position within the radio structures for 41 sources. Half of the sample shows jetted morphologies. The remaining half shows single radio cores or complex morphologies. LINERs show radio structures more core-brightened than Seyferts. Radio luminosities of the sample range from 10$^{32}$ to 10$^{40}$ erg s$^{-1}$: LINERs and HII galaxies show the highest and the lowest radio powers respectively, while ALGs and Seyferts have intermediate luminosities. We find that radio core luminosities correlate with black hole (BH) mass down to $\sim$10$^{7}$ M$_{\odot}$, but a break emerges at lower masses. Using [O III] line luminosity as a proxy for the accretion luminosity, active nuclei and jetted HII galaxies follow an optical fundamental plane of BH activity, suggesting a common disc-jet relationship. In conclusion, LINER nuclei are the scaled-down version of FR I radio galaxies; Seyferts show less collimated jets; HII galaxies may host weak active BHs and/or nuclear star-forming cores; and recurrent BH activity may account for ALG properties.

NEPHELE: An End-to-End Scalable and Dynamically Reconfigurable Optical Architecture for Application-Aware SDN Cloud Data Centers

The efficient integration of optical switching in data center networks is being studied as a means to cope with surging traffic demands. Optically switched, flatter network architectures more efficiently handle the east-west traffic profiles of modern data centers. Limitations in the port count and reconfiguration speed of optical switches require novel network designs offering network scalability and dynamicity. Interaction of the optically switched data plane with a software-defined control and orchestration framework, meeting current common practices in data centers, necessitates the design of custom network control algorithms and software modules as well as the integration of novel functionalities. The approach of the European project NEPHELE is presented, offering an endto- end solution that addresses the optical data plane, the control plane, and its interaction with the application layer.

Theoretical and experimental evaluation of piezo-optic parameters and photoelastic constant in tetragonal PWO.

The tetragonal PbWO4 (PWO) is one of the most important scintillating crystals, being used both in the Compact Muon Solenoid (CMS) experiment at the European Organization for Nuclear Research (CERN) and in the PANDA project at the Facility for Antiproton and Ion Research (FAIR). Light yield and other relevant scintillation properties depend, among many factors, also on the crystal mechanical quality. Accordingly, a detailed knowledge of crystal piezo-optic properties is a mandatory step toward understanding elasto-optic behavior and performing crystal quality control. In this paper, we evaluate for the first time, to the best of our knowledge, by means of both photoelastic and x-ray measurements, some components of the piezo-optic tensor; moreover, when the crystal is acted upon by a uniaxial stress, we obtain an evaluation for the rotation angle of the optic plane under stress as well as the photoelastic constant. These parameters are necessary to detect the residual stresses within the crystal, if any, and to give an overall quality measure. Such a methodology is in general suitable for any tetragonal crystals.

Focusing optical waves with a rotationally symmetric sharp-edge aperture

While there has been various kinds of patterned structures proposed for wave focusing, these patterned structures usually involve complicated lithographic techniques since the element size of the patterned structures should be precisely controlled in microscale or even nanoscale. Here we propose a new and straightforward method for focusing an optical plane wave in free space with a rotationally symmetric sharp-edge aperture. The focusing phenomenon of wave is realized by superposition of a portion of the higher-order symmetric plane waves generated from the sharp edges of the apertures, in contrast to previously focusing techniques which usually depend on a curved phase. We demonstrate both experimentally and theoretically the focusing effect with a series of apertures having different rotational symmetry, and find that the intensity of the hotspots could be controlled by the symmetric strength of the sharp-edge apertures. The presented results would advance the conventional wisdom that light would diffract in all directions and become expanding when it propagates through an aperture. The proposed method is easy to be processed, and might open potential applications in interferometry, image, and superresolution.

A differential-imaging polarimeter for high-contrast exoplanet imaging

Starlight is generally unpolarized, but the light reflected from the planet is linearly polarized as the result of the Rayleigh scattering. For ground-based exoplanet imaging, atmospheres turbulence is changing from time to time, which induces speckle noise and hampers the high-contrast imaging of the faint exoplanets. In this paper, we propose a differential-imaging polarimeter dedicated for exoplanet high-contrast imaging. The system contains a zero-order half-wave plate (HWP) located on the optical pupil plane, which can rotate to modulate the incoming light, and a Wollaston prism (WP) is used to generate two polarized images, which is used for simultaneously polarization differential imaging and thus our system is fundamentally immune to the atmospheric turbulence induced temporally-variable wavefront aberration. Our polarimeter can be inserted near the telescope image focal plane, and provide an extra contrast for the exoplanet high-contrast imaging. To achieve best differential-imaging performance, dedicated algorithm is developed, which can effectively correct the distortion and the intensity unbalance between the two differential images. The system successfully achieves an extra contrast of ~30~50 times, which can be used with current adaptive optics and coronagraph system for directly imaging of giant Jupiter-like exoplanets.

Irradiance scintillation models of plane and spherical waves considering the general distribution of anisotropic turbulence cells

Theoretical investigations and experiments have shown the atmosphere turbulence exhibit anisotropic properties. In this work, the irradiance scintillation of optical plane and spherical waves in weak anisotropic turbulence will be investigated. Previously derived irradiance scintillation index of plane and spherical waves in weak anisotropic turbulence assumed the circular symmetric distribution of turbulence cells in the plane orthogonal to the direction of propagation. This assumption is very special for the real anisotropic turbulence. To consider the general distribution of turbulence cells in anisotropic turbulence, new expressions for the irradiance scintillation index of plane and spherical waves in weak anisotropic non-Kolmogorov turbulence have been derived with the Rytov approximation theory. In the investigations, two anisotropic factors are introduced to parameterize the asymmetric distribution of turbulence cells in anisotropic turbulence. In addition, the general spectral power law α in the range 3–4 and the finite turbulence inner and outer scales are considered in the modeling. Calculations are performed to analyze these parameters’ influences on the derived irradiance scintillation index models of optical waves.

Quantitative estimation of crazing in sol-gel layers by automated optical microscopy analysis

This paper describes how to quantify the scattering that appears in thin films deposited on a flat substrate. The defects appear during the deposition process and are hard to identify from classical optical microscopy pictures due to their small surface and contrast. A new way to probe the microroughness of optical components is described for heterogeneous or large samples (cm2) that requires a statistical analysis of each image over a full mapping of the sample. Due to possible optical misalignment or surface waviness, an automatic adjustment of the optical focus plane was implemented for each image during the surface mapping. In this way, we could measure the scattering using a microscope set-up. The results are linked to diffuse reflection and transmission losses (extinction coefficient k) and several different contributions from the total scattering are identified.

Optical focal plane based on MEMS light lead-in for geometric camera calibration

The focal plane of a collimator used for the geometric calibration of an optical camera is a key element in the calibration process. The traditional focal plane of the collimator has only a single aperture light lead-in, resulting in a relatively unreliable calibration accuracy. Here we demonstrate a multi-aperture micro-electro-mechanical system (MEMS) light lead-in device that is located at the optical focal plane of the collimator used to calibrate the geometric distortion in cameras. Without additional volume or power consumption, the random errors of this calibration system are decreased by the multi-image matrix. With this new construction and a method for implementing the system, the reliability of high-accuracy calibration of optical cameras is guaranteed.

Three-dimensional photolithography using built-in lens mask

Three-dimensional lithography processes are required to fabricate the complex structures of advanced MEMS devices. The built-in lens mask has a complex transmittance amplitude and emulates the optical wave planes of arbitrarily shaped images that are to be focused on a focal plane. In our previous work, the authors proposed a novel three-dimensional imaging method using a multifocusing built-in lens mask in a computational simulation study. In this work, the authors study the three-dimensional photolithography process experimentally using this built-in lens mask. A pyramidal frame pattern is used to expose a negative thick resist layer (SU-8), and three-dimensional structures are successfully obtained using a single mask and a single-shot photolithography process. The experimental results agree fairly well with those from the computational simulations.

RoboPol: connection between optical polarization plane rotations and gamma-ray flares in blazars

We use results of our 3 year polarimetric monitoring program to investigate the previously suggested connection between rotations of the polarization plane in the optical emission of blazars and their gamma-ray flares in the GeV band. The homogeneous set of 40 rotation events in 24 sources detected by {\em RoboPol} is analysed together with the gamma-ray data provided by {\em Fermi}-LAT. We confirm that polarization plane rotations are indeed related to the closest gamma-ray flares in blazars and the time lags between these events are consistent with zero. Amplitudes of the rotations are anticorrelated with amplitudes of the gamma-ray flares. This is presumably caused by higher relativistic boosting (higher Doppler factors) in blazars that exhibit smaller amplitude polarization plane rotations. Moreover, the time scales of rotations and flares are marginally correlated.

Refractive-index fluctuations spectrum considering the general distribution of turbulence cells in moderate-to-strong anisotropic turbulence

For the moderate-to-strong anisotropic turbulence, the previously derived turbulence refractive-index fluctuations spectral models assumed the circular symmetric distribution of turbulence cells in the plane orthogonal to the direction of propagation. For the real anisotropic turbulence, this kind of distribution is very special and not always fit the real turbulence. In this work, to describe the general distribution of turbulence cells in the moderate-to-strong anisotropic turbulence, new turbulence refractive-index fluctuations spectral model is derived with the extended Rytov approximation theory. Then, it is applied to investigate the irradiance scintillation index for optical plane and spherical waves propagating through moderate-to-strong anisotropic turbulence. Two anisotropic factors are introduced to describe the asymmetric distribution of turbulence cells. Compared with the Kolmogorov turbulence, the general spectral power law in the range of 3–4 is also considered. The derived irradiance scintillation index models of optical waves are applicable in a wide range of turbulence strength. In the special case of weak anisotropic turbulence, they have good consistency with those derived in weak anisotropic turbulence.

Effect of eddy diffusivity ratio on underwater optical scintillation index.

The performance of underwater optical wireless communication systems is severely affected by the turbulence that occurs due to the fluctuations in the index of refraction. Most previous studies assume a simplifying, yet inaccurate, assumption in the turbulence spectrum model that the eddy diffusivity ratio is equal to unity. It is, however, well known that the eddy diffusivities of temperature and salt are different from each other in most underwater environments. In this paper, we obtain a simplified spatial power spectrum model of turbulent fluctuations of the seawater refraction index as an explicit function of eddy diffusivity ratio. Using the derived model, we obtain the scintillation index of optical plane and spherical waves and investigate the effect of the eddy diffusivity ratio.

Experimental demonstration of an intelligent control plane with proactive spectrum defragmentation in SD-EONs.

The cooperation of software-defined networking and flexible grid optical transport technology allows operators to elastically control the network using software running on a network operating system within a centralized way. However, existing approaches dealing with spectrum fragmentation are mostly the reactive strategy, which reconfigures network resources to overcome spectrum fragmentation when the controller detects the fragmentation. In this paper, we focus on how to improve the control plane intelligence of software-defined elastic optical networks (SD-EONs) by using a proactive strategy. More specifically, we design a novel routing, modulation level and spectrum allocation algorithm (RMLSA) based on spectral efficiency and connectivity (SEC) i.e., SEC-RMLSA, in order to improve the utilization efficiency of network resources. Meanwhile, we develop a routing application and an extended OpenFlow protocol to achieve a seamless operation between the controller and the optical data plane. Moreover, all the proposed methodologies are implemented and demonstrated in an SD-EON testbed that has both OpenFlow-based control plane and data plane. Finally, the proposed framework, experimental demonstration, and numerical evaluation are reported for different optical flows. The results show the system's overall feasibility and efficiency.

Comparison and combination of rotational imaging optical coherence tomography and selective plane illumination microscopy for embryonic study.

Several optical imaging techniques have been applied for high-resolution embryonic imaging using different contrast mechanisms, each with their own benefits and limitations. In this study, we imaged the same E9.5 mouse embryo with rotational imaging optical coherence tomography (RI-OCT) and selective plane illumination microscopy (SPIM). RI-OCT overcomes optical penetration limits of traditional OCT imaging that prohibit full-body imaging of mouse embryos at later stages by imaging the samples from multiple angles. SPIM enables high-resolution, 3D imaging with less phototoxicity and photobleaching than laser scanning confocal microscopy (LSCM) by illuminating the sample with a focused sheet of light. Side by side comparisons are supplemented with co-registered images. The results demonstrate that SPIM and RI-OCT are highly complementary and could provide more comprehensive tissue characterization for mouse embryonic research.

Revisiting FiWi: On the Merits of a Distributed Upstream Resource Allocation Scheme

To improve fiber-wireless (FiWi) access network performance, this work proposes a distributed control plane by simply shifting the centralized control task away from the distant central office (optical plane) towards the closely clustered wireless nodes (wireless plane) at the access end. This distributed scheme results in a globally optimized upstream resource allocation scheme, thus paving the way for improved performance.

Imaging the Root Hair Morphology of Arabidopsis Seedlings in a Two-layer Microfluidic Platform.

Root hairs increase root surface area for better water uptake and nutrient absorption by the plant. Because they are small in size and often obscured by their natural environment, root hair morphology and function are difficult to study and often excluded from plant research. In recent years, microfluidic platforms have offered a way to visualize root systems at high resolution without disturbing the roots during transfer to an imaging system. The microfluidic platform presented here builds on previous plant-on-a-chip research by incorporating a two-layer device to confine the Arabidopsis thaliana main root to the same optical plane as the root hairs. This design enables the quantification of root hairs on a cellular and organelle level and also prevents z-axis drifting during the addition of experimental treatments. We describe how to store the devices in a contained and hydrated environment, without the need for fluidic pumps, while maintaining a gnotobiotic environment for the seedling. After the optical imaging experiment, the device may be disassembled and used as a substrate for atomic force or scanning electron microscopy while keeping fine root structures intact.

Infrared dispersion analysis and Raman scattering spectra of taurine single crystals

A comprehensive set of optical vibrational modes of monoclinic taurine crystals was determined by Raman scattering, and infrared reflectivity and transmission spectroscopies. By using appropriate scattering/reflection geometries, the vibrational modes were resolved by polarization and the most relevant modes of the crystal could be assigned. In particular, we were able to review the symmetry of the gerade modes and to resolve ambiguities in the literature. Owing to the non-orthogonal character of Bu modes in monoclinic crystals (lying on the optic axial plane), we carried out a generalized Lorentz dispersion analysis consisting of simultaneous adjust of infrared-reflectivity spectra at various light polarization angles. The Au modes (parallel to the C2-axis) were treated within the classical Lorentz model. The behavior of off-diagonal and diagonal terms of the complex dielectric tensors and the presence of anomalous dispersion were discussed as consequences of the low symmetry of the crystal.

A dual-modality optical coherence tomography and selective plane illumination microscopy system for mouse embryonic imaging.

Both optical coherence tomography (OCT) and selective plane illumination microscopy (SPIM) are frequently used in mouse embryonic research for high-resolution three-dimensional imaging. Each of these imaging methods provide a unique and independent advantage: SPIM provides morpho-functional information through immunofluorescence and OCT provides a method for whole-embryo 3D imaging. In this study, we have combined rotational imaging OCT and SPIM into a single, dual-modality device to image E9.5 mouse embryos. The results demonstrate that the dual-modality setup is able to provide both anatomical and functional information simultaneously for more comprehensive tissue characterization.