Intermediate Plane Research Articles

Laser-induced damage threshold of camera sensors and micro-optoelectromechanical systems

The continuous development of laser systems toward more compact and efficient devices constitutes an increasing threat to electro-optical imaging sensors, such as complementary metal–oxide–semiconductors (CMOS) and charge-coupled devices. These types of electronic sensors are used in day-to-day life but also in military or civil security applications. In camera systems dedicated to specific tasks, micro-optoelectromechanical systems, such as a digital micromirror device (DMD), are part of the optical setup. In such systems, the DMD can be located at an intermediate focal plane of the optics and it is also susceptible to laser damage. The goal of our work is to enhance the knowledge of damaging effects on such devices exposed to laser light. The experimental setup for the investigation of laser-induced damage is described in detail. As laser sources, both pulsed lasers and continuous-wave (CW)-lasers are used. The laser-induced damage threshold is determined by the single-shot method by increasing the pulse energy from pulse to pulse or in the case of CW-lasers, by increasing the laser power. Furthermore, we investigate the morphology of laser-induced damage patterns and the dependence of the number of destructive device elements on the laser pulse energy or laser power. In addition to the destruction of single pixels, we observe aftereffects, such as persistent dead columns or rows of pixels in the sensor image.

Extension of the angular spectrum method to model the pressure field of a cylindrically curved array transducer.

An extension to the angular spectrum approach for modelling pressure fields of a cylindrically curved array transducer is described in this paper. The proposed technique is based on representing the curved transducer surface as a set of planar elements whose contributions are combined at a selected intermediate plane from which the field is further propagated using the conventional angular spectrum approach. The accuracy of the proposed technique is validated through comparison with Field II simulations.

Three-dimensional microscopic light field particle image velocimetry

A microscopic particle image velocimetry ( $$\mu \text {PIV}$$ ) technique is developed based on light field microscopy and is applied to flow through a microchannel containing a backward-facing step. The only hardware difference from a conventional $$\mu$$ PIV setup is the placement of a microlens array at the intermediate image plane of the microscope. The method combines this optical hardware alteration with post-capture computation to enable 3D reconstruction of particle fields. From these particle fields, we measure three-component velocity fields, but find that accurate velocity measurements are limited to the two in-plane components at discrete depths through the volume (i.e., 2C-3D). Results are compared with a computational fluid dynamics simulation.

Accurate Hologram Generation Using Layer-Based Method and Iterative Fourier Transform Algorithm

Random phase is always added to the object to diffuse the object light in computer-generated holograms. However, this addition causes considerable speckle noise in the reconstructed image. For improving the speckle noise problem, we propose a new method, which can reconstruct the 3-D object with higher image quality. A virtual intermediate plane is introduced between the object and the hologram plane. A three-dimensional object is first sliced into multiple layers according to their depth information. Then, each layer is added with uniform constant phase and propagates to the intermediate plane with an angular spectrum diffraction algorithm. Complex amplitude from each layer is added together as the desired distribution in the signal area in the intermediate plane. Then, the iterative Fourier transform algorithm is taken between the hologram and the intermediate plane to achieve the phase-only computer-generated hologram (CGH). Feasibility of the proposed method is verified with simulations and experiments.

Light Sheet Microscopy by Dual Line Scanning of Two Bessel Beams

We have developed a light-sheet microscope that uses confocal scanning of dual-Bessel beams for illumination. A digital micro-mirror device (DMD) is placed in the intermediate image plane of the objective used to collect fluorescence and is programmed with two lines of pixels in ‘on’ state such that the DMD functions as a spatial filter to reject the out-of-focus background generated by the side-lobes of the Bessel beams. The optical sectioning and out-of-focus background rejection capabilities of this microscope were demonstrated by imaging of human A431 cells whose actin was fluorescently stained. The dual-Bessel beam system enables twice as many photons to be detected per imaging scan, which is useful for low light applications (e.g. single molecule localization) or imaging at high speed with superior signal to noise. While demonstrated for two Bessel beams, this approach is scalable to a larger number of beams.

Light-sheet microscopy by confocal line scanning of dual-Bessel beams.

We have developed a light-sheet microscope that uses confocal scanning of dual-Bessel beams for illumination. A digital micromirror device (DMD) is placed in the intermediate image plane of the objective used to collect fluorescence and is programmed with two lines of pixels in the “on” state such that the DMD functions as a spatial filter to reject the out-of-focus background generated by the side-lobes of the Bessel beams. The optical sectioning and out-of-focus background rejection capabilities of this microscope were demonstrated by imaging of fluorescently stained actin in human A431 cells. The dual-Bessel beam system enables twice as many photons to be detected per imaging scan, which is useful for low light applications (e.g., single-molecule localization) or imaging at high speed with a superior signal to noise. While demonstrated for two Bessel beams, this approach is scalable to a larger number of beams.

Ultrathin flexible memory devices based on organic ferroelectric transistors

Here, we demonstrate ultrathin, flexible nonvolatile memory devices with excellent durability under compressive strain. Ferroelectric-gate field-effect transistors (FeFETs) employing organic semiconductor and polymer ferroelectric layers are fabricated on a 1-µm-thick plastic film substrate. The FeFETs are characterized by measuring their transfer characteristics, programming time, and data retention time. The data retention time is almost unchanged even when a 50% compressive strain is applied to the devices. To clarify the origin of the excellent durability of the devices against compressive strain, an intermediate plane is calculated. From the calculation result, the intermediate plane is placed close to the channel region of the FeFETs. The high flexibility of the ferroelectric polymer and ultrathin device structure contributes to achieving a bending radius of 0.8 µm without the degradation of memory characteristics.

Structural Parameters Calibration for Binocular Stereo Vision Sensors Using a Double-Sphere Target.

Structural parameter calibration for the binocular stereo vision sensor (BSVS) is an important guarantee for high-precision measurements. We propose a method to calibrate the structural parameters of BSVS based on a double-sphere target. The target, consisting of two identical spheres with a known fixed distance, is freely placed in different positions and orientations. Any three non-collinear sphere centres determine a spatial plane whose normal vector under the two camera-coordinate-frames is obtained by means of an intermediate parallel plane calculated by the image points of sphere centres and the depth-scale factors. Hence, the rotation matrix R is solved. The translation vector T is determined using a linear method derived from the epipolar geometry. Furthermore, R and T are refined by nonlinear optimization. We also provide theoretical analysis on the error propagation related to the positional deviation of the sphere image and an approach to mitigate its effect. Computer simulations are conducted to test the performance of the proposed method with respect to the image noise level, target placement times and the depth-scale factor. Experimental results on real data show that the accuracy of measurement is higher than 0.9‰, with a distance of 800 mm and a view field of 250 × 200 mm2.

SPECTRAL FILTRATION OF IMAGES BY MEANS OF DISPERSIVE SYSTEMS

Instruments for spectral filtration of images are an important element of the systems used in remote sensing, medical diagnostics, in-process measurements. The aim of this study is analysis of the functional features and characteristics of the proposed two image monochromator versions which are based on dispersive spectral filtering. The first is based on the use of a dispersive monochromator, where collimating and camera lenses form a telescopic system, the dispersive element of which is within the intermediate image plane. The second version is based on an imaging double monochromator with dispersion subtraction by back propagation. For the telescopic system version, the spectral and spatial resolutions are estimated, the latter being limited by aberrations and diffraction from the entrance slit. The device has been numerically simulated and prototyped. It is shown that for the spectral bandwidth 10 nm (visible spectral range), the aberration-limited spot size is from 10–20 μm at the image center to about 30 μm at the image periphery for the image size 23–27 mm. The monochromator with dispersion subtraction enables one to vary the spectral resolution (up to 1 nm and higher) by changing the intermediate slit width. But the distinctive feature is a significant change in the selected central wavelength over the image field. The considered designs of dispersive image monochromators look very promising due to the particular advantages over the systems based on tunable filters as regards the spectral resolution, fast tuning, and the spectral contrast. The monochromator based on a telescopic system has a simple design and a rather large image field but it also has a limited light throughput due to small aperture size. The monochromator with dispersion subtraction has higher light throughput, can provide high spectral resolution when recording a full data cube in a series of measuring acts for different dispersive element positions.

Motion-Compensated Frame Interpolation With Multiframe-Based Occlusion Handling

In this paper, an occlusion handling algorithm is presented for motion-compensated frame interpolation (MCFI). The proposed algorithm first estimates the unidirectional motion vector fields (MVFs) between two reference frames in both forward and backward directions. Then, a multiframe-based occlusion detection method is presented to identify the uncovered, covered, and motion ambiguity regions within the intermediate frame plane. Based on the detection results, bidirectional motion vectors of the intermediate frame are assigned accurately from unidirectional MVFs. For bidirectional motion compensation, the conventional overlapped block motion compensation (OMBC) method is improved by adjusting the support weight of each pixel within the overlapped window to suppress the blurring and ghost artifacts. Experimental results show that the proposed method not only provides interpolation results with better subjective visual quality, but can also improve the average peak signal-to-noise ratio of the interpolated frames by up to 1.788 dB, when compared to benchmark algorithms.

Hiding in encrypted images: a three tier security data hiding technique

This paper presents a new crypto domain data hiding technique based on Intermediate Significant Bit Plane Embedding (ISBPE). The cover image is encrypted; the information to be secured is scrambled, and then embedded in the Intermediate Significant Bit (ISB) planes of encrypted cover image, at the locations determined by a Pseudorandom Address Vector (PAV). The pseudorandom embedding of the scrambled data in the ISB planes of encrypted image results in a three tier security of the data to be secured. The ISBPE embedding results in an important advantage that the proposed scheme becomes completely robust to commonly employed attack of Least Significant Bit (LSB) removal/replacement. A novel concept of embedding a very small size fragile watermark in addition to the secret information has been used which facilitates early tamper detection. This feature could save crucial processor time in critical situations of national security issues/warfare etc. Experimental results show that the proposed scheme is more robust to various signal processing attacks like Joint Picture Expert Group compression, Additive White Gaussian Noise and `salt and pepper' noise as compared to conventional LSB based embedding techniques. Comparison results with some well-known techniques show that besides providing high degree of security and robustness to various malicious attacks the proposed technique is capable of embedding a fairly large amount of secret data in the host image while maintaining a good stego-image quality.

X-y curvature wavefront sensor.

In this Letter, we propose a new curvature wavefront sensor based on the principles of optical differentiation. The theoretically modeled setup consists of a diffractive optical mask placed at the intermediate plane of a classical two-lens coherent optical processor. The resulting image is composed of a number of local derivatives of the entrance pupil function whose proper combination provides the wavefront curvature. In contrast to the common radial curvature sensors, this one is able to provide the x and y wavefront curvature maps simultaneously. The sensor offers other additional advantages like having high spatial resolution, adjustable dynamic range, and not being sensitive to misalignment.

Fully differential cross sections for low to intermediate energy perpendicular plane ionization of xenon atoms

Triple differential cross section (TDCS) results are reported for the perpendicular plane ionization of Xe (5p) at incident electron energies 5eV, 10eV, 20eV, and 40eV above ionization potential. The modified distorted wave Born approximation formalism with first as well as the second order Born terms has been used to calculate the TDCS. Effects of target polarization and post collision interaction have also been included. We compare the (e, 2e) TDCS results of our calculation with the recent available experimental data and theoretical results and discuss the process contributing to structure seen in the differential cross section. It has been observed from the present study that the second order effect and target polarization make significant contribution in description of collision dynamics of xenon at the low and intermediate energy for the perpendicular emission of electrons.

A secure and robust information hiding technique for covert communication

The unprecedented advancement of multimedia and growth of the internet has made it possible to reproduce and distribute digital media easier and faster. This has given birth to information security issues, especially when the information pertains to national security, e-banking transactions, etc. The disguised form of encrypted data makes an adversary suspicious and increases the chance of attack. Information hiding overcomes this inherent problem of cryptographic systems and is emerging as an effective means of securing sensitive data being transmitted over insecure channels. In this paper, a secure and robust information hiding technique referred to as Intermediate Significant Bit Plane Embedding (ISBPE) is presented. The data to be embedded is scrambled and embedding is carried out using the concept of Pseudorandom Address Vector (PAV) and Complementary Address Vector (CAV) to enhance the security of the embedded data. The proposed ISBPE technique is fully immune to Least Significant Bit (LSB) removal/replacement attack. Experimental investigations reveal that the proposed technique is more robust to various image processing attacks like JPEG compression, Additive White Gaussian Noise (AWGN), low pass filtering, etc. compared to conventional LSB techniques. The various advantages offered by ISBPE technique make it a good candidate for covert communication.

Simple structured illumination microscope setup with high acquisition speed by using a spatial light modulator.

We describe a two-beam interference structured illumination fluorescence microscope. The novelty of the presented system lies in its simplicity. A programmable spatial light modulator (ferroelectric LCoS) in an intermediate image plane enables precise and rapid control of the excitation pattern in the specimen. The contrast of the projected light pattern is strongly influenced by the polarization state of the light entering the high NA objective. To achieve high contrast, we use a segmented polarizer. Furthermore, a mask with six holes blocks unwanted components in the spatial frequency spectrum of the illumination grating. Both these passive components serve their purpose in a simpler and almost as efficient way as active components. We demonstrate a lateral resolution of 114.2 ± 9.5 nm at a frame rate of 7.6 fps per reconstructed 2D slice.

Boundary-artifact-free phase retrieval with the transport of intensity equation II: applications to microlens characterization.

Boundary conditions play a crucial role in the solution of the transport of intensity equation (TIE). If not appropriately handled, they can create significant boundary artifacts across the reconstruction result. In a previous paper [Opt. Express 22, 9220 (2014)], we presented a new boundary-artifact-free TIE phase retrieval method with use of discrete cosine transform (DCT). Here we report its experimental investigations with applications to the micro-optics characterization. The experimental setup is based on a tunable lens based 4f system attached to a non-modified inverted bright-field microscope. We establish inhomogeneous Neumann boundary values by placing a rectangular aperture in the intermediate image plane of the microscope. Then the boundary values are applied to solve the TIE with our DCT-based TIE solver. Experimental results on microlenses highlight the importance of boundary conditions that often overlooked in simplified models, and confirm that our approach effectively avoid the boundary error even when objects are located at the image borders. It is further demonstrated that our technique is non-interferometric, accurate, fast, full-field, and flexible, rendering it a promising metrological tool for the micro-optics inspection.

Snapshot, reconfigurable multispectral and multi-polarization telecentric imaging system.

A reconfigurable telecentric imaging system that can simultaneously capture multispectral and multi-polarization information in a single snapshot is demonstrated. The proposed design utilizes a telecentric imaging objective and a light pipe for image multiplexing. An array of filters is used to filter each of the multiplexed images at an intermediate image plane. In this paper, we will discuss the system configuration and present the experimental results.

Polarization-independent distortion corrector fabricated using polymer-dispersed liquid crystals

We demonstrate a polarization-independent distortion corrector fabricated using a polymer-dispersed liquid crystal (PDLC) cell placed on the intermediate image plane of an optical system. At low voltage, a hazy PDLC cell scatters the incident rays and redirects the off-axis propagated chief ray. The chief ray approaches the principal point of the lens element, thereby decreasing image distortion. At high voltage, the PDLC cell becomes transparent, thereby restoring the image distortion. The PDLC-based distortion corrector is an easy-to-fabricate universal device that can be applied to various optical systems. With a large lens diameter, the distortion of a PDLC-corrected image is approximately 1/5 of that of an uncorrected image.

Elementary-field analysis of partially coherent beam shaping

We consider spatial shaping of partially coherent fields in two types of optical systems: a 2F Fourier-transforming system with the beam shaping element in the input plane and a 4F imaging system with the element in the intermediate Fourier plane. Different representations of the spatially partially coherent field in terms of fully coherent fields are examined to permit reduction of the dimensionality of the propagation integrals. The standard Mercer-type coherent-mode representation of the incident cross-spectral density (CSD) function is compared to expansions of CSD in either spatially or angularly shifted elementary field modes, all sharing the same spatial profile. In Fourier-transforming systems, the angular elementary-field representation proves computationally superior, while in imaging systems the spatially shifted elementary-field expansion is the best choice. Considering the Fourier-plane element as a generalized pupil, the latter leads to the concept's generalized amplitude associated with the elementary field and to a generalized transfer function of the system. These concepts reduce to the standard point spread function and the optical transfer function in the limit of spatial incoherence at the object plane. Examples of the effects of partial coherence in spatial beam shaping are given.

Axial Magnetic Field Strength Needed for a 126-kV Single-Break Vacuum Circuit Breaker During Asymmetrical Current Switching

The objective of this paper is to investigate how strong an axial magnetic field (AMF) is needed in test duty T100a for a 126-kV single-break vacuum circuit breaker (VCB) when interrupting a rated short circuit current of 40-kA rms in light of arcing contact gap, arc duration and phase shift effect. The AMF is generated by a pair of 2/3 coil-type AMF contacts. First, the accuracy of a 3-D finite element simulation of AMF is validated by an AMF measurement at a contact gap 30 mm and the error is <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${&lt;}{10\%}$</tex></formula> . After that test duty T100a of the 126-kV single-break VCB are carried out 18 times with arc duration from 3.3 to 19 ms at 40-kA rms. With a given opening displacement curve, the contact gap as arc extinguishes within a range from 12 to 50 mm corresponding to the arc duration from 3.3 to 19 ms. Then the AMF distribution of the 126-kV single-break VCB at each contact gap at which arc extinguished is simulated to analyze the current interrupting results. The results show that there are successful interruptions at the short-circuit current 40-kA rms in test duties T100a, with the shortest arcing contact gap window from 18 to 23 mm and the longest arcing contact gap of 44 mm. The shortest arcing contact gap window corresponds to the maximum AMF at the intermediate plane of the contact gap per kilo-ampere of the breaking peak current from 9.3 to 8.5 mT/kA. In addition, the longest arcing contact gap corresponds to the value of 6.1 mT/kA. The phase shift time at the center of intermediate plane of the contact gap ranged from 1.36 to 0.75 ms corresponding to an increase of arcing contact gap from 12 to 50 mm in the tests.