Some people can be just downright mean. The pen (now keyboard) and the tongue can cut people in damaging ways. A quick online search shows that some pretty famous people have said some really mean things. Walter Kerr once said, “You have delusions of adequacy.” Winston Churchill, who was famously insulting, once said, “You have all the virtues I despise and none of the vices I admire.” Then there’s the well-known intellectual insult, “I could agree with you, but then we would both be wrong.”

Silicon photomultiplier (SiPM)-based optoelectronic mixing (OEM) is studied for the first time. The validity of SiPM-based OEM is experimentally verified. Compared with the avalanche photodiodes-based OEM, the SiPM-based OEM is less noisy and easy to realize for its low voltage operation and high responsivity.

Within the field of spectral imaging, the vast majority of instruments used are scanning devices. Recently, several snapshot spectral imaging systems have become commercially available, providing new functionality for users and opening up the field to a wide array of new applications. A comprehensive survey of the available snapshot technologies is provided, and an attempt has been made to show how the new capabilities of snapshot approaches can be fully utilized.

Manipulation of optical fields by micro- and nanostructured media has undergone millions of years of evolution. The structural color identified in some animals is one example that permits the study of the role of light in ecosystems and its evolution history. To transfer this natural concept of subwavelength-structured optical interfaces to provide state-of-the-art optical systems, diffractive optics’ essential role must be thoroughly understood. Diffractive optics is widely recognized as an important growth area in modern optics. The successful insight into the field of optical engineering and photonics offered by diffractive optics proves tremendous advantages over conventional bulk optics. The increasing demands and desire to improve telecommunication, optical computing, consumer electronics, laser material processing, biomedical sciences, and manipulation of nano-objects through micro-optical systems have driven the advance in diffractive optics, which creates a large number of new avenues in optical research and new directions in nanophotonics research.

Hyper numerical aperture (NA) and off-axis illumination enable extension of ArF lithography for 45 nm technology node and beyond. Also, rigorous electromagnetic field modeling is taken into account for the optical and topographical properties of the mask. A rigorous three-dimensional mask model for bilayer absorber alternating phase shift mask (AltPSM) with the rigorous coupled-wave analysis (RCWA) is established. First, the harmonic waves are expanded based on the least common multiple of the periods in order to model the diffraction of multiple grating layers with different periods. Second, Lalanne’s formulation is used to improve the convergence of RCWA for multiple grating layers in conical diffraction. Third, the enhanced transmittance matrix approach is also extended to conical diffraction to avoid the numerical instability. Given the chromium oxide/chromium AltPSM, the change of polarization state as a function of mask and incident light properties is investigated. When the linewidth is below 30 nm, the mask acts as a transverse magnetic field polarizer, which is not preferred in terms of image quality, so the mask-induced polarization effects must be considered in the hyper NA lithography.

A new aperture-synthesis approach in femtosecond-pulse digital holography for obtaining a high-resolution and a whole field of view of the reconstructed image is proposed. The subholograms are recorded only by delay scanning holograms that have different delay times between the object and reference beams. In addition, by using image processing techniques, the synthesis aperture digital hologram can be superposed accurately. Analysis and experimental results show that the walk-off in femtosecond off-axis digital holography caused by low coherent can be well eliminated. The resolution and the field of view of the reconstructed image can be improved effectively.

Nonparaxial diffractive lenses are without the “spherical” (aperture) aberration for two prespecified conjugate points on the axis. The distribution of zones is characteristic for each location of conjugate points. The existing relations for calculation of zone distribution by the relation for two prespecified conjugate points located in finite distances and the spherically curved substrate of the lens is completed. The relation has been reduced to a compact and simple form.

The simulation of light focusing by a gradient, secant-plane lens was performed. The simulation using a finite-difference time-domain method shows that by combining the gradient-index hyperbolic secant (HS) lens with a subwavelength diffraction grating or by replacing the lens with its binary analog, the focal spot size can be reduced by 10% and 20%, respectively, with respect to the diffraction-limited resolution in the two-dimensional medium. We design a planar, binary-silicon HS microlens that generates a near-surface focal spot with a full-width, half-maximum diameter equal to 0.102λ and almost without sidelobes. It is shown that about 10% of the incident beam total power goes to the far-field zone.

The blazed grating is one of the key elements in a spectrometer. Hence we have adopted a new method of its fabrication. First, the combination of ion beam etching (IBE) and reactive IBE is used to fabricate a native substrate grating mask to replace the traditional photoresist grating mask. This is because the former mask allows for more accurate control of the profile than the latter. Then tilted IBE is used to etch the native substrate grating to ensure the precise control of the blazed angle and antiblazed angle. Therefore, an optimal blazed grating profile is successfully fabricated. Two types of blazed gratings with the same period of 833 nm have been fabricated: one with the blaze angle of 11 deg and the antiblaze angle of 72 deg; and one with the blaze angle of 20 deg and the antiblaze angle of 68.5 deg, respectively.

We derive a general nonparaxial analytical representation of the eikonal function for the design of diffractive optical elements (DOE) producing a line focus. The eikonal is given in special curvilinear coordinates. The eikonal’s calculation, from the condition of focusing into a line with prescribed intensity distribution, is reduced to the solution of a first-order explicit differential equation. We design DOEs and nondiffractive refractive optical elements to generate a line-segment focus and a circular-arc focus. The simulation data demonstrates that the designed optical elements produce high-quality lines.

Optical technology is poised to revolutionize short-reach communication systems, and the leading technology is silicon photonics. Silicon photonic devices have attracted more and more attention and have been increasingly studied in recent years. Grating, which functions as a building block for many passive and active devices, is widely used in silicon photonics. This review presents some silicon photonic devices based on binary blazed gratings, such as grating couplers, beam splitters, polarization beam splitters, broadband reflectors, and narrow filters, that demonstrate much better performance than those based on uniform gratings, owing to the novel characteristics of binary blazed gratings.

The problem of metrological standards development for aspherical wavefronts is discussed. A method for aspherical wavefront shaping by means of combined (or twin, multiplexed) computer generated hologram (CCGH) is presented. The CCGH reconstructs two wavefronts: the first one is used for calibration of the second one by means of a Fizeau interferometer and a highly reflective flat reference surface. Different CCGH encoding methods are discussed. The design of a CCGH with subaperture division in the shape of angular sectors is presented. The absence of cross-talk errors in both wavefronts was demonstrated experimentally.

We analyze the properties of silicon integrated photonic lenses based on scattering optical elements. The devices have been inverse-designed by combining genetic algorithms and the multiple scattering theory. These lenses are able to focus an infrared plane wave front on a position freely determined during the design stage. The nanofabricated silicon integrated lenses have proved effective over a large range of wavelengths, measured to be of the order of 100 nm. The lenses show chromatic aberration, with a displacement of the position of the focus measured to be higher than 1.5 μm when the wavelength varies from 1500 to 1600 nm. Moreover, we analyze the polarization of the focused beam thanks to a polarization-sensitive scanning near-field optical microscope. The measurements show that the lenses focus on a definite point only for the design’s polarization. The properties of these lenses enable them to assume the function of a nanofocusing device in silicon-on-insulator integrated optics.

It is shown that a decrease in the size of the focal spot produced by a high numerical aperture focusing system comes as the result of the spatial redistribution of different electric field components in the focal region. The focal distribution of electric field components can be controlled using vortex or binary phase diffractive elements. Situations for differently polarized incident laser beams are discussed and illustrated.

This paper describes a successful technological transfer, from a state laboratory to an industrial company, for writing long and large submicron period gratings (potentially square-meter sized), implemented in an industrial direct laser beam writing equipment at 355 nm wavelength (Dilase 750 from KLOE SA company). The writing head, which has been inserted in the machine, consists of a phase mask which enables it to project a set of fringes pattern of small area onto a photoresist-coated substrate. As the substrate is continuously moving, one-dimensional or two-dimensional gratings can be fabricated over large areas limited only by the machine’s stage displacement range. The optical scheme is described from the beam shaping to the printing processes and the phase mask optimization. In order to demonstrate the technology, 600 nm period gratings of over 20 cm in length have been fabricated. Such submicron structures can be used in solar cell modules for photon trapping and as antireflection coatings.

A type of tunable liquid crystal diffractive lens (TLCDL) for monochromatic wave base on multiorder diffraction is proposed and demonstrated. Two TLCDLs were designed using patterned indium tin oxide and a conductive surface relief electrode, respectively. The focus tuning mechanism of the lens has been proved using multiorder diffractive structure. One TLCDL with three switchable focal lengths was fabricated using an imprinting technique, which significantly reduced fabrication complexity. Electro-optic performances of the TLCDL were studied with monochromatic illumination. High image quality with low operating voltage and fast response time has been realized.

We studied the use of Talbot pattern illumination in scanning optical microscopy (SOM). Unlike conventional illumination spots used in SOM, the focal spots in Talbot pattern are more complicated and do not have a simple Gaussian intensity distribution. To find out the resolution of SOM using Talbot pattern, we characterized the evolution of the full-width-at-half-maximum spot size of the Talbot focal spots by computer simulation. We then simulated the SOM imaging under Talbot pattern illumination using the razor blade and the U.S. Air Force target as the sample objects, and compared the results with those performed with Gaussian spots as illumination. Using several foci searching algorithms, the optimal focal distances were found to be shorter than the theoretical Talbot distances. The simulation results were consistent with the experiment results published previously. We then provide a practical guidance for searching for optimal focal distances in the SOM based on these studies.

An optimized microcavity structure is proposed to enhance the emission efficiency of the bottom-emitting gallium nitride (GaN) light emitting diode. This structure contains a SiO ₂ layer below the n -GaN layer to enhance transmission through the bottom layer and a SiO [sub]2 /Ag reflector coated on the p -GaN layer to raise the reflection on the upper surface of the GaN layer. The thicknesses of the two SiO ₂ layers are optimized to improve the light extraction efficiency and internal quantum efficiency. The 200-nm-thick p -GaN layer signifies high current injection efficiency. The calculations reveal that the TM-polarized intensity in the normal direction from the optimized sample is about eight times stronger than that from the reference sample. Our designation offers the advantages of simplifying the fabricating process and reducing the manufacturing cost.

Two approaches to describe nonparaxial optical vortices were considered. One approach is to use a revised Kirchhoff integral, which does not neglect the relief of an optical element. Using this integral and the finite-difference time-domain method it is shown that an optical vortex generated by a refractive spiral plate with a relief step has an asymmetric profile. The annular diffraction pattern in the vortex beam cross-section is found to be disturbed not only for the near-field diffraction but also for the middle-field diffraction, at a distance of several Fresnel lengths. Another approach is to solve the Helmholtz equation without any approximations. An analytical solution to describe propagation of a light beam in the positive direction of the optical axis was found. The complex amplitude of such a beam is found to be in direct proportion to the product of two linearly independent solutions of Kummer’s differential equation. Relationships for a particular case of such beams—namely, the Hankel-Bessel (HB) beams—are deduced. The autofocusing of the HB beams is studied.

The vibrational state of an array of microcantilevers piezoelectrically excited has been characterized analyzing the far-field diffraction pattern produced by the structure. A model based on the definition of a complex reflectivity window has been developed to fully understand the dynamic of the elements and the diffraction pattern produced by them. This model is parameterized by the driving voltage of the excitation, the vibration mode, and the phase correlation among cantilevers. An experimental set-up has been developed to register the far-field diffraction patterns, avoiding some undesired reflections from the surrounding structures. The experimental results have been fitted with those obtained from the simulation. This fitting allows for identifying the vibration mode and the phase relation among cantilevers.

We propose and analyze new polarization converters to transform the linearly polarized laser modes into axially symmetric modes, which show more promise in various applications, as well as generating various inhomogeneously polarized configurations. Designed converters are based on the coherent composition of the modal beams with different amplitude-phased distribution and polarization states. What makes the systems simple and universal is the use of diffractive optical elements (DOEs) to generate required mode patterns with specific space orientation alongside the simultaneous generation of different beams with different transverse mode content, which can be subsequently combined. The numerical modeling of the polarization mode converters has made it possible to analyze its performance and capabilities. The DOEs in question have been designed and fabricated. Natural experiments that demonstrate the generation of vector higher-order cylindrical beams have been conducted.

This article presents a vector algorithm of the solution of the Helmholtz equation by beam propagation method (BPM), based on representation of calculations in the single instruction, multiple data model. Use of this algorithm on the graphic NVIDIA GeForce GTX 660Ti processor on the compute unified device architecture technology results in 30-times acceleration of calculations in comparison with calculations on the Intel Core2 Duo CPU E8500.

We designed two pieces of rotary diffractive optical elements (DOE) to control the incident light beam in ptychography. The incident light beam is shaped into the required complex amplitude as employed probes by using double DOEs. The high-quality probes are generated to illuminate on the different positions of the object, which leads to achieving superior ptychographical imaging by rotating DOEs. Consequently, mechanical movement of the specimen is avoided in the imaging process. The numerical experiments demonstrate the double-wheeling DOEs are effective for the ptychographical imaging. Further, the double discs containing several pairs of DOEs are designed for a larger field of view. As a result, the flexibility of ptychography may be improved by employing the rotary double DOEs.

The generation of vortex laser beam by using phase-only liquid crystal spatial light modulator (LC-SLM) combined with the spiral phase screen is experimentally and theoretically studied. Results show that Gaussian and dark hollow vortex laser beams can be generated by using this method successfully. Differing with the Gaussian and dark hollow beams, far field intensities of the generated vortex laser beams still exhibit dark hollow distributions. The comparisons between the ideal generation and experimental generation of vortex laser beams with different optical topological charges by using phase only LC-SLM is investigated in detail. Compared with the ideal generated vortex laser beam, phase distribution of the experimental generated vortex laser beam contains many phase singularities, the number of which is the same as that of the optical topological charges. The corresponding near field and far field dark hollow intensity distributions of the generated vortex laser beams exhibit discontinuous in rotational direction. Detailed theoretical analysis show that the main reason for the physical phenomenon mentioned above is the response error of phase only LC-SLM. These studies can provide effective guide for the generation of vortex laser beam by using phase only LC-SLM for optical tweezers and free space optical communication.

Detailed analysis of etch depth map for phase binary computer-generated holograms intended for testing aspheric optics is a very important task. In particular, diffractive Fizeau null lenses need to be carefully tested for uniformity of etch depth. We offer a simplified version of the specular spectroscopic scatterometry method. It is based on the spectral properties of binary phase multi-order gratings. An intensity of zero order is a periodical function of illumination light wave number. The grating grooves depth can be calculated as it is inversely proportional to the period. Measurement in reflection allows one to increase the phase depth of the grooves by a factor of 2 and measure more precisely shallow phase gratings. Measurement uncertainty is mainly defined by the following parameters: shifts of the spectrum maximums that occur due to the tilted grooves sidewalls, uncertainty of light incidence angle measurement, and spectrophotometer wavelength error. It is theoretically and experimentally shown that the method we describe can ensure 1% error. However, fiber spectrometers are more convenient for scanning measurements of large area computer-generated holograms. Our experimental system for characterization of binary computer-generated holograms was developed using a fiber spectrometer.

This paper [Opt. Eng. 52(9), 091723 (2013)] was removed from the SPIE Digital Library on 24 July 2013 by the publisher upon verifying that a significant portion of Section 4 of the paper was taken directly from the following previously published paper without attribution:

Ping Zhou and James H. Burge, “Optimal design of computer-generated holograms to minimize sensitivity to fabrication errors,” Optics Express 15(23), 15410 (2007).

The citation is provided here so that interested readers can access the information from the original source.

Space telescopes for astrophysics and astronomy have provided some of the most significant contributions to science throughout the history of the international space program. The Hubble Space Telescope (HST) continues to amaze and astound the astronomical community with a seemingly endless stream of new discoveries and measurements while further captivating the public eye with its observations and imagery. The last HST servicing mission, which repaired existing instruments and installed two completely new instruments, has helped to ensure a continuation of the images and discoveries that have long captured the global public attention. In addition, the observations from HST are complemented by others, notably from the “warm” Spitzer Space Telescope mission, the Chandra X-Ray Observatory, the recently completed Herschel Space Observatory, and the Fermi Gamma-Ray Space Telescope (celebrating its fifth year on orbit). With these space-based observations complemented by observations from ground and airborne systems, the world is poised for continued discovery for many years to come. Though the budgetary environment remains challenging for all of these programs, in particular for new programs, significant future investment is in place for continued progress. As a major example, we are actively preparing for the results from the James Webb Space Telescope (JWST), on track for launch in 2018.

We present a new approach to building a modular segmented space telescope that greatly leverages the heritage of the Hubble Space Telescope and the James Webb Space Telescope. The modular design in which mirror segments are assembled into identical panels allows for economies of scale and for efficient space assembly that make a 20-m aperture approach cost effective. This assembly approach can leverage NASA’s future capabilities and has the power to excite the public’s imagination. We discuss the science drivers, basic architecture, technology, and leveraged NASA infrastructure, concluding with a proposed plan for going forward.

The need for both high quality images and lightweight structures is one of the main drivers in space telescope design. An efficient wavefront control system will become mandatory in future large observatories, retaining performance while relaxing specifications in the global system’s stability. We present the mirror actively deformed and regulated for applications in space project, which aims to demonstrate the applicability of active optics for future space instrumentation. It has led to the development of a 24-actuator, 90-mm-diameter active mirror, able to compensate for large lightweight primary mirror deformations in the telescope’s exit pupil. The correcting system has been designed for expected wavefront errors from 3-m-class lightweight primary mirrors, while also taking into account constraints for space use. Finite element analysis allowed an optimization of the system in order to achieve a precision of correction better than 10 nm rms. A dedicated testbed has been designed to fully characterize the integrated system performance in representative operating conditions. It is composed of: a telescope simulator, an active correction loop, a point spread function imager, and a Fizeau interferometer. All conducted tests demonstrated the correcting mirror performance and has improved this technology maturity to a TRL4.

The near-earth object camera (NEOCam) is a proposed infrared space mission designed to discover and characterize most of the potentially hazardous asteroids larger than 140 m in diameter that orbit near the Earth. NASA has funded technology development for NEOCam, including the development of long wavelength infrared detector arrays that will have excellent zodiacal background emission-limited performance at passively cooled focal plane temperatures. Teledyne Imaging Sensors has developed and delivered for test at the University of Rochester the first set of approximately 10 μm cutoff, 1024×1024 pixel HgCdTe detector arrays. Measurements of these arrays show the development to be extremely promising: noise, dark current, quantum efficiency, and well depth goals have been met by this technology at focal plane temperatures of 35 to 40 K, readily attainable with passive cooling. The next set of arrays to be developed will address changes suggested by the first set of deliverables.

Parametric cost models are an important tool routinely used to plan missions, compare concepts, and justify technology investments. In 2010, the article, “Single-variable parametric cost models for space telescopes,” was published [H. P. Stahl et al., Opt. Eng. 49(7), 073006 (2010)]. That paper presented new single-variable cost models for space telescope optical telescope assembly. These models were created by applying standard statistical methods to data collected from 30 different space telescope missions. The results were compared with previously published models. A postpublication independent review of that paper’s database identified several inconsistencies. To correct these inconsistencies, a two-year effort was undertaken to reconcile our database with source documents. This paper updates and revises the findings of our 2010 paper. As a result of the review, some telescopes’ data were removed, some were revised, and data for a few new telescopes were added to the database. As a consequence, there have been changes to the 2010 published results. But our two most important findings remain unchanged: aperture diameter is the primary cost driver for large space telescopes, and it costs more per kilogram to build a low-areal-density low-stiffness telescope than a more massive high-stiffness telescope. One significant difference is that we now report telescope cost to vary linearly from 5% to 30% of total mission cost, instead of the previously reported average of 20%. To fully understand the content of this update, the authors recommend that one also read the 2010 paper.

We present our design method for a 1 m lightweight mirror in a space optical system. The mirror made of Zerodur® has pockets at the back surface and three square bosses at the rim. Metallic bipod flexures support the mirror at the bosses and adjust the mirror’s surface distortion due to gravity. Their dimensional parameters cannot be optimized independently from each other in a conventional design process, where the mirror’s optical performance is greatly influenced by the flexure configuration. With our method, the design problem is separated into two independent problems; mirror design and flexure design. Resources required to achieve the design goals are reduced by almost one order of magnitude in time. We implemented a multi-objective genetic algorithm to optimize the mirror design and satisfied the design goals. We also present a new adjustable bipod flexure as an optical compensator for the gravity-induced aberration, instead of using a monolithic bipod flexure.

Scientists are interested in using digital micromirror devices (DMD) as slit-masks in multiobject spectrometers on future space missions. A favored orbit is at the second Lagrangian point (L2). A requirement for mission planning is to determine how long such microelectrical mechanical systems devices would remain operational given the L2 radiation environment, which is primarily composed of solar protons and cosmic rays. To this end, we initiated DMD proton testing. Three DMDs were irradiated with high-energy protons (35 to 50 MeV) at the Lawrence Berkeley National Laboratory 88 in. Cyclotron. Assuming a typical spacecraft shielding of 100 mils of aluminum, our tests imply that DMDs remain fully operable in a five-year mission at L2 with a margin of safety of 4.5.

Kepler is NASA’s first space mission dedicated to the study of exoplanets. The primary scientific goal is statistical—to estimate the frequency of planetary systems associated with sun-like stars, especially the detection of earth-size planets in the habitable zones. Kepler was launched into an Earth-trailing heliocentric “drift-away” orbit (period=372  days ) in March 2009. The instrument detects the faint photometric signals of transits of planets across the stellar disks of those systems with orbital planes fortuitously oriented in our line of sight. Since the probability of such alignments is small, Kepler must observe a large number of stars. In fact, Kepler is monitoring approximately 150,000 stars with a 30-min cadence. The scientific goals led to the choice of a classical Schmidt telescope, and requirements on field-of-view, throughput, spectral bandpass, image quality, scattered light, thermal and opto-mechanical stability, and in-flight adjustment authority. We review the measurement requirements, telescope design, prelaunch integration, alignment, and test program, and we describe the in-flight commissioning that optimized the performance. The stability of the flight system has enabled increasing recognition of small effects and sophistication in data processing algorithms. Astrophysical noise arising from intrinsic stellar variability is now the dominant term in the photometric error budget.

Future lightweight and long-focal-length x-ray telescopes must guarantee a good angular resolution (e.g., 5 arc sec HEW) and reach an unprecedented large effective area. This goal can be reached with the slumping of borosilicate glass sheets that allow the fabrication of lightweight and low-cost x-ray optical units (XOU). These XOUs, based on mirror segments, have to be assembled together to form complete multishell Wolter-I optics. The technology for the fabrication and the integration of these XOUs is under development in Europe, funded by European Space Agency, and led by the Brera Observatory (INAF-OAB). While the achievement of the required surface accuracy on the glass segments by means of a hot slumping technique is a challenging aspect, adequate attention must be given to the correct integration and coalignment of the mirror segments into the XOUs. To this aim, an innovative assembly concept has been investigated, based on glass reinforcing ribs. The ribs connect pairs of consecutive foils, stacked into a XOU, with both structural and functional roles, providing robust monolithic stacks of mirror plates. Moreover, this integration concept allows the correction of residual low-frequency errors still present on the mirror foil profile after slumping. We present the integration concept, the related error budget, and the results achieved so far with a semi-robotic integration machine especially designed and realized to assemble slumped glass foils into XOUs.

Traditional mirror manufacturing, particularly for astronomical purposes, requires substantial lead time, due to the nature of the materials and the grinding/polishing process. We propose a new technique for rapid, low-cost production of large, lightweight precision optics by fusing several technologies which in combination we call frozen membrane mirror technology (FMMT). FMMT combines well-understood subsystem technologies, including electrostatic control of membrane mirrors, adaptive optics, wavefront sensing and control, and inflatable structures technology to shorten production time. The basic technique is to control the surface of a reflective coated membrane mirror with electrostatic actuation and wavefront sensor feedback and freeze the membrane shape. We discuss the details of the concept and present results of early lab testing. We focus on the optical regime, but this technology has applicability from the microwave to x-ray spectral bands. Starting with a flexible membrane mirror, one can envision techniques for deployment of large apertures in space.

Space-based observation of gravitational waves promises to enable the study of a rich variety of high energy astrophysical sources in the 0.0001 to 1 Hz band using signals complementary to traditional electromagnetic waves. Gravitational waves represent the first new tool for studying the sky since gamma ray telescopes debuted in the 1970s, and we expect compelling science to be the result. The fundamental measurement is to monitor the path length difference between pairs of freely falling test masses with laser interferometry to a precision of picometers over gigameter baselines. The test masses are arranged in an equilateral triangle to allow simultaneous measurement of both gravitational wave polarizations. The heliocentric orbital space environment enables the test masses to be shielded from large ground motions at low frequencies, and allows the construction of long measurement baselines that are well matched to the signal wavelengths. Optical telescopes play an important role in the measurement because they deliver laser light efficiently from one spacecraft to another. The telescopes are directly in the measurement path, so there are additional performance requirements to support precision metrology beyond the usual requirements for good image formation.

Following the fact that a large collection of ink and wash paintings (IWP) is being digitized and made available on the Internet, their automated content description, analysis, and management are attracting attention across research communities. While existing research in relevant areas is primarily focused on image processing approaches, a style-based algorithm is proposed to classify IWPs automatically by their authors. As IWPs do not have colors or even tones, the proposed algorithm applies edge detection to locate the local region and detect painting strokes to enable histogram-based feature extraction and capture of important cues to reflect the styles of different artists. Such features are then applied to drive a number of neural networks in parallel to complete the classification, and an information entropy balanced fusion is proposed to make an integrated decision for the multiple neural network classification results in which the entropy is used as a pointer to combine the global and local features. Evaluations via experiments support that the proposed algorithm achieves good performances, providing excellent potential for computerized analysis and management of IWPs.

We analyze the effect of aperture width of the parallax barrier on the viewing angle of one-dimensional integral imaging (1-DII) display and propose a 1-DII display that consists of a display panel and a variable parallax barrier. When the variable parallax barrier changes its aperture width, the viewing angle and the optical efficiency of the proposed 1-DII display are compared. The viewing angle is increased by decreasing the aperture width of the variable parallax barrier, while the optical efficiency is increased by increasing the aperture width of the variable parallax barrier.

Optical imaging systems are often degraded by scattering due to atmospheric particles such as haze, fog, and mist. According to the physical model of atmospheric scattering, two major factors that affect the effect of fog removal are discussed. By using joint probability density definition and the proposed joint mean shift filtering algorithm, discontinuity preserving smoothing and image segmentation are addressed in the sequel to refine the atmospheric veil and estimate the atmospheric light, which overcomes the inherent limitations of the state-of-the-art methods. Simulation results on a variety of outdoor foggy images demonstrate that the proposed method achieves short computation time and good restoration for visibility and color fidelity. An embedded vision enhanced system based on a DSP is designed and runs the proposed algorithm at 15 fps for a color frame of 720×576  pixels .

In the field of photography measurement, parameterized models are usually established to account for lens distortions, such as the radial, tangential, affine, and nonorthogonality deformations. However, all of these models are the approximations of the realistic model of lenses, instead since some distortions cannot be parameterized accurately. This restricts the improvement of measuring accuracy. Moreover, the nonlinear minimization, which has been widely used with the pin-hole model and lens distortion model coupled, always converges to local solution because of the correlation of the parameters in the two models. Several researchers have proposed generic nonparametric idea, which can be applied equally well to all types of cameras, but the accuracy cannot meet the requirement of close-range photogrammetry. So an optical calibration method based on nonparametric ideas is proposed to find the mapping between incoming scene rays and image points, and subpixel image processing was used to position the image points. It is applicable to a central (single viewpoint) camera equipped with any lenses. This method is applied to the stereoscopic system, and the results show a good measuring accuracy.

A method to detect generic objects by training with a few image samples is proposed. A new feature, namely locally adaptive steering (LAS), is proposed to represent local principal gradient orientation information. A voting space is then constructed in terms of cells that represent query image coordinates and ranges of feature values at corresponding pixel positions. Cell sizes are trained in voting spaces to estimate the tolerance of object appearance at each pixel location. After that, two detection steps are adopted to locate instances of object class in a given target image. At the first step, patches of objects are recognized by densely voting in voting spaces. Then, the refined hypotheses step is carried out to accurately locate multiple instances of object class. The new approach is training the voting spaces based on a few samples of the object. Our approach is more efficient than traditional template matching approaches. Compared with the state-of-the-art approaches, our experiments confirm that the proposed method has a better performance in both efficiency and effectiveness.

Banknote recognition systems have many applications in the modern world of automatic monetary transaction machines. They are traditionally based on simple classifiers applied over manually selected areas. A new solution in this field, borrowed by content-based image retrieval (CBIR), which is based on dense scale-invariant feature transform features in a bag-of-words framework followed by a support vector machine (SVM) classifier, is explored. The proposed computer vision system for banknote recognition, on one hand, enables recognition at high accuracy and speed, and, on the other hand, provides basis for further applications, e.g., counterfeit detection and fitness test. This approach makes the system robust to various defects, which may occur during image acquisition or during circulation life of banknote. We implemented and tested on an embedded platform three state-of-the-art classification techniques [SVM, artificial neural network (ANN), and hidden Markov model (HMM)]. The comparative results are reported for accuracy with different sizes of the training datasets and with various types of datasets. In this framework, the SVM classifier outperforms ANN and HMM on the basis of speed and accuracy on our embedded platform.

We have designed and built a time-gated continuous wave stimulated emission depletion (CW-STED) nanoscopy to visualize microstructures beyond the diffraction limit. An off-line time-gating detection was performed with the help of time-correlated single-photon counting technique. Experimental results showed that before time-gating, the resolution of our system was about 75 nm with a depletion beam (592 nm) power of 200 mW. By using the off-line time-gating detection, the resolution was further improved to 38 nm. Biological samples were also used to test the performance of our time-gated CW-STED, and a resolution of 70 nm was achieved with a depletion beam (592 nm) power of 85 mW. Detailed principles of time-gated CW-STED were discussed in the text. The time-gated STED provides a better resolution with finite laser power.

Measuring the flow velocity in small gaps or near a surface with a nonintrusive optical measurement technique is a challenging measurement task, as disturbing light reflections from the surface appear. However, these measurements are important, e.g., in order to understand and to design the leakage flow in the tip gap between the rotor blade end face and the housing of a turbomachine. Hence, methods to reduce the interfering light power and to correct measurement errors caused by it need to be developed and verified. Different alternatives of minimizing the interfering light power for optical flow measurements in small gaps are presented. By optimizing the beam shape of the applied illumination beam using a numerical diffraction simulation, the interfering light power is reduced by up to a factor of 100. In combination with a decrease of the reflection coefficient of the rotor blade surface, an additional reduction of the interfering light power below the used scattered light power is possible. Furthermore, a correction algorithm to decrease the measurement uncertainty of disturbed measurements is derived. These improvements enable optical three-dimensional three-component flow velocity measurements in submillimeter gaps or near a surface.

A two-beam phase-sensitive optical time domain reflectometer (OTDR) is proposed and experimentally demonstrated. Optical pulses are launched into two distributed fibers. With the interference effect of two channel Rayleigh scattering signals and the positioning principle of the traditional OTDR, detection and location of vibration events along sensing fibers can be achieved using a new signal processing scheme. What is more, to investigate the sensitivity fading problem that often occurred when polarization controller (PC) is not utilized, the optical polarization model based on the equivalent Jones matrices of sensing fibers is established. Simulation results show that due to the polarization characteristic discrepancy of the sensing fibers, the signal amplitude varies a lot for different polarization states of the incident light. Experimental result shows that with the PC, the signal signal to noise ratio can be stabilized as 9.5 dB, which verifies the effectiveness of the sensor.

A modified Michelson interferometer for spatial phase shifting speckle shearography is presented. The interferometer consists of one slit aperture, one beam splitter, and two spherical mirrors. Spatial carrier frequency and shear are both generated by one translated spherical mirror. The slit aperture controls the speckle size. These arrangements make the system simple and easy to align. The shear is proportional to the translation of the spherical mirror. Shear distortion due to the rotated mirror in a traditional Michelson interferometer is avoided as well. The carrier frequency is proven to be constant in image plane and can be conveniently adjusted by translating the spherical mirror without changing imaging setup. Fourier analysis method is applied to accurately calibrate carrier frequency. Finally, experimental dynamic deformation results of a center loaded metal plate using the proposed method are provided.

Two optical techniques, m-lines and spectroscopic ellipsometry, are compared for their suitability for obtaining the wavelength and the temperature dispersion of the refractive index of thin-film layers used in gas detector devices. Two types of materials that are often integrated into gas sensors are studied: a polymer organic–inorganic blend deposited by spin coating typically used in near-infrared waveguides and the ceramic semiconductor SrTi _1−x Fe _x O ₃ (strontium titanate) doped with iron at concentrations x=0.075 and 0.1 deposited by electron beam deposition. The refractive index dispersion obtained by m-lines and ellipsometry is compared, and the differences between the measured parameters for the two materials are discussed. The chromatic dispersion will be represented by a three-term Cauchy law. An intuitive method for verifying the measured indices using an integrating sphere and reflexion coefficient modeling techniques are also demonstrated. Thermo-optic coefficients in the order of −1×10 ⁻⁴ /K for both materials are reported, and very low chromatic dispersions are also measured, thanks to the high sensitivity of the m-lines technique. The uniaxial anisotropic properties of the polymer-blend films are measured and discussed in the case of the semiconductor films.

An algorithm for interpolation of central fringe position in low-coherence interferometry measurements is presented. The algorithm is based on a polynomial curve fitting. Fast calculation of interpolation is possible due to the use of an NVIDIA Compute Unified Device Architecture (CUDA) technology, which allows independent analysis of different points of a high-resolution detector matrix on separate cores of a graphics processing unit (GPU). The dependency of the method’s accuracy on the spectral width of the light source is checked. The computation times on a GPU are compared with those achieved with a multicore central processing unit, showing nearly 30 times faster calculations when using CUDA technology. The algorithm accuracy is tested by measuring a flat glass surface with two different cameras—an ordinary CCD camera and a cooled EMCCD camera. Finally, the algorithm is applied to measurements of a populated optical fiber connector array prototyped using deep proton writing technology.

The reliability of ray tracing simulations is strongly dependent on the accuracy of the input data such as the bidirectional reflectance distribution function (BRDF). Software developers offer the possibility to implement BRDF data in different ways, ranging from simple predefined functions to detailed tabulated data. The impact of the accuracy of the implemented reflectance model on ray tracing simulations has been investigated. A light-emitting diode device including a frequently employed diffuse reflector [microcellular polyethylene terephthalate (MCPET)] was constructed. The luminous intensity distribution (LID) and luminance distribution from a specific viewpoint were measured with a near-field goniophotometer. Both distributions were also simulated by use of ray tracing software. Three different reflection models of MCPET were introduced, varying in complexity: a diffuse model, a diffuse/specular model, and a model containing tabulated BRDF data. A good agreement between the measured and simulated LID was found irrespective of the applied model. However, the luminance distributions only corresponded when the most accurate BRDF model was applied. This proves that even for diffuse reflective materials, a simple BRDF model may only be employed for simulations of the LID; for evaluation of luminance distributions, more complex models are needed.

The Solar Ultraviolet Imager (SUVI) is one of the several instruments that will fly on board the next generation of Geostationary Operational Environmental Satellites R-U platforms, as part of the National Oceanic and Atmospheric Administration’s space weather monitoring fleet. SUVI is a generalized Cassegrain telescope that employs multilayer-coated optics that operate in six extreme ultraviolet (EUV) narrow bandpasses centered at 93.9, 131.2, 171.1, 195.1, 284.2 and 303.8 Å. The innovation of the design is that SUVI is the first EUV solar telescope that has six different wavelength channels accommodated on each mirror. And despite having six segmented multilayer-coatings, shadowing (due to the mask) is minimized allowing SUVI to exceed its effective area specifications. Once operational, SUVI will record full-disk, spectroheliograms every few minutes, where this data will be used to better understand the effects of solar produced EUV radiation on Earth and the near-Earth environment. The material presented discusses general aspects of the SUVI optical design, mirror fabrication, super polishing, and metrology carried out to verify optical surface quality and in-band, EUV reflectivity performance of the multilayer coatings. The power spectral density and EUV measurements are shown to exceed performance requirements and are critical for the overall calibration and monitoring of SUVI’s throughput and imaging performance, once operational.

A holographic lithography method for fabricating large-scale photonic phased array is presented. The large-scale array could be generated using a specially designed holographic optical element and the period could be decreased by half with the help of a half-wave plate. This method provides a convenient way to obtain the photonic array with a smaller period without shortening the recording wavelength. matlab simulations and primary experimental results have demonstrated that the phase modulation and nonlinear photoresist response played collectively significant roles in tuning the distribution of the array. The large-scale photonic phased array with a smaller period is an ideal candidate as a Raman substrate.

By methods of cross-sectional transmission electron microscopy and small-angle x-ray scattering (λ=0.154  nm ) the influence of Ar gas pressure (1 to 4 mTorr) on the growth of amorphous interfaces in Mo/Si multilayers (MLs) deposited by DC magnetron sputtering is studied. The significant reduction in the ML period, which is evident as a volumetric contraction, is observed in MLs deposited at Ar pressure where the mean-free path for the sputtered atoms is comparable with the magnetron-substrate distance. Some reduction in the thickness of the amorphous interlayers with Ar pressure increase is found, where the composition of the interlayers is enriched with molybdenum. The interface modification resulted in an increase in EUV reflectance of the Mo/Si MLs.

Transmission-link induced-intensity noise, as well as the conversion of intensity fluctuation to demodulated phase noise in a 400-km interrogated hydrophone array with a phase-generated carrier (PGC) scheme are investigated. Theoretical and experimental results all show that a PGC scheme can increase the erbium-doped fiber amplifiers-induced phase noise level by ∼3.7  dB in intensity to phase noise conversion. However, it can significantly reduce the coherent double Rayleigh scattering (DRS)-induced phase noise by ∼11.7  dB when compared with the unmodulated DRS intensity noise. Considering the effects of these two kinds of noises, a PGC scheme still has significant advantages for noise suppression in the remote system, and the total phase noise of the 400-km hydrophone system is shown to be only 11 to 14  μrad/sqrt (Hz) . Moreover, it is demonstrated that the spectra of DRS-induced relative intensity noise and phase noise all have Lorentzian line shapes and the full widths at half maximum are twice the width of the laser source. This result is helpful for us to choose a suitable laser source in long-distance hydrophone systems.

The hybrid Raman and erbium-doped fiber amplifier is investigated for a 16×40  Gbps differential phase-shift keying (DPSK) modulation system at different channel spacings. It is reported that the proposed hybrid optical amplifier (HOA) provides better gain, signal quality and induces lesser crosstalk even when 640 Gbps DPSK signals are transmitted over 100 km of pumped single mode fiber. Further, the proposed system performance is compared with the current state-of-the-art HOA schemes.

The hybrid mid-link spectral inversion (H-MLSI) and digital signal processing techniques to compensate for the optical Kerr effects in 224  Gbit/s DP-16QAM transmission over 640 km of single-mode fiber are numerically evaluated. Digital signal processing methods, i.e., electronic dispersion compensation (EDC) and digital backward propagation (DBP) techniques, are implemented. The system is evaluated for diverse signal input launch powers for both single-channel and multichannel transmission in which five channels are multiplexed with a channel spacing of 100 GHz with central wavelength at 1550 nm. The system performance is enumerated by monitoring the bit error ratio. From the results, it is clear that the nonlinear threshold point is improved by 2 and 3 dBm signal power by using H-MLSI and DBP, respectively, with 20 steps per fiber span as compared to EDC. Furthermore, we have also evaluated the DBP complexity as compared to H-MLSI and the resultant impact on maximum transmission distance. Moreover, the performance penalty coming from the span-offset of H-MLSI can be reduced by employing DBP to compensate for the residual Kerr effects.

A new wavelength locking method for tunable diode lasers based on a photoacoustic (PA) detection unit is presented. A wavelength modulated laser is repeatedly tuned over an absorption line of a small molecule in the gaseous phase and the generated PA signal is recorded. In the phase variation curve of the recorded PA signal, there is a 180-deg phase reversal around the peak of the absorption line, and the corresponding inflection point is a characteristic wavelength feature to be used for wavelength locking. An automated algorithm has been developed, which has <2  s execution time if the optical absorption coefficient at the peak of the absorption line is at least 2×10 ⁻⁵   cm ⁻¹ . With this algorithm, the wavelength of a near-infrared distributed feedback diode laser can be locked with an absolute accuracy of 60 fm (i.e., relative accuracy of 4×10 ⁻⁸ ) or better even at atmospheric sample gas pressure. As there is no need to stabilize the gas pressure or temperature or the concentration of the light absorbing component and the PA detection unit can be easily integrated into various experimental setups, the proposed method has the potential to be applicable even under demanding industrial or field conditions.

A monolithic tunable laser on a quantum well (QW) structure is demonstrated by integrating an optical beam-steering section with an area-selectively intermixed QW gain section. Wavelength tuning is achieved by guiding an amplified optical beam over an optical gain medium that consists of three laterally adjacent regions containing a quantum well that has been selectively intermixed to varying extents. The laser light output can be tuned over a total of a 17-nm wavelength range by separately injecting electrical current pulses to each of the two parallel contacts in the steering region and to the optical amplifier contact.

To characterize nonlinear optical fiber, a semi-analytical formulation using variational principle and the Nelder–Mead Simplex method for nonlinear unconstrained minimization is proposed. The number of optimizing parameters in order to optimize core parameter U has been increased to incorporate more flexibility in the formulation of an innovative form of fundamental modal field. This formulation provides accurate analytical expressions for modal dispersion parameter (g ) of optical fiber with Kerr nonlinearity. The minimization of core parameter (U), which involves Kerr nonlinearity through the nonstationary expression of propagation constant, is carried out by the Nelder–Mead Simplex method of nonlinear unconstrained minimization, suitable for problems with nonsmooth functions as the method does not require any derivative information. This formulation has less computational burden for calculation of modal parameters than full numerical methods.

A multiwavelength midinfrared quasi-phase-matched (QPM) difference frequency generation (DFG) scheme is proposed based on a segmented temperature controlling technique for the uniform grating periodically poled lithium niobate (PPLN). The QPM DFG output performances have been investigated under the fixed pump and signal wavelength conditions, respectively. Our theoretical results show that when the pump wavelength is fixed at 1.08 μm, three idler QPM bands, located at 3.46, 3.50, and 3.57 μm, have been obtained, where the temperatures of the three PPLN segments with the same length are set at 20°C, 70°C, and 100°C. However, when the signal wavelength is fixed at 1.58 μm, six idler QPM bands, located at 2.95, 3.06, 3.14, 3.63, 3.72, and 3.83 μm, have been achieved with the same crystal temperature distribution of 20°C, 70°C, and 100°C.

An approach for the implementation of microwave photonic filter with positive and negative coefficients using an unbalanced Mach–Zehnder modulator (MZM) is proposed and demonstrated. In the proposed filter, a microwave signal to be filtered is applied to the unbalanced MZM via the radio frequency port. Thanks to the unbalance between the two arms of the modulator, a π -phase shift is obtained by adjusting the wavelength spacing between the adjacent wavelengths, which leads to the generation of the positive and the negative coefficients. An equivalent experiment is performed to verify our approach. A four-tap and a six-tap microwave photonic filter with positive and negative coefficients are experimentally demonstrated. The tunability and the reconfigurability of the microwave photonic filter are also investigated.

A survivable wavelength-division multiplexing passive optical network (WDM-PON) with centralized protection scheme and colorless optical network units is proposed. The sideband channels generated via optical carrier suppression technique are used to carry both the downstream (DS) and the upstream (US) remodulated signals for two neighboring sub-PONs. By employing alternate path routing of sideband channels, the centralized protection scheme can provide reliable protection against any failure in feed fibers, remote node, and distribution fibers. The number of extra fibers is greatly reduced, and efficient utilization of wavelength resource is achieved. The feasibility of the proposed system is verified by 10-Gb/s DS and 1.25-Gb/s US signals over 25-km single-mode fiber transmission in both working and protection modes.

A highly birefringent dispersion compensating microstructure optical fiber (MOF) based on a modified spiral (MS)-MOF is presented that successfully compensates the dispersion covering the E- to L-communication bands ranging from 1370 to 1640 nm. It is shown theoretically that it can obtain a negative dispersion coefficient of about −221 to −424  ps/(nm⋅km) ) over S to L bands and −327  ps/(nm⋅ km) ) at the operating wavelength of 1550 nm. The relative dispersion slope is perfectly matched to that of single-mode fiber of about 0.0036  ^{nm −1} . Besides, the proposed MS-MOF offers high birefringence of 1.79×10 ⁻² with a large nonlinear coefficient of about 41.8  W ⁻¹  km ⁻¹ at the operating wavelength along with two zero dispersion wavelengths at 610 and 1220 nm. Futhermore, the variation of structural parameters is also studied to evaluate the tolerance of the fabrication.

The results of a theoretical study of pump absorption properties in the colinear side-pumping schemes with pumping loops and absorption loops are presented. For side-pumping schemes with pumping loops, the number of pumping loops affects the pump absorption obviously: the more pumping loops, the higher pump absorption; and the pump light is absorbed effectively after propagating through all the loops. For side-pumping schemes with absorption loops, more loops results in a larger doped region, which leads to higher pump absorption efficiency.

Nowadays, optical networks are becoming dense while detecting faulty branches in the tree-structured networks has become problematic. Conventional methods are inconvenient as they require an engineer to visit the failure site to check the optical fiber using an optical time-domain reflectometer. An innovative monitoring technique for tree-structured network topology in Ethernet passive optical networks (EPONs) by using the erbium-doped fiber amplifier to amplify the traffic signal is demonstrated, and in the meantime, a residual amplified spontaneous emission spectrum is used as the input signal to monitor the optical cable from the central office. Fiber Bragg gratings with distinct center wavelengths are employed to reflect the monitoring signals. Faulty branches of the tree-structured EPONs can be identified using a simple and low-cost receiver. We will show that this technique is capable of providing monitoring range up to 32 optical network units using a power meter with a sensitivity of −65  dBm while maintaining the bit error rate of 10 ⁻¹³ .

Orthogonal on–off keying (O ³ K ) is a coded modulation technique, where the input digital signal is mapped into a block of orthogonal codes. The encoded data, which is in orthogonal space, modulates the laser beam by means of O ³ K . At the receiver, two photocells are cross coupled to compensate for the sunlight and other atmospheric noise. Since the laser beam is highly directional and can only be acquired by one photocell, the input laser signal can then be received with little noise, and signal processing is made easier. These techniques are especially beneficial in high bandwidth, long distance secure laser communication applications, such as for use in unmanned aerial vehicles.

A model is presented to explain the refractive index changes in the ion-implanted neodymium-doped yttrium vanadate waveguide region, which is helpful for characterizing index profile dependence on implantation parameters. It indicates that the lattice damage is the main factor for the refractive index changes. Waveguide structure is formed mainly due to an increase of ordinary refractive index in the ion-implanted region. The theoretical results based on this model are in good agreement with the experimental data from 500 keV Si⁺ ion implantations and keV He⁺ ion implantations.

The grating lobes of the liquid crystal optical-phased array (LCOPA) based on blazed grating theory is studied. Using the Fraunhofer propagation principle, the analytical expressions of the far-field intensity distribution are derived. Subsequently, we can obtain both the locations and the intensities of the grating lobes. The derived analytical functions that provide an insight into single-slit diffraction and multislit interference effect on the grating lobes are discussed. Utilizing the conventional microwave-phased array technique, the intensities of the grating lobes and the main lobe are almost the same. Different from this, the derived analytical functions demonstrate that the intensities of the grating lobes are less than that of the main lobe. The computer simulations and experiments show that the proposed method can correctly estimate the locations and the intensities of the grating lobes for a LCOPA simultaneously.

We present innovative structures for ring-based Raman amplifier with two separate entrances for the pump and signal. In this way, only the pump is coupled into the ring and the signal passes directly through the path that the amplified pump is propagating inside the ring without a destructive effect on signal pulse. Using engineered nanoholes filled with optofluidic material in the signal and pump paths, we reduce pump and signal group velocity to improve the structure and achieve larger Raman gain. The time evolution and propagation of picosecond signal pulses and dispersion inside the device are analyzed. Maxwell equations are solved using finite difference time-domain method considering optical nonlinear parameters like two photon absorption, free-carrier absorption, and Kerr effect.

Guidelines for the design and fabrication of polymer photonic crystal channel drop filters for coarse wavelength division multiplexing are provided. A Fabry-Perot cavity consisting of a membrane-type slab photonic crystal, where a hole row perpendicular to the propagation direction is removed, is considered. We selected nanoimprinting as the manufacturing technique. The influence on the cavity performance of several key parameters, i.e., polymer core material, lattice geometry, defect length, and holes’ radius, has been investigated in a device compliant with the requirement of the ITU-T G.694.2 standard. A detailed analysis of the fabrication tolerances has been carried out at 1551 nm. The maximum acceptable drift of the geometrical parameters has been accurately evaluated by using the finite element method to prove that the fabrication tolerances do not significantly affect the performance of polymer filters for coarse wavelength division multiplexing, when manufactured by thermal nanoimprinting lithography.

An image-based technique for measuring the complex field in the pupil of an imaging system is presented. Two point source images, one with a small modification introduced in the pupil, are combined using a simple and non-iterative algorithm. The non-interferometric method is based on the change in the optical transfer function (OTF) giving a differential optical transfer function (dOTF). The dOTF includes two images of the complex pupil field, conjugated and reflected about the position of the pupil modification, leaving an overlap that obscures some of the pupil. The overlap can be minimized by introducing the modification near the edge of the pupil. The overlap region can be eliminated altogether by using a second modification and a third point source image. The pupil field is convolved by the change in the pupil field, so smaller modification areas are preferred. When using non-monochromatic light, the dOTF incurs a proportional radial blurring determined by the fractional bandwidth. We include some simple demonstration experiments, including using a pupil blockage and moving a single deformable mirror actuator as the pupil modification. In each case, the complex wavefront is easily recovered, even when the pupil mask is unknown and the wavefront aberrations are large.

The efficient application of the Mach–Zehnder interferometer (MZI) structure for the construction of the well-known logic gates is described. It deals with the effect of the varying voltages of each electrode on the performance of MZI. It has been found that power transmission gets switched with the variation of voltage in the electrodes. The results are of prime importance for optical gate implementation as well as being useful in the signal router. There is a commercial demand of optical gates and signal routers in dense wavelength division multiplexing. The result is also verified by proper analysis using OptiBPM and matlab softwares.

Brillouin optic time-domain analysis/reflectometry (BOTDA/R) is a fully distributed optical sensing technique that can provide strain or temperature information along the whole length of a single-mode fiber and has attracted worldwide attentions in recent years. However, both spatial and distance resolution of BOTDA/R are too low to satisfy the measurement of local damage, and enhancing the performance of spatial or distance resolution is considered to be a problem. A novel equidistance difference optimum method is proposed to compensate for the weak spatial and distance resolution of BOTDA/R. The principle of the proposed method is introduced, and two demonstration tests are carried out to validate the local damage detection ability. The experimental results show that the Brillouin optical fiber sensor measuring space can cover any part of the sensor without changing the default values of the Brillouin system, which can greatly enrich the information of measured elements and detect the local damages well.