I am writing the editorial this month with my daughter, Madison Driggers (otherwise known as Maddie). She is 14 years old, beautiful, makes good grades, has lots of friends, is very popular, and overall, is a great daughter. She really likes Justin Bieber and is going to one of his concerts in a week. I asked her today what she wanted to do after high school. She said she definitely wants to go to college, but her primary interest is medicine. Her reasons are: her mom is an OB/GYN doctor (a big influence), doctors make really good money, and they help people (so it’s satisfying and gratifying). Maddie likes babies, so she is likely to be an OB/GYN doctor.

We propose a different reflection-based technique, named efficient neighbor channel reservation, where a contending burst is reflected from a suitable neighbor node and then resumes its original path. Our proposed scheme does not use any extra hardware and addresses several limitations of other schemes including: (a) eliminating the use of bulky fiber delay lines, (b) avoiding complexity required with burst segmentation, (c) preventing resource wastage that occurs with prereservation schemes, and (d) preventing loop formation inherent in most deflection routing schemes.

An effective way to resolve the viewing-angle characteristics of microcavity red emission top-emitting organic light-emitting diodes (TOLEDs) by introducing grating and filling process into TOLEDs is demonstrated. From this approach, gradually changed cavity length can be obtained and the range of the resonant wavelength in these devices can be broadened. As a result, TOLEDs with grating exhibit a quasi-Lambertian emission pattern and have no color shift at different viewing angles. In addition, we can almost observe the same luminance and efficiency in TOLEDs with and without grating.

A method for generating a high-order (≥2 ) polarized vortex beam by using achromatic meniscus axicon doublets (MADs) is described. The MAD has a rotationally symmetric structure and consists of a pair of identical meniscus axicons with the same apex angle. It exploits four total internal reflections when collimated rays pass through it to produce a half-wave retardation, but with azimuth-variant polarization orientations. The characteristics of high achromatism of retardance, reasonable acceptance angular aperture for MAD, are numerically demonstrated. The effect of the remaining stress birefringence of optical materials on retardation is also discussed.

This special section of Optical Engineering is focused on ground-based telescopes and instrumentation. Several new ground-based facilities have started operations, and astronomical instrumentation has been developed from new and creative technologies. The papers that are contained in this special section include upgrades to existing telescopes/observatories to improve image quality. They also describe new accurate tracking control systems that are being deployed from small to large telescopes in multiple wavelengths.

LINC-NIRVANA (LN) is the near-infrared, Fizeau-type imaging interferometer for the large binocular telescope (LBT) on Mt. Graham, Arizona (elevation of 3267 m). The instrument is currently being built by a consortium of German and Italian institutes under the leadership of the Max Planck Institute for Astronomy in Heidelberg, Germany. It will combine the radiation from both 8.4 m primary mirrors of LBT in such a way that the sensitivity of a 11.9 m telescope and the spatial resolution of a 22.8 m telescope will be obtained within a 10.5×10.5 arcsec ² scientific field of view. Interferometric fringes of the combined beams are tracked in an oval field with diameters of 1 and 1.5 arcmin. In addition, both incoming beams are individually corrected by LN’s multiconjugate adaptive optics system to reduce atmospheric image distortion over a circular field of up to 6 arcmin in diameter. A comprehensive technical overview of the instrument is presented, comprising the detailed design of LN’s four major systems for interferometric imaging and fringe tracking, both in the near infrared range of 1 to 2.4 μm, as well as atmospheric turbulence correction at two altitudes, both in the visible range of 0.6 to 0.9 μm. The resulting performance capabilities and a short outlook of some of the major science goals will be presented. In addition, the roadmap for the related assembly, integration, and verification process are discussed. To avoid late interface-related risks, strategies for early hardware as well as software interactions with the telescope have been elaborated. The goal is to ship LN to the LBT in 2014.

Movies with fields-of-view larger than normal, for high-resolution telescopes, will give a better understanding of processes on the Sun such as filament and active region developments and their possible interactions. New active regions can serve as an igniter of the eruption of a nearby filament. A method to create a large field-of-view is to join several fields-of-view into a mosaic. Fields are imaged quickly, one after another, using fast telescope-pointing. Such a pointing cycle has been automated at the Dutch open telescope (DOT), a high-resolution solar telescope located on the Canary Island La Palma. The number and positions of the subfields are calculated automatically and represented by an array of bright points in the guider image which indicates the subfield centers inside the drawn rectangle of the total field on the computer screen with the whole-sun image. Automatic production of flats is also programmed. For the first time, mosaic movies were programmed from stored information on automated telescope motions. The mosaic movies show larger regions of the solar disk in high resolution and fill a gap between available whole-sun images with limited spatial resolution of synoptic telescopes including space instruments and small-field high-cadence movies of high-resolution solar telescopes.

Images obtained with the Southern African Large Telescope (SALT) during its commissioning phase in 2006 showed degradation due to a large focus gradient, astigmatism, and higher order optical aberrations. An extensive forensic investigation exonerated the primary mirror and the science instruments before pointing to the mechanical interface between the telescope and the spherical aberration corrector, the complex optical subassembly which corrects the spherical aberration introduced by the 11-m primary mirror. Having diagnosed the problem, a detailed repair plan was formulated and implemented when the corrector was removed from the telescope in April 2009. The problematic interface was replaced, and the four aspheric mirrors were optically tested and re-aligned. Individual mirror surface figures were confirmed to meet specification, and a full system test after the re-alignment yielded a root mean square wavefront error of 0.15 waves. The corrector was reinstalled in August 2010 and aligned with respect to the payload and primary mirror. Subsequent on-sky tests revealed spurious signals being sent to the tracker by the auto-collimator, the instrument that maintains the alignment of the corrector with respect to the primary mirror. After rectifying this minor issue, the telescope yielded uniform 1.1 arcsec star images over the full 10-arcmin field of view.

The segmented large millimeter telescope (LMT/GTM) is the largest spatial light modulator capable of producing vortex beams of integer topological charge. This observing mode could be applied for direct exoplanet searches in the millimeter or submillimeter regimes. The stability of the vortex structure against aberrations and diffraction effects inherent to the size and segmented nature of the collector mirror was studied. In the presence of low-order aberrations, the focal distribution of the system remains stable. Results show that these effects depend on the topological charge of the vortex and the relative orientation of the aberration with respect to the antenna axis. Coma and defocus show no large effects in the image at the focal plane; however, the system is very sensitive to astigmatism. Heat turbulence, simulated by random aberrations, shows that the system behaves in a similar way as astigmatism dissociating the vortices. The segmented vortex telescope is proposed as a novel approach for the detection of giant planets outside circumstellar disks around nearby stars. Since results are applicable to other facilities with segmented surfaces, it is suggested that this idea should be considered as a regular observation mode complementary to interferometric methods.

The GREGOR Fabry-Pérot Interferometer (GFPI) is one of three first-light instruments of the German 1.5-m GREGOR solar telescope at the Observatorio del Teide, Tenerife, Spain. The GFPI allows fast narrow-band imaging and postfactum image restoration. The retrieved physical parameters will be a fundamental building block for understanding the dynamic sun and its magnetic field at spatial scales down to ∼50  km on the solar surface. The GFPI is a tunable dual-etalon system in a collimated mounting. It is designed for spectrometric and spectropolarimetric observations between 530–860 nm and 580–660 nm, respectively, and possesses a theoretical spectral resolution of R≈250,000. Large-format, high-cadence charged coupled device detectors with sophisticated computer hard- and software enable the scanning of spectral lines in time-spans equivalent to the evolution time of solar features. The field-of-view (FOV) of 50′′×38′′ covers a significant fraction of the typical area of active regions in the spectroscopic mode. In case of Stokes-vector spectropolarimetry, the FOV reduces to 25′′×38′′. The main characteristics of the GFPI including advanced and automated calibration and observing procedures are presented. Improvements in the optical design of the instrument are discussed and first observational results are shown. Finally, the first concrete ideas for the integration of a second FPI, the blue imaging solar spectrometer, are laid out, which will explore the blue spectral region below 530 nm.

We describe the details of telescope control system design for the 50/80  cm Schmidt telescope at the Aryabhatta Research Institute of Observational Sciences. The overall control hardware architecture features a distributed network of microcontrollers over controller area network for interfacing the feedback elements and controlling the actuators. The main part of the hardware is a controller whose final objective is to provide position control with 10 arcsec accuracy and velocity control with 1  arcsec/s accuracy. For modeling and simulation, the telescope parameters were experimentally determined. A linear proportional integral (PI) controller was designed for controlling the twin-motor drive mechanism of the telescope axes. The twin-motor drive is provided with differential torque for backlash-free motion reversal. This controller is able to maintain negligible rms errors at all velocities. At higher speeds over 2  deg/s , the PI controller performs with peak errors less than 1%. Whereas at fine speeds, depending upon the preload on bearings, limit cycles are exhibited due to nonlinear friction posing control related problems. We observed that the effect of nonlinear friction dynamics can be reduced by reducing the preload on the drive bearings and the peak errors at fine speeds using a linear controller can be maintained within 25%.

A satellite image enhancement method based on singular value decomposition (SVD) is presented. The proposed method consists mainly of four steps: image decomposition, adjustable contrast enhancement, noise reduction, and image composition. The method decomposes an image into its singular values, from which the luminance information can be obtained using SVD. In turn, adjustable contrast enhancement is applied by changing the singular values, which are controlled by characteristic-based contrast-level parameters. In the noise reduction process, the high-frequency elements, such as noise, are removed using rank approximation. In the final image composition process, the proposed algorithm combines color and luminance components in order to preserve color consistency. Experimental results show that the proposed scheme has less noise than the conventional methods and improves contrast performance while preserving details.

The design of two new three-level (3-L) microbolometer structures together with their absorption coefficient optimizations are reported. Three-level microbolometers are the detectors where three sacrificial layers are used during their fabrication process. They are needed to increase the performance of the microbolometer detectors when the lithography and etch-process capabilities of the fabrication facility are limited. Two new 3-L microbolometers are proposed and the absorption simulations of these detectors are performed using a cascaded transmission line model of the detectors. The thermal simulations of the proposed detectors are also done using CoventorWare FEM software. The absorption coefficient of the detectors can be as high as 92%, and their thermal conductance values can be as low as 2.4×10 ⁻⁸   W/K depending on the type of the detector, resulting in an improvement of 50% on the NETD value when compared with a standard 2-L microbolometer structure fabricated using the same technology. The proposed detector structures can be used to decrease the need for high-process capabilities and make it possible to fabricate high-performance microbolometer detectors especially for universities and research centers.

An optical indicator is designed to detect the moving targets in complex-valued synthetic aperture radar (SAR) images and estimate their azimuth velocity components. The indicator consists of two subsystems, and each of them is composed of one phase-only filter and two cylindrical lenses. The subsystems refocus the SAR image by changing the parameters of the phase-only filters to get two refocused images in which the background is defocused to the same extent while the moving targets are defocused differently. The indicator involved detects moving targets by comparing the sharpness of two defocused SAR images piece-by-piece, and then estimates the azimuth velocity of each detected target from its sharpness difference curve. The effectiveness of the optical architecture is investigated, and the proposal is confirmed by theoretical analysis and experiments with simulated and field data.

Large-scale psychophysical experiments are carried out on two types of mobile displays to evaluate the perceived image quality (IQ). Eight perceptual attributes, i.e., naturalness, colorfulness, brightness, contrast, sharpness, clearness, preference, and overall IQ, are visually assessed via categorical judgment method for various application types of test images, which were manipulated by different methods. Their correlations are deeply discussed, and further factor analysis revealed the two essential components to describe the overall IQ, i.e., the component of image detail aspect and the component of color information aspect. Clearness and naturalness are regarded as two principal factors for natural scene images, whereas clearness and colorfulness were selected as key attributes affecting the overall IQ for other application types of images. Accordingly, based on these selected attributes, two kinds of empirical models are built to predict the overall IQ of mobile displays for different application types of images.

A high-speed digital streak camera designed for simultaneous high-resolution color photography and focusing schlieren imaging is described. The camera uses a computer-controlled galvanometer scanner to achieve synchroballistic imaging through a narrow slit. Full color 20 megapixel images of a rocket sled moving at 480  m/s and of projectiles fired at around 400  m/s were captured, with high-resolution schlieren imaging in the latter cases, using conventional photographic flash illumination. The streak camera can achieve a line rate for streak imaging of up to 2.4  million lines/s .

This paper is to account for joint detection, tracking, and classification (JDTC) of an unknown and time-varying number of maneuvering targets in clutter. Unlike most tracking algorithms that use only the kinematic measurements, this paper proposes a recursive JDTC algorithm to exploit the coupled information between target detection, tracking and classification based on the Gaussian mixture probability hypothesis density filter (GMPHDF) in the linear Gaussian jump Markov systems (LGJMS) multitarget model. The original LGJMS-GMPHDF, devoted to joint detect and track all potential targets utilizing an identical and fixed set of models, has been modified to incorporate target class information and the class-dependent kinematic model set. The mutual dependence between target kinematics and class is exploited twice: first to construct the combined model sets, then to compute the combined measurement likelihood. The proposed algorithm is illustrated via a simulation example involving tracking of two closely spaced parallel moving targets and two crossing moving targets from different classes, where targets can appear and disappear.

For the purpose of extracting moving objects from H.264/advanced video coding (AVC) bit stream of a complex scene, an algorithm based on maximum a posteriori Markov random field (MRF) framework to extract moving objects directly from H.264 compressed video is proposed in this paper. It mainly involves encoding information of motion vectors (MVs) and block partition modes in H.264/AVC bit stream and utilizes temporal continuity and spatial consistency of moving object’s pieces. First, it retrieves MVs and block partition modes of identical 4×4 pixel blocks in P frames and establishes Gaussian mixture model (GMM) of the phase of MVs as a reference background, and then creates MRF model based on MVs, block partition modes, the GMM of the background, spatial, and temporal consistency. The moving objects are retrieved by solving the MRF model. The experimental results show that it can perform robustly in a complex environment and the precision and recall have been improved over the existing algorithm.

All optical systems that operate in or through the atmosphere suffer from turbulence induced image blur. Both military and civilian surveillance, gun sighting, and target identification systems are interested in terrestrial imaging over very long horizontal paths, but atmospheric turbulence can blur the resulting images beyond usefulness. This work explores the mean square error (MSE) performance of a multiframe blind deconvolution (MFBD) technique applied under anisoplanatic conditions for both Gaussian and Poisson noise model assumptions. The technique is evaluated for use in reconstructing images of scenes corrupted by turbulence in long horizontal-path imaging scenarios. Performance is evaluated via the reconstruction of a common object from three sets of simulated turbulence degraded imagery representing low, moderate, and severe turbulence conditions. Each set consisted of 1000 simulated turbulence degraded images. The MSE performance of the estimator is evaluated as a function of the number of images, and the number of Zernike polynomial terms used to characterize the point spread function. A Gaussian noise model-based MFBD algorithm reconstructs objects that showed as much as 40% improvement in MSE with as few as 14 frames and 30 Zernike coefficients used in the reconstruction, despite the presence of anisoplanatism in the data. An MFBD algorithm based on the Poisson noise model required a minimum of 50 frames to achieve significant improvement over the average MSE for the data set. Reconstructed objects show as much as 38% improvement in MSE using 175 frames and 30 Zernike coefficients in the reconstruction.

A novel technique for oil spill detection in an ocean environment from ultrasonic hyperspectral imagery (UHI) using spectral fringe-adjusted joint transform correlation (SFJTC) is presented. Since UHI is a new concept and such data are not available, for this work an UHI dataset is created from pure target (oil) and background (sea water) signatures using a linear mixing model. A new SFJTC-based technique for oil spill detection in ocean environment has been developed and tested by using the UHI dataset. To evaluate the performance of the proposed technique, we used the receiver operating characteristics (ROC) curves and the area under the ROC. Test results confirm that the proposed technique shows excellent results even in the presence of a large amount of noise in the UHI data.

A stereoscopic visual fatigue measurement model based on Bayesian networks (BNs) is presented. Our approach focuses on the interdependencies between factors, such as contextual and environmental, and the phenomena of visual fatigue in stereoscopy. Specifically, the implementation of BN with the use of multiple features provides a systematic way to project and evaluate visual fatigue. Compared with another measurement model, our present BN-based scheme is more comprehensive. The test validation also indicates that our proposed model can be used as a reliable method for the visual fatigue inferring in stereoscopy.

Based on the two-step phase-shifting interference (PSI) technique in fractional Fourier transform (FRT) domain and random mixed encoding, we present a new scheme for double image encryption. In the proposed scheme, information of each primitive image is recorded in two intensity interference patterns of FRT spectra by PSI technique, from which an encrypted image for each primitive image can be digitally derived. Random mixed encoding is then employed to divide and recombine both encrypted images into a single synthetic encrypted image. During the mixed encoding process, repositioning operations based on shift-variance of FRT are performed on the encrypted images to realize the spatial separation of decoded results in the output plane. By inverse FRT with correct fractional order, any of the primitive images can be easily retrieved directly from the synthetic encoded image with the corresponding phase encoding key. Crosstalk effect due to the overlapping of decoded images is alleviated for their spatial separation. Computer simulation and experimental results are presented to verify the validity and efficiency of our scheme.

Noncontact optical measurement methods are essential tools in many industrial and research domains. A family of new noncontact optical measurement methods based on the polarization states splitting technique and monochromatic light projection as a way to overcome ambient lighting for in-situ measurement has been developed. Recent works on a birefringent element, a Savart plate, allow one to build a more flexible and robust interferometer. This interferometer is a multipurpose metrological device. On one hand the interferometer can be set in front of a charge-coupled device (CCD) camera. This optical measurement system is called a shearography interferometer and allows one to measure microdisplacements between two states of the studied object under coherent lighting. On the other hand, by producing and shifting multiple sinusoidal Young’s interference patterns with this interferometer, and using a CCD camera, it is possible to build a three-dimensional structured light profilometer.

Previously, we reported a simple method to obtain lateral shear in both the x - and y -directions using a multiplexing technique. The phase data was extracted using the inherent spatial carrier fringes formed due to the tilt in the two sheared beams. In this article, we report that an error in phase map is introduced when the band-pass-filtered Fourier transform (FT) spectrum is not centered prior to performing the inverse FT to obtain the phase. We also found that intentionally introducing aberrations when capturing dynamic fluctuations in the wave front, resulted in controlling the spread of the Fourier spectrum.

A procedure that uses computer-generated holograms (CGHs) to align an optical system’s meters in length with low uncertainty and real-time feedback is presented. The CGHs create simultaneous three-dimensional optical references, which are decoupled from the surfaces of the optics allowing efficient and accurate alignment even for systems that are not well corrected. The CGHs are Fresnel zone plates, where the zero-order reflection sets tilt and the first-diffracted order sets centration. The flexibility of the CGH design can be used to accommodate a wide variety of optical systems and to maximize the sensitivity to misalignments. An error analysis is performed to identify the main sources of uncertainty in the alignment of the CGHs and to calculate the magnitudes in terms of general parameters, so that the total uncertainty for any specific system may be estimated. A system consisting of two CGHs spaced 1 m apart is aligned multiple times and re-measured with an independent test to quantify the alignment uncertainty of the procedure. The calculated and measured alignment uncertainties are consistent with less than 3 μrad of tilt uncertainty and 1.5 μm of centration uncertainty (1σ ).

A method to obtain the absolute shape of a large plane or sphere surface in the subaperture testing with multiangle averaging and Zernike polynomial fitting method is proposed. The subaperture data obtained by the interferometer contain not only the test mirror deviation but also the reference surface deviation. The reference surface deviation has become the main limit of the subaperture testing accuracy. To correct the deviation, the measurements are made so that the reference deviation could be eliminated by rotational asymmetric deviation and the rotational symmetric deviation. This technique can get not only the full absolute shape of the large mirrors, but also the reference surface shape. Experimental results have been given to verify the effectiveness of this method.

A simple and general approach for implementing all-fiber high-order optical temporal differentiator based on twin-core fiber (TCF) is presented and demonstrated. Specifically, the core 2 (or core 1) of the TCF should be cut in N sections with the same length for achieving N ’th-order optical temporal differentiator, which can be considered to consist ofN cascaded first-order optical temporal differentiators based on TCF. Our simulations show that the proposed approach can provide optical operation bandwidths in the several THz regime, which is capable of accurately processing time features as short as subpicoseconds. Performance analysis results show a good accuracy calculating the high-order time differentiation of the optical signal launched at core 2 (or core 1).

The effect of mode matching on the preparation of the squeezed light at 1064 nm with periodically poled KTiOPO ₄ (PPKTP) crystal is reported. We can derive the desired mode by improving the spatial mode matching into optical cavities, including the beam from the laser mode matched to the optical parametric amplifier cavity and mode cleaning cavity; also it is useful for the stability of the locking systems. By increasing the fringe visibility between the squeezed light and the local oscillator beam, a squeezing level of −8.75  dB or even higher could be observed, even with the same experimental parameters as described elsewhere.

Rugate and high/low quarter-wave stacks high reflector coatings for 1064 nm have been prepared with Ta ₂ O ₅ and SiO ₂ by an ion-beam sputtering technique. A laser-induced damage experiment of the samples has been conducted at 1064 nm with pulse duration of 5 ns [full width at half maximum (FWHM)]. These two samples’ damages both initiate at defects and show almost the same damage threshold within the experimental error. Nevertheless, the damage morphology on rugate is less severe at higher fluences. The thermal shock wave induced by a nanosecond pulsed laser is considered to be the main cause of catastrophic damage.

A multicladded normally dispersive erbium-doped fiber amplifier (ND-EDFA) is designed for a short length to operate at the wavelength of 1550 nm with a dispersion of −6.5  ps/km nm and parabolic pulse generation through the proposed fiber is studied. The proposed ND-EDFA shows a flattened gain spectrum in C -band. The nonlinear Schrödinger equation is solved numerically in presence of fiber gain, nonlinearity, and dispersion to investigate the pulse propagation through the proposed fiber. While continuous wave (CW) sources are considered, parabolic self-similar pulses with structure factor of 0.072 are created at suitable values of optimum fiber length when input pulse properties and fiber parameters are optimized accordingly. Side by side with a low repetition rate laser source, the pulse propagation equation is controlled by the gain dispersion term and dipole relaxation time, such that the evolution of Gaussian pulses may lead to nonparabolic regime. The effects of pulse parameters like power level, pulse width, and dipole relaxation time on the propagation of input Gaussian pulses through the so-designed ND-EDFA are investigated. Our results depict that the pulses with same input energy reshape into exactly parabolic shape for CW laser source or nonparabolic profile for a laser source with low repetition rate.

Two kinds of thulium-doped fiber ring lasers based on a spatial mode beating filter and comb filtering effect are presented and experimentally demonstrated, which all show multiwavelength laser spectrum around 2 μm. In the implementation of the first type of experiment configuration by the use of a piece of multimode fiber (MMF) as a spatial mode beating filter, dual-,triple-, and quadruple-wavelengths appeared whose extinction noise ratio is 25 dB by adjusting the angle of polarization controller. Different wavelength spaces are obtained by inserting different lengths of MMF. The second type is achieved by inserting a Sagnac loop mirror, which was constructed by a 3-dB coupler and a piece of polarization maintaining fiber. Seven stable wavelengths with channel spacing of 0.65 nm and an extinction ratio of 35 dB was achieved. These systems are simple and easy to construct, which can be useful for 2 μm wavelength-division-multiplexed applications.

A few-mode microstructured optical fiber is designed for low bending loss applications. Low-index rods and air-holes are applied to lower the splicing loss with the standard single-mode optical fiber (SMF) and to achieve ultra-low bending loss. Numerical results show that the proposed fiber can realize low bending loss of 0.004  dB/turn at the bending radius of 5 mm and low splicing of 0.04 dB with the standard SMF.

A third-harmonic-generation picosecond pulse with several millijoules per pulse at 355 nm has been achieved by nonlinear optical materials LiB ₃ O ₅ (LBO). The single pulse energy of third harmonic was up to 2 mJ at the repetition rate of 1 kHz. The conversion efficiency was up to 33.3% from 1064 to 355 nm with the M ² factor of 2.4. The system is based on a Nd:YAG regenerative amplifier with a simple double-pass post-amplifier.

An efficient dynamic bandwidth allocation (DBA) algorithm for multiclass services called MSDBA is proposed for next-generation time division multiplexing (TDM) passive optical networks with network coding (NC-PON). In MSDBA, a DBA cycle is divided into two subcycles with different coding strategies for differentiated classes of services, and the transmission time of the first subcycle overlaps with the bandwidth allocation calculation time at the optical line terminal. Moreover, according to the quality-of-service (QoS) requirements of services, different scheduling and bandwidth allocation schemes are applied to coded or uncoded services in the corresponding subcycle. Numerical analyses and simulations for performance evaluation are performed in 10 Gbps ethernet passive optical networks (10G EPON), which is a standardized solution for next-generation EPON. Evaluation results show that compared with the existing two DBA algorithms deployed in TDM NC-PON, MSDBA not only demonstrates better performance in delay and QoS support for all classes of services but also achieves the maximum end-to-end delay fairness between coded and uncoded lower-class services and guarantees the end-to-end delay bound and fixed polling order of high-class services by sacrificing their end-to-end delay fairness for compromise.

A subwavelength interference lithography method is numerically demonstrated based on surface plasmon polaritons excited by unidirectional couplers, and the unidirectional coupler is composed of a conventional nanoslit with a nanochannel excavated from one side of this nanoslit. Simulation results show that a feature size of 50 nm half-pitch pattern can be obtained at the working wavelength of 365 nm, and this method can enhance the intensity of the interference pattern with higher contrast and field depth and is advantageous to the fabrication process in practical applications.

The use of rare-earth-doped fiber section working in amplified spontaneous emission regime for different emission wavelengths is analyzed theoretically. From simulation results, the design of all-fiber superluminescent sources employing different rare earths as dopants for new optical windows and different applications is proposed. Results on different pump and signal powers in forward and backward propagation direction with respect to fiber length are presented.

Long-period fiber gratings (LPFGs) and tapered fibers are spectrally selective devices with important applications in sensing, especially for monitoring chemical and physical parameters. When combined, they can give rise to devices with enhanced characteristics that can be tailored by varying their fabrication parameters. We analyze the characteristics of arc-induced LPFGs written on the longer transition of asymmetric tapers, which provide a variable diameter section whose slope can be adjusted in order to tailor the device performance. In comparison with LPFGs fabricated in nontapered fibers, the grating inscription in the linear taper transition produces deeper notches (<20  dB ), whose bandwidth and separation increase with the transition slope. The simplicity of the electric arc technique to fabricate LPFGs, and the degrees of freedom added by the tapered fiber open up the possibility to realize thorough studies on the many possible combinations, to develop devices with characteristics designed on purpose.

Fiber optic strain sensors have significantly evolved and have reached their market maturity during the last decade. Their widely recognized advantages are high precision, long-term stability, and durability. In addition to these benefits, fiber optic (FO) techniques allow for affordable instrumentation of large areas of civil structures and infrastructure enabling global large-scale monitoring based on long-gauge sensors, and integrity monitoring based on distributed sensors. The FO techniques that enable these two approaches are based on fiber Bragg-gratings and Brillouin optical time-domain analysis. The aim of this paper is to present both FO techniques and both structural assessment approaches, and to validate them through large-scale applications. Although many other currently applied methods fail to detect the damage in real, on-site conditions, the presented approaches were proven to be suitable for damage detection and characterization, i.e., damage localization and, to certain extent, quantification. This is illustrated by two applications presented in detail in this paper: the first on a post-tensioned concrete bridge and the second on segmented concrete pipeline.

When designing a light-emitting diode (LED), to avoid the material and time cost in packaging and testing, a Gauss function is usually used to simulate its performance. However, for YAG:Ce phosphor coated LEDs (PC-LEDs), such a simulation is often inaccurate. The Gauss-simulated spectra are compared to spectra measured from respective LEDs, and the method of moving the YAG:Ce peak to the right in Gauss simulation is proposed. The amount depends on the kind of YAG:Ce phospher and the kind of blue light. Then PC-LEDs are designed using the modified Gauss simulation under specific performance requirements, and the packaged LEDs have performance that is acceptable for these requirements. Designing with modified Gauss simulation is particularly effective for pure white LEDs.

The properties of quadratic spatial solitons generated in periodically poled lithium tantalite in the femtosecond regime are investigated. By using only a fundamental frequency beam as the input to excite quadratic spatial solitons, single and spatially anisotropic multiple solitons are generated. Our experiments demonstrate that the number of solitons is dependent on the input power. In the experiment, beam narrowing occurs first, leading to single-soliton generation. The threshold for multiple solitons is around 1.5 mW. The number of solitons does not increase indefinitely with input power. Multiple soliton generation only occurs in the input power range of 1.5 to 6.3 mW. The number of solitons decreases to 1 when the input power is 6.3 mW. The temporal and spectral characteristics of the spatial solitons are measured by using the GRENOUILLE technique.

A composite structure with silicon nanowire arrays on germanium substrate is proposed as a good candidate for highly efficient solar cells. The Bruggeman approximation considering anisotropic wave propagating in uniaxial media is employed to calculate the radiative properties. Meantime, finite-difference time-domain (FDTD) method is used to verify for both normal and oblique incidence. It is found that the composite structure has superior absorption characteristics over thin Si film, particularly near the bandgap. With a thickness only of 4 μm, the composite structure improved the absorptance to above 0.6 across the whole wavelength band with the lattice constant of 100 nm, and the ultimate efficiency about 10% is higher than that of infinite bulk silicon, owing to the combined effects of suppressed reflection and high light trapping capability. To better understand the absorption enhancement process in the composite structure, the photogeneration profiles are provided by using FDTD method.

A compact crossing for silicon-based slot and strip waveguides is proposed by utilizing a strip-multimode waveguide (SMW) crossing at the center and two logarithmically tapered slot-to-strip mode converters at the ports with slot waveguides. For input/output ports with slot waveguides, the guided modes are efficiently transformed through the mode converter and then enter into the SMW (without mode converters for those ports with strip waveguides), where the fields converge at the center of the intersection due to the self-imaging effect. Hence, the size of the input beam is much smaller than the width of the SMW at the crossing center, leading to significant reductions of the crosstalk and radiation loss. The numerical results show that a hybrid waveguide crossing operating at the wavelength of 1.55  μm with the insertion loss, crosstalk, and reflection of 0.14/0.164 , −35.88/−38.79, and −35.35/−40.5 dB for input ports with slot/strip waveguides, respectively, is achieved. Moreover, the fabrication tolerances to the structural parameters are investigated by using a finite-difference time-domain method and evolution of the injected field along the propagation distance through the crossing structure is also demonstrated.

The reflectances of a thin-film solar cell were computed, using the rigorous coupled-wave approach, as functions of the angle of incidence and the free-space wavelength for illumination by linearly polarized plane waves. A tandem solar cell made of amorphous-silicon alloys was considered. The metallic back-reflector was taken to be periodically corrugated. Both the simple and the compound periodic corrugations of the metallic back-reflector (surface-relief gratings) were investigated. Low-reflectance bands in the reflectance spectrums were correlated with the solutions of the underlying canonical boundary-value problem to delineate the excitation of multiple surface-plasmon-polariton (SPP) waves. For the standard AM1.5 solar irradiance spectrum, we found that the light absorption efficiency in the near-infrared spectral regime can be increased up to 100% when multiple SPP waves of both linear polarization states are excited.

The spectral emissivity and transmissivity of zinc sulphide (ZnS) infrared windows in the spectral region from 2 to 12 μm and temperature range from 20 to 700°C is measured by a facility built at the Harbin Institute of Technology (HIT). The facility is based on the integrating-sphere reflectometry. Measurements have been performed on two samples made of ZnS. The results measured at 20°C are in good agreement with those obtained by the method of radiant energy comparison using a Fourier transform infrared spectrometer. Emissivity measurements performed with this facility present an uncertainty of 5.5% (cover factor=2 ).

A Flyeye concentrator with improved irradiance distribution on the solar cell in a concentrator photovoltaic system is proposed. This Flyeye concentrator is composed of four surfaces: a refractive surface, mirror surface, freeform surface, and transmissive surface. Based on the principles of geometrical optics, the contours of the proposed Flyeye concentrator are calculated according to Fermat’s principle, the edge-ray principle, and the ray reversibility principle without solving partial differential equations or using an optimization algorithm, therefore a slope angle control method is used to construct the freeform surface. The solid model is established by applying a symmetry of revolution around the optical axis. Additionally, the optical performance for the Flyeye concentrator is simulated and analyzed by Monte-Carlo method. Results show that the Flyeye concentrator optical efficiency of <96.2% is achievable with 1333× concentration ratio and ±1.3  deg acceptance angle, and 1.3 low aspect ratio (average thickness to entry aperture diameter ratio). Moreover, comparing the Flyeye concentrator specification to that of the Köhler concentrator and the traditional Fresnel-type concentrator, results indicate that this concentrator has the advantages of improved uniformity, reduced thickness, and increased tolerance to the incident sunlight.

A new simple bias control scheme for Mach–Zehnder modulator is proposed. Its effectiveness is demonstrated with simulations and experiments. The results showed that this is an effective ditherless bias control technique suitable for a variety of modulation formats. The system bit error rate performance has been observed for 72 h without degradation.

A p-i-p configuration of an electro-optical modulator based on hydrogenated amorphous silicon (a-Si:H) is characterized and compared with an a-Si:H based p-i-n modulator. In particular, we estimate the performances in terms of optical losses, voltage-length product, and bandwidth at λ=1550  nm for waveguide-integrated p-i-p versus p-i-n configurations. Both devices are fabricated on a silicon substrate by plasma enhanced chemical vapor deposition at low temperature ensuring the back-end integration with a CMOS microchip. We demonstrate a factor of merit for the p-i-p waveguide integrated Fabry-Perot resonator of Vπ×Lπ=19  V×cm allowing the design of shorter devices with respect to p-i-n structure.

Two kinds of optical modulation processes are designed based on nested split-ring resonators in the terahertz regime. By photo-conductivity induced mode switching effect, the resonant structure and resonant mode will be changed, and the two contrary tunable resonant properties are obtained. Without illumination, the two designs both have three resonant peaks. As the intensity of illumination increases, for the first design, the first and the third resonant peaks disappear and a broadband resonant peak at the second resonant frequency is formed eventually; however, the second design realizes an exactly opposite modulation process. Moreover, in order to identify the modulation mechanism, we discuss and analyze the distributions of the electric fields and surface currents in detail. Our designs can be implemented in tunable terahertz functional devices and provide important reference value for the design of terahertz metamaterial.

A Kretschmann-Raether prism-based three-layer structure consisting of a prism, gold (Au) metal film, and dielectric sample has been investigated with the use of admittance loci method in attenuated total internal reflection mode. High index prism materials like silicon, chalcogenide (2S2G), and SF14 have been used to study their effect on surface plasmon resonance (SPR) sensing (at 1200-nm wavelength) in infrared region by corresponding admittance loci plots and also by SPR sensing curves. The performance of the sensor based on the choice of the prism material has been discussed with the help of sensitivity plots giving due importance to the dynamic range of the designed sensor.

Infrared absorption of high-quality, commercial, polycrystalline MgAl₂O₄ spinel is ∼40% greater in the range of 3.8 to 5.0 μm than the value predicted by the computer code OPTIMATR®, which has been used for window and dome design for more than 20 years. As a result, spinel and a -plane sapphire windows designed to support the same external pressure with the same probability of survival have approximately the same infrared absorptance in the range 3.8 to 5.0 μm. c -Plane sapphire has greater absorptance than spinel in the range 3.8 to 5.0 μm. Spinel has two weak absorption bands near 1.8 and 3.0 μm. At 1.064 μm, the laser calorimetric absorption coefficient of spinel is 10 to 50 times greater than that of sapphire. New measurements of specific heat capacity, thermal expansion, thermal conductivity, elastic constants, and refractive index (including dn/dT) of spinel are reported.

This article [Opt. Eng.. 52, (8 ), 081605 (2013)] was originally published on 21 February 2013 with Figs. 4 and 5 reversed, although the captions were correct. The corrected figures and captions are reprinted below.