I can’t believe we’re almost halfway through 2013. It sure seems like time flies by faster and faster each year. I know that I joked about time a number of editorials ago using Fermat’s principle, but I can also quote William Penn on the subject: “Time is what we want most, but what we use the worst.” There’s a funnier reference that I don’t know who to attribute to: “If time is money, then all ATMs are time machines!” This month I am thinking about time because I have been Editor of Optical Engineering for three and a half years and it feels like yesterday that I accepted the assignment.

By manipulating the principal stretches during a two-step space mapping within the framework of transformation optics, the input spatial frequency bandwidth of a conventional Fourier lens can be extended based on an isotropic transformation material. Isotropy is important for easy fabrication, low loss, and broadband application; moreover, it suggests a route for realizing Fourier transforms of continuous fractional order with enhanced input spatial frequency bandwidth.

The add drop filter (ADF) is one of the most significant devices for coarse wavelength division multiplexing (CWDM) systems to add and/or drop a required channel individually from multiplexed output channels without disturbing other channels. The important parameters of the ADF are coupling efficiency, dropping efficiency, passband width and Q factor. Photonic crystal (PC)-based optical devices have attracted great interest due to their compactness, speed of operation, long life period, suitability for photonic integrated circuits, and future optical networks. Here, an extensive overview of a photonic crystal ring resonator (PCRR)-based ADF using a different shape of ring resonator is presented, and its corresponding functional parameters are discussed. Finally, the designed circular PCRR-based ADF for an ITU-T G 694.2 CWDM system is presented. Approximately 100% of coupling efficiency and dropping efficiency, 114.69 of Q factor, and 13 nm of passband width is obtained through simulation, which outperforms the reported one.

Infrared sensing technology has come a long way since Hershel made the unexpected discovery in 1800 that radiation at wavelengths beyond the visible spectrum were measurable by his rudimentary bolometer instrument. The tremendous advancements in this technology have been propelled heavily through defense research and development, aimed at providing important night vision and target detection capabilities for surveillance, reconnaissance, targeting, and threat warning systems. The maturation of the underlying infrared sensing technology, specifically infrared optics and focal plane arrays, has not only enhanced the system capabilities for these missions, but has also resulted in the proliferation of infrared systems into a more diverse set of air, land, sea, and space-based platforms. Furthermore, infrared sensing has become more affordable through the advent of uncooled and high-operating-temperature focal plane arrays, which has opened up civilian and commercial applications such as thermography, law enforcement, fire and security, weather monitoring, transportation, and spectroscopy.

Using infrared hyperspectral imaging, microscopy of small particles of the explosives compounds RDX, tetryl, and PETN with near diffraction-limited performance is demonstrated. The custom microscope apparatus includes an external cavity quantum cascade laser illuminator scanned over its tuning range of 9.13 to 10.53 μm in 4 s, coupled with a microbolometer focal plane array to record infrared transmission images. The hyperspectral microscopy technique is used to study the infrared absorption spectra of individual explosives particles, and demonstrate subnanogram detection limits.

The increasing availability of sensors that can image in the 1 to 5 μm region has allowed for systems to be developed that utilize the full spectrum. Current mid-wave infrared (MWIR) systems have typically only imaged in the 3 to 5 μm region, but the new detectors allow imaging in the short-wave infrared (SWIR) and MWIR bands on the same image plane. Night Vision and Electronic Sensors Directorate (NVESD) had a requirement to design and build a multiple field of view (FOV) optical system that could image the 1 to 5 μm spectral band utilizing a single, cooled infrared detector. The primary challenge of designing this particular optical system was to get the 1 to 2 (SWIR) μm band to focus at the same image plane as the 3 to 5 (MWIR) μm band in all FOVs. A three-FOV broadband optical system that can image the 1 to 5 μm band on the same image plane was designed and built. Several optical concepts were looked at, and it was decided that a combination of a reflective afocal and refractive imager was the best way to meet the system requirements. The use of a catadioptric system with a single focal plane that images in the 1 to 5 μm spectrum reduces the size of the system and provides the user with see-spot capability.

Advances in microbolometer detectors have led to the development of infrared cameras that operate without active temperature stabilization. The response of these cameras varies with the temperature of the camera’s focal plane array (FPA). This paper describes a method for stabilizing the camera’s response through software processing. This stabilization is based on the difference between the camera’s response at a measured temperature and at a reference temperature. This paper presents the mathematical basis for such a correction and demonstrates the resulting accuracy when applied to a commercially available long-wave infrared camera. The stabilized camera was then radiometrically calibrated so that the digital response from the camera could be related to the radiance or temperature of objects in the scene. For FPA temperature deviations within ±7.2°C changing by 0.5°C/min , this method produced a camera calibration with spatial-temporal rms variability of 0.21°C, yielding a total calibration uncertainty of 0.38°C limited primarily by the 0.32°C uncertainty in the blackbody source emissivity and temperature.

There is a strong motivation for smaller pixels based on end-user demand for lower-cost, higher-resolution camera systems both for military and commercial applications. Uncooled detector technology fits the need for a low size, weight, and power system. We explore the tradeoffs and challenges to achieving pixel designs smaller than the current 17-μm state-of-the-art detectors without loss in sensitivity or resolution. For illustration we consider a 12-μm design. We also address modulation transfer function issues as the pixel size shrinks, and examine the difference between the performance of present devices and the theoretical performance limit for uncooled detectors.

Dual band infrared focal plane arrays (FPA) are designed to act as two independent focal planes located at a common image plane which detects both the mid-wave infrared and the long-wave infrared images. The imagery produced is simultaneous and separable for the two bands. Systems utilizing these focal planes have often been designed to operate the same way as single band infrared sensors, except that two images of the same scene but different spectral bands are simultaneously captured, and displayed independently or as a fused image. An alternative method of exploiting dual band FPA is to utilize the dual band nature of the focal plane to simultaneously view different scenes. It is feasible to provide a picture-in-picture capability where one spectral band views a narrow field of view (FOV) to identify targets while the other spectral band images the wide FOV to provide situational awareness. We explore this capability, including design concepts and issues associated with the development of a dual band picture-in-picture infrared system.

The performance of midwavelength infrared type II superllatice InAs/GaSb PIN and nBn (AlGaSb barrier) photodetectors in a reverse bias voltage range and a temperature range from 77 to 240 K is described. The PIN and nBn structures are modeled by a bulk based model, i.e., type II superllatice is treated as an artificial semiconductor material where parameters describing its physical properties are extracted from the experimental data. The model assumes that position of the effective trap energy level depends on temperature, what allowed to obtain a very good fitting to the measurements. Temperature and bias dependent dark current and differential resistance area product of the both devices have been analyzed to investigate contributing mechanisms such as: diffusion, generation-recombination, band-to-band and trap-assisted tunneling that limit the electrical performance of both types of the detectors. The I−V and RA(V) product characteristics of both types of type II superllatice InAs/GaSb photodetectors were found to be dominated by diffusion and generation-recombination currents in the nearly zero-bias region. At medium values of reverse bias, the trap-assisted tunneling reveals its significance, while at higher reverse voltages—the band-to-band tunneling is decisive to I−V and RA(V) characteristics. The fitting procedure allowed to extract both generation-recombination and diffusion components of carrier lifetimes pointing out that the carrier lifetimes range from 2 to 10 ns at T=200  K . Detectivity for T=240  K and V=50  mV was estimated to be 10⁹   cmHz^1/2 /W and 4×10⁹   cmHz ^1/2/W for PIN and nBn detector, respectively. Finally, type II superlattice InAs/GaSb PIN and nBn structures’ performance is compared to both unipolar barrier nBn HgCdTe detector and bulk HgCdTe photodiodes operated at near-room temperature. It is shown that the performance of SL and HgCdTe photo detectors with a cut-off of about 5 μm is comparable at operation temperatures around 240 K.

With recent developments in multispectral detector technology, the interest in common aperture, common focal plane multispectral imaging systems is increasing. Such systems are particularly desirable for military applications, where increased levels of target discrimination and identification are required in cost-effective, rugged, lightweight systems. During the optical design of dual waveband or multispectral systems, the options for material selection are limited. This selection becomes even more restrictive for military applications, where material resilience, thermal properties, and color correction must be considered. We discuss the design challenges that lightweight multispectral common aperture systems present, along with some potential design solutions. Consideration is given to material selection for optimum color correction, as well as material resilience and thermal correction. This discussion is supported using design examples currently in development at Qioptiq.

In sonic infrared (SonicIR) imaging, heat is generated in defect areas during the sonic pulse; the heat appears bright in SonicIR images as the indication of a defect. However, in practical applications of SonicIR, there are lots of disturbing bright areas in infrared images, such as heat reflection and paint problem. When crack size is small, the generated heat appears not bright enough to be recognizable. Based on heat diffusion properties in the one-dimensional temporal and two-dimensional spatial domain, a method is developed to automatically recognize defect signals from SonicIR image sequences. The algorithm is verified with the SonicIR image sequences of 100 metal plates which may have different thickness, materials, or crack sizes.

Today, requirements for imaging systems are shifting from standard definition to high-definition (HD) imaging systems. Along with HD imagers, users are also requiring embedded metadata and high precision pointing. These requirements place new demands on the opto-mechanical, thermal, and electrical subsystems of stabilized platforms that use these imagers. This paper discusses the impact of HD imagers on gimbal design, including requirements for better stabilization, better thermal management, and better electronics to handle the high data rates associated with HD imagers. We also discuss how the requirements for wide area surveillance sensors will further impact the gimbal designs for these sensors.

Various approaches now exist for obtaining spectral imagery over a broad range of infrared wavelengths. One approach involves the use of a single grating element in two grating orders with dualband focal plane array (FPA) technology. This approach offers greater efficiency over the mid-wave infrared and long-wave infrared and eliminates the need for separate FPAs, dispersing elements, and optical beamsplitters. Another approach achieves similar results by exploiting an FPA which has a broad wavelength response with an innovative grating which has useable efficiency that extends beyond the single octave limits of traditional gratings. Significant advantages result, in either case, for space-based hyperspectral imagers, for which a reduction in cryo-cooled mass translates into prodigious savings in overall payload mass, cryo-cooling requirements, and waste heat removal. By contrast, longer term approaches might realize infrared “hyperspectral pixels” in two-dimensional imaging FPAs. In this case, each pixel would detect different wavelengths of radiation, at different depths, and the resulting “spectral photocurrents” would be transported to read-out circuitry through a vertical grid of electrical contacts. Although not yet realized in practice, the conceptual basis for accomplishing this, with the widely available HgCdTe detector material, has been described. With regard to employment, space-based thermal hyperspectral imaging is characterized by coarser ground resolution as a result of aperture diameter limitations and diffraction considerations at the longer infrared wavelengths. The resulting subpixel detections, based on spectral signature, are often complementary with higher resolution, shorter wavelength, panchromatic imagery.

In designing the optics of an imaging multi-etalon spectropolarimeter as a post-focus instrument for the Advanced Technology Solar Telescope (ATST), many constraints must be considered. Among these are the large entrance pupil diameter of the telescope (4 m), the demanded large field of view (≥90  arc sec ), high spectral resolving power (≥200,000 ), and limited field-dependent blue-shift of the instrumental profile [≤3 full width at half maximum (FWHM)], which require Fabry-Perot interferometers of large diameter (≥200  mm ), lighted by highly collimated beams. This implies large optical elements and long optical paths. Moreover, to use interference pre-filters with a relatively small diameter (≤70  mm ) and placed between the interferometers to reduce the inter-reflections in axial-mount, a “pupil adapter” must be included with a further increase of the optical path length. Although a multi-etalon spectropolarimeter works in quasi-monochromatic light, the Fraunhofer lines of interest cover a wide range of wavelengths (850 to 1650 nm), which demands a good chromatic aberration control. A low instrumental polarization (≤0.5% ) is also required to allow a high polarimetric precision. Finally, some secondary optical paths are required to perform the initial instrumental setup and to secure the best instrumental performances. A diffraction-limited optical solution for ATST is described that fulfills all the above requirements in a relative small volume.

The need for affordable and sustainable ophthalmic systems for measurement and correction of refraction is well recognized. Power-adjustable spectacles based on the Alvarez principle (transversal lateral movement of two lenses) have emerged as an innovative technology for this purpose. Within this framework, our aim is to design a new power-adjustable sphero-cylindrical refractor. The system is comprised of two lenses and three independent lateral movements. The lenses have a planar and a third-degree polynomial surface. They are arranged with their planar surfaces in contact, so that the incoming light is only refracted by two surfaces. First, we present the theory of such a system. Second, we propose an optical design methodology. Third, we provide a design example capable of measuring sphere powers ranging from −5.00 D to +5.00 D and cross-cylinders from −2.00 D to 2.00 D. Finally, a prototype of the lenses was manufactured using free-form machining.

We present a superresolution imaging method based on the dynamic single-pixel compressive sensing (CS) system. Different from the traditional static CS, this system is slowly moving in parallel with the scene during the compressive sampling, implying that the measurements are possible to contain the information about the scene with the subpixel resolution. Here we first build the dynamic compressive sampling model and give the recovery method via traditional CS scheme, and then we propose the image superresolution recovery method in the CS framework, where a subdivision scheme is used. The proposed method not only has remarkable superresolution performance, but also has low requirements on the imaging system, since it is associated with the single-pixel imager, which is one of the simplest systems in the existing CS imaging architectures. The feasibility of the proposed method is demonstrated by the numerical simulations as well as the optical experiments.

In recent years, much effort has been invested to develop room temperature inexpensive, but sensitive, millimeter wave (MMW) and terahertz (THz) detectors that can be used as pixels in focal plane arrays, which is important for real-time imaging. A new 18×2 neon indicator lamp MMW/THz scanner was developed. The components of the camera include horizontally shifted two-column glow discharge detectors in a scanning array. The detectors, costing about 50 cents each, are wired to a preprocessing card, a VLSI board, and a motor for scanner movement. A description of the VLSI Verilog programmable hardware of the new scanner, the physical architecture, the software user interface, and imaging results at 97 GHz are presented. At this stage, the emphasis is focused on the lamp exposure time and spatial resolution when the scanning is performed horizontally. In the future it is planned to expose all pixels simultaneously for real-time imaging. New software capabilities allow the application of digital image enhancement algorithms. Fast scanning permits obtaining images in 1 to 5 s. Oversampling yields a sharper edge response and a higher signal-to-noise ratio.

Here, we introduced a new method to fabricate a shape-controllable microlens array (MLA). A conductive membrane was deformed by electrostatic force through applied voltage on its underneath electrodes, and polymer primer was poured in this concave template to form an MLA after curing and a demolding process. Through changing the initial contour of the template as well as the location and bias of the underneath electrodes, the so-called molding by electrostatic force deformed template (MEFDT) method has the ability to realize a shape-controllable microsized MLA in a flexible, easy-to-design, and low-cost way. Polydimethylsiloxane MLAs were fabricated to verify this MEFDT method, and the fabricated MLAs had a surface roughness less than 2 nm that showed acceptable optical smoothness, and their focal lengths were demonstrated to be adjustable by applying different voltage on their affiliated templates.

GaN-based light-emitting diodes (LED) on a patterned sapphire substrate with a novel hybrid atomic layer deposition (ALD)-TiO ₂ Al ₂ O ₃ distributed Bragg reflector (DBR) and Ag mirror have been proposed and fabricated. Due to the excellent thickness uniformity of ALD for the proposed reflector, high reflectivity over 99.3% at an incident angle of 5 deg has been achieved. It was also found that the reflectivity of a backside reflector with an Ag mirror slightly depends on incident light wavelength and incident angle. Moreover, because of the good adhesion between TiO ₂ /Al ₂ O ₃ DBR and the Ag mirror, the fabrication process was simplified and reliable. With a 60 mA current injection, an enhancement of 5.2%, 8.9%, and 47.1% in light output power (LOP) at the 460 nm wavelength was realized for the proposed LED with Ag mirror and 3-pair ALD-TiO ₂ Al ₂ O ₃ DBR as compared with a LED with a traditional Ag mirror and 3-pair TiO ₂ /SiO ₂ DBR, with Al mirror and 3-pair ALD-TiO ₂ Al ₂ O ₃ DBR, and without backside reflector, respectively. This result shows that the ALD-TiO ₂ /Al ₂ O ₃ DBR can be used to enhance the LOP greatly and improve adhesion between the sapphire substrate and the metallic mirror, and thus is very promising for fabricating high performance GaN-based LEDs.

We demonstrate the use of ultraviolet (UV) laser lithography in the production of subwavelength metal gratings. A laser writing system with a 413-nm Kr laser is used to write patterns on a resist-coated fused silica substrate mounted on a rotating table with a linear slider. One- and two-dimensional patterns are written in the resist at a selected sampling pitch or grating period, and the substrate is dry etched and coated with Au to obtain metallized gratings. Surface plasmon resonance dips, which appear in the reflectance spectra of the gratings, shift depending on the orientation of the incident polarization, because the gratings lack perfect symmetry owing to a system-induced skew in the writing beam. This dip shift can be considered tolerable when the gratings are used as a signal enhancer in Raman sensing applications. We conclude that UV laser writing based on polar coordinates is a candidate method for surface structuring on submicron scales. Devising a method to attain an unskewed beam will be the subject of future work.

Different concepts of correspondence findings in contactless optical three-dimensional (3-D) measurement systems using fringe projection are analyzed concerning the accuracy of the 3-D point calculation. These concepts are different concerning the kind of performance of the triangulation procedure in order to calculate the resulting 3-D points and the use of geometric constraints versus second projection sequence. Triangulation may be alternatively performed between camera pixels and the phase origin of the projection, between one camera pixel in the prior camera and the image of the corresponding measured phase value in the second camera, or between the image points of certain raster phase values in the two observation cameras. Additionally, triangulation procedures can be distinguished concerning the use of two perpendicular projection directions of the fringes versus the use of geometric constraints, i.e., epipolar geometry instead of the second projection direction. Advantages and disadvantages of the different techniques are discussed. In addition, a theoretical analysis of the application of synthetic data has been simulated as well as experiments performed on real measurement data. Both simulations and real data experiments confirm the theoretical assumptions concerning the magnitudes of the random errors occurring in 3-D point determination.

An in situ aberration measurement technique based on an aerial image with an optimized source is proposed. A linear relationship between the aerial image and Zernike coefficients is established by the principal components and regression matrices, which are obtained in a modeling process through principal component analysis (PCA) and regression analysis. The linear relationship is used to extract Zernike aberrations from the measured aerial image in a retrieval process. The characteristics of regression matrix are analyzed, and the retrieval process of Zernike coefficients is optimized. An evaluation function for the measurement accuracy of Zernike aberrations is proposed, and then a fast procedure to optimize the illumination source is designed. Parameters of the illumination source are optimized according to the evaluation function and applied in our method. The simulators Dr.LiTHO and PROLITH are used to validate the method. Compared to the previous aberration measurement technique based on principal component analysis of an aerial image (AMAI-PCA), the number terms of Zernike coefficients that can be measured are increased from 7 to 27, and the measurement accuracy of Zernike aberrations is improved by more than 20%.

A different real-time self-wavelength calibration method for spectral domain optical coherence tomography is presented in which interference spectra measured from two arbitrary points on the tissue surface are used for calibration. The method takes advantages of two favorable conditions of optical coherence tomography (OCT) signal. First, the signal back-scattered from the tissue surface is generally much stronger than that from positions in the tissue interior, so the spectral component of the surface interference could be extracted from the measured spectrum. Second, the tissue surface is not a plane and a phase difference exists between the light reflected from two different points on the surface. Compared with the zero-crossing automatic method, the introduced method has the advantage of removing the error due to dispersion mismatch or the common phase error. The method is tested experimentally to demonstrate the improved signal-to-noise ratio, higher axial resolution, and slower sensitivity degradation with depth when compared to the use of the zero-crossing method and applied to two-dimensional cross-sectional images of human finger skin.

A prototype infrared (IR) acousto-optic tunable filter (AOTF)-based point spectrometer has been designed for examining and analyzing potential biological samples collected in situ from the planets or other solar system objects. The reflectance spectrometer operates at a wavelength range of 1.6 to 3.6 μm, which is diagnostic of minerals and organics, and inspects a 1-mm sized spot on the sample. The tuning component is the AOTF that has been utilized in a variety of spectral detection applications. The instrument’s specification and design approach including the selected components is described. The data acquisition system, the electronic components, and their interconnections are presented. The instrument’s radiometric performance is examined and described by a noise equivalent reflectance value of 0.13% that is obtained from the laboratory measurements. The device has been demonstrated by measuring the reflectance spectra for a variety of geological samples and comparing the results with the United States Geological Survey data.

An opportunity to exploit specific mechanisms of the acousto-optic nonlinearity to regulate performances of the collinear acousto-optical filter, realizing the sequential spectrum analysis of optical signals, is considered. This possibility is theoretically analyzed and experimentally confirmed with an advanced filter based on calcium molybdate (CaMoO ₄ ) single-crystal with a 15-μs time-aperture. It is able to operate over red and near-infrared light at relatively low radio-wave frequencies providing almost lossless regime for controlling acoustic waves of the finite amplitude. Under certain conditions, the transmission function of electronically tunable filter exhibits a marked dependence on the applied acoustic power density, and as a result, one can significantly squeeze the transmission function, i.e., improve the spectral resolution of this filter at the cost of decreasing the efficiency of the device partially. The identified and observed non-linear effect makes possible varying the performance data of similar advanced collinear acousto-optical filter governed by external signals of the finite amplitude.

Improving spectral photon harvesting is important for thin-film multijunction cells. We show that efficient spectral flux management can be achieved using genetic algorithm-optimized surface plasmon (SP) cavity-resonant type multijunction cells. We also observe that the excitation of the SP quasi-guided mode, Fabry–Perot mode, and SP polariton significantly enhance the photocurrent of multijunction cells. Two types of cavity structures are investigated. For the optimized SP intermediate reflector and bottom-grating cavity, the resonant cavity mode efficiently increases the long-wavelength absorption in the bottom cell by 63.27%, resulting in reduced absorbance asymmetry between the top and the bottom cells. Accordingly, the matched integrated absorbance is increased by 14.92%. For the optimized SP top- and bottom-grating (TBG) cavity, the integrated absorbance and current matching are improved due to the higher transmission through the solar cell front surface and the excitation of the quasi-guided mode with a more localized field in the bottom cell. The matched integrated absorbance is improved by 85.68% for the TBG cavity.

Compact 2×2 couplers based on silicon nanowires are fabricated and tested. They include a directional (X) coupler, a cross-gap coupler (CGC), and a multimode interference (MMI) coupler. The length of the X coupler’s parallel film waveguide is 1 μm. The theoretical minimum excess loss of the X coupler is 0.73 dB, whereas its experimental value is 1.0817 dB. CGC has a coupling region length of 24 μm. The minimum excess loss of CGC, which is 0.6 dB in theory, is experimentally determined to be 0.6737 dB. Taper waveguides are used as input/output waveguides for the MMI coupler. The footprint of the MMI region is only 6×57  μm ² . The excess loss of the MMI coupler is theoretically 0.46 dB, but its experimental value is 0.5423 dB. The experimental nonuniformity of the MMI coupler is 0.0063 dB when the center wavelength is 1.55 μm. The maximum excess loss of the MMI coupler is 0.8233 dB in the wavelength range of 1.52 to 1.58 μm. The simulated and experimental results show that a small 2×2 MMI coupler that is suitable for optoelectronic integration exhibits lower excess loss, wider bandwidth, and better uniformity.

Detailed modeling results of 100 J class laser systems with respect to the output energy, beam propagation, nonlinear phase accumulation, wavefront aberrations, and adaptive optics performance obtained in MIRÓ and MATLAB codes are presented here. The laser system is based on a cryogenically cooled Yb 3+ ∶YAG multislab amplifier with two identical amplifier heads and operates at 10 Hz repetition rate with an average power above 1 kW.

We fabricated a one-dimensional nanoporous silicon photonic crystal on a silicon insulator substrate by a cost-effective electrochemical method as an optical biosensor for the detection of DNA hybridization. In the first step, a transfer matrix method was used to calculate the corresponding reflectivity spectrum for the design of nanoporous silicon photonic crystals. Then silicon-on-insulator-based photonic crystals were prepared by a novel simple electrochemical etching. Genes were hybridized inside the porous silicon (PS) pores by aminopropyltriethoxysilane and glutaraldehyde and detected through frequency resolved reflectance measurements. A detection sensitivity of 17.445  nm/μM is demonstrated with good specific detection. The linear response range covers a concentration range of antifreeze protein gene from 0.625 to 10.000 μM. This high responsivity indicates that the silicon-on-insulator-based PS photonic crystal has significant potential for application in biological micro-electro-mechanical-systems technologies.

We have demonstrated a Ti∶LiNbO ₃ electro-optic electric-field sensor based on 1×2 directional optical waveguide coupler. The symmetric geometry of the 1×2 directional coupler provided the sensor with unique characteristics of intrinsic 3-dB operating point and two complementary outputs. A DC switching voltage of ∼12  V and an extinction ratio of ∼8.1  dB were observed with the coupler at a wavelength of 1.3 μm. The minimum detectable electric fields are ∼0.99 and ∼1.67  V/m corresponding to a dynamic range of ∼29.5 and ∼25  dB at frequencies of 20 and 50 MHz, respectively. The sensors exhibit almost linear response for the applied electric-field intensity from 0.29 to 29.8  V/m .

In the fabrication of a polymeric arrayed waveguide grating (AWG) device, the cores of the channels and the arrayed waveguides exhibit smooth trapezoid cross-sections instead of originally designed rectangular ones after reactive ion etching and steam-redissolution. By employing the Marcatili theory, a method called “equivalent energy flow method” is proposed for analyzing the transmission characteristics of the polymeric AWG with trapezoid core cross-sections. The AWG parameters have been fixed, and a 17×17 polymeric AWG multiplexer has been designed and fabricated. Experimental results show that the central wavelength is 1550.83 nm, and the bandwidth at half maximum is about 0.478 nm; insertion loss is 10 to 13 dB, and crosstalk is about −21  dB .

We have designed, fabricated, and characterized a 1×8 ultra-small compact arrayed-waveguide grating (AWG) on silicon-on-insulator (SOI) in a fiber grating demodulation integration microsystem. The miniature AWG, consisting of Si photonic wire waveguides, was designed using the complete modeling simulation in the beam propagation method. The device was fabricated on an SOI substrate and evaluated in the wavelength range around 1.55 μm, with an effective area of 230×160  μm . Clear demultiplexing characteristics were observed with a channel spacing of 1.91 nm. The influence of the waveguide widths on crosstalk defined by adjacent channel crosstalk and phase error is discussed. Insertion loss, crosstalk, and nonuniformity of loss were measured to be −3.18 , −23.1 , and −1.35  dB , respectively. Thus, the AWG design is the best choice for a fiber Bragg grating demodulation microsystem.

Plasmonics combines attractive features of nanoelectronics and optics enabling highly integrated, subwavelength optical and electronic circuits. The wide application of plasmonic devices hinges on practical demonstrations with low losses at optical and infrared wavelengths. In this frequency regime, noble metals suffer from large losses that are difficult to compensate by adding gain material. Transparent conducting oxides, e.g., ZnO, are good alternatives to metals for plasmonic applications in the optical regime since they exhibit high conductivity and relatively small negative real permittivity values. We study Ga-doped ZnO layers grown on Al ₂ O ₃ at 200°C by pulsed laser deposition in Ar ambient. The bulk electrical properties, determined by Hall effect, were ρ=2.93×10 ⁻⁴   Ω-cm ; μ=25.5  cm ² /V-s ; and [i]n=8.36×10 ²⁰   cm −³ . These values of μ and n were used to predict optical properties through the Drude dielectric function. The optical and electrical properties of the material were used to design insulator-metal-insulator (in our case, ZnO embedded in polymer) waveguides for long-range plasmons using full-wave electromagnetic models built with finite element method simulations. The models were used to predict the effect of device geometry on propagation length and losses of the plasmon mode.

Iterative clipping and filtering (ICF) is a useful technique to reduce the peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signals. However, the classical ICF with Fast Fourier Transform/Inverse Fast Fourier Transform requires much iteration to approach a specified PAPR threshold in the complementary cumulative distribution function. To reduce the nonlinear distortion in both electrical and optical devices and in the optical fiber, we propose a novel ICF based on discrete cosine transform/inverse discrete cosine transform to reduce the PAPR in an intensity modulator and direct detection (IM/DD) optical OFDM system. Furthermore, the new technique considerably improves bit error rate (BER) and reduces the PAPR with just few iterations. The experimental results show that the receiver sensitivity at a BER of 1×10 ⁻³ for a 2.5-Gbytes/s OFDM signal and after 200-km standard single-mode fiber transmission has been improved by 1.1, 2.3, and 3.6 dBm with launch powers of 6, 8, and 12 dBm respectively.

Long period fiber grating (LPFG) upon all-solid photonic bandgap fiber with a bandgap at 1.068 to 1.180 μm is fabricated by high-frequency CO ₂ laser pulse irradiation. The resonance wavelength is 1335.76 nm with a modulation depth of 15 dB and a 3-dB bandwidth of 2.6 nm. Bending response of the LPFG is dependent on the axial orientations and the input polarization states. The maximum bending sensitivity is achieved at 52  nm/m . The temperature response is weakly dependent on the polarization state, and is achieved around 20.47  pm/°C at a 0-deg polarization azimuth. The bending measurement error resulting from temperature can be negligible within the range of 0.4 to 0.82  m ⁻¹ . It is be beneficial to avoiding cross-sensitivity of temperature in bending measurements.

Aligning two optical fibers is a crucial step in designing good optical fiber–based systems and networks. Good alignment optimizes the power transmitted between the fibers, especially when a microstructured optical fiber (MOF) is interfaced with a single-mode fiber (SMF). In this paper, we present a self-alignment algorithm based on particle swarm optimization (PSO). The PSO algorithm is used to locate the optimal coupling position with the highest optical power for alignments with multiple degrees of freedom. The proposed algorithm is validated by applying it for two different sources and checking the achieved alignment of SMF and MOF and that of two SMFs.

It is desirable to remove the optical de-multiplexer in reconfigurable optical add/drop multiplexers (OADM) and use coherent receivers instead for channel selection. We set up a wavelength division multiplexed orthogonal frequency division multiplexed system with a raw bit rate of 66.7  Gb/s per channel and a transmission distance of 2,240 km. We show that the OADM can broadcast more than 64 WDM channels to a coherent balanced receiver and can select out a single channel with less than 1 dB of Q-factor degradation.

Ultrasound generation from an optical fiber, based on the photoacoustic principle, is a promising approach to many ultrasonic applications, specifically those requiring wide bandwidth and compact size in order to achieve high resolution as well as the capability of being operated in limited space. A fiber-optic ultrasound generator using gold nanopores is reported. The gold nanopores, having high absorption efficiency, were fabricated using a focused ion beam (FIB) on the fiber endface, which was excited by a nanosecond laser in order to generate ultrasound signals via the photoacoustic principle. Experimental results demonstrate that these wide bandwidth ultrasound signals can be generated by this compact fiber-optic ultrasound generator fabricated using a FIB.

A novel structure of single-polarization single-mode photonic crystal fiber (SPSM-PCF) is proposed by introducing two large semicircular holes on both sides of the core region. The characteristics of SPSM fibers are numerically analyzed using the finite-element method. The SPSM operating range can be adjusted with the parameters of the elliptical ratio γ and the spacing Λ ₁ between the semicircular hole and the adjacent circular hole. The SPSM bandwidth of about 0.7 μm and operating range from 1.0 to 1.7 μm for the PCF have been obtained with the silica–air holes structure. An all-solid PCF structure is proposed, and the SPSM bandwidth of about 0.30 μm is predicted. With the increase in refractive index difference between the substrate and filling materials the SPSM operating range is blue-shifted, and with the decrease in the refractive index difference the bandwidth of the SPSM is reduced.

A fiber-optic sinusoidal phase-modulating (SPM) interferometer for fringe projection is presented. The system is based on the SPM technique and makes use of the Mach–Zehnder interferometer structure and Young’s double pinhole interference principle to achieve interference fringe projection. A Michelson interferometer, which contains the detection of Fresnel reflection on its fiber end face and interference at one input port of a 3 dB coupler, is utilized to achieve feedback precise control of the fringe phase, which is sensitive to phase drifting produced by the nature of the fiber. The phase diversity for the closed-loop SPM system can be real-time measured with a precision of 3 mrad. External disturbances mainly caused by temperature fluctuations can be reduced to 57 mrad for the fringe map. The experimental results have shown the usefulness of the system.

Background suppressing is the main technology for infrared target detection. We present a new small infrared target detection (SIRTD) method that is also based on background suppressing. First, a new matrix decomposition model, named harmonic and sparse matrix decomposition (HSMD), is put forward for decomposing an image into a harmonic and a sparse component, which are seen as a background component and a small target component, respectively. Then, an algorithm based on augmented Lagrangian alternating direction method (ALADM) for solving HSMD is described. The main computational cost of the proposed algorithm in each iteration is that of a fast Fourier transform (FFT), which makes the proposed algorithm very fast. By searching for the maximum local energy regions in the target component, the infrared targets can be easily and accurately located. Experimental results on some infrared images show that HSMD solved by ALADM is very suitable for real-time infrared image decomposing and SIRTD.

A fusion algorithm of hyperspectral and high-resolution images based on principal component analysis (PCA) and second generation Bandelet transform is proposed. Primarily, the numerous components of the hyperspectral image are divided. Subsequently, the maximum rule is used to select the Bandelet coefficients and geometry flows of the hyperspectral image which are transformed by PCA in the following step. Finally, the fused image is reconstructed by taking inverse PCA and Bandelet transform. Some numerical simulations are made to test the validity and capability of the proposed fusion algorithm.

We propose an example-based superresolution algorithm that adaptively exploits multiple dictionaries based on local image structures. Noise, irregularities, and blurred textures are noticeable artifacts in the reconstructed image due to a shortage of relevant examples and false exploration in the dictionary. These artifacts are emphasized during successive enhancement. We alleviate the artifacts by constructing multiple dictionaries coupled with different sharpness levels during the learning phase. We exploit these dictionaries adaptively based on local image structures during the synthesis phase. Experimental results show that the proposed algorithm provides more detailed images with significantly reduced artifacts while consuming only 8.6% of storage capacity and 0.25% of CPU running time in comparison with a typical example-based superresolution algorithm based on neighbor embedding.

Complex motion patterns of natural systems, such as fish schools, bird flocks, and cell groups, have attracted great attention from scientists for years. Trajectory measurement of individuals is vital for quantitative and high-throughput study of their collective behaviors. However, such data are rare mainly due to the challenges of detection and tracking of large numbers of objects with similar visual features and frequent occlusions. We present an automatic and effective framework to measure trajectories of large numbers of crowded oval-shaped objects, such as fish and cells. We first use a novel dual ellipse locator to detect the coarse position of each individual and then propose a variance minimization active contour method to obtain the optimal segmentation results. For tracking, cost matrix of assignment between consecutive frames is trainable via a random forest classifier with many spatial, texture, and shape features. The optimal trajectories are found for the whole image sequence by solving two linear assignment problems. We evaluate the proposed method on many challenging data sets.

Existing fingerprint segmentation methods usually process fingerprint images captured by different sensors with the same feature or feature set. We propose to improve the fingerprint segmentation result in view of an important fact that images from different sensors have different characteristics for segmentation. Feature usability evaluation, which means to evaluate the usability of features to find the personalized feature or feature set for different sensors to improve the performance of segmentation. The need for feature usability evaluation for fingerprint segmentation is raised and analyzed as a new issue. To address this issue, we present a decision-tree-based feature-usability evaluation method, which utilizes a C4.5 decision tree algorithm to evaluate and pick the best suitable feature or feature set for fingerprint segmentation from a typical candidate feature set. We apply the novel method on the FVC2002 database of fingerprint images, which are acquired by four different respective sensors and technologies. Experimental results show that the accuracy of segmentation is improved, and time consumption for feature extraction is dramatically reduced with selected feature(s).

We present a fire alarm system based on image processing that detects fire accidents in various environments. To reduce false alarms that frequently appeared in earlier systems, we combined image features including color, motion, and blinking information. We specifically define the color conditions of fires in hue, saturation and value, and RGB color space. Fire features are represented as intensity variation, color mean and variance, motion, and image differences. Moreover, blinking fire features are modeled by using crossing patches. We propose an algorithm that classifies patches into fire or nonfire areas by using random forest supervised learning. We design an embedded surveillance device made with acrylonitrile butadiene styrene housing for stable fire detection in outdoor environments. The experimental results show that our algorithm works robustly in complex environments and is able to detect fires in real time.

We report a polarization-dependent reflector beyond normal incidence with a subwavelength nanoparticle chain. Polarization-dependent reflection with high reflectivity or high transmissivity can be obtained with this structure. Light waves of transverse electric/magnetic mode will be reflected, while the transverse magnetic/electric mode will transmit through. The structure shows a certain degree of tolerance of incident angle, technical fabrication, and even particle shape. We hope the low-loss and compact structure can find applications in photonic circuits such as gallium nitride-based light sources.

The slice absorption method (SAM) is a numerical parallel solution reported by Rumpf et al. for analyzing large-scale devices with a complex structure. We use this method to simulate diffraction of the lamellar crossed gratings, and we use the wave matrix for the Fourier modal method (FMM) for SAM formulation. For this formulation, gratings with arbitrary profiles can be viewed as a stack of lamellar gratings via a staircase approximation, which is different from the difference approximation in the original SAM. In addition, an improved cascading-doubling algorithm is implemented, and not only for long uniform regions or repeated units. This algorithm provides a concurrent result with the FMM and promises an efficient application in scatterometry for multilevel gratings.

The continuous fractional Fourier transform (FRFT) can be interpreted as a rotation of a signal in the time-frequency plane and is a powerful tool for analyzing and processing nonstationary signals. Because of the importance of the FRFT, the discrete fractional Fourier transform (DFRFT) has recently become an important issue. We present the computation method for the DFRFT using the adaptive least-mean-square algorithm. First, the DFRFT computation scheme with single angle parameter of the signal block using the adaptive filter system is introduced. Second, considering the transform angles always change in practical applications, the DFRFT computation scheme with adjustable-angle parameter of the signal block using the adaptive filter system is presented. Then we construct two realization structures of the DFRFT computation with simultaneous multiple-angle parameters for each signal block. The proposed computation approaches have the inherent parallel structures, which make them suitable for efficient very large scale integration implementations.

Reconstructing the dielectric permittivity profile (depth dependence of sample dielectric permittivity) is an important inverse problem. We present a new method for permittivity profile reconstruction based on terahertz time-domain spectroscopy signal processing. Reconstruction is accomplished in two steps. First, the sample pulse function is reconstructed using sample time-domain reflection data. Low- and high-frequency noise filtering and the interpolation of the pulse function at low frequencies are then applied. Second, an invariant embedding technique is used to calculate the dielectric permittivity profile based on the sample pulse function. Samples with known permittivity profiles have been studied experimentally using this procedure in order to verify this algorithm. This algorithm is stable to additive Gaussian white noise as shown using mathematical modeling based on the finite-difference time-domain technique. Possible applications of this permittivity profile reconstruction technique are discussed.

The Turning Eyes to the Big Sky project offered schools in southwestern Montana a unique opportunity to strengthen science instruction. The project implemented, in a formal setting, a nationally established informal science curriculum on light and optics, the Hands-on Optics Terrific Telescopes curriculum. Terrific Telescopes was implemented in eight middle-school classrooms and reached 166 students during the 2010 to 2011 school year. As part of the project, we conducted a teacher workshop and assessed student learning outcomes and teachers’ experiences with the curriculum. The goals of our assessments were to improve our understanding of how students learn key optics-related principles, provide evidence of the learning outcomes of Terrific Telescopes, and find out how teachers adapt the curriculum for use in formal settings. Our research established that students in every classroom learned optics concepts, uncovered student ideas about telescope optics, and identified ways to support and supplement the curriculum for use in classrooms.

This article was originally published in Vol. 52, No. 6 of Optical Engineering on 19 June 2013 with an incorrect citation identifier (CID) of 064603. The paper was removed and republished online with a correct CID of 064003 on 21 June 2013. The typical structure of the six-digit CID for OE uses the first two digits to indicate the volume number, and the middle two digits to indicate the section category. This paper was originally published under the heading “Integrated Optics” (section code 46), but has been republished under the category “Optical Components, Detectors, and Displays,” which uses section code 40.