This PDF file contains the editorial “Drought” for OE Vol. 46 Issue 12

All-optical single-to-dual channel format converter from non-return-to-zero (NRZ) to return-to-zero (RZ) is proposed and demonstrated using cascaded sum- and difference-frequency generation (SFG+DFG) in a periodically poled LiNbO₃ (PPLN) waveguide. The pump optical clock is generated from the active mode locking in a reflective semiconductor optical amplifier (RSOA)-based fiber ring laser. We successfully observe 10- and 20-Gbit/s single-to-dual channel NRZ-to-RZ format conversions in the experiment.

Feature extraction is a crucial step for pattern recognition. Recently, some manifold learning algorithms have drawn much attention. Although their properties of locality preserving are fairly significant, most manifold-based algorithms have limits to solve classification problems. First, they do not have good discriminant ability. Second, they fail to remove the redundancy among the extracted features. We present a new feature extraction method, called kernel uncorrelated neighborhood discriminative embedding (KUNDE), which integrates two abilities of manifold learning and pattern classification. The purpose of KUNDE is to preserve the within-class neighboring geometry while maximizing the between-class scatter. Optimizing an objective function in a kernel feature space, nonlinear features are extracted. Moreover, by putting a simple uncorrelated constraint on the computation of the basis vectors, the extracted features via KUNDE are statistically uncorrelated and thus contain minimum redundancy. Experimental results on radar target recognition indicate the promising performance of the proposed method.

An astigmatic optical surface has two different orthogonal curvatures. There are a great number of them, but only a few are in common use in optical instruments. These are similar in shape but have some important differences to be considered. These differences must be taken into account during the design, fabrication, and testing of optical systems that includes such surfaces. A comparative description of some surfaces is made with some of its characteristics reviewed. Finally, an analysis of their properties and testing possibilities is made. An important conclusion of this analysis is that the two main surfaces, the toroidal and the spherocylindrical surfaces, may differ in their shape by an ashtray component (an x²y² term) as large as several wavelengths.

The purpose of this study is to design and analyze a new asymmetrical liquid-filled lens. By controlling the tilt angle of the pressure ring and the hydraulic pressure of this lens, either the light direction or the focal length can be changed. For this study, the ANSYS workbench program is employed to analyze the membrane deformation of the lens under different liquid pressures and asymmetrical conditions. ZEMAX is used to compute its effective focal length. To demonstrate the feasibility of the asymmetrical lens, a prototype is developed and tested. The analysis and experimental results show good agreement.

Multispectral scattering is a promising nondestructive technique for assessing the firmness of fruit. We report on the development of a laser-based multispectral imaging prototype for real-time detection of apple firmness. The prototype consists of a common aperture multispectral imaging unit, a specially designed multilaser unit, and a fruit handling unit, which simultaneously capture and process four spectral scattering images at a speed up to two fruit per second. The multispectral imaging system is tested for detecting the firmness of Golden Delicious and Red Delicious apples at a rate of one fruit every two seconds. The original 2-D scattering images are corrected by removing noise pixels and incorporating fruit size into the calculations of the scattering distance and intensity. The 1-D scattering profiles are fitted with a four-parameter Lorentzian distribution function. Multilinear regression models are developed using the four Lorentzian parameters for the four wavelengths to predict the firmness of apples. The multispectral imaging system achieves good firmness predictions with the correlation coefficient of 0.86 for both Golden Delicious and Red Delicious. The technique is fast and relatively easy to implement, and has the potential to meet the requirement for online sorting and grading of apples.

An optical film with some microstructures can enhance external quantum efficiency of a bottom-emission type organic light emitting diode (OLED) by out-coupling the light trapped inside its substrate. We measure the luminous intensity of two OLEDs coupled to several optical films. The films we try are four types of prism films and three kinds of diffuser films. A CCD-based measurement system rapidly evaluates the angular dependency of luminous intensity for each film and OLED combination. Integration of these distributions over the azimuth and polar angles gives luminous flux. We define an enhancement factor as the ratio of the luminous flux of an OLED-film combination to that of an OLED alone. In all the cases, the largest factor is 1.60 and the second largest is 1.54. The OLED with a higher reflectance always has a larger enhancement factor. A highly reflective OLED recycles the light reflected or scattered by the microstructure of the film more efficiently. Ray tracing analysis, assuming a Lambertian source, more or less reproduces the enhancement factors and their dependency on the OLED reflectance. It also indicates that an OLED with 100% reflectance coupled to a film with some spherical surface would give the highest efficiency of 1.68.

LED-based projectors have numerous advantages compared to traditional projectors. They are more compact, they exhibit a larger color gamut and a longer lifetime, the supply voltage is lower and they can even operate on batteries. LEDs can switch rapidly (possibility to pulse) and they have a high dimming ratio (contrast considerations). However, they have low optical power per étendue, although this is also improving consistently. With an efficient illumination engine design we can build an LED projector with a moderate light output and with superior properties. We present a relatively compact LED projector with two liquid crystal on silicon (LCOS) light valves (LVs). One of these LVs alternately modulates red and blue information, while the other permanently modulates green information to achieve a good color balance. Additionally, we apply some methods to increase the brightness on the screen. Our two-LCOS approach results in a compact, efficient LED projector that produces 171 lm projected D65 flux.

A United Kingdom consortium (MI3) is founded to develop advanced CMOS image sensors for scientific applications. "Vanilla," a 520×520 array of active pixels with 25-μm pitch is fabricated in the 0.35-μm 4M2P (4 metal, 2 poly) CMOS process and uses a 3.3-V supply. It has flushed reset circuitry to attain low reset noise and random pixel access for high-speed region-of-interest (ROI) readout. "OPIC" is a 64×72 test structure array of digital pixels with 30-µm pitch, fabricated in 0.25-μm 5M1P (5 metal 1 poly) CMOS process with a 3.3/2.5-V supply. It can perform thresholding via an in-pixel comparator for sparse readout at a high frame rate. Characterization of both sensors is performed under optical illumination and x-ray exposure. For x-ray characterization, both sensors were coupled to a structured thallium-doped cesium iodide (CsI:Tl) scintillator via a fiber optic plate. Vanilla has been found to exhibit 34±3e^-; read noise and a spectral response of 225±5 mA/W at 500 nm and can read a 6×6 ROI at 24,395 frames/s. OPIC has 46±3e^-; read noise and can perform sparse readout at up to 3700 frames/s. Based on these results, Vanilla could be employed for applications where only a small portion of the image contains relevant information, while OPIC is suited to high-speed imaging applications.

The evolution of the gradient force pattern of hyperbolic-cosine-Gaussian beams induced by a three-zone pure phase plate is numerically investigated. The pure phase plate consists of three concentric zones—the center circular zone, the inner annular zone—and the outer annular zone and the phase variance of inner annular zone is adjustable. The results show that the proposed plate may induce tunable gradient force on the particles in the focal region. The optical trap shape is obviously tunable and multiple traps may occur with changing geometrical parameters of the phase plate. An optical trap shift can be induced by changing the phase variance of the inner annular zone portion. The phase plate may be a very promising method of transporting trapped particles and can be used to construct controllable optical tweezers.

We propose and demonstrate a novel high-gain-efficiency long-wavelength band (L-band) erbium-doped fiber amplifier with a double-pass backward-pump configuration, in which the strong backward C-band amplified spontaneous emission is effectively utilized. The L-band gain is greatly enhanced in comparison with the copumped configuration. Without using any excessive components, the new configuration can provide the same gain as the conventional configuration, but only using 40% pump power. Meanwhile, the noise figure is also effectively improved under the low pump power.

We report the first experiments showing structural changes in borosilicate glass using just a short-cavity Ti:sapphire oscillator at 800 nm and 90 MHz. Micromachining is achieved with infrared femtosecond pulses having record-low energies. We show 3-D patterning capability, including waveguides and 3-D gratings embedded in the volume of a glass slab.

We present a simple and practical method for the single-ended distributed fiber temperature measurements using microwave (11-GHz) coherent detection and the instantaneous frequency measurement (IFM) technique to detect spontaneous Brillouin backscattered signal in which a specially designed rf bandpass filter at 11 GHz is used as a frequency discriminator to transform frequency shift to intensity fluctuation. A Brillouin temperature signal can be obtained at 11 GHz over a sensing length of 10 km. The power sensitivity dependence on temperature induced by frequency shift is measured as 2.66%/K.

We present an all-in-one, computer-controlled, measurement setup able to evaluate propagation losses, effective group index, and mode size of integrated optical devices and optical fibers. The possibility to use a single setup, instead of three separate ones, enables faster measurements, improvements in terms of reproducibility and precision, and reduction of systematic errors. Control of the operating conditions, easier system upgrade besides cost and laboratory space savings are other additional features of this system. To confirm proper operation and versatility of the proposed setup, different samples are successfully characterized, and results are presented and discussed.

A new broadband filter, based on the high level bandgap in 1-D photonic crystals (PCs) of the form Si|air|Si|air|Si|air|Si|air|Si|air|Si is designed by the plane wave expansion method (PWEM) and the transfer matrix method (TMM) and fabricated by lithography. The optical response of this filter to normal-incident and oblique-incident light proves that utilizing the high-level bandgaps of PCs is an efficient method to lower the difficulties of fabricating PCs, increase the etching depth of semiconductor materials, and reduce the coupling loss at the interface between optical fibers and the PC device.

The intrachannel collision of optical solitons with power law nonlinearity is studied using the quasiparticle theory. The perturbation terms considered are the nonlinear gain and saturable amplifiers along with filters. The suppression of soliton-soliton interaction, in presence of these perturbation terms, is achieved. The numerical simulations support the quasiparticle theory.

Identifying various impairments is critically important in optical channel monitoring. We present a new approach for analyzing and characterizing the amplitude histogram of optical signals. This new approach is based on the X² distance, which was originally used in digital image processing. To effectively distinguish various impairments, we introduce two different metrics: (1) the difference between the X² distance of the mark histogram and the X² distance of the space histogram, and (2) the asymmetry property of the mark and space histograms. Using these two metrics together, we show by simulation that three major impairments, namely, inband crosstalk, amplified spontaneous emission (ASE) noise, and chromatic dispersion can be effectively identified.

Taking into account ultrafast carrier dynamics, we model 640 Gbit/s wavelength conversion based on nonlinear polarization rotation (NPR) assisted with sideband filtering in a single semiconductor optical amplifier (SOA) and investigate the performance of two types of wavelength conversion schemes: one based only on NPR and the other based on NPR assisted by red-shifted filtering. Simulated results show that the two types of wavelength conversion schemes are achieved with clear open-eye diagrams and have signal regeneration capability at 640 Gbits/s. Simulated analyses also show that the wavelength conversion based on NPR assisted by red-shifted filtering scheme exhibits better performance in terms of wavelength conversion and signal regeneration.

We present experiments of line and parallel configurations of hybrid erbium-doped fiber amplifiers/fiber Raman amplifiers (EDFAs/FRAs). For the line structure, a gain flatness of ±1.15 dB over a range of 47 nm (1483 to 1530 nm) is obtained. In the parallel configuration, the gain flatness is below ±2 dB for 1487 to 1507 nm and 1520 to 1550 nm. Using a high-birefringence fiber loop mirror as a signal reflector, a noise figure is less than 6 dB in the gain bandwidth. Then performances of different hybrid configurations are compared.

The feasibility of optical wireless communication links using high-brightness illumination light-emitting diodes (LEDs) is experimentally verified. We measure the modulation bandwidths of red-, green-, and blue-colored LEDs and the eye patterns for optical wireless links incorporating single- and multi-LED transmitters. The eye patterns of single-color red, green, and blue LEDs are compared. An optical communication link consists of an optical transmitter module with seven LEDs, and a packaged silicon photodiode as a receiver. The bit error rate (BER) curves are measured by varying the link distance and the horizontal offset to check their dependencies on the BER. The optical wireless communication link incorporating the transmitter with seven high-brightness illumination LEDs can support 10-Mb/s data transmission without any optimized optical filter to enhance optical gain. Based on the experimental results, it is demonstrated that a communication link with illumination LEDs could be used for short-reach optical wireless communication systems.

A simple scheme for an all-optical AND logic gate is proposed based on a sagnac interferometric structure. The operations of this scheme with a 40-Gbit/s return-to-zero (RZ) pseudorandom bit stream (PRBS) are simulated correctly with an output extinction ratio (ER) of about 14.7 dB. Through numerical analyses and discussions, it can be seen that the output ER of the AND operation is improved more than 6 dB, and the output pattern effect is decreased by about 0.4, compared to terahertz optical asymmetric demultiplexer schemes under the same condition. Furthermore, the carrier recovery time of a semiconductor optical amplifier (SOA) is no longer a crucial parameter to restrict the operation speed of this scheme. This scheme is potentially capable of AND operation rates to 100 Gbit/s.

We report the two-stage single-pump configuration of an erbium-doped fiber amplifier, in which a Sagnac interferometer is introduced to reduce the most important contribution of amplified spontaneous emission (ASE) noise, providing significant improvement on the amplifier performance. A Sagnac interferometer, made from a high-birefringence fiber loop, is included between the first and second stages. It is designed to provide transmittance with a period of 46 nm that allows us to adjust the minimum transmission around 1530 nm (peak of ASE noise) and maximum transmission at 1550 nm (signal wavelength). For optimizing the configuration, we measure the erbium-doped fiber parameters and simulate the amplification of the signal along the fiber. In the experiment, a significant absorption coefficient for pump and signal is found. The absorption looks to be too strong for the background absorption, and we suppose that it may be caused at least partly by excited-state absorption (ESA). Including the absorption coefficient allows very good correspondence between simulation and experiment. Experimental results show that with a simple configuration, we obtain up to 53-dB amplification with only 73 mW of pump power.

A four-wave mixing assisted multiwavelength semiconductor optical amplifier laser is experimentally demonstrated in a fiber ring cavity. A sampled linearly chirped fiber Bragg grating is used as the wavelength-selective component. Four-wave mixing enhances the number of peak-power-equalized lasing wavelengths and operation stability of the ring laser. The extinction ratio of the 20 multiwavelengths output is greater than 40 dB, and the peak-power difference is less than 3 dB.

For practical holographic video display, it is important to generate holographic fringes as fast as possible. It is also important to display the full-color image with a simple display system. In our previous study, a full-color hologram was realized as a rainbow hologram, which discards the vertical parallax to reduce computation complexity. Its color reproduction, however, is not enough. Since this hologram uses the horizontal slit, proper color reproduction can be obtained only from a narrow viewing area in the vertical direction. In contrast, the image hologram provided a good contrast image, although it had only a single color. Also, the image hologram has full-parallax information. In this work, we investigate the image hologram for fast calculation and the display optics for full-color holograms with full parallax. Since image points are located close to the hologram, the required computation area of the image hologram becomes much smaller than that of the entire hologram. Therefore, vastly improved computational speed is obtained. The full-color hologram is displayed on a holographic video display system, which uses part of the original optics and liquid crystal on silicon (LCoS) panels of the conventional video projector to separate and combine color components. From the experimental results, we obtain a full-parallax reconstructed image and better color reproduction compared with the rainbow hologram.

A method is developed to study the synergism that can exist between horizon search radar and IR search and track (IRST) systems onboard ship under various meteorological conditions within the marine surface layer (<50 m). The method shows that four operational regions can be defined through the effect of the air-sea temperature difference and the air-sea water vapor pressure difference to produce sub- or superrefractive IR and rf propagation. It is also shown that no conditions can exist such that both IR and rf have subrefractive propagation. Applying the method to many meteorological observations shows that the method works quite well; however, it also indicates that there is not necessarily a detection range advantage to having both an optical and a radar system. However, the advantages to having an optical system are not solely dependent on its range performance. The precision with which an optical system can provide target track parameters, its ability to maintain track when radar systems cannot, and its ability to identify targets are synergisms that are quite significant.

Blind superresolution (BSR) is one of the challenges in image superresolution. We propose a new approach using a unified regularization framework, which solves image registration, point spread function (PSF) estimation, and high-resolution (HR) image reconstruction simultaneously. To achieve this, the anisotropic diffusion techniques are employed as one regularization term to preserve edge information in the HR image estimation, and a generalized version of the eigenvector-based (EVAM) constraint is developed to regularize the PSF. An alternating minimization algorithm is devised to find optimal solutions, and an effective numerical implementation scheme, based on local filtering, is proposed to suppress the ringing artifacts in the image reconstruction. Finally, experiments with synthetic and real data are presented to demonstrate the effectiveness and robustness of our approach, which can handle motion blur well and enhance resolution notably for very noisy images.

We propose a unified approach that incorporates the mean shift-based image segmentation algorithm and the SST (shortest spanning tree)-minmax-based graph grouping method to achieve effective IR object segmentation performance amenable for real-time application. It preprocesses an image by using the mean shift algorithm to form segmented regions that can not only remove the noise, but also preserve the desirable discontinuity characteristics of the ship object. The segmented regions can then effectively represent the original image by using the graph structures, and we apply the SST-minmax method to perform merging procedure to form the final segmented regions. Due to the good discontinuity-preserving filtering characteristic, we can effectively remove the clutter disturbance of the sea background without loss of the IR ship object information, and significantly reduce the number of basic image entities. Therefore, the region merging based on SST-minmax can produce excellent segmentation performance at low computational cost due to smaller clutter disturbance and less region nodes. The superiority of the proposed method is examined and demonstrated through a large number of experiments using a real IR ship image sequence.

We present a robust and efficient approach for zoom-based super-resolution (SR) reconstruction problems. We employ the total variation (TV) of the desired image priori in the maximum a-posteriori estimation. An efficient algorithm based on iterative methods and preconditioning techniques is employed to solve the resulting variational problem. To suit the proposed algorithm for realistic imaging situations, a registration method is presented to simultaneously solve the zooming factors, image center shifts, and photometric parameters. Experimental results show that the proposed TV-based algorithm performs quite well in terms of both quantitative measurements and visual evaluation. We also demonstrate that the proposed algorithm is robust for SR image inpainting, where some pixels are missed in the SR reconstruction model.

We propose an algorithm to detect shot transitions of video data in the compressed domain and then extend its effect to the spatial domain. This algorithm is an improvement of the conventional solution, where energy histograms of the DC coefficients are used to calculate the distance between consecutive frames. The DC coefficients of compressed MPEG video data are obtained either through direct extraction [intraframes (I-frames)] or by frame conversion [predicted frames (P-frames)] while those of uncompressed video data are calculated by 8×8 block pixel averaging. The key contribution of this approach is to enhance the detection result by using the ratio between two sliding windows to attenuate the low-pass-filtered frame distance, resulting in the amplification of the transitional regions. The experimental results demonstrate that this algorithm achieves high detection rates with low computational complexity.

Depth from defocus(DFD) measures defocus blur, which determines the point spread function (PSF) of an image formation system. Most DFD research has been investigated with a fixed focal length, where two or more defocus images are obtained with different image distances or lens apertures. To apply DFD techniques using a zoom lens, extensive calibration of the image formation system is needed. This work presents a simple calibration technique of defocus blur for a zoom lens system. We derive the relationship of defocus blur with respect to different focal lengths of the lens. The proposed technique is applied to a spatial domain DFD technique for error analysis.

A maximum a priori (MAP) estimation technique for the detection of focus aberrations in electro-optical imaging systems is developed. The technique simplifies the equipment required in focus aberration detection over previous methodologies. The magnitude of the focus aberration is estimated from a single image. The MAP estimation technique uses a Poisson distribution of the photons arriving at the detector from the object. A Gaussian distribution is added to the statistical model to account for the focus aberration. Using the imaging system statistical model and real laboratory images from a charge-coupled device (CCD) camera, the focus aberration detection (FAD) algorithm produces estimates of the focus aberrations. The results demonstrate a viable approach for estimation and potential removal of focus aberrations in electro-optical systems, without the need to divert any light from the primary channel, or for additional complicated equipment and associated calibration requirements.

Most image data that we encounter is in color, thus measuring clutter in color images has become increasingly important. The extension of phase correlation to quaternion space, which can measure color similarity as well as the structural similarity between two color images, is defined. It is used to describe the global clutter in color images. The correlation degrees between the experimental probability of detection and that predicted by the clutter metric are presented. Experiment results show that the quaternion phase-correlation-based clutter metric can perform well in quantifying color image clutter.

We describe an experiment to quantify the exploitation performance benefits of acquired site-specific algorithm performance knowledge, applied to the problem of motion detection. Automated object detection algorithms typically suffer from high false alarm rates that can be distracting to an operator, in some cases rendering the algorithm useless. The experiment is designed to reduce the false alarm rate of a surveillance algorithm in scenarios that involve repeated observation of the same location using an algorithm as a cuer to an operator who accepts or rejects algorithm reports. The experiment involves using a wrapper that records the operator decisions, and modulates algorithm reports using acquired knowledge of high-false-alarm areas and high-true-detection areas. The wrapper also uses an a priori operator segmentation of the scene that marks some regions for which no algorithm reports will be passed on to the operator. The experiment demonstrates a 35% reduction in the time required for an analyst to find vehicles in a search scenario, without any negative impact on accuracy.

In a real-time vision navigation system, an accurate and fast convergent pose estimation algorithm is required for the video guidance sensor. The orthogonal iteration (OI) algorithm is fast and globally convergent, but its results have a large translation error at a close range, and sometimes it fails to give a correct rotation matrix when the data are severely corrupted, when using the 3-D feature points. When the rotation matrix solution in the OI algorithm has been refined, an efficient pose estimation algorithm is derived. Simulation of the improved algorithm shows that the rotation matrix is always proper, which in turn improves the accuracy of the translation vector. The noise resistance and the outlier tolerance are enhanced by using the improved algorithm. The two algorithms are applied to our experimental system for an unmanned vehicle rendezvous and docking simulation separately. The comparison experiments show that the relative distance error is less than 0.28% from 1.5 to 5 m, and the rotation angle error is within ±0.7 deg in 5 m using the improved algorithm. These are better than the results using the OI algorithm.

We provide a derivation of bidirectional coupled-mode equations from Maxwell's equations. The theoretical description of the collinear magneto-optical interaction of magnetostatic forward volume waves with guided optical modes is generalized. Its behavior is expressed using solutions to the coupled-mode equations. In some cases, applying the conservation of energy yields exact solutions that can be formed in terms of elementary transcendental functions. The auxiliary function method is used to find a series solution based on the solution of the homogeneous boundary value problem. Using the derived solutions, simulations show that the parallel antiparallel magneto-optical interaction bandwidth and structure can be tuned through selection of power applied to two transducers. They also show that equivalent mode power conversion can take place in half the propagation distance for parallel anitparallel magneto-optical interaction compared to pure traveling wave magneto-optical interaction.

The purpose of fake iris detection is to discriminate between real and fake iris images and to defeat fake (forged) iris images. A robust fake iris detection method should be able to detect various types of fake iris images obtained from a fake printed iris, an artificial eye, or a fake contact lens, correctly and nonintrusively. To solve the problem, we propose a new fake iris detection method. We measure distinctive physiological multifeatures [the first and second features refer to the reflectance ratios of the iris to the sclera (RRIS) at 750 and 850 nm, respectively, and the third feature refers to the thickness of the corneoscleral limbus], and classify those features extracted from live irises and fake irises using a support vector machine (SVM). Using the proposed method, we can discriminate various types of fake iris images without inconveniencing users by shining visible light. To measure the performance of the method, three types of fake irises are made: a printed iris, an artificial eye, and a fake contact lens. Our experimental results show that it is possible to detect those fake iris images with high accuracy.

Variable-length coding (VLC) is widely used in video coding to improve compression efficiency. However, suffering from loss of synchronization, the VLC bit stream is much more sensitive to random errors than a fixed-length coding (FLC) bit stream. Error-resilient entropy coding (EREC) is a valid tool combating random errors in a VLC bit stream. Due to its intrinsic property of error propagation, when EREC is applied to a video bit stream, those blocks placed later become much more likely to be lost. We propose a simple method to further improve the error robustness of a video bit stream by interleaving transform coefficients of blocks so that low-frequency information is always placed ahead of high-frequency information. Thus, low-frequency information of greater significance is less likely to be lost. Experimental results prove the superiority of the proposed method. In addition, block interleaving can also be used in a data-partitioned video bit stream with ease.

A nondestructive technique, based on Fresnel diffraction from phase objects, is proposed for specifying the refractive indices of optical fibers without requiring index matching liquid. The method involves measurement of normalized intensity distribution on the Fresnel diffraction pattern of a monochromatic plane wave diffracted from a fiber, and evaluation of the fiber core refractive index from the intensity distribution by the least-square method. It is also shown that for the case of an unknown fiber core radius, by fitting a suitable theoretical intensity distribution on the corresponding experimental intensity distribution, the core radius and refractive index can be obtained with reasonable accuracy. Simulation and experimental studies show that the technique is reliable and quite sensitive to refractive index change.

Slight geometrical imperfections that can occur during the fabrication process, in the lattice of index-guiding photonic crystal fibers (PCF), are evaluated to determine the sensitivity of the chromatic dispersion and the birefringence to these defects. Furthermore, the impact of fluctuations in the lattice profile of a real photonic crystal fiber on its propagation characteristics is pointed out. Numerical and experimental analyses show that chromatic dispersion of a large core PCF is more robust to the geometrical imperfections, while its birefringence reveals more sensitivity to these defects. This analysis is performed using the finite element method, which assures high solution accuracy.

We experimentally observe saturable absorption and dra-matic three-photon absorption in various colloidal solutions of cadmium selenide quantum dots, with a strong size dependence witnessed for these properties. We also develop a model for the electronic portion of the nonlinearities that illustrates well the trends exhibited by our experi-mental data. The model incorporates six bands (three each in the va-lence and conduction bands).

This PDF file contains the errata for “OE Vol. 46 Issue 12 Paper 2822869” for OE Vol. 46 Issue 12