This PDF file contains the editorial “Editorial: Digital Choices” for OE Vol. 44 Issue 12

Sb-based dual-band detectors were fabricated and characterized. The first band consists of an InGaAsSb pn junction for long wavelength detection, while the second band consists of a GaSb pn junction for shorter wavelength detection. Both bands were grown, lattice-matched to a GaSb substrate, using metal-organic vapor phase epitaxy. Three metal contacts were deposited to access the individual junctions. Spectral response measurements indicated either independent operation of both detectors simultaneously, or bias selective operation for one detector while serially accessing both devices.

A novel fabrication scheme to develop high-throughput plastic microlenses using injection-molding techniques is realized. The initial microlens mold is fabricated using the well-known reflow technique. The reflow process is optimized to obtain reliable and repeatable microlens patterns. The master mold insert for the injection-molding process is fabricated using metal electroforming. The electroplating process is optimized for obtaining a low stress electroform. Two new plastic materials, cyclo olefin copolymer (COC) and Poly IR 2 are introduced in this work for fabricating microlenses. The plastic microlenses have been characterized for their focal lengths that range from 200 µm to 1.9 mm. This technique enables high-volume production of plastic microlenses with cycle times for a single chip being of the order of 60 s.

We present a purely mechanical means of producing highly concentric spherical lenses at the endfaces of optical fibers. The production process has two stages. First, conical lenses are produced in a grinding process that ensures excellent concentricity. Then, the conical lenses are transformed to spherical lenses using a novel process called loose abrasive blasting. The cone grinding is carried out on a microgrinding machine, which has a sophisticated control system that enables the production of precision conical lenses. The blasting is carried out on a diamond blasting machine. Plots showing automatic centering performance of the microgrinding machine and scanning electron microscopy images of the conical and spherical lenses are presented.

We propose a novel structured light method, namely a trapezoidal phase-shifting method, for 3-D shape measurement. This method uses three patterns coded with phase-shifted, trapezoidal-shaped gray levels. The 3-D information of the object is extracted by direct calculation of an intensity ratio. Compared to traditional intensity-ratio-based methods, the vertical or depth resolution is six times better. Also, this new method is significantly less sensitive to the defocusing effect of the captured images, which makes large-depth 3-D shape measurement possible. If compared to sinusoidal phase-shifting methods, the resolution is similar, but the data processing speed is at least 4.5 times faster. The feasibility of this method is demonstrated in a previously developed real-time 3-D shape measurement system. The reconstructed 3-D results show similar quality to those obtained by the sinusoidal phase-shifting method. However, since the data processing speed is much faster (4.6 ms per frame), both image acquisition and 3-D reconstruction can be done in real time at a frame rate of 40 fps and a resolution of 532×500 points. This real-time capability allows us to measure dynamically changing objects, such as human faces. The potential applications of this new method include industrial inspection, reverse engineering, robotic vision, computer graphics, medical diagnosis, etc.

A simple interferometric scheme is presented to characterize the 2-D distribution of linear birefringence with full-range capability. Since the interference images are obtained with respect to different orientations of a linearly polarized incident laser beam, the measurement speed can be improved once the orientation adjustment is achieved electronically. In addition, the measurement is independent of a nonuniform distribution of laser intensity, which is demonstrated experimentally and briefly explained theoretically. Furthermore, the measurement of residual linear birefringence distribution is also demonstrated successfully and verified by error analysis.

Holographic retarders based on form birefringence are shown to have controllable dispersion properties. Significantly, we show that the dispersion properties of these retarders can be adjusted over a large wavelength range by varying the periodicity of the index of refraction profile. These retarders with controllable dispersion characteristics are of high value for applications such as the compensation of liquid crystal displays.

The design of a new multifunctional integrated optical device capable of operating simultaneously as an optical switch and optical isolator is presented. The device consists of a multilayer directional coupler employing one nonlinear and one magneto-optic layer, with all other layers being linear and isotropic. Therefore, only phase matching conditions are required for the device operation irrespective of the propagation directions and operation regime (linear/nonlinear). The structure is optimized via a genetic algorithm and tested with a numerical formalism based on the wide-angle finite-difference beam propagation method. The results clearly demonstrate the ability of performing two distinct functions on the same device.

A near-ultraviolet (UV)-based white light-emitting diode (LED) lighting system linked with a semiconductor InGaN LED and compound phosphors for general lighting applications is proposed. We have developed for the first time a novel type of high-color rendering index (Ra) white LED light source, which is composed of near-UV LED and multiphosphor materials showing orange (O), yellow (Y), green (G), and blue (B) emissions. The white LED shows the superior characteristics of luminous efficacy and high Ra to be about 40 lm/W and 93, respectively. Luminous and chromaticity characteristics, and their spectral distribution of the present white LED can be evaluated using the multipoint LED light source theory. It is revealed that the OYGB white LED can provide better irradiance properties than that of conventional white LEDs. Near-UV white LED technologies, in conjunction with phosphor blends, can offer superior color uniformity, high Ra, and excellent light quality. Consequently we are carrying out a "white LEDs for medical applications" program in the second phase of this national project from 2004 to 2009.

We report a new mode-locking phenomenon in which ultra-high peak or "giant" pulse trains have certain pulse drops in an active mode-locked fiber ring laser. Generated pulse trains have properties similar to a return-to-zero format with a clear pedestal, with pulse trains circulating in the ring of peak power reaching 575 mW, which is about ten times higher than the actual peak output power. The temporal pulse trains and their optical spectra are described and discussed. It is believed that this is due to the interaction between copropagating pulses in the ring and the supermode competition.

This research concentrates on the implementation of 16 pairs of optical sensors in a process tomography system. The working principle is based on the switch and measure principle in electrical capacitance tomography (ECT), but uses fan beam shaped projection from light emitters. The fast settling time of optical sensors and wide coverage of an optical beam forms the interest to be implemented in a tomography system. At the initial stage, modeling has been carried out to predict the output from 16 pairs of optical sensors implemented with the switching principle. The 16 pairs of optical sensors consist of 16 3-mm PIN photodiodes and 16 3-mm LEDs. The idea is applied with the assumption that the emission angle of the source is large enough to illuminate all the receivers and the emission power is uniform along the projection. The linear back projection algorithm is used to predict the result from the modeling. The results for concentration profiles and reconstructed images of the original objects show significant agreement for further research.

There is a critical need for pressure sensors that can operate reliably at high temperatures in many industrial segments such as in the combustion section of gas turbine engines for both transportation and power generation, coal gasifiers, coal fired boilers, etc. Optical-based sensors are particularly attractive for the measurement of a wide variety of physical and chemical parameters in high-temperature and high-pressure industrial environments due to their small size and immunity to electromagnetic interference. A fiber optic pressure sensor utilizing single-crystal cubic zirconia as the sensing element is reported. The pressure response of this sensor has been measured at temperatures up to 1000 °C. Additional experimental results show that cubic zirconia could be used for pressure sensing at temperatures over 1000 °C. This study demonstrates the feasibility of using a novel cubic-zirconia sensor for pressure measurement at high temperatures.

An optical sensor to be used for gas pressure detection is described. The device is based on the spectral response associated with the surface plasmon resonance (SPR) occurring on a 50-nm gold surface. The operation of the device relies on the fact that the refractive index of a gas changes with pressure, which leads to a shift in the resonance wavelength dip λ_SPR in the SPR curve. Experiments performed on nitrogen gas at room temperature demonstrated the sensor resolution of 4.4×10^–5 RUI, which corresponds to a pressure resolution of 16 kPa. The new device offers the benefits of wide dynamic range, no moving parts, and possibly 2-D imaging of pressure distribution. Further development of the device may lead to a new type of optical pressure sensors.

A practical reflectometric fiber optic displacement sensor is reported. The sensor is based on the principle of optical frequency-modulated continuous-wave (FMCW) interference and primarily consists of a single-mode laser diode, a Y-type fiber optic directional coupler, and a quarter-pitch gradient-index lens. The displacement of the target is determined by measuring the phase shift of the beat signal with a special signal-processing method. An accuracy of 0.02 µm in a measurement range of 1000 µm has been achieved.

The waveguiding properties of SC-450 photoresist films are presented. The basic waveguiding properties such as refractive index, propagation losses, thickness, and birefringence of photoresist film are optimized. The effect of dye doping and UV exposure on photoresist film is also observed. The film shows excellent transmission (above 90%) in the wavelength range of 500 to 1500 nm. The present results suggest that photoresist films may be the good option to be used as an optical component.

A simple numerical method is developed to analyze how the intrinsic birefringence of silica-based ridge waveguides changes with waveguide dimensions and UV irradiation. Identical Bragg gratings were induced on waveguides with different widths which varied from 5 µm×6 µm to 9 µm×6 µm with ArF excimer irradiation and a phase mask. The variation of the waveguide effective index and birefringence as a function of the waveguide dimensions and UV processing are observed and quantified by monitoring the shifts in Bragg wavelength with UV irradiation. With UV irradiation, zero birefringence was easily realized in the waveguides, having an initial birefringence of <2.5×10^–4. The mechanism for controlling the waveguide birefringence with UV irradiation is verified both in the theoretical analysis and experimentally. Additionally, the ±0.1-nm variation in Bragg wavelength for waveguides with the same nominal width corresponds to a ±0.1-µm dimensional change in the actual waveguides geometry. This result is used as a way for improving quality control over the waveguide dimensions obtained from the photolithographic and RIE processes.

The transfer matrix method combined with the effective index method is adopted to model the silica-based channel waveguide patterned by UV writing. The effective indexes of the graded index channel waveguides with different dimension are calculated. The maximal error of the effective index is less than 3×10^–5. By this method, the number of the guided mode and the dimension range to guide certain modes can be obtained easily. Finally, the dimension range to guide a single mode is presented.

Continuously tunable optical true time-delay (TTD) modules based on dispersion-enhanced photonic crystal fibers (DEPCFs) are demonstrated to provide continuous microwave squint-free beam scanning for an X-band (8 to 12 GHz) phased-array antenna (PAA) system. The dispersion of the fabricated photonic crystal fibers (PCFs) is as high as –600 ps/nm km at 1550 nm. By employing PCFs to increase the dispersion, the TTD module size can be proportionally reduced. The time delay is continuously tunable from –31 ps to 31 ps between adjacent delay lines by tuning the laser wavelength continuously from 1528 to 1560 nm. The far-field radiation patterns of a 1×4 subarray were measured from –45 to 45 deg scanning angles. Squint-free operation is experimentally confirmed. Wavelength conversion is also demonstrated to confirm that time-delay information can be successfully transferred from one wavelength to the other without being changed, which is suitable to be implemented in 2-D phased-array antenna systems. The TTD formation idea presented is suitable for not only the X band, but also the other higher microwave frequencies, such as the K band.

The absorption efficiency of graded-index double-clad fiber lasers and amplifiers is investigated. As ray optics are no longer valid in the case of a graded index, a mode analysis method is used. The calculated results show that, in symmetric cases, absorption efficiency is higher with graded index than that with step index. In the case of an offset core, graded index can achieve the same absorption efficiency with a much smaller offset distance. Absorption efficiency for different graded-index profiles of the inner cladding is also studied and compared.

We present the construction of photonic crystal in-fiber devices. The presented devices include modulators and spectral filters. The manufacturing process related to the fabrication of these devices includes two building stones. The first one is the insertion of microwires into one of the capillaries of the photonic crystal fiber and the second one is the twisting of the fibers while drawing. Combining both technologies may yield the realization of an in-fiber solenoid that could be used for generation of in-fiber magnetic fields. We present the fabrication of the suggested devices as well as their experimental characterization.

A dispersion-managed soliton transmission using an unsymmetric dispersion map in a lumped amplifier system is investigated. For a soliton dispersion management system with equal-length segments of both normal and anomalous dispersion fibers, it is shown that the initial fiber length of the unsymmetric dispersion map must be shorter than that of the symmetric map to attain a chirp-free pulse at the beginning of a dispersion management unit cell. By properly adjusting the initial fiber length of the unsymmetric dispersion map, the dispersive wave is reduced and the allowed transmission distance can be increased when compared to the symmetric map system with optimum prechirping.

A two-step digit-set-restricted modified signed-digit (MSD) adder based on symbolic substitution is presented. In the proposed addition algorithm, carry propagation is avoided by using reference digits to restrict the intermediate MSD carry and sum digits into {1‾,0} and {0,1}, respectively. The algorithm requires only 12 minterms to generate the final results, and no complementarity operations for nonzero outputs are involved, which simplifies the system complexity significantly. An optoelectronic shared content-addressable memory based on an incoherent correlator is used for experimental demonstration.

We have proposed a new confocal readout system which is based on the combination of two N-zone circular phase-only transverse superresolving pupils to improve transverse superresolution. The procedure for designing such an improved system is presented. Results of comparisons between the performance of the proposed system and the transverse superresolving pupils indicate that with the same Strehl ratio the former has much higher transverse superresolution capacity and significantly lower sidelobe intensity.

We present a new type of point diffraction interferometer that employs single-mode optical fibers instead of traditional pinholes. Two optical fibers with different exit endfaces are used; one is normally cut and the other obliquely cleaved. The normally cut fiber is used to generate a near-perfect spherical reference wave. The test wave is produced from the oblique fiber that performs two functions: generating a spherical wave to illuminate the test optics, and reflecting the test wave for common-path combination with the reference wave. The interferometer proposed in this investigation is found suitable for testing large size mirrors with a relatively simple overall hardware configuration.

A disturbance-free sinusoidal phase modulating laser diode interferometer using an accelerated integrating-buckets processing system is described. Several techniques make it suitable for use in on-machine measurements: the charge-coupled device (CCD)-based additive operation on integrating buckets shares the burden of data processing imposed on the computer to shorten the measurement time; the use of high-speed shutter function of the CCD camera enables each bucket to be collected without disturbance, while the interference signal's stability is enhanced with the feedback control during the entire data-collecting time; by using a dedicated waveform generator, the phase modulating system is more compact and the modulating signal matches the CCD camera's exposure time easily and exactly. A surface profile measurement on a diamond-turned aluminum disk is demonstrated to evaluate the performance of this system.

We propose and physically discuss a kind of holographic Fourier synthesis in the profile of dynamic Moiré-like patterns. The interference patterns are obtained by progressively controlling the superposition of more than two dynamic sinusoidal phase gratings. It represents a new holographic optical nondestructive testing routine in real time for metrological purposes. The sinusoidal phase gratings with slightly different pitches are dynamically generated by photorefraction in the Bi₁₂TiO₂₀ (BTO) crystal sample. The photorefractive holographic medium is used in anisotropic self-diffraction configuration and in a diffusion-only recording mechanism.

Modified light-diffusion patterns created by contact-copy interference of diffused laser lights are proposed. A conventional light-diffusion pattern is created by means of a diffuser and a noncontact photosensitive plate (a noncontact or sandwich method). The proposed method uses a contact photosensitive plate and allows implementation of new applications such as surface-relief holograms, anticounterfeiting, and light-diffusion eyemarks.

A novel iterative method of generating three-plane, phase-only computer-generated holograms is presented. It is based on the iterative Fresnel ping-pong two-plane algorithm. A modification is introduced to extend the method for three planes, i.e., two object planes and a hologram itself. The described method enables the design of low-noise and high-efficiency phase-only holograms using a numerical Fresnel propagation algorithm. The source method is described, followed by the modified algorithm. Numerical simulation results and algorithm parameters are discussed, followed by a discussion of the method limitations.

A known target buried underground and illuminated from the air on its top flat surface by a ground-penetrating radar (GPR) is used to verify the results of a polarization approach that uses the Huynen parameters. The target is a dielectric cylinder of diameter d and height h that simulates a land mine buried in soil, flat top surface looking up. A method-of-moments (MoM) approach (and codes) is used to generate the complex elements of the scattering matrix S of the present target. These elements are obtained in modulus and phase as functions of frequency in the wide band; 0≤f≤5 GHz, for various angles of incidence of the radar beam on the air-ground interface. That matrix S is then used to generate the elements of the traditional Mueller matrix M' by several methods, which are described. The Huynen parameters are then extracted from M' and the pertinent nonvanishing ones are plotted versus frequency in the same band. This extraction is done with care because Huynen defined his M' differently than in the traditional fashion—a great source of confusion. After several appropriate changes the results agree with those of earlier works. As confirmation, the values of the Huynen parameters revert and recover the original elements of M' they are extracted from. The plots of the Huynen parameters for this target indeed give a general phenomenological description of the buried, symmetric object with differences in local curvatures and somewhat irregular structure that was originally conceived. The displayed plots of various nonvanishing elements of M' and of the Huynen parameters, at normal and oblique incidences verify our conclusions and the method.

The weighted information entropy (WIE) is a criterion to evaluate the complex degree of sea-sky infrared (IR) backgrounds, but it cannot describe the complex degree of local IR backgrounds. A new criterion named the mean variance WIE is proposed to evaluate the complex degree of sea-sky IR backgrounds. Experimental results show that this criterion can not only combine the merits of the WIE and the variance of a sea-sky IR background, but also contain the information of local gray values in the background.

We present a method to compress ray information in three-dimensional (3-D) integral imaging (II) using the Karhunen-Loeve transform (KLT). Elemental images in II are highly correlated because they are picked-up by numerous lenslets, thus, the KLT can compress an integral image more effectively than 2-D ordinary images. In the hybrid coding scheme, the KLT is distinctly applied to disjoint subsets which are partitioned by a vector quantization (VQ). In the optical experiments, we show that 3-D image quality degradation is negligible if approximately 10% of eigenvectors with the largest eigenvalues are used. We also evaluate the quality of uncompressed images by signal-to-noise ratio (SNR) and peak-to-peak signal-to-noise ratio (PSNR). The presented coding scheme is shown to be better than JPEG (Joint Photographic Experts Group) for the lower bit rates in the II compression. Optical and numerical experiments are presented.

This study proposes a rapid rate-control framework for low-delay video coding. The proposed framework includes a fast frame-rate controller, a frame-level bit-allocation operator, and an adaptive rate-quantization (R-Q) model. The frame-rate controller and the frame-level bit-allocation operator determine the encoding frame rate per time slot and the bit target per frame, which specify motion continuity and consistency of quality, respectively. When a cluster of macroblocks (MBs) in an encoding frame is set by a progressive union process, the adaptive R-Q model is modified by the Kalman filter. The newest R-Q characteristic linear curves of the adaptive R-Q model can be used to obtain the MB-level quantization parameters in a new cluster of MBs (COB). The proposed new framework exhibits higher objective and perceptual qualities than the TMN8 rate control, using a TMN11 frame-rate control module, with a lower computational load.

We tackle the problem of burst error in wireless video transmission. Burst error damages video information so severely that it is very difficult to restore the lost information. For restoration, it is advantageous to retain a part of block information. To achieve this, we propose a coefficient sampling and interleaving method, where texture coefficients are grouped into several coefficient groups (CGs) so that the groups have equal importance. The CGs are interleaved so that burst error cannot damage all CGs from one block. A restoration method is proposed to utilize the retained coefficients. The simulation results show that the proposed coefficient sampling scheme and the restoration method restore the lost information very well.

We propose a modified structure-adaptive anisotropic filter, which uses local intensity orientation and an anisotropic measure to control the shape of the filter kernel, and apply it to fingerprints. The modification is made in the frequency domain by converting the common structure-adaptive anisotropic filter from a low-pass filter to a band-pass one. We show that the modified structure-adaptive anisotropic filter can be effectively applied to applications, such as fingerprint image enhancement, in which the oriented patterns in local neighborhood form a sinusoidal-shaped plane wave with a well-defined frequency and orientation. The performance of the proposed structure-adaptive anisotropic filter is compared to some other filters used for minutiae detection. The proposed filter shows some improvement in terms of computational time and efficiency.

A novel contour extraction scheme for detecting a moving target is proposed. This scheme consists of three steps. First, motion segmentation is applied respectively to infrared (IR) and visible image sequences to acquire an initial contour of the moving target. Second, dynamic contours are applied to make the initial contour converge to the target's contour with the Newmark-based iteration. Finally, two novel image fusions are applied to restrict the convergent dynamic contour in a visible image with that in an IR image. The first fusion minimizes the B-spline L₂ norm's square of the difference of control point vectors in the two modal images without image registration. The second fusion is realized by the revised differential coupling with image registration. A contrasting experiment on image sequence of a moving vehicle indicates that the contour extraction's average error decreases by 58.14% for the first fusion and 65.12% for the second fusion. Both image fusions are implemented with the control point vector of a dynamic contour and are suitable for practical application. Moreover, the Newmark based iteration is contrasted with the Wilson-θ-based iteration, which indicates that its iteration time requirement for convergence decreases by 21.01%.

The problem of recovering full-color images from a noisy and color-sampled observation is considered. The noise in imaging sensors corrupts the color filter array (CFA) and introduces artifacts during the color interpolation step. Instead of filtering the noise before or after the color interpolation step, we remove the noise during the color interpolation step. This allows us to obtain a color interpolated image without noise and artifacts, especially along the edges and in the detail of the image. Color interpolation is carried out on the weighted color difference domain to consider cross-channel correlation. To avoid artifacts in high frequency regions and improve the performance, an edge indicator function is used and directions of edges are considered in the proposed interpolation method, while noise is simultaneously removed by adaptive noise filtering. As postprocessing, modified filtering on the color difference domain is adopted to improve the quality of the image. Experimental results illustrate the benefits of the proposed method. When compared to conventional methods, the proposed method outperforms them on quantitative and qualitative criteria.

For 3-D reconstruction from uncalibrated sequences, projective reconstruction is needed as a preceding step, which is classified into a merging method and factorization. Factorization-based methods generally suffer less from drift and error accumulation than sequential merging. However, they assume that most corresponding points must remain in all frames. To overcome this limitation, we present a new frame grouping method for factorization-based projective reconstruction over long image sequences. The proposed method breaks a full sequence into subsequences by considering a survival rate of the corresponding points over a sequence, the reprojection error, and the distribution of matching points on the image. All projective reconstructions in subsequences are registered into the same coordinate frame for a complete description of the scene. Experimental results demonstrate that our algorithm can recover more precise 3-D structure than the sequential merging method.

We derive a pair of algorithms, one optimal and the other approximate, for recognizing three-dimensional objects from a collection of points chosen from their surface according to some probabilistic mechanism. The measurements are assumed to be noisy, and the measured location of a given point is translated according to a noise probability distribution. Distributions governing surface point selection and measurement noise can take a variety of forms depending upon the particular measurement scenario. At one extreme, each measurement is assumed to yield values restricted to a one-dimensional ray, a special case commonly adopted in the literature. At the other extreme, measured points are chosen uniformly from the object's surface, and the noise distribution is spherically symmetric, a worst-case scenario that involves no prior information about the measurements. We apply these two algorithms to shape recognition problems involving simple geometrical objects, and examine their relative behavior using a combination of analytical derivation and Monte Carlo simulation. We show that the approximate algorithm can be far simpler to compute, and its performance is competitive with the optimal algorithm when noise levels are relatively low. We show the existence of a critical noise level, beyond which the approximate algorithm exhibits catastrophic failure.

A novel algorithm for shape detection based on mathematical morphology is presented. Two stages are involved. In the first stage, a shape model is learned automatically from learning examples belonging to the same object class. It is a collection of subparts with the description of relations among subparts, represented by a fuzzy graph. In the second stage, the generated model is used to detect similar shapes from images of complex real scenes. Subparts of the shape are detected in sequence based on their saliency, and then the geometric configuration among those detected subparts is checked. A morphological component detector is proposed to detect each subpart by using a soft structuring element, derived from the shape model. Satisfactory results are shown when testing the algorithm on synthetic and real images.

We analyze the optical transmission characteristics of prism sheet layers based on a geometrical approach. An analytic method for finding the radiant intensity profile of the light transmitted through a single prism sheet for an incident light with arbitrary radiant intensity profile is developed. It is shown that the output radiant intensity profile is the inner product of the newly defined partial transmission coefficient distribution of the prism sheet and the input radiant intensity profile. The developed analysis method for a single prism sheet is immediately generalized to analyze prism sheet layer being composed of several prism sheets.

A new fabrication approach, virtual gray-scale mask via focused ion beam (FIB) direct milling for fabrication of micro-optical elements (MOEs), is introduced. The designed MOEs, e.g., micro-diffractive lenses with continuous relief and micro-gratings, are directly milled by the FIB by means of the method of the virtual gray-scale mask with ion energy and ion beam current of 30 keV and 3 nA, respectively. The method has a one-step fabrication process and is free of user computer programming for the one-step direct writing. It is a useful approach for those FIB machines without the user programming function. It will be helpful for integration of MOEs with top-end optical fibers for applications of miniaturization of spectrometers, optical fiber sensors, and micro-optical systems in biochemistry analysis use.

We present a concise method for the design of arrayed waveguide gratings (AWGs) with a minimum number of arrayed waveguides and polarization independence. As an example to demonstrate the effectiveness of the proposed method, a 16×16 AWG using silica-based sol-gel material is optimally designed with the following practical specifications: central wavelength of 1.554 µm, channel spacing of 100 GHz or 0.8 nm, crosstalk between adjacent channels of <–30 dB, insertion loss of <3 dB, and nonuniform power level of the channels of <1.75 dB. We present, to our knowledge, for the first time, a simple criterion for determining the minimum number of arrayed waveguides with polarization independence. The criterion ensures that lights diffracted in the first slab are transferred into the second slab without loss of the image information. The criterion is perfectly verified by simulating the design of the AWG using a beam propagation method of analysis. In addition, the design procedure also allows the optimization of the parameters and structure of the AWG to achieve the required performance specifications.

An array of phase retarders can be used as an optical phased array (OPA) to steer light [McManamon et al., Proc. IEEE 84(2), 268–298 (1996)]. The introduction of resets enables steering to larger angles without requiring an optical path difference (OPD) greater than one wavelength. These resets, however, are correct only at the design wavelength. The beam steerer is therefore very dispersive. It has been shown theoretically that resets of an integer multiple of the wavelength will make the beam steerer less dispersive [McManamon and Watson, Proc. SPIE 4369, 140–148 (2001)]. We offer the first experimental proof that resets of nλ are less dispersive than resets of a single λ. We also show experimentally that the dispersion associated with fixed period resets does vary, but only within a fixed limit. Last, we show the equivalent of power shifting from one order to the next as larger resets move from being divisible by one integer times the nondesign wavelength toward being divisible by the next integer times the nondesign wavelength.