This PDF file contains the editorial “Becoming an Engineer” for OE Vol. 41 Issue 03

An all-fiber Sagnac interferometer using a bire- fringent fiber loop is used to determine the coupling coefficients of a fiber directional coupler. These coefficients are estimated by identifying the minimum value of the normalized transmittance of the filtered spectrum through the allfiber Sagnac interferometer with respect of a simple appropriate model.

We report a novel, to our knowledge, current sensor based on a fiber Bragg grating (FBG). Using a cantilever beam and a linear magnetic actuator, the change of current is transferred to the Bragg wavelength shift of the FBG with good linearity and repeatability. The current sensor thus gains the merits of FBG sensors, and thus is immune to light intensity fluctuation, multiplexing capability, etc., and can be adopted for real industrial monitoring.

Nd3+:GdCa4O(„BO3…)3 laser, i.e., Nd:GdCOB, is a new self-frequency-doubling laser crystal. By using a GaAs saturable absorber as a passive Q-switched, the Q-switched Nd:GdCOB laser at 0.53?m is successfully realized. Meanwhile, the pulse width and the single pulse energy are measured and the numerical solutions of the coupling wave rate equations are in agreement with the experimental results.

A micromachined deformable mirror (?-DM) for optical wavefront correction is described. Design and manufacturing approaches for ?-DMs are detailed. The ?-DM employs a flexible silicon membrane supported by mechanical attachments to an array of electrostatic parallel plate actuators. Devices are fabricated through surface micromachining using polycrystalline silicon thin films. ?-DM membranes measuring 2 mmx2 mmx2 ?m, supported by 100 actuators are described. Figures of merit include stroke of 2 ?m, resolution of 10 nm, and frequency bandwidth dc to 7 kHz in air. The devices are compact, inexpensive to fabricate, exhibit no hysteresis, and use only a small fraction of the power required for conventional DMs. Performance of an adaptive optics system using a ?-DM is characterized in a closed-loop control experiment. Significant reduction in quasistatic wavefront phase error is achieved. Advantages and limitations of ?-DMs are described in relation to conventional adaptive optics systems and to emerging applications of adaptive optics such as high-resolution correction, small-aperture systems, and optical communication.

Adaptive optics are regularly used in ground-based astronomical telescopes. These applications are characterized by a very narrow (~1 arcmin) field of view. For economic reasons, commercial space- based earth-observing optical systems must have a field of view as large as possible. We develop a new error function that is an extension of conventional adaptive optics for wide field-of-view optical systems and show that this new error function enables diffraction-limited performance across a large field of view with only one deformable mirror. This new error function allows for reprogramming of aberration control algorithms for particular applications by the use of an addressable weighting function.

A new geometrical optical method has been developed for the design of optical systems that perform intensity reshaping of spatially coherent input light, particularly that of plane parallel or spherical beams. The computation is based on the principle of automated optimization, making it available for the design of beam shapers of diverse structures (aspheric, diffractive, etc.), and especially for those where no analytic solution exists to calculate the necessary device geometry (e.g., in case of all-spherical systems). Novelty, and thus efficiency, of the method lies in its simplified definition of the error function, used for the evaluation of optical systems by optimization algorithms during the design process. Another advantage of the method is that it can be easily implemented in commercially available optical design programs commonly used by optical designers. The operation of the new method is shown for the particular case of Gaussian-to-uniform beam transforming systems, and a concrete design example is given for its application. Wave-optical calculations verify the accuracy of our computations and check the diffraction behavior of the geometrically designed device.

One of the most important characteristics of a Gaussian-to- uniform beam shaping system is the ratio of the entrance pupil radius to the spot size of the input Gaussian beam, i.e., its 1/e2 intensity radius. This parameter, called the beam shaping power, must be increased above a certain value, otherwise the homogeneity of the output beam decreases (due to Fresnel diffraction on the entrance pupil), and the power transmission of the optical system drops. We develop a new method for achieving a sufficiently large beam shaping power without the need for a special fabrication technology or design technique. The basic idea of our method is to place a number of low beam shaping power subsystems one after the other into a cascade, to obtain a system of increased beam shaping power. The subsystems can be constructed from simple elements (e.g., spherical lenses), which are easy to design and fabricate. We describe our method, develop simple formulas for its theoretical discussion, and present a design example to demonstrate its operation.

The diffraction-based optical frequency response characteristic of a birefringent crystal lens sandwiched between two linear polarizers has been studied analytically using the autocorrelation of the pupil function over the lens aperture. The optical transfer function (oTf) of this proposed system depends on the material as well as design parameters of the crystal lens, along with the orientations of the transmission axes of the two polarizers relative to each other and to the optic axis of the birefringent lens. Naturally, the OTF of such a system can be varied at the lens fabrication stage like other lenses. An online variation of the OTF is also possible just by rotating any of the two polarizers included in the system. It has been shown that the proposed system can be adapted either for apodization or for super-resolution simply by rotating any of the two polarizers. This system may be designed for obtaining high depth of focus without significant image degradation, as well as for image processing operations like high frequency enhancement. The response of the system is studied at the Gaussian image plane as a function of the line frequencies in the object for different values of the birefringent lens parameters, and also for two different settings of the analyzer. The results are compared with the response of an ideal lens.

The behavior of an evanescent field sensor is important for design purposes. This work gives an approximate and simple equation to estimate the absorption of light in an optical fiber with lossy cladding. The formula is based on the weakly guiding approximation and estimates the output power fraction of the sensor in terms of the fiber and the surrounding parameters. The formula is then related to the concentration of the surrounding medium.

A new method is presented for the localization of synthetic references (SRs) in digital images based on normalized correlation. An augmented search template is used, which consists not only of occupied pixel fractions of the desired SR, but also of derivatives of these fractions with respects to shifts along the image axes. The resulting correlation values are higher than those based on standard correlation, especially for small SRs and unfavorable subpixel displacements between the template and the scene. The augmented template can also be used to determine the location of the SR to subpixel accuracy. The precision of this determination is affected less by systematic and random error than is the case for centroiding or sampled correlation interpolation, and can be estimated explicitly from the calculated correlation value. Numerical examples are given.

We describe a novel technique for color image segmentation. This technique includes three components: a color space transformation, Markov random field expectation-maximization (MRF-EM) segmentation, and a multiresolution implementation termed ‘‘narrow band.’’ The color space transformation, from RGB to LUV, contributes to a perceptually reasonable segmentation result. The MRF-EM algorithm enables unsupervised segmentation and enforces a region smoothness constraint. The narrow-band, multiresolution implementation confines fine resolution processing to a small fraction of the image, thereby achieving acceleration over traditional multiresolution schemes. Experimental results with medical and TV images demonstrate the efficacy of the proposed technique.

The IR absorption method is a traditional spectral analysis method in the analysis of gas components. Nevertheless, the absorption spectrum lines of a certain kind of gas often intercross with those of another, which means that the absorption peak of one kind of gas is close to that of another. Thus, when these kinds of gases are mixed together, there will be cross-sensitivity in the concentration measurement using the gas sensor system. We adopt the genetic neural network algorithm to recognize the patterns of the mixed gas with two components and three components respectively in the simulation recognition. The staged-sectional recognition method is used to increase the recognition precision at various critical values of the mixed gases. The simulation results indicate that the staged-sectional method based on the genetic neural networks decreases the cross-sensitivity of the gas sensor and increases the recognition precision at various critical values.

Analysis of microelements requires a local approach to their mechanical behavior and material constants distribution. This requires modern full-field measurement tools, among which automated grating (moire) interferometry (GMI) is one of the best-suited measurement methods. A new type of grating microinterferometer is presented. It is based on the concept of an achromatic grating interferometer combined with a glass block waveguide and designed to work with standard optical microscopes. The various types of waveguide plates are presented and discussed. The interferogram obtained may be modified and design for analysis by means of carrier frequency phase shifting methods. The methodology of measurement is described. The usefulness of the microinterferometer is demonstrated by an example of in-plane displacement and strain distribution determination in the two-phase steel polycrystalline material. 0-

A high-performance laser tracker that is used for the calibration of a coordinate measuring machine (CMM) is introduced. A specially designed hemispherical-shape articulating mirror is used in the tracking mechanism, which enables reduction of the measurement uncertainties so that they are not more than 0.3 ?m. The uncertainty analysis of the laser tracker is also described.

The helical pitch of the cholesteric liquid crystal (CLC) can be adjusted to reflect the colors red, green, and blue. Additive mixing of these colors in displays results in multicolor images and it is easy to use pure primary blue and green colors, but the red color is in general very unsaturated. We show by simulations that this poor red color performance is due to reflection sidebands on the smaller wavelength side of the normal red Bragg reflection band. We discuss five approaches to improve the red color performance, namely, two types of spectral filtering (dyes or filters), a very low birefringence CLC, a gradient in the birefringence of the CLC, and the use of a bluish reflector. The two methods of spectral filtering are also experimentally tested.

We establish the groundwork for a phase theory applicable to multiple aperture systems. To do this, we define ideal behavior as the phase behavior of an off-axis piece of a system that has rotational symmetry. Then we examine the phase behavior of a more general system that has only a single plane of symmetry. This system represents a branch of a multiple aperture system. Comparison of the two systems leads to conditions for which the plane symmetric system has ideal behavior. As a result of this comparison, design rules that are commonly applied to multiple aperture systems appear naturally, including the well- known requirement that the exit pupil is a scaled copy of the entrance pupil. The phase theory that we present is cohesive, provides useful design guidelines, and can be considered an addition to wave aberration theory.

We focus on reliably estimating the information conveyed to a user by multispectral image data. The goal is establishing the extent to which an increase in spectral resolution can increase the amount of usable information. As a matter of fact, a trade-off exists between spatial and spectral resolution, due to physical constraints of sensors imaging with a prefixed SNR. After describing some methods developed for automatically estimating the variance of the noise introduced by multispectral imagers, lossless data compression is exploited to measure the useful information content of the multispectral data. In fact, the bit rate achieved by the reversible compression process takes into account both the contribution of the "observation" noise, i.e., information regarded as statistical uncertainty, whose relevance is null to a user, and the intrinsic information of hypothetically noise free multispectral data. An entropic model of the image source is defined and, once the standard deviation of the noise, assumed to be white and Gaussian, has been preliminarily estimated, such a model is inverted to yield an estimate of the information content of the noise-free source from the code rate. Results of both noise and information assessment are reported and discussed on synthetic noisy images and on Landsat thematic mapper (TM) data.

A novel method for nanometer indicating based on surface plasmon resonance (SPR) is introduced. A fiber probe with a semispherical end approaching a coated Kretschmann (1971) prism is equivalent to a four-layer prism-metal-air-fiber structure. Theoretical analysis shows that the transmitted intensity coupling into the fiber probe changes as the thickness of the air gap varies. Owing to this property, a noncontact nanometer indicating system can be built. The SpR nanometer indicator can be integrated into a heterodyne interferometer to reduce drift. Askew retroreflector is designed so that the incident angle of its first reflection surface is equal to the resonance angle of SPR to implement the integration SPR indicating experiments show that a maximum deviation of 12 nm and a resolution of 0.1 nm/nV can be achieved. Moreover, the uncertainty of an integrated interferometer whose optical path difference is 300 mm is reduced from 60 to 10 nm when air-conditioning is 0.5 °C/h.

A new kind of polarizing beamsplitters (PBSs) based on the effects of a birefringent and resonance anomaly is presented. Its properties are analyzed using the correct Fourier modal method and the reflective and transmissive coefficient matrix (RTCM) recursion method. Two examples, one for the IR and the other for the visible, are given. An extremely high polarization extinction ratio is obtained in transmitting space. The effects of small variations in the parameters of the PBSs performance are also investigated.

The distortions in the perceived image from a stereoscopic image pair displayed on a screen are analyzed for different conditions of photographing, projecting, and viewing for the cases of both a stereo camera and a stereo projector with a parallel configuration. The conditions used for the analysis are positions and stereo bases of viewer and the camera and magnification of the displayed image. The possible location of the image is also found for given locations of the camera and the viewer. The obtained resulted can be used to optimize stereo image display systems.

A moving ship in a synthetic aperture radar (SAR) image produces a multiscale wake with a characteristic linear V-shaped pattern. Detection of the wake can provide substantial information about the ship, such as its size, direction, and speed of movement. In general, shipgenerated wakes in SAR images are associated with high sea clutter, which causes the deterioration of detection performance. We present a hybrid method that combines the wavelet technique and the Radon transform technique to detect the ship wake. The wavelet technique is first applied to generate a set of multiscale images. An orthogonal basis function is adopted so that three high-pass images in the horizontal, vertical, and diagonal directions are generated for each resolution scale. Then a spatial correlator is applied among the moduli of different scale, where modulus images are formed from three high-pass images. The output of the correlation process is shown to be highly representative at ship wake edges. Comparisons with other methods indicate the superior performance of this approach in that not only are the wakes detected, but the V-shaped pattern is well preserved. The second stage of the method involves the application of the Radon transform technique to estimate the V opening angle from the detected ship wakes. Compared with a direct Radon transform, the greater effectiveness of the proposed scheme is demonstrated in terms of efficiency as well as reliability for ship wake detection in noisy backgrounds.

Conventional approaches to object tracking through an image sequence either use area correlation or extraction of contrast edges and other features from the target image, taken as the target signature. However, it is often difficult to reliably extract the target signature when the target and background image, as well as target/background polarity and contrast, change drastically over time. One of the major neurobiological discoveries in the last two decades is that the visual "what" processes, which determine the identity of an object, are segregated from the "where" processes, which determine the spatial location and motion of an object. Biological visual motion tracking does not require continuously detecting the target signature. It simply maintains the target signature throughout the image sequence via an adaptive process of the receptive fields of neurons. Formulated as a pure "where" process that maintains the Gabor representation of the target surface signature, we reduce the tracking process to the analytical computation of affine transformations of the surface signature through the image sequence. Experiments on realistic infrared image sequences demonstrate the great simplicity, high accuracy, and robustness of the proposed analytical target tracking algorithm.

We conduct a comparative study of polarization properties of vertical-cavity surface-emitting lasers (VCSELs) from various sources, fabricated either by ion implantation or by the oxide-confinement method. An integrated test bench (iTB) for photonic devices is used to characterize the VCSELs. The ITB setup enabled simultaneous monitoring of the polarization state, transverse modes, wavelength spectrum, and optical power of the VCSELs under test. VCSELs commonly exhibit polarization noise, switching, and instability. The polarization behavior and related modal properties of various VCSELs are investigated based on aperture size, geometry, and fabrication processes. From the cw and pulsed pumping data, a general trend and inherent behavior is identified and polarization-related limitations are discussed.

The image sequence discrimination model we use models optical blurring and retinal light adaptation. Further, two parallel channels, sustained and transient, with different masking rules based on contrast gain control, are also used. Performance of the model is studied for two tasks representative of a video communication system with versions of monochrome H.263 compressed images. In the first study, five image sequences constitute pairs of noncompressed and compressed images to be discriminated with a two-alternative-forced-choice method together with a staircase procedure. The discrimination thresholds for each subject are calculated. Analysis of variance shows that the differences between the pictures are significant. The model threshold is close to the average threshold of the subjects for each picture, and the model thus predicts these results quite well. In the second study, the effect of transmission errors on the Internet, i.e., packet losses, is tested with the method of constant stimuli. Both reference and comparison images are distorted. The task of the subjects is to judge whether the presented video quality is worse than the initially seen reference video. Two different quality levels of the compressed sequences are simulated. The differences in the thresholds among the different video scenes are to some extent predicted by the model. Category scales indicate that detection of distortions and overall quality judgements are based on different psychological processes.

A novel multimode interference optical filter design in SiGe/Si for 1.3- and 1.55-?m operation is investigated. From the theory of large single-mode rib waveguides, the width of the rib waveguide and its height and etched depth were derived for a Ge content of x= 0.04. Using the modal propagation analysis method, the coupler length of the device is evaluated and the transmission characteristics are investigated. The results show that for 1.3 ?m, the optimum coupler length of the filter is 4710 ?m, with an extinction ratio of 17 dB; and for 1.55 ?m, the optimum coupler length of the filter is 5180 ?m, with an extinction ratio of 30 dB. For both filters, insertion loss is less than 0.1 dB.