This PDF file contains the editorial “Editorial: Publication of proceedings papers in Optical Engineering: A topic revisited--again!” for OE Vol. 32 Issue 09

This PDF file contains the editorial “Guest Editorial: Optical Science and Engineering in Canada” for OE Vol. 32 Issue 09

A tunable Q-switched thulium-doped single-mode silica fiber laser is presented for the first time. Its performance is analyzed as a function of pulse repetition rate and pumping power. The optimization of laser parameters resulted in 4 W/130 ns, 1.92-μm wavelength pulses generated at a 4-kHz repetition rate. From the measured values of small-signal attenuation and intrinsic saturation power, the thulium ion parameters at the pump and signal wavelength are derived and used in theoretical modeling of the laser. The moderate power required from the Ti:sapphire pump laser used in the experiment suggests that similar resuIts can be obtained using a laser diode pump.

We report on the demonstration of a Q-switched erbium-doped fiber laser using a novel all-fiber intensity modulator acting as an efficient intracavity switching element. Switching speed and holdoff losses are compatible with the Q-switching dynamics of rare-earth-doped fiber lasers. The modulator is completely integrated in a spliceless erbium- doped fiber cavity. Pulses of less than 15 ns full width at half maximum (FWHM) and peak power close to 400 W were obtained for a launched pumping power of 100 mW at 980 nm. This compact source could find many uses in applications such as nonlinear optics, laser ranging and remote sensing, eyesafe free-space communication, time-gated fiber sensor systems, and long-distance optical time-domain reflectometry.

A Q-switched fiber laser is developed for eyesafe ranging applications. Using a highly doped erbium fiber pumped with a 30-mW laser diode at 980 nm, pulses of 290-W peak power and 20-ns duration are obtained. The laser consists of all-fiber elements, with the exception of a high-efficiency bulk acousto-optic Bragg cell aligned to the laser on the diffracted beam to provide Q-switching with high hold-off. Three emission bands of erbium are made to lase in continuous wave (cw) and Q-switched operation. It is established that optimal cw lasing is achieved at 1560 nm, and maximum intensity Q-switch pulses are produced at 1530 nm. The laser was packaged and tested in the field, demonstrating the readiness of this technology for ranging applications.

A new type of double-heterojunction lateral current injection GaAs/AIGaAs p-i-n ridge waveguide laser is described. The device employs intrinsic materials in the active region to reduce the parasites in the laser, thereby lowering the required threshold current and increasing the quantum efficiency of the device. The use of ridge waveguide structure provides better optical confinement than the conventional lateral injection lasers and avoids the regrowth required for buried heterostructure transverse junction stripe (TJS) lasers. Two-dimensional self-consistent simulations have been carried out, using our finite-element light emitter simulator (FELES), for the purpose of proof of concept and evaluation of the device operation and performance. The results show that the device has a low threshold current, a good differential efficiency, a low capacitance (0.028 pF at zero bias), and a low dynamic resistance (< 2.3 Ω).

The newly developed photothermal detection technique of rate-window infrared radiometry is applied to the measurement of the metastable state deexcitation parameters of a ruby laser rod. The technique employs a square laser pulse and monitors the infrared photothermal radiometric response of the sample. By applying the photothermal lock-in rate-window concept, the radiative lifetime and quantum efficiency of Cr³⁺:Al₂O₃ are measured with optimal SNR and simple, unambiguous interpretation from the extremum in the lock-in analyzer in-phase rate-window signal. This technique simplifies significantly the experimental methodology; optimizes the photothermal SNR, which is inherently low in conventional frequency or time-domain photothermal measurements; and offers extended measurement dynamic range for both radiative quantum efficiency and lifetime in laser materials, as compared to frequency-scanned harmonic detection. Therefore, rate-window infrared photothermal radiometry may prove a valuable tool for the combined measurement of metastable lifetime and nonradiative energy conversion efficiency in laser materials with fast deexcitation rates.

We present a detailed coupled-mode analysis of superimposed phase grating guided-wave structures for multibeam splitting (MBS) and wavelength demultiplexing (WDM) applications, taking into account the intergrating coupling effects. The case of small angular separation between the output waves and the case of small wavelength separation between the spectral components of the input wave, which are of great importance for high fanout devices and have so far not been adequately treated, have been examined. For the MBS case (single-wavelength diffraction), critical parameters affecting the diffraction characteristics are found to be the relative index modulation between the gratings, the relative and absolute angular positions of the diffracted waves, the number of gratings, and the wavelength and polarization of the incident wave. For the WDM case (multiwavelength diffraction), wavelength separation between the spectral components of the incoming beam is shown to be an additional critical parameter, due to parasitic waves in undesired output channels. To obtain high-performance devices (high fanout density, high channel efficiencies, high angular and wavelength selectivities, and low cross talks between channels), the analysis suggests the use of long grating structures with large diffraction angles and gratings with close index modulations.

A technique to find the steady-wave solutions in slab waveguides with or without Kerr nonlinearities is presented. This approach is based on the use of space-phase diagrams. It can simplify the resolution and the interpretation of linear problems, as well as provide a way to get the dispersion relation and power dependence of nonlinear waveguides. The technique is applied to a variety of three-layer waveguides exhibiting Kerr nonlinearities. The power dependence of the effective index is computed for all of these waveguides.

Fiber optic polarization splitters are demonstrated in polarization-maintaining fiber, using polished-type fiber couplers having intermediate copper thin-film layers. The splitters operate to give four port-symmetric 19-dB polarization isolation with less than 1-dB TM coupling loss. The effects of asymmetric longitudinal displacements on the devices are considered, and positional asymmetry is used to realize higher perlormance 1 x 2 port devices, with up to 25 dB isolation and 0.5 dB loss.

Two difterent concepts for 1.30- and 1 .55-μm dual-wavelength demultiplexers/multiplexers, based on glass waveguides, the symmetric directional coupler, and the asymmetric Mach-Zehnder interlerometer, are analyzed and compared. Attention is given mainly to the sensitivity to fabrication parameter changes. The rather strict fabrication conditions needed to obtain satisfactory performance from directional couplers are examined. With Mach-Zehnder interferometers, the sensitivity is considerably lower, which indicates that the fabrication of these devices is uncomplicated.

Structural, electrical, and optical properties of the polycrystalline films of VO₂, V₂O₅, and mixtures of these two oxides are presented. Resistivity change by a factor larger than 10³ accompanying the semiconductor-metal phase transition in the VO₂ films is reported. A significant contrast in optical transmittance for the two phases of VO₂ is observed. High temperature resistivity and optical transmittance of the V₂O₅ films are shown. Values of the temperature coefficient of resistance in some of the VO₂ films in their semiconducting phase and in some of the V₂O₅ films are as high as 5.2 and 4% per degree Celsius, respectively. Phase switching properties of the VO₂-V₂O₅ films are described. Applications of the fabricated films include optical switches and bobmetric-type light detectors.

The behavior of a chain of sensors based on highly birefringent fibers and operating in two multiplexing configurations was studied as a function of alignment. The analytical relations between alignment at each splice in the chain and the visibility of the interference pattern associated with each sensor were found. These relations make it possible to determine alignment that ensures the desired visibility distributions for sensors along the cascade. In the experimental part of this work, the derived formulas were verified for a few specific chains composed of a limited number of multiplexed sensors.

The beam quality factor M²Q of the LP₀₁ mode of the step-index fiber is calculated in a closed form. Propagation of the mode through an optical system can thereafter be described using the ABCD ray's matrix.

Introducing a wavelength-tunable source and a wavemeter, make it possible to modify a conventional optical time-domain reflectometer (OTDR) to measure chromatic dispersion and modal interference levels in addition to transmission attenuation, return loss, and fiber length.

Wireless in-building local area network (LANs) systems based on IR technology are being introduced to overbuild or replace traditional wired networks. We describe a free-space infrared local area network (FIRLAN)-its design and implementation. The FIRLAN system provides point-to-point or point-to-multipoint transmission of Ethernet signals. It provides full 10-Mb/s bit-rate seamless Ethernet integration with performance equal to wired systems.

By following the basic principles of the design of nonfullaperture Luneburg lenses, a new solution, or a new family of lenses has been found. The new lens has in the outer shell the profile of a refractive index characterized as n=exp(P²/h²). In practice, each particular solution is characterized by the focal length and the value of the refractive index at the edge of the lens. The value of the refractive index at the edge can be arbitrarily selected within a certain range. This range is different for different focal lengths.

A historic perspective to the development of the D SIGHT™ surface inspection technique from a laboratory curiosity to a mature technology is presented. A brief description of the experimental process that led to the discovery of the phenomenon is followed by a discussion of how the optical process functions and how varying the hardware configuration affects the system output. Illustrations of a wide variety of surfaces, imaged using double-pass retroreflection, are used to show its evolution from a purely optical, visual enhancement technique to a computer-based, image acquisition system, which, through digital image processing, enables a user to quantify, annotate, and record the quality of a given surface. Possible directions for future development are discussed briefly.

Recent work on the development of optical sensors for on-line inspection of industrial materials is reviewed. Examples include on-line thickness profilometry for sawmill process control, polymer morphology analysis by light-scattering techniques, lubricant oil quantifcation on aluminum sheets, in-process inspection of plasma sprayed particles, and infrared temperature sensing in a continuous annealing furnace. The emphasis is on noncontact techniques well suited to automation and specifically adapted to each particular application with minimal perturbation of the industrial process.

Anisotropy resulting from fiber orientation distribution is an important factor in paper mechanical strength and dimensional stability. An optical method designed to measure this property in paper and other dielectric sheet materials, using far-infrared waves, is presented. Paper acts as a dichroic polarizer in a narrow band around 100 cm^-1, and, according to correlations with other characterization techniques, the amplitude of this polarizing effect is related to fiber orientation anisotropy. After a description of this technique and the hardware involved, several results and applications of this type of measurement are presented and discussed.

The use of two optical diagnostic techniques for the visualization of low-gravity experiments is described. The analysis of requirements relevant to the low-gravity environment led to the choice of real-time holographic interferometry and moiré deflectometry as suitable optical visualization techniques. An optical setup designed to operate in the KC-135 aircraft is described. An interactive fringe analysis system is also presented. Fringe center lines are extracted using a special onedimensional algorithm. The reconstruction of physical parameters from axisymmetrical objects is achieved using direct and inverse Abel transforms on moiré and interferometric fringe fields. The applicability of the optical diagnostic techniques to the visualization of laser processing with liquids and solids in a low-gravity environment is demonstrated and experimental results on laser beam interaction with plastic, quartz, and water are presented.

A new approach to designing spatial filters for the detection of point sources is presented. The technique has been developed for the detection of missiles in infrared images. A missile is generally assumed to be a point source and the image of a point source is called the point spread function (PSF). Exploiting the fact that the PSF of many systems exhibits a circular symmetry, we propose a filter implemented in two steps. First, we apply a circularly symmetrical bandpass filter to the image. Unfortunately, this filter retains the edges of extended objects. To overcome that problem, we propose, in a second stage of processing, different techniques to attenuate those edges without aftecting the point sources amplitude by noting that most of the edges appear in the magnitude of the Fourier transform of the image as a concentration of energy in spatial frequencies distributed along straight lines at different angles, whereas the Fourier transform of point sources is circularly symmetrical. We show some examples where the resulting filter attenuates significantly the extended targets while the amplitude of the point sources remains the same.

We use a commercially available liquid crystal television (LCTV) for encoding the on-axis phase-only filter (POF) in a real-time VanderLugt-type optical correlator. Diffraction theory, computer simulation, and optical experiments show that the coupled amplitude modulation and the phase mismatching in the LCTV yield a zero-order spot in the response of the POF and reduce the diffraction efficiency to about 60 to 70%. The correlation output of the filter is a superposition of the POF correlation peak and an image of the input. The filter, referred to as the phase-dominant filter, behaves like the POF with advantages of on-axis correlation, high light efficiency, and utilization of all the available space bandwidth product of the LCTV. Optical experimental results are shown.

We introduce a new approach for the segmentation of planes and quadrics of a 3-D range image using the Fourier transform of the phase image. We show how it is possible to get a spectrum that contains the planes only and another one that contains the quadrics only. We determine the invariant properties of these spectra and show how our method is suitable for real-time applications.

We propose the use of Fresnel diffraction from an edge to produce a fringe pattern illumination with large depth of focus. The line separating dark and bright areas of the fringe pattern is used for light sectioning of the object, and the height profile is obtained through triangulation. The properties and advantages of this illumination approach are discussed. Experimental 3-D measurements are shown for various objects having large depth variations and are obtained with a height resolution of 1 mm at a distance of 500 mm, within a field of view of 25 deg.

A careful analysis of a scattering and absorption database of the waters off the coasts of Canada shows that a laser-assisted camera system will have a significantly improved viewing performance over conventional systems. The laser underwater camera image enhancer system is a range-gated laser system that can be mounted on a remotely operated vehicle. The system uses a 2-kHz diode-pumped frequency-doubled Nd:YAG laser as an illumination source. The light is collected by a 10-cm-diam zoom lens. The detector is a gated image intensifier with a 7-ns gate and a gain that is continuously variable from 500 to 1,000,000. The system has been tested in a water tank facility at Defence Research Establishment Valcartier and has been mounted on the HYSUB 5000 remotely operated vehicle for sea trials. In the strongly scattering waters typical of harbor approaches, this system has a range of from three to five times that of a conventional camera with floodlights.

Prototyping is an essential step in the manufacture of many objects, both consumer and industrial. A fundamental step in this process is the definition of the 3-D form of the object shape, for example, a designer's model created in clay or wood. A 3-D vision system (range sensor) offers the advantage of speed in defining shapes compared to a traditional tactile sensor. The viability of using range sensors is demonstrated by the development of a rapid prototyping system comprised of a laser-based range sensor and software that creates a computer model of the object. One particularly important area of application is the reverse engineering of models comprised of free-form surfaces. This is important in mold and die manufacture for aerodynamic and ergonomic object surfaces. Several methods of modeling free-form surfaces from irregular data are examined and a radial basis function approach is used in developing a self-contained, interactive software package utilizing the laser-generated range data.

The vision-based coordinate measurement system, developed at the National Research Council Canada, is a multicamera passive system that combines the principles of stereo vision, photogrammetry, knowledge-based techniques, and an object-oriented design methodology to provide precise coordinate and dimension measurements of parts for applications such as dimensional inspection, positioning and tracking of objects, and reverse engineering. For a vision system to be considered for such applications, its performance and design parameters must be well understood. A description of the system, the techniques employed for calibration, a performance evaluation procedure, an accuracy analysis, and test results are presented.

A global iterative coding method for computer-generated holograms (CGH) is introduced. The method is based on the iterative correction of a CGH using standard Lee coding. The correction, i.e., the difference between the desired and the obtained reconstruction, is coded and added to the current CGH. The coding and weighting factors are introduced to control the speed of convergence and the SNR. Advantages lie in low computing time and improvement of the object SNR, the neighborhood SNR, and the background SNR. Reducing the standard deviation of the phase of the reconstructed object also results. A slight improvement of the diffraction efficiency is also observed. The comparison is realized using the Lee interferogram method as a reference. This method is tested on binary and complex gray-level objects. Simulation results and optical reconstruction are also presented.

We used a binary coding scheme based on optical density inside a basic cell to produce a smooth multilevel phase pattern on a photoresist film. This technique, which is as simple as a contact copy, is very easy to control for our type of computer-generated holograms. Preliminary results show that a good blazed profile can be obtained with minimum equipment at low cost. Specialized transmission holograms produced with this technique showed a 40% diffraction efficiency and good quality for 632.8-nm radiation.

Star couplers are fanin-fanout devices with each input beam split into several output beams with arbitrary intensities traveling at different angles. We demonstrate a 4 x 4 holographic star coupler fabricated as multiplexed holographic gratings in silver-halide sensitized gelatin (SHSG) derived from Agfa-Gevaert plates. The processing formula is modified to achieve high diffraction efficiency and an acceptable modulation transfer function within the region of spatial frequencies of interest. The holographic characteristics of the processed SHSG are measured. The required gratings are recorded simultaneously to avoid reciprocity law failure, which occurs in SHSG as well. The gratings are recorded to ensure equal grating strength, which gives an acceptable intensity ratio between the output beams. The star coupler is examined for use as a broadcast medium in fiber-based local area networks (LAN5), where relatively high loss and inhomogeneity between the outputs could be tolerated.

Polymer-based materials exhibit excellent properties such as ease of handling, high environmental stability, etc., and thus are promising candidates for alternate optical recording materials for holography and nonlinear optics. Polyvinyl alcohol doped with ferric chloride (FePVA) has been employed as a recording material for volume transmission holograms. A detailed characterization study of this media for volume transmission holograms has been made with the various material parameters taken into consideration. The angular selectivity of the recorded holograms and the frequency response of the media were studied in detail and the results are presented. Changes in the refractive index as a function of exposure energy were also evaluated using a prism-film coupler method. Although volume holograms recorded in FePVA films exhibited a high peak diftraction efficiency of ≈80%, the energy sensitivity of this recording medium is low. To improve the energy sensitivity, t-butyl hydroperoxide has been introduced into the film and the results of this study are presented.

Third-order nonlinear optical susceptibilities of substituted polythiophenes, polyanilines, and polysilanes have been estimated by third-harmonic generation measurements at 1.053 μm. Values of x³(-3ω,ω,ω,ω) for new polymers-two poly(alkoxyphenylthiophenes), a fluorinated poly(alkylthiophene), and a poly(alkoxyaniline)-were found to be in the range 0.7 x 10^-12 to 2.3 x 10^-12 esu, similar to those for other substituted polythiophenes and polyanilines. Values of x³(-3ω,ω,ω,ω)) are correlated with the absorption maxima for series of polythiophenes, polysilanes, and polyanilines. Third-order nonlinearities are found to depend strongly on the nature of the polymer backbone and only slightly on substituents.

Optical absorption is obviously of prime interest in the efficiency of laser generation of ultrasound in graphite-epoxy laminates. However, no quantitative spectrum of optical absorption in this composite material has yet been published in the literature. Transmission techniques are inefficient, and other techniques, like attenuated total reflectance or diffusive reflectance, do not give absolute values. The Fourier transform photoacoustic spectroscopy technique seems to be a good alternative that can analyze adequately and quantitatively a graphite-epoxy laminate. We used three different methods to compute the absolute optical absorption from the photoacoustic signal. The three methods are: the saturation of the real part of the photoacoustic spectrum, the comparison of the spectra obtained with two different mirror velocities, and the calibration of the photoacoustic cell with a transmission measurement. The spectra obtained in the IR band of 2.5 to 25 μm are presented, and the problems and limitations of each method are discussed. The results permit a better understanding of the absorption process in the composite laminate, and in this way, will help us enhance the efficiency of laser generation of ultrasound in graphite epoxy.

The calculation of the solid angle subtended by a given surface is required in a wide variety of applications, ranging from optics to particles transport. Integration via a Monte Carlo process is prohibitive from the computational point of view even with state-of-the-art variance reduction techniques. Exact computation of the solid angle from the distance z between the emission and the detection plane and the lateral distance ρ to the detector center requires the two-dimensional integration of a density function. We develop an approximation strategy whose form optimizes the precision requirements and the computational speed. One way to achieve this simplification is to approximate the trigonometric function in the full description of the solid angle by a series of line segments. The approximation obtained gives results that are precise to at least 1 part in 1000 and that are as fast as known algorithms.

Previously, we developed a classical solid angle function that is valid only when the light is traveling within a homogeneous medium. As soon as the light path contains a refractive interface, the direct solid angle formula is invalid. A different approach must be used if one is to include refraction effects in the solid angle formulation. The variables of integration are given more of a physical interpretation than a geometrical one: by using the emitting point instead of the detection aperture as the basis for the coordinates system, we are able to use the symmetry of the light distribution to simplify the bounds of integration. With carefully chosen coordinate changes, we are thus able to obtain an expression for the solid angle subtended by a circular aperture from a point source situated in a different optical medium. The final refracted solid angle formula also includes the expression of Fresnel's transmission coefficient.

The image quality of airborne photographs is influenced by the atmosphere. Several factors affect the atmosphere, such as temperature, pressure, humidity, and wind speed. Furthermore, these atmospheric influences are dependent on the flight altitude. The MTF of the atmospheric influences and its dependence on the altitude are examined theoretically and experimentally. Several airborne photographs taken at different altitudes have been evaluated with edge gradient analysis as well as with a grating pattern method. Results are shown, discussed, and compared with model calculations.

A narrowband ultraviolet (UV) filter would allow the first monochromatic two-dimensional images of astrophysical plasmas to be obtained in UV emission lines. The high etendue and spectral resolving power of the Fabry-Perot (FP) interferometer make it an excellent candidate for use in a tunable UV filter, provided that adequate optical performance can be obtained. Laboratory measurements of three UV FP interferometers with progressively greater dielectric mirror reflectances are described. The measurements demonstrate the adequate reflectivity, absorption, and small-scale smoothness of currently available coatings and substrates for UV interferometry. The measurements are conducted at 228.8 nm utilizing a cadmium hollow cathode light source. The best performing interferometer has a finesse of 41 and maximum transmittance of 0.38 over a coating-performance-dominated 3-mm-diam subaperture and a finesse of 26 and maximum transmittance of 0.32 over a parabolic-defect-dominated 30-mm-diam aperture. This interferometer is well suited for use in a UV filter system.

Fourier transform fringe-pattern analysis is a wide-spread technique with many applications to optical metrology. Introducing a spatial carrier into a holographic moiré pattern is also a well-known technique to obtain observable moiré fringes. Preprocessing of the holographic moiré pattern includes optical or digital Fourier filtering to remove the carrier. The pattern is then processed by employing time-consuming and less accurate fringe-counting algorithms. This work presents a new application of the Fourier transform method to automated analysis of holographic moiré fringe patterns. The method has the advantage of instantaneous determination of both phase functions in the fringe pattern. Investigations are carried out on the frequency limitation imposed on the spatial carrier. The technique is demonstrated on computer-generated noisy holographic moiré patterns. The technique does not complicate the conventional holographic moiré arrangement.

Statistical indicator functions are developed that evaluate 10-cal hypothesis tests to detect the location of generalized boundaries within images. Functions based on T test, F test, and nonparametric Kolmogorov-Smirnov tests are developed, and implementation strategies for use as image processing operators are presented. The statistical indicator functions are compared to previously proposed indicator functions and the performance of each is evaluated in tests involving images corrupted with additive, multiplicative, and textured noise, as well as on real images. The statistical indicator functions are evaluated in a probabilistic framework, are sensitive to local context and, thus, detect generalized image boundaries with very low sensitivity to threshold selection. The test results show that the statistical indicator functions provide a more consistent response over a variety of image types than can be obtained using nonstatistical indicator functions. Statistical indicator functions are suitable for implementation in two-step image processing strategies such as those used for adaptive enhancement or adaptive quantization.

This PDF file contains the editorial “Book Rvw: Introduction to Photorefractive Nonlinear Optics," by Pochi Yeh for OE Vol. 32 Issue 09

This PDF file contains the editorial “Book Rvw: Optical Waveguide Analysis," by Masanori Koshiba for OE Vol. 32 Issue 09