This PDF file contains the editorial “Surgeon Maturin” for OE Vol. 42 Issue 12

We propose and demonstrate a loop configuration of an all-fiber acousto-optical tunable filter (AOTF). The configuration makes use of a single acoustic source to couple simultaneously flexural acoustic waves to two cascading acousto-optical (AO) sections. In comparison with conventional AOTFs, the proposed configuration greatly enhances the AO coupling efficiency and overcomes the synchronization problem in the conventional cascading configuration of AOTFs.

To extend the application of self-development sol-gel glass, we report a simple method to fabricate arbitrary multilevel structures in self-development photosensitive hybrid sol-gel glass by using a high-energy beam-sensitive gray scale mask under UV radiation. Characterization results showed that the maximum depth of deformation induced by the UV light can be more than 1.3 μm, which makes it possible to fabricate diffractive optical elements with a 2π phase delay for visible light. As an example, the self-development sol-gel glass was used for fabrication of blazed gratings with excellent surface smoothness.

Packet clock generation from flag bits is demonstrated, using a Fabry-Perot filter followed by a semiconductor optical amplifier. Ten clock pulses are generated from a single pulse with less than 0.45 dB amplitude modulation.

All-optical Boolean XOR operation is demonstrated on pseudo-data patterns at 20 Gb/s with a three optical input semiconductor optical amplifier-assisted Sagnac switch. Bit pattern switching has been achieved with low energies of the incoming clock and data pulses and low pattern dependence on the switched-out pulses.

The performances of a digital optical switch, operating at the infrared communications wavelength of 1550 nm and based on the thermo-optic effect in amorphous silicon, are investigated for the first time. We prove that the strong thermo-optic effect of amorphous silicon, combined with the possibility of realizing micrometric integrated structures, allows the design of promising integrated switches. The device, designed for low-cost photonic applications, could be easily integrated in silicon optoelectronic circuits.

Strong Bragg gratings are realized in silica channel optical channel waveguides by plasma-enhanced chemical vapor deposition and reactive ion etching. In the gratings, the insertion of 0.2-μm-thick SiO2 layers with a relatively low refractive index between the cores and claddings successfully yields high reflectance, high extinction ratio, and low polarization dependence.

A new wavelength monitor based on a multimode interference waveguide is proposed for multiwavelength communication applications. The device characteristics are studied using the beam propagation method. By adjusting the waveguide's geometric length, different wavelength ranges can be addressed. Each device can monitor up to a 50-nm range and has accuracy <5 Å.

We present a new image processing strategy that enables an automated comparison of striation patterns. A signal model is introduced to describe the interesting features of forensically relevant striation marks. To provide a high image quality, several images of the same surface area are recorded under systematically varying conditions and then combined for an improved result by means of data fusion techniques. Based on the signal model, the signal of interest is concentrated, and a compact representation of the marks is obtained. To enable an efficient description of the relevant features, even in the cases of deformed surfaces or curved striation marks, a straightening of the grooves is performed beforehand. Following, a meaningful "signature" describing the information of interest is extracted using the whole length of the grooves. This signature is used for an objective evaluation of similarity of the striation patterns.

The out-of-plane displacement field at the crack tip region of a compact tension specimen is measured by stereo vision and used to generate a shadow spot on the virtual screen placed behind the specimen by using the mapping equation of reflected caustics. The J values are then computed using the maximum transverse diameter of the generated shadow spot. In the experiment, the in-plane displacement data are also recorded to obtain J measurements along contours surrounding the crack tip. Results indicate that for crack extensions up to 0.275 mm, the J values evaluated using the generated shadow spot are in good agreement with the measurements from the in-plane displacement data and the Merkle-Corten formula. However, the J values obtained using in-plane displacement data are still close to the Merkle-Corten results, even when the crack growth of Δa≈4.0 mm is reached.

A digital holographic method for simultaneous measurement of the displacement and its spatial derivatives is described. In this method, two holograms are first recorded in the undeformed and deformed states of the specimen; then two object waves related to the two states of the specimen are numerically reconstructed. The phase maps of the displacement and its derivatives can be generated simultaneously from these two reconstructed object waves with a numerical method. This proposed method offers a simple experimental setup, flexibility in handing the data, and high quality of phase maps.

This paper presents a novel design of a gain-flattened amplifier that covers an ultra-wide band including the S, C, and L bands. The amplifier has a split-band architecture, which amplifies the S-, C-, and L-band signals in separate paths and then recombines the amplified signals for the final output. Using a commercial software package VPI Component Maker^TM, the design was simulated and tested for optimization. The gain and noise figure of the new amplifier were analyzed by computer simulation. A gain of ≈29 dB, a ripple factor of about 1.7 dB, a nominal low noise figure <5 dB, and gain-bandwidth products >120 nm can be achieved.

A wedge-adjusted Talbot interferometer is presented to change the inscribed Bragg wavelength of fiber Bragg gratings. In this system, the grating is written by UV interference stripes of 193 nm derived from two combined mirrors, where a phase mask is used as a beamsplitter of ±1 order of diffraction light. It is noteworthy that the adjustor transforms the shift of wedge into the rotation of the two mirrors, and alters the mutual angle of two interfering beams in writing fiber Bragg gratings.

This paper numerically compares the performance of 10-Gbit/s standard forward error correction (SFEC) and enhanced forward error correction (EFEC) in coded systems disturbed by high polarization mode dispersion (PMD). The simulation results show that EFEC, based on the concatenated Reed-Solomon codes RS(247, 239) and RS(255, 247), can increase the system PMD tolerance to 70 ps, compared with about 40 ps for SFEC, while keeping the PMD-induced power penalty (at a bit error rate of 10^–10) below 1 dB.

We develop a new projection weighting function for interpolation and reconstruction of multislice helical computed tomography (CT) data with the hope of improving longitudinal resolution and reducing longitudinal aliasing in reconstructed volumes. The weighting function is based on the application of the Papoulis generalized sampling theorem to the interlaced longitudinal samples acquired by the multislice scanner. We call the approach 180MII, for multislice interlaced interpolation. For pitch 3, the 180MII approach yields high-quality images of the 3-D Shepp-Logan phantom as well as a longitudinal modulation transfer function (MTF) superior to that of the widely used 180MLI approach, which is based on the use of linear interpolation. The approach also suppresses the aliasing component expected from analysis of the longitudinal sampling pattern that arises when one neglects the small cone angle present in multislice helical CT. The approach is not as successful at mitigating an additional "unexpected" aliasing component that can be attributed to this cone angle. The presence of this conebeam effect is interesting and significant in its own right since it reveals the limitations of any multislice helical CT algorithm that ignores the cone angle.

We present a novel approach to restoring images blurred by rotational motions, without experiencing geometric coordinate transformations as in traditional restoration. The space-variant blur is decomposed into a series of space-invariant blurs along the blurring paths. By incorporating Bresenham's algorithm into our work, the blurred gray values of the discrete pixels can be fetched along the blurring paths in real time. Thus, the space-variant blur can be quickly removed along the blurring paths. We apply a two-stage process to restore the rectangular blurred image, which results in the proposal of two corresponding restoration algorithms. One removes the blur by deconvolution along the blurring paths, which are completely inside the rectangular image. The other is used in the case when only some of the pixels of some blurring paths are inside the rectangular image, so based on a neighborhood knowledge guide, the information of these pixels is restored with the least cost in terms of the constrained optimization estimation theory. Furthermore, these two restoration algorithms avoid iteration calculations and some time-consuming operations. To determine the blur center and the blur extents from the blurred image in a case of not knowing the rotational motion parameters, we present, based on cross correlation, an effective blur identification method, which becomes an integral part of the proposed approach. The experimental results demonstrate the efficiency of the proposed restoration algorithms and the effectiveness of the blur identification method.

A high-efficiency beamsplitter for the equipartition of infrared input power using combined reflection and transmission is described. The new design does not use a back metal reflector coating, and hence is more efficient than those previously described. The beamsplitter uses a parallel slab of fused silica that is strip coated with a germanium film on the front and back sides to generate four beams of equal powers. A specific design for operation at the 1.55-μm fiber communication wavelength is presented. Power, efficiency, and polarization analysis of fractional beams in the presence of angular, film-thickness, and spectral deviations near the equipartition condition are discussed. The following results are obtained. An angular deviation of ±0.5 deg has no significant effect on power (<0.1%), efficiency (<0.02%), or polarization (ellipsometric) parameters (< 1 deg) of the fractional beams. A film-thickness deviation of ±10 nm results in a small change in power (<2%), efficiency (<0.1%), and polarization (<0.5 deg) of the fractional beams. A spectral variation of ±25 nm also has a small effect on power (<1.5%), efficiency (<0.01%), and polarization (<1 deg).

Incident earth radiation recorded in mercury-cadmium-telluride photoconductive detectors is usually a nonlinear function of the incident signal. This nonlinear characteristic must be taken into account for interferometric data transformation processes to avoid measurement errors of the incident light intensity. In this work, we investigate the effects of nonlinearity contributed by various factors, especially the nonlinearity contributed by the illuminated and nonilluminated detector areas, which to our knowledge was not investigated earlier for a constant current biased detector circuit. The effects of wire resistance and detector preamplifier loading as well as the impact of off-centered detector illumination compared to the centered detector illumination on the nonlinearity are also investigated. Computer simulation results are presented for constant current biased detector circuits to estimate the effects of nonlinearity. Finally, we show that the nonlinearity can be estimated by using a third-order parametric equation.

Hitherto, two families of multielement detectors have been used for IR applications: scanning systems (first generation) and staring systems (second generation). Third-generation systems are being developed nowadays. In the common understanding, third-generation IR systems provide enhanced capabilities-like larger numbers of pixels, higher frame rates, and better thermal resolution as well as multicolor functionality and other on-chip functions. In the paper, issues associated with the development and exploitation of third-generation IR photon detectors are discussed. In this class of detectors two main competitors, HgCdTe photodiodes and quantum-well photoconductors, are considered. The main challenges facing multicolor devices concern complicated device structures, thicker and multilayer material growth, and more difficult device fabrication, especially when the array size gets larger and pixel size gets smaller. Also, technical developments that are key to third-generation devices, such as vapor phase epitaxy and advanced readout concepts, are discussed.

We propose to use the rare-earth-doped silica as the IR-to-visible converter. Its principle of operation employs the up-conversion on pumping with the near-IR radiation. A time-dependent 3-D heat transfer model for fiber geometry, incorporating the finite element method appropriate to the fiber geometry, is developed to perform the resolution analysis. The simulation results of the study demonstrate the spatial and temporal resolution of this transducer for the constant and impulse irradiation profile, confirming the concept feasibility. The performance in terms of temporal and spatial resolution is appreciably improved when the Er-doped silica fiber is in contact with a cold reservoir. The cold sink also enhances the speed of device response, as the latent image is quickly erased.

A novel two-step phase-shifting algorithm for use in detecting wavefront phase is presented. This algorithm is very insensitive to detuning. The short time needed to acquire and process interferograms helps to minimize phase errors caused by vibration, temperature effects, and nonlinear errors of the piezoelectric transducer. The rms error due to detuning does not change as in classical phase-shifting algorithms with respect to the selected ideal phase shift. The resulting wrapped phase is modulo 2π. Finally the phase error is analyzed.

We present a new concept for a phase-shifting diffraction-grating interferometer, which is intended to test concave mirrors simply using a single reflective diffraction grating and fiber optic confocal microscope focusing optics. Our configuration allows generating a high-quality reference wave from a small active grating area that can be readily fabricated with good homogeneity of grating substrate and uniformity of groove spacing. The test and reference waves encounter no other optical components, so only a small active surface area of the grating affects the test result. The fiber optic confocal microscope design adopted to solve the alignment problem between the grating and the converging wave greatly reduces systematic errors of the interferometer. In addition, the phase-shifting capability provided by translating the grating using a microactuator enables one to attain nanometer accuracy in optical figure metrology.

Phase difference amplification is a technique used to produce a fringe contour map in which the optical path difference between one fringe and the next is a fraction of a wavelength. To ensure high accuracy of the technique, it is usually necessary to generate interference between the high-order diffracted beam and its conjugate beam by means of a holographic recording material that provides sufficiently large nonlinearity to record the original fringe pattern from the test object. This paper shows that not only the nonlinearity of the recording material, but also multiple-beam interference, can be used to produce high-order diffracted beams. A Tolansky-type multiple-beam interferometer has been used in conjunction with an optically addressed liquid-crystal spatial light modulator to set up a system that functions in near real time and provides high accuracy.

Rapid calculation methods for both transient temperature fields and steady-state temperature fields of laser heat treatments and their theoretic relation are discussed, with application examples of simulating calculation. The applicable conditions of rapid calculation methods for temperature fields are also investigated. The obtained results show that steady-state temperature fields are the ultimate solution of transient temperature fields, in which the time of laser interaction with matter is infinite, and the rapid calculation of transient temperature fields can describe heat interaction of a real laser much better. A quantitative criterion of the rapid calculation methods is given in the application research.

Liquid crystal on silicon (LCoS) is a relatively new technology that can be used as the spatial light modulator in projection systems. It can offer high performance at low cost. Various optical architectures have been proposed that can be used with LCoS panels. All of these systems have their own specific advantages and disadvantages. Efficiency, color gamut, and contrast ratio are three quality parameters that are largely dependent on the optical engine that is used. An optical engine with a high performance that is relatively compact is proposed. Realistic optical simulations are used to demonstrate the performance of this system. Two different optical configurations are investigated.

An interlaced composition of odd and even subimage fields is a very common video formation technique. Motion degradation is an inherent problem in portable imaging systems, such as airborne imaging, mobile phones, robots, etc. When relative motion between the interlacing camera and the scene occurs during imaging, two distortion types degrade the image: the edge "staircase effect" due to shifted appearances of objects in successive fields, and blur due to scene motion during each field exposure. In contrast to other previous works that dealt with only uniform velocity motion, here we consider a more general, realistic, and complicated case, in which the motion velocity is not necessarily uniform. The motion in each field and the displacement are assumed to be space invariant. Since conventional motion identification techniques used in other works cannot be employed in the case of variable velocity motion, a new method for identification of the motion from each field is used, and different point spread functions are identified for each field. The restored image is achieved by deblurring each field separately, and then realigning the fields. Results of motion identification and image restoration for various motion types are presented and analyzed for simulated and real-degraded images.

We propose a new method to encrypt and decrypt a two-dimensional amplitude image, which uses a jigsaw transform and a localized fractional Fourier transform. The jigsaw transform is applied to the original image to be encrypted, and the image is then divided into independent nonoverlapping segments. Each image segment is encrypted using different fractional parameters and two statistically independent random phase codes. The random phase codes, along with the set of fractional orders and jigsaw transform index, form the key to the encrypted data. Results of computer simulation are presented to verify the proposed idea and analyze the performance of the method. We also propose an optical implementation, which may find application for encrypting data stored in holographic memory.

A through-beam configuration optical sensor is designed, fabricated, and tested for chip bonding. The tip taper angle was designed based on a cone condensor theory for maximal optical power collection at the tip's output. Experiments conducted to determine the optical power collected using a series of tip taper angles confirm the general applicability of the cone condenser theorem. The optical sensor was found to perform extremely well when incorporated in an actual chip bonding machine, where chips of 3.4×3.4 mm in dimension were tested.

A high-speed all-optical switch using a fiber optic coupler and a light-sensitive variable-index material is described. The mechanism of index variation with light is discussed, as well as the results of switching with polydialkylsilane and polythiophene for index modulation.

Optical and electro-optical properties of pulse laser deposited PLZT thin films are measured using the m-lines technique. Sample preparation is described. Correlation between the deposition process and optical and electro-optical properties is presented.

A new method, extrusion after a sol-gel process, is put forward for fabricating Ag-doped polarizing glass, which has some special optical characteristics according to the size and shape of the silver particles in the glass. The results of x-ray diffraction and differential thermal analysis show that the glass from the gel had a similar structure to that from quenching from a melt. Experiments on heat treatment showed that to get a suitable size of silver particles the glass should be held 0.5 h at 630°C and the time at temperatures above 500°C should be controlled. From scanning electron microscopy and absorption spectra it can be concluded that the elongated silver particles have been produced and the polarizing property has been achieved in the wavelength range from 850 to 1100 nm after extrusion. The silver particles were formed, not just on the surface, but almost throughout the glass, indicating that this new method is an easy way to produce Ag-doped polarizing glass.

Low-cost infrared emitters and detectors are used for the recognition of surfaces with different properties in a location-invariant manner. The intensity readings obtained with such devices are highly dependent on the location and properties of the surface in a way that cannot be represented in a simple manner, complicating the recognition and localization process. We propose the use of angular intensity scans and present an algorithm to process them. This approach can distinguish different surfaces independently of their positions. Once the surface is identified, its position can also be estimated. The method is verified experimentally with the surfaces aluminum, white painted wall, brown kraft paper, and polystyrene foam packaging material. A correct differentiation rate of 87% is achieved, and the surfaces are localized within absolute range and azimuth errors of 1.2 cm and 1.0 deg, respectively. The method demonstrated shows that simple infrared sensors, when coupled with appropriate processing, can be used to extract a significantly greater amount of information than they are commonly employed for.

A laser diode array probe design concept utilizing an optical scanning technique for high-speed and high-precision 3-D profile measurement is presented. The probe consists of 100 laser lines emerging from 100 laser diodes, arranged in five rows. This measurement method adopts the idea of a fringe projection technique. A profile is obtained by projecting multiple laser beams simultaneously onto the surface or using single-beam scans on the surface. The specimen profile data are obtained without the need for a scanning mechanism. The beams projected onto the surface could cause distinguishing difficulties for a complicated profile. This problem was resolved using a computer to control the on/off sequences for the diode array light source. The measurement accuracy is equivalent to the conventional single laser beam scanning measurement system. The measurement speed depends on the optical scanning process and usually occurs in less than 1 s when multibeam scanning is used.

Onboard calibration of radiometric measurements in remote sensing is often achieved by observation of a sun-illuminated reflectance secondary standard using previously calibrated reflecting diffusers. In the calibration procedure, information such as the bidirectional reflectance distribution function (BRDF) of the diffuser outside the measured calibration set, or a model of the degradation of the diffuser performance in space conditions, is required. We have modeled the measured BRDF calibration data of the Spectralon^® diffusers used in the Medium Resolution Imaging Spectrometer (MERIS) currently operated as part of the Earth-observing satellite ENVISAT. The diffuser is modeled by a layered structure where the light transport in the layers is described by radiative transfer theory. The BRDF is characterized by a limited number of parameters describing the optical properties of the material, e.g., albedo, optical thickness, and anisotropy of the scattering. We also describe the result of modeling the degradation of a Spectralon diffuser after deposition, under UV radiation, of a silicone layer.

Based on the self-triggering pulsed technique, a novel pulsed time-of-flight (TOF) laser range-finding method is proposed to improve the accuracy and measuring speed of laser distance measurement. A theoretical analysis is carried out, and three basic equations are presented to describe the method. Furthermore, a measurement device is described and experimental evidence is presented to show the feasibility of measuring distance with 0.5-mm resolution over a 10-m range.

Details are provided regarding the design, construction, and performance of a compact (≈0.6-m² footprint), single-channel surface discharge system and its application to optically pumping the XeF(C→A) and iodine atomic lasers in the blue-green (≈480 nm) and near infrared (1.315 μm), respectively. The system has a gain (active) length of ≈50 cm, and triggering the discharge requires no high-voltage or high-current switches. Measurements of the velocity of the photodissociation bleaching wave and the small-signal gain of the XeF(C→A) system are described. At 488 nm, the gain coefficient γ was found to be ≈0.3% cm^–1, a value comparable to those reported previously for systems dissipating considerably higher power per unit length. Single-pulse energies <50 mJ from the XeF(C→A) laser (≈485 nm) and <0.7 J on the 5p ²P_1/2→5p ²P_3/2 transition of atomic iodine at 1.315 μm have been obtained with nonoptimized resonator output couplings (5% and 10%, respectively). The rate of erosion of the dielectric surface has been measured to be ≈0.1 to 0.3 μm/shot for a glass ceramic dielectric, and the performance of two electrical configurations for the ballasting pins (feedthrough and V) is compared.

For microfocusing x-ray mirrors, an elliptical shape is essential for aberration-free optics. However, it is difficult to polish elliptical mirrors to x-ray quality smoothness. A differential coating method to convert a cylindrical mirror to an elliptical one has been previously reported. The coating was obtained by varying the sputter source power over a moving substrate. Here we report a new method of profile coating: the sputter source power is kept constant, while the substrate is passed over a contoured mask at a constant speed to obtain a desired profile along the direction perpendicular to the direction of substrate motion. The shape of the contour depends on the desired profile and the thickness distribution directly above the gun at the substrate level. The thickness distribution was measured on films coated on Si wafers using a spectroscopic ellipsometer with computer-controlled X-Y translation stages. A model was developed to fit the measured thickness distribution, which determines the relative thickness weightings. When the substrate moves during a deposition, the film thickness is proportional to the length of the opening on the shield can along the direction of motion. By equating the sum of relative weightings to the required relative thickness at the same position, the length of the opening at that position can be determined. By repeating the same process for the whole length of the required profile, a contour can be obtained for a desired thickness profile. The number of passes and the speed of the substrate are determined according to the required thickness and the growth-rate calibration of a test run. The mirror coating profile is determined from the difference between the ideal surface figure of a focus ellipse and the surface figure obtained from a long-trace profiler measurement on the substrate. A Kirkpatrick-Baez (KB) mirror pair was made using Au as a coating material and cylindrically polished mirrors as substrates. Synchrotron x-ray results using this KB mirror pair showed a focused spot size of 0.4×0.4 μm².