This PDF file contains the front matter associated with SPIE Proceedings Volume 8494, including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

Insight into transient structural interactions, including coupled vibrations and modal non-degeneracy (mode splitting) is important to the development of current and next generation vibratory gyroscopes and MEMS resonators. Device optimization based on characterization of these effects is currently time consuming and limited by the requirement to perform spatially distributed measurements with existing single point sensors. In addition, the effects of interest and the diagnosis of their underlying causes and dependences are not readily revealed by traditional modal and finite element analyses. This paper, accordingly, discusses the design of a novel multi-channel fiber-optic heterodyne vibrometer which addresses this requirement directly. We describe a fiber-optic interferometer design which incorporates many standard fiber-optic telecommunications components, configured to support dynamic imaging of the real-time structural behavior of macro and micro vibratory resonators, including planar and 3D micro electromechanical systems (MEMS). The capabilities of the new sensor are illustrated by representative data obtained from a variety of 3D vibratory MEMS structures currently under development.

We present the development of an array-type micromachined Mirau interferometers, operating in the regime of low coherence interferometry (LCI) and adapted for massively parallel inspection of MEMS. The system is a combination of free-space microoptical technologies and silicon micromachining, based on the vertical assembly of two glass wafers. The probing wafer is carrying an array of refractive microlenses, diffractive gratings to correct chromatic and spherical aberrations and reference micro-mirrors. The semitransparent beam splitter plate is based on the deposition of a dielectric multilayer, sandwiched between two glass wafers. The interferometer matrix is the key element of a novel inspection system aimed to perform parallel inspection of MEMS. The fabricated demonstrator, including 5x5 channels, allows consequently decreasing the measurement time by a factor of 25. In the following, the details of fabrication processes of the micro-optical components and their assembly are described. The feasibility of the LCI is demonstrated for the measurement of a wafer of MEMS sensors.

In this paper we present a simple method of manufacturing micrometer-sized polymer elements at the extremity of both single mode and multimode optical fibers and its possible modifications in order to provide requested functionalities. We show that the knowledge about 3D distribution of refractive index and birefringence in these elements is required and that interferometric and elastooptics tomography are the methods which provide these data. Exemplary polymer microtips manufactured from the polymeric material with different concentration of heptafluorobutyric acid are investigated in tomographic systems and the obtained results are discussed in reference to the theoretically expected refractive index distributions.

Multipoint Diffraction Strain Sensor (MDSS) is a non-contact whole field strain sensing system. DOE-based lens arrays are designed and used to replace the typical micro-lens array in our MDSS system. These DOE patterns are displayed on the liquid crystal spatial light modulator. So with different focal length, tunable strain sensitivity is achieved. Calibrations are performed to test the measurement accuracy and precision of the system.

We report on a new system for measuring the vibration simultaneously at multiple positions (multipoint vibrometry) using multiple individual channels, each consisting of a complete heterodyne interferometer. The core element for controlling the three-dimensional position of the measurement spots is a liquid crystal on silicon (LCoS) HDTV spatial light modulator. Unwanted modulation effects, especially unwanted diffraction orders and crosstalk effects are taken into account for the design of the optical system and the computation of the holograms. We present a general discussion with an emphasis on the LCoS related considerations and first measurement results.

Systems that attempt to image or project optical energy or information through a turbulent atmosphere are limited by aberrating, refractive index variations. The processes can be improved in a variety of ways if the complex wave function of the aberrated wave can be recorded, reconstructed and analyzed at a sufficient speed. This paper describes application of digital holography for recording, reconstructing, and processing complex wave functions to complement methods such as adaptive optics and lucky imaging. Having the complex waveform provides all of the information required by adaptive optical procedures and also enables improved image processing that is not applicable to real images. Unlike intensity averaging, when complex wave functions are averaged, the random fluctuations in the phase cancel since phase terms include both positive and negative values. In this paper we describe the application of digital holography for recording, reconstructing, and processing complex wave functions of atmospherically aberrated wave functions and report demonstrations in correcting for atmospheric turbulence.

Phase-shifting digital holography is a convenient method to measure displacement and strain distributions. To simplify the optical setup is required for producing more compact equipment. In this paper, a calibration method using a sampling moire method for phase-shifting digital holography with multiple imaging devices is proposed. It is, however, difficult to find the corresponding points on the each reconstructed images taken by each imaging sensors. A 2-D grating reference plate is used. The two-dimensional (2-D) phase map of the 2-D grating pattern can be analyzed accurately. The principle and the experimental results to apply to the deformation measurement are shown.

We are developing an advanced computer-controlled digital optoelectronic holographic system (DOEHS) for diagnosing middle-ear conductive disorders and investigating the causes of failure of middle-ear surgical procedures. Our current DOEHS system can provide near real-time quantitative measurements of the sound-induced nano-meter scale motion of the eardrum. The DOEHS have been deployed and is currently being tested in clinical conditions, where it is being optimized for in-vivo measurements of patients. The stability of the measurement system during examination is crucial as the non-ideal clinical environment presents disturbances larger than the measured quantities from several domains - thermal, optical, electrical and mechanical. Examples include disturbances are due to heartbeat breathing, patients head’s motion as well as environment induced mechanical disturbances (0.1-60Hz, 0.01-100 μm). In this paper we focus on our current progress in the analysis and implementation of various acquisition strategies and algorithms for minimization of the measurement error due to mechanical disturbances in a clinic. We have also developed and implemented a versatile and modular otoscope head (OH) design providing a variety of capabilities for acoustic and displacement measurements of both post-mortem samples of varying sizes (1-12mm) as well as in-vivo examination of patients. The OH offers hybrid on-axis and off axis digital Furrier holographic setup for high resolution (λ/35) 4 phase step measurements as well as fast (<0.1ms) single frame measurements for improved performance in the clinical environment. We also focus on the development of a mechatronic positioning system (MOP) for aiding in the localization of the TM in patients.

Quantitative techniques to characterize thermomechanical effects of light on canvas paintings are necessary in order to better understand the deleterious effects that light has on precious art collections in museum exhibitions. In this paper, we present advances in the development of a customized laser shearography system for temporal characterization of inplane displacements of canvas paintings when subjected to specific lighting conditions. The shearography system is synchronized with a thermal IR camera and concomitant measurements of derivatives of displacements along two orthogonal shearing directions as well as thermal fields are performed. Due to the nature of the measurements, we have developed real-time temporal phase unwrapping algorithms and high-resolution Fast Fourier Transform (FFT) methods to calibrate applied shearing levels. In addition, we are developing methods to isolate thermally-induced components from randomly-induced mechanical vibrations that occur in museum environments by application of IR imaging data. Representative examples are shown, which illustrate capabilities to measure, detect, and map crack propagation as a function of lighting conditions and time.

Shearography is an optical and nondestructive technique that has been used for damage detection in layered composite materials. In order to facilitate and speed the process of marking of defects during a shearographic inspection of large structures of composite materials, a multimedia projector has been employed. The phase map of the geometry measured by fringe projection is used to mapping the coordinates of the shearographic image acquired during the inspection process with their respective pairs in the projection image. Animations of the shearographic result can be projected on the real structure during the inspection, facilitating the identification and marking of defects by the inspector. This paper shows the principle and algorithms used for the projection of detected defects.

A Sampling moire method is one of the convenient phase analysis methods. The accuracy of phase difference analysis is from 1/100 to 1/1000 of the grating pitches. This method is useful to a real-time deformation measurement because the two-dimensional phase analysis can be performed from a single shot two-dimensional grating image. We developed a sampling moire camera which can analyze the two-dimensional displacement images in real-time by using the sampling moire method. The camera is composed of a C-MOS sensor, an FPGA, memory modules and a USB interface. A two-dimensional grating image on the object is taken by the CMOS sensor in synchronization with a camera trigger. The algorithm mentioned previous was written into the FPGA. The two-dimensional grating images analyzed from one-shot image by the FPGA and outputted in real-time. It is confirmed that the camera can measure static displacement in high accuracy. However, it is not confirmed that the camera can measure dynamic displacement in high accuracy. In this paper, the accuracy of dynamic displacement measurement by using sampling moire camera is confirmed. And the sampling moire camera was applied to measure dynamic displacement of train bridges while a train is passing.

A new fisheye lens design is used as a miniature probe to measure the velocity distribution of an imploding surface along many lines of sight. Laser light, directed and scattered back along each beam on the surface, is Doppler shifted by the moving surface and collected into the launching fiber. The received light is mixed with reference laser light in each optical fiber in a technique called photonic Doppler velocimetry, providing a continuous time record. An array of single-mode optical fibers sends laser light through the fisheye lens. The lens consists of an index-matching positive element, two positive doublet groups, and two negative singlet elements. The optical design minimizes beam diameters, physical size, and back reflections for excellent signal collection. The fiber array projected through the fisheye lens provides many measurement points of surface coverage over a hemisphere with very little crosstalk. The probe measures surface movement with only a small encroachment into the center of the cavity. The fiber array is coupled to the index-matching element using index-matching gel. The array is bonded and sealed into a blast tube for ease of assembly and focusing. This configuration also allows the fiber array to be flat polished at a common object plane. In areas where increased measurement point density is desired, the fibers can be close packed. To further increase surface density coverage, smaller-diameter cladding optical fibers may be used.

FSI system, one of the most promising optical surface measurement techniques, generally results in superior optical performance comparing with other 3-dimensional measuring methods as its hardware structure is fixed in operation and only the light frequency is scanned in a specific spectral band without vertical scanning of the target surface or the objective lens. FSI system collects a set of images of interference fringe by changing the frequency of light source. After that, it transforms intensity data of acquired image into frequency information, and calculates the height profile of target objects with the help of frequency analysis based on FFT. However, it still suffers from optical noise from target surface and relatively long processing time due to the number of images acquired in frequency scanning phase. First, a polarization-based frequency scanning interferometry (PFSI) is proposed for optical noise robustness. It consists of tunable laser for light source, λ/4 plate in front of reference mirror, λ/4 plate in front of target object, polarizing beam splitter, polarizer in front of image sensor, polarizer in front of the fiber coupled light source, λ/2 plate between PBS and polarizer of the light source. Using the proposed system, we can solve the problem low contrast of acquired fringe image by using polarization technique. Also, we can control light distribution of object beam and reference beam. Second, the signal processing acceleration method is proposed for PFSI, based on parallel processing architecture, which consists of parallel processing hardware and software such as GPU (Graphic Processing Unit) and CUDA (Compute Unified Device Architecture). As a result, the processing time reaches into tact time level of real-time processing. Finally, the proposed system is evaluated in terms of accuracy and processing speed through a series of experiment and the obtained results show the effectiveness of the proposed system and method.

Phase-shifting fringe projection is an effective method for 3D-shape measurements. Conventional fringe projection systems utilize a digital projector that images fringes into the measurement plane. The performance of such systems is limited to the visible spectral range, as most projectors experience technical limitations in UV or IR spectral ranges. However, for certain applications these spectral ranges are of special interest. A novel fringe projector was developed on the basis of a single tailored free-form mirror. The freeform mirror generates a sinusoidal fringe pattern by redistribution of light. Phase-shifting can be realized by a slight rotation of the free-form mirror. In this system, the fringe pattern is generated by illuminating the free-form surface and not by the classical imaging technique. As the system is based on a single mirror, it is wavelength independent in a wide spectral range and therefore applicable in UV and IR spectral ranges. Additionally it does not feature any chromatic aberrations. We present the design and realization of this novel fringe projection system. The tailored freeform mirror is realized using ultra-precision turning. Experimental results demonstrate the functionality of the novel measurement system in VIS and UV spectral range.

Deflectometry utilises the deformation and displacement of a sample pattern after reflection from a test surface to infer the surface slopes. Differentiation of the measurement data leads to a curvature map, which is very useful for surface quality checks with sensitivity down to the nanometre range. Integration of the data allows reconstruction of the absolute surface shape, but the procedure is very error-prone because systematic errors may add up to large shape deviations. In addition, there are infinitely many combinations for slope and object distance that satisfy a given observation. One solution for this ambiguity is to include information on the object’s distance. It must be known very accurately. Two laser pointers can be used for positioning the object, and we also show how a confocal chromatic distance sensor can be used to define a reference point on a smooth surface from which the integration can be started. The used integration algorithm works without symmetry constraints and is therefore suitable for free-form surfaces as well. Unlike null testing, deflectometry also determines radius of curvature (ROC) or focal lengths as a direct result of the 3D surface reconstruction. This is shown by the example of a 200 mm diameter telescope mirror, whose ROC measurements by coordinate measurement machine and deflectometry coincide to within 0.27 mm (or a sag error of 1.3μm). By the example of a diamond-turned off-axis parabolic mirror, we demonstrate that the figure measurement uncertainty comes close to a well-calibrated Fizeau interferometer.

Despite the introduction of phase-shifting interferometers in the 1980's, high volume catalog and camera production lenses are still inspected using qualitative visual fringe inspection methods. This error-prone inspection technique requires the human operator to quickly judge whether the lens “passes” or “fails” based on the appearance of the fringes. Although this method is sufficient for optics with < 0.25 wave of surface figure irregularity, it is not sensitive enough to properly inspect surfaces in the increasingly common 0.1 wave regime. Furthermore, as visual fringe inspection is not quantitative, it does not produce the statistical surface measurement data that is necessary to monitor and optimize production polish process yields. To overcome these disadvantages, we have developed a robust, quantitative lens surface inspection instrument. A compact, user-friendly, and economical 60 mm aperture Fizeau interferometer directly addresses production optical test applications, providing rapid vibration-robust optical surface measurements of P-V irregularity, RMS irregularity, astigmatism magnitude, and power via a simple touch-screen interface. Pass/Fail criteria are applied to these values, enabling accurate and repeatable sorting of production optics based on these quantitative values and eliminating human interpretive error. Batch statistics are also displayed and stored for customer inspection reports and rapid polish process feedback. This paper will also describe how next-generation Fizeau interferometers serve as part of a total optical production process improvement strategy.

Finding a reliable technique to determine clamping load in bolted joint has been a challenging problem for several years. A new technique that was recently introduced, addresses this problem by deploying the Digital Speckle Pattern Interferometry (DSPI) technique to measure the deformation of the surface being clamped and correlate it to the clamping load. The optical part of the system has been developed using the Spatial Phase Shifting technique to determine the deformation caused by the applied torque. The images produced by this technique are of low signal-to-noise ratio and require filtering in order to achieve accurate deformation calculation. However, image filtering requires significant processing time, particularly in video streams, which can cause delays in the system and therefore undesirable results. In this paper we propose a method to automate the process of calculating the deformation in a suitable time frame. This method uses a new filtering technique to reduce the computation overhead of the controlling software and therefore increase the overall speed of the system by up to seven times. Achieving a practical processing time in the software will result in more robust and reliable control over the fastener and therefore higher accuracy of clamping load. The methods used to design this system ultimately can automate the entire process of clamping and provide a reliable closed-loop clamping load controller for bolted joint.

This work shows the measurement of the refraction index of a glass plate using a Point Diffraction Interferometer (PDI). The plate of the PDI has a micro-hole and transmittance of less than 10%. The experimental setup consists in a He-Ne laser illuminating a spatial filter, a collimated beam is produced by an achromatic lens, and close to the focal point of a second lens (focusing lens), the plate of the Point Diffraction Interferometer is located. When the laser light pass through the plate of the PDI, it is generated an interference reference pattern, called I_r, which is recorded. As a second step, a glass plate with unknown index refraction is introduced between the focusing lens and the plate of the PDI, obtaining a new modified interference pattern, called I_t. We use the geometrical of figure of interference fringe for analysis of the interferograms. Value of the refraction index of the glass plate, n_t, can be derived, with the previous knowledge of the glass plate thickness. Some experimental results will be shown.

An optical system formed by four point-diffraction interferometers is used for measuring the refractive index distribution of a phase object. The phase of the object is assumed enough smooth to be computed in terms of the Radon Transform and it is processed with a tomographic iterative algorithm. Then, the associated refractive index distribution is calculated. To recovery the phase from the inteferograms we use the Kreis method, which is useful for interferograms having only few fringes. As an application of our technique, the temperature distribution of a candle flame is retrieved, this was made with the aid of the Gladstone-Dale equation. We also describe the process of manufacturing the point-diffraction interferometer (PDI) plates. These were made by means of the thermocavitation process. The obtained three dimensional distribution of temperature is presented.

An aspheric testing system based on subaperture stitching interferometry has been developed. A procedure involving subaperture aberration compensation and radial position scanning was established to resolve discrepancies in the overlapped regions. During the aspheric measuring process, the Fizeau-interferometer axis, the optical axis of the asphere, and the mechanical rotation axis have to be aligned. Due to the tolerance of alignment mechanisms, subaperture interferograms would be contaminated by various amounts of aberrations associated with the rotation angle. These aberrations introduce large inconsistencies between adjacent subapertures in the stitching algorithm. Zernike coefficients of the subapertures in one annulus were examined and each coefficient term was found to be a sinusoidal function of the rotation angle. To eliminate the influence of misalignments, each subaperture was compensated with appropriate amounts of coma and astigmatism to make the resulting Zernike coefficients converge to the mean values of the sinusoidal functions. In addition, the determination of the overlapped regions relies on the precise estimate of the distance between the center of each subaperture and the center of the aspheric optics. This distance was first provided by the encoder and then estimated by position scanning along the radial direction pixel-by-pixel in numerical computations. The means of the standard deviation in the overlapped regions in the simulation and the experimental measurement of an aspheric lens were 0.00004 and 0.06 waves, respectively. This demonstrates the reliability of the subaperture aberration compensation and position scanning process.

We present detection of inhomogeneities in amorphous corundum layers by optical coherence tomography system with CMOS matrix detector. The presented setup is based on modified Twyman-Green interferometer with specially designed scanning module. The module consists of two beam directing mirrors, a beam splitter, an objective lens and it's illuminated by a high-power pig-tailed light emitting diode. The system is calibrated that the objective gives image of zero optical path difference plane in infinity. Due to this and because the matrix detector is placed in the focal plane of an imaging lens, therefore even if distance between the objective and the imaging lens changes during scanning process, the zero optical path difference plane is always in-focus. Hence the system focuses itself on imaged layers and there is no drop in transverse resolution coming from defocusing. In the paper we present, the idea of self-focusing tomographic system, its theoretical analysis and design aspects. Calibration of proposed system and its application for measurement of amorphous corundum layers are also presented. The measurements results show occurrences of the inhomogeneities in the investigated samples.

In this paper, we present a novel approach for the collection of computed tomography data. Non-uniform increments in projection angle may be used to reduce data acquisition time with minimal reduction in the accuracy of the reconstructed profile. The key is to exploit those projection angles which correspond to regions where the object contains few high spatial frequency components. This technique is applicable to optical phase computed tomography, as well as X-ray computed tomography. We present simulation results on intraocular lenses used in cataract surgery.

Using the analogy of the double-slit experiment developed by Young and using interferometric technique developed by Chalmers, we built an interferometric arrangement that can analyze local defects of an optical surface. With a reflective spatial light modulator (RSLM) controlled by a PC, two apertures are open each time, and the apertures became as secondary light sources, producing interference pattern for specific zones for the surface under test. The interference pattern is observed, and storage into a computer by using a CCD camera. Finally the results are compared with the results obtained using a Fizeau commercial interferometer.

The temporal phase unwrapping will become unstable, if fewer numbers of fringe patterns with different spatial frequencies are used. In this paper, we present a modified phase unwrapping method based on the phase filtering, which can be used to achieve correct phase-unwrapping with use of fewer numbers of fringe frequencies. An adaptive phase filter is designed according to the phase-jumping characteristics to eliminate the phase noise. The window size of the filter is adaptively determined according to the local noise levels. After filtering operation, we are able to obtain the approximate phase value with filtering errors. In order to further eliminate the filtering residual errors, we take unwrapping operation again to get the correct phase value. The simulation experimental results are also presented to validate our proposed approach.

We present a phase shifting interferometry system for the study of the early adhesion process for osteoblast-like cells, through an interference microscope. Optical phase maps from the cells are obtained experimentally as a function of cell adhesion time. The process is carried out on surfaces of metallic materials relevant to the development of bone implants. The surfaces were subjected to various levels of mechanical polishing and their roughness was measured using the same experimental technique mentioned before. Morphological changes of the cell can be measured over their optical phase maps while the cell adhesion process is accomplished. The experimental technique shows a suitable feature as to the observed time scale, and also shows a high stockiness and precision for the determination of the optical phase.

The phase of light propagating through a bent optical fibre is shown to depend on the refractive index of the medium surrounding the fibre cladding when there is resonance coupling between the guided core mode and cladding modes. This shifts the spectral maxima in the bent fibre-optic Fabry-Perot interferometer. The highest phase and spectral sensitivities achieved with this interferometer configuration are 0,71 and 0,077, respectively, and enable changes in the refractive index of the ambient medium down to 5·10^-6 to be detected. This makes the proposed approach potentially attractive for producing highly stable, precision refractive index sensors capable of solving a wide range of liquid refractometry problems.

MEMS devices are exposed to a variety of environmental effects, making a prediction of operational reliability difficult. Here, we investigate environmental effects on properties of piezoelectrically actuated microcantilevers, where AlN is used as actuation material. The environmental effects to be considered include thermal and humid cycling, as well as harsh electrical loading performed under normal conditions. Investigated properties are defined for the static and dynamic behavior of microcantilevers. A Twyman-Green interferometer, operating in both stroboscopic regime and time-average interferometry mode, is used as a metrology tool. Monitoring the micromechanical behaviors of devices driven by AlN during the lifetime tests assists monitoring of their long-term stability. FEM calculation is also used to further explain various failure mechanisms.