We propose a stress measurement system based on a projection moiré method and heterodyne interferometry for thin films on a flexible substrate. In the measurement setup, a CMOS camera in which every pixel can receive a series of heterodyne moiré signals by using a continuously relative displacement with a constant velocity is used. Furthermore, the phase of the optimized sinusoidal curve and the surface profile of the flexible substrate are determined using a least-squares sine fitting algorithm. The thin-film stress is obtained by representing the cross-sectional curve of the surface profile by using a polynomial fitting method, estimating the resultant curvature radii of the uncoated and coated substrates, and using these two radii in the corrected Stoney formula. The proposed measurement system has the advantages of high accuracy, high resolution, and high capacity for substrates with high flexibility and a large measurement depth.
This study proposes an alternative and simple method for measuring full-field refractive index. This method is based on the phase-shifting technique with a modulated electro-optical (EO) modulator and the phenomenon of total internal reflection. To this purpose, a linear polarized light is expanded and incident on the interface between the prism and the tested specimen, and the reflected light passes through an analyzer for interference. The phase difference between the s- and p-polarized light is sensitive to the refractive index of the tested specimen when the total internal reflection appears on this interface. Based on this effect, the resulting phase differences make it possible to analyze the refractive index of the tested specimen through a phase-shifting technique with a modulated EO modulator. The feasibility of this method was verified by experiment, and the measurement resolution can reach a value of refractive index unit of at least 3.552×10−4. This method has advantages of simple installation, ease of operation, and fast measurement.
This paper proposes a thin-film stress measurement system. By applying a constant velocity to the projection grating along the grating plane, a series of sampling points of the sinusoidal wave can be recorded using a CCD camera. The phase distribution of the optimized heterodyne moiré signal can be extracted by the least-squares sine fitting algorithm and then the surface profile of the tested flexible substrate can subsequently be acquired. Using polynomial fitting method to depict the cross-section curve of the substrate, estimating the resultant curvature radii of the uncoated and coated substrates, and substituting these two radii into the corrected Stoney formula, the thin-film stress of the flexible substrate can consequently be obtained. This method features high stability and high resolution due to the introduction of the projection moiré and heterodyne interferometry.
This study proposes a simple method for measuring two-dimensional temperature distributions. Using the significant
phase difference between p- and s-polarizations of the reflected light of a surface plasmon resonance (SPR) detector, the
variation in the phase difference, which is caused by a variation in the temperature, can be accurately measured by
phase-shifting interferometry. Then, by substituting the phase distribution into special derived equation, the temperature distribution can be determined. In order to show the feasibility of this method, different temperature distributions were
measured. The measurement resolution is about 0.186°C. Due to the introduced common-path configuration and the high-sensitivity characteristic of surface plasmon resonance, this method should have merits of easy operation, high sensitivity, high accuracy and rapidly measurement.
In this paper, we propose a simple method for reconstructing the corneal surface profile by using the Talbot effect, projection moiré method, and heterodyne interferometry. A linear grating is obliquely illuminated by an expanding collimated light, and a self-image of this grating can be generated and projected on the corneal surface. The deformed grating fringes are imaged on the second grating to form the moiré fringes. If the first grating is moved with a constant velocity along the grating plane, a series of sampling points of the sinusoidal wave which behave like the heterodyne interferometric signal can be recorded by a CMOS camera. The phase distribution of the corneal surface then can be obtained with the IEEE 1241 least-square sine fitting algorithm and 2D phase unwrapping. Finally, the corneal surface profile can be reconstructed by substituting the phase distribution into special derived equation. This method provides the advantages of a simple optical setup, ease of operation, high stability, and high resolution.
In this study a non-contact method for accurately measuring small concentration of solutions by surface plasmon
resonance heterodyne interferometer is proposed. Firstly, a linearly polarized heterodyne light source is transmitted
through a test box filled with pure water. The transmitted light is incident on the base of a hemi-spherical prism of a
surface plasmon resonance apparatus. Then the reflected light passes through an analyzer and generates an interference
signal on a photo-detector. Secondly, when the incident angle is chosen at resonant angle, a significant phase difference
between the s- and p-polarized components occurs. This phase difference is a function of the incident angle at the base of
the hemi-spherical prism. Finally, when the test box is filled with a test solution, the incident angle at the base of the
hemi-spherical prism is changed. This causes a variation in the phase difference that can be detected by the heterodyne
interferometry. Therefore, the concentration of the tested solution can be accurately determined with special derived
equations. The validity of this method was demonstrated experimentally. The advantages of the propose method include
a simple apparatus, rapid measurement, high stability, and high resolution. Due to the introduction of a common-path
structure, the interference signal is not affected by surrounding fluctuations and can be captured easily.
In this study, the optical activity of cholesteric liquid crystal and common-path heterodyne interferometry are used in a
simple measurement technique that was developed to measure small wavelength differences. A circularly polarized
heterodyne light passes through a cholesteric liquid crystal cell and an analyzer. Consequently, an interference signal is
generated. When the cholesteric liquid crystal cell is properly chosen at circular regime, it owns strongly optical activity.
Accordingly, the phase difference between the s- and p-polarized components of the interference signal depends strongly
on the wavelength. As the wavelength changed, a variation of the phase difference can be accurately detected by
heterodyne interferometry. Substituting the variation of phase difference into specially derived equations, the wavelength
variations can be estimated accurately. The feasibility of this method was demonstrated and this method provides the
advantages of a simple structure, easy operations, rapid measurement, high stability, and high sensitivity.
This study proposes a method for measuring small displacements. To this purpose, a circularly polarized heterodyne light beam, reflected from a mirror, impinges into a semispherical prism in a radial direction and is reflected at the flat base of the prism passing then through a properly oriented analyzer for interference. The phase difference between s- and p-polarized light results are sensitive to the impinging angle when it is equal to the internal reflection polarization angle. If the mirror is displaced, then it causes a small variation of the impinging angle and phase changes. The phase difference obtained allows evaluating the mirror displacement through heterodyne interferometry. The feasibility of this method was demonstrated, and the displacement measurement resolution is ~46 nm.
To achieve high luminescence white LEDs by UV excited phosphors, this research work presents theoretical results to
demonstrate a novel white light LED structure and performance. The main purpose of our work is to solve two issues
encountered, one is UV leak and another is low conversion efficiency of phosphors. A photonic crystal or an omnidirectional
reflector (ODR) can be used to achieve this goal, as compared with a distributed Bragg reflector (DBR). The
advantage of the ODR is that the UV light beam at any incidence can be omni-directionally reflected. In this study, a UV
LED with a 380-nm wavelength with RGB phosphors and a photonic crystal with specific function were used. This
novel white LED was constructed with an air gap between the phosphors layer and the ODR. Theoretical simulation
study shows that the ODR will enhance the white light generation and prevent UV leak from the device. Theoretical
simulation shows that a white light LED with an air gap located between the phosphors layer and ODR will have better
performance than that without it. The simulation data shows that an ODR is the optimized way to reduce UV leak.
The feasibility of conventional polarization-selective substrate-mode holograms is usually limited by the finite refractive index modulation strength. Therefore, in this study, a novel design of polarization selective element with a large diffraction angle is proposed based on the coupled-wave theory. The polarization selective element for 632.8nm is fabricated with VRP-M silver-halide recording material. The diffraction efficiencies of s- and p- components are 83% and 5%, and the calculated extinction ratios are 5.58 and 275, respectively. Polarization selective elements fabricated by the proposed method have all the merits of conventional substrate-mode hologram but not limited by the finite refractive index modulation of common recording materials.
In angle multiplexing, the angle between the reference light and the object light is slightly changed in different
recordings. In reconstruction, only the reference beam with an accurate angular position can retrieve the corresponding
object beam due to the characteristics of Bragg condition. Accordingly, a suitable angular separation of the reference
beam should be decided for angle multiplexing. A larger angular separation will decrease the storage density, and a
smaller angular separation will increase the cross-talk noise in small bi-angles. In general speaking, only one condition
of full angle of lights is involved to calculate the angular separation with coupled-mode theory or with experiment. Thus
the angular separation is fixed in the whole procedure of angle multiplexing. As a result, the angular separations of most
multiplexed holograms are either larger or smaller. Only one hologram is multiplexed in the critical angular condition. In
this paper, angle multiplexing with different angular separations were performed to quantitatively demonstrate the effect.
The possible method to deal with the issue was also proposed.
In this study, a simple method for measuring the small displacements is presented. When a circularly polarized
heterodyne light beam reflected from a mirror is incident into a hemi-spherical prism and is reflected at the base of the
prism. Then the reflected light beam passes through an analyzer for interference. With properly chosen azimuth angles of
transmission axis of the analyzer, the phase difference between s- and p- polarized light is sensitive to the incident angle
near the internal reflection polarization angle. The phase difference can be accurately measured with the heterodyne
interferometry. The small displacement of the mirror causes a small variation of incident angle and a phase change.
Therefore, substituting the phase difference into special derived equations; the small displacement can be determined.
The proposed method has advantages of common-path configuration and heterodyne interferometry.
A simple method is presented to determine small wavelength differences based on the dispersion properties of a uniaxial crystal and circularly polarized heterodyne interferometry. A circularly polarized heterodyne light beam is incident on a uniaxial crystal at the Brewster's angle, and the reflected light beam passes through an analyzer for interference. Owing to proper azimuth angles of the transmission axis of the analyzer and the optical axis of the crystal, the variation of the phase difference determined with the heterodyne interferometric technique of the interference signal is significantly enhanced, resulting in an accurate wavelength variation. The feasibility of this method was demonstrated, and the sensitivity of wavelength differences is about 0.001 nm. The proposed approach has a simple structure, straightforward operation, high stability, and high sensitivity.
We derive the phase difference equation between the p- and s-polarizations of reflection light based on the Kretschmann-Raether configuration. This phase difference equation is used to examine the relationship of the incident angle and metal film thickness versus the phase differences under a small refractive index variation. For a fixed incident angle, the phase difference has a higher measurement sensitivity than the reflectivity change. At the critical angle, there is a higher sensitivity when the metal film thickness is smaller than the skin depth. The surface plasmon resonant (SPR) angle dominates when the metal film thickness is greater than the skin depth. The phase measuring sensitivity at the SPR angle is higher than that at the critical angle by 1 order.
An alternative type of 3-port polarization-independent optical quasi-circulator by utilizing a pair of holographic spatial walk-off polarizers (HSWPs) is proposed. This device consists of a reflection prism, three polarization beamsplitters cubes, a pair of HSWPs, a Faraday rotator, and a half-wave plate. The operating principles, the characteristics and the performances of this device and HSWPs are discussed. In order to show the validity, the prototype device operating in 1300nm is assembled and tested experimentally. The merits of this design include polarization-independence, compactness, high isolation, and easy fabrication. It should also be possible to design the device operating at 1550 nm wavelength range.
A light beam is incident on the boundary surface between the thin metal film of a surface-plasmon-resonance (SPR) apparatus and the test medium. If the incident angle is equal or very near to the resonant angle, then the phase difference between p- and s- polarizations of the reflected light is related to the associated physical parameter. The phase difference can be measured accurately by the heterodyne interferometry. If the relation between the phase difference and the associated physical parameter is specified, the associated physical parameter can be estimated with the data of the phase difference. This method has the advantages of both common-path interferometry and heterodyne interferometry.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.