Ming-Wen Chang

Zernike polynomial fitting of lateral shearing interferometry

For a wavefront tested by shearing interferometer, the Zernike polynomial coefficients of the wavefront are found in an analytic form expressed by the Zernike polynomial coefficients of the shearing interferograms. The validity of the new algorithm is tested by numerical simulations and real interferograms.

Distance- and velocity-detection interferometer by using a frequency triangular-modulated laser diode

A scheme for distance and velocity signal detection is implemented. This technique is based on a laser diode with its frequency modulated by a triangular waveform and followed by time gating.

DISTANCE AND VELOCITY MEASUREMENTS BY THE USE OF AN ORTHOGONAL MICHELSON INTERFEROMETER

A novel signal processing scheme for detecting distance and velocity signals simultaneously is demonstrated. In this method, a frequency-modulated diode laser is used to illuminate a dual-channel Michelson interferometer with two orthogonal output signals. The distance and the velocity signals then exist on the beat frequencies of the output interferometric signal. Two interferometric output signals with a quadrature phase shift are used to adjust the gating time period of frequency counters for beat-frequency measurement. The distance and velocity signals can thus be obtained from the counting number within the gated-in time period.

Matrix-matrix multiplication by using anisotropic self-diffraction in BaTiO(3).

We propose a matrix-matrix multiplication by using anisotropic self-diffraction in BaTiO(3). The input matrices are carried by the two incident beams with special Bragg-matched incident angles. The output matrices are produced by anisotropic self-diffraction with the polarization orthogonal to those of the incident matrices. By thresholding the output this architecture is particularly suitable for the applications of optical interconnects and an optical switch.

Temperature dependence of two-beam coupling and dark decay in photorefractive BaTiO3

The temperature dependence of two-beam coupling and dark decay in photorefractive BaTiO3 is reported. We show that the competition between deep and shallow traps depends on temperature and writing intensity, and influences two-beam coupling and dark decay. The dynamics of dark decay, characterized by a fast decay of partial erasure and a subsequent slow decay, is influenced by the presence of deep and shallow traps. Partial erasure, due to thermal excitation of charges from the shallow traps, decreases with temperature and increases with writing intensity. The time constant of the slow decay, due to thermal excitation of charges from the deep traps, depends strongly on temperature, but not on the writing intensity. At room temperature, the existence of deep and shallow trap leads to intensity-dependent photorefractive gains. As temperature increases, the influence from the shallow trap decreases, and the photorefractive gain becomes independent of the intensity. However, at much higher temperatures (∼100°C), the photorefractive gain resumes its dependence on intensity due to an increase in dark conductivity at elevated temperature.

Random phase-coded multiplexing in LiNbO3 for volume hologram storage by using a ground glass

An encoding method, random phase-coded multiplexing, was applied to the volume hologram multiplexing and demonstrated the recording of 100 holograms in a LiNbO3:0.01% Fe. The multiplexing method is simple because the encoding material is just a ground glass. A theory was also developed to interpret the properties of the method.

Experimental demonstration of phase-only circular harmonic filtering using computer generated filters

Experimental results of phase-only circular harmonic filtering implemented in a standard Fourier transform correlator are presented. The filter is a computer generated hologram which contains only the phase information of a single circular harmonic component of the target. The result with simple binary objects bears out the simulation result published earlier [H. F. Yau and C. C. Chang, Appl. Opt. 28, 2070-2074 (1989)] in that the filter is indeed shift- and rotational-invariant and that the correlation peak is more prominent than that produced by ordinary circular harmonic filtering.

Photorefractive effect in hydrogen-reduced BaTiO3

Abstract Optical and photorefractive properties of hydrogen-reduced BaTiO3 are investigated. Hydrogen-reduction induced a broad optical absorption around 620 nm. From two beam coupling, the electrooptic gain is highly dependent on intensity, with electrons being the major carriers. When the annealing temperature increases, the electrooptic gain decreases, though the trap density increases. From light-induced erasure decay measurement, the response time has a little change with intensity at low intensity, though it is much faster than that of the as-grown sample. These properties can be attributed to high dark conductivity of the reduced sample. The dark conductivity increases about three orders after hydrogen-reduction. It is about 6.6 × 10 −11 1/( cm Ω) for the reduced sample, compared with 2.3 × 10 −14 1/( cm Ω) for the as-grown.

Vibration Suppression in a Flexible Structure Based on Fiber Optics Michelson Interferometric Sensor

A two-wavelength fiber optics Michelson interferometric sensor has been employed to detect the vibration signal in a flexible beam. The synthetic wavelength and synthetic heterodyne detection schemes have been adopted for signal processing on optical phase detection. The active control technique was also developed and implemented to suppress the vibration signal that was generated from the piezoelectric transducer. A 38 dB suppression has been obtained.

Application of a Shack cube as a beam splitter in interferometers with a local reference beam

A different setup of the Mach-Zehnder interferometer for testing the convergent wave front is described. A Shack cube is used to replace a traditional recollimator and a parallel-plate beam splitter. An equivalent pupil model has been suggested that describes the point diffraction mechanism. The calibration procedures for the Mach-Zehnder interferometer are described. The Shack-cube beam splitter has the advantages of compactness and better reference-beam quality compared with the recollimator and the parallel-plate beam splitter.