Browsing by Author "Chen, Kun-Huang"

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A fiber Bragg grating based passive semicircular sensor architecture with fault monitoring
(2019-03-01)
Yeh, Chien-Hung
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Chang, Yao-Jen
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Huang, Tzu-Jung
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Yang, Zi-Qing
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Chow, Chi-Wai
In the investigation, we investigate a fiber Bragg grating (FBG) based semicircular sensor architecture with fiber fault monitoring experimentally. Two erbium-doped fiber amplifiers (EDFAs) are used in the monitoring center to generate a broadband light source for sensing the strain and temperature simultaneously. Here, we utilize six FBG based sensors with different reflected wavelength for proof-of-concept demonstration. There is no optical filter used in the FBG sensor system for wavelength-selection. In addition, the proposed sensor system can monitor one to two fiber faults. In the measurement, the temperature-and strain-induced changes are also analyzed and discussed. Therefore, the proposed multiple FBG based semicircular sensor system not only can sense the temperature and strain simultaneously, but also can be used to monitor where is the fiber fault.
A new type of liquid refractometer
(2008)
Lin, Jiun-You
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Chen, Jing-Heng
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Chen, Kun-Huang
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Su, Der-Chin
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光電工程學系
A new liquid refractometer is proposed based on the phenomenon of total-internal reflection and the technique of heterodyne interferometry. A special designed glass probe is immersed in the tested liquid, and a light beam is guided within this probe due to the total internal reflections. After the light beam is totally reflected at the other end of the probe, it goes back in an anti-parallel direction of the original path. Because of multiple total-internal reflections, the phase difference, which is determined by the heterodyne interferometry between the p- and s-polarizations, is greatly enhanced to result in an accurate refractive index. The feasibility of this method was demonstrated by our experimental results, and a resolution of 5x10(-3) is obtained with our method. This method should, therefore, bear the merits of high accuracy, high stability, and easy operation.
An alternative method for simultaneously measuring cell parameters of a twisted-nematic liquid crystal cell
(2008)
Chen, Kun-Huang
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Chen, Jing-Heng
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Lin, Jiun-You
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Su, Der-Chin
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Su, Jung-Chieh
A phase-sensitive method is developed to simultaneously measure the cell parameters of a TNLC (twisted-nematic liquid crystal) cell based on Jones calculus and the heterodyne interferometric ellisometry. These cell parameters include the twist angle, the cell gap, and the angle of the entrance LC director. When a circularly polarized heterodyne light beam normally passes through a TNLC cell, the phase difference between the p- and s- polarization of the interference signal can be measured accurately with an analyzer and the heterodyne interferometric ellisometry. The phase difference depends on the azimuth angle of the analyzer and the parameters. By substituting the measured values of the phase differences at three different azimuth angles of the analyzer into the special equations derived with Jones calculus. Hence these three para meters can be esitimated by using a personal computer with numerical analysis technique. Because of its common path optical configuration and its heterodyne interferometric ellisometry, this method has many merits such as high stability against the surrounding vibration, high resolution, and easy operation.
Collimation testing and calibration using a heterodyne Moire method
(2014-11-01)
Chang, Wei-Yao
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Hsu, Ken Y.
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Chen, Kun-Huang
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Chen, Jing-Heng
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光電工程學系
This study proposes a simple, rapid, and highly accurate method to achieve the collimation testing and calibration of laser light beams. By applying a relative constant velocity to two gratings, every pixel of a CMOS camera can receive a series of heterodyne moire signals. Based on the least squares sine fitting algorithm, the phase of the optimized sinusoidal wave can be obtained. Consequently, the phase slope along the direction perpendicular to the grating lines can be estimated and then used to judge the degree of collimation. Furthermore, by measuring only two phase slopes at two positions of the collimating lens, the calibration of the light beam collimation can also be achieved. The experiment validated the proposed method, and the positioning error of the light beam collimation was approximately 7 mu m. (C) 2014 Elsevier Ltd. All rights reserved.
Corneal surface reconstruction by using heterodyne moire method
(2013)
Chang, Wei-Yao
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Chen, Kun-Huang
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Chen, Der-Chin
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Tseng, Jung-Kai
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Chen, Shyan-Tarng
In this paper, we propose a simple method for reconstructing the corneal surface profile by using the Talbot effect, projection moire 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 moire 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.
Full-field refractive index measurement with simultaneous phase-shift interferometry
(2014)
Chu, Yen-Chang
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Chang, Wei-Yao
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Chen, Kun-Huang
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Chen, Jing-Heng
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Tsai, Bo-Chung
Using the phenomenon of total internal reflection and a beam splitting device, a technique of simultaneous phase-shift interferometry is proposed for measuring the full-field refractive index. Because this method applies a beam splitting device that mimics the characteristics of beam splitting and phase modulation, four interferemetric images of various phase distributions can be simultaneously captured. Therefore, this setup can avoid errors caused by non-simultaneous capturing of images and offers the benefits of high stability, ease of operation, and real-time measurement. Furthermore, using the phenomenon of total internal reflection, the phase difference between p- and s-polarized light varies considerably with the refractive index of a tested specimen. This can substantially increase the measurement resolution. The feasibility of this method is verified using an experiment, and the measurement resolution can be higher than 3.65 x 10(-4) RIU. (C) 2014 Elsevier GmbH. All rights reserved.
Generating Radially and Azimuthally Polarized Beams by Using a Pair of Lateral Displacement Beamsplitters
(2016-09-01)
Han, Chien-Yuan
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Wei, Zhi-Hao
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Hsu, Yung
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Chen, Kun-Huang
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Yeh, Chien-Hung
This paper proposes a modified polarization converter for generating radially and azimuthally polarized beams. Based on a Mach-Zehnder-like interferometric structure, the device consists of a pair of lateral displacement beamsplitters (LDBs) and two half-wave plates that manipulate the states of polarization of incident linearly polarized light. Through the coherent superposition of two orthogonal Hermite-Gaussian modes in the far field, radially and azimuthally polarized beams can be obtained simultaneously. A prototype was assembled to demonstrate the feasibility of the design. The proposed design has the advantage of having a simple, symmetric, compact, and robust structure. In addition, the introduction of LDBs substantially reduces the cost of this device. Moreover, the design can be applied to a broadband pulsed laser with considerable potential in high-power applications.
Heterodyne moire interferometry for measuring corneal surface profile
(2014-03-01)
Chang, Wei-Yao
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Chen, Kun-Huang
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Chen, Der-Chin
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Tseng, Jung-Kai
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Chen, Shyan-Tarng
This study proposes an accurate method for reconstructing the corneal surface profile. By applying a constant velocity to the projection grating along the grating plane, a series of sampling points of the sinusoidal wave, which behaves in the manner of heterodyne interferometric signals, can be recorded using a CMOS camera. The phase distribution of the moire fringes can then be obtained using the IEEE 1241 least-square sine fitting algorithm and two-dimensional (2D) phase unwrapping. Finally, the corneal surface profile can be reconstructed by substituting the phase distribution into a specially derived equation. To validate the proposed method, the corneal surface of a pig eyeball was measured. The measurement resolution was approximately 3.5 mu m. Because of the introduction of the Talbot effect, the projection moire method, and heterodyne interferometry, this approach provides the advantages of a simple optical setup, ease of operation, high stability, and high resolution. (C) 2013 Elsevier Ltd. All rights reserved.
Heterodyne moire surface profilometry
(2014-02-10)
Chang, Wei-Yao
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Hsu, Fan-Hsi
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Chen, Kun-Huang
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Chen, Jing-Heng
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Hsu, Ken Y.
In this study, a novel moire fringe analysis technique is proposed for measuring the surface profile of an object. After applying a relative displacement between two gratings at a constant velocity, every pixel of CMOS camera can capture a heterodyne moire signal. The precise phase distribution of the moire fringes can be extracted using a one-dimensional fast Fourier transform (FFT) analysis on every pixel, simultaneously filtering the harmonic noise of the moire fringes. Finally, the surface profile of the tested objected can be generated by substituting the phase distribution into the relevant equation. The findings demonstrate the feasibility of this measuring method, and the measurement error was approximately 4.3 mu m. The proposed method exhibits the merits of the Talbot effect, projection moire method, FFT analysis, and heterodyne interferometry. (C) 2014 Optical Society of America
Optimized design of multiport optical circulator
(2014)
Hsu, Fan-Hsi
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Chen, Jing-Heng
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Chen, Kun-Huang
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Yeh, Chien-Hung
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Hsu, Ken Y.
This research proposes a practical multiport optical circulator design by using polarizing beam splitter cubes as spatial walk-off polarizers. The use of Porro prisms for directing light requires fewer components and improves space-efficiency. Therefore, a high performance device can be produced at a reduced cost. A six-port optical circulator prototype was fabricated to show the feasibility of the proposed design. The insertion losses range between 0.52 and 1.05 dB, the isolations range between 26.20 and 45.13 dB, and the return losses are 27.72 dB. The benefits of this design\'s simple and symmetrical structure include costefficiency, simple fabrication processes, polarization-independence, the resolve of polarization-mode dispersion issues, and high performance. Additionally, the number of ports can be increased easily. (c) 2014 Elsevier GmbH. All rights reserved.
Prism-hologram-prism sandwiched recording method for polarization-selective substrate-mode volume holograms with a large diffraction angle
(2018-08-06)
Hsu, Fan-Hsi
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Han, Chien-Yuan
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Chen, Kun-Huang
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Hsu, Ken-Yuh
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Chen, Jing-Heng
We propose a prism-hologram-prism sandwiched recording method for the fabrication of polarization-selective substrate-mode volume holograms with a large diffraction angle. In fabrication, the C-RT20 photopolymer is sandwiched between two 45 degrees-90 degrees-45 degrees prisms and the interference fringes can be easily recorded in the recording material. The experimental results are in good agreement with the theoretical predictions. The proposed method features of a reflection-type recording setup for a transmission element and belongs to a technique of longer-wavelength construction for shorter-wavelength reconstruction. In addition, the method is much easier than the traditional recording method of two incident beam interference and has application potential in holographic photonics. (c) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
Reconstruction of surface profile by using heterodyne moire method
(2012-11-01)
Chang, Wei-Yao
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Hsu, Fan-Hsi
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Chen, Kun-Huang
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Chen, Jing-Heng
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Hsieh, Hung-Chih
Based on the projection moire method and heterodyne interferometry, this study proposes an alternative method for reconstructing the surface profile of an object. Obliquely illuminating a linear grating with an expanding collimated light, a self-image of this grating can be generated and projected on the surface of the tested object. The grating fringes distorted by the surface profile are imaged on the reference grating to form the moire fringes. These moire fringes are then captured by a CMOS camera. If the projection grating moves with a constant velocity along the grating plane, each pixel of the CMOS camera records a series of sampling points of the sinusoidal wave. These sinusoidal waves behave like heterodyne interferometric signals. Hence, the accurate and stable phase distribution of the tested object surface can be obtained using the IEEE 1241 least-squares sine fitting algorithm and 20 phase unwrapping. Substituting the phase values into the derived equation, the surface profile of the tested object can be reconstructed. The experiments in this study verified the feasibility of this method, showing a measurement resolution of approximately 1.9 mu m. The proposed measurement method has the merits of both the projection moire method and the heterodyne interferometry. (C) 2012 Elsevier B.V. All rights reserved.
Stress measurement of thin film on flexible substrate by using projection moire method and heterodyne interferometry
(2016-06-01)
Chen, Kun-Huang
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Chen, Jing-Heng
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Tseng, Hua-Ken
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Chang, Wei-Yao
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光電工程學系
We propose a stress measurement system based on a projection moire 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 moire 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. (C) The Authors.
Switchable dual-wavelength single-longitudinal-mode erbium fiber laser utilizing a dual-ring scheme with a saturable absorber
(2018-06-01)
Yang, Zi-Qing
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Huang, Tzu-Jung
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Chang, Yao-Jen
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Yeh, Chien-Hung
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Chow, Chi-Wai
In this work, we propose and demonstrate a switchable dual-wavelength erbium-doped fiber (EDF) ring laser with stable single-longitudinal-mode (SLM) output. Here, a dual-ring (DR) structure with an unpumped EDF of 2 m is designed to achieve SLM oscillation. Five fiber Bragg gratings (FBGs) are applied in the laser cavity serving as the reflective element to generate different dual-wavelength outputs. In the measurement, six sets of generated dual-wavelengths with various mode-spacing (Delta lambda) can be achieved via the five FBGs. Additionally, the stability performance of the proposed EDF DR laser is also demonstrated.
Wavelength-selectable and steady single-mode erbium-doped fiber multiple ring laser
(2017-11-01)
Yeh, Chien-Hung
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Yang, Zi-Qing
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Huang, Tzu-Jung
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Chow, Chi-Wai
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Chen, Jing-Heng
To achieve a stable and selectable C-band erbium-doped fiber (EDF) laser with single-longitudinal-mode output, a multiple ring architecture is proposed and demonstrated experimentally. In this work, we design a passively quadruple-ring structure in the cavity of an EDF laser to produce a Vernier effect with a mode filter for suppressing the multimode spikes significantly. In addition, the output performance and stability of the proposed EDF ring laser are discussed.