• Journal of Sensor Science and Technology
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• v.22 no.2
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• pp.95-99
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• 2013

We proposed and demonstrated a fiber optic sensor for detecting the thermo-optic coefficient of a liquid, based on a cascade of two different FBGs. One of the two FBGs was etched, and its cladding was removed, for evanescent wave coupling with an external liquid. The Bragg wavelength of the non-etched FBG was used as a reference for the temperature of the surrounding liquid. The refractive index (RI) and thermo-optic (T-O) coefficient of a liquid can be detected from the difference between the Bragg wavelengths of the two FBGs, and the variation of the difference in accordance with temperature.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.06a
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• pp.247-251
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• 1998

This work presents the analysis of $1\times2$ polymer waveguide thermo-optic switch using asymmetric Y-splitter at the wavelength of 1300nm. Because of the high thermo-optic coefficient of polymeric materials the design of efficient switches were feasible. For the numerical simulation of these switches the finite difference beam propagation method has been employed. Design rules for a $1\times2$ polymeric switch have been defined by using the numerical techniques.

• ETRI Journal
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• v.28 no.6
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• pp.739-744
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• 2006

In this paper, we report numerically calculated results of testing a temperature-insensitive refractive sensor based on a planar-type long-period waveguide grating (LPWG). The LPWG consists of properly chosen polymer materials with an optimized thermo-optic coefficient for the core layer in a four-layer waveguide structure. The resonant wavelength shift below the spectral resolution of the conventional optical spectrum analyzer is obtained accurately over a temperature change of ${\pm}7.5^{\circ}C$ even without any temperature control. The refractive index sensitivity of the proposed grating scheme is about 0.004 per resonant wavelength shift of 0.1 nm for an optimized thermo-optic coefficient.

• Korean Journal of Optics and Photonics
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• v.10 no.3
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• pp.248-253
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• 1999

In this paper, we have investigated a fiber type active coupler which utilizes the mode coupling between the side polished single mode optical fiber and the active multimode planar waveguide. The proposed device can be used for not only tunable wavelength filter or optical intensity modulator but also a tool for measuring optical properties of guiding material such as refractive index, birefringence, electro-optic coefficient, and thermo-optic coefficient. We gave designed and optimized a coupler structure using the BPM and fabricated the device using thermo-optic polymer as active planar waveguide overlay. The device showed that insertion loss was less then 0.5 dB, extinction ratio was -13 dB at the resonance wavelength, and the wavelength tunablity due to thermo-optic effect was -1.5 nm/$^{\circ}C$. The active coupler using thermo-optic effect can be used as a wavelength tunable filer, an optical intensity modulator and an optical sensor. pulses that are subsequently compressed by a dispersive optical fiber. Experimental results show that $sech^2$ shape pulses with a pulse width of ~14 ps and a time bandwidth product of ~0.34 are successfully generated at 10 GHz repetition rate. In contrast to other methods, such as higher order soliton compression, this approach does not depend on the optical power and thus shows promise for application to low-power lasers.

• Journal of Sensor Science and Technology
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• v.15 no.4
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• pp.263-268
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• 2006

We have demonstrated a highly sensitive temperature sensor using an etched single mode fiber with a thermally expanded core region. Large core size of thermally expanded core facilitates access to evanescent wave by the wet etching. The etched region was surrounded by a low dispersive external medium with high thermo-optic coefficient. Due to the large difference between the dispersion property of the fiber and that of the external medium, the device reveals a cut-off properties at spectral region. The cut-off wavelength was shifted by the variations of the environmental temperatures because of thermo-optic effect of the external medium. The sensitivity of the fabricated device was found to be $45nm/^{\circ}C$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.3
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• pp.195-198
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• 2014

In this paper, a measurement method to obtain the optical properties of a liquid base on a side-polished single mode fiber was proposed and demonstrated. The device showed periodic resonance coupling against wavelengths. The refractive index and dispersion characteristics of a liquid were calculated by use of the spacings of periodic resonance wavelengths of the device. The thermo-optic coefficient of the liquid was obtained by monitering the shift of resonance wavelengths of the devices with change of environmental temperature.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1997.06a
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• pp.163-170
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• 1997

The MgO-doped LiNbO$_3$ single crystals were grown along c-axis by the Czochralski method with the pulling rate of 3mm/h and the rotation of 10rpm. The MgO contents were form 1 to 4 mole%. The SHG properties were investigated with the pulsed Nd:YAG laser, and thermo-optic coefficient, electro-optic coefficient of birefringence and curie temperature were measured. Phase matching temperature and Curie temperature increase similarly with MgO content until 4 mole%.

• Korean Journal of Optics and Photonics
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• v.14 no.2
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• pp.135-141
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• 2003

In arrayed waveguide grating (AWG) devices whose waveguides were composed of polymer with negative thermo-optic coefficient as overcladding, and silica with positive thermo-optic coefficient as both core and undercladding, we investigated the temperature dependence of the central wavelength using two-dimensional SFDM. From these results, it was confirmed that the temperature dependence can be nearly eliminated by adjusting the refractive index of the cladding and the thickness of the silica thin film upper-loaded on the core. Based on the numerical calculations, the AWG device with polymer overcladding was fabricated. and its optical characteristics were compared with those of the orginal silica AWG device. The introduction of polymer overcladding decreased the temperature dependence of the central wavelength from 0.0130 nm/$^{\circ}C$ to 0.0028 nm/$^{\circ}C$ without deteriorating the insertion loss and crosstalk characteristics.

• Journal of the Optical Society of Korea
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• v.7 no.2
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• pp.84-88
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• 2003

A new method for temperature compensation of fiber Bragg grating (FBG) using hi-metal is proposed and experimentally demonstrated. Bi-metal bends toward the metal of low temperature expansion coefficient as the temperature increases, and this property is utilized to cancel the thermo-optic effect of the fiber. The optimum thickness of the high coefficient metal was empirically found by the trial-and-error method. The temperature sensitivities were 8.1 pm/$^{\circ}C$ and -0.018 pm/$^{\circ}C$ for the uncompensated and compensated FBGs, respectively, which indicates a reduction to a mere 0.22 % of the original sensitivity. No appreciable change in the spectral shape was observed. The packaging technique described in this paper is simple and compact, and it can be used for FBGs in WDM and DWDM communication systems that have stringent requirements on the temperature stability of the components.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.8
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• pp.999-1005
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• 2013

A fiber Bragg grating sensor is considered a smart sensor that shows outstanding performance in the field of structural health monitoring (SHM). It has a powerful advantage, especially that of multiplexing, which enables several parameters to be sensed at multiple points by using a single optical fiber line. Among several parameters, the thermal expansion coefficient and thermo-optic coefficient are required to measure temperature. In previous studies, these were considered constant variables. This study shows that two parameters vary with temperature and newly proposes a temperature function for these two parameters. Specifically, these two parameters were defined as a single variable, and then, it was experimentally verified that this variable is a function of temperature. Finally, it was shown that temperature from RT to $100^{\circ}C$ was precisely measured by using the temperature function that was defined through the experiment.