• Korean Journal of Optics and Photonics
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• v.35 no.4
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• pp.175-183
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• 2024

Research into optical signal processing using photonic integrated circuits (PICs) has been actively pursued in various fields, including optical communication, optical sensors, and quantum optics. Among the materials used in PIC fabrication, polymers have attracted significant interest due to their unique characteristics. To fabricate polymer-based PICs, establishing an accurate manufacturing process for the cross-sectional structure of an optical waveguide is crucial. For stable device performance and high yield in mass production, a process with high reproducibility and a wide tolerance for variation is necessary. This study proposes an efficient method for fabricating polymer optical-waveguide devices by introducing the atomic layer deposition (ALD) process. Compared to conventional photoresist or metal-film deposition methods, the ALD process enables more precise fabrication of the optical waveguide's core structure. Polyimide optical waveguides with a core size of 1.8 × 1.6 ㎛² are fabricated using the ALD process, and their propagation losses are measured. Additionally, a multimode interference (MMI) optical-waveguide power-splitter device is fabricated and characterized. Throughout the fabrication, no cracking issues are observed in the etching-mask layer, the vertical profiles of the waveguide patterns are excellent, and the propagation loss is below 1.5 dB/cm. These results confirm that the ALD process is a suitable method for the mass production of high-quality polymer photonic devices.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.2
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• pp.279-285
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• 2013

The feasibility of substituting a composite mold for an aluminum mold in the fabrication of a small ship propeller was investigated. A small three-blade aluminum propeller was used as a plug for manufacturing the composite mold. A GRPG composite mold and propeller were made from an unsaturated polyester resin, Epovia gelcoat, and woven and mat glass fibers using the compression and vacuum method at room temperature. The hardness and surface roughness and the strength and deformation of the compression and suction molds were experimentally determined. The results were compared with the ISO 484/2 standard and some aluminum alloy materials. The results showed that the deformation of the mold satisfied the tolerance of the thickness of the blade. Some characteristics of the GRPG composite mold were better than those of the aluminum alloy mold (surface smoothness, weight, performance, and cost), and some characteristics were similar (detachment ability and life-cycle). Therefore, the composite mold is considered suitable for the fabrication of a small composite ship propeller.

• Composites Research
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• v.16 no.2
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• pp.33-40
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• 2003

In order to overcome one of the most pronounced shortcomings of conventional laminated composites, such as the low damage tolerance due to delamination, the thermoplastic materials and 3D (three-dimensional) preforms have been utilized in the manufacture of composite materials. From the newly developed process termed as the co-braiding, hybrid yarns of the thermoplastic fibers (PEEK) and reinforcing fibers (carbon) have been fabricated. In order to further enhance the delamination suppression, through thickness fibers have been introduced by way of 3D weaving technique in the fabrication of textile preforms. The preforms have been thermoformed to make composite materials. Complete impregnation of the PEEK into the carbon fiber bundles has been confirmed. For the comparison of mechanical performance of 3D woven composites, quasi-isotropic laminates using APC-2/AS4 tapes have been fabricated. Tensile and compressive properties of both the composites have been determined. Furthermore. the open hole, impact and CAI(Compression After Impact) tests were also carried out to assess the applicability of 3D woven textile reinforced thermoplastic composites in aerospace structures.

• Journal of Sensor Science and Technology
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• v.12 no.5
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• pp.199-204
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• 2003

This paper describes on the fabrication and characteristics of a ceramic thin-film pressure sensor based on Ta-N strain-gauges for harsh environment applications. The Ta-N thin-film strain-gauges are sputter-deposited onto a micromachined Si diaphragms with buried cavity for overpressure protectors. The proposed device takes advantages of the good mechanical properties of single-crystalline Si as diaphragms fabricated by SDB and electrochemical etch-stop technology, and in order to extend the operating temperature range, it incorporates relatively the high resistance, stability and gauge factor of Ta-N thin-films. The fabricated pressure sensor presents a low temperature coefficient of resistance, high-sensitivity, low non-linearity and excellent temperature stability. The sensitivity is $1.097-1.21\;mV/V{\codt}kgf/cm^2$ in the temperature range of $25-200^{\circ}C$ and the maximum non-linearity is 0.43%FS.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.35 no.4
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• pp.407-411
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• 2022

Bulk-sized PbTiO₃ (PT), which is widely known as a high-performance ferroelectric oxide but cannot be fabricated into a monolithic ceramic due to its high c/a ratio, was successfully prepared with a high tetragonality by partially substituting Ni ions for Pb ions using a solid-state reaction method. We found that Ni-doped PT was well-fabricated as a bulk monolith with a significant c/a ratio of ~1.06. X-ray diffraction on as-sintered and crushed samples revealed that NiTiO₃ secondary phase was present at the doping level of more than 2 at.%. Scanning electron microscopic study showed that NiTiO₃ secondary phase grew on the surface of PT specimens regardless of the doping level possibly due to the evaporation of Pb during sintering. We demonstrated that an unconventional introduction of Ni ions into A-site plays a key role on the fabrication of bulk PT, though how Ni ion functions should be studied further. We expect that this study contributes to a further development of displacive ferroelectric oxides with a high c/a ratio.

• Korean Journal of Optics and Photonics
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• v.7 no.4
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• pp.414-418
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• 1996

An electro-optic polymer digital optical switch was fabricated by using a photobleached waveguide and a self-aligned electrode. It features wavelength insensitive operation, fabrication tolerance and flexible design. And its possible advantages include low coupling losses to the fibers and wide bandwidths. For improving its switching performance, the guided mode profiles of the photobleached waveguides were controlled by photobleaching times to achieve optimized coupling in the branch. And the self-aligned electrode was employed to achieve both efficient overlap of the optical and electric fields and easy introduction of the adiabatically tapered electrodes. The measured crosstalks were better than -21dB at 1.32 ${\mu}{\textrm}{m}$ and 1.55 ${\mu}{\textrm}{m}$, and the extinction ratios of each output port were also more than 20 dB.

• Publications of The Korean Astronomical Society
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• v.30 no.1
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• pp.17-29
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• 2015

The IGRINS is a near infrared high resolution spectrograph jointly developed by the Korea Astronomy and Space Science Institute and the University of Texas at Austin. We present design and fabrication of the optomechanical mount for the five mirrors, i.e., an input fold mirror, a slit mirror, a dichroic, and two camera fold mirrors. Based on the structure analysis and the thermal analysis of finite element methods, the optomechanical mount scheme satisfies the mechanical and the thermal design requirements given by the optical tolerance analysis. The performance of the fabricated mirror mounts has been verified through three IGRINS commissioning runs.

• Composites Research
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• v.15 no.6
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• pp.24-29
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• 2002

For the development of all composite unmanned aerial vehicle(UAV), the consideration for manufacturing in design phase and events in composite parts fabrication, subassembly and final assembly are summarized. In design phase, to maximize the advantages of composite material such as cocuring, cobonding and secondary bonding for manufacturing, the advanced structural concept is introduced. For the curing of designed parts, the manufacturing tools for composite parts are designed and manufactured. The assembly jigs are designed to meet dimensional tolerance requirements of the vehicle structure. And the inspection criteria are established and applied for the manufacturing. Technical data for inspection items and methodologies are summarized to utilize for the exclusive specifications of the manufacturing sequence.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.62.2-62.2
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• 2010

The CQUEAN (Camera for QUasars in EArly uNiverse) is an optical CCD camera optimized for the observation of high redshift QSOs to understand the nature of early universe. The focal reducer, which is composed of four spherical lens, is allowed to secure a wider field of view for CQUEAN, by reducing the focal length of the system by one third. We designed the lens configuration, the lens barrel, and the adapters to assemble to attach focal reducer to the CCD camera system. We performed tolerance analysis using ZEMAX. The manufacturing of the focal reducer system and its lab test of optical performance were already finished. It turned out that the performance can meet the original requirement, with the aberration and alignment error taken into account. We successfully attached the focal reducer and CQUEAN to the cassegrain focus of 2.1m telescope at McDonald Observatory, USA, and several tests of CQUEAN system were carried out. In this presentation, I will show the process of focal reducer fabrication and the result of performance test.

• Journal of Korean Society for Quality Management
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• v.44 no.4
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• pp.935-949
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• 2016

Purpose: This study attempts to find out the optimum condition of the rotary cutter making pellet in the footwear outsole process. The pellets are used in the process of outsole rubber fabrication to reduce cycle time and save raw material. Methods: Computer simulations are used to analyze the maximum stress in the rotary cutter after designing a variety of cutter shapes. Taguchi method is used to identify the robust condition of the cutter. In $L_{18}$ orthogonal array, the control factors such as knife width, twisted angle, number of knives, diameter, knife depth and supported angle are considered and noise factors like assembly tolerance and amount of antifriction are allocated. Results: It is found that the most important factors to reduce maximum stress in the cutter are supported angle and diameter. Using Tacuchi's results, we can reduce 70% cycle time and 9% raw material compared to the traditional method using cutting die. Conclusion: When designing the rotary cutter, the best conditions are the diameter at its maximum allowable value and supported angle in the boundary of machine inner space.