Do-Hwan Kim

Kwangwoon University, Seoul, Seoul, South Korea

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Publications (7)10.59 Total impact

  • Ju-Han Song, Do-Hwan Kim, Sang-Shin Lee
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    ABSTRACT: A polymeric ring resonator filter enabling electrically variable extinction ratio has been implemented, incorporating a ring waveguide coupled to a bus waveguide and an electrode which is separated from it with a gap. When an electrical power is applied to the electrode, the refractive index of the polymers underneath it is lowered through the thermo-optic effect so that the guided-mode confinement in the ring is strengthened to reduce its bending loss. Consequently, for a constant bus-to-ring coupling the attenuation depth at resonant wavelengths could be adjusted electrically. As for the achieved performance, the extinction ratio was changed by ˜9 dB for the electrical power of ˜12 mW while the corresponding bending loss was improved by ˜86 dB/cm.
    Japanese Journal of Applied Physics 01/2007; 46. · 1.07 Impact Factor
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    ABSTRACT: A tunable wavelength filter was proposed and demonstrated by using the ultraviolet nanoimprint technique. It consists of a Bragg grating in polymer waveguides and a heating electrode. The creation of the grating was substantially simplified with the introduction of a smart imprint stamp containing a waveguide pattern integrated with the grating pattern. The center wavelength of the filter was successfully tuned by taking advantage of the thermooptic effect in polymers, which was induced by supplying electrical power to the electrode. For the fabricated device, a transmission dip of ∼ 15 dB and a 3 dB bandwidth of 0.8 nm were obtained at the Bragg wavelength of ∼ 1560 nm. The achieved thermooptic tuning rate was ∼ 0.28 nm/mW, while the center wavelength was shifted from 1560 nm to 1558 nm with the electrical power consumption of 7 mW.
    Applied Physics Letters 02/2006; 88(7):071120-071120-3. · 3.79 Impact Factor
  • Ju-Han Song, Do-Hwan Kim, Sang-Shin Lee
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    ABSTRACT: A polymeric ring resonator with variable extinction ratio was fabricated by controlling the ring propagation loss through the thermooptic effect. The extinction ratio was adjusted by ~9 dB for the electrical power of ~12 mW
    01/2006;
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    ABSTRACT: An integrated photonic microwave bandpass filter has been demonstrated incorporating a coherently coupled microring resonator in low-loss polymers. The resonator was designed to have an extremely small bandwidth so that it could be used to selectively pass the optical signal carrying the microwave signal to attain efficient bandpass filtering. The demonstrated device may feature compact size, simple structure, stable operation, possible tuning via the thermooptic effect, and furthermore flexible integration with other electrical/optical devices. We made and tested two resonators with a single ring and double rings, and performed a theoretical fitting of their measured transfer characteristics in order to precisely predict the performance of the resultant microwave filters. For the microwave filter, the bandwidth becomes smaller, the roll-off sharper and the band rejection higher, as the number of the rings increases. Our filter exhibited the center frequency of 10 GHz, the 3-dB bandwidth of 1.0 GHz, the corresponding quality (Q) factor of 10, and the rejection outside of the passband of ˜25 dB.
    Japanese Journal of Applied Physics 01/2006; 45:2576-2579. · 1.07 Impact Factor
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    ABSTRACT: A polymeric microring resonator has been proposed and fabricated using the nanoimprint technique based on a stamp incorporating a smoothing buffer layer. It played a pivotal role in improving the sidewall roughness of the waveguide pattern engraved on the stamp and thus reducing its scattering loss. Eventually, the quality factor of the resonator could be enhanced. It also helped narrow down the gap between the ring and the bus effectively to strengthen the coupling between them. For the fabricated device, the quality factor of ∼103 800 and the extinction ratio of ∼11 dB were achieved at 1550 nm, while the estimated scattering loss was reduced from 38 to 0.0005 dB/mm with the help of the smoothing layer.
    IEEE Photonics Technology Letters 12/2005; · 2.04 Impact Factor
  • [show abstract] [hide abstract]
    ABSTRACT: A polymeric waveguide-type wavelength filter based on a Bragg grating has been proposed and fabricated using the simple nanoimprint technique, for the first time to our knowledge. An ultraviolet transparent stamp with the single-mode waveguide pattern incorporating a surface-relief-type Bragg grating was efficiently developed using laser interference lithography and a specially designed selective dry-etching process. Using this stamp, the device fabrication was substantially simplified involving just a single-step process of imprint followed by polymer spin-coating. The achieved maximum reflection was higher than 25 dB at the center wavelength of 1569 nm. And the 3-dB bandwidth was 0.8 nm for the device length of 1.5 cm.
    IEEE Photonics Technology Letters 11/2005; · 2.04 Impact Factor
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    ABSTRACT: A photonic microwave true-time delay, based on a partially side-polished fiber Bragg grating with heating electrode, is proposed and fabricated. It features continuous voltage-controlled operation, which requires no mechanical perturbation and no moving parts. For a microwave signal carried over an optical signal, the time delay has been obtained by controlling the voltage applied to the electrode and thus adjusting its reflection positions from the fiber grating via the thermo-optic effect. The achieved time delay is about 100 ps with electrical-power consumption of 280 mW. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 44: 35–37, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20539
    Microwave and Optical Technology Letters 01/2005; 44(1):35 - 37. · 0.59 Impact Factor