• 전기전자학회논문지
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• 제19권1호
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• pp.27-32
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• 2015

A flexible and tunable microwave photonic filter based on adjustable optical frequency comb source is demonstrated. We use a combination of a dual parallel Mach Zehnder modulator and an intensity modulator to generate fifteen comb lines with proper weights to implement a desired filter. The optical comb weights, corresponding to the tap coefficients of the filter, are flexibly changed by adjusting the operation parameters of the modulators. The achieved bandwidth and stopband attenuation of the tunable filter are 0.7 GHz and 20 dB, respectively. In addition, we overcome the undesired low frequency suppression appeared in a conventional scheme by applying a dual parallel Mach Zehnder modulator for single sideband suppressed carrier modulation.

• Current Optics and Photonics
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• 제2권1호
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• pp.34-38
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• 2018

An X-band microwave photonic (MWP) filter using switch-based fiber-optic delay lines has been proposed and experimentally demonstrated. It is composed of two electro-optic modulators (EOMs) and $2{\times}2$ optical MEMS-switch-based fiber-optic delay lines. By changing time-delay difference and coefficients of each wavelength signal by using fiber-optic delay lines and an electro-optic modulator, respectively, a bandpass filter or a notch filter can be implemented. For an X-band MWP filter with four channel elements, fiber-optic delay lines with the unit time-delay of 50 ps have been experimentally realized and the frequency responses corresponding to the time-delays has been measured. The measured frequency response error at center frequency and the time-delay difference error were 180 MHz at 10 GHz and 3.2 ps, respectively, when the fiber-optic delay line has the time-delay difference of 50 ps.

• Current Optics and Photonics
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• 제2권6호
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• pp.563-567
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• 2018

We propose and experimentally demonstrate a simple tunable photonic microwave band-pass filter with high resolution using a reflective semiconductor optical amplifier (RSOA) and an optical time-delay line. The RSOA is used as a gain medium for generating cross-gain modulation (XGM) effect as well as an optical source. The optical source provides narrow spectral width by self-injection locking the RSOA in conjunction with a partial reflection filter with specific center wavelength. Then, when the RSOA is operated in the saturation region and the modulated recursive signal is injected into the RSOA, the recursive signal is inversely copied to the injection locked optical source due to the XGM effect. Also, the tunability of the passband of the proposed microwave filter is shown by controlling an optical time-delay line in a recursive loop.

• 한국전자파학회논문지
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• 제26권2호
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• pp.213-217
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• 2015

본 논문에서는 밴드 패스 필터 및 노치 필터로의 용도 변환이 가능하고, 대역폭 변화가 용이한 새로운 구조의 MWP 필터를 제안하였다. 인접 채널의 단위 시간지연 차이가 50 ps인 $4{\times}2$ 광섬유 지연선로 행렬로 구성된 MWP 필터를 제작하였고, 각 채널의 시간 지연 및 MWP 필터의 주파수 응답 등의 특성을 측정하였다. RF 변조 광 신호의 시간 지연 차이와 계수를 변화시킴으로써 20 GHz와 6.67 GHz의 FSR 변화 특성을 확인하였다.

• 한국광학회지
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• 제16권3호
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• pp.266-274
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• 2005

본 논문에서는 2차원 광결정 공진기의 결합을 통해 WDM시스템에 적합한 특성을 가지는 공진 필터를 설계하였다. 공진기간의 결합에 있어서 고려해야 할 요소를 시영역에서의 모드 결합이론(coupling modes in time)을 적용하여 이론적으로 분석하였으며, 전자회로 등가화를 이용하여 쉽게 그 요소를 결정할 수 있음을 보였다. 공진기 결합에 있어서 공진기 간의 간격에 따른 위상천이에 대해서 외부감쇄에 의한 Q-factor를 조정함으로써 보상할 수 있음을 확인하였고, 2차원 광결정 점결함 공진기를 이용하여 500GHz의 대역폭을 가지며 통과대역에서 0.5 dB 리플을 가지는 3차 Chebyshev 대역 통과 필터를 설계하였다.

• 한국전자파학회논문지
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• 제12권4호
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• pp.611-621
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• 2001

본 논문에서는 포토닉 밴드갭(PBG)의 결합모드(defect-mode)를 이용한 대역통과 여파기를 구현하는 방법에 대해 연구하였다. PBG 구조를 구현하기위하여 마이크로스트립 라인의폭을 달리하면 PBG 셀(cell)을 형성한 후, 이들 셀들을 주기적으로 배열하였으며, PBG 구조 일부분의 주기를 변화시킬 경우에 발생하는 결함모드를 이용하여 저지대역 내에서 통과대역을 구현하였다. 또한, 집중정수소자(Iumped-element)를 이용하여 PBG 구조의 등가회를 구현하였다.

• Current Optics and Photonics
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• 제2권1호
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• pp.27-33
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• 2018

We report the physical implementation of a tunable photonic microwave delay line filter based on injection locking of a single Fabry-Perot laser diode (FP-LD) to a reflective semiconductor optical amplifier (RSOA). The laser generates equally spaced multiple wavelengths and a single tapped-delay line can be obtained with a dispersive single mode fiber. The filter frequency response depends on the wavelength spacing and can be tuned by the temperature of the FP-LD varying lasing wavelength. For amplitude control of the wavelengths, we use gain saturation of the RSOA and the offset between the peak wavelengths of the FP-LD and the RSOA to decrease the amplitude difference in the wavelengths. From the temperature change of total $15^{\circ}C$, the filter, consisting of four flat wavelengths and two wavelengths with slightly lower amplitudes on both sides, has shown tunability of about 390 MHz.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2008년도 International Meeting on Information Display
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• pp.1656-1659
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• 2008

The reflective type color filter for the liquid crystal displays (LCD) was produced using cholesteric liquid crystal monomers whose phase is characterized by the unique optical features of selective reflection. Periodic micrometer scale hemi-spherical photoresist (PR) patterns were formed on glass substrates by thermal reflow method after photolithography. Cholesteric color filter films for red, green and blue light reflections were then produced and the viewing angle dependence was investigated and compared with that of reflected light on the non-patterned substrates.

• 한국광학회지
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• 제17권5호
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• pp.475-479
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• 2006

본 논문에서는 폴리머 링 광공진기를 이용하여 집적광학형 K-band용 마이크로웨이브 대역통과 필터를 제안하고 구현하였다. 특히, 열광학 효과를 이용하여 광공진기의 공진파장을 변화시킴으로써 대역통과 필터의 전달특성을 전기적으로 조절하였다. 측정된 필터의 중심주파수는 20 GHz, 소멸비는 약 15 dB, 3 dB 대역폭은 2 GHz, 그리고 Q값은 10이었다. 마이크로웨이브 필터에서 중심주파수의 출력특성을 27 dB범위 내에서 ${\sim}6.7dB/mW$로 조절할 수 있었다. 전기적으로 조절되는 전달특성을 갖는 이 필터는 마이크로웨이브스위치 등으로 응용할 수 있을 것으로 기대된다.

• 한국광학회:학술대회논문집
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• 한국광학회 2008년도 하계학술발표회 논문집
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• pp.139-140
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• 2008

We demonstrate a novel acousto-optic filter using a two-mode photonic crystal fiber. Thanks to endless two-mode operation of the fiber, single notch over a whole spectrum is obtained with tuning range of> 1000 nm.