• 조명전기설비학회논문지
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• 제27권12호
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• pp.10-15
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• 2013

In this paper, we propose a Lyot-type optical fiber comb filter based on a polarization-diversity loop structure (PDLS), which has flat-top pass bands and multiwavelength switching capability. Generally, the PDLS can remove the dependency of the filter on input polarization. The proposed filter is composed of a polarization beam splitter, two half-wave plates (HWPs), and two polarization-maintaining fiber loops concatenated with a $60^{\circ}$ offset between their principal axes. By controlling two HWPs, it can operate in a flat-top band mode or a lossy flat-top band mode with an inherent insertion loss of ~3.49dB. In particular, flat-top bands can be interleaved in both modes, which cannot be realized in a Lyot-Sagnac comb filter based on a fiber coupler. Compared with Solc-type high-order comb filters with the same order, the proposed filter shows sharper transition between pass and stop bands.

• 조명전기설비학회논문지
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• 제24권12호
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• pp.33-37
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• 2010

In this paper, we have demonstrated absolute wavelength tuning in an optical fiber comb filter based on a polarization-diversity loop configuration by controlling the current injected into enameled wires wound on polarization-maintaining fibers (PMF's), that is, adjusting Joule heat generated from enameled wires. The proposed fiber comb filter consists of a polarization beam splitter, a half-wave plate, a quarter-wave plate, and PMF's. And we observed wavelength change of spectral dips in transmission spectra of the fabricated filter by varying an input current applied to enameled wires. The absolute wavelength of the filter could be controlled in proportional to the square of the input current with good linearity, and the rate of the wavelength shift with respect to the input current was measured as 36.79[nm/$A^2$].

• 조명전기설비학회논문지
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• 제29권12호
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• pp.1-7
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• 2015

In this paper, we propose a second-order fiber flexible comb filter based on a polarization-diversity loop(PDL). The proposed filter consists of a polarization beam splitter, four half-wave plates(HWPs), and three high birefringence fiber(HBF) segments. In the previous Solc-type second-order filter based on the PDL, HBF segments were fusion-spliced with a fixed angle offset between their principal axes with each other. But, the proposed filter implemented by inserting two HWPs between three HBF segments has a great flexibility in adjusting relative angular difference between the principal axes of two adjacent HBF segments. Owing to this flexibility, second-order transmission spectra, which had a channel spacing of ~0.8nm, could be interleaved by controlling the orientation angles of four HWPs. The output transmission spectra of the proposed filter were theoretically analyzed and experimentally verified.

• 조명전기설비학회논문지
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• 제26권6호
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• pp.8-15
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• 2012

In this paper, we investigated possible optical parameters causing deviation of experimentally observed output spectra from theoretically predicted results in a high-order fiber comb filter based on a polarization-diversity loop configuration. They include wavelength dependency of half-wave plates (HWPs) inserted in the filter for wavelength switching and the modal birefringence of single-mode fibers (SMFs) with which optical components comprising the filter are connected. In order to consider the effect of the modal birefringence of the SMF on a filter performance, it is modeled as a low birefringence fiber with an arbitrary orientation angle and birefringence. It is found from the simulation results that the modal birefringence of SMFs strongly affects the spectral characteristics of the filter and decreases the extinction ratio of the filter, compared with the wavelength dependency of HWPs. In particular, it is also confirmed that the spectral deviation and asymmetric distortions of side-lobes in narrow band transmission spectra result mainly from the modal birefringence of SMFs.

• Current Optics and Photonics
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• 제3권2호
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• pp.111-118
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• 2019

The optical characteristics of a tunable flattened-pass-band fiber comb filter, based on the polarization-diversified loop configuration, are investigated using the $Poincar{\acute{e}}$-sphere representation. In the design process, the spectral flatness is checked quantitatively, and the tunability of the pass band is demonstrated experimentally. Theoretical calculations show that the filter also exhibits desirable dispersion and polarization properties. The orientation angles of rotatable wave plates for the wavelength tunability of the filter are obtained. Furthermore, we elaborate on the multiple angle loci produced by degeneracies through the combination of optical elements within the loop of the filter.

• 조명전기설비학회논문지
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• 제29권10호
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• pp.17-24
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• 2015

In this paper, we investigated the output polarization of a Lyot-type optical fiber comb filter based on a polarization-diversity loop structure. It was found that the output state of polarization (SOP) of the filter made a wavelength-dependent evolution, and the spectral periods of the output SOP variation in flat-top and lossy flat-top band modes were the channel separation of the filter and its half, respectively. For a certain input SOP, the filter could pass or reject specific spectral sections by adding and controlling an output analyzer. In particular, it was theoretically anticipated that the filter with the output polarizer could provide the fine continuous tuning of its pass band center in a wavelength range corresponding to the ${\pm}9.5%$ of channel spacing(0.8nm) when the input SOP was properly adjusted. It is expected that this tuning function can be effectively applied to suppress unwanted spectral portions in modulated optical signals.

• 한국광학회지
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• 제13권6호
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• pp.461-466
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• 2002

파장분할 다중화 시스템의 다중 채널분리 필터가 측면연마 광섬유 결합기를 이용한 빗살필터로 구현됨을 제안하였다 단일 모드 광섬유의 기본모드와 결합하는 상부 평면 도파로의 모드가 고차일수록 광 전력전달 효율은 낮아지는데, 두 도파로 사이 에 중간 결합층을 삽입함으로서 개선시킬 수 있고 최적화 조건에서 20dB 이상의 채널간 소멸비를 얻을 수 있음을 보였다. 200fm두께의 리튬나오베이트를 상부 평면 도파로로 적용한 경우 4m의 채널간격을 가지는 빗살필터 특성을 얻었으며, 중간 결합층의 두께가 1 Um일 때 굴절률이 1.52-1.53 범위에서 최대 광 전력전달이 일어남을 관측하였고 빔 전파 방법을 이용하여 계산한 결과와 거의 일치함을 보였다.

• 한국광학회:학술대회논문집
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• 한국광학회 2002년도 하계학술발표회
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• pp.192-193
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• 2002

지금까지 측면이 코어 가까이 연마된 잔일모드 광섬유와 평면 도파로 사이의 광결합을 이용한 소자들이 많이 연구되고 있다. 이를 이용한 소자들로는 광필터, 광변조기, 광스위치, 굴절계, 편광기 등이 있으며 최근에는 파장분할다중화(WDM)에서 인접채널간의 채널분리를 위한 소자로서 빗살필터의 연구 또한 활발히 이루어지고 있다. 이에 본 논문에서는 측면이 코어 가까이 연마된 단일모드 광섬유와 평면도파로 사이의 광결합을 이용한 빗살필터를 제작하였으며 열광학 효과를 이용하여 파장 가변 빗살 필터를 구현해 보았다. (중략)

• 한국광학회:학술대회논문집
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• 한국광학회 2002년도 제13회 정기총회 및 2002년도 동계학술발표회
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• pp.182-183
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• 2002

• 한국광학회지
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• 제15권1호
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• pp.28-33
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• 2004

상부 도파로와 중간 결합층이 적층된 단일모드 광섬유를 기본구조로 하는 측면 연마 광섬유 결합기를 상호 광 결합이 일어나는 영역을 다층막 도파로로 등가화하여 결합 효율을 해석하였다. 다층막 구조에서 중간 결합층의 유무에 따른 반사도를 계산하여 상부 도파로의 굴절률의 함수로 도시하였고, 상부 도파로의 굴절률이 광섬유 코어의 굴절률보다 클 경우 중간 결합층의 조건에 의해서 광 결합이 증가되어짐을 보였다. 리튬나오베이트를 상부 도파로로 가지는 결합기의 실험결과를 톤해 이론적 해석의 타당함을 보였고 계산 결과와 일치함을 보였다.