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편광상이 고리 기반 광섬유 다파장 필터의 입력 편광으로 제어되는 채널 간격 스위칭에 대한 연구
이슬이(Seul-Lee Lee),이용욱(Yong Wook Lee) 한국조명·전기설비학회 2020 조명·전기설비학회논문지 Vol.34 No.2
In this paper, we propose an optical fiber multiwavelength filter based on a polarization-diversified loop (PDL), whose channel spacings (CSs) can be controlled by its input state of polarization (SOP). The PDL-based filter consists of a polarization beam splitter, three half-wave plates (HWPs), a Faraday rotator (FR), and two polarization-maintaining fiber (PMF) segments with equal birefringence and different lengths. At proper orientation angle sets (θ<SUB>h1</SUB>, θ<SUB>h2</SUB>, θ<SUB>h3</SUB>) of the three HWPs, the proposed filter can have its polarization-dependent transmittance, offering the CS-switchable operation realized by switching between two orthogonal input SOPs of linear horizontal polarization (LHP) and linear vertical polarization (LVP). In particular, at a fixed input SOP, a half-period wavelength switching operation, i.e., an interleaving operation, can also be implemented by controlling only one HWP angle (θ<SUB>h1</SUB> or θ<SUB>h3</SUB>). Theoretical prediction was verified by experiments. For orthogonal input SOPs of LHP and LVP, the fabricated PDL-based filter could provide transmission spectra with CSs of ∼0.9 and ∼0.3nm or vice versa at appropriate sets of (θ<SUB>h1</SUB><SUB></SUB>, θ<SUB>h2</SUB>, θ<SUB>h3</SUB>), respectively, and each of the transmission spectra could be interleaved by adjusting only θ<SUB>h1</SUB> or θ<SUB>h3</SUB>.
병원성 박테리아 검출용 헤테로다인 복조 기반 광섬유 바이오 센서
이슬이(Seul-Lee Lee),고영종(Youngjong Ko),김장현(Jang Hyun Kim),강현욱(Hyun Wook Kang),이용욱(Yong Wook Lee) 한국조명·전기설비학회 2020 조명·전기설비학회논문지 Vol.34 No.11
In this paper, we demonstrated an optical fiber biosensor based on heterodyne demodulation to detect five pathogenic bacteria species forming biofilms, such as Escherichia Coli, Vibrio Vulnificus, Pseudomonas Aeruginosa, Staphylococcus Aureus, and Streptococcus Iniae, with their fluorescence characteristics. The proposed sensor detects the fluorescence of the five bacteria species with the intrinsic fluorescence characteristics of amino acid tryptophan, whose excitation and emission wavelengths are 280 and 350 nm, respectively. The fabricated sensor consists of an UV light source for excitation of bacteria, a high sensitivity detector for detection of fluorescence signals emitted from the excited bacteria, and a lock-in amplifier for amplification of the detected fluorescence signals. The lock-in amplifier can remove various noise signals coupled with the desired fluorescence signals and amplify the magnitude of the desired signal through the heterodyne demodulation technique. This signal processing technique enables the detection of the weak picowatt (pW) fluorescence signals. Consequently, it is concluded that our sensor can successfully detect the intensity of the fluorescence signal emitted from five pathogenic bacteria species whose concentration lies within 10² to 10<SUP>7</SUP> CFU/ml.
직교 입력 편광에 따른 위상 천이 장주기 격자의 pH 및 온도 응답에 관한 연구
이슬이(Seul-Lee Lee),이용욱(Yong Wook Lee) 한국조명·전기설비학회 2021 조명·전기설비학회논문지 Vol.35 No.3
In this paper, we demonstrated an optical fiber sensor based on a phase-shifted long-period fiber gratin g (PS-LPFG) that could realize simultaneous measurement of surrounding pH and temperature variations. The PS-LPFG composed of a grating-free fiber region (GFFR) in the middle of two identical LPFGs was fabricated on high-birefringence fiber (HBF) with CO₂ laser pulses. In addition, a π phase shift formed by setting the length of the GFFR as half of the grating period of an LPFG allows a transmission dip to split into two attenuation bands at two different resonance wavelengths. Since HBF can preserve a linear state of polarization (SOP) if the input SOP is aligned with one of its two principal axes (fast or slow axis), a PS-LPFG inscribed on HBF (HB-PS-LPFG) can create two different transmission spectra for two orthogonal input SOPs, i.e., linear horizontal polarization (LHP) and linear vertical polarization (LVP). To investigate pH and temperature responses of the fabricated HB-PS-LPFG, the dip wavelength separation bet ween two different attenuation bands was used as a sensor indicator for an LHP or LVP input SOP. Consequently, pH- and temperature-induced wavelength variations of the two sensor indicators showed linear and independent spectral responses to both pH and temperature variations in a pH range from 3 to 11 and a temperature range from 25 to 65 °C. With these unique pH or temperature responses of the two sensor indicators, the fabricated sensor could realize simultaneous measurement of pH and temperature.