Gil Hwan Kim

Simultaneous independent measurement of strain and temperature based on long-period fiber gratings inscribed in holey fibers depending on air-hole size.

We propose and experimentally demonstrate a simple and flexible scheme for the simultaneous measurement of strain and temperature using long-period fiber gratings (LPFGs) based on versatile holey fibers (HFs) with different air-hole sizes. The strongly resonant LPFGs (as much as approximately 24 dB) can be successfully achieved. The LPFGs inscribed in the HFs have similar temperature sensitivities regardless of air-hole size because of the same material composition. The strain sensitivities of the LPFGs, however, are different, since holey fibers have different cross-sectional areas depending on the air-hole size. The strain sensitivities of the HF-based LPFGs are enhanced by a factor larger than 2 as the air-hole size increases.

Transmission characteristics of fiber Bragg gratings written in holey fibers corresponding to air-hole size and their application

Transmission characteristics of fiber Bragg gratings (FBGs) written in holey fibers with different air-hole size are investigated. The cladding mode coupling of FBGs inscribed on holey fibers is remarkably suppressed due to air holes inside of the silica cladding. The wavelength spacing between the main peak due to the core mode coupling and side peak due to the first-order cladding mode coupling increases as the air-hole size increases because the reduction of the effective index of cladding mode depends on the air-hole size within the fiber. The strain and temperature sensitivities of FBGs are also investigated corresponding to air-hole size of holey fibers. The temperature sensitivities of holey-fiber-based FBGs are similar regardless of air-hole size of holey fibers (~1.9%), but their strain sensitivities are enhanced (~28.4%) as the air-hole size increases

A Novel Birefringent Photonic Crystal Fiber and Its Application to Curvature Measurement

We demonstrate a curvature sensor with a newly designed photonic crystal fiber of high birefringence (Hi-Bi PCF). The proposed PCF has two large air holes in the outer cladding region that give rise to core ellipticity during the fabrication process. The curvature sensor is based on the PCF Sagnac interferometer, the output spectrum shift of which provides information on the PCF curvature. It turns out that the curvature sensitivity depends on the bending directions with respect to the large-air-hole alignment. For the two orthogonal bending directions, the curvature sensitivities near 1480 nm are -1.87 nm/m-1 (parallel to the axis of the two large air holes) and 1.24 nm/m-1 (perpendicular to the axis of the two large air holes), respectively, and are also insensitive to environmental temperature variation. The proposed curvature sensor may be useful in thin structural deflection measurement.

A novel fabrication method of versatile holey fibers with low bending loss and their optical characteristics

We propose a novel fabrication method of holey fibers with different size, pitch, and shape of air holes. By expanding a Ge-doped preform with air holes at high temperature, the size and shape of air holes can be readily modified

Characteristics of in-fiber Mach-Zehnder type interferometer in hollow-core photonic bandgap fiber

Mach-Zehnder interferometer based on off-set splicing technique of HC-PBGF and SMFs was fabricated. Interference fringe is observed with a maximum interferometric contrast of better than 12dB. We measured the strain, temperature, and refractive index response of the interferometer based on HC-PBGF.

Effect of air hole size on transmission characteristics of fiber Bragg gratings written in holey fiber

We discuss effect of air hole size on transmission characteristics of fiber Bragg gratings written in holey fiber. The strain and temperature sensitivities of grating strongly depend on the air hole size of holey fibers

Polarization characteristics of highly birefringent photonic crystal fiber with squeezed lattice

We fabricated the highly birefringent photonic crystal fibe with squeezed lattice. The polarization dependent loss (PDL), differential group delay (DGD) and modal birefringence of fabricated fiber at 1550nm were measured to be 0.11dB, 2.18ps and 2.29×10−4, respectively.

Fiber Interferometers Based on Low Loss Fusion Splicing of Photonic Crystal Fibers

본 논문에서는 포토닉 밴드갭 광섬유(Photonic Bandgap Fiber: PBGF) 사이에 중공광섬유(Hollow Optical Fiber: HOF)를 융착접속시켜 만든 광섬유 간섭계와 넓은 모드 면적을 가지는 광자결정 광섬유 (Large Mode Area-Photonic Crystal Fiber: LMA-PCF) 사이에 HOF를 융착접속시켜 만든 광섬유 간섭계의 온도 및 스트레인에 대한 광학적 특성을 분석하였다 . PBGF 또는 LMA-PCF와 HOF의 융착접속시 광섬유내 공기구멍을 최대한 유지하도록 융착조건을 최적화하여 접속 손실을 줄였다 . PBGF와 HOF로 구성된 광섬유 간섭계의 온도 및 스트레인에 대한 민감도는 각각 15.4 pm/℃와 0.24 pm/μe으로 측정되었으며, LMA-PCF와 HOF로 구성된 광섬유 간섭계의 온도 및 스트레인에 대한 민감도는 각각 17.4 pm/℃와 0.2 pm/μe으로 측정되었다.

Temperature-insenstive curvature sensor using a Hi-Bi photonic crystal fiber based Sagnac loop interferometer

We propose and demonstrate a Sagnac loop interferometer composed of a novel Hi-Bi photonic crystal fiber with two large air holes in the outer cladding region as a curvature sensor. It has been shown that it has an insensitivity to temperature and a curvature sensitivity of 0.159 nm/m−1 when the fiber is bent in the slow axis.

Investigation of curvature sensitivity of arc-induced long-period fiber gratings inscribed in a pure silica photonic crystal fiber with two large air holes in the outer cladding region

An arc-induced long period grating within a photonic crystal fiber with two large-diameter air holes in the cladding region has been shown as a novel curvature sensor. Due to its panda structure, the sensitivity to curvature has been shown to be angular dependent.