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Jeong, Jun Hyeok,Choi, Sungwook,Lee, Seul-Lee,Jeong, Sun Jae,Christian, Nouaze Joseph,Kim, Jihoon,Kang, Hyun Wook,Nam, Seung Yun,Oh, Junghwan,Lee, Yong Wook American Scientific Publishers 2017 Journal of nanoscience and nanotechnology Vol.17 No.11
<P>In this paper, we demonstrated a polarimetric fiber vibration sensor based on a polarization-diversified loop (PDL) with short polarization-maintaining photonic crystal fiber (PM-PCF) as a sensor head and investigated the dependence of its frequency response on the sensing fiber length. The fabricated PM-PCF vibration sensor is composed of a polarization beam splitter for forming the PDL, PM-PCF as a sensor head, and two wave plates such as a quarter-wave plate and a half-wave plate. A laser diode and a photodetector were also utilized for intensity-based vibration measurement. In particular, two kinds of PM-PCF segments with fiber lengths of similar to 6 and similar to 10 cm were employed to explore the effect of the sensor head length on the sensor frequency response. The frequency response was examined over 1-3000 Hz using a piezoelectric transducer that can apply single-frequency vibration to the sensor head. Every measured frequency response showed a resonance peak at each sensor head length, and cut-off frequencies were measured as similar to 1240 and similar to 794 Hz for PM-PCF lengths of similar to 6 and similar to 10 cm, respectively. That is, a higher cut-off frequency was obtained in a shorter sensor head length. Moreover, it was observed that the sensor head length dependence of the frequency response was maximized in a frequency range from 1000 to 2400 Hz and faded away beyond 2400 Hz. From the measurement results, it is concluded that the short sensor head can provide higher normalized sensitivity, i.e., better signal to noise ratio, at frequencies higher than the resonance frequency, let alone convenience of installation and in sensitiveness to external perturbations in a PDL-based PM-PCF vibration sensor. The phase shift per unit strain and the minimum detectable strain perturbation, regarded as sensitivity and resolution, were measured as similar to 0.377 mrad/mu epsilon and similar to 0.16 n epsilon/Hz(1/2) at 2000 Hz for similar to 6-cm-long PM-PCF, respectively.</P>
Transmission-Type Polarization-Insensitive Polarization Plane Excitation
Ryu, Uh-Chan,Jo, Songhyun,Choi, Sungwook,Lee, Seul-Lee,Jeong, Jun Hyeok,Jeong, Sun Jae,Christian, Nouaze Joseph,Kim, Jihoon,Kang, Hyun Wook,Nam, Seung Yun American Scientific Publishers 2017 Journal of nanoscience and nanotechnology Vol.17 No.11
<P>In optical communications, light polarization of optical signals is randomly varied during the signal transmission, and system performances can be deteriorated by polarization-dependent loss and gain or polarization-mode dispersion. Polarization scrambling that actively changes the state of polarization (SOP) using a polarization modulation method is often utilized to reduce polarization-related impairments. To make use of polarization-dependent routing devices during the transmission, however, scrambled or depolarized light should be polarized and then scrambled again after passing through the routing devices. Here, we suggest a novel polarization-insensitive polarization plane excitation scheme that enables transmission-type polarization-dependent routing elements to exploit their polarization-dependent routing functions irrespective of the SOP and degree of polarization of an input beam. The proposed scheme is composed of a polarization beam splitter (PBS) for a polarization-diversified loop, two half-wave plates (HWPs) and two 45 degrees Faraday rotators (FRs) for irreciprocal polarization transformation. We could make unpolarized light selectively excite one of the two principal axes of a polarization-dependent element using the polarization decomposition/superposition property of the polarization-diversified loop and the irreciprocal nature of optical Faraday rotation. The operation principle of the proposed scheme is explained using the polarization evolution of light passing through the PBS, FRs, and HWPs that comprise the scheme. The theoretically predicted operation was experimentally verified by utilizing a long-period fiber grating (LPFG) inscribed on high birefringence fiber (HBF) as a polarization-dependent element. The LPFG written on HBF has polarization-dependent loss bands at two resonance wavelengths. By controlling the four waveplates, one of the two loss bands of the LPFG could be selected even for unpolarized input light.</P>
Second-order fiber interleaving filter based on polarization-diversified loop
Park, Kyongsoo,Choi, Sungwook,Lee, Seul-Lee,Jeong, Jun Hyeok,Jeong, Sun Jae,Christian, Nouaze Joseph,Kim, Min Seok,Kim, Jihoon,Kang, Hyun Wook,Nam, Seung Yun,Oh, Junghwan,Lee, Yong Wook SPIE - International Society for Optical Engineeri 2017 Optical engineering Vol.56 No.6
Wavelength-Switchable Erbium-Doped Fiber Ring Laser Using Inline Fiber Bragg Grating Filter
Lee, Seul-Lee,Park, Kyongsoo,Jo, Songhyun,Choi, Sungwook,Jeong, Jun Hyeok,Jeong, Sun Jae,Christian, Nouaze Joseph,Kim, Jihoon,Lee, Yong Wook American Scientific Publishers 2017 Journal of nanoscience and nanotechnology Vol.17 No.10
<P>Here, we propose a wavelength-switchable erbium-doped fiber (EDF) ring laser by harnessing the unique switching feature of an inline fiber Bragg grating (FBG) filter based on a polarization-diversified loop. The inline filter consists of a four-port polarization beam splitter, three quarter-wave plates (QWPs), and two FBGs with different Bragg wavelengths. By adjusting the orientation angles of the three QWPs, this inline filter can select one of the two different resonances of the two FBGs. The proposed laser is composed of EDF pumped by a 980 nm laser diode, a wavelength-division multiplexing coupler, an optical isolator, a 3 dB optical coupler, and the inline FBG filter. At a special combination of the orientation angles of the three QWPs, one of the two reflection spectra of two FBGs could be chosen and thus the lasing wavelength of the proposed laser, which corresponds to the Bragg wavelength of the selected FBG, could be switched by adjusting the QWP angles. The fabricated ring laser accomplished stable and uniform lasing at each Bragg wavelength or switching operation between two wavelengths at proper QWP angle sets.</P>