• Smart Structures and Systems
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• 제9권5호
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• pp.461-472
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• 2012

This study proposes an optics-based active sensing system for continuous monitoring of underground pipelines in nuclear power plants (NPPs). The proposed system generates and measures guided waves using a single laser source and optical cables. First, a tunable laser is used as a common power source for guided wave generation and sensing. This source laser beam is transmitted through an optical fiber, and the fiber is split into two. One of them is used to actuate macro fiber composite (MFC) transducers for guided wave generation, and the other optical fiber is used with fiber Bragg grating (FBG) sensors to measure guided wave responses. The MFC transducers placed along a circumferential direction of a pipe at one end generate longitudinal and flexural modes, and the corresponding responses are measured using FBG sensors instrumented in the same configuration at the other end. The generated guided waves interact with a defect, and this interaction causes changes in response signals. Then, a damage-sensitive feature is extracted from the response signals using the axi-symmetry nature of the measured pitch-catch signals. The feasibility of the proposed system has been examined through a laboratory experiment.

• 한국광학회:학술대회논문집
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• 한국광학회 2001년도 제12회 정기총회 및 01년도 동계학술발표회
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• pp.168-169
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• 2001

1.55 $\mu\textrm{m}$ 파장 대역에서 동작하는 파장가변 단일 주파수 레이저는 WDM 통신 시스템, 광섬유 센서, 분광학 분야에 유용하게 사용될 수 있다. 특히 어븀첨가 광섬유 레이저로 파장가변 단일 주파수 레이저를 구현하면 선폭이 가늘고, 세기 잡음이 작고, 출력 세기가 크다는 장점이 있기 때문에 많은 연구가 있어 왔다. 본 논문에서는 음향광학 대역투과 필터 (acousto-optic tunable bandpass filter, AOTBF)와 광섬유 흡수 격자를 사용하는 선형공진기 형태의 파장가변 단일 주파수 광섬유 레이저에 대해서 제안하고 구현하였다. (중략)

• Current Optics and Photonics
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• 제5권4호
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• pp.384-390
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• 2021

This paper presents a wide-range tunable wavelength-locking technology based on optoelectronic oscillation (OEO) loops for optical fiber sensors and microwave photonics applications, explains the theoretical fundamentals of the design, and demonstrates a method for locking the relative wavelength differences between a leader semiconductor laser and its follower lasers. The input of the OEO loop in the proposed scheme (the relative wavelength difference) determines the radio-frequency (RF) signal frequency of the oscillation output, which is quantized into an injection current signal for feedback to control the wavelength drift of follower lasers so that they follow the wavelength change of the leader laser. The results from a 10-hour continuous experiment in a field environment show that the wavelength-locking accuracy reached ±0.38 GHz with an Allan deviation of 6.1 pm over 2 hours, and the wavelength jitter between the leader and follower lasers was suppressed within 0.01 nm, even though the test equipment was not isolated from vibrations and the temperature was not controlled. Moreover, the tunable range of wavelength locking was maintained from 10 to 17 nm for nonideal electrical devices with limited bandwidth.

• Journal of the Optical Society of Korea
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• 제7권2호
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• pp.97-101
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• 2003

The transmission characteristics of multi-channel long period fiber gratings (LPFGs) in terms of the physical parameters like the separation distance, grating length and number of gratings will be discussed. Their transmission characteristics such as channel spacing, number of channels, loss peak depth, and channel bandwidth can be easily controlled by physical parameters. Based on the experimental results, their applications to optical multiwavelength Raman lasers and optical sensors will be investigated. A multiwavelength Raman fiber ring laser with 9 WDM channels with 100 ㎓ spacing and 19 channels with 50 ㎓ spacing using tunable multi-channel LPFGs will be experimentally demonstrated. The fiber-optic sensing applications with high resolution and sensitivity based on multi-channel LPFGs will be also presented.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.222-227
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• 2003

Recent advances in room-temperature, visible and near-IR diode laser sources for telecommunication, optical data storage applications are enabling combustion diagnostics system based on diode laser absorption spectroscopy. In contrast to some traditional sampling-based gas-sensing instruments, tunable diode laser absorption spectroscopy system is advantageous because of their non-invasive nature, high sensitivity, fast response time and real-time measurement capability. So, combined with fiber-optics and high sensitive detection strategies, compact and portable sensor system arc now appearing for a variety of applications. The objective of this research is to take advantage of distributed feed-back diode laser and measure the $CO_{2}$ concentration (by using direct absorption and wavelength modulation spectroscopy methods). In addition to survey spectra of $CO_{2}$ bands and spectroscopic parameters between 1565 and 1579 run were computed at temperatures between 296 and 1200 K (by using HITRAN 2000 database). It experimentally found out that the features of direct absorption and wavelength modulation spectroscopy methods.

• 한국음향학회지
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• 제30권1호
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• pp.33-41
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• 2011

음압을 감지할 수 있는 Sagnac 간섭계 센서와 온도 및 스트레인을 측정할 수 있는 FBG센서를 결합한 새로운 형태의 하이브리드 광섬유 센서 시스템을 구축하기 위하여 입력 광원인 CW를 TLS로 대체할 필요가 있어 이에 따라 광원의 변화와 맨드릴 재료의 변화에 따른 광섬유 센서의 응답 특성 연구가 필요하게 되었다. 제작된 맨드릴 재료는 PTFE와 PTFE에 카본을 섞어 만든 두 종류로 선택하여 중공 원통형 맨드릴 겉면에 광섬유를 18 m 감아 광섬유 센서로 제작하였다. CW 광원에 대하여 음원의 입력 주파수를 1 kHz~20 kHz까지 바꾸어 가며 트랜스포머 오일이 채워진 유조에서 실험하였다. 또한 FBG와 맨드릴형 광섬유 센서를 결합한 하이브리드형 광섬유 센서 시스템을 구성하고 TLS 광원을 입사광으로 실험하였다. 실험 결과 PTFE 센서의 탐지 크기는 카본 센서 탐지 크기보다 높게 나타났고 맨드릴 재질의 탄성계수 값이 적을수록 커진다는 이론 결과와 잘 일치함을 보였다. CW 광원과 TLS 광원에서 응답한 PTFE 센서의 특성을 주파수별로 상호 비교하여 보면 광원이 CW일 때 보다 TLS일 때 응답 특성이 우수함을 알 수 있었다. 본 연구를 통하여 TLS를 이용한 광섬유 센서는 FBG와의 하이브리드 시스템에 적용 가능하리라 사료된다.

• 센서학회지
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• 제29권1호
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• pp.51-58
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• 2020

In this study, a novel method for sweeping automatic linearization of wavelength swept laser is proposed. Through the test performed on the implemented laser, the linear sweeping is held up well with a 97% decrease in nonlinearity, and 60 nm sweeping range, 1 kHz sweeping frequency, and 8.8 mW average optical power were obtained. The proposed method uses fiber Bragg grating array, optical-electronic conversion circuit, FPGA embedded module, and a LabVIEW program to generate new compensated wave patterns which were applied to the fiber Fabry-Perot tunable filter. Linear sweeping can reduce the cumbersome and time-consuming recalibration process required for nonlinear sweeping. Additionally, the proposed method provides more accurate measurement results for the structure safety monitoring system.

• 한국광학회지
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• 제20권3호
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• pp.189-194
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• 2009

광섬유 일체형으로 된 파브리-페롯 가변 필터를 레이저 공진기에 삽입하고, 1300 nm 대역의 반도체 광 증폭기를 이득매질로 이용하여 링 공진기 형태의 파장 훑음 레이저를 구현하였다. 파장 훑음 레이저의 훑음 주파수에 따른 레이저 출력 특성을 시간영역과 파장영역에서 분석하였다. 파장 훑음 주파수가 증가하면 레이저 출력이 급격하게 줄어들고, 훑음 반치폭도 감소한다. 또한 훑음 주파수 증가에 따라 전방 훑음과 후방 훑음의 광 세기가 비대칭으로 나타나며, 실제 응용 시스템에 적용할 수 있는 제한요소로 작용한다.

• 한국광학회:학술대회논문집
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• 한국광학회 2000년도 제11회 정기총회 및 00년 동계학술발표회 논문집
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• pp.238-239
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• 2000

The optical fibers are an interesting medium for effective tunable optical frequency conversion in the spectral range of UV, Visible, and near-IR through the nonlinear processes. A number of papers for developing the wideband and flat-gain amplifier for the WDM system applications through the combination of EDFA or thulium-doped fluoride fiber amplifier and Raman amplifier, are reported$^{(1)}$ . Even though a variety of papers related to Raman amplifications are published, the amplification with the feedback of the residual pump is not investigated yet. Accordingly, in this paper, we report the characteristics of forward Raman amplification by the simple and double-pass fiber Raman configuration through the feedback of residual pump beam. (omitted)

• 한국광학회지
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• 제11권3호
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• pp.166-170
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• 2000

고리형 광섬유 공전기 안에 반도체 광 증폭기를 삽입하여 1530 nm에서 1570까지 파장을 가변할수 있는 전광 동기 신호 재생 방식을 제안하고 구현하였다. 임의 파형을 갖는 10 Gbps와 30 Gbps 광 펄스열로부터 injection locking 방법에 의해 동기화된 광 펄스열을 재생하였다. 또한, 대신호 시영역 모델링을 이용하여 입력 광 펄스열의 평균 파워의 변화, 섭동에 대한 시스템의 반응을 해석하였다.