• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.16 no.10
• /
• pp.2287-2292
• /
• 2012

In this study, $Co^{60}$ gamma-ray induced loss on Ge-doped single mode (SM) fiber has been measured. Gamma-ray is irradiated for 4 hours at the dose rate of 0.5 kGy/hr, 2 kGy/hr, 8 kGy/hr. Consequently, gamma-ray induced loss based on radiation effects in Ge-doped SM fiber occur significantly. Furthermore, dose rate effect was observed, that dose rate using the same total dose increased higher, then optical fiber loss increased more. Also annealing effect was observed, that the loss after irradiation, increased higher, then the recovery rate of loss was increased. This results are foreseen to be base data in the future radiation-hardened optical fiber study.

• Korean Journal of Optics and Photonics
• /
• v.21 no.5
• /
• pp.185-189
• /
• 2010

We demonstrate a single-frequency wavelength tunable erbium-doped fiber (EDF) ring laser. We used an unpumped-EDF as a saturable-absorber in order to obtain a stable single-frequency with a narrow-linewidth single-polarization mode in the ring cavity. The lasing wavelength was controlled by using bending-induced strain, such as tension and compression strain corresponding to the bending direction, applied to the fiber gratings. The fiber laser exhibited an output power of -1.85 dBm at a wavelength of 1540.72 nm for a pumping power of ~400 mW. An extinction ratio was measured to be more than 60 dB. The proposed tunable fiber laser maintains nearly the same output power while its lasing wavelength is controlled over in a wavelength range of 5 nm.

• ETRI Journal
• /
• v.27 no.5
• /
• pp.551-556
• /
• 2005

We have demonstrated a high-power widely tunable sampled grating distributed Bragg reflector (SGDBR) laser integrated monolithically with a semiconductor optical amplifier (SOA) having a lateral tapered waveguide, which is the first to emit a fiber-coupled output power of more than 10 dBm using a planar buried heterostructure (PBH). The output facet reflectivity of the integrated SOA using a lateral tapered waveguide and two-layer AR coating of $TiO_2\;and\;SiO_2$ was lower than $3\;{\times}\;10^{-4}\;over$ a wide bandwidth of 85 nm. The spectra of 40 channels spaced by 50 GHz within the tuning range of 33 nm were obtained by a precise control of SG and phase control currents. A side-mode suppression ratio of more than 35 dB was obtained in the whole tuning range. Fiber-coupled output power of more than 11 dBm and an output power variation of less than 1 dB were obtained for the whole tuning range.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.25 no.5
• /
• pp.356-361
• /
• 2005

A temperature-compensating double fiber Bragg grating(FBG) sensor having two different FBGs in one fiber line was proposed for real time measurement of mechanical normal strain in structures. Measurement of mechanical strains of the aluminum beam surface by the double FBG sensor was performed under various thermal conditions, and the results were compared with those of electrical resistance strain gage. The FBG sensor fabricated in this study was able to measure accurately the mechanical strains without containing any thermal strain component.

• 한국신재생에너지학회:학술대회논문집
• /
• 2007.06a
• /
• pp.395-399
• /
• 2007

Renewable energy sources such as wind energy is copiously available without any limitation. Wind turbines are used to tap the potential of wind energy which is available in millions of megawatt. Reliability of wind turbine is critical to extract this maximum amount of energy from the wind. We reviewed different techniques, methodologies, and algorithms developed to monitor the performance of wind turbine as well as for an early fault detection to keep away the wind turbines from catastrophic conditions due to sudden breakdowns. To keep the wind turbine in operation, implementation of Condition Monitoring System (CMS) is paramount, and for this purpose ample knowledge of these types of system is mandatory. So, an attempt has been made in this direction to review maximum approaches related to CMS in this piece of writing.

• Journal of Korean Association for Spatial Structures
• /
• v.16 no.1
• /
• pp.85-94
• /
• 2016

In this study, an acceleration sensor that has optical fibers to measure the inclination and acceleration of a structure through contradictory changes in two-component FBG sensors was examined. The proposed method was to ensure precise measurement through the unification of the deformation rate sensor and the angular displacement sensor. A high sensitivity three-axis accelerometer was designed and prepared using this method. To verify the accuracy of the accelerometer, the change in wavelength according to temperature and tension was tested. Then, the change in wavelength of the prepared accelerometer according to the sensor angle, and that of the sensor according to the change in ambient temperature were measured. According to the test results on the FBG-based vibration sensor that was developed using a high-speed vibrator, the range in measurement was 0.7 g or more, wavelength sensitivity, 2150 pm/g or more, and the change in wavelength change, $9.5pm/^{\circ}C$.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.33 no.5
• /
• pp.459-464
• /
• 2013

Structures can be evaluated their health status by allowable loading criteria. These criteria can be determined by the maximum strain. Therefore, in order to detect this maximum strain of structures, fiber optic Bragg grating(FBG) sensor probes are newly designed and fabricated to perform the memorizing detection even if the sensor system is on-and-off. The probe is constructed with an FBG optical fiber embedded in silver epoxy. When the load is applied and removed on the structure, the residual strain remains in the silver epoxy to memorize the maximum strain effect. In this study, a commercial Al-foil bonded FBG sensor probe was tested to investigate the detection feasibility at first. FBG sensor probes with silver epoxy were fabricated as three different sizes. The detection feasibility of maximum strain was studied by doing the tensile tests of CFRP specimens bonded with these FBG sensor probes. It was investigated the sensitivity coefficient defined as the maximum strain divided by the residual strain. The highest sensitivity was 0.078 of the thin probe having the thickness of 2 mm.

• Journal of the Institute of Electronics and Information Engineers
• /
• v.50 no.12
• /
• pp.287-291
• /
• 2013

The low- frequency hydrophone sensor, using the recently developed FBG has an excellent merits which the existing fiber-optic sensor has and also it has an excellent signal sensing effect in the environment of low-frequency(30Hz-300Hz), not to be detected by the PZT sensor. we have the detection of frequency 19KHz right signals when was using more Hopper lenz WDM than $1{\times}3$ optical coupler. furthermore, we can expect the uitilization of low-frequency signal detection to be used for the military purpose and also it can be developed as the high-sensibility multiplexing through the sensor array system.

• Korean Journal of Optics and Photonics
• /
• v.15 no.6
• /
• pp.495-502
• /
• 2004

We proposed an analysis model for a Fabry-Perot cavity constructed with a plane-mirrored optical fiber and a concave-mirrored one. We presented the analysis results calculated by inserting practical values into the equations derived. The coupling loss of the cavity and the mirror loss are the most important parameters in reducing the insertion loss of the filter. In order to build a filter of finesse 600, FSR 57 nm, and insertion loss < 3 dB, the plane-concave cavity using mirrors of loss < 0.09% should be aligned for the coupling loss to be less than 0.1 %.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2013.05a
• /
• pp.732-735
• /
• 2013

In this study, we are measured gamma-ray induced loss on single-mode (SM) fibers from a total of four different manufactures. The $Co^{60}$ gamma-ray source was used in this test. The gamma-ray is irradiated for 2 hours at the dose rate of 0.6 kGy/hr, 1.2 kGy/hr, 2.4 kGy/hr. In test results, We clearly confirm the dose rate effect in different fiber types and evaluate the radiation sensitivity by the change of the radiation-induced loss.