• International Journal of Aeronautical and Space Sciences
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• v.17 no.1
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• pp.37-44
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• 2016

Optical fiber temperature sensing systems have incomparable advantages over traditional electrical-cable-based monitoring systems. However, the fiber optic interrogators and sensors have often been rejected as a temperature monitoring technology in real-world industrial applications because of high cost and over-specification. This study proposes a multiplexed fiber optic temperature monitoring sensor system using an economical Optical Time-Domain Reflectometer (OTDR) and Hard-Polymer-Clad Fiber (HPCF). HPCF is a special optical fiber in which a hard polymer cladding made of fluoroacrylate acts as a protective coating for an inner silica core. An OTDR is an optical loss measurement system that provides optical loss and event distance measurement in real time. A temperature sensor array with the five sensor nodes at 10-m interval was economically and quickly made by locally stripping HPCF clad through photo-thermal and photo-chemical processes using a continuous/pulse hybrid-mode laser. The exposed cores created backscattering signals in the OTDR attenuation trace. It was demonstrated that the backscattering peaks were independently sensitive to temperature variation. Since the 1.5-mm-long exposed core showed a 5-m-wide backscattering peak, the OTDR with a spatial resolution of 40 mm allows for making a sensor node at every 5 m for independent multiplexing. The performance of the sensor node included an operating range of up to $120^{\circ}C$, a resolution of $0.59^{\circ}C$, and a temperature sensitivity of $-0.00967dB/^{\circ}C$. Temperature monitoring errors in the environment tests stood at $0.76^{\circ}C$ and $0.36^{\circ}C$ under the temperature variation of the unstrapped fiber region and the vibration of the sensor node. The small sensitivities to the environment and the economic feasibility of the highly multiplexed HPCF temperature monitoring sensor system will be important advantages for use as system-integrated temperature sensors.

• Photonics industry news
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• s.34
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• pp.12-17
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• 2006

대만은 광산업 분야를 OE(Optoelectronics Components, FPD(Flat Panel Display), Optical Storage, Optical Lens Components & Laser Applications, OFC(Optical Fiber Communications, Optical Input & Output Devices 등 6개 대분류로 나누고 있으며 수년간 중점적으로 육성해 온 분야는 OE 및 FPD와 관련이 큰 LED 분야이다.

• Journal of the Optical Society of Korea
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• v.17 no.2
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• pp.177-181
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• 2013

We present an all-fiberized power-scalable, sub-nanosecond mode-locked laser based on a frequency-shifted-feedback ring cavity comprised of an erbium-doped fiber, a downshifting acousto-optic modulator (AOM), and a bandpass filter (BPF). With the aid of the frequency-shifted feedback mechanism provided by the AOM and the narrow filter bandwidth of 0.45 nm, we generate self-starting, mode-locked optical pulses with a spectral bandwidth of ~0.098 nm and a pulsewidth of 432 to 536 ps. In particular, the output power is readily scalable with pump power while keeping the temporal shape and spectral bandwidth. This is obtained via the consolidation of bound pulse modes circulating at the fundamental repetition rate of the cavity. In fact, the consolidated pulses form a single-entity envelope of asymmetric Gaussian shape where no discrete internal pulses are perceived. This result highlights that the inclusion of the narrow BPF into the cavity is crucial to achieving the consolidated pulses.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.38 no.3
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• pp.174-184
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• 2001

Wavelength tunable fiber ring laser can be tuned by causing a resonance on the optical path having the least loss which is controlled by a polarization adjustment. It is observed that lasing wavelengths having 1 nm FSR(Free Spectral Range) can be tuned over the range of 1540~1560 nm when a polarization controller and an intra-cavity polarizer are adjusted. The tuning mechanism can be expected by analyzing the characteristics of the laser output using an optical path model and the concept of a birefringence loss. It is found that the constructive interference between longitudinal modes of different optical paths may cause wavelength tuning in the fiber ring laser.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.1
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• pp.139-146
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• 2001

This paper presents a study on heat transfer and residual distortion analysis of laser welded EDFA(Erbium Doped Fiber Amplifier) LD(Laser Diode) Pump using the finite element method. In the production process of LD Pump in light-wave communication system, ferrule and saddle are welded by Nd-YAG laser. These parts experience thermal and mechanical effect during heating and cooling cycle with the laser welding. Thus distortion happens in the laser-welded packaging, and it makes an error in detecting the light signal translate through optical fiber in LD Pump. The amount of final displacement produced by the laser welding is predicted using the finite element method. And the optimal shape of saddle is proposed with the results of numerical analyses to minimize the displacement.

• Current Optics and Photonics
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• v.7 no.6
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• pp.708-713
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• 2023

A robust all-fiber nonlinear amplifying loop-mirror-based mode-locked femtosecond laser is demonstrated. Power-dependent nonlinear phase shift in a Sagnac loop enables stable and power-efficient mode-locking working as an artificial saturable absorber. The pump power is adjusted to achieve the lowest intensity noise for stable long-term operation. The minimum pump power for mode-locking is 180 mW, and the optimal pump power is 300 mW. The lowest integrated root-mean-square relative intensity noise of a free-running mode-locked laser is 0.009% [integration bandwidth: 1 Hz-10 MHz]. The long-term repetition-rate instability of a free-running mode-locked laser is 10^-7 over 1,000 s averaging time. The repetition-rate phase noise scaled at 10-GHz carrier is -122 dBc/Hz at 10 kHz Fourier frequency. The demonstrated method can be applied as a seed source in high-precision real-time mid-infrared molecular spectroscopy.

• Journal of the Optical Society of Korea
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• v.20 no.6
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• pp.716-721
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• 2016

A single-and dual-wavelength switchable polarized Yb-doped double-clad fiber laser around 1120 nm based on a pair of fiber Bragg gratings (FBGs) is demonstrated. The polarization-maintaining (PM) linear cavity is composed of a double clad PM Yb-doped fiber (YDF) and a pair of PM FBGs. The laser can operate in stable dual-wavelength or wavelength-switching modes due to the polarization hole burning (PHB) and the spatial hole burning (SHB) enhanced by the PM linear cavity. In dual-wavelength operation, the two orthogonally polarized wavelengths are centered at 1118.912 nm and 1119.152 nm, with an interval of 0.24 nm and a signal to noise ratio (SNR) of 35 dB. The maximum output power is 14.67 W when the launched LD pump is 24 W corresponding to an optical efficiency of 61.1%. The lasing lines switchover may be realized by adjusting the polarization controller (PC) fitted in the cavity. The two single-wavelengths are 1118.912 nm and 1119.152 nm. When the injected LD pump is 24 W, the highest output powers are 7.68 W and 8.64 W corresponding to optical efficiencies of 32% and 36% respectively. The spectral linewidth of the lasing lines are 0.075 nm and 0.07 nm, and the average numerical values of PER aredB and 19.9 dB, respectively.

• Korean Journal of Optics and Photonics
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• v.32 no.4
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• pp.187-194
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• 2021

This paper presents a study of laser output characteristics. We fabricated a MOPA (master oscillator power amplifier)-type high-power, narrowbandwidth fiber laser with a bidirectional pumping configuration in its main amplifier. As signal beams, light sources with bandwidths of 3 GHz and 10 GHz-phase-modulated through a PRBS (pseudo-random binary sequence)-were used interchangeably. Furthermore, the characteristics of the SBS (stimulated Brillouin scattering) were analyzed using a signal beam with 3 GHz bandwidth, by adjusting the forward to backward pumppower ratio. Moreover, the characteristics of the transverse mode instability were analyzed by adjusting the forward to backward pump-power ratio, using a signal beam with 10-GHz bandwidth. Finally, the output power from 10 GHz bandwidth was amplified to more than 1 kW using a forward to backward pump-power ratio of 1.6. The beam quality M² was measured to be approximately 1.36, and the optical-to-optical efficiency was 80% at maximum output power.

• Korean Journal of Optics and Photonics
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• v.26 no.6
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• pp.306-311
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• 2015

We report the characteristics of a single-wavelength-tunable fiber laser using a polymer waveguide Bragg grating (PWBG) wavelength filter. The output of the laser depends on environmental conditions, such as temperature and polarization states in the laser cavity. Wavelength tuning can be achieved, about 16.29 nm from 1548.24 nm to 1531.95 nm, according to the electric power applied to the PWBG wavelength filter. The achieved efficiency slope is about -0.16 nm/mW. A side-mode suppression ratio (SMSR) of more than 35 dB can be obtained by adjusting the polarization state in the laser cavity. A stable wavelength-tunable fiber laser can be achieved using the PWBG wavelength filter with a TEC module and a polarization-maintaining fiber.

• Proceedings of the Optical Society of Korea Conference
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• 2001.08a
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• pp.160-161
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• 2001

A diode laser system has been developed for the refractory glaucoma therapy. The diode lasers have merits in clinical usage including reduction of beam dispersion, higher absorption such as in melanin pigment, and lower complication in treatment. We present the system specification of laser diodes in 810mm with 3W power, which is delivered into the optical fiber core of 600${\mu}{\textrm}{m}$.