• Korean Journal of Optics and Photonics
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• v.10 no.3
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• pp.243-247
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• 1999

We report the generation of inherently stable, high-speed, nearly transform-limited, optical pulses by chirped pulse compression, in which sinusoidally driven phase modulator generates frequency chirped pulses that are subsequently compressed by a dispersive optical fiber. Experimental results show that $sech^2$ shape pulses with a pulse width of ~14 ps and a time bandwidth product of ~0.34 are successfully generated at 10 GHz repetition rate. In contrast to other methods, such as higher order soliton compression, this approach does not depend on the optical power and thus shows promise for application to low-power lasers.

• Korean Journal of Optics and Photonics
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• v.4 no.1
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• pp.114-119
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• 1993

We constructed a laser-heated pedestal growth station using a 25 W $CO_2$ laser to grow various single crystal fibers. The LHPG system consists of the optical system which includes a reflaxicon, an elliptic mirror and a parabolic mirror with their centers drilled, and the translation system to move a source and a seed independently. To test the system, we pulled a few ruby fibers with diameter of 600 ${\mu}m$ and length of 2 cm, and studied characteristics of their photoluminescence.

• Korean Journal of Optics and Photonics
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• v.11 no.3
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• pp.166-170
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• 2000

A wavelength tunable all-optical clock recovery using a semiconductor optical amplifier in a fiber ring cavity is proposed and demonstrated at the wavelength of 1530 nm to 1570 nm. A synchronized optical pulse train is recovered from 10 Gbps and 30 Gbps randomly generated optical pulse streams with injection locking technique. Also, the system responses to the perturbation and the input average power variation are analyzed by a large-signal model based on time-domain travelling wave equation. ation.

• Korean Journal of Optics and Photonics
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• v.17 no.5
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• pp.455-460
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• 2006

The output characteristics of a ceramic Nd:YAC laser pumped by a fiber-coupled laser diode was investigated. An efficiency and a slope efficiency of 33.8 % and 39.3 % respectively were obtained, under an output coupler reflectance of 90.4 %. The laser power has decreased suddenly due to the thermal tensing effect more than 6 W pumping powers.

• Korean Journal of Optics and Photonics
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• v.14 no.3
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• pp.338-342
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• 2003

We have studied the properties of stimulated Brillouin scattering (SBS) in an optical fiber using optical pulses and continuous wave light. We find that the thresholds for SBS are the same when the averaged power of pulse light is the same as the power of cw light. From this result, the SBS threshold of pulse light can be deduced from that of continuous wave light, which can be obtained easily and accurately.

• Current Optics and Photonics
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• v.3 no.2
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• pp.111-118
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• 2019

The optical characteristics of a tunable flattened-pass-band fiber comb filter, based on the polarization-diversified loop configuration, are investigated using the $Poincar{\acute{e}}$-sphere representation. In the design process, the spectral flatness is checked quantitatively, and the tunability of the pass band is demonstrated experimentally. Theoretical calculations show that the filter also exhibits desirable dispersion and polarization properties. The orientation angles of rotatable wave plates for the wavelength tunability of the filter are obtained. Furthermore, we elaborate on the multiple angle loci produced by degeneracies through the combination of optical elements within the loop of the filter.

• Current Optics and Photonics
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• v.5 no.4
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• pp.375-383
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• 2021

We present a simulation method to design antireflection coating (ARCs) for fiber-coupled superconducting nanowire single-photon detectors. Using a finite-element method, the absorptance of the nanowire is calculated for a defined unit-cell structure consisting of a fiber, ARC layer, nanowire absorber, distributed Bragg reflector (DBR) mirror, and air gap. We develop a method to evaluate the uncertainty in absorptance due to the uncontrollable parameter of air-gap distance. The validity of the simulation method is tested by comparison to an experimental realization for a case of single-layer ARC, which results in good agreement. We show finally a double-layer ARC design optimized for a system detection efficiency of higher than 95%, with a reduced uncertainty due to the air-gap distance.

• Current Optics and Photonics
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• v.6 no.2
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• pp.196-201
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• 2022

Collagen fibers tens of nanometers in size, which constitute most of the corneal volume of the human eye, are layered in a uniform direction, and adjacent fiber layers are arranged at an angle of 90° to each other. According to the results of this study, the transmittance at 45° of interlayer rotation angle is highest, and higher than that of the 90° body structure. The transmittance is examined, concerning the polarization state of the incident light; circularly polarized light case shows higher transmittance than linearly polarized. Through this, a simulation to confirm the deformed structure of collagen fibers, which show higher transmittance than the anatomical structure of the cornea, is attempted.

• Current Optics and Photonics
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• v.7 no.2
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• pp.176-182
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• 2023

Optical coherence tomography (OCT) is being developed to guide various ophthalmic surgical procedures. However, the high cost of the intraoperative OCT system limits its availability mostly to the largest hospitals and healthcare systems. In this paper, we present a design and evaluation of a low-cost intraoperative common-path free-hand scanning OCT system. The lensed fiber imaging probe is designed and fabricated for intraocular use and the free-hand scanning algorithm that could operate at a low scanning speed was developed. Since the system operates at low frequencies, the cost of the overall system is significantly lower than other commercial intraoperative OCT systems. The assembled system is characterized and shows that it meets the design specifications. The handheld OCT imaging probe is tested on multilayer tape phantom and ex-vivo porcine eyes. The results show that the system could be used as an intraoperative intraocular OCT imaging device.

• Current Optics and Photonics
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• v.7 no.1
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• pp.28-32
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• 2023

Frequency characteristics of gain-saturated erbium-doped fiber amplifier (EDFA) are experimentally evaluated to mitigate the optical signal fluctuation induced by atmospheric turbulence in terrestrial freespace optical communication systems. Here, an acousto-optic modulator (AOM) is used to emulate optical signal fluctuations induced by atmospheric turbulence. The waveform which is generated in proportion to the refractive-index structural parameters is used to drive the AOM at various periodic frequencies. Thus, the dependence of the signal fluctuation suppression on the frequency is evaluated. The experiment is conducted using a periodic frequency sweep of the AOM driving voltage waveform and signal input power variation of the amplifier. It is observed that a low periodic frequency and high input signal power effectively suppress the optical signal fluctuation. This study evaluates the experimental results from the high-pass filter and gain-saturation characteristics of the EDFA.