• Journal of IKEEE
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• v.13 no.1
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• pp.65-70
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• 2009

We propose an ultrashort pulse optical code-division multiple-access (O-CDMA) scheme based on a pseudorandom binary M-sequence spectral phase encoding and decoding of coherent mode-locked laser pulses and perform a numerical simulation to analyze its feasibility. We demonstrate the ability to properly decode any of the multiple (eight) 10 Gbit/s users by the matched code selection of the spectral phase decoder. The peak power signal to noise ratio of properly and improperly decoded $8{\times}10 Gb/s$ signals could be greater than 15 for 127 M-sequence coding.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.10
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• pp.85-92
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• 1997

For a InGaAsP buried - heterostructrue $1.3\mu\textrm{m}$ LD with fabry-perot cavity structure, the procedures of ultra-short optical pulse genration ar eanalyzed by simulating the rate equations. Investigting the effects of injected current pulse parameters such as bias $J_b$, pulse width $T_d$ and pulse amplitude $J_p$ on the generated optical pulses, we derive the optimum conditions to obtain a single optical pulse with strong peak value. We also observe that the repetition rate of current pulses needs to be restricted under a certain threshold to generate a train of single optical pulses, and that the period doubling phenomenon takes place by increasing the repitition rate.

• Journal of the Optical Society of Korea
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• v.17 no.5
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• pp.357-361
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• 2013

A regenerative Er-doped fiber amplifier system for a high-repetition-rate optical pulse train is investigated for the first time. A signal pulse train with a wavelength tuning range of 18 nm is produced by a passive mode-locked fiber laser based on a nonlinear polarization rotation technique. In order to realize the amplification, an optical delay-line is used to achieve time match between the pulses' interval and the period of pulse running through the regenerative amplifier. The 16 dB gain is obtained for an input pulse train with a launching power of -30.4 dBm, a center wavelength of 1563.4 nm and a repetition rate of 15.3 MHz. The output properties of signal pulses with different center wavelengths are also discussed. The pulse amplification is found to be different from the regenerative amplification system for CW signals.

• Medical Lasers
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• v.9 no.2
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• pp.142-149
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• 2020

Background and Objectives A picosecond-domain laser treatment using a microlens array (MLA) or a diffractive optical element elicits therapeutic micro-injury zones in the skin. This study examined the patterns of tissue reactions after delivering multiple pulses of 1,064-nm, MLA-type, picosecond neodymium:yttrium-aluminum-garnet laser treatment. Materials and Methods Multiple pulses of picosecond laser treatment were delivered to ex vivo human or brown micropig skin and analyzed histopathologically. A high-speed cinematographic study was performed to visualize the multiple pulses of picosecond laser energy-induced skin reactions in in vivo human skin. Results In the ex vivo human skin, a picosecond laser treatment at a fluence of 0.3 J/cm² over 100 non-stacking passes generated multiple lesions of thermally-initiated laser-induced optical breakdown (TI-LIOB) in the epidermis and dermis. In the ex vivo micropig skin, stacking pulses of 20, 40, 60, 80, and 100 at a fluence of 0.3 J/cm² generated distinct round to oval zones of tissue coagulation in the mid to lower dermis. High-speed cinematography captured various patterns of twinkling, micro-spot reactions on the skin surface over 100 stacked pulses of a picosecond laser treatment. Conclusion Multiple pulses of 1,064-nm, MLA-type, picosecond laser treatment elicit marked TI-LIOB reactions in the epidermis and areas of round to oval thermal coagulation in the mid to deep dermis.

• Proceedings of the Optical Society of Korea Conference
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• 1991.06a
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• pp.102-108
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• 1991

Utilizing self-phase modulation effects of a dispersion-shifted fiber and delay-line characteristics of two gratings, mode-locked 80 ps pulses at 1.319${\mu}{\textrm}{m}$ wavelength from a Nd: YAG laser are compressed down to 2.1 ps. These pulses are further compressed down to 340 fs using higher order soliton effects in a common single mode fiber.

• Journal of Sensor Science and Technology
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• v.29 no.3
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• pp.180-186
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• 2020

In this study, we applied edge-pulse modulation to prevent the flicker of light-emitting diode (LED) light in a visible light identification system. In the visible light transmitter, positive pulses were transmitted at the edges of the low-to-high transition points, and negative pulses were transmitted at the edges of the high-to-low transition points of the non-return-to-zero (NRZ) data waveforms. In the visible light receiver, the NRZ waveforms were regenerated by making low-to-high and high-to-low transitions at the point of the positive and negative pulses, respectively. This method has two advantages. First, it ensures that the LED light is flicker-free because the average optical power of the LED was kept constant during data transmission in the transmitter. Second, the 120 Hz optical noise from the adjacent lighting lamps was easily cut off using a simple RC-high pass filter in the receiver.

• 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.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.11B
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• pp.1607-1611
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• 2001

The dependence of the performance of 40-Gb/s optical transmission using short pulses on the fiber chromatic dispersion is numerically studied. When very short pulses are used, the wide spectrum of the optical signal and the chromatic dispersion of the fiber interact in such a way that results in the reduction of nonlinear impairments of the transmission performance. The degree of this reduction is determined by the combined effects of chromatic dispersion of the fiber and the strength of the optical signal and the transmission distance. When 3ps-long pulses were used for the transmission, the eye-closure penalty was highest with the dispersion D=4ps/nm/km.

• Journal of the Optical Society of Korea
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• v.8 no.3
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• pp.127-131
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• 2004

This paper investigates applications of femtosecond lasers for the micromachining of transparent materials and fabrication of optical devices. We show commercial micromachining examples of transparent materials which have been fabricated for various applications. Near infrared femtosecond laser processing is an attractive method to fabricate three-dimensional optical waveguides into various transparent materials. Focused femtosecond laser pulses induce a permanent refractive-index change only near the focal point. We also demonstrate a Y coupler with the splitting ratio of 1:1 written by femtosecond laser pulses into a fused silica glass. The minimum propagation loss of 0.8 ㏈/㎝ awl the refractive-index change of 0.006-0.01 at the wavelength of 1550 ㎚ were achieved by optimization of the laser fluence.

• ETRI Journal
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• v.27 no.4
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• pp.446-448
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• 2005

Using tightly focused femtosecond laser pulses, we produce an optical waveguide and devices in transparent materials. This technique has the potential to generate not only channel waveguides, but also three-dimensional optical devices. In this paper, an optical splitter and U-grooves, which are used for fiber alignment, are simultaneously fabricated in a fused silica glass using near-IR femtosecond laser pulses. The fiber- aligned optical splitter has a low insertion loss, less than 4 dB, including an intrinsic splitting loss of 3 dB and excess loss due to the passive alignment of a single-mode fiber. Finally, we present an output field pattern, demonstrating that the splitting ratio of the optical splitter becomes approximately 1:1.