• Laser Solutions
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• v.9 no.3
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• pp.1-5
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• 2006

Diffraction grating is the optical device which has periodic pattern. Decorative logotypes is the one of application of diffraction grating. In this paper diffraction grating for decorative logotype is fabricated by dot pattern in stead of line pattern. A metallic mold for diffraction gratings is fabricated with a mode-locked 12 ps Nd:YVO4 laser. Laser pulses with a wavelength of 355nm are irradiated on the surface of NOK 80, a mold material, to generate dot patterns. In order to minimize the dot diameter, laser power is set just above the ablation threshold of NOK 80. Results show that the spectrum from the fabricated mold is good enough for some industrial application

• Proceedings of the Korean Society of Laser Processing Conference
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• 2006.11a
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• pp.114-117
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• 2006

Diffraction grating is the optical device which has periodic pattern. Decorative logotypes is the one of application of diffraction grating. In this paper diffraction grating for decorative logotype is fabricated by dot pattern in stead of line pattern. A metallic mold for diffraction gratings is fabricated with a mode-locked 12 ps $Nd:YVO_4$ laser. Laser pulses with a wavelength of 355nm are irradiated on the surface of NOK 80, a mold material, to generate dot patterns. In order to minimize the dot diameter, laser power is set just above the ablation threshold of NOK 80. Results show that the spectrum from the fabricated mold is good enough for some industrial application.

• Korean Journal of Optics and Photonics
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• v.5 no.1
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• pp.90-99
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• 1994

Picosecond time-correlated single photon counting system and time-resolved luminescence spectrometer were constructed, employing a mode-locked picosecond laser, fast electronics, and microchannel plate tube. It has been shown that the instrument response function critically depends on laser pulse shape, timing jitter and walk of the electronics, and characteristics of detector and amplifier. Correcting time dispersion in the optical system, the best instrument response function obtained appears to be 25 ps, which made it possible to measure the luminescence lifetime with less than 10 ps resolution in the picosecond to microsecond range. range.

• Journal of the Optical Society of Korea
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• v.11 no.3
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• pp.124-129
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• 2007

For the first time we compare two kinds of optical frequency combs, one of which is based on a Ti:sapphire femtosecond laser and the other is based on a mode-locked erbium-doped fiber laser. The comparison is performed by measuring an optical frequency standard with these two combs simultaneously. The two frequency measurements agree within 1.8 Hz ($3.8{\times}10^{-15}$) with the uncertainty of 17.2 Hz ($3.6{\times}10^{-14}$), from which it can be concluded that the Ti:sapphire-based frequency comb and the fiber-based frequency comb have no systematic discrepancy at this level of uncertainty.

• Korean Journal of Optics and Photonics
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• v.11 no.5
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• pp.330-334
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• 2000

A new pha~e lock loop (PLL) IS proposed and demonstrated fat clock recovery from 40 Gblt/s time-dIvision-multiplexed (TDM) optical pulse tri.lin, The proposed clock lecovery scheme lmproves the Jitter effecl cOlmng from the clock. pulse laser of harmonically-mode locked flber laser The cross-corrdation frequency component between the optical Signa] and an optical clock pulse tram is deteCled as a fonr-wave-mixing (FWM) SIgnal generated in SOA. The lock-in freqnency range of the clod. recovery IS found to be within 10 KHz. 0 KHz.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.54 no.6
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• pp.286-292
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• 2005

Terahertz wave is a kind of electromagnetic radiation whose frequency lies in 0.1THz $\~$10THz range. In this paper, generation and detection characteristics of terahertz (THz) radiation by photoconductive antenna (PCA) method has been described. Using modern integrated circuit techniques, micron-sized dipole antenna has been fabricated on a low-temperature grown GaAs (LT-GaAs) wafer. A mode-locked Ti:Sapphire femtosecond laser beam is guided and focused onto photoconductive antennas (emitter and detector) to generate and measure THz pulses. Ultra-wide band THz radiation with frequencies between 0.1 THz and 3 THz was observed. Terahertz field amplitude variation with antenna bias voltage, pump laser power, pump laser wavelength and probe laser power was investigated. As a primary application example. a live clover leaf was imaged with the terahertz radiation.

• Korean Journal of Optics and Photonics
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• v.9 no.4
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• pp.270-273
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• 1998

We have demonstrated the wavelength tunable ultrashort pulse fiber ring laser proposed the novel method for measuring the cavity loss from relaxation oscillation frequency and the pump power. To suppress the polarization instability the laser cavity is configured with polarization maintaining fibers and to control the center wavelength a 2.4 nm bandwidth tunable wavelength filter was inserted in the cavity. The laser has 8 picosecond pulse width, 10 GHz repetition rate and 1.2 mW average power in 1530-1560 nm operation range.

• Current Optics and Photonics
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• v.5 no.3
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• pp.289-297
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• 2021

We describe a comb-mode resolving spectroscopic technique by direct time-domain phase correction of unstable interferograms obtained from loosely locked two femtosecond lasers. A low-cost continuous wave laser and conventional repetition rate stabilization method were exploited for locking carrier and envelope phase of interferograms, respectively. We intentionally set the servo control at low bandwidth, resulting in severe interferograms' fluctuation to demonstrate the capability of the proposed correction method. The envelope phase of each interferogram was estimated by a quadratic fit of carrier peaks to correct timing fluctuation of interferograms in the time domain. After envelope phase correction on individual interferograms, we successfully demonstrated 1 Hz linewidth of RF comb-mode over 200 GHz optical spectral-bandwidth with 10-times signal-to-noise ratio (SNR) enhancement compared to the spectrum without correction. Besides, the group delay difference between two femtosecond pulses is successfully estimated through a linear slope of phase information.

• Korean Journal of Optics and Photonics
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• v.10 no.5
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• pp.430-438
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• 1999

We have utilized soft-aperturing by gain media to develop a high-power tunable Ti:Sapphire laser with sub-40-fs and broad tuning range. The tunable spectral range was only limited by the bandwidth of mirrors. We made use of knife-edge slits near an intra-cavity prism controlled by micro-stepping-motors to tune the center wavelength continuously. The tunability of the center wavelength was ranged from 770 nm to 870 nm, and the measured pulsewidth was sub-40 fs throughout the above spectral range. The shortest pulsewidth was about 17 fs at the center wavelength of 820 nm and the spectral bandwidth was 72 nm. At 5 W pumping power of the Ar-ion laser we obtained average output power of 440 mW~580 mW. For the cw and Kerr-lens mode-lodking conditions, we have evaluated the value of an amplitude modulation to be ${\gamma}=2.5{\times}10^{-8}/W$ from the calculated waists of a Gaussian beam on the Ti:sapphire crystal surface. Using this result we demonstrate that the generation of sub-40-fs Kerr-lens mode-locked pulse can be described by the Ginzberg-Landau model which is a weak pulse shaping model.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.5 s.347
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• pp.59-67
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• 2006

We demonstrate bidirectional long-reach 35-channel dense wavelength division multiplexing-passive optical network(DWDM-PON) based on wavelength-locked Fabry-Perot laser diodes (F-P LDs). The mode control of F-P LD enhances output power at decreased the required injection power. We show packet-loss-free transmission in all 70 channels at 125 Mb/s per channel line rate through 70 km of single mode fiber without optical amplifier The DWDM-PON can consolidate a metro network into an access network by bypassing the central offices within its reach. The proposed DWDM-PON can accommodate about 80 subscribers with an EDFA-based broadband light source. Further expansion up to 100 subscribers is possible with a semiconductor-based BLS.