• Korean Journal of Optics and Photonics
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• v.8 no.6
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• pp.471-475
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• 1997

We investigate the gain dynamics of erbium-doped fiber amplifiers during single- and multi-channel amplification. Power transients due to the changes in the number of channels in the amplifier chain are measured. We successfully suppress power transients by using a fast pump control circuit with<$\mu$s response time.

• Proceedings of the Optical Society of Korea Conference
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• 2000.02a
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• pp.258-259
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• 2000

Quantum Well Disordering (QWD) has drawn a considerable attention in recent years$^{(1-3)}$ due to its wide applicability to optoelectronic devices. QWD allows modification of the shape of QW in selected regions, hence it modifies the subband energies in conduction and valance bands$^{(4)}$ . This leads to changes in optical properties such as band gap, absorption coefficient and refractive index. Thus such disordering in selected areas enables monolithic integration of various optoelectronic devices such as lasers, EA/EO modulators, waveguides and optical amplifiers. In this paper, we investigate the quantum well disordering effects on photoluminescence spectra by using experimental measurements and theoretical analysis$^{(5)}$ . (omitted)

• Korean Journal of Optics and Photonics
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• v.29 no.1
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• pp.32-39
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• 2018

The impact of the amplified spontaneous emission (ASE) on the gain recovery time of a bulk semiconductor optical amplifier (SOA) is investigated. The gain-recovery time is obtained by determining the time evolution of the gain, carrier density, and ASE in an SOA, after the propagation of a short pump pulse and continuous-wave (CW) probe of gain dynamics. In the simulation, a wide-band-semiconductor model, which can be characterized by the material gain coefficient over a wide wavelength range, is used, because the gain bandwidth of a practical SOA is very wide. The pump pulse and counterpropagating CW probe field are considered in the simulation, with the ASE noise spectrum equally divided.

• Korean Journal of Optics and Photonics
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• v.10 no.1
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• pp.64-67
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• 1999

We have been implemented 10 Gb/s-320 km of dispersion-shifted fiber (DSF) transmission. The optical link consists of a 10 Gb/s optical transceiver, an optical booster amplifier, 3 sets of optical in-line amplifiers, an optical preamplifier and transmission fibers. Firstly, we investigated the Q-factor characteristics in terms of optical signal to noise ratio (OSNR) of 320 km of DSF, measured receiver sensitivity is -27 dBm and power penalty is 2 dB, respectively. We concluded that optical SNR degradation and path penalty gives rise to 1 dB penalty, respectively.

• Korean Journal of Optics and Photonics
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• v.31 no.5
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• pp.218-222
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• 2020

In this paper, we have experimentally demonstrated a 2-kW-class spectrally-beam-combined laser with high beam quality, using narrow-linewidth ytterbium-doped polarization-maintaining fiber amplifiers. Five fiber amplifiers with different center wavelengths were implemented for the spectrally-beam-combined laser. The center wavelengths of the five amplifiers were 1062, 1063, 1064, 1065, and 1066 nm, respectively. A phase-modulated laser diode was used as a seed source for each amplifier. The seed sources were modulated by filtered pseudorandom-bit-sequence (PRBS) signals 5 GHz in linewidth. The polarization-maintaining large-mode-area fiber with a core size of 30 ㎛ was used as a delivery fiber to mitigate the stimulated Brillouin scattering (SBS) effect. The laser beams from five amplifiers were spectrally combined by a multilayer dielectric diffraction grating. The maximum output power and beam quality M² of the combined laser were measured to be 2.3 kW and 1.74, respectively.

• Korean Journal of Optics and Photonics
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• v.19 no.3
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• pp.237-241
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• 2008

An all-optical encryption system built on the basis of electrical logic circuit design principles is proposed, using semiconductor optical amplifier (SOA) exclusive or (XOR) logic gates. Numerical techniques (steady-state and dynamic) were employed in a sequential manner to optimize the system parameters, speeding up the overall design process. The results from both numerical and experimental testbeds show that the encoding/decoding of the optical signal can be achieved at a 10 Gbps data rate with a conventional SOA cascade without serious degradation in the data quality.

• Journal of the Optical Society of Korea
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• v.20 no.6
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• pp.694-697
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• 2016

Up-converted phase noise, which is induced by the low-frequency relative intensity noise (RIN) of a laser through AM-PM conversion within a photodetector (PD), is first measured here by means of a cross-correlation method. Our proposed measurement system can isolate the RIN-induced phase noise from noise contributions of other components, such as amplifiers, modulators, and mixers. In particular, shot noise and thermal noise generated from the PD are also suppressed by this method, so that standalone characteristics of the RIN-induced phase noise can be obtained. Experimental results clearly show the quantitative relationship between the RIN-induced phase noise and the incident optical power of the PD. Our findings indicate that the least RIN-induced phase noise appeared at the saturation point of the PD, which is about -162 dBc/Hz at 10 kHz offset.

• Korean Journal of Optics and Photonics
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• v.8 no.3
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• pp.236-240
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• 1997

We compare feedback wavelength-dependent performances of all-optical gain-clamped 980-nm pumped erbium-doped fiber amplifiers. In a 2.5-Gbps 8-channel WDM system, we have measured and compared gain compressions, signal power variations due to cross-saturation, power penalties caused by relaxation oscillations and noise figures for three different feedback wavelengths - 1532, 1543, and 1565 nm.

• Current Optics and Photonics
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• v.2 no.6
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• pp.519-524
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• 2018

We propose a transverse load sensor with reconfigurable measurement accuracy based on a microwave photonic filter in the $K_u$ band, incorporating a polarization-maintaining fiber Bragg grating. A prototype sensor with a reconfigurable measurement accuracy tuning range from 6.09 to 9.56 GHz/(N/mm), and corresponding minimal detectable load range from 0.0167 to 0.0263 N/mm, is experimentally demonstrated. The results illustrate that up to 40% manufacturing error in the grating length can be dynamically calibrated to the same corresponding measurement accuracy for the proposed transverse load sensor, by controlling the semiconductor optical amplifier's injection current in the range of 154 to 419 mA.

• Proceedings of the Optical Society of Korea Conference
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• 2000.02a
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• pp.96-97
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• 2000

Incoherent broadband optical sources have been applied in various areas such as a light source for optical device characterization, fiber-optic gyroscopes$^{(1)}$ , and spectrum sliced light source in wavelength division multiplexing (WDM) system$^{(2)}$ . To utilize the inherent low loss in silica optical fibers, various types of incoherent light sources are being developed. Among the light sources, the amplified spontaneous emission (ASE) from a rare earth doped fiber has benefits in temperature stability, high output power, low polarization dependence over semiconductor diodes$^{(3)}$ . Recently erbium doped fibers (EDF) have been intensively researched for ASE sources as well as optical amplifiers$^{(4)}$ . The spectrum of ASE from an EDF, however, is limited in the 1520~1560 nm range in conventional configurations. In this letter we described a new broadband ASE source which included both the conventional ASE band of Er$^{3+}$ ion, 1520nm~1560nm and ASE band from Tm$^{3+}$ ions that extends the bandwidth further. For the first time, to the best knowledge of authors, a fiber ASE source based on the energy transfer between Er$^{3+}$ and Tm$^{3+}$ ions in the range of 1460~1550 nm, has been demonstrated using a single 980nm pump laser diode. (omitted)omitted)