• Korean Journal of Optics and Photonics
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• v.11 no.1
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• pp.37-42
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• 2000

We have numerically solved rate-equations of semiconductor optical amplifier (SOA) to understand the characteristics of SOA. The rate-equations we have used can describe injection carrier density, amplified spontaneous emission and signal photon density in spatial and time domain by dividing the cavity into multi-section. We have investigated injection carrier density, amplified spontaneous emission and signal photon density as a function of position and time in the case of single channel input in the form of square pulse. Also we have analyzed the non-linear phenomena of SOA in the case of injecting multi-channel wavelengths as in WDM. Intermodulation distortion (IMD) caused by beat among channels has significant effects on the signal distortion as the channel spacing becomes narrower, and channel crosstalk becomes larger as the power of signals increases. In the case of the injection of another CW laser whose wavelength is far enough from the signal wavelengths, the crosstalk and the output signal distortion can be significantly reduced. duced.

• Proceedings of the IEEK Conference
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• 2007.07a
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• pp.159-160
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• 2007

Two analog predsitorters (PDs) using the mixing operation are proposed to compensate for the memory effects of the power amplifier and then significantly cancel IM3 components with the independent control of IM3 terms. In the first PD, IM3 terms are generated by using mixing operation of low frequency terms. In the second PD, the double mixing operation of the fundamental components is used. For a two-tone signal with 20-MHz tone spacing, the notable IM3 suppression is achieved over a whole output power range.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.5
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• pp.366-372
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• 2017

In this paper, the analysis of baluns that are inevitably required to design a differential low noise amplifier, The balun converts a single signal input from the antenna into a differential signal, which serves as an input to the differential amplifier. In addition, it protects the circuit from ESD(Electrostatic Discharge) coming through the antenna and helps with input matching. However, in the case of a passive balun used in general, since the AC signal is transmitted through electromagnetic coupling formed between two metal lines, it not only has loss without gain but also has the greatest influence on the total noise figure of the receiving end. Therefore, the design of a balun in a low-noise amplifier is very important, and it is important to design a balun in consideration of line width, line spacing, winding, radius, and layout symmetry that are necessary. In this paper, the factors to be considered for improving the quality factor of balun are summarized, and the tendency of variation of resistance, inductance, and capacitance of the balun according to design element change is analyzed. Based on the analysis results, it is proved that the design of input balun allows the design of low noise, high gain differential amplifier with gain of 24 dB and noise figure of 2.51 dB.

• Journal of electromagnetic engineering and science
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• v.10 no.2
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• pp.73-77
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• 2010

This paper proposes a novel memory effect measurement technique in RF power amplifiers(PAs) using a two-tone intermodulation distortion(IMD) signal with a very simple and intuitive algorithm. Based on the proposed predistortive tone cancellation technique, the proposed measurement method is capable of measuring the relative phase and magnitude of the third-order and fifth-order IMDs, as well as the fundamental signal. The measured relative phase between the higher and lower IMD signal for specific tone spacing can be interpreted as the group delay(GD) information of the IMD signal concerned. From the group delay analysis, we can conclude that an adaptive control of GD as well as the magnitude and phase is a key function in increasing the linearization bandwidth and the dynamic range in a predistortion(PD) technique.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.12 s.91
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• pp.1207-1215
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• 2004

A Gigabit Ethernet upstream transmission over a WDM-PON employing remotely wavelength-locked Fabry-Perot lasers has been demonstrated. We have successfully demonstrated a WDM transmission of four Gigabit Ethernet channels with 100 GHz channel spacing over 30 km conventional single mode fiber. The measured f-factor was larger than 17.1 dB. We have also investigated the beating noise characteristics of a wavelength-locked Fabry-Perot laser and showed the remotely wavelength-locked Fabry-Perot laser suppresses the intensity noise of the incoherent light injected, which cause a 6.3 dB SNR improvement compared with that of the conventional spectrum-sliced light source.

• Proceedings of the IEEK Conference
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• 2000.07b
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• pp.1009-1012
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• 2000

In this paper, we have designed and fabricated power PHEMT’s with an unit gate width of 80$\mu\textrm{m}$ and 4 fingers, and MIMIC power amplifiers using the PHEMT’s as well. The PHEMT’s have a 0.2$\mu\textrm{m}$ gate length and source to drain spacing of 3$\mu\textrm{m}$. The characteristics of the fabricated PHEMT’s are 4.08dB of S$\sub$21/ gain at the 35GHz and 317mS/mm of gm, and 62GHz of f$\sub$T/ and 120GHz of f$\sub$max/. The designed and fabricated MIMIC’s power amplifiers with 6 PHEMT’s and MIN capacitors were fully passivated by 1000 Α of Si$_3$N$_4$ film for higher performance and surface protects. The chips were processed using the MINT processes, and size was 3.25 ${\times}$ 1.8$\textrm{mm}^2$. The fabricated MIMIC power amplifiers have RF characteristics such as 11.25dB of S$\sub$21/ gain, 11.37dB of input return-loss and 12.69dB of output return-loss at the 34.55GHz.

• Korean Journal of Optics and Photonics
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• v.22 no.3
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• pp.122-128
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• 2011

The AWG-filtering effect was investigated on a bidirectional 100-GHz-channel-spacing WDM-PON link using spectrum-sliced and RSOA-amplified light sources for downstream signals and a wavelength reuse technique for upstream signals. Signal performances of three different filtering AWGs, including Gaussian, trapezoidal, and rectangular types, were compared on link transmission with fiber nonlinear effects. As an extinction ratio of a downstream signal varied, the effect for both directional signals was analyzed and optimized. It was found that there was an optimal pass bandwidth of an AWG for the balance between relative intensity noise decrement and cross phase modulation noise increment as the bandwidth got wider.

• Journal of Sensor Science and Technology
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• v.3 no.1
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• pp.40-45
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• 1994

$112^{\circ}$ rot. x-cut $LiTaO_{3}$ wafer was used as the substrate of SAW gas sensor. Dual delay line SAW device with IDTs which consist of the reference delay line and the sensing delay line was fabricated using photolithigraphy. Each IDTs had 10 finger pairs and finger spacing is 10 microns. One delay line channel is the reference, while the second is the sensing channel with Pb-phthalocyanine film in the propagation path. Pb-phthalocyanine film which is p-type organic semiconductor was evaporated in $10^{-5}$ torr vacuum using shadow mask selectively. Dual delay line oscillator was constructed by using the rf amplifier and AGC. Frequency of the IDTs had the range of $87{\sim}$89 MHz oscillation frequency. Oscillation frequency shifts were investigated as a function of the temperature and the concentration of $NO_{2}$ gas.

• Journal of the Optical Society of Korea
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• v.15 no.3
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• pp.293-299
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• 2011

In this study, we demonstrated Fourier-domain/swept-source optical coherence tomography (FD/SS-OCT) at a center wavelength of 800 nm for in vivo human retinal imaging. A wavelength-swept source was constructed with a semiconductor optical amplifier, a fiber Fabry-Perot tunable filter, isolators, and a fiber coupler in a ring cavity. Our swept source produced a laser output with a tuning range of 42 nm (779 to 821 nm) and an average power of 3.9 mW. The wavelength-swept speed in this configuration with bidirectionality is 2,000 axial scans per second. In addition, we suggested a modified zero-crossing method to achieve equal sample spacing in the wavenumber (k) domain and to increase the image depth range. FD/SS-OCT has a sensitivity of ~89.7 dB and an axial resolution of 10.4 ${\mu}m$ in air. When a retinal image with 2,000 A-lines/frame is obtained, an acquisition speed of 2.0 fps is achieved.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.4
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• pp.576-585
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• 2001

In this paper, we investigated the method of compensation for optical pulse shape distortion due to both chromatic dispersion and SPM(self phase modulation) in a single mode fiber We selected MSSI(mid-span spectral inversion) as compensation method using OPC(optical phase conjugator). We used EOP(eye-opening penalty) parameter in order to evaluate the efficiency of waveform distortion compensation. In this paper, we induced optimum pump power level in optical phase conjugator through analytic method of computer simulation. And we investigated input signal power range being able to maintain stable reception performance under the condition of optimum pump power. We verified the possibility of high performance optical transmission system realization through the inducement and application of optimum pump power, input signal power and in-line amplifier spacing, because power control is important in the compensation for optical pulse distortion.