• Journal of IKEEE
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• v.19 no.1
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• pp.27-32
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• 2015

A flexible and tunable microwave photonic filter based on adjustable optical frequency comb source is demonstrated. We use a combination of a dual parallel Mach Zehnder modulator and an intensity modulator to generate fifteen comb lines with proper weights to implement a desired filter. The optical comb weights, corresponding to the tap coefficients of the filter, are flexibly changed by adjusting the operation parameters of the modulators. The achieved bandwidth and stopband attenuation of the tunable filter are 0.7 GHz and 20 dB, respectively. In addition, we overcome the undesired low frequency suppression appeared in a conventional scheme by applying a dual parallel Mach Zehnder modulator for single sideband suppressed carrier modulation.

• 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.

• Conservation Science in Museum
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• v.16
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• pp.114-121
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• 2015

Two pieces of comb-shaped jewelry which are made of animal bones were discovered in Daeseong-dong tomb No.88 in Gimhae. Foreign material was removed from the surface of the objects using ethanol and various small instruments. Fractures or cracks were repaired using cellulose-type synthetic resin and epoxy resin. Acrylic paint was applied repaired areas to match the color and finished conservation treatment. The two comb-shaped accessories, although differing in number of teeth and thickness, were produced by using the same method. A series of fine bone pieces, shaped like comb teeth, are placed between two long bones, assuming animal ulnas, and are fastened together by tying silk thread around them several times, then by placing a coat of lacquer.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.42 no.1
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• pp.87-94
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• 2005

In this paper a low-power DWT(Discrete Wavelet Transform) design technique is proposed. As basic low-pass filter for analysis bank, comb filter is utilized, and in order to improve frequency response for the comb filter, a fourth order polynomial is also proposed. Another filters are designed by using perfect reconstruction conditions. The lowpass filter coefficients of the analysis filter bank are optimized based on the cost function and perfect reconstruction condition. The number of the multiplications and MSE(Mean Squared Error) performance of the proposed DWT filter bank are compared with those of the JPEG2000 (9, 7) filter bank. It is shown that number of multiplications of the proposed filter bank are saved with 33.3%, and MSE values of the proposed filter bank are also superior to those of the JPEG2000 (9, 7) filter bank.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.45 no.4
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• pp.7-12
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• 2008

This paper presents a lateral resistive contact RF MEMS switch using comb drive. Our goal was to fabricate the RF MEMS switch with high reliability and good RF characteristics for front end module in wireless transceiver system. Therefore, comb drive is used for large contact force in order to achieve low insertion loss and small off-state capacitance in order to achieve high isolation. The single crystalline silicon is used for mechanical reliability. As a result, the developed switch showed insertion loss less than 0.44 dB at 2 GHz, isolation greater than 60 dB, and low actuation voltage at 26 V.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.4
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• pp.399-407
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• 2010

SC-FDMA system uses DFT-spreading method for reducing the PAPR of OFDM signal, which improves the power efficiency. Block type pilot is used in SC-FDMA system. However, there are ICI due to the inevitable phase noise and frequency offset that can be generated from the Doppler frequency and inaccuracy between the transceiver oscillators. This ICI definitely degrades the BER performance. To overcome this problem and estimate the channel efficiently, we like to propose ICI compensation algorithm for the SC-FDMA system with comb type pilot. SLM method is additionally included for the PAPR reduction when pilot is assigned in comb type. Finally, it is confirmed that the ICI due to the phase noise and frequency offset is efficiently compensated by the suggested algorithm.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.27 no.12
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• pp.10-15
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• 2013

In this paper, we propose a Lyot-type optical fiber comb filter based on a polarization-diversity loop structure (PDLS), which has flat-top pass bands and multiwavelength switching capability. Generally, the PDLS can remove the dependency of the filter on input polarization. The proposed filter is composed of a polarization beam splitter, two half-wave plates (HWPs), and two polarization-maintaining fiber loops concatenated with a $60^{\circ}$ offset between their principal axes. By controlling two HWPs, it can operate in a flat-top band mode or a lossy flat-top band mode with an inherent insertion loss of ~3.49dB. In particular, flat-top bands can be interleaved in both modes, which cannot be realized in a Lyot-Sagnac comb filter based on a fiber coupler. Compared with Solc-type high-order comb filters with the same order, the proposed filter shows sharper transition between pass and stop bands.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.39 no.1
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• pp.87-96
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• 2002

This paper proposes an efficient decimation filter structure in programmable down converter for software radio. The decimation filter consists of the cascaded integrator-comb(CIC) filter, a compensation filter for CIC, cascaded comb and modified halfband filters, and programmable FIR filter. Since the compensation filter is used in CIC, the passband drooping is compensated and stopband attenuation is improved. Therefor the more decimation can be implemented in CIC filter. The compensation filter in CIC reduced the computational complexity of other decimation filters and the coefficients of PFIR, thereby achieving a significant hardware reduction over existing approaches. We can reduce the multiply operator by 20% in hardware and operation by 50% as compared with PDC of Harris.

• The Journal of the Acoustical Society of Korea
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• v.35 no.2
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• pp.158-165
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• 2016

Many researches for improving detection performance in the reverberation environment have been conducted in active sonar systems. Especially the type of active pulse makes an impact on the detection performance in the reverberation environment. Thus, this paper describes the detection performance of PTFM (Pulse Trains of Frequency Modulated waveform), Costas, and Geometric Comb pulses which are known for their outstanding performance against the reverberation. Sea trial data of those pulses was analyzed and it was figured out that the range resolution of PTFM pulse was deteriorated by its sub-pulses. Costas pulse showed performance degradations of the doppler resolution by multipath signals. Geometric Comb pulse showed the best doppler resolution.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.216-219
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• 2005

In precision length measurements using optical interferometry based on homodyne or heterodyne principles, it is crucial to have frequency-stabilized monochromatic light sources. To the end, we investigate the possibility of utilizing the optical comb constituted by ultrashort femtosecond pulse lasers generated from a gain medium of titanium-doped aluminium oxide $(Ti:Al_2O_3)$. The optical comb is stabilized by locking to the caesium atomic clock, which allows all the modes of the comb to maintain an extremely high level of frequency stabilization to precision of one part in $10^{16}$. Then, high precision length measurements are realized by extracting a single or group of particularly wanted optical frequency components or by adopting a third-party light source locked to the comb. Required measurement system setup will be presented in detail along with experimental results.