• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.22 no.2
• /
• pp.318-324
• /
• 1997

Chua's circuit is a simple electronic network which exhibits a variety of bifurcation and attractors. The circuit consists of two capacitors, a linear resistor, and a nonlinear resistor. In this papre we analyze a circuit obtained by replacing the parallel LC resonator in the Chua's circuit by lossless transmission line. By using the method of characteristics of this circuit we show that various periodic motions and chaotic motions can the attained according to parameter variations. From Chua's circuit with a lossless transmission line a variely of chaotic attractors which are similar to those of the normal Chua's circuit are observed.

• Korean Journal of Optics and Photonics
• /
• v.9 no.3
• /
• pp.186-190
• /
• 1998

We fabricated a diode-side pumped high power Nd:YAG laser with a gold coated flow tube(diameter of 10mm) and three sets of 140W diode bar. The diameter of Nd:YAG rod was 6mm and its length was 130mm. We obtained 130W cw power from a linear resonator with an 11% output coupler, which corresponds to the slope efficiency of 43% and the optical efficiency of 31%. The measured beam quality factor(M$^2$) reached about 85 which is fairly large due to the large size of the rod. Thermal lensing of the rod was measured to be 5.3-7.4D/$kW_{pump}$ when the laser was operating.

• Korean Journal of Optics and Photonics
• /
• v.7 no.4
• /
• pp.390-396
• /
• 1996

A pulsed Ti : sapphire laser with a Z-folded cavity, which was pumped by a frequency-doubled Nd : YAG laser, was developed. A laser output energy of 822 $\mu$J with a pulsewidth of 5 ns and an output efficiency of 27.4% was obtained at a center wavelength of 790 nm using an output coupler of 18% reflectance. The slope efficiency was 35%. The output beam diameter was 0.9 mm, and the divergence angle was 1.8 mrad. The spectrum tunability was about 120 nm from 740 nm to 860 nm with a FWHM of 90 nm at an 18% output coupler and a pumping energy of 3 mJ.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.52 no.11
• /
• pp.536-543
• /
• 2003

In this paper, we describe a unique self oscillating and mixing (SOM) down-converter design using a modified defected ground structure (DGS). The proposed SOM converter is consisted of self-oscillator, which can produce negative resistance and select resonance frequency, RF matching circuit, and IF low pass filter. As the advantage of this SOM converter can mix LO and RF signals as well as inducing LO signal with only one active device. it is designed as a simple structure and the low cost. Also, there is easy advantage to be applied in RFIC/MMIC technology because it offers excellent phase noise performance in spite of using micro-strip structure. The LO signal for the proposed SOM converter is designed at 1㎓ and RF frequency was chosen to be 800MHz. The achieved conversion loss and phase noise performances of the implemented SOM converter are 15㏈ and -95dBc/Hz at 100KHz offset frequency respectively. The equivalent circuit parameters for DGS are extracted by using a three dimensional EM simulator and simple circuit analysis method.

• Journal of the Korean Vacuum Society
• /
• v.16 no.4
• /
• pp.273-278
• /
• 2007

For the simulation of active region in the quantum cascade lasers (QCL), we solved Schrodinger equation utilizing Runge-Kutta method and Shotting method. Wavelength, phonon resonant energy, and dipole matrix element were simulated with the variation of active region thickness. As a result of such simulation, it was suggested the tolerance range of epi-layer thickness error when 3-quantum well QCL structures are grown.

• Journal of Broadcast Engineering
• /
• v.15 no.2
• /
• pp.217-223
• /
• 2010

In this paper, an interchannel interference (ICI) cancellation method is proposed for multiple frequency offsets in orthogonal frequency division multiplexing (OFDM) systems. When several same signals are received from different transmitters simultaneously, multiple frequency offsets may occur at the receiver because of the frequency difference of the oscillators of the two transmitters and the receiver. This causes degradation of system performance because OFDM systems are very sensitive to the frequency offsets. In this paper, we propose a method to eliminate the effect of the multiple frequency offsets for OFDM systems. The method is accomplished in two steps: compensation of the frequency offset in the time domain and subsequent cancellation of the ICI in the frequency domain. Through computer simulations, we verify the effectiveness of the proposed ICI cancellation method.

• Korean Journal of Optics and Photonics
• /
• v.8 no.1
• /
• pp.47-51
• /
• 1997

A Cr:LiSAF laser pumped by semiconductor lasers was constructed. The pumping laser was a high-power semiconductor laser (SDL 7432-H1) of wavelength 674 nm and maximum power of 500 mW. The laser crystal was a Cr:LiSAF of plano-Brewster shape with 3% Cr3+ion concentration and 3 mm in length. The plane facet of the crystal was coated to get the maximum transmittance of pupmping laser and maximu reflection over the 800 - 880 nm bandwidth. V-shaped resonator was used to compensate the astigmatism induced by the crystal. The output power of the Cr:LiSAF laser was 19.4 mW at the pumping power of 290 mW. The wavelength was tuned by a steep dive-angled birefringent filter from 840 nm to 880 nm and the characteristics of the filter were agreed well with a theory.

• Korean Journal of Optics and Photonics
• /
• v.8 no.6
• /
• pp.450-455
• /
• 1997

A pulsed Ti:sapphire laser with a Z-folded cavity, which was pumped by a freqeuncy-doubled Nd:YAG laser, was developed. It shows 120 nm wavelength tuning range from 740 nm to 860 nm with 90 nm FWHM under a pumping energy of 3 mJ with 18% output coupler. Using a birefringent filter, the effective efficiency was improved about 10 times compare to without a birefringent filter. The output energy obtained was $\365mu$Jwith 4 nm FWHM. And the wavelength tuning range was broadened to about 160 nm within an output energy fluctuation of $\pm$10%.

• Journal of the Institute of Electronics Engineers of Korea SC
• /
• v.42 no.1
• /
• pp.23-31
• /
• 2005

Recently, the multimedia and high speed telecommunication systems needs a high frequency and high stability oscillator. The VCXO(voltage controlled -crystal oscillator) have continually downsized to gratify a thin and small size of the telecommunication systems. In his paper, we have developed the small ceramic PECL(positive emitter-coupled logic) VCXO of the 5×7 mm size for gratifying the requested specifications from user, and then use the multilayer ceramic SMD(surface mounted device) package technology. The ceramic SMD PECL VCXO is operating at the 3.3 Voltage and have the frequency range of 120MHz～180MHz. The Q factor is over 5K and it has the low jitter characteristics of 3.5 ps and low phase noise.

• Korean Journal of Optics and Photonics
• /
• v.18 no.3
• /
• pp.208-215
• /
• 2007

A fiber-coupled laser-diode pumped ceramic Nd:YAG laser for compensating the thermal tensing effect was developed. The thermal tensing effect was compensated using a convex lens, which was 25 mm away from the laser rod, with a focal length of 30 mm and an effective clear aperture of 22 mm. Without a compensator, the laser output power decreased suddenly above a pump power of 6 W. Using a compensator, the laser output power increased linearly according to the pump power. The beam propagation factor $M^{2}$ was 2.4 under a pump power of 12 W.