• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.9
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• pp.3435-3440
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• 2010

Unlike the electric method capable of checking only product defect, the real time optical metrology is suggested for measuring and visualizing vibration with respect to position of surface acoustic wave in RF device. The measuring limits and conditions for surface acoustic wave is given, and the interference and diffraction due to RF signal are analyzed by optical interpretation. A single mode laser and a 105MHz-center-frequency repeater filter were employed for experiments and theoretical analysis. In this paper, the optical metrology providing visual energy distribution and real time inspection for surface acoustic wave is proposed for development of high quality multi-service and multi-frequency RF module.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.2
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• pp.199-204
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• 2008

The generation of axisymmetric Lamb waves and interaction with wall thinning (corrosion) defects in hollow cylinders are simulated using the finite element method. Guided wave interaction with defects in cylinders is challenged by the multi-mode dispersion and the mode conversion. In this paper, two longitudinal, axisymmetric modes are generated using the concept of a time-delay periodic ring arrays (TDPRA), which makes use of the constructive/destructive interference concept to achieve the unidirectional emission and reception of guided waves. The axisymmetric scattering by the wall thinning extending in full circumference of a cylinder is studied with a two-dimensional FE simulation. The effect of wall thinning depth, axial extension, and the edge shape on the reflections of guided waves is discussed.

• Journal of the Korean Institute of Telematics and Electronics
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• v.22 no.2
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• pp.1-5
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• 1985

In this paper, temperature-induced optical phase shifts in single-mode fibers are studied both analytically and experimentally. Temperature sensor using single-mode fiber interferometer is designed and the temperature sensitivity of the sensor system is investigated. This fiber-optic temperature sensor which employs the Mach-Zehnder arrangement is a high sensitivity sensor of phase detection type. In this type, temperature changes are ob-served as a motion of an optical interference fringe pattern. In the measurements using interferometer, one of the important problems is to detect simultaneously the number and direction of fringe displacement resulting from physical perturbations (temperature, pressure, etc.). To realize this, the array detector using multi-mode fiber is designed. By this array detector the number and direction of fringe displacement is Ineasured very conveniently.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.11
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• pp.5209-5228
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• 2016

Device-to-device (D2D) communication underlaying cellular networks can bring significate benefits for improving the performance of mobile services. However, it hinges on elaborate resource sharing scheme to coordinate interference between cellular users and D2D pairs. We formulate a joint mode selection, link allocation and power control optimization problem for D2D communication sharing uplink resources in a multi-user cellular network and consider the efficiency and the fairness simultaneously. Due to the non-convex difficulty, we propose a three-step scheme: firstly, we conduct mode selection for D2D pairs based on a minimum distance metric after an admission control and obtain some cellular candidates for them. And then, a cellular candidate will be paired to each D2D pair based on fairness. Finally, we use Lagrangian Algorithm to formulate a joint power control strategy for D2D pairs and their reused cellular users and a closed-form of solution is derived. Simulation results demonstrate that our proposed algorithms converge in a short time. Moreover, both the sum rate of D2D pairs and the energy efficiency of cellular users are improved.

• Proceedings of the IEEK Conference
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• 2003.07b
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• pp.791-794
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• 2003

The increasing computational capability of processors is driving the need for high bandwidth links to communicate and store the information that is processed. Such links are often an important part of multi processor interconnection, processor-to-memory interfaces and Serial-network interfaces. This paper describes a 0.11-${\mu}{\textrm}{m}$ CMOS 4 Gbp s/pin 3-Level transceiver using RSL/(Rambus Signaling Logic) for high bandwidth. This system which uses a high-gain windowed integrating receiver with wide common-mode range which was designed in order to improve SNR when operating with the smaller input overdrive of 3-Level. For multi-gigabit/second application, the data rate is limited by Inter-Symbol Interference (ISI) caused by low pass effects of channel, process-limited on-chip clock frequency, and serial link distance. In order to detect the transmited 4Gbps/pin with 3-Level data sucessfully ,the receiver is designed using 3-stage sense amplifier. The proposed transceiver employes multi-level signaling (3-Level Pulse Amplitude Modulation) using clock multi phase, double data rate and Prbs patten generator. The transceiver shows data rate of 3.2 ~ 4.0 Gbps/pin with a 1GHz internal clock.

• Korean Journal of Optics and Photonics
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• v.22 no.1
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• pp.5-9
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• 2011

There are technical difficulties in measuring the numerical apertures of multi-mode gradient-index plastic optical fibers (GI-POFs) due to their strong speckle noise originating from dopants, non-uniformity of gradient-index profile, and multi-mode interference. Therefore, we propose a new method of obtaining the numerical aperture by controlling the size of the incident laser beam and measuring the numerical aperture of GI-POF. The results show that we can get a value for the numerical aperture of GI-POF very similar to that measured by the conventional method. We can also obtain the optimum launching condition of input beam and maximum coupling efficiency.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.5
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• pp.7-15
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• 2007

In wireless communication networks, single-radio single-channel architecture degrades throughput and end-to-end delay due to half-duplex transmission of wireless node and route intra interference. Also, In contention-based MAC (Medium Access Control) architecture, channel contention reduces throughput and packet collision enlarges end-to-end delay. In this paper, we use multi-radio multi-channel architecture which will make wireless node to operate in full duplex mode, and exclude route intra interference. Based on this architecture, we propose a new link metric, ccf which reflects the characteristics of a contention-based wireless link, and propose a routing path metric MCCR considering channel switching delay and route intra interference. MCCR is compared with MCR by simulation, the performance of a route established by MCCR outperforms the performance of a route by MCR in terms of throughput and end-to-end delay.

• Korean Journal of Optics and Photonics
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• v.31 no.2
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• pp.105-110
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• 2020

A compact beam combiner based on two-mode interference (TMI) in multimode waveguides is proposed, and its feasibility is shown through simulation with the three-dimensional beam propagation method. The input waveguides are separated by about 1 ㎛ at the interface with the multimode waveguide, so that the fabricated waveguide pattern is well repeated. The power transmission to the output port from the red, green, and blue input port is 93.5%, 94%, and 93%, respectively. When the wavelength deviation from a center wavelength is 10 nm, the power transmission is maintained to be greater than 90%. When the waveguide width error is 40 nm, the power transmission is maintained to be greater than 85% for all the three colors. The polarization dependence of the beam combiner is almost negligible, and its size is as tiny as 0.02 × 4 ㎟.

• Korean Journal of Optics and Photonics
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• v.17 no.3
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• pp.268-272
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• 2006

We have demonstrated the selection and the amplification of the components of an optical frequency comb using femto-second laser injection-locking technique. We used a mode-locked Ti:sapphire laser as a master laser and a single-mode diode laser as a slave laser. After passing through the interference filter with the center wavelength 794.7 nm and the transmittance bandwidth 1.5 nm, the optical frequency comb by mode-locked femto-second laser was injected into the slave laser. The injection-locked slave laser had $3{\sim}4$ multi-mode with the mode spacing 100.5 MHz, whichcorrespond to the repetition rate of a mode-locked Ti:sapphire laser. The power of the modes selected by femto-second laser injection-locking technique was amplified to several thousands times

• Journal of Communications and Networks
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• v.13 no.4
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• pp.360-366
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• 2011

In this paper, we investigate the problem of power allocation in a heterogeneous network that is composed of a pair of cognitive users (CUs) and an infrastructure-based primary network. Since CUs have only limited effective spectrum-sensing ability and primary users (PUs) are not active all the time in all locations and licensed bands, we set up a new multi-area model to characterize the heterogeneous network. A novel combined interference-avoidance policy corresponding to different PU-appearance situations is introduced to protect the primary network from unacceptable disturbance and to increase the spectrum secondary-reuse efficiency. We use dual decomposition to transform the original power allocation problem into a two-layer optimization problem. We propose a low-complexity joint power-optimizing method to maximize the transmission rate between CUs, taking into account both the individual power-transmission constraints and the combined interference power constraint of the PUs. Numerical results show that for various values of the system parameters, the proposed joint optimization method with combined PU protection is significantly better than the opportunistic spectrum access mode and other heuristic approaches.