• Korean Journal of Optics and Photonics
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• v.2 no.1
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• pp.36-49
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• 1991

The coherence properties of electromagnetic fields are reviewed, based on both the classical and quantum theories. The elementary concepts, employed frequently in the discussion of interference phenomena, are summarized. The well-known interference phenomena are described in terms of second-order coherences. The coherence theory in space-frequency domain is introduced and the coherent mode representation is presented. The generation and propagation of coherence of light are analysed and it is shown that the coherence of light is developed as light propagates. The quantum theory goes parallel with the classical theory, via the optical equivalence theorem. There are, however, certain nonclassical characteristics of light, which may not be easily understood in classical therms. These nonclassical phenomena are believed to originate from the particle aspects of light. The quantum effect on the interfernce phenomena is analysed and finally the outlook of the future research is briefly mentioned.

• Korean Journal of Optics and Photonics
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• v.10 no.2
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• pp.114-119
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• 1999

In an interation-free measurement system with the polarization-based Mach-Zehnder interferometer structure, effects of two system imperfections, i.e., the system loss and the low quantum efficiency of photon detectors, on the system perfomance are analyzed, Although both the two system imperfections limit the maximal defection efficiency that can be achievable, we show that the quantum efficiency of photon detectors is less important when the system loss becomes small. In addition, for given system losses and quantum efficiencies, we derive the maximal detection efficiencies that can be achievable.

• Korean Journal of Optics and Photonics
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• v.16 no.2
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• pp.162-167
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• 2005

An optical directional coupler, which consists of quantum wells with nanothickness, is designed by using Modal Transmission Line Theory (MTLT). To demonstrate the validity and usefulness, the propagation characteristics and the coupling efficiencies are rigorously evaluated at nanoscale couplers, which consist of double quantum wells with different effective masses. The numerical result reveals that the coupling efficiency of nanoscale couplers is maximized at a coupling length 2052.3 nm, if the total electron energy is 83.9 meV. Furthermore, the coupler operates as a filter with narrower band as the barrier thickness increases.

• Korean Journal of Optics and Photonics
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• v.14 no.3
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• pp.286-291
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• 2003

Asymmetric multiple quantum well ridge waveguide laser diodes (AMQW RWG LDs) with a wide and flat gain spectrum were designed and fabricated. The operating parameters and gain spectra were measured and analyzed for uncoated and anti-reflection (AR) coated LDs. For AR coated 500 mm-long RWG LOs, the extremely flat gain spectrum over a spectral range of 90 nm was obtained at the current 75 ㎃.

• Current Optics and Photonics
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• v.2 no.5
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• pp.468-473
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• 2018

We investigate the temperature dependence of efficiency droop in InGaN/GaN multiple-quantum-well (MQW) blue light-emitting diodes (LEDs) in the temperature range from 20 to $80^{\circ}C$. When the external quantum efficiency (EQE) and the wall-plug efficiency (WPE) of the LED sample were measured as injection current and temperature varied, the droop of EQE and WPE was found to be reduced with increasing temperature. As the temperature increased from 20 to $80^{\circ}C$, the droop ratio of EQE was decreased from 16% to 14%. This reduction in efficiency droop with temperature can be interpreted by a temperature-dependent carrier distribution in the MQWs. When the carrier distribution and radiative recombination rate in MQWs were simulated and compared for different temperatures, the carrier distribution was found to become increasingly homogeneous as the temperature increased, which is believed to partly contribute to the reduction in efficiency droop with increasing temperature.

• Korean Journal of Optics and Photonics
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• v.4 no.2
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• pp.233-241
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• 1993

Quantum superposition states are reviewed from an optical point of view. Production of the optical superposition states, nonclassical properties of the superposition states and influence of vacuum on the nonclassical properties of the superposition states are discussed.

• Korean Journal of Optics and Photonics
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• v.5 no.1
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• pp.173-181
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• 1994

An experiment on the correlation of a photon pair is introduced. The results are analyzed in the framework of quantum optics. It is shown that the vacuum state of light plays an important role for the manifestation of the non local correlation. The correlation can be explained neither by classical wave optics nor by any theory based on the idea of local reality. ality.

• Current Optics and Photonics
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• v.1 no.5
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• pp.491-499
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• 2017

Ghost imaging offers great potential, with respect to standard imaging, for imaging objects in optically harsh or noisy environments. It can solve the problems that are difficult to solve by conventional imaging techniques. Recently, it has become a hot topic in quantum optics. In this paper, we propose a scheme for ghost imaging based on rosette scanning, named rosette ghost imaging. Sampling a small area sampling instead of the whole object, the instantaneous field of view of rosette scanning is used as the modulation light field in ghost imaging. This scheme reduces energy loss, the number of samples, and the sampling time, while improving the quality of the reconstructed image.

• Korean Journal of Optics and Photonics
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• v.7 no.3
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• pp.219-226
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• 1996

The wave-particle duality of light plays important role in quantum optics and it often produces a result different from that of classical wave theory. In this paper, we study the intensity and phase fluctuation of light which show certain change after light goes through a beam splitter, and show the difference between the classical and quantum theory. We show quantitatively that the uncertainty of phase increases at the output of a beam splitter due to the contribution of vacuum fluctuation, even though classical theory predicts no such change in phase fluctuation. The expectation values of normally ordered operators are introduced where the vacuum effect is naturally eliminated, and it is shown that the classical informations are recovered in this way. Analysis on the expectation values produces a distinction between measured phase and inferred phase values and they are related through the contribution of vacuum field.

• Advances in nano research
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• v.3 no.1
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• pp.1-11
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• 2015

Thin film ethanol sensors made from ${\alpha}-Fe_2O_3$ decorated with multiwall carbon nanotubes(MWCNTs) were manufactured by the electron beam deposition method. The morphology of the decorated ${\alpha}-Fe_2O_3$/MWCNTs (25:1 weight ratios) nanocomposite powder was investigated using the scanning electron microscopy and X-ray diffraction techniques. The thickness of thin films has been determined from ellipsometric measurements. The response of manufactured sensors was investigated at different temperatures of the sensor work body and concentration of gas vapors. Good response of prepared sensors to ethanol vapors already at work body temperature of $150^{\circ}C$ was shown.