• Current Optics and Photonics
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• v.6 no.1
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• pp.23-31
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• 2022

Heterodyne efficiency is an indicator to evaluate the performance of space coherent laser communication systems. It is affected by signal light and local oscillator (LO) light amplitude, phase and polarization state. In this paper, based on the common heterodyne efficiency, a heterodyne efficiency model that can reflect polarization aberration of optical system is proposed. The heterodyne efficiency is analyzed when the signal light and the LO light are linearly polarized or circularly polarized. For a coherent communication optical system, when the incident signal light is right-circularly polarized light and the incident LO light is 45° linear polarized light. Based on the three-dimensional ray tracing theory and the heterodyne efficiency proposed in this paper, the change of polarization states and the distribution of heterodyne efficiency of the signal light and LO light influenced by the optical system's polarization aberration are analyzed. Analysis shows that the heterodyne efficiency model proposed in this paper can be used to evaluate coherent communication systems and reflect the influence of optical system polarization aberration.

• Journal of Radiation Industry
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• v.11 no.3
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• pp.157-165
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• 2017

In this paper, we calculate the light photons collection efficiency of large-volume plastic scintillation detector mainly used for radiation portal monitor (RPM). A Monte Carlo light photon transport code, DETECT2000, were used to quantitatively evaluate light collection efficiency of plastic scintillation detector. DETECT2000 calculated the placement of light collection efficiency based on the energy spectrum. We calculated the light collection efficiency relative to the position of the energy spectrum that proportional to the placement of the source. The $850{\times}285{\times}65mm^3$ size of polyvinyl toluene (PVT) scintillator was used for measurements. Through DETECT2000 simulation, the light collection efficiency of $5{\times}5$ arrays were calculated and verification was performed by comparing with experimentally measured. And then, the corrected MCNP simulation by applying the light collection efficiency in $21{\times}13$ arrays was compared and analyzed. Comparing the Monte Carlo simulation with measured results, it shows an average difference of 10.1% in $5{\times}5$ arrays. Particularly, about twice of the difference was found in the edge of first column, which coupled with PMT. In whole $5{\times}5$ array, the overall ratio was the same except for the first column. And then comparing the energy spectra of the $21{\times}13$ array with and without the light collection efficiency, it shows a difference of 6.69% in Compton edge area. The DETECT2000 based light collection efficiency simulation showed well agreement with the point source experiment. And comparing with measured energy spectra, we could compare the differences according to whether or not the light collection efficiency was applied. As a results, it is possible to increase the accuracy and reliability of Monte Carlo simulation results by pre-calculating the light collection efficiency according to the PVT geometry by using the DETECT2000.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.10
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• pp.676-681
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• 2015

Recently many studies being carried out to increase the light efficiency of LED. The external quantum efficiency of LED, generally the light efficiency, is determined by the internal quantum efficiency and the light extraction efficiency. The internal quantum efficiency of LED was already reached to more than 90%, but the light extraction efficiency is still insufficient compared with the internal quantum efficiency because the total internal reflection is generated in the interface between the LED chip and air. Thus, we studied about flip chip LED with PSS and performed the optical simulation which find more optimized PSS for flip chip LED to increase the light extraction efficiency. Decreasing of the total internal reflection and effect of diffused reflection according to PSS improved the light extraction efficiency. To get more higher the efficiency, we simulated flip chip with PSS that the parameters are arrangement, edge spacing, radius, height and shape of PSS.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.38.2-38.2
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• 2010

Biomimetc is a new domain of learning that proposes a solution getting clues from nature. There seems to be a sign of this phenomenon in fields of Renewable Energy. Foe example, Wind power was imitate the whale's fin that was improve efficiency of generating energy. This study focused on the photovoltaic generation as the instance of applying biomimetic. Efficiency is the most important factor in field of Photovoltaic generation. When given solar cell taking the sun light, most important fields of the study are absorb more light and increase the quantity of generation. For improving efficiency, the solar cell were builded up textures of taking a pyramid form, such a surface structure taking a role for remaining the light. This effects do the role as increasing absorbing efficiency. Such phenomenon calls Light Trapping, locking up the light on the surface of solar cell for a long time. Light is a vital factor to plants in the nature. Plants grow up through the photosynthesis that absorbing light for growth and propagation. So, plants make a effort how can absorb more the light in poor surroundings. This study set up a goal that imitates the minute surface structure of plants and applies to the existing solar cells's surface structure, so it can improve the efficiency of absorbing light. We used Light Tools software analyzing geometrical optics to analyze efficiency about new designed textures on the computer. We made a comparison between existing textures and new designed textures. Consequently, new designed textures were advanced efficiency, absorbing rates of light increasing about 7 percent. In comparison with existing and new textures, advancing about 20 percent in the efficient aspect.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.421-421
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• 2006

The light and energy-efficiency of classical liquid crystal displays is notoriously poor due to the use of absorption-based linear polarisers and colour filters. For instance, the light efficiency of PVAL polarisers is typically between 40 and 45 % and the colour filters have a typical efficiency below 35 % which results in a total light and energy-efficiency of the display below 10 %. In the past, a variety of polarizers were developed with an enhanced efficiency in generating linearly polarized light. Typically, these polarizers are based on the polarisationselective reflection, scattering or refraction of light i.e. one polarisation direction of light is directly transmitted to the LCD/viewer and the other polarization direction of light is depolarised and recycled which results in a typical efficiency for generating linearly polarized light of 70-85 %. Also, special colour filters have been proposed based on chiral-nematic reactive mesogens which increase the efficiency of generating colour. Despite the enormous progress in this field, a need persists for improved methods for generating polarized light and colour based on low cost optical components with a high efficiency. Here, the use of holographic phase gratings is reported for the generation of polarized light and colour. The phase grating are recorded in a photopolymer which is coated onto a backor frontlight for LCDs. Typically the recording is performed in the transmisson mode or in the waveguiding mode and slanted phase gratings are generated with their refractive index modulation at an angle between 20o and 45o with the normal of the substrate. It is shown that phase gratings with a high refractive index modulation and a high efficiency can be generated by a proper selection of the photopolymer and illumination conditions. These phase gratings coupleout linearly polarized light with a high contrast (> 100) and the light is directed directly to the LCD/viewer without the need for redirection foils. Dependent on the type of phase grating, the different colours are coupled-out at a slightly different angle which potentially increases the efficiency of classical colour filters. Moreover, the phase gratings are completely transparent in direct view which opens the possibility to use them in frontlights for LCDs. Holographic polarization gratings posses a periodic pattern in the polarization state of light (and not in the intensity of light). A periodic pattern in the polarization direction of linearly polarized light is obtained upon interference of two circularly polarized laser beams. In the second part of the lecture, it is shown that these periodic polarization patterns can be recorded in a linear photo-polymerizable polymer (LPP) and that such an alignment layer induces a period rotation in the director of (reactive and non-reactive) liquid crystals. By a proper design, optical components can be produced with only first order diffraction and with a very high efficiency (>0.98). It is shown that these diffraction gratings are potentially useful in projection displays with a high brightness and energy efficiency

• Korean Journal of Materials Research
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• v.22 no.10
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• pp.519-525
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• 2012

Enhancement of light trapping in solar cells is becoming increasingly urgent for the development of next generation thin film solar cells. One of the possible candidates for increasing light trapping in thin film solar cells that has emerged recently is the use of scattering from metallic nanostructures. In this study, we have investigated the effects of the geometric parameters of Ag nanorings on the light scattering efficiency by using three dimensional Finite Different Time Domain (FDTD) calculations. We have found that the forward scattering of incident radiation from Ag nanorings strongly depends on the geometric parameters of the nanostructures such as diameter, height, etc. The forward scattering to substrate direction is increased as the outer diameter and height of the nanorings decrease. In particular, for nanorings larger than 200 nm, the inner diameter of Ag nanorings should be optimized to enhance the forward scattering efficiency. Light absorption and scattering efficiency calculations for the various nanoring arrays revealed that the periodicity of nanorings arrays also plays an important role in the absorption and the scattering efficiency enhancement. Light scattering efficiency calculations for nanoring arrays also revealed that enhancement of scattering efficiency could be utilized to enhance the light absorption through the forward scattering mechanism.

• Journal of Photoscience
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• v.7 no.4
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• pp.139-142
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• 2000

To examine applicability of some optical indices from reflectance to estimate photosynthetic light use efficiency, photosynthesis, and narrow band spectral reflectance were simultaneously measured at various intensities of light with mongolian oak leaves. Narrow band of the broad-band NDVI was better than photochemical reflectance index and simple ratio to estimate photosynthetic light use efficiency in this study. Changes in spectral reflectance were detected at several wavelengths (540nm, 690nm, 740nm, and 800nm) associated with physiological status of plant leaves that could be components for new optical indices.

• Journal of Electrochemical Science and Technology
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• v.1 no.2
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• pp.69-74
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• 2010

Methodologies to improve photovoltaic performance of dye-sensitized solar cell (DSSC) are reviewed. DSSC is usually composed of a dye-adsorbed $TiO_2$ photoanode, a tri-iodide/iodide redox electrolyte and a Pt counter electrode. Among the photovoltaic parameters of short-circuit photocurrent density, open-circuit voltage and fill factor, short-circuit photocurrent density is the collective measure of light harvesting, charge separation and charge collection efficiencies. Internal quantum efficiency is known to reach almost 100%, which indicates that charge separation occurs without loss by recombination. Thus, light harvesting efficiency plays an important role in improvement of photocurrent. In this paper, technologies to improve light harvesting efficiency, including surface area improvement by nano-dispersion, size-dependent light scattering efficiency, bi-functional nano material, panchromatic absorption by selective positioning of three different dyes and transparent conductive oxide (TCO)-less DSSC, are introduced.

• Journal of the Optical Society of Korea
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• v.17 no.1
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• pp.22-26
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• 2013

The author analyzes the luminous efficiency of the phosphor-conversion white light-emitting diode (LED) that consists of a blue LED chip and a yellow phosphor. A theoretical model is derived to find the relation between luminous efficiency (LE) of a white LED, wall-plug efficiency (WPE) of a blue LED chip, and the phosphor absorption ratio of blue light. The presented model enables to obtain the theoretical limit of LE and the lower bound of WPE. When the efficiency model is applied to the measured results of a phosphor-conversion white LED, the limit theoretical value of LE is obtained to be 261 lm/W. In addition, for LE of 88 lm/W at 350 mA, the lower bound of WPE in the blue LED chip is found to be ~34%. The phosphor absorption ratio of blue light was found to have an important role in optimizing the luminous efficiency and colorimetric properties of phosphor-conversion white LEDs.

• Korean Journal of Materials Research
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• v.32 no.6
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• pp.293-300
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• 2022

This study investigated a graded-refractive-index (GRIN) coating pattern capable of improving the light extraction efficiency of GaN light-emitting diodes (LEDs). The planar LEDs had total internal reflection thanks to the large difference in refractive index between the LED semiconductor and the surrounding medium (air). The main goal of this paper was to reduce the trapped light inside the LED by controlling the refractive index using various compositions of (TiO₂)_x(SiO₂)_1-x in GRIN LEDs consisting of five dielectric layers. Several types of multilayer LEDs were simulated and it was determined the transmittance value of the LEDs with many layers was greater than the LEDs with less layers. Then, the specific ranges of incident angles of the individual layers which depend on the refractive index were evaluated. According to theoretical calculations, the light extraction efficiency (LEE) of the five-layer GRIN is 25.29 %, 28.54 % and 30.22 %, respectively. Consequently, the five-layer GRIN LEDs patterned enhancement outcome LEE over the reference planar LEDs. The results suggest the increased light extraction efficiency is related to the loss of Fresnel transmission and the release of the light mode trapped inside the LED chip by the graded-refractive-index.