• 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.

• Journal of the Optical Society of Korea
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• v.13 no.4
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• pp.468-471
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• 2009

We propose a simple nondestructive method to obtain refractive-index profiles of a graded-index (GRIN) light-focusing rod by means of a diffraction grating. In our proposed method, a laser beam is illuminated through a diffraction grating perpendicular to the axis of the GRIN lens and the separation between the zeroth and first-order diffraction peaks is measured and analyzed. The results demonstrate that the refractive-index profiles of commercially available GRIN lenses can be successfully reconstructed.

• Macromolecular Research
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• v.11 no.4
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• pp.236-240
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• 2003

Fabrication of a graded index profile was possible via photochemical reaction of cinnamoyl groups with 350 nm wavelength UV light to form crosslinked structures. Such structural change may induce the change in the refractive index. In order to generate graded index profile in the PMMA polymer optical fiber (POF) with cinnamoyl groups by photochemistry, a methyl methacrylate monomer containing a cinnamoyl functional group in the side chain were prepared. This monomer was then copolymerized with methyl methacrylate with various compositions not only to utilize advantages of poly(methyl methacrylate) but also to overcome the drawbacks of the cinnamate homopolymer. Changes of refractive indices were investigated with various contents of cinnamoyl group and varying irradiation time. Large change in the refractive index (${\Delta}{\approx}0.01$) and its proper profile shape ($g{\approx}2.2$) can be obtained by changing irradiation time.

• Journal of the Optical Society of Korea
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• v.7 no.3
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• pp.156-159
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• 2003

Permanent structure of photoinduced singlemode waveguide in optical fluoride glasses was demonstrated using the self-channeled plasma filament excited by a femtosecond (110 fs) Ti:sapphire laser ($λ_p$ = 800 nm). The photoinduced refractive index modification in ZBLAN glasses reached a length of approximately 10 - 15 mm from the input surface of the optical glass with the diameters ranging from 5 to 8 ${\mu}{\textrm}{m}$ at input intensities more than l.0 ${\times}$ $10^{12}$ W/$\textrm{cm}^2$. The graded refractive index profiles were fabricated to be a symmetric form from the center of an optical fluoride glass and a maximum value of refractive index change (ㅿn) was measured to be l.3${\times}$$10^{-2}$. The beam profile of the output beam transmitted through the modified region showed that the photoinduced refractive index modification produced a permanent structure of singlemode waveguide.

• Laser Solutions
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• v.15 no.1
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• pp.15-19
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• 2012

The fabrication of internal diffraction gratings with photoinduced refractive index modification in transparent materials was demonstrated using low-density plasma formation excited by a femtosecond (130 fs) Ti: sapphire laser (${\lambda}_p$=800 nm). The refractive index modifications with diameters ranging from $1{\mu}m$ to $3{\mu}m$ were photoinduced after plasma formation occurred upon irradiation with peak intensities of more than $2.0{\times}10^{13}W/cm^2$. The graded refractive index profile was fabricated to be a symmetric around from the center of the point at which low-density plasma occurred.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.9
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• pp.36-42
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• 1997

Optical filters with graded index profiles are designed by applying the fourier transform to a riccati equation which governs the reflection and transmission characteristics of inhomogeneous refractive index distributions. The inhomogeneous refractive index profile of an optical filter with specified target spectrum is obtained through iterations. The spectra response of the inhomogeneous refractive index layers are analyzed by using runge-dutta numerical method to solve the differential euations of the amplitude and the phase of reflection coefficient derived from the riccati equation and the results are in good agreement with the resutls obtained by using matrix method.

• Laser Solutions
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• v.17 no.2
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• pp.19-25
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• 2014

Optical embedded diffraction gratings with the bulk modification in BK-7 glass plates excited by tightly focused high-intensity femtosecond (130fs) Ti: sapphire laser (peak wavelength = 790nm) were demonstrated. The structural modifications with diameters ranging from 400nm to $4{\mu}m$ were photo-induced after plasma formation occurred upon irradiation with peak intensities of more than $1{\times}1013W/cm^2$. The graded refractive index profile was fabricated to be a symmetric around from the center of the point at which low-density plasma occurred. The maximum refractive index change was estimated to be $1.5{\times}10^{-2}$. The two optical embedded gratings in BK-7 glass plate were demonstrated with refractive index modification induced by the scanning of low-density plasma formation.

• Laser Solutions
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• v.14 no.1
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• pp.1-5
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• 2011

Photo-induced gratings m flexible PDMS (polydimethly siloxane) film are directly written by a high-intensity femtosecond (130fs) Ti: Sapphire laser (${\lambda}_p$ = 800nm). The refractive index modifications with $4\;{\mu}m$ diameters were photo-induced after the femtosecond irradiation with peak intensities of more than $1{\times}10^{11}W/cm^2$. The graded refractive index profile was fabricated to be a symmetric around the center of the point at which femtosecond laser by controlling both laser power and focused depth. The change on refractive index in the laser-modified regions was estimated to be approximately $10^{-3}$. The internal flexible symmetric diffraction gratings in PDMS film was successfully fabricated using a femtosecond laser.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.14 no.4
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• pp.307-320
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• 1989

This paper presetns new design of the Modified Chemical Vapor Deposition(MCVD) system for optical fiber preform fabrication. It contains a glass working lathe, raw material supplier and exhaust gas treatment apparatus as fundamental instruments for MCVD process, graded index fiber design, characteristic of process and the experimenta arrangement to measure the refractive index profile of MCVD preforms, respectively. From the investigation results, it is shown that an ideal graded index fiber preform does not exhibit a center dip or bump.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.5
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• pp.565-570
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• 2017

The various techniques proposed previously to obtain a good antireflection(AR) coating induce a scattering of incident light by nanoparticles or control the refractive index by using different materials. This paper compares a suggested graded index profile with the quintic index profile previously suggested for producing an index profile that gives good performance from an AR coating. We assume the structure of the AR coating has three, six, and nine layers with 180 nm total thickness. The wavelength of incident light ranges from 300 nm to 1100 nm. We use the transfer matrix theory for a single layer to obtain the reflectivity of three, six, and nine layers. The reflectivity of two different index profiles with three, six, and nine layers is compared. As a result, the suggested graded index profile shows lower reflectivity than the quintic index profile with three layers, especially in the wavelength range from about 600 nm to 1100 nm. Therefore, we expect that these results can be applied to optical devices and filters in the range from visible(red) to near infrared.