• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.7
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• pp.56-65
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• 1999

In this paper, a pixelated binary phase grating to generate $5{\times}5$ spots in designed using simple Genetic Algorithm(sGA) composed of selection, crossover, and mutation operators, and it can be applied for the optical interconnection. So as to adapt that GA is a robust and efficient schema, a chromosome is coded as a binary integer of length $32{\times}32$, the ranking method for decreasing the stochastic sampling error is performed, and a single-point crossover having $16{\times}16$ block size is used. A designed grating when the probabillty of mutation is 0.001, the probability of crossover is 0.75 and the population size is 300 has a 74.7[%] high diffraction efficiency and a $1.73{\times}10^{-1}$ uniformity quantitatively.

• Korean Journal of Optics and Photonics
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• v.17 no.3
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• pp.273-277
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• 2006

In this paper, we constructed the Littman type and fixed Littrow type tunable external-cavity diode laser systems. The laser output, which is the 0th-order diffracted beam from the diffraction grating in an external cavity, was the single longitudinal mode. Its FWHM was measured as less than 9MHz. With the diode driving current of 140mA and operating temperature of $25^{\circ}C$, the coarse tuning range of 5.375nm was measured for the Littman type, and of 13.65nm was measured for the fixed Littrow type. A fine tuning experiment in which an external mirror was rotated by a PZT driven by a sawtooth wave was performed, and its tuning range of 0.042nm was measured for both types. The fixed Littrow type tunable external-cavity diode laser system was an improvement on the conventional Littrow type tunable laser system in which the output direction varies due to the grating embedded in the mirror plate.

• Korean Journal of Optics and Photonics
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• v.12 no.2
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• pp.83-90
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• 2001

The Talbot effect for periodic objects with the spatial period p illuminated by expanded coherent light is analyzed by Fresnel diffraction theory, and the Talbot distance (Zr) at which we can observe 1: 1 imaging without any lenses can be defined. We confmned experimentally the Talbot imaging of line, circular, X -type and '||'&'||'copy;-type 2 dimensional alTay gratings at ZT. At the same time, we observed phase reversed Talbot imaging at Zr/2 and Talbot subimage with p/2 at Zr/4 and 3Zr/4. The visibility of Talbot images as a function of the number of slits of the input grating was measured by the FFf (Fast Fourier Transform) results of these images. As a result stationary maximum visibility of V = 0.25 was obtained from grating numbers with more than 15 slit pairs.

• 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 Optics and Photonics
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• v.7 no.3
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• pp.238-243
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• 1996

We have developed XeCl laser pumped double-resonator Dye laser and two-stage amplifier system, and generated simultaneously of alternatively two wavelengths suitable in DIAL system. The developed double-resonator is composed of 1st and 2nd diffraction orders on light incidence angle in grazing-incidence grating method with 1200 g/mm. We have obtained spectral linewidth below 10 pm and the total efficiency dependent on pump energy over 6%. The tuning ranges dependent on 1st and 2nd diffraction orders are 434~470 nm and 436~468 nm, respectively. The amplification gain and rine-450 dye laser by using the double-resonator laser system and measured the distribution of $NO_2$ concentration over Suwon as the result of transmission of laser output of 6 mJ in this DIAL system. Consequently, we have confirmed that the developed dye laser system is very useful as the tunable source for DIAL.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.5
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• pp.31-38
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• 2000

We propose a new photorefractive demultiplexer(DMUX) which can select the 16 channel signal in WDM optical communication system using the wavelength selectivity and the demultiplexing property through multiple recording of holographic volume grating in photorefractive Fe-LiNbO$_{3}$ crystal. For the multiple writing of the 16 channels having uniform diffraction efficiency, the rotation multiplexing technique and the exposure time schedule are used. Designed DMUX has the 16 channels with 0.5nm spacing between 670nm and 677.5nm and the bandwidth of 0.16nm. From the experimental results, the diffraction efficiency of each channel is 8.3 $\pm$0.62%, the optical loss from fresnel reflection and absorption on the crystal is 0.4cm-1, the 3㏈ bandwidth is 0.16 $\pm$0.005nm and the channel spacing is 0.46~0.5nm.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.6
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• pp.79-86
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• 1999

We propose a new photorefractive demultiplexer(DMUX) for WDM communicaytion system using a wavelength selectivity and demultiplexing properties of a volume holographic grating filters formed in $LinbO_3$ crystal doped with 0.015wt.% Fe. The wavelength selectivity properties of the filter are analyzed and experimentally investigated as a function of the following parameters : the crossing angle of the two writing beams, the reading-beam angle and writing-beam size. In addition, applying these wavelength selectivity properties and the multiplexing technique for recording multiple-exposure filters with equal diffraction efficiency, some preliminary experimental results are presented for use as DMUX.

• The Journal of the Acoustical Society of Korea
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• v.33 no.3
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• pp.200-209
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• 2014

In this paper, we present a general model for synthetic transmit focusing method using plane waves (STF-PW) of which the properties are investigated through mathematical analysis and compared with those of the conventional focusing method. The analysis results show that STF-PW produces non-diffracting beams in the sense that their main lobe widths do not change with depth. We also present a method for synthesis of plane waves to obtain a desired main lobe width while preventing grating lobe generation and a method for broadening the region over which the non-diffracting property is maintained. The proposed model and analysis results were validated through computer simulations.

• Korean Journal of Optics and Photonics
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• v.12 no.4
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• pp.257-262
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• 2001

A Littman type tunable external-cavity diode laser system was developed. The laser output which is the Oth-order diffracted beam from a diffraction grating in an external cavity is a single longitudinal mode. Its FWHM was measured as less than 9 MHz. With the diode driving current of 140 mA and operating temperature of $25^{\circ}C$, the coarse tuning range of 3.475 urn was measured. A fine tuning experiment in which an external mirror was rotated by a PZT driven by a sawtooth wave was performed, and its tuning range of 0.042 urn was measured. sured.

• Journal of the Optical Society of Korea
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• v.13 no.3
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• pp.330-334
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• 2009

A simple and compact frequency swept laser is demonstrated at $1.3{\mu}m$ using a wavelength scanning filter based on a rotating slit disk. The laser is comprised of a pigtailed semiconductor optical amplifier, a circulator, and a wavelength scanning filter in an extended cavity configuration. The wavelength scanning filter is composed of a collimator, a diffraction grating, a rotating slit disk, and a mirror. The instantaneous laser output power is more than 5 mW. The scanning range of the laser is extended to 80 nm at the maximum level, and 55 nm in the full width at half maximum at a scanning rate of 2 kHz.