• Proceedings of the Optical Society of Korea Conference
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• 1990.02a
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• pp.227-231
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• 1990

A SiO2/Si concave diffraction grating(period: 1.3${\mu}{\textrm}{m}$) for the angular dispersive element of WDM was fabricated by sandwiching the SiO2/Si plane diffraction grating between a slab waveguide and a cylindrical concave block. Using this concave grating and input/output fiber, and wavelength division demultiplexer was composed. The demultiplexer has five channels, the insertion loss of 30dB, the wavelength spacing per channel of 7nm and crosstalk of-15dB.

• ETRI Journal
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• v.31 no.2
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• pp.228-230
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• 2009

InP-based planar waveguide 48-channel concave grating demultiplexers with a channel spacing of 0.8 nm (100 GHz) are described and demonstrated. Polarization insensitivity and flattened spectral response are successfully achieved by the introduction of a polarization compensator and a two-focus grating, respectively. The fabricated device shows a polarization-dependent wavelength shift of less than 20 pm and a -3 dB spectral width of about 0.55 nm (68.75 GHz) over all channels.

• Korean Journal of Optics and Photonics
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• v.3 no.2
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• pp.77-85
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• 1992

The design of a flat-field XUV spectrograph is optimized for a high throughput, aberration-corrected spectral image in the wavelength region of 50-300 $\AA$ The varied-line spacing (VLS) concave grating theory for an XUV spectrograph with a toroidal mirror in front of an entrance slit is derived. Since the derived theory includes the arbitrary shaped source, it is able to correct the limit of the simple optimization theory which considers only a point source at the center of the entrance slit. The reflection matrix at the toroidal mirror and the diffraction matrix at VLS grating are derived and compared with those of a holographic grating. The absolute energy efficiency of a flat-field spectrograph is calculated by considering the reflectivities of the toroidal mirror and the Au coated concave grating and the grating efficiency. The alignment sensitivity of the toroidal mirror and the concave grating is investigated, and the method to achieve the best imaging of XUV spectrum is discussed. The calculated resolving power of the flat-field XUV spectrograph is more than 4000 in the aberration-corrected wavelength range. The focused spot size at the dispersion plane is less than $20\mu \textrm m\times \mu \textrm m$at the wavelength 100$\AA$ It is shown that a high throughput characteristic can also be achieved through a careful adjustment of alignment parameters.

• Korean Journal of Optics and Photonics
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• v.13 no.3
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• pp.189-196
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• 2002

The components and alignment parameters of a flat-field soft x-ray spectrometer used in the wavelength range below 50 $\AA$ are determined, and the characteristics of the spectrometer are analyzed. It consists of a toroidal mirror, a slit, a varied line-spacing concave grating, and a soft x-ray detector. The space-resolved spectral image of a source is formed on a single plane using the tordidal mirror and the 2400-grooves/mm varied line-spacing concave grating. The former is used to compensate for the astigmatism caused by the grazing incidence of soft x-ray light on the concave grating. The spectral and spatial resolutions of the spectrometer are calculated by applying the wave front aberration theory, and the diffraction efficiency is calculated by applying the scalar diffraction theory.

• Korean Journal of Optics and Photonics
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• v.14 no.4
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• pp.392-398
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• 2003

We present a novel concept of a phase-shifting diffraction-grating interferometer, which is intended for the optical testing of concave mirrors with high precision. The interferometer is configured with a single reflective diffraction grating, which performs multiple functions of beam splitting, beam recombination, and phase shifting. The reference and test wave fronts are generated by means of reflective diffraction at the focal plane of a microscope objective with large numerical aperture, which allows testing fast mirrors with low f-numbers. The fiber-optic confocal design is adopted for the microscope objective to focus a converging beam on the diffractive grating, which greatly reduces the alignment error between the focusing optics and the diffraction grating. Translating the grating provides phase shifting, which allows measurement of the figure errors of the test mirror to nanometer accuracy.

• Current Optics and Photonics
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• v.5 no.3
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• pp.220-228
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• 2021

To improve the measurement accuracy of a solar-radiation observer instrument, aiming at the problem of multiorder-stray-light interference caused by the diffraction of the flat-field concave grating in the spectroscopic system, straylight suppression methods for different forms of optical traps are studied. According to the grating surface-scattering distribution-function model, the bidirectional scattering distribution function (BSDF) of a dust-polluted surface and the flat-field concave grating's transition area of the spectroscopic system is calculated, and a Lyot stop with blade baffle is designed to suppress this kind of stray light. For diffraction multiorder stray light, based on the theory of light-energy transmission, a design for precise positioning of the trench optical trap is proposed. The superiority of the method is verified through simulation and actual measurement. The simulation results show that in a spectroscopic system approximately 160 mm × 140 mm × 80 mm in size, the energy of the stray light is reduced by one order of magnitude by means of the trench optical trap and Lyot stop, and the number of beams is reduced from 5664 to 1040. The actual measurements show that the stray-light-suppression efficiency is about 69.4%, which is effective reduction of the amount of stray light.

• The Journal of the Acoustical Society of Korea
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• v.35 no.6
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• pp.452-465
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• 2016

In this study, the structure of a concave annular array transducer was optimized to generate high intensity focused ultrasound for medical therapeutic application. The transducer has a phased array structure composed of several concentric channels that have 40 mm as the radius of curvature. We derived theoretical equations to analyze the sound field of the transducer and verified the validity of the equations by comparing the results calculated by the equations with those from finite element analyses. We also checked the possibility of dynamic focusing at around the geometric focal point. Further, the level of a grating lobe occurring at an unwanted position in the transducer sound field was confirmed to be reducible through the relation between the number of channels and the frequency of the transducer. Hence, the structure of the transducer was optimized to place the main lobe within a specific range from the zenith while systematically reducing the level of the maximum sidelobe including the grating lobe. The designed structure showed the performance better than that targeted at all the focal points.

• Korean Journal of Optics and Photonics
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• v.15 no.6
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• pp.495-502
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• 2004

We proposed an analysis model for a Fabry-Perot cavity constructed with a plane-mirrored optical fiber and a concave-mirrored one. We presented the analysis results calculated by inserting practical values into the equations derived. The coupling loss of the cavity and the mirror loss are the most important parameters in reducing the insertion loss of the filter. In order to build a filter of finesse 600, FSR 57 nm, and insertion loss < 3 dB, the plane-concave cavity using mirrors of loss < 0.09% should be aligned for the coupling loss to be less than 0.1 %.

• Publications of The Korean Astronomical Society
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• v.19 no.1
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• pp.65-70
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• 2004

An imaging spectrograph concept optimized for extended far-ultraviolet emission sources is presented. Although the design was originally developed for FIMS aboard the first Korean science satellite STSAT-l launched on September 27, 2003, no rigorous theoretical background of the spectrograph design has been published. The spectrograph design employs an off-axis parabolic cylinder mirror in front of a slit that guides lights to a diffraction grating. The concave grating provides moderate spatial resolution over a large field of view. This mapping capability is absent in most astronomical instruments but is crucial to the understanding of the nature of a variety of astrophysical phenomena. The aberration theory presented in this paper can be extended to holographic gratings in order to improve the spatial as well as the spectral resolutions.

• Journal of the Microelectronics and Packaging Society
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• v.22 no.3
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• pp.73-77
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• 2015

This paper presents integrated polymeric spectrometer module which offers compact size, easily-fabricated structure and low cost. The proposed spectrometer module includes the nano diffraction grating with non-uniform pitch and planar optical waveguide with concave mirror to be fabricated by UV imprint lithography. To increase the reflection efficiency, we designed the nano diffraction grating with triangular profiles. The polymeric planar spectrometer includes a spectral bandwidth of 700 nm, resolution of 10 nm and precision below 5 nm. This polymeric planar spectrometer is well-suited for sensor system.