Hojun Ryu

Holographic polarization-selective module based on a small Dove prism coupler for magneto-optical pickup heads

A new structure for polarization-selective elements, consisting of two holographic gratings and a Dove prism coupler, is proposed. The absence of a multistage waveguide and the benefits of compact size and lightweight volume are the outstanding features of the new structure. Based on the coupled-wave theory, the analysis and design of the structure are discussed in detail to calculate the required index modulation. Several parameters, such as the recording intensity, the exposure time, and the recording angles for the fabrication of the proposed element, are determined. Under these conditions, the element is fabricated in Dupont photopolymer HRF-150-38 material and with an operating wavelength of 532 nm. A simplified pickup head is constructed to evaluate the performance of the fabricated element.

Ultraviolet-replicated focusing grating coupler in polymers at a wavelength of 405 nm

A focusing grating coupler (FGC) in a polymer for a wavelength of 405 nm was implemented on a slab waveguide using nanoscale ultraviolet (UV) replication process. The polymer FGC with a high numerical aperture of 0.85 was designed by Bloch wave theory with the minimum spacing between adjacent grating ridges of 85 nm and replicated from the master pattern. After UV irradiation at an energy density of 2.68J∕cm2 and a loading force of 1 kN for 2 min, the replicated polymer FGC produced a spot size of 347 nm on the focal plane measured at the full width at half maximum. The out-coupling efficiency of the grating is 34%.

Focusing grating coupler for blue laser light

A focusing grating coupler (FGC) for use with a blue laser of 400-nm wavelength as a light source was fabricated for the first time. The FGC was designed to have a numerical aperture of 0.48 and a minimum period of 0.2 /spl mu/m when the focal length and the grating area were 900 /spl mu/m and 1/spl times/1 mm/sup 2/, respectively. Grating pattern of minimum line of 0.1 /spl mu/m was fabricated on a waveguide based on the boron phosphor-silicate glass material by electron-beam lithography process using the vector scan method. The spot size at the full width (1/e/sup 2/) was measured as 0.92 and 0.85/spl mu/m in x and y directions and was nearly the same as the diffraction limit.

Nanoimprinted Focusing Grating Coupler for an Ultra Slim Optical Pickup Head

Nanoimprinted focusing grating couplers (FGCs) for ultra slim optical pickup head application have been investigated. Inorganic electron beam resist hydrogen silsesquinoxane (HSQ) was used as a master for FGC replication, and polymethylmethacrylate (PMMA) as a transparent stamper for ultra violet (UV) exposure embossing. UV embossing was employed to replicate the fine featured grating patterns in FGC. The focused spot size measured from the replicated coupler showed almost the same quality as theoretically predicted one.

Fabrication of focusing grating coupler using e-beam lithographed hydrogen silsesquioxane

A focusing waveguide grating coupler made of hydrogen silsesquioxane is fabricated successfully. The size of the focusing grating coupler is 1 mm×1 mm and the total device size is 8 mm×2 mm. The numerical aperture and the minimum line width of the device are 0.85 and 85 nm, respectively. The spot size of this coupler is 335 nm for blue laser and the out-coupling efficiency is 25.7%.

High-NA focusing grating coupler using a blue laser

A focusing grating coupler (FGC) using a blue laser of a wavelength of 400 nm as a light source was fabricated for the first time. The FGC was designed to have a numerical aperture of 0.48 and a focusing angle of zero. The focal length and the grating area were 900 μm and 1×1mm2, respectively. Grating pattern of a minimum period of 0.2μm was fabricated on a single mode waveguide based on the boron phosphor silicate glass (BPSG) material by electron-beam lithography process using the vector scan method. The spot size at the full width (1/e2) was measured at 0.85 and 0.92μM in x and y direction, respectively, and these values are nearly same as the diffraction limited size.

Polymer focusing grating coupler implemented by nanoimprinting method for the use of blue laser

A polymer focusing waveguide grating coupler(FGC) was implemented by UV nanoimprinting method. The size of this focusing grating is 1 mm X 1 mm and the total device size is 8 mm X 2 mm. We used the UV sensible polymer which is coated by spin coating method. After nanoimprinting the device, the residual thickness on the slab waveguide is about 10 nm ~ 30 nm. The numerical aperture (NA) and the minimum line width polymer FGC are 0.85 and 85 nm, respectively. The spot size of this polymer FGC is 347 nm for blue laser and the out-coupling efficiency is 27.7%.

Magneto-Optical Properties of Multilayered FePt for High Density Recording

The Si 3 N 4 /FePt/Si3N4/Al/Si structures have been fabricated. 57 nm silicon nitride films have been used as dielectric layer for heat dissipation and 500 nm Al film used for reflection layer. The Kerr rotation angle was changed with the FePt layer thickness. At the 65 % Pt composition in 10 nm FePt layer, the maximum Kerr rotation angle was 0.82°. As increase with FePt thickness the Kerr angle is slightly decreased. The change of Kerr rotation angle and the thermal behavior of multilayered structure according to FePt thickness variation were also calculated by computer simulation.

An UV-Replicated Polymer Focusing Grating Coupler for Blue Light

A polymer focusing grating coupler was implemented on a slab waveguide using nanoscale UV-replication process. Numerical aperture and spot size were measured at 0.85 and 347 nm, respectively. The out-coupling efficiency was 28 % although aberration induced distortion of the beam shape should be further reduced.

Implementation of a micro-optical pickup using a focusing waveguide grating coupler

A micro-optical pickup has been implemented by using a focusing waveguide grating coupler. The grating coupler was designed and fabricated on a single mode BPSG (boron phosphor silica glass) waveguide layer. The coupling area was 1×1mm2 containing more than 1,500 grating lines, where the maximum and minimum grating pitch were 296nm and 811nm, respectively. The focal length and the numerical aperture of the present grating coupler were 530 μm and 0.68 with 632.8nm He-Ne red laser. The full width half maximum diameter of the focal spot was measured to be 450 nm and 510 nm in x and y direction.