Jin-Seung Sohn

Two-dimensional photonic crystal color filter development

Reflective color filters using two-dimensional photonic crystals based on sub-wavelength gratings were proposed and constructed. Using low-cost nanoimprint lithography, an amorphous silicon layer was deposited through the low-temperature PECVD process and patterned into two-dimensional structures. The isolated amorphous silicon patterns were readily crystallized using a multi-shot excimer laser annealing at low energy. A study of the close relationship between color filter reflectance and silicon pattern crystallinity is introduced. Theoretical and experimental results show that the proposed color filters have high reflectance and, moreover, decrease the dependence on incident angle compared to one-dimensional photonic crystal color filters.

Design of multi-functional dual hole patterned carbon nanotube composites with superhydrophobicity and durability

AbstractMost current research on nanocomposites has focused on their bulk attributes, i.e., electrical, microwave, thermal, and mechanical properties. In practical applications, surface properties such as robustness against environmental contamination are critical design considerations if intrinsic properties are to be maintained. The aim of this research is to combine the bulk properties of nanocomposites with the superhydrophobic surface properties provided by imprinting techniques to create a single multi-functional system with enhanced bulk properties. We report the development of a highly conductive superhydrophobic nanotube composite, which is directly superimposed with a durable dual hole pattern through imprinting techniques. The dual hole pattern avoids the use of high slenderness ratio structures resulting in a surface which is robust against physical damage. Its stable superhydrophobic properties were characterized both theoretically and experimentally. By incorporating high aspect ratio carbon nanotubes (CNTs), the dual patterned composites can also be effectively used for anti-icing and deicing applications where their superhydrophobic surface suppresses ice formation and their quick electric heating response at low voltage eliminates remaining frost. In addition, superior electromagnetic interference (EMI) shielding effectiveness (SE) was attained, with one of the highest values ever reported in the literature.

Development of Integrated Small-Form-Factor Optical Pickup with Blu-ray Disc Specification

In this study, a small-form-factor optical pickup (SFFOP), corresponding to the Blu-ray disc (BD) specifications has been developed. The developed SFFOP is composed of an integrated optical pickup and a swing-arm-type actuator. The integrated optical pickup has been developed in the form of an array using wafer-level fabrication technology. The developed SFFOP is composed of the fundamental optics which yields a numerical aperture (NA) of 0.85 and uses a blue laser diode having a short wavelength of 407 nm and a silicon optical bench, which consists of a laser diode, a photodiode and several mounts for the laser diode, an objective lens and mirrors. The micro objective lens is bonded to the lens holder on the SFFOP by an active alignment using a modified Mach–Zehnder interferometer. Also, a static focus error signal was detected to assemble a polarized holographic optical element. Through the measurement of the focus error signal with a swing-arm-type actuator, which was developed for the SFFOP, it is estimated that the developed SFFOP satisfies the BD specifications with the balance of the focus error signal below 10%.

The fabrication of Co-Pt electro-deposited bit patterned media with nanoimprint lithography.

Bit patterned media with 25 nm hole diameter and 50 nm pitch size were fabricated with serial processes comprising master patterning with electron-beam lithography, a Si etching process, multi-layer soft stamp replication, and UV nanoimprinting, followed by Co-Pt magnetic material filling by electro-deposition. From these processes, the designed patterns were well defined, and perpendicular magnetic anisotropy of the fabricated bit patterned media was obtained.

Dynamic absorber for actuator arm in a disk drive

Dynamic absorber is introduced to assist in controlling the amplitude and acceleration of the actuator arm in disk drive so that it can improve the shock handling capability in both operation and non-operating condition. The effect of the dynamic absorber on shock performance is examined through numerical simulation and experimental test.

Development of Microlens for High-Density Small-Form-Factor Optical Pickup

A microlens of numerical aperture (NA) 0.85 a small-form-factor optical pickup, following the specifications of the Blu-ray disc (BD), was designed, fabricated and evaluated. To avoid difficulties in the fabrication of a high-NA objective lens and to obtain a low chromatic aberration, a new hybrid lens unit was designed to have a refractive lens and a diffractive lens. The micro-plano-aspheric refractive lens was fabricated using glass molding technology, and the diffractive lens was fabricated in a two-dimensional array using the electron beam mastering and consecutive UV embossing process. For the evaluation of the developed lens unit, diffraction efficiency was measured with the proposed diffraction efficiency measurement method, and the wavefront error of the lens unit was evaluated using a modified Mach–Zehnder interferometer. The measured average efficiency of the diffractive lens was approximately 85% and the RMS wavefront error of the lens unit was 0.0376 λrms.

Polymeric light delivery via a C-shaped metallic aperture

A polymeric light delivery system with a C-shaped metallic nanoaperture is proposed for the heat-assisted magnetic recording. This light delivery system has high optical efficiency and easy fabricability in the low temperature process that is compatible with the conventional magnetic head. The light delivery characteristics are demonstrated analytically and experimentally. In particular, the near-field spot size of the light delivery system was measured using the virtual scanning near-field optical microscopy (VSNOM) method, in which the probe tip geometry is not reflected. The probable spot size of the developed light delivery is under 100 nm at a wavelength of 780 nm from a polymeric light delivery with the C-shaped metallic nanoaperture.

90° bent metallic waveguide with a tapered C-shaped aperture for use in HAMR

An efficient and compact method of introducing light into a magnetic recording head for use in Heat Assisted Magnetic Recording (HAMR) is proposed. The technique uses a polymer waveguide to source light into a novel metallic structure consisting of a sub-wavelength C-aperture waveguide with a 90° bend and a tapered section. The structure is modeled using Finite Difference Time Domain (FDTD) simulations and it is shown that the 90° bend allows for low loss near-field optical access into a conventional magnetic recording head while the tapered C-waveguide allows for maximum input coupling and a minimum spot size at the recording media.

Single crystal-like Si patterns for photonic crystal color filters

A novel fabrication method for a two-dimensional photonic crystal color filter based on guided mode resonance is proposed. An amorphous silicon layer deposited through the low-temperature plasma enhanced chemical vapor deposition (PECVD) process is patterned into two-dimensional structures using low-cost nanoimprint lithography. It is then effectively crystallized using multi-shot excimer laser annealing at low energy. We have demonstrated analytically and experimentally that single crystal-like silicon patterns on a glass substrate can offer high-efficiency photonic crystal color filters for reflective display applications. The highly crystallized silicon patterning scheme presented here may be very attractive for a variety of devices requiring high carrier mobility and high optical efficiency.

Super slim optical pickup for mobile storage device applications

This paper addresses the design, fabrication and packaging issues of SSOP(super slim optical pickup) module using blury technology. By using blu-ray technology, which uses a 407nm LD (Laser Diode) and an objective lens having NA (Numerical Aperture) 0.85, storage devices become miniaturized but have a high capacity. The developed prototype uses the integrated structure of a SiOB (Silicon Optical Bench) and a mirror substrate. The SiOB should be processed in order that a thin film PD(Photodiode) and interconnections, LD, Lens, QWP(Quarter Wave Plate) and HOE can be placed, and on the Silicon Substrate should Micromachined Silicon Mirror be formed. The SiOB is aligned and bonded with the wafer on which Silicon Mirror was formed. Then, it is diced. Because it is fabricated through this order, the super slim optical pickup can be fabricated by using wafer-level process. As a final step LD on the SiOB and HOE are mounted, assembled and bonded using an active alignment. The proposed SSOP was prototyped and characterized by measuring wavefront error and detecting static focusing and tracking error signals.