Ju-Seung Lee

A gain-clamped SOA-Raman hybrid amplifier for a CWDM access network without gain-saturation induced crosstalk

We demonstrate an 80-nm flat gain-bandwidth gain-clamped SOA-Raman hybrid amplifier for CWDM access networks. Four channels of 2.488 Gb/s CWDM signals were amplified and no gain-saturation induced bit-error-rate power penalty was observed.

Low-current spin transfer torque MRAM

This talk presents the discovery of interface perpendicular anisotropy in the Ta-CoFeB-MgO system and its development for perpendicular magnetic tunnel junctions used in spin transfer torque magnetic random access memories. Experimental results show low switching current threshold and high efficiency. Theoretical predictions for further lowering of the switching current is also discussed.

Spot size converter integrated semiconductor optical amplifier

Spot size converter (SSC)-SOA consists of a slightly tensile bulk 0.2 /spl mu/m thick InGaAsP (/spl lambda/=1.55 /spl mu/m) active layer and 0.1 /spl mu/m thick InGaAsP (/spl lambda/=1.3 /spl mu/m) waveguides, which were grown by selective area growth (SAG) using MOCVD to implement SSC. The total device length is 1500 /spl mu/m. The thickness enhancement factor was greater than 3 by using SiO/sub 2/ mask. The SAG method with lateral tapering technique provided a typical beam divergences of 8/spl deg//spl times/15/spl deg/. To reduce facet reflectivity, window regions of 20 /spl mu/m length were introduced and the waveguides were tilted by 7/spl deg/. Both facets were antireflection coated to minimize the reflection from the cleaved facet. The gain measurement was done by coupling lensed fibers to both sides. To obtain the higher coupling efficiency in SOA module, taper lensed fiber with AR coating were used. Larger than 22 dB of the fiber to fiber gain was obtained for -20 dBm input power and 150 mA at 1540 nm.

Temperature Control Method of Hard Disk Drives With TuMR Head

The use of tunneling magneto-resistive (TuMR) head, at low temperature, has bad read/write characteristics for the disk regions with high data transfer rate. To prevent the bit error rates (BERs) degradation at low temperature, a solution which can quickly increase temperature more than specific value is proposed. A random seeking method with heater is operated to rapidly increase the rising speed of internal temperature and the weak writing/reading problems is solved.

Small DVB-H antennas using ferrites substrate

Cellular phones which is considered a first step of next generation information technology. The frequency ranges of these digital broadcasting services such as DMB and DVB-H were assigned from 170 MHz to 800 MHz. Thus the miniaturization of antennas in DMB and DVB-H phones becomes a hot issue because the antenna size is inversely proportional to the frequency. In principle, the miniaturization of antennas relies on two approaches; pattern and material design. The former is extending the electrical length of antenna radiator and the latter contracting the propagation wavelength by the increment of materials permittivity or permeability.

Design and fabrication of novel double core spot size converter integrated optical devices

We have developed novel double core spot size converter integrated optical devices which are provided by selective area growth. We have obtained a narrow circular beam divergence angle of 11/spl deg//spl times/12/spl deg/.