Kyoung-Hwan Oh

Hard polymer cladding fiber (HPCF) links for high-speed short reach 1/spl times/4 passive optical network (PON) based on all-HPCF compatible fused taper power splitter

We report a novel 4/spl times/4 hard polymer clad fiber (HPCF) splitter fabricated by a fusion and tapering technique showing an excess loss less than 4.58 dB and insertion loss of 10.50 dB, which can be directly applied in short reach (SR) HPCF optical links. The device also showed an excellent uniformity in the power splitting ratio with power fluctuation less than 0.25 dB over a wide spectral range, 600-900 nm, which can significantly alleviate the spectral requirements in transmitters and enable wavelength-division multiplexing. The 1/spl times/4 passive optical network SR HPCF link for Ethernet communication was experimentally demonstrated over 100 m of HPCF at the data rate of 1.25 Gb/s for the optical signal at 850 nm.

Characterization of uniplanar compact photonic-bandgap finite-width conductor-backed coplanar waveguide by using an electrooptic near-field mapping technique

An electrooptic near-field mapping system based on a gain-switched distributed-feedback pulsed laser and a CdTe electrooptic crystal was used for characterizing transient and stationary near-field patterns of conventional and uniplanar compact photonic bandgap (UC-PBG) finite-width conductor-backed coplanar waveguides (FW-CBCPWs). Comparison of transient and stationary near-field patterns of FW-CBCPWs visually shows that parasitic parallel-plate modes in the FW-CBCPW are effectively suppressed by the UC-PBG pattern on side-ground plates.

Investigation of Surface-Wave Reduction in UC-PBG Patch Antenna by Using a Transient Electrooptic Near-Field Mapping Technique

A transient electrooptic near-field mapping system based on a gain-switched distributed feedback (DFB) pulsed laser and a CdTe electrooptic crystal was used for characterizing transient near-field patterns of conventional and uniplanar compact photonic bandgap (UC-PBG) patch antennas fabricated on a low-cost FR4 substrate. Effect of the UC-PBG structure on reduction in surface waves in the UC-PBG patch antenna was investigated experimentally by comparing transient near-field patterns of the conventional and UC-PBG patch antennas

Investigation of parallel plate mode suppression in UC-PBG FW-CBCPW by using a transient electrooptic field-mapping

A transient electrooptic near-field mapping system based on a gain-switched distributed feedback (DFB) pulsed laser and a CdTe electrooptic crystal was used for measuring near-field patterns of conventional and uniplanar compact photonic band gap (UC-PBG) finite-width conductor-backed coplanar waveguides (FW-CBCPWs). Comparison of transient near-field patterns of the FW-CBCPWs visually shows that parasitic parallel plate modes in the UC-PBG FW-CBCPW are effectively suppressed by using the UC-PBG structure on side-ground plates.

Crystalline quality improvement of In/sub 0.52/Al/sub 0.48/As/In/sub 0.53/Ga/sub 0.47/As heterostructure on InAlAs/InGaAlAs/GaAs metamorphic buffer by post-growth rapid thermal annealing

Effects of post-growth rapid thermal annealing (RTA) on optical and structural properties of an In/sub 0.52/Al/sub 0.48/As/In/sub 0.53/Ga/sub 0.47/As multi-quantum-well (MQW) structure on a GaAs substrate by using an InAlAs/InGaAlAs metamorphic buffer were investigated. Photoluminescence spectrum and triple-axis (004) contour maps showed improvement in crystalline quality of the metamorphic MQW structure through the post-growth RTA.

Characterization of near-field patterns of a novel UC-PBG FW-CBCPW by using an electrooptic field-mapping technique

An electrooptic field-mapping system based on a gain-switched distributed feedback (DFB) pulsed laser and a CdTe electrooptic crystal is used for characterizing near-field patterns of conventional and uniplanar compact photonic band gap (UC-PBG) finite-width conductor-backed coplanar waveguides (FW-CBCPWs). Comparison of near-field patterns of the FW-CBCPWs visually shows that microstrip-like (MSL) modes in the FW-CBCPW are effectively suppressed by using the UC-PBG pattern on the side-ground plates.

The application of a passive mode-locked fiber laser including NALM to electro-optic sampling

We constructed an electro-optic sampling (EOS) system using a passive mode-locked fiber laser including nonlinear amplifier loop mirror (NALM). We used an optical band-pass filter and a polarization dependent isolator to get a pure single soliton pulse having the stable polarization state. The pulse width and the repetition rate were about 600 fs and 2 MHz respectively. We could achieve the impulse response measurement of the Schottky-type InGaAs photodetector (PD) using EOS system utilizing this fiber laser.

Investigation of strain effects on performance of high-speed Schottky-type photodetectors

PIN and Schottky photodetectors (PDs) having an InGaAs absorption layer are widely used for long distance optical communication. The speed of those PDs is generally limited by hole transition time in the absorption layer. This limit can be overcome by using a tensile-strain In/sub x/Ga/sub 1-x/As (x<0.53) absorption layer. We fabricated and characterized Schottky-type PDs having a lattice-matched In/sub 0.53/Ga/sub 0.47/As absorption layer and a tensile-strained In/sub 0.48/Ga/sub 0.52/As absorption layer. Photocurrent impulse response of the tensile-strained InAlAs/In/sub 0.48/Ga/sub 0.52/As PD showed an improved FWHM of 13 ps, while that of the the lattice-matched InAlAs/In/sub 0.53/Ga/sub 0.47/As PD was 16 ps.

Speed performance comparison of InP/InGaAs UTC photodiodes utilizing compositionally graded and exponentially doped photo-absorption layers

The photocurrent responses of InP/InGaAs uni-traveling-carrier photodiodes having conventional, compositionally graded, and exponentially doped photo-absorption layer were investigated with photo-absorption layer doping concentrations and current densities as parameters. The speed performance of these photodiodes was calculated including the effects of conduction band potential difference associated with the hole current, the p-type doping concentration, and the built-in electric field in the photo-absorption layer. According to the simulation results, the compositionally graded and the exponentially doped UTC-PDs had a superior speed performance compared with that of the conventional one regardless of the current density and the doping concentration in the photo-absorption layer.

Improved speed performance of tensile-strained In/sub x/Ga/sub 1-x/As (x<0.53) photodetectors utilizing a patterned substrate growth

Photodetectors (PDs) play an important role in optical communication systems and measurement systems. As the bandwidth of the optical communication system is increasing rapidly, high-speed PDs are needed. The mesa-type PDs such as Schottky and PIN-type PDs having InGaAs absorption layers are generally used for that field. The speed of those PDs in general is limited by hole transition time in the absorption layer. The speed performance limitation of mesa-type PDs due to the hole transition time can be improved by using a tensile-strained In/sub x/Ga/sub 1-x/As (x<0.53) absorption layer. It was shown by simulations that the effective hole mass could be reduced by utilizing a tensile-strained In/sub x/Ga/sub 1-x/As (x<0.53) absorption layer. Tensile-strained InAlAs/In/sub 0.48/Ga/sub 0.52/As and lattice-matched InAlAs/In/sub 0.53/Ga/sub 0.47/AS Schottky-type PDs were fabricated and characterized. Impulse response (FWHM) of the tensile-strained PD was reduced to 13 ps as compared with that (16 ps) of the lattice-matched PD, which is attributed to the improved hole transport property in the tensile-strained In/sub 0.48/Ga/sub 0.52/As absorption layer.