Su Hwan Oh

Continuously tunable compact lasers based on thermo-optic polymer waveguides with Bragg gratings

Based on the thermo-optic tuning of a polymer waveguide Bragg reflector, we demonstrated a cost-effective tunable wavelength laser for WDM optical communications. The excellent thermo-optic effect of the polymer waveguide enabled direct tuning of the Bragg reflection wavelength by controlling the electrical power on a micro-heater. Wavelength tuning for 32 channels with 0.8 nm wavelength spacing was demonstrated as well as a continuous tuning with wavelength steps of 0.1 nm. To be qualified as a tunable laser for WDM-PON applications, wavelength stability within 0.15 nm was confirmed for an operating temperature range from -10 to 70 degrees C.

2.5-Gb/s hybridly-integrated tunable external cavity laser using a superluminescent diode and a polymer Bragg reflector

We presented a hybridly-integrated tunable external cavity laser with 0.8 nm mode spacing 16 channels operating in the direct modulation of 2.5-Gbps for a low-cost source of a WDM-PON system. The tunable laser was fabricated by using a superluminescent diode (SLD) and a polymer Bragg reflector. The maximum output power and the power slope efficiency of the tunable laser were 10.3 mW and 0.132 mW/mA, respectively, at the SLD current of 100 mA and the temperature of 25 degrees C. The directly-modulated tunable laser successfully provided 2.5-Gbps transmissions through 20-km standard single mode fiber. The power penalty of the tunable laser was less than 0.8 dB for 16 channels after a 20-km transmission. The power penalty variation was less than 1.4 dB during the blue-shifted wavelength tuning.

Multiwavelength Lasers for WDM-PON Optical Line Terminal Source by Silica Planar Lightwave Circuit Hybrid Integration

We have demonstrated a very compact eight-channel 200-GHz-spacing multiwavelength laser (MWL) module for the optical line terminal source of wavelength-division-multiplexing passive optical network. The wavelength shift of MWLs and external cavity lasers from the ITU grid was within +0.14 nm for eight channels, which was well matched to the target wavelength shift of less than plusmn0.2 nm. The oscillation characteristics of our MWL module are better than those of conventional MWLs with hybrid integration.

Design and analysis of widely tunable sampled grating DFB laser diode integrated with sampled grating distributed Bragg reflector

A new widely tunable laser diode structure that requires only two tuning currents is proposed. The laser diode consists of a sampled grating distributed feedback (SGDFB) laser diode monolithically integrated with a sampled grating distributed Bragg reflector (SGDBR). The phase control sections are properly inserted between the grating bursts of the SGDBR and SGDFB sections for the discrete and continuous tuning. To confirm the feasibility of the new structure, the split-step time domain model is used. The simulation result for a particular design shows that the tuning range as wide as 27 nm is possible with side-mode suppression ratio exceeding 35 dB. Furthermore, the output power is larger than that from SGDBR laser diodes with similar parameters.

Tunable External Cavity Laser by Hybrid Integration of a Superluminescent Diode and a Polymer Bragg Reflector

We report a tunable external cavity laser (T-ECL) using a superluminescent diode (SLD) and a polymer Bragg reflector with 0.8-nm mode spacing 25 channels operating in the direct modulation of 2.5 Gb/s for a low-cost source of a wavelength division multiplexed passive optical network (WDM-PON) system. The maximum output power is 12.2 mW and the slope efficiency of the T-ECL is about 0.12-0.17 mW/mA in the tuning range of 20 nm at the SLD current of 50 mA and at the temperature of 25°C. The T-ECL successfully operated in the direct modulation for 2.5-Gb/s transmission through 20-km standard single-mode fiber. The power penalty of the T-ECL is less than 0.8 dB for 25 channels after the 20-km transmission. The power penalty variation is less than 1.5 dB in the wavelength-tuning range of 20 nm. The performance of the T-ECL satisfies the requirements of the WDM-PON system.

The design and the fabrication of monolithically integrated GaInAsP MQW laser with butt-coupled waveguide

We optimized the etching process for butt coupling to improve the reproducibility and the uniformity of the process for the integrated GaInAsP multiquantum-well laser with a butt-coupled waveguide. Three different ways of etching process were tested, which are reactive ion etching (RIE), RIE followed by a small amount (50 nm thick) of selective wet etching, and RIE followed by an adequate amount (125 nm thick) of selective wet etching. RIE followed by an adequate amount of selective wet etching showed the superior properties to the common expectation on RIE only, giving the measured coupling efficiency 96/spl plusmn/1.7% versus 34/spl plusmn/8%. The high coupling efficiency and the very small variation across a quarter of a 2-in wafer demonstrate that RIE coupled with an adequate amount of selective wet etching can also replace the conventional process for butt coupling, RIE followed by HBr-based nonselective wet etching, to fabricate high-quality integrated photonic devices.

Tunable external cavity laser employing uncooled superluminescent diode.

We have fabricated a tunable external cavity laser (T-ECL) based on a superluminescent diode and a polymeric waveguide Bragg reflector, providing a cost-effective solution for wavelength division multiplexing-passive optical network (WDM-PON) systems. The wavelength of the T-ECL is tuned through 100 GHz-spacing 16 channels by the thermo-optic tuning of the refractive index of the polymer waveguide at a low input power of 70 mW. The maximum output power and the slope efficiency of the uncooled diode at 20 (75) degrees C are 8.83 (3.80) mW and 0.107 (0.061) W/A, respectively. The T-ECL operated successfully in the direct modulation for 1.25 Gbit/s transmissions over 20 km.

Fabrication of InGaAsP/InP Two-Dimensional Periodic Nanostructure with Variable Sizes and Periods Using Laser Holography and Reactive Ion Etching

Two-dimensionally arrayed nanocolumns of InGaAsP/InP were fabricated using double-exposure laser holography and reactive ion etching (RIE). The size and period of nanocolumns could be controlled accurately from 80 to 150 nm in diameter and 220 to 450 nm in period by changing the incident angle of the laser beam. RIE for a typical time of 30 min using CH 4 /H 2 plasma enhanced the aspect ratio by more than 1.5 with a slight increase of the bottom width of columns. Furthermore, a wet-treatment after RIE showed a large enhancement of photoluminescence intensity, suggesting that the damage was cured effectively on the sidewalls of the nanocolumns.

200 GHz-spacing 8-channel multi-wavelength lasers for WDM-PON optical line terminal sources.

We have fabricated modules of 8-channel multi-wavelength lasers (MWLs) with a wavelength separation of 200 GHz for the wavelength division multiplexed-passive optical network (WDM-PON) optical line terminal sources. The variation in the output power is minimized by inserting silicone between the superluminescent diode (SLD) and the silica waveguide. The wavelength shift of each channel is less than 0.21 nm from the ITU grid and can be controlled in the range of 0.36 nm without any reductions of the output power by a tuning heater. MWLs operated successfully in the direct modulation for 1.25 Gbit/s transmissions over 20 km.

High-Performance 1.55-

We report the design and fabrication of a novel 1.55-m spot-size converter superluminescent diode (SLD) for optical access networks. The active section of SLD was fabricated by using a planar buried heterostructure to adopt the double-waveguide-core structure for low-threshold and high-output power operation at a low injection current. A ridge-based passive waveguide was employed for an efficient coupling to a planar lightwave circuit. The threshold current was as low as 14 mA, and the maximum output power was as high as 28 mW with ripple less than 3 dB at an injection current of 200 mA.