Jeong Hwan Song

Bragg grating-assisted WDM filter for integrated optical triplexer transceivers

We designed and experimentally demonstrated a Bragg grating-assisted wavelength-division-multiplexing filter for the three-wavelength multiplexing on a planar-lightwave-circuit platform. The 1310- and 1550-nm lights were designed to be separated after passing the directional coupler by a half-cycle and a full-cycle coupling actions with losses of 0.07 and 0.19 dB, respectively. The 1492-nm light was reflected back by a Bragg grating fabricated on the directional coupler and its loss was less than 2.0 dB. We also introduced and discussed the new concept of an integrated optical triplexer transceiver using this filter.

Thin film filter-embedded triplexing-filters based on directional couplers for FTTH networks

We designed and experimentally demonstrated a thin film filter (TFF)-embedded directional coupler-type triplexing-filter on the planar-lightwave-circuit platform. The triple-play multiplexing was significantly simplified by using one TFF. The 1.31- and 1.55-/spl mu/m lights were designed to be divided after passing the directional coupler by half-cycle and full-cycle coupling actions, respectively. The 1.49-/spl mu/m light was reflected by a TFF inserted in a trench on the directional coupler. The insertion losses of fabricated triplexing-filters were less than 2.0 dB with bandwidths of 20 nm. The newly proposed triplexing-filter provides a cost-effective high-performance solution for fiber-to-the-home networks.

Triple Wavelength Demultiplexers for Low-Cost Optical Triplexer Transceivers

We report triple wavelength demultiplexers adopting a thin-film filter (TFF) and a waveguide Bragg grating as a reflector for low-cost integrated optical triplexer transceivers deployed for the triple play service-based fiber-to-the-home (FTTH) networks. In the proposed demultiplexers, 1310- and 1550-nm lights were designed to be divided after passing the planar lightwave circuit-based directional coupler by half-cycle and full-cycle coupling actions, respectively. The 1490-nm light was reflected by a TFF or Bragg grating. The losses of the demultiplexers were less than 2.0 dB at all ports. The average crosstalk among the three lights for the demultiplexers was about -20 dB or better. Through a single reflector, the demultiplexer structures are significantly simplified, and cost is reduced. The proposed triple wavelength demultiplexers provide cost-effective and high-performance solutions for FTTH network systems

Reduction of insertion loss of thin film filters embedded in PLC platforms

We propose and experimentally demonstrate a method of reducing insertion loss of a thin-film-filter-embedded planar-lightwave-circuit platform for a triplexer transceiver module. Significant loss reduction was achieved by adding horn waveguide elements at the interfaces between the thin film filter and the output-port (transmission and reflection) waveguides.

External cavity laser with high-sidemode suppression ratio using grating-assisted directional coupler

We propose and demonstrate, for the first time, a method to improve the sidemode suppression ratio (SMSR) of an external cavity laser (ECL) with a grating-assisted directional coupler as an external mirror. The ECL consisting of a Fabry-Pe/spl acute/rot laser diode and a grating-assisted coupler exhibited single-longitudinal-mode oscillation at Bragg wavelength with a high SMSR of 60 dB without any additional devices.

Highly linear-polarized external cavity lasers hybrid integrated on planar lightwave circuit platform

We propose and demonstrate, for the first time, a highly linear-polarized external cavity laser (ECL) integrated on planar lightwave circuit (PLC) with an in-PLC polarizer designed to improve polarization extinction ratio (PER). The in-PLC polarizer based on a 45deg-tilted grating was simply formed in the laser cavity composed of a Fabry-Peacuterot laser diode and a Bragg grating. The proposed ECL exhibited a PER value as high as 30 dB and single longitudinal mode oscillation with a high sidemode suppression ratio of 50 dB at 1310 nm

Crosstalk enhancement of AWG fabricated by flame hydrolysis deposition method

The crosstalk of arrayed-waveguide grating (AWG) multi/demultiplexer has been reduced through the modification of the torch for flame hydrolysis deposition (FHD) process. The conventional type FHD torch was changed into a precursor-premixed type torch, which enhanced the AWG crosstalk level by 5-8 dB. The results were also compared with the characteristics of AWGs of which the core layers were fabricated by the plasma-enhanced chemical vapor deposition process.

Investigation of grating growth characteristics in planar lightwave circuits for external cavity laser

Abstract We fabricated Bragg gratings in planar lightwave circuits and investigated their growth characteristics. The refractive index modulation of the gratings grew in the PLC with total fluence F by the power law δ n = AF B with A = 8.6 ± 0.9 × 10−8 and B = 1.47 ± 0.02. The PLC gratings as external reflectors for ECLs were controlled reasonably well by adjusting the writing conditions based on the power law and the coupled mode theory. The properties of fabricated PLC gratings were closely matched to the design parameters of the PLC grating. The single longitudinal mode oscillations of the ECLs were also demonstrated at 1309.5 nm and 1550.5 nm.

Circularly Polarized External Cavity Laser Hybrid Integrated With a Polyimide Quarter-Wave Plate on Planar Lightwave Circuit

We propose and demonstrate a circularly polarized external cavity laser (ECL) hybrid integrated on a planar lightwave circuit (PLC). The ECL is composed of a spot-size converter integrated laser diode, a UV-written grating, and a polyimide quarter-wave plate on the PLC using hybrid-integration technology. The polyimide quarter-wave plate of an 8.8-mum thickness was inserted in a trench with a 20-mum width and a 300-mum depth on the PLC platform, and fixed with a UV-curable adhesive. The ECL hybrid integrated with the polyimide wave plate becomes highly circular-polarized with a degree of circular polarization of 0.992. This circularly polarized ECL operated with a sidemode suppression ratio of >50 dB at ~1550 nm.

Waveguide design and fabrication of trench for hybrid integrated optic devices

The hybrid integration of passive and optoelectronic devices has been widely researched. One of the main applications of this technique is for the fiber to the home (FTTH) network. In bi-directional transceivers, integrated WDM filters have been used to separate or combine the optical signals. Thin film filter (TFF) embedded waveguide type is effective for an application requiring wide bandwidth and low loss. Although the insertion loss of TFF itself is quite low, significant loss occurs at the trench and it depends on the geometrical structure and fabrication errors of the trench waveguide. The conventional sawing method and deep reactive ion etching technique were used for trench fabrication. In the case of using DRIE process, fabrication error was reduced and position error of the trench was controlled within 1um. This method could also enhance the platform design flexibility. To reduce the coupling loss between input and reflection waveguides with high tolerance of filter position, a few mode waveguide and horn waveguide were proposed. The insertion losses of transmission and reflection were less than 0.5dB and 0.7dB respectively. The 1dB tolerance of filter position was improved to be nearly twice than that of the conventional waveguide.