Silica-Based Planar Lightwave Circuits
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MUX/DMUX: W DMmuiti/demultiplexer OPXC: Optical path cross-connect OADM: Optical add/drop muitiplexer OLT: Optical lineterminator ONU:Optical network unit AWG: Arrayed-waveguide grating TOSW: Thermo-optic switch
Fig. 1.PLC applications infiber-optic network
41 Mat. Res. Soc. Symp. Proc. Vol. 597 C 2000 Materials Research Society
FABRICATION
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SI02 -GeOcglass particl C SiO2 glass particles Silica-based optical waveguides are SFHD fabricated on silicon substrates by a combination of [ý_ Si2 glass flame hydrolysis deposition (FHD) and reactive ion 1 Consolidation particles CoreaCosoidaio etching [7]. FHD has the advantage of a high glass deposition rate and provides good coverage, even in Undercladding Consolidaton Overcladding narrow waveguide gaps. A schematic of the waveguide fabrication process is shown in Fig. 2. SFHD:Flamehyrlyi depositin First, two successive glass particle layers which form the undercladding and core are deposited on a substrate in an oxy-hydrogen flame. After Fig. 2. PLC fabrication process deposition, the substrate with these two porous glass layers is heated to about 1300 °C for consolidation. The core is doped with Ge to increase the refractive index. The waveguide core ridges are then defmed by photolithography and the unwanted parts of the core region are removed by reactive ion etching. Finally FHD is used again to cover the core ridges with an overcladding. The well-defined and rectangular waveguide structure formed by the reactive ion etching also enables us to design complicated circuits by using various numerical simulation techniques such as the beam propagation method. We fabricated waveguides whose refractive index difference (A) between core and cladding ranged from 0.3 to 1.5% and chose the A to suit the device requirements. The propagation loss is around 0.1 dB/cm. A ftirther loss reduction down to 0.017 dB/cm was achieved in a 10 in-long waveguide with A =0.45% [81.
OPTICAL SPLITTERS AND RELIABILITY Optical power splitters [9] are widely used for branching and combining optical signals. They are also a key device in the passive double-star based optical access network. It is essential to guarantee splitter reliability, as well as that of other PLCs, to enable optical networks to be introduced throughout the world. The structure of a PLC module is shown in Fig. 3. Input and output fiber arrays are mounted on glass V-grooves. The end facets of the V-grooves and the PLC chip are polished at an angle of 8 degrees, and the V-grooves are connected to opposite ends of the chip by using UV curable adhesive. The main cause of PLC module failure is an insertion loss increment resulting from exfoliation at the interface between the PLC chip and the V-grooves. Reliability tests have been carried out on unpackaged modules, based on the Bellcore requirements, and have confirmed that these modules have sufficient durability as regards environmental and mechanical stress [10]. Furthermore accelerated lifetime tests have been performed in damp heat environments. Weibull dist
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