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Silicon V-Groove Alignment Bench for Optical Component Assembly
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Authored By:Terry Bowen TE Connectivity Harrisburg, PA, USA SummaryOne of the primary technical challenges associated with the manufacture of optical assemblies, especially systems with higher levels of integration, is component to component optical alignment. Components must be brought into precise spatial relationship and the precision of this alignment must be captured and maintained throughout the useful lifetime of the assembly. The alignment step can be done actively or passively. The active approach is more complicated involving powering up devices and measuring optical coupling results while moving the components into the aligned position. The passive approach relies on building precision into the parts so that they can be directly assembled into the aligned position without activating the components. This paper describes the use of a large Vgroove wet etched into a silicon wafer to form an alignment bench component, which can be used in combinations with silicon based interposer / photonic integrated circuit (PIC) die and either additional similar die, or optical fibers assembled with cylindrical ferrules such as the LC connector ferrule. The silicon interposer die / PIC die are constructed with wet etched v-grooves along the locations where the die will be diced. This allows the sidewalls of these edge locator grooves to be used in combination with the alignment bench to precisely position features on the die relative to other similarly constructed components or optical fibers. The accuracy achieved by the photolithographic processes employed allow passive alignment to be used for constructing these assemblies. ConclusionsThe use of a Wide Alignment Groove (WAG) that is wet etched from a silicon wafer to form an alignment bench component as been presented. The WAG, is used to align a combination of components such as a Silicon based Interposer (SI) / Photonic Integrated Circuit (PIC) die to either additional similar die, or to cylindrical ferrule connector receptacle sub-assemblies such as the LC connector ferrule receptacle sub-assembly described here. The silicon interposer die / IC die are constructed with wet etched locator v-groove sidewalls along the locations where the die are diced. The sidewalls are used in combination with the WAG to precisely position features on the die relative to features on other similarly constructed die or to optical fibers. The accuracy achieved by the photolithographic processes employed enable passive alignment to be used for the construction of these assemblies. The Silicon Interposer described provided electrical interconnects to an edge emitting laser die and a laser monitor detector die. The electrical interconnects were formed using an advanced electrical interconnect process developed at MA/COM for their glass microwave integrated circuits (GMIC process). It involved etching pockets into the silicon wafer and then filling the pockets with glass frit material and processing the wafer to produce a surface with areas of glass and areas of silicon. The metallic electrical traces for this SI were run on the glass material areas in order to provide impedance control and dielectric isolation from the silicon substrate. Through Silicon Vias (TSVs)were used to interconnect the top surface pads of the SI to the back surface ground layer in order to provide top surface grounding. One of the primary technical challenges associated with the manufacture of optical assemblies, especially systems with higher levels of integration, is the component to component optical alignment. The alignment step can be done actively or passively. The active approach is more complicated involving powering up devices and measuring optical coupling results while robotically moving the components into the optimum aligned position. The passive approach as described in this paper, relies on building precision into the parts using wafer scale photolithography. This approach provides component parts that can be directly assembled into the aligned position without activating the components. Once the components are brought into precise spatial relationship the precision of this alignment is captured and maintained throughout the useful lifetime of the assembly. The resulting assembly provides a chip-to-world interconnect that can be automated to produce high volumes. Initially Published in the SMTA Proceedings |
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