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Alignment Structures for Integrating Optical Fibers into PCBs

IP.com Disclosure Number: IPCOM000132311D
Original Publication Date: 2005-Dec-07
Included in the Prior Art Database: 2005-Dec-07
Document File: 9 page(s) / 139K

Publishing Venue

IBM

Abstract

The disclosed concept is directed to a selection of steps to facilitate alignment of optical fibers in PCBs. It comprises a transfer process of fiber connectors that have alignment structures, and an in situ cleaver.

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Alignment Structures for Integrating Optical Fibers into PCBs

Disclosed is a concept for the integration of alignment and stacking structures into PCBs to precisely position one or multi layers of optical fibers and passively align optical elements on these optical fibers. It overcomes the use of expensive fiber connectors, enables access to the embedded fibers at arbitrary positions in the board and fiber facet preparation using an in situ cleaver. The realization of alignment structures for placing fibers into PCBs and the stacking of multi fiber layers is addressed.

A first alignment structure (base alignment structure) is used as a reference element for placing the fibers, and is then used to passively align optical elements onto the fibers. For the next fiber layers, a separation structure is then placed on top of the first fiber layer to define the stacking pitch and align the next fiber layer onto the first one. The fiber length doesn't have to be controlled precisely, as the end facets will be defined when all fibers will be in place in the board. The fiber placing can be realized directly by taking them from the fiber roller, no individual preparation is needed. The passive alignment onto fibers of two type of optical elements is specially addressed; first, active optical modules used to couple light in and out of the fibers and second, a board-backplane connector.

The integration of fibers into PCB is already a technology available on the market, mainly for routing fibers from one card edge to another one with standard fiber connectors. The main issue with this existing approach is the cost of the fiber foils, which is mainly caused by the optical connectors at the end of the fiber bundles. Furthermore, this technology is mostly suited for routing signals from one card edge to another and does not provide much flexibility for more general interconnect links that require access to the fibers embedded in the board itself.

General process flow

The typical process flow consists of (see Figure 1)
* Approximate placing of the base alignment structures onto the PCB or a provisory substrate
* Positioning of the fibers into the base structure alignment grooves (Either accurate alignment of fiber end-facet or post processing of fiber bundles to obtain a high quality optical interface)
* For multi layer fiber stack:

o Placing of the separation structure o Positioning of the fibers into the separation structure alignment grooves o For more layers same procedure

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Figure 1: Process flow

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An important process step will be the preparation of the fiber end facets. Several methods of doing this are proposed:

a) "The in-situ cleaver" (Figure 2).

Here, a little spike or wedge is integrated at the front of the fiber alignment structure. When the fibers are laid into the structure, this spike/wedge will make a small cut into the cladding, which can serve as a nuc...