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Free Space Optical Coupler Modules Disclosure Number: IPCOM000016016D
Original Publication Date: 2002-Aug-28
Included in the Prior Art Database: 2003-Jun-21

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1. Introduction and overview

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Free Space Optical Coupler Modules

1. Introduction and overview

Signal speeds within data processing systems (such as switch/routers, servers, high-end computers) are approaching 10 Gb/s and more. At the same time, system size (in particular for Internet switches) is expected to increase, because the speed of the processing electronics (network processors) isn't increasing as fast as fiber bandwidth (driven by the introduction of wavelength division multiplexing, or WDM). This means that more electronics working in parallel is needed to process the incoming datastreams. As a consequence, future switches are expected to be multi-rack systems instead of single-shelf systems. Obviously, this increase in system size is also reflected in the length of the intra-system interconnects, which will be increased to tens of meters.

At these speeds and lengths, conventional copper interconnects are reaching fundamental bandwith limits. It is generally believed that the use of optical interconnects is a valuable approach to overcome these limitations. While the longest interconnects (rack-to-rack) will be the first that have to "go optical", it can be expected, that optics will soon also be required within a single shelf or box. Apart from interconnect length considerations, there are also scalability requirements: From a customers point of view, a scalable switch system should have the potential to start as a single-shelf setup and then grow to a multi-rack configuration. If this system growth shall be achieved without replacing all the components, then optics will also be needed at the shelf-level, even if the shelf-internal interconnect lengths could still be handled by conventional copper lines. Other arguments for optical interconnects include density advantages (e.g. at the card edge) and immunity of optical signals to electromagnetic interference.

There are many different approaches to implement optical interconnects from one board to another board within the same box/shelf/enclosure. One particular approach is to add/embed one or more waveguide layers to conventional electronic boards. Typically, such hybrid boards have conventional copper layers for power, ground and slow (control) signals, plus one or more glass or polymer waveguide layers for high-speed data signals. This proposal adresses the problem of how to cheaply and efficiently couple light from an optoelectronic source (such as a vertical cavity surface emitting laser, or VCSEL) into such an embedded waveguide layer, and back out of the waveguide layer onto a detector. In addition, the proposed approach can also be used to couple light from one waveguide-equipped board to an other, such as in a card-to-backplane interface

The proposal is motivated by the intention to keep the waveguide and board fabrication as simple (i.e. cheap) as possible, by not integrating any mirror structure directly with the waveguides. On the other hand, one also wants to package the VCSEL chip in a...