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Small Form Factor Optoelectronic Transceivers for the MTRJ Connector Based on TO-Can Packaging

IP.com Disclosure Number: IPCOM000013642D
Original Publication Date: 2001-Nov-19
Included in the Prior Art Database: 2003-Jun-18
Document File: 4 page(s) / 83K

Publishing Venue

IBM

Abstract

The demanding requirements of the new small-form-factor (SFF) optoelectronic transceivers put stringent constraints on the transceiver design, primarily because the components must be packaged within a very small space while still meeting the operating specifications, and because low fabrication costs must be maintained. A special challenge is presented by a SFF transceiver designed to mate with the MTRJ connector since the spacing between the two fibers of that connector is only 750 ยต m. This close spacing necessitates a space transform of the optical path which permits separation of the transmitter optical subassembly (TOSA) from the receiver optical subassembly (ROSA) by several mm in order to permit incorporation of the two TO cans containing the respective optoelectronic chips. The increased spacing also serves to reduce electrical crosstalk between the TOSA and ROSA.

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  Small Form Factor Optoelectronic Transceivers for the MTRJ Connector Based on TO-Can Packaging

  The demanding requirements of the new small-form-factor (SFF) optoelectronic transceivers put stringent constraints on the transceiver design, primarily because the components must be packaged within a very small space while still meeting the operating specifications, and because low fabrication costs must be maintained. A special challenge is presented by a SFF transceiver designed to mate with the MTRJ connector since the spacing between the two fibers of that connector is only 750 µm. This close spacing necessitates a space transform of the optical path which permits separation of the transmitter optical subassembly (TOSA) from the receiver optical subassembly (ROSA) by several mm in order to permit incorporation of the two TO cans containing the respective optoelectronic chips. The increased spacing also serves to reduce electrical crosstalk between the TOSA and ROSA.

It is suggested that the required space transform may be implemented through the use of two optical fibers connecting the MTRJ connector and the optoelectronic chips in TO cans, which are mounted at the far end of the SFF board used to mount all the necessary components. The fibers are closely spaced at the MTRJ connector, but widely spaced at the TO cans.

In this approach an MTRJ connector is bonded to one end of the board as illustrated in Fig. 1. Mounting the two TO cans at the far end of the board provides sufficient space between the connector and the TO cans so that the fibers can make a gentle curve in their trajectory between the two components. Strain in the fiber caused by a small radius of curvature is therefore not of concern. The intervening region on the board between the MTRJ connector and the TO cans can be populated with the usual electronic chips associated with the transmitter and receiver functions.

Fig. 1. Illustrating the space transform with fibers with the TO cans at the end of

the board

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While this straightforward technique solves the space-transform problem in a very simple manner, the problem of light transfer between the end of the fiber and the chip housed in each TO can must also be addressed. To implement this transfer an OSA is used which consists of a "housing" which contains a bore to receive an optical fiber, and a lens (assuming that the TO can does not itself have a built-in lens); the housing mates to a TO can. Several choices may now be considered:

The two fibers originating in the MTRJ connector could each terminate in a ferrule, which would be inserted into the bore of the OSA (Fig. 1) which would have the diameter required to accept the ferrule. (To save space an MU ferrule of 1.25 mm diameter could be used). The housings for such OSAs could be similar in design to those developed for small-form-factor LC connectors, as discussed in "A Novel Low-Cost Small-Form...