Packaging for a 40-channel parallel optical interconnection module with an over 25-Gb/s throughput

NTT is currently working on a project aimed at developing an interconnection module which has high throughput and is both compact and cost-effective. This project is called “parallel interboard optical interconnection technology”, or “ParaBIT”. The ParaBIT module being developed as the first step in this project is a front-end module with 40 channels, throughput of over 25 Gb/s, and transmission over 100 m along multimode fibers. One major feature of this module is the use of vertical-cavity surface-emitting laser (VCSEL) arrays as very cost-effective light sources. These arrays also enable a packaging structure that includes transmitter and receiver in one package. To achieve super-multichannel performance, new high-density multiport Bare Fiber (BF) connectors have been developed for the optical interface of the modules. Unlike conventional optical connectors, the BF connectors do not need a ferrule or spring. This ensures physical contact with excellent insertion loss of less than 0.1 dB for every channel. A polymeric optical waveguide film with a 45° mirror for coupling to the VCSEL/PD arrays by passive optical alignment has also been developed. Also to ensure easy coupling between the VCSEL/PD array chips and the waveguide, a packaging technique has been developed to align and diebond the optical array chips on a substrate. This technique is called Transferred Multichip Bonding (TMB), and can be used to mount optical array chips on a substrate with a positioning error of only several micrometers. These packaging techniques offer the performance of an ultra-parallel interconnection in prototype ParaBIT modules