Assembling Active Optical Cables


Assembling Active Optical Cables

The amount of data we “consume” every day increases continuously. Be it for the sake of information, of communication, of gaming, or of social networking it all comes down to that this data has to be stored, processed, and routed. All this happens on hardware networks, even wireless connections eventually end up in physical webs of cables.

With the amount of processed data also the rate of the data with which it has to be exchanged between hosts increases. The physical network, namely the interconnecting cables have to account for that driving the traditional copper based technology to its limits. Active optical cables overcome the bottleneck of slow copper cables in two ways. Firstly a single optical fiber can transmit data faster than its mate made from copper, secondly an optical cable can consist of more than one fiber boosting the possible transfer rate by factors.

Active optical cables connect to the peers by means of electrical connectors. The transformation into optical signals and the multiplexing takes place within the connector. Each connector therefore has to contain laser diodes as transmitting sources and photodiodes as receiving detectors.

Commercially available fiber ribbons guide the light to the other side of the connection. The pitch of the individual optical fibers in such ribbons is precisely fixed and usually is 250 µm. Other key components are the laser diodes and the photodiodes. Both appear as monolithic linear arrays of diodes. The pitch of the individual diodes is lithographically exact and matches the pitch of the fiber ribbon.

In general the transmitting as well as the receiving channels travel in a common fiber ribbon with a fixed pitch between the individual fibers.  Basically all active areas namely the individual photo diodes and the laser diodes have to sit on an imaginary grid. Therefore the two diode arrays have to be aligned to each other very precisely with two dimensions to be controlled at the same time. The distance between the arrays is as important as the angle between the arrays to match the fiber grid.

Since the diodes at this moment are not yet electrically functional the alignment of the array chips has to be performed passively. Typically the assembly process starts with placing one of the arrays purely by fiducial recognition and machine precision. The other chip then is placed by recognizing the active elements of the array, i.e. photodiodes or laser diodes and referencing them to their counterparts respectively.

The ficonTEC approach utilizes a top side vision system not only to recognize the active features before pick-up. Instead the vision system observes the features during the entire bonding process, from pick-up thru alignment. This method is advantageous over the alternative approach where positions of the active features are recognized only for the pick up process and discarded thereafter to purely rely on the performance of the (expensive) motion system.

The ficonTEC AssemblyLine is the platform of your choice for this demanding application.