Page 351 - System on Package_ Miniaturization of the Entire System

Integrated Chip-to-Chip Optoelectr onic SOP 325

Wireless data communication
Remote base station 3
Wireless video distribution
Remote base station 2
Distribution

Feed Cell phone
Central station Mobile communication
Remote base station 1
Optical electronic RF SOP system

RF/Opto data 60 GHz 60 GHz
at 60 GHz Opto/RF 60 GHz RF encoder
optical carriers conversion TIA & antenna
Fiber

FIGURE 6.2 High-frequency RF information is distributed over long distances by fi rst converting
the RF coding to optical coding, transporting the information over optical fi bers, and recovering
the RF signal for broadcast at the destination. A land signal is returned by recycling the power
available in the baseband optical signal.

Hence, parallel waveguides need only be separated by a few micrometers. This flexibility
and the density characteristics of optical waveguides will eventually find application in
laptops, mobile palm computers, and cell phones primarily due to effective isolation from
electromagnetic interference (EMI).
Optical frequency isolation in mobile communication SOP hardware is a leading-edge
concept that should find commercialization in the future. To date the concept of opto-RF
SOP is embodied in the fast-growing field of “RF over fiber.” RF waves are strongly absorbed
in the atmosphere above frequencies of a few gigahertz. Yet, high RF frequencies are
necessary for transmitting data at bit rates above a few gigabytes per second. A solution to
this problem is to convert the high-frequency, amplitude- and phase-modulated RF waves
into identical amplitude- and phase-modulated optical waves. At the destination, the optical
signal is converted to the original RF signal and broadcast over a local area such as in a
conference room, as depicted in Figure 6.2. At the source, the optical signal is encoded by
readily available external modulators. At the destination, high-frequency photodetectors
and microwave amplifiers can be used to restore and broadcast the original RF message. In
some configurations, it is possible to recirculate the optical power and use it for a land-based
return signal. This bidirectional RF over fiber technology is summarized in [6].

6.3 Integration Challenges in Thin-Film Optoelectronic SOP
The concept of transporting data optically over short distances of less than 1 m is
relatively new when compared to conductive information transport. Thus the processes,
materials, and architecture needed for integrating optoelectronic actives into passive
lightwave circuits are quite new and tentative. Nevertheless, two major challenges