In-home Fiber Wireless Networks Incorporating Optical Microwave Beam Steering: System Architecture and Integrated Device

The current explosion of communication tra-c volume is driven by an insatiable ap- petite for high speed internet connectivity and video-based content delivery to wireless and mobile terminal users, especially for in-home scenarios. A lot of research has been carried out to exploit wireless capacity. In the spatial domain, spatial multiplexing, spatial isolation (pico/femto-cells), and spatial flltering (beam-steering) attract lots of attention due to their abilities to boost capac- ity immensely. Spatial isolation requires many wireless access points and its successful deployment depends on building structures. These features limit its applications. Unlike spatial multiplexing which requires complicated digital signal processing, beam-steering (BS) directs signals to the desired user with minimum interference. Phased array antennas (PAAs) are widely considered as the best candidate for microwave beam-steering due to their fast steering and compactness (1). The operational bandwidth of a conventional PAA is limited. Speciflcally, a severe limitation is often caused by the use of phase shifters to scan the beam, which results in beam deformations (\squint") in the measured antenna pattern. The use of true time delay (TTD) technology poten- tially eliminates such bandwidth restriction, as it provides a theoretically frequency-independent time delay on each channel of the array (2). Standard TTD technology typically consists of digitally-switched transmission line sections wherein weight, loss and cost increase rapidly with increased operational frequency and/or phase tuning resolution. These issues can be avoided by adopting optical TTD microwave beam steering (OTTD-MBS). However, most OTTD-MBS schemes are investigated mainly for radars rather than wireless broadband data communications. No experimental results reveal the system performance for the latter applications. Recently, we have proposed and investigated radio-over-flber systems incorporating optical true-time-delay mi- crowave beam steering (3,4). However, the employed optical tunable delay lines (OTDLs) based on bulk-optics components limit their further applications (3,4). Obviously an integrated solu- tion is the key to future successfull implementation. To pave the way for its flnal applications, a compact and fabrication-tolerant OTDL based on a silicon-on-insulator (SOI) generic plat- form is proposed and characterized. Such OTDL is based on a re-circulating symmetric arrayed waveguide grating loop (AWG-loop) and is passively controlled by tuning the wavelength of the input optical signal. In this talk, we will review our current research on both advanced system architecture for in-home flber wireless networks with optical microwave beam steering and the novel realization of integrated optical tunable delay lines.