May 16, 2018
Jolley Hall, Room 309
"Polarization Division Multiplexing for Optical Data Communications"
Advisers: Roger Chamberlain and Viktor Gruev
Multiple parallel channels are ubiquitous in optical communications, with spatial division multiplexing (separate physical paths) and wavelength division multiplexing (separate optical wavelengths) being the most common forms. Here, we investigate the viability of polarization division multiplexing, the separation of distinct parallel optical communication channels through the polarization properties of light.
We investigate usage of a proposed Polarization Division Multiplexing (PDM) Visible Light Communication (VLC) system based on Division of Focal Plane (DoFP) polarimeters mounted on a custom CMOS integrated chip. A CMOS based and designed modulated light sources (e.g. lasers) encode two or more linearly polarized optical signals (at different polarization angles). These optical signals are transmitted through a common transmission medium (e.g. free space, waveguides, fiber optic cable with preservation of polarization and fiber optic cable without preservation of polarization), filtered using aluminum nanowire optical filters fabricated on-chip, and received using individual silicon photodetectors (one per channel). The entire designed receiver (including optics) is compatible with standard CMOS fabrication processes. The filter model is based upon an input optical signal formed as the sum of the Stokes vectors for each individual channel, transformed by the Mueller matrix that models the filter proper, resulting in an output optical signal that impinges on each photodiode. The optical signal received on each photodiode is converted to electrical signal and then it is processed through a Transimpedance Amplifier (TIA) circuit and the output of each channel TIA represents high-speed digital data that was sent from the input laser sources.
The entire PDM VLC system is designed using standard Cadence 180nm node library tools and it is simulated for two, three and four channels system cases. The results show that two- and three-channel systems can operate with a fixed-threshold comparator in the receiver circuit, but four-channel systems (and larger) will require channel coding of some form. For example, in the four-channel system, 10 of 16 distinct bit patterns are separable by the receiver.
The simulation model will support investigation of system speed, power dissipation/noise margins versus number of channel trade-offs and possible communication distances that can be achieved using this type of system. Also the simulation model supports investigation of the range of variability tolerable in the fabrication of the on-chip polarization filters.
The laser transmission input device design and the transmission media design have been done before and we will use existing models for these two parts of the system. The receiver CMOS-based part of the system is new and in addition to the simulation model we will design and test receiver CMOS integrated chip that has DoFP polarimeters mounted on the surface of the chip. We plan to show that a CMOS-based receiver chip with DoFP polarimeters can be used for optical signal communications using polarization division multiplexing.