May 2, 2019
Jolley Hall, Room 309
Title: Polarization Division Multiplexing for Optical Data Communications
Abstract: 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. In this research work, we investigate the viability
of polarization division multiplexing, the separation of distinct parallel optical communication
channels through the polarization properties of light. We investigate polarization division
multiplexing based optical communication systems in five distinct parts.
In the first part of the work, we define a simulation model of two or more linearly polarized
optical signals (at different polarization angles) that are transmitted through a common
medium (e.g., air), filtered using aluminum nanowire optical filters fabricated on-chip, and
received using individual silicon photodetectors (one per channel). 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 simulation 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.
The entire simulation model is designed in Cadence tools and the receiver (including optics) is
compatible with standard CMOS fabrication processes.
In the second part of the work, we design and manufacture a two channel chip that is
used as the light receiver to confirm the simulation results from the first part of the research.
Since logistics for the receiver’s chip testing were not favorable we constrained our testing
to single channel operation, which we demonstrated functionality using both electrical and
optical inputs. In addition, we used data from a pair of optical imagers (one linear and the
second with a logarithmic response) to investigate the noise properties of both the optical
and electrical signals within the system.
In the third part of the work, we provide examples of channel coding that enable the four
channel system to operate with positive noise margins.
In the fourth part of the work, we define an end-to-end simulation model of two, three or
four channel systems that utilize air, fiber, and a pair of mirrors in the optical path from
transmitter to receiver. Each of these systems is shown to have positive noise margins (albeit
using channel coding on the four channel editions); however, there are many circumstances
where the noise margins are quite small.
In the final part of the work, we examine the trade-offs between number of channels, signal
power, and noise margins, including the use of pulse amplitude modulation within the two
Advisor: Roger Chamberlain