2014 Research Highlights
Breaking Single-Mode Fiber Transmission Capacity Using Space-Division Multiplexing
Optical fiber communication is the backbone for the telecommunications infrastructure. Fueled by emerging bandwidth-hungry
applications, the Internet traffic has sustained an exponential growth in the past and this trend is expected to continue
for the foreseeable future. It is well known that the capacity of a communication channel cannot exceed the Shannon limit.
In the past two decades, the Internet traffic demand was mainly met by the wavelength-division multiplexing (WDM) technology
using single-mode fibers (SMF), which can increase the number of channels by two orders of magnitude. Even though the number
of communication channels in a SMF can be further increased by exploiting the low-loss transmission window of the optical
fiber beyond the C and L bands, the resulting capacity increase is limited to below one order of magnitude.
Making Arbitrary Waveform Generation a Reality
The generation of arbitrary optical waveforms in real time is of keen interest owing to their use in a broad range of applications,
spanning secure communications, advanced radar and lidar systems, and control of complex optically induced phenomena. The
ability to modify such signals at ultrafast rates would make radar systems more accurate, secure, and with better resolution,
and could also usher in new modalities in laser-based material interactions for manufacturing.
Single-Mode Microring Lasers
Since the invention of the laser, there has been a continuous effort to increase its coherence. High temporal and spatial
coherence is what makes lasers indispensable tools in many areas of research and technology ranging from spectroscopy to
optical communications. Most lasers, especially those employing semiconductors as the active gain material, tend to support
multiple spectral lines or longitudinal modes. Over the years, several schemes have been adopted to effectively suppress
undesired excess longitudinal modes. In this regard, distributed feedback (DFB) structures and vertical cavity surface emitting
lasers (VCSEL) have been routinely used to select a predetermined frequency line by employing intracavity dispersive elements.
However, these techniques are not universally applicable to all types of lasers. Hence the quest for other more-robust methods
is still ongoing.
Flexible Glass Integrated Photonics: Engineering optical function and mechanical flexibility
In recent years, the increasing penetration of flexible devices into the consumer products market has led to a surge of
interest in flexible photonics, i.e., integrated optical systems fabricated on flexible polymer substrates that can be mechanically
deformed without compromising their optical performance. In addition to being an essential component in consumer electronics,
flexible photonics also have enormous application potential for board-to-board optical interconnects, epidermal sensors,
wearable photonics and flexible displays as well as other arenas where light-weight, compact optical function is required.
Prime Time for Quantum-Dot-Enhanced LCD is Around the Corner
The liquid crystal display (LCD) has become ubiquitous and indispensable in our daily life. It is widely used in applications
such as smart phones, pads, computer screens, TVs, and data projectors. Recently, the LCD is facing competition from the
organic light emitting diode (OLED) display, especially in smart phones. LCDs advantage lie in their low cost, low power
consumption, and high resolution density, but lags behind the OLED in the response time, color saturation, and flexibility.
To achieve fast response time, Prof. Shin-Tson Wu’s group has developed a new polymer-stabilized blue phase LCD. In the
voltage-off state, the blue phase liquid crystal is optically isotropic so that it does not require surface alignment. This
greatly simplifies the manufacturing process. In the voltage-on state, the isotropic-to-anisotropic transition induced by
the Kerr effect takes place.