Introduction to Resonant Tunnelling Diode
OptoElectronic Integrated Circuits
OEIC
OptoElectronic Integrated Circuits (OEIC)
is a general term for a technology that targets integrating optical
devices and electronic devices on the same semiconductor chip; for
example, an optical detector on the same chip as a transistor amplifier
or a semiconductor laser on the same chip as transistor. The objective
is
to emulate the success that silicon technology has demonstrated with
integration and to produce chips with increased functionality, speed
and reliability and reduced cost and size. Most work so far has been
carried out on receiver chips for optical communication systems but
there has been some work on transmitters and on this web site we
concentrate on a particular type of OEIC technology that uses resonant
tunnelling diodes (RTDs) with electroabsorption
modulators and laser
diodes.
Why Resonant
Tunnelling Diode (RTD) OptoElectronic Integrated Circuits?
RTD OEIC technology is a monolithic technology that uses a
vertical
stacking of epitaxial
layers of semiconductor
alloys -each section of
the stack has a different function - the RTD section of the stack is
particularly simple consiting of three epitaxial layers, in total,
about
10nm thick. The effect of the RTD layers is to give the device a highly
nonlinear current voltage characteristic that can be configured to give
the device
electrical gain through negative
differental resistance (NDR) - this
leads to large reductions in the energy required to switch the device
on and off as is required for digitally encoding optical
signals in an optical communications system. Furthermore, appropriately
configured the RTD OEIC devices can behave as optoelectronic voltage
controlled oscillators (OVCOs)
which
opens out the possibility of a whole new range of
applications. Because RTD have very broad bandwidth gain RTD
based oscillators have reached the highest frequency of any electronic
oscillator at 831 GHz (Suzuki, S. et al.). Click here for a recent review of RTD-OEICs.
Examples of RTD
OEICs
RTDs have been integrated with electroabsoprtion modulators
to form a
RTD-EAM and with laser diodes to form a RTD-LD. Integration of RTD in
both these devices has been shown to reduce significantly the energy
required to switch the device. The RTD-EAM work is reported in the PhD thesis
of Jose Figuiredo (click
for summary paper) and the RTD-LD is reported in
the PhD thesis
of Thomas Slight - click for
a recent paper.
A recent spin off from the work on the RTD-LD has been a hybrid
integrated device that behaves as OVCO and displays classic nonlinear
systems behaviour such as self
sustained oscillation, synchronisation
and chaos.
-click for a
recent paper
The operation of RTD-LD oscillator can be accurately described using
classic nonlinear systems theory and it has been shown to operate as a Lienard's Oscillator - a generalisation of the Van der Pol Oscillator - click for a recent paper on this.
Applications of RTD
OEICs - The wireless/optical interface
RTD-OEIC
technology has recently been applied to a wireless/optical interface
technology - potentially providing a single chip solution for
converting digital information from the wireless domain to the optical
domain and back again. Wireless signals are phase shift keyed (PSK) and the RTD-LD acts like an injection locked oscillator (ILO)
that can have its phase controlled by a weak wireless signal thus
transferring phase encoded digital signals from the wireless to the
optical domain. It works the other way round, optical to wireless, by
using a resonant tunnelling diode photodiode (RTD-PD) configured as a
oscillator - then an optical signal - the optical sub-carrier -
controlls the phase of wireless signal. Click here for a link to a more detailed paper.
Last Updated 15/02/10
Prof.
C. N. Ironside