Introduction to Resonant Tunnelling Diode OptoElectronic Integrated Circuits
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 oscillationsynchronisation 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