Scientists at Hitachi Ltd’s UK research facility, in conjunction with Cambridge University’s Microelectronics Research Centre claim to have made a scientific breakthrough in the development of fast opto-electrical switches. Demonstrations carried at the Cambridge Laboratory have shown that synchronised pulses of light from a laser can be used to control the flow of electrons passing into a switch and in so doing control when it is switched on and off. The flow of electrons within a switch activates transistors within a logic circuit. However, optical switch speeds have been historically limited by an inability to control the flow of electrons through a switch. The operating speed of today’s optoelectronic devices is limited by the time to taken for electrons to disappear from the switch which is usually one nanosecond in semiconductors, said Dr Jeremy Allam, senior research and group leader at the Hitachi Cambridge Laboratory. However by using the principle of synchronising light pulses the researchers have increased this speed to 100 femtoseconds. In the past scientists have controlled the passage of electrons through a switch by applying an electronic charge to dissipate electrons or by using semiconductor material with a high density of defects so that electrons generated by a light pulse are quickly trapped at the defects and reset the device for the next pulse. However, these methods have only increase the switch speed to one picosecond. In the demonstration, two synchronised pulses were created by splitting the light beam from an ultrafast pulsed laser. The pulses were then sent to the semiconductor along different paths with their arrival times controlled by varying the length of the path travelled by each pulse. However, the demonstration was at -269oC in Gallium Arsenide and will obviously not be commercially viable until the process will work at room temperature.
