Electronics Weekly
It is a modulator with two gold electrodes on a substrate facing each other across 10nm wide slot 10µm long (see artists impression).
Inside the slot is a substance only described as a ‘non-linear organic electro-optic material’, and at opposite ends of the slot are silicon waveguides that are finally coupled to the input and output optical fibres.
Modulation is through variation of refractive index as the electric field changes – the Pockels effect.
Fed with 1,545nm light, the modulator worked continuously across 1MHz to 1.14THz – with eight different signal generators needed to test performance from end to end. 3dB roll-off was at 997GHz.
“This achievement confirms the potential of plasmonic modulators to bring THz frequencies to photonic integrated circuits,” said researcher Yannik Horst. For many years, its capability beyond 500 GHz was just theory.”
In the proof-of-concept device, there are actually three electrodes in a row leaving gaps for two parallel channels.
The two outer electrodes are grounded and the centre one gets the input signal. What is planned for the second channel?
“We only need one channel, the 2nd port is not needed, but a high speed signal usually is fed in as a ground-signal-ground electrode arrangement,” fellow researcher Professor Juerg Leuthold told Electronics Weekly. “In a Mach-Zehnder configuration however, we would use this second port.”
Results are available in the Optical paper ‘Ultra-wideband MHz to THz plasmonic EO modulator‘.
Image: Johannes Grewer Polariton Technologies
