Plasmonic Mach-Zehnder modulator operates at 108 Gbit/s, is only 12.5 µm long

Aug. 3, 2015
The device works over the 1500 to 1600 nm telecommunications wavelength range.

Waveguide-based Mach-Zehnder modulators (MZMs) provide a clean and high-speed way to modulate light (converting an electronic signal into an optical signal) on a silicon photonic chip. Now, researchers at the Karlsruhe Institute of Technology (KIT; Karlsruhe, Germany) and the ETH Zurich (Zurich, Switzerland) have developed a plasmonic MZM that is smaller and faster than an optical MZM.1

The new device is only 12.5 µm long and has a modulation rate of up to 108 Gbit/s. The MZM has two arms, each of which contains one electro-optical modulator. Each modulator is made up of a metal-insulator-metal waveguide with a gap approximately 80 nanometers wide and filled with an electro-optical polymer, and sidewalls made of gold which, at the same time, act as electrodes. The electrodes carry a voltage that is modulated in line with the digital data. The electro-optical polymer changes its index of refraction as a function of the voltage. The waveguide and the coupler, made of silicon, route the two parts of a split light beam to the gaps or from the gaps.

In the respective gap, the light beams of the waveguides initiate electromagnetic surface waves -- in other words, surface plasmons. The voltage applied to the polymer modulates the surface waves. Modulation is different in both gaps but coherent, as the same voltage is applied with different polarities. After passing through the gaps, the surface waves initially enter the output optical waveguides as modulated light beams and are then superimposed. The result is a light beam in whose amplitude the digital information is encoded.

Covers the 1550 nm band
In the experiment, the MZM works reliably over the 1500 to 1600 nm telecommunications wavelength range at an electric bandwidth of 70 GHz with data flows of up to 108 Gbit/s. The large depth of modulation is a consequence of the high manufacturing accuracy in silicon technology. The MZM can also be made by means of the standard CMOS processes in microelectronics, and thus can easily be integrated into current chip architectures.

"Optical technologies offer an enormous potential especially in transmitting data between computer chips," says Manfred Kohl of the KIT.

Source: http://www.kit.edu/kit/english/pi_2015_085_nature-compact-optical-data-transmission.php

REFERENCE:

1. C. Haffner et al., Nature Photonics AOP (2015); DOI: 10.1038/nphoton.2015.127

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