"Bacteria" in the car: the smallest electro-optical modulator

At first, the man invented and created new devices. Then he improved their work. What's next? And then - reducing the size of this device with the same (or even better) performance and power. So the scientists from the University of Oregon went along the same path and created the smallest at the moment electro-optical modulator. The size of this invention is 0.6 microns by 8 microns. Only bacteria can boast of such dimensions, and that is not all. Being 10 times smaller than such devices, the mini-modulator consumes 100 times less energy. At the same time, its working efficiency has not decreased due to reduction in size and reduction of consumed energy.

We all now one way or another use devices that connect to optical fiber optical networks. Fiber-optic networks transmit information in the form of a binary code. This is a very exaggerated description of the application. In order for everything to work as planned, and the information was not damaged and was transferred to the right place, a control device is needed. Such a device is an electro-optical modulator. These miniature instruments control the photon fluxes of light that pass through the device. Then the optical signal of the information that is transmitted is modulated.

The basis for creating a mini-modulator served as transparent oxides with the properties of semiconductors. Such a material allowed not only connecting the gate with a metal-oxide semiconductor capacitor and an ultra-compact photonic crystal, but also reducing the level of optical loss to 0.5 dB. And the efficiency of the mini-modulator was 46 fJ / bit (femtojoules per bit).

The creators themselves in their report say the following:

Silicon photonics has the potential to transform future optical systems by reducing the energy consumption and increasing the bandwidth of current electronic systems through the use of CMOS (Complementary Metal-Oxide-Semiconductor - a complementary metal oxide semiconductor structure). In addition to using silicon photon devices in optical networks, they can control logic gates to perform certain optical calculations. However, the effectiveness of silicon photonic devices remains limited to the limit of defecation and the rather low effect of plasma dispersion. Although silicon has a relatively high refractive index, it can shorten the wavelength inside the silicon waveguide in proportion to the λ / n scale, to about 400-600 nm. Further reduction in the size of the device requires the use of a surface polariton, which binds waves at the interface between the metal and the dielectric. The extremely strong light distribution of the metal-insulator-metal waveguide (MIM) demonstrated the capabilities of ultra-compact and high-frequency plasmon modulators. However, plasmonic structures and devices are very small and can only carry information over a very short distance. Therefore, for real optical networks, it is necessary to use a hybrid plasma-dielectric waveguide interaction, which increases the complexity of design and manufacture.

Modulator structure


(a) - 3D modulator circuit;
(b) color micrograph of the scanning electron of the modulator. The image shows an enlarged MOS capacitor region (metal oxide semiconductor);
(c) optical image of the modulator.

Diagram (a) shows a 1-D silicon polycarbonate nano-plate indium tin oxide. The device consists of a MOS capacitor embedded in the center of the nano-cavity on a silicon half-word waveguide, which is located on a SOI (silicon on an insulator) based 500 nm in width and 250 nm in length. A pair of diffraction couplers is integrated for defecation of light in an optical fiber. Polycarbonate plate sets the boundaries of electron-beam lithography and reactive ion etching. Two mirror segments of photonic crystals are located on the nano-plate. The size of the air hole narrows quadratically from the center of the plate to the edges of the two mirror segments. Each of them has 12 such holes. The fill factor decreases from 0.23 in the center to 0.1 at the edges. This coefficient is expressed by the formula f = A / pw , where A is the area of ​​the air hole, p is the gap between the holes, w is the width of the waveguide. In order that the modulator could work within the telecommunication waveguides, p is equal to 340 nm. In the center of the plate, the ITO / SiO2 / Si film creates a MOS capacitor, its sectional image is presented below:



If you want to learn more about this modulator, you can click on the link to the report on the authorship of its creators .

Epilogue

Technologies are developing and improving. And this process is not always associated exclusively with an increase in their efficiency or power. At the moment, the development of mankind more and more attention is paid to thumbnails of existing devices. The main task in this process is to preserve energy efficiency and device performance or even improve these indicators while reducing its actual size.

The created mini-modulator is a vivid example of how to reduce. It has become 10 times smaller than its predecessors and, at the same time, 100 times more energy efficient. Such characteristics are very interesting for researchers of supercomputers who need maximum performance at minimal cost. In terms of this, one might say so - who does not want to create a supercomputer capable of answering any question that works from the fingers of the batteries, like a TV remote control.

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