Novel Nanomaterial Enables Rewritable Optical Circuits

For the first time, a wave guide is rewritable using an all-optical technique

3 min read

Image of Mona Lisa that appears and disappears
Image: The University of Texas at Austin

Researchers at the University of Texas at Austin have developed a hybrid nanomaterial that enables the writing, erasing and rewriting of optical components. The researchers believe that this nanomaterial and the techniques used in exploiting it could create a new generation of optical chips and circuits.

In research published in the journal Nano Letters, the Texas team describe creating their novel hybrid nanomaterial by starting with a plasmonic surface.

Plasmonics is the field that exploits the oscillations in the density of electrons that occur when photons hit a metallic surface. These oscillations of electrons that resemble waves are called surface plasmons. In this case, the metal surface is made up of aluminum nanoparticles topped with a polymer layer embedded with molecules responsive to light.

These photochromic molecules undergo quantum interactions with the light that can either make the molecules transparent or opaque. In the photonic circuit that the Texas researchers created, the metallic plasmonic surface and the photochromic molecules represent two quantum systems. The interaction, or coupling, between these two quantum systems in this design is very strong. By exploiting these phenomena, the researchers created a waveguide that controls the direction of light, critical to integrated photonic circuits. 

The researchers first created their waveguide in the nanomaterial with a green laser. They were then able to erase the waveguide using a UV light, and then they rewrote the waveguide pattern again using the green laser. The team believes that this is the first time anyone has been able to rewrite a waveguide using an all-optical technique.

“In our work, we have the hybrid plasmonic waveguides as one quantum system, and add the molecules to the polymer to serve as the second quantum system,” explained Linhan Lin, who was co-author of the research, in an e-mail interview with IEEE Spectrum. “Once the strong coupling between these two quantum systems occurs, we split the resonant frequency of our hybrid plasmonic waveguides towards two different new frequencies by simply shining our sample with a UV light. “

At the moment the sample is hit with the UV light, the hybrid plasmonic waveguide cannot work at its resonant frequency, or, in other words, the waveguide is erased, according to Lin. The resonant frequency will return once the green laser is shined on the sample (the molecules become transparent). “In this way we get the waveguide working, so we say we create the waveguide,” adds Lin.

Of course, the concept of rewritable optics is not altogether new; it forms the basis of optical storage mediums like CDs and DVDs. However, CDs and DVDs require bulky light sources, optical media and light detectors. The advantage of the rewritable integrated photonic circuits developed here is that it all happens on a 2-D material.

“To develop rewritable integrated nanophotonic circuits, one has to be able to confine light within a two-dimensional (2-D) plane, where the light can travel in the plane over a long distance and be arbitrarily controlled in terms of its propagation direction, amplitude, frequency and phase,” explained Yuebing Zheng, a professor at the University of Texas who led the research, in a press release. “Our material, which is a hybrid, makes it possible to develop rewritable integrated nanophotonic circuits.”

Some engineering is required to see these rewritable integrated nanophotonic circuits come to fruition. Lin explained to me that to move this technology beyond the lab, they will need to improve the stability of this rewriteable device and increase its lifetime. Also, they need to match the working frequency of hybrid plasmonic waveguides with the on-chip communication frequency.

Zheng added: “Our aim is to develop rewritable optical components beyond waveguides, which will lead to rewritable optical filters, channel drop filters, delay lines, sensors, lasers, modulators, dispersion compensators and so on. These are critical components for future photonic integrated circuits.”

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