New all-optical switching method makes optical computing and communication systems more energy efficient

Photonics researchers have introduced a new method to control a beam of light with another beam through a single plasmonic metasurface in a linear medium at very low power. This simple linear switching method makes nanophotonic devices such as optical computing and communication systems more durable requiring low light intensity.

All-optical switching is the modulation of the signal light due to the control light in such a way that it has the ON/OFF conversion function. In general, a light beam can be modulated by another intense laser beam in the presence of a nonlinear medium.

The switching method developed by the researchers is fundamentally based on the quantum optical phenomenon known as refractive index enhancement (EIR).

“Our work is the first experimental demonstration of this effect on the optical system and its use for linear all-optical switching. The research also enlightens the scientific community to obtain loss-compensated plasmonic devices operating at resonant frequencies through enhancement extraordinary refractive index without using any gain media or non-linear processes,” says Humeyra Caglayan, Tenure Track Associate Professor of Photonics at the University of Tampere.

Optical switching enabled with ultra-fast speed

High-speed switching and low-loss medium to avoid high signal dissipation during propagation are the basis for the development of integrated photonics technology where photons are used as information carriers instead of electrons. To realize ultra-fast on-chip all-optical switching networks and photonic CPUs, all-optical switching must have ultra-fast switching time, ultra-low threshold control power, ultra-high switching efficiency, and feature size at the nanometer scale.

“Switching between signal values ​​of 0 and 1 is fundamental in all digital electronic devices, including computers and communication systems. Over the past decades, these electronic elements have become progressively smaller and faster. For example, ordinary calculations performed with our computers on command of seconds could not be done with old room-sized computers, even in several days!” Caglayan’s remarks.

In conventional electronics, switching relies on controlling the flow of electrons on the microsecond (10-6 sec) or nanosecond (10-9 sec) range by connecting or disconnecting the electrical voltage.

“However, the switching speed can be scaled up to an ultra-fast time scale (femtosecond 10-15 sec) by replacing electrons with plasmons. Plasmons are a combination of photons and a collection of electrons on the surface of metals. This allows optical switching with our device with femtosecond (10-15 sec) speeds,” she says.

“Our plasmonic nano-switch consists of an L-shaped combination of metal nanorods. One of the nanorods receives a linearly polarized signal and the other receives another linearly polarized ‘control’ beam perpendicular to the first beam,” Rakesh explains. Dhama, postdoctoral researcher. , the first author of the article.

Polarization means the direction in which the electric field of the beam oscillates. The control beam can attenuate or amplify the signal depending on the phase difference between the beams. Phase difference refers to the time difference when each beam reaches its maximum intensity. Signal amplification occurs due to the transfer of some optical energy from the control beam to the signal through constructive superimposition with a carefully designed phase difference.

Improved performance of plasmonic devices

Similarly, signal attenuation is achieved by destructive superposition when the beams have the opposite phase shift. This discovery makes nanophotonic devices such as optical computing and communication systems more durable requiring low light intensity. This simple linear switching method can replace current optical processing, computing, or communication methods by accelerating the development and realization of nanoscale plasmonic systems.

“We expect to see further studies of plasmonic structures using our improved switching method and possibly the use of our method in plasmonic circuits in the future. Additionally, the L-shaped metasurface could be studied further. forward to reveal ultra-fast switching under the illumination of femtosecond laser pulses and to investigate nonlinear enhancement and control of plasmonic nanoparticles,” notes Humeyra Caglayan.

Nonlinear response control of nanostructures offers even more exciting applications and functionality to nanophotonic devices such as optical computing and communication systems.

“This approach also has the potential to improve the performance of plasmonic devices by creating broadband transparency for a signal beam without any gain medium. It can open multiple ways to design smart photonics for integrated photonics,” she points out.

The research received funding from the H2020 European Research Council (Starting Grant project aQUARiUM, Academy of Finland Flagship Program (PREIN) and H2020 Research and Innovation Program (Marie Sk?odowska-Curie MULTIPLY).

The research was carried out by Metaplasmonics Research Group members Rakesh Dhama, Tuomas Pihlava, Dipa Ghindani and Humeyra Caglayan at TAU ​​and visiting researcher Ali Panah Pour.

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