Researchers in photonics have developed a novel method for controlling a light beam with another beam using a unique plasmonic metasurface in a linear medium at ultra-low power. This simple linear switching method makes nanophotonic devices such as optical computing and communication systems that require low light intensity more sustainable.
The modulation of signal light by control light in such a way that it has the ON/OFF conversion function is known as all-optical switching. In the presence of a nonlinear medium, a light beam can be modulated with another intense laser beam. The researchers’ switching method is fundamentally based on the quantum optical phenomenon known as Enhancement of Index of Refraction (EIR).
“This is the first experimental demonstration of this effect on the optical system and its use for linear all-optical switching. The study also enlightens the scientific community on how to create loss-compensated plasmonic devices that operate at resonance frequencies through extraordinary refractive index enhancement without the use of any gain media or nonlinear processes” Humeyra Caglayan, Associate Professor (tenure track) in Photonics at Tampere University, concurs.
This is the first experimental demonstration of this effect on the optical system and its use for linear all-optical switching. The study also enlightens the scientific community on how to create loss-compensated plasmonic devices that operate at resonance frequencies through extraordinary refractive index enhancement without the use of any gain media or nonlinear processes.
Humeyra Caglayan
Optical switching enabled with ultrafast speed
High-speed switching and low-loss medium to avoid signal dissipation during propagation are the foundations for developing integrated photonic technology in which photons are used as information carriers rather than electrons. All-optical switching must have ultrafast switching time, ultralow threshold control power, ultrahigh switching efficiency, and nanoscale feature size to realize on-chip ultrafast all-optical switch networks and photonic central processing units.
“The ability to switch between 0 and 1 signal values is fundamental in all digital electronic devices, including computers and communication systems. These electronic elements have gotten smaller and faster over the last few decades. Ordinary calculations performed by our computers on the order of seconds, for example, could not be performed by old room-sized computers in several days!” Caglayan makes a remark.
Switching in conventional electronics is based on controlling the flow of electrons on a time scale of a microsecond (10-6 sec) or nanosecond (10-9 sec) by connecting or disconnecting electrical voltage.
“By replacing electrons with plasmons, the switching speed can be increased to an ultrafast time scale (femtosecond 10-15 sec). Plasmons are a combination of photons and electrons on the surface of metals. This enables optical switching with our device at femtosecond (10-15 sec) speeds” She says.
“Our plasmonic nano-switch is made up of an L-shaped array of metallic nanorods. One of the nanorods receives a linearly polarized signal and the other receives another linearly polarized “control” beam perpendicular to the first beam,” says Postdoctoral Research Fellow Rakesh Dhama, the first author of the article.
Polarization refers to the direction in which the beam’s electric field oscillates. Depending on the phase difference between the beams, the control beam can attenuate or amplify the signal. The phase difference is the difference in time between when each beam reaches its maximum intensity. The transfer of some optical energy from the control beam to the signal via a constructive superposition with a carefully engineered phase difference causes signal amplification.
Enhancing the performance of plasmonic devices
When the beams have the opposite phase difference, destructive superposition is used to attenuate the signal. This discovery makes nanophotonic devices such as optical computing and communication systems that require low light intensity more sustainable. By accelerating the development and realization of nanoscale plasmonic systems, this simple linear switching method can replace current ones of optical processing, computing, or communication.
“In the future, we expect to see more studies of plasmonic structures using our improved switching method, as well as the use of our method in plasmonic circuits. Furthermore, the L-shaped metasurface could be studied further to reveal ultrahigh-speed switching under femtosecond laser pulse illumination and to investigate the nonlinear enhancement and control of plasmonic nanoparticles “Humeyra Caglayan makes a point.
Controlling the nonlinear response of nanostructures adds new applications and functionalities to nanophotonic devices like optical computing and communication systems.
“This method has the potential to improve the performance of plasmonic devices by generating broadband transparency for a signal beam with no gain medium. It has the potential to open up new avenues for designing smart photonic elements for integrated photonics” She sketches.
