Nanophotonic device reads twisted light to unlock 100X fiber capacity

The world-first nanophotonic device encodes more data and processes it much faster than conventional fiber optics by using a special form of ‘twisted’ light.

The tiny nanophotonic device built for reading twisted light is the missing key required to unlock super-fast, ultra-broadband communications.

“Present-day optical communications are heading towards a ‘capacity crunch’ as they fail to keep up with the ever-increasing demands of Big Data,” Ren said.

New cables would be required to effectively twist light, any upgrade could involve replacing existing fiber networks.

They accurately can transmit and read data via light at its highest capacity in a way that will allow us to massively increase our bandwidth.

Current state-of-the-art fiber-optic communications, like those used in Australia’s National Broadband Network (NBN), use only a fraction of light’s actual capacity by carrying data on the color spectrum.

New broadband technologies under development use the oscillation, or shape, of light waves to encode data, increasing bandwidth by also making use of the light we cannot see.

This latest technology, at the cutting edge of optical communications, carries data on light waves that have been twisted into a spiral to increase their capacity further still. This is known as light in a state of orbital angular momentum, or OAM.

In 2016 the same group from RMIT’s Laboratory of Artificial-Intelligence Nanophotonics (LAIN) published a disruptive research paper in Science journal describing how they’d managed to decode a small range of this twisted light on a nanophotonic chip. But technology to detect a wide range of OAM light for optical communications was still not viable, until now.

“Our miniature OAM nano-electronic detector is designed to separate different OAM light states in a continuous order and to decode the information carried by twisted light,” Ren said.

“To do this previously would require a machine the size of a table, which is completely impractical for telecommunications. By using ultrathin topological nanosheets measuring a fraction of a millimeter, our invention does this job better and fits on the end of an optical fiber.”

LAIN Director and Associate Deputy Vice-Chancellor for Research Innovation and Entrepreneurship at RMIT, Professor Min Gu, said the materials used in the device were compatible with silicon-based materials use in most technology, making it easy to scale up for industry applications.

“Our OAM nano-electronic detector is like an ‘eye’ that can ‘see’ information carried by twisted light and decode it to be understood by electronics. This technology’s high performance, low cost and tiny size makes it a viable application for the next generation of broadband optical communications,” he said.

“It fits the scale of existing fiber technology and could be applied to increase the bandwidth, or potentially the processing speed, of that fiber by over 100 times within the next couple of years. This easy scalability and the massive impact it will have on telecommunications is what’s so exciting.”

Gu said the detector can also be used to receive quantum information sent via twisting light, meaning it could have applications in a whole range of cutting-edge quantum communications and quantum computing research.

“Our nano-electronic device will unlock the full potential of twisted light for future optical and quantum communications,” Gu said.

Optical imaging, sensing and metrology have been significantly advanced with the development of complementary metal–oxide–semiconductor (CMOS) technology. Its unique capability to support photonic devices with high-spatial and -spectral resolution has allowed the detection of optical signals in different physical dimensions. The orbital angular momentum (OAM) of light carried by a helical wavefront with a physically unbounded set of spatial modes has emerged as a physically orthogonal dimension of light. Although the generation and measurement of the OAM of light have recently been exploited by nanophotonic methods the separation of OAM modes has been limited to bulk optics that accomplish the linear displacement of OAM-carrying beams due to the lack of OAM-dispersive materials or detectors at a nanoscale.

They have demonstrated a CMOS-integratable OAM nanometrology, through the spatial engineering of plasmonic angular momentum modes in an ultrathin OAM-dispersive plasmonic topological insulator film. They have applied the outperforming plasmonic effect in an ultrathin topological insulator Sb2Te3 thin film for on-chip OAM nanometrology with an integratable CMOS camera at a visible wavelength. Notably, the current OAM nanometrology signals were imaged by a CMOS detector via a magnifying 4f optical system in the far-field region. However, owing to the recent rapid progress in nanotechnology, our demonstration holds great promise for future all-on-chip integration of the OAM nanometrology chip with a high-resolution CMOS detector.

This kind of CMOS-compatible ultrathin OAM nanometrology device with a small footprint is highly compatible with other integrated devices such as vortex emitters, OAM microlasers, OAM manipulation metasurfaces and photodetectors. The high-precision OAM nanometrology in a CMOS-compatible plasmonic topological insulator material holds a great promise for the development of ultrathin optoelectronics with versatile functionalities and ultracompact photonic integrated circuits.

Nature Communications – Angular-momentum nanometrology in an ultrathin plasmonic topological insulator film

Complementary metal–oxide–semiconductor (CMOS) technology has provided a highly sensitive detection platform for high-resolution optical imaging, sensing and metrology. Although the detection of optical beams carrying angular momentum have been explored with nanophotonic methods, the metrology of optical angular momentum has been limited to bulk optics. We demonstrate angular-momentum nanometrology through the spatial displacement engineering of plasmonic angular momentum modes in a CMOS-compatible plasmonic topological insulator material. The generation and propagation of surface plasmon polaritons on the surface of an ultrathin topological insulator Sb2Te3 film with a thickness of 100 nm is confirmed, exhibiting plasmonic figures of merit superior to noble metal plasmonics in the ultraviolet-visible frequency range. Angular-momentum nanometrology with a low crosstalk of less than −20 dB is achieved. This compact high-precision angular-momentum nanometrology opens an unprecedented opportunity for on-chip manipulation of optical angular momentum for high-capacity information processing, ultrasensitive molecular sensing, and ultracompact multi-functional optoelectronic devices.

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