Abstract-Photonic amorphous topological insulator

Peiheng Zhou, Gui-Geng Liu, Xin Ren, Yihao Yang, Haoran Xue, Lei Bi, Longjiang Deng, Yidong Chong, Baile Zhang,

Transition of photonic lattices with increasing disorder

https://www.nature.com/articles/s41377-020-00368-7#:~:text=Photonic%20topological%20insulators%20(PTIs)1,insulator%20materials%20do%20for%20electrons.

The current understanding of topological insulators and their classical wave analogs, such as photonic topological insulators, is mainly based on topological band theory. However, standard band theory does not apply to amorphous phases of matter, which are formed by non-crystalline lattices with no long-range positional order but only short-range order, exhibiting unique phenomena such as the glass-to-liquid transition. Here, we experimentally investigate amorphous variants of a Chern number-based photonic topological insulator. By tuning the disorder strength in the lattice, we demonstrate that photonic topological edge states can persist into the amorphous regime prior to the glass-to-liquid transition. After the transition to a liquid-like lattice configuration, the signatures of topological edge states disappear. This interplay between topology and short-range order in amorphous lattices paves the way for new classes of non-crystalline topological photonic bandgap materials.

NTU Singapore and Osaka University scientists build ultra-high-speed Terahertz wireless chip

https://media.ntu.edu.sg/NewsReleases/Pages/newsdetail.aspx?news=ceb7dbf3-6d6a-493d-b9a8-0bcf25954c10&utm_source=miragenews&utm_medium=miragenews&utm_campaign=news

To enable data transmission speeds that surpass the 5th Generation (5G) standards for telecommunications, scientists from Nanyang Technological University, Singapore (NTU Singapore) and Osaka University in Japan have built a new chip using a concept called photonic topological insulators.

Published recently in Nature Photonics, the researchers showed that their chip can transmit terahertz (THz) waves resulting in a data rate of 11 Gigabits per second (Gbit/s), which is capable of supporting real-time streaming of 4K high-definition video, and exceeds the hitherto theoretical limit of 10 Gbit/s for 5G wireless communications. 

THz waves are part of the electromagnetic spectrum, in between infrared light waves and microwaves, and have been touted as the next frontier of high-speed wireless communications. 

However, fundamental challenges need to be tackled before THz waves could be used reliably in telecommunications. Two of the biggest issues are the material defects and transmission error rates found in conventional waveguides such as crystals or hollow cables.

These issues were overcome using Photonic Topological Insulators (PTI), which allows light waves to be conducted on the surface and edges of the insulators, akin to a train following railroads, rather than through the material. 

When light travels along photonic topological insulators, it can be redirected around sharp corners and its flow will resist being disturbed by material imperfections.

By designing a small silicon chip with rows of triangular holes, with small triangles pointing in the opposite direction to larger triangles, light waves become “topologically protected”.

This all-silicon chip demonstrated it could transmit signals error-free while routing THz waves around 10 sharp corners at a rate of 11 gigabits per second, bypassing any material defects that may have been introduced in the silicon manufacturing process.

Leader of the project, NTU Assoc Prof Ranjan Singh, said this was the first time that PTIs have been realised in the terahertz spectral region, which proves the previously theoretical concept, feasible in real life. 

Their discovery could pave the way for more PTI THz interconnects – structures that connect various components in a circuit – to be integrated into wireless communication devices, to give the next generation ‘6G’ communications an unprecedented terabytes-per-second speed (10 to 100 times faster than 5G) in future.

“With the 4th industrial revolution and the rapid adoption of Internet-of-Things (IoT) equipment,  including smart devices, remote cameras and sensors, IoT equipment needs to handle high volumes of data wirelessly, and relies on communication networks to deliver ultra-high speeds and low latency,” explains Assoc Prof Singh. 

“By employing THz technology, it can potentially boost intra-chip and inter-chip communication to support Artificial intelligence and cloud-based technologies, such as interconnected self-driving cars, which will need to transmit data quickly to other nearby cars and infrastructure to navigate better and also to avoid accidents.”

This project took the NTU team and their collaborators led by Professor Masayuki Fujita at Osaka University two years of design, fabrication, and testing.

Prof Singh believes that by designing and producing a miniaturised platform using current silicon manufacturing processes, their new high-speed THz interconnect chip will be easily integrated into electronic and photonic circuit designs and will help the widespread adoption of THz in future.  

Areas of potential application for THz interconnect technology will include data centres, IOT devices, massive multicore CPUs (computing chips) and long-range communications, including telecommunications and wireless communication such as Wi-Fi. 

Paper titled “Terahertz topological photonics for on-chip communication”, published in Nature Photonics, 13 Apr 2020. 

Novel Materials Could Help Terahertz Chips Deliver Data at Terabits-Per-Second Rates

Photonic topological insulators and terahertz waves could together deliver data at ultra-fast speeds

Image: Nanyang Technological University/Nature Photonics

An artist's representation of the silicon chip. The orange wavy line represents terahertz rays, which travel topologically protected in the interface between the two different sets of triangular holes. On the right, data is encoded into transmitted terahertz rays. On the left, data is received from the terahertz rays in applications involving wireless communication.

By Charles Q. Choi

https://spectrum.ieee.org/nanoclast/computing/hardware/terahertz-chip

Novel materials known as photonic topological insulators could one day help terahertz waves send data across chips at unprecedented speeds of a trillion bits per second, a new study finds. 

Terahertz waves fall between optical waves and microwaves on the electromagnetic spectrum. Ranging in frequency from 0.1 to 10 terahertz, terahertz waves could be key to future 6G wireless networks. With those networks, engineers aim to transmit data at terabits (trillions of bits) per second.

Such data links could also greatly boost intra-chip and inter-chip communication to support artificial intelligence (AI) and cloud-based technologies, such as autonomous driving.

"Artificial intelligence and cloud-based applications require high volumes of data to be transmitted to a connected device with ultra-high-speed and low latency," says Ranjan Singh, a photonics researcher at Nanyang Technological University in Singapore and coauthor of the new work. "Take for example, an autonomous vehicle that uses AI to make decisions. In order to increase the efficiency of decision-making tasks, the AI-sensors need to receive data from neighboring vehicles at ultra-high speed to perform the actions in real time."

Conventional terahertz waveguides are vulnerable to fabrication defects and considerable signal loss at sharp bends. Now, researchers find the burgeoning field of topological photonics may help solve these problems.

Topology is the branch of mathematics that explores what features of shapes can survive deformation. For instance, an object shaped like a doughnut can get pushed and pulled into the shape of a mug, with the doughnut's hole forming the hole in the cup's handle, but it could not get deformed into a shape that lacked a hole without ripping the item apart.

Using insights from topology, researchers developed the first electronic topological insulators in 2007. Electrons traveling along the edges or surfaces of these materials strongly resist any disturbances that might hamper their flow, much as a doughnut might resist any change that would remove its hole.

Recently, scientists have designed photonic topological insulators in which photons of light are similarly "topologically protected." These materials possess regular variations within their structures that lead specific wavelengths of light to flow within them without scattering or losses, even around corners and imperfections.

Image: Nanyang Technological University/Nature Photonics

An optical image of the silicon chip. The white dashed line represents the interface between the two different sets of triangular holes.

Prior work on photonic topological insulators was largely focused on microwave and optical frequencies. Now researchers say they have for the first time experimentally achieved topological protection of terahertz waves.

Scientists fabricated a silicon chip that was 190 microns thick and measuring 8 millimeters by 26 millimeters. They perforated it with rows of triangular holes that alternated in size between 84.9 microns and 157.6 microns, with the smaller triangles pointing the opposite direction of the larger ones. These rows of holes were arranged in clusters where all the larger triangles either pointed up or down. Light entering this chip flowed topologically protected along the interface between the different sets of holes.

Photos: Nanyang Technological University/Nature Photonics

An experimental demonstration of uncompressed 4K high-definition video transmission using the new chip (right). The transmitted 4K high-definition video is shown on the monitor in the background. The terahertz-signal transmitter is on the left side; the receiver is on the right side.

In experiments, the researchers found terahertz waves could also travel smoothly with virtually no losses even when routed around 10 sharp corners, including five 120-degree turns and five 60-degree turns. They achieved data transfer rates of 11 gigabits per second at a frequency of 0.335 terahertz with a bit error rate of less than 1 in 100 billion. They also showed they could transmit uncompressed 4K high-definition video in real-time through their chip across those 10 sharp bends at a rate of 6 gigabits per second.

Previous research achieved data rates of 1.5 gigabits per second with terahertz waves and photonic crystals (structures possessing features smaller than the wavelengths of light they’re designed to deal with). Not only does the photonic topological insulator in the new work display higher data transfer rates, but traditional photonic crystals experience huge signal loss at bends, whereas such losses are negligible in the new material. "This is important when we consider miniaturization of devices in designing on-chip multiplexers and splitters, which normally require bending of waveguides," says Masayuki Fujita, a coauthor and photonics researcher at Osaka University in Japan.

The researchers note there are a number of ways to boost the data rates of their setup to achieve terabit-per-second speeds, though they haven’t yet demonstrated those rates in an experiment. These techniques include using higher frequencies, more bandwidth, and more complex data-encoding schemes.

The scientists detailed their findings on 13 April in the journal Nature Photonics.