Photodetector Mimics Directional Hearing in Small Animals

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Researchers from Stanford University have drawn from nature — specifically, from the ear structure of the gecko — to devise a subwavelength photodetector that can measure both the intensity and incident angle of light.

Nano photodetector based on gecko ear structure. Stanford University.
Gecko ears contain a mechanism similar to the Stanford researchers’ system for detecting the angle of incoming light. Courtesy of Vitaliy Halenov.

Geckos and many other animals have heads that are too small to triangulate the location of noises the way humans do. Instead, they have a tiny tunnel through their heads that measures the way incoming sound waves bounce around. If a sound isn’t coming from directly over the top of the gecko, one eardrum essentially steals some of the sound wave energy that would otherwise tunnel through to the other. This inference helps the gecko (and about 15,000 other animal species with a similar tunnel) understand where a sound is coming from.

The researchers mimicked this structure in their photodetector by lining up two silicon nanowires, each about 100 nm in diameter, next to each other, like the gecko’s eardrums. The nanowires were positioned so closely that when a light wave came in at an angle, the wire closest to the light source interfered with the waves hitting its neighbor, basically casting a shadow. Consequently, the first wire to detect the light sent the strongest current. By comparing the current in both wires, the researchers could map the angle of incoming light waves.

Such a system could be used by tiny cameras to detect where light is coming from, without the bulk of a large lens.

“Making a little pixel on your photo camera that says light is coming from this or that direction is hard because, ideally, the pixels are very small — these days about 1/100th of a hair,” said professor Mark Brongersma. “So it’s like having two eyes very close together and trying to cross them to see where the light is coming from.”

The tiny detectors that the team is developing can record many characteristics of light, including color, polarity, and now angle of light. The researchers believe their system is the first to demonstrate that it’s possible to determine angle of light with a nanoscale setup.

“The typical way to determine the direction of light is by using a lens. But those are big and there’s no comparable mechanisms when you shrink a device so it’s smaller than most bacteria,” said professor Shanhui Fan. More detailed light detection could support advancements in lensless cameras, augmented reality, and robotic vision, the researchers said.

Geckos were not the inspiration for the construction of the system, at least not initially. One of the researchers discovered the similarities between the team’s design and the gecko’s ear structure after work on the project had begun. The researchers further discovered that the same math that explains both the gecko ears and their tiny photodetector also describes an interference phenomenon between closely arranged atoms.

“On the theory side, it’s actually very interesting to see many of the basic interference concepts that go all the way to quantum mechanics show up in a device that can be practically used,” Fan said.

The researchers look forward to building on the results of their current proof of concept. Next steps include deciding what else they might want to measure from light and putting several nanowires side by side to see if they can build a complete imaging system that records all the details they’re interested in at once.

The research was published in Nature Nanotechnology (

Published: November 2018
An SI prefix meaning one billionth (10-9). Nano can also be used to indicate the study of atoms, molecules and other structures and particles on the nanometer scale. Nano-optics (also referred to as nanophotonics), for example, is the study of how light and light-matter interactions behave on the nanometer scale. See nanophotonics.
Nanopositioning refers to the precise and controlled movement or manipulation of objects or components at the nanometer scale. This technology enables the positioning of objects with extremely high accuracy and resolution, typically in the range of nanometers or even sub-nanometer levels. Nanopositioning systems are employed in various scientific, industrial, and research applications where ultra-precise positioning is required. Key features and aspects of nanopositioning include: Small...
Nanophotonics is a branch of science and technology that explores the behavior of light on the nanometer scale, typically at dimensions smaller than the wavelength of light. It involves the study and manipulation of light using nanoscale structures and materials, often at dimensions comparable to or smaller than the wavelength of the light being manipulated. Aspects and applications of nanophotonics include: Nanoscale optical components: Nanophotonics involves the design and fabrication of...
A photodetector, also known as a photosensor or photodiode, is a device that detects and converts light into an electrical signal. Photodetectors are widely used in various applications, ranging from simple light sensing to more complex tasks such as imaging and communication. Key features and principles of photodetectors include: Light sensing: The primary function of a photodetector is to sense or detect light. When photons (particles of light) strike the active area of the photodetector,...
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