Optics Inspired By the Eyes of Insects

By Lakshmi Supriya, PhD.Apr 17 2018

There may have been times when you’ve wished you had eyes in the back of your head. That’s where insects are one-up on humans. Most insects have large bulging eyes that can even look back without them having to turn their heads.

Insect Eyes

Unlike humans, who have a single eye and lens, insects have what are called compound eyes. These compound eyes consist of several tiny eyes called ommatidia with one lens each. Their numbers can range from hundreds to several thousand. Dragonflies, for example, have about 30,000 ommatidia. In both humans and insects, the lens focuses light on light-sensitive cells at the back of the eye, which sends a signal to the brain to analyze and form an image.

Although this large number of ommatidia provides insects with almost 360° vision, they do have some disadvantages. Insects cannot perceive depth as well as humans do and nor can they see sharp images with fine details. They usually see blurry outlines and images are mostly devoid of any color.

Image Credit: Waravut Wattanapanich/Shutterstock

But, they can also do many other things human eyes cannot. Unlike humans who can only see colors from violet to red, insects can see over a much broader wavelength range and can see quite well in low light. Several insects including bees can detect ultraviolet signals. Such signals, sent by flowers, help insects select their preferred food choice. Insect eyes are also extremely good at detecting even the smallest movement, useful in pouncing on prey or taking cover from predators. In addition, they have large depths of field, making it possible to keep in focus objects that are close as well as those very far away at the same time.

How it Helps us Make Better Optics

The drive to utilize the unique properties of insect eyes to help us see better has led to significant advances in optics technologies. In 2013, researchers reported a digital camera with a lens mimicking insect compound eyes that took black and white pictures with a 160° field of view and almost infinite depth of field.¹ By making several hundred tiny lenses first on a flat surface and then inflating it to form a balloon, they copied the bulging insect eyes.

Later, in 2015, researchers from the Pennsylvania State University in the USA developed artificial compound eyes using liquid crystals.² Unlike human eyes that form only one image, the artificial eyes formed many images at different depths, something that can be used in 3D imaging.

Another aspect of insect eyes, particularly moth eyes, is an anti-reflective coating on them that allows moths to see in the dark and prevent reflections that predators can see. This is made possible by the many nanostructures that make up this film. Inspired by this design, scientists created a thin coating with an array of periodic dimples that greatly reduced reflection.³ Such films can potentially be used on mobile phones and tablets to allow for readability even in bright sunlight.

One of the latest technologies reported that takes inspiration from insect eyes is a camera that can help in cancer surgeries. During cancer surgeries, the tumor cells are labeled so that they fluoresce, but they are too dim to see under the bright lights of the operating room. Current infrared cameras used for such surgeries have poor sensitivity, making them almost useless for this application.

However, the eyes of the morpho butterfly can process colors of different wavelengths at the same time, including infrared, because of unique nanostructural formations in its compound eyes. Taking a cue from this, researchers at the University of Illinois at Urbana-Champaign, USA, linked several nanoscale structures to camera photodetectors, allowing them to collect color and infrared fluorescence information in a single device.⁴ This increased the sensitivity to fluorescence almost 1000 times. The camera is compact and can be made for about $20, according to the researchers.

As optics inspired by the unique properties of insect eyes advances, their potential applications are also growing and perhaps soon some of these may become commercially available. Although it will not make our eyes as adept as those of insects, it will be several steps forward in that direction.

Sources

1. Song et al., “Digital cameras with designs inspired by the arthropod eye,” Nature, 497, 95, (2013). 10.1038/nature12083
2. Serra et al., “Curvature‐Driven, One‐Step Assembly of Reconfigurable Smectic Liquid Crystal “Compound Eye” Lenses,” Advanced Optical Materials, 3(9), 1287, (2015). https://doi.org/10.1002/adom.201500153
3. Tan et al., “Broadband antireflection film with moth-eye-like structure for flexible display applications,” Optica, 4(7), 678, (2017). https://doi.org/10.1364/OPTICA.4.000678
4. Garcia et al., “Bio-inspired imager improves sensitivity in near-infrared fluorescence image-guided surgery,” Optica, 5(4), 413, (2018). https://doi.org/10.1364/OPTICA.5.000413

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