Technology today has made large improvements in shrinking down everyday objects. Your phones and vacuum cleaners are but two of millions of other inventions that have been minimised. But when it comes to scaling down optical technology, or optics, progress has not been very… visible.
In medicinal fields, cameras are used to peer into bodies to receive visual feedback. To minimise discomfort, the cameras used are small, and navigating inside the pitch black darkness of the body often renders low quality images. In space exploration, high resolution images give astronomers a greater look at the universe, amidst the pitch black darkness of space. But we are only able to glimpse a fraction of the insanely far celestial phenomenon with images that looked like it came from the 90s. We have hit a wall when it comes to optics, since we are not able to scale the size of our lenses down.
Optics traditionally involves the precise engineering of glass to concentrate light entering the lens to converge at a point close to it. This distance is known as the focal length. In general, the shorter the focal length, the easier it is to focus on objects that are really close up. Like really close. To understand the difficulties, place your finger upright between your eyes, and move your finger closer to your nose. You’d realise that as your finger gets closer, the clearer it becomes(You can see the skin wrinkles). But once a certain distance is reached, your eyes are no longer able to focus on it as you did previously. Hence downsizing optics while maintaining image focus and quality have been a challenge. Nevertheless, the bemoans of photography enthusiasts as well as scientists have not gone unheard, and research from a team of professors from the esteemed Harvard University can potentially revolutionise the optics world after obtaining significant results from a metalens.
The metalens that was developed is not like those on a DSLR camera. In fact, instead of glass, it is a flat piece of quarts lined with an array of titanium dioxide dominos, arranged in a specific pattern. Similar to how a fingerprint is mapped to an individual, this pattern allows the metalens to focus light of specific wavelengths. Size wise, it is only 600 nanometers in length, compared to a standard one of about 5 centimeters. That’s a hundred thousand times smaller!
Looking at their methods, the researchers fired a laser beam through a small object, with the metalens on the other side to capture the laser. The images was then focused on a camera sensor to assess the quality of the image. They repeated this experiment with lasers of different wavelength, such as blue and green light, and the image quality they got was astounding — It fared better than a regular camera lens, and the image when magnified had incredible detail, signaling its use in nanomechanics!
Alas, we rejoice as we herald the new age of optics. Deep space exploration and photography, satellite imagery, microscopy are going to be boosted to the next level with this new metalens. Lenses used for peering into human insides will allow doctors to have a clearer picture of what is going on. And we cannot forget, the eagle-eyed photographers rejoicing at the thought of having lighter and cheaper lenses that gives them the same if not better quality images. (I’d like to see Ronaldo in action up close in high quality too.)
To excite the hearts of photographers even further(and maybe to a certain extent some scientists), a team of researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences have further developed upon this significant discovery and have made it commercially viable. The metalens was initially able to focus specific wavelengths of light, but this ground-breaking feat accomplished by the team has seen the metalens being able to focus the whole visible spectrum(all the colours we can see) onto a single point. It’s a transition from monochrome to vibrant hues — a déjà vu considering how cameras were initially black and white and later developed to have colour.
The metalens has been projected to decrease common lens sizes by about 3 fold, and also bring down prices tremendously. Previously, lenses had to be stacked to remove chromatic aberration, an issue that stems from single lenses refracting different wavelengths of light at different speeds, causing light to ‘split’ into a rainbow like fashion. However, with the help of metalenses, this mystery will soon be history with the new metalenses being able to focus all light onto a single point. Your smartphone camera will soon have better quality images than your four thousand dollar DSLR camera.
Despite all the feats the metalens has accomplished, professor Khorasaninejad, leading professor of the metalens research, has acknowledged that we still have a bit more to go as the quality of images also depends on the sensor that captures it. To put it simply, we’ve discovered how to focus light using a small lens, but we have not found a way to capture it in all its entirety. But he thinks that this reality is not far.
The evolution of lenses have come a long way. The shrinking of lenses will pave the way for more advanced technology, not only in optic fields but in other areas as well. Satellite imagery can potentially give up accurate information and greater weather prediction precision. Virtual and augmented reality screens will also take a leap forward once we are able to project high quality images from a metalens. And then comes the next question — what’s the next small thing?
References:
Khorasaninejad, M., Chen, W. T., Devlin, R. C., Oh, J., Zhu, A. Y., & Capasso, F. (2016). Metalenses at visible wavelengths: Diffraction-limited focusing and subwavelength resolution imaging. Science, 352(6290), 1190–1194. doi: 10.1126/science.aaf6644
Revolutionary ‘Metalens’ Can Focus All Visible Light on One Point. (2018, January 4). Retrieved from https://petapixel.com/2018/01/04/revolutionary-metalens-can-focus-visible-light-one-point/.
