A microlens is a tiny lens, typically smaller than a millimeter in diameter, that focuses or redirects light at a miniature scale. Most microlenses range from about 50 to 240 micrometers across, making them smaller than the width of a human hair in some cases. Despite their size, they play a critical role in technologies you use every day, from the camera in your phone to the screen you’re reading this on.
How Small Are Microlenses?
A standard microlens has a diameter measured in micrometers (thousandths of a millimeter). To put that in perspective, a grain of table salt is roughly 500 micrometers wide, so many microlenses are smaller than a single salt crystal. Their focal lengths, the distance at which they bring light into focus, are similarly tiny, often just a few hundred micrometers to a couple of millimeters. One research example produced a microlens 240 micrometers wide with a focal length of 2.1 millimeters.
These lenses are almost never used alone. They’re typically arranged in grids called microlens arrays, where thousands or even millions of identical lenses sit side by side on a flat surface. The spacing between lens centers (called pitch) can be as tight as 85 micrometers, and the physical curvature of each lens may rise only about 1 micrometer above the surface. That’s a bump so slight it’s invisible to the naked eye, yet it’s enough to bend light precisely where it needs to go.
The Camera in Your Phone
Every digital camera sensor, from a smartphone to a professional DSLR, relies on a microlens array layered directly over its pixels. The problem microlenses solve here is straightforward: not all of a pixel’s surface area is sensitive to light. Wiring, transistors, and other electronics take up space between the photosensitive areas. Without help, a lot of incoming light would land on those dead zones and be wasted.
A microlens sits over each pixel and acts like a tiny funnel, bending incoming light so it lands on the active, light-sensitive portion instead of the gaps. This dramatically increases the amount of light each pixel captures, which translates directly into brighter, cleaner images, especially in low light. Metal layers between individual microlenses also help prevent light from leaking sideways into neighboring pixels, which would otherwise cause color errors and blurriness.
Light Field and 3D Photography
Plenoptic cameras, sometimes called light field cameras, use microlens arrays in a fundamentally different way. Instead of one microlens per pixel, the array sits between the main lens and the sensor, and each microlens covers a small cluster of pixels. This setup captures not just the brightness and color of light, but also the direction each ray was traveling when it arrived.
Each microlens creates its own tiny sub-image on the pixels beneath it. That sub-image contains spatial information (where the light came from in the scene), while the individual pixels within it record angular information (what direction the light was heading). Together, these two layers of data create what’s called a 4D light field. Software can then use that information to refocus the image after it was taken, shift the apparent perspective, or generate depth maps for 3D applications.
Making OLED Screens Brighter
OLED displays generate their own light, but a significant portion of that light gets trapped inside the screen’s layers and never reaches your eyes. Microlens arrays bonded to the display surface help extract that trapped light by redirecting it outward at angles that allow it to escape.
The efficiency gains are substantial. Researchers embedding microlens arrays beneath the electrode layer of green OLEDs achieved an external quantum efficiency of 70%, meaning seven out of every ten photons generated actually made it out of the display. For white OLEDs, the figure reached 50%. Without microlenses, typical OLEDs lose the majority of their light to internal reflections. This technology is particularly valuable because it improves brightness without increasing power consumption, extending battery life in phones, tablets, and wearables.
Connecting Lasers to Fiber Optics
Fiber optic networks depend on efficiently coupling light from a laser diode into a glass fiber thinner than a human hair. The challenge is that the laser emits an elliptical beam, while the fiber accepts a circular one. Simply butting the two together wastes a significant amount of light due to this shape mismatch.
A microlens fabricated directly onto the tip of the fiber reshapes the incoming beam to better match the fiber’s acceptance profile. These fiber-tip microlenses come in conical, hemispherical, or hyperbolic shapes, each designed to minimize the mismatch and maximize how much light enters the fiber. Because the lens is built right on the fiber tip, it’s naturally self-centered, eliminating one of the trickiest alignment problems in optical packaging.
Upgrading Low-Cost Microscopes
One of the more striking applications is in medical diagnostics. A microlens substrate placed on a standard low-magnification microscope can boost its resolution to match a much more powerful (and expensive) instrument. In one demonstration, researchers used a microlens array to give a basic 10x objective the resolving power of a 40x lens, enough to clearly visualize deformed blood cells that were invisible without the upgrade.
The practical implications are significant for clinics and field hospitals in low-resource areas. The microlens substrate costs less than $1.50 to manufacture and requires no modifications to the microscope itself. You simply place it in the light path. This turns a portable, battery-powered mobile microscope into a diagnostic tool capable of identifying cellular abnormalities that would otherwise require equipment costing thousands of dollars.
How Microlenses Are Made
Manufacturing microlenses at scale requires precision at the micrometer level. Several techniques exist, but one of the most common is photoresist thermal reflow. The process starts by coating a glass or silicon wafer with a light-sensitive polymer. Patterns are etched into the polymer using ultraviolet light (similar to how computer chips are made), creating tiny cylindrical posts. The wafer is then heated on a hotplate, causing the polymer to soften and flow into smooth, dome-shaped profiles under surface tension, the same physics that makes water bead up on a waxed surface.
Other fabrication methods include ink-jetting (depositing tiny droplets that naturally form lens shapes as they dry), laser ablation (carving lens profiles with a focused laser beam), and grayscale lithography (using varying light intensities to sculpt three-dimensional curves directly into the material). The choice depends on the application. Camera sensor microlenses demand extreme uniformity across millions of units, while fiber-tip lenses prioritize individual shape precision.
Flat Optics on the Horizon
Traditional microlenses, even at their tiny scale, still rely on curved surfaces to bend light through refraction. A newer approach called metalenses replaces that curvature with a flat surface covered in nanoscale structures, each smaller than a wavelength of light. These structures manipulate light through carefully engineered interference patterns rather than physical curvature, allowing a completely flat sheet to focus light just like a curved lens would.
Metalenses can be thinner, lighter, and easier to integrate into compact devices. They also open the door to optical functions that are difficult or impossible with traditional curved lenses, like focusing multiple wavelengths of light to the same point without the color fringing that plagues conventional optics. For now, traditional microlenses remain dominant in commercial products, but flat optics are steadily closing the performance gap.