Rhys Hanak - September 13, 2018
Flat optics have been, and continue to be, an integral part of our Blade Optics™ portfolio of optical technologies. Our proof-of-concept prototype, which incorporates our patented flat optical design, formed the very foundation of our company—and as such marked the beginning of our journey as a creative optical design house.
To say that we have a soft spot for flat optics would be putting it lightly.
But what exactly are flat optics? Although there are numerous flat-surface optical elements (such as mirrors), this discussion is going to center around the three most common types of flat optical elements:
1. Metamaterials & Nanomaterials
2. Microlens Arrays & Diffractive Elements (Micro-optics)
3. Flat Prisms
What Are Metamaterials?
Metamaterials are any such material that has been engineered to possess electromagnetic properties that do not occur in nature (ie. electromagnetic cloaking).
And before you ask, yes: electromagnetic cloaking is exactly as cool as it sounds.
So what exactly “makes up” metamaterials? Simply put: a multitude of unit cells that are precisely arranged at the microscopic level.
“These unit cells are microscopically built from conventional materials such as metals and dielectrics like plastics. However, their exact shape, geometry, size, orientation, and arrangement can macroscopically affect light in an unconventional manner such as creating resonances or unusual values for macroscopic permittivity and permeability.”
Note: The word metamaterial comes from the Greek word μετά meta, meaning “after” or “beyond”
While the future for metamaterials is promising, scientists still have a ways to go.
This is because metamaterials are specifically engineered to work in a controlled laboratory setting, meaning they are often too expensive to produce and too sensitive for use in real-world applications—much like their “cousin” nanomaterials.
The Science Behind Nanomaterials
We’re no stranger to the concept of nanomaterials. After all, when it comes to optics, the tolerancing of some optical elements can occur at the nanometer level (10-9 meter, or one billionth of a meter).
A nanomaterial is a material that has at least one dimension in the nanometer range. It’s important to recognize that metamaterials can be nanomaterials, and vice versa.
Although the potential benefits for nanotechnology are far reaching—from healthcare to renewable energy—it shares many of the same shortcomings (ie. production cost and sensitivity concerns) associated with metamaterials, meaning that both metalens and nanolens technologies are limited to the laboratory domain for the foreseeable future.
Note: In modern circuit board manufacturing, wires can be etched in at the nanometer level.
While the real-world applications for nano and meta materials are minimal at this stage, these technologies do hold the potential to drastically shrink the size of conventional optics by reducing (or outright removing) some of the “classical” aberrations seen in optics.
Introducing the Microlens Array
Let’s move on to the concept of micro-optics. Both microlens arrays and diffractive elements appear to be flat—but in reality, are simply groupings of micro-sized units that give the illusion of being flat.
A microlens array is, as you can imagine, an array of micro-lenses.
This array of lenses generally goes on top of an array of micron-sized pixels, and in effect, helps to put more light onto these very tiny pixels, thus boosting the performance of the imaging sensor (ie. a mobile phone camera sensor).
However, microlens arrays are not ideal for an imaging application on its own, as each lens in the array creates a distinct image (similar to what occurs in a fly’s eye).
Explaining Diffractive Elements
Diffractive elements are often used to separate or combine wavelengths of light. As light enters a medium, it bends each wavelength differently depending on the refractive index of the medium. Diffractive elements add “micro-sized” features to enhance this effect and thus separate wavelengths very quickly.
Note: refractive index is defined as the measure of the bending of a ray of light when passing from one medium into another.
While diffractive elements are useful for combining or separating different wavelengths of light, they are quite sensitive to temperature. Temperature can cause small deviations in the features of diffractive elements, which in turn can cause large changes in how these elements deal with different wavelengths of light.
To review, micro-optics (optics with micron-sized features) are incredibly useful for enhancing the light gathering area of small detectors, or by spreading out light in a very particular fashion. As such, they often function as highly specialized tools. While micro-optics can perform certain tasks exceptionally well, their niche use-cases and sensitivity to temperature limit them from broader optical applications.
How Do Prisms Work?
Prisms, which are typically built from common materials such as glass and or plastic, can be understood as flat, transparent optical elements that refract light. The underlying principle behind prisms is that light changes in speed as it travels from one medium to another.
It is the change in the light’s speed as it enters the prism that causes light to refract (or bend) as the light passes through the prism.
Because prisms are well understood and simple to manufacture at low costs, they are one of the most widely used components in optics—acting as diffractive elements, mirror elements, beam correction elements, image orientation correction elements and more.
Transforming the Flat Prism: Blade Optics™
Our Blade Optics™ portfolio includes a flat prism configuration that is designed to anamorphically expand or compress a beam of light in a compact space—thus maximizing light-gathering while minimizing the bulkiness often associated with large, heavy prisms.
Note: To anamorphically expand or compress is to expand or compress in 1 axis (ie. in X, Y, or Z plane)
It’s important to understand that our flat prism design compresses the light before focusing, which functionally adds a multiplier to the final focal length of the imaging lens—meaning we can achieve a much longer effective focal length with a smaller lens.
As optical technology continues to evolve, you can be sure that we’ll be there every step of the way. With this design and more, we continue to explore new ways of enhancing the human experience through optics.