Microlens arrays are a vital optical component in many of today's advanced optical systems and Nalux is an expert in the fabrication of both glass and plastic microlens arrays. Nalux has made microlens arrays for many different applications including the Subaru astronomical telescope in Japan (see picture above). Microlens arrays are simply a matrix of many lenses placed side by side with lens diameters anywhere between a few microns to about a millimeter. There is no firm cut off diameter, but the term microlens arrays usually stops being used when lens diameters get around a millimeter. There are a number of ways to make these optics and a great deal of design freedom with different methods having different advantages (cost, speed, design freedom, surface quality, etc.). Shapes can be spherical, aspherical, torroidal, or freeform.
Microlens arrays are used in a wide variety of applications in addition to astronomy. They are used in the military for tracking systems, they are used in telecommunications for optical switching, they are used in beam splitter applications where a single beam enters the array and each lens creates a separate smaller beam. Microlens arrays are used to focus the output of an array of laser diodes, they are used in conventional laser systems, some photocopiers, digital projectors, cell phones, embedded computer cameras, and in a host of other applications.
Accuracies from one lens to another in microlens arrays can be as close as within 250 nanometers of it's perfect position and this accuracy can be either in glass or in plastic. Additionally, if an optic has microlens arrays both the front surface and the back surface, the center to center alignment of the lenses on the opposing sides can be as close as 1 micron.
There are several methods for making microlens arrays. Binary mask lithography and plasma etching can be used to make what is known as reflow microlens arrays. This method creates tiny pillars of photoresist on a glass wafer. The photoresist is then heated so that it "reflows" and surface tension causes the pillar of photoresist to flow into a spherical shape, just like a small bead of water sitting on a table. Plasma etching then transfers this shape into the glass so that you end up with glass microlens arrays. This method is beneficial when many parts are needed. Tooling costs and set up costs can be high but the cost for each copy are relatively lower.
Diamond milling is another method for making microlens arrays. Using this method the microlens arrays are created by mechanically removing material to shape the lenses into the glass.
Focused ion beam milling is another method to make microlens arrays using ions to ablate away the material. This method allows for a great deal of design freedom in microlens arrays because very fine control over surface shape can be achieved using this method.
Microlens arrays can also be molded out of plastic. This provides for a very inexpensive way of making these optics although tooling costs can be high and accuracy of the surface shape is not as good as in other methods such as focused ion beam etching.
So, you can see that these optics are an important part of our everyday life and Nalux is ready to help with your next microlens array project.