PrintMicro optics within the micro injection molding space requires expert engineering and experience, especially when your goal is to achieve tolerances down to the half micron. Here are common questions our resident micro optics engineer Rick Brown gets on a frequent basis.
What is the highest refractive index polymer that can be micro molded?
Engineers care about refractive index because better clarity and less light loss through the lens are important in micro optics, specifically imaging optics. Couplers and sensors are less affected by light loss and clarity.
The highest refractive index polymer that can be molded is 1.68 on the refractive index. The material used to achieve this is from Osaka chemical. Osaka chemicals has a line of optical grade materials that go up to 1.68. It’s important to note, these criteria aren’t set in stone to achieve the 1.68, IR is determined by the micro mold materials used.
How is purity of transparent materials/resins determined in the micro molding process?
Micro molders don’t determine purity, but there are many materials to consider. Ultem, for example is a go-to material in the datacom industry but there are other choices that are more pure. Datacom picks it because of its low CTE and high temperature rate, but under the microscope it’s not that clear. For ultem, a 50 micron filter is used on the materials, but there may be some black specs visible that are obviously smaller than the 50 micro filter.
If an engineer needs ultimate purity, there are other materials that are specially optical grade materials. Some COPs and COCs are a good example like Xenex and Topaz. PMMAs and optical grade polycarbonates come to mind as well. The purity in these materials is very good. They also do well when it comes to scratch/dig specifications.
What is the angular control accuracy for different surfaces in a micro mold?
The angular control accuracy for different surfaces in a mold is certainly feature dependent, but typically hovers somewhere around 1/10 to half a degree for most applications. At Accumold, when we build these molds, the optic is on an insert with a very long aspect ratio to the lens. It helps to picture an on-axis a-sphere where the a-sphere is 1mm diameter cut on the end of a pin. That pin could be 1-2 inches long, fitting into the end of the block. In this case, when the aspect ratio is held accurately, less than a 1/2 degree is attainable.