The True Value of Microlens Arrays
When we talk about Microlens arrays we are referring to microlenticular arrays or even lenslet arrays. These are used to increase the optical fill factor in CCDs like interline-transfer devices that are limited by reduced aperture because of metal shielding. According to IGI plotter experts, these tiny lens aim to focus and concentrate light onto a photodiode surface as opposed to letting it dissipate on non-photosensitive sections of a device where it becomes lost from the information that is collected by the CCD.
How does it Work
A very small optical lens is placed in a strategic position over a dye layer and metal shield of a photodiode. The Microlens array are either placed in parallel arrays during the CCD fabrication or simply made from quartz material that is then placed on the array surface during packaging. According to view phototooling specialists specialists, each lenslet features a high quality optical surface that contains refractive elements that range in size from several hundred to about 10 microns. The quality of these lenses is very exceptional that they are of equal value to single-element lens.
The addition of microlens array to the CCD photodiodes increases the optical fill factor by about three times its value. Moreover, increasing the fill factor also gives a corresponding increase in the sensitivity of the photosite. We can then appreciate a better performance of the interline-transfer CCD imaging arrays that feature lateral overflow drains and a good amount of shielded pixel space. Normally, these devices are burdened by reduced optical fill factors due to the reduced active pixel area when compared to the sum of the total pixel size.
Limitations are outweighed by the resulting increased sensitivity of the devices having these optical components present. A limitation that can be expected occurs when light rays from outer portions of the pixel concentrate onto a nearby lens, which result to a mis-registration. To correct the problem, better quality lenses are required to create images on these arrays.