Dyeing of the circumferential part of a plastic rod lens for improving its optical resolution

A plastic rod-lens array that we developed industrially with a continuous spinning technique has an optical resolution of 200dpi (4 lp/mm), and it has been used for facsimile machines and other applications. However, this resolution is still insufficient for its application in image scanners, copy machines, and light emitting diode (LED) printers. During the study for improving the optical resolution of the plastic rod-lens array, we have confirmed that this resolution is determined by the deviation of refractive index distribution from the ideal one at the outer circumferential part. Therefore, we have developed a technique for dyeing the outer circumferential part of the rod lens in order to achieve the higher optical resolution power of 300 dpi (6 lp/mm).