Evaluation of gradient-index array alignment

A gradient-index (GRIN) array is used as an imaging unit in light-emitting diode (LED) printers. In this study, we measure tilts of GRINs in an array and analyze the intensity distribution of the image to clarify the tilting amount and to evaluate the relation between the GRIN tilt and the degradation of the image. The arrangement intervals of the GRINs are measured, and the GRIN tilts are calculated from the differences between the arrangement intervals of the surfaces on one side and the other side. In our previous study, we show from ray matrix analysis that the images obtained using accurately arranged GRINs are superposed on a single image. However, images obtained using tilted GRINs are not superposed on a single image resulting in the image degradation. Measuring the tilt of the GRIN in the array is useful for improving the image. The upper limit on the tilt of the GRINs in the array for the LED printer is evaluated from a symmetric property of the image.