By Innofocus Photonics Technology Pty Ltd
Micro lens arrays are one of the main applications where our technology is highly advantageous. A mature process for fabricating quartz micro lenses is the lithography method using photoresist to fabricate patterns with etching. This method currently faces the following problems. a. Low flexibility: The design of the lens is determined by the mask patterns and cannot be freely adjusted. b. Long cycle of testing: Since each design update involves processing new masks, the fabrication process is complicated and time-consuming. c. Long cycle of testing: Since each design update involves processing new masks, the fabrication process is complicated and time-consuming. d. Surface morphology cannot be precisely controlled: Since the lithography process is a technique to produce two-dimensional graphics, the three-dimensional surface morphology of the fabricated lens cannot be directly controlled. However, the focal length of the lens, the imaging quality mainly depends on the surface shape of the lens. Therefore, the focal length of the lens and the imaging quality are seriously affected when the surface morphology cannot be accurately controlled. e. Inability to fabricate aspheric lens, combined with the elimination of phase aberration function: due to the method of heating to form an arch, the most likely surface shape formed by its thermal stabilization is spherical according to the principle of uniform distribution of heat deformation, and it cannot be precisely controlled. f. Inability to fabricate high numerical aperture micro lenses: Due to the heating method to form an arch-shaped surface, it is not possible to fabricate lenses with a small radius of curvature to meanwhile achieve high numerical apertures. Therefore, the resolution of imaging is greatly limited. g. Low uniformity: Since it is controlled by heating, the curvature of each lens depends on the temperature applied to it. And the difference of temperature will cause the difference of curvature and thus affect the focal length. Also, even if the temperatures are all the same, there is no guarantee that each lens will form the same change in curvature under heating conditions. Therefore the uniformity of the lens array cannot be guaranteed. h. Specific requirements of photoresist choice: the photoresist to be used has three requirements: 1) photosensitive to UV light; 2) able to heat deform to an arch; 3) able to resist argon ion etching for pattern transfer. Therefore, the choice of photoresist is limited. i. Low yield: Even if the process can achieve stable control, during the heating, the quality of each of its micro lens arrays is difficult to be completely consistent when its surface morphology is not accurately controlled. This leads to a compromised yield and repeatability. However, fabricating micro lens arrays using femtosecond laser nanofabrication technology has several advantages: a. High flexibility: Based on laser 3D nano-fabrication technology, no mask is required, and lens arrays with arbitrary spatial distribution can be fabricated. b. Low cost: The cost of laser processing is extremely low because there is no need for fabricating any mask. c. Short optimization time: Since no mask is required, for each new lens array design, only new processing files is needed to generate, the design can be quickly optimized for comparison. d. Precise control of surface morphology: The surface morphology of each lens can be controlled independently. The high resolution of 3D laser nanofabrication technology can be combined with the spatial position of each micro lens to produce the surface shape of the micro lens accordingly, and then fabricate the micro lens array to meet the specific light field distribution. e. Ability to fabricate aspheric achromatic lenses: Due to the precise control of the structure's three-dimensional surface morphology by 3D laser nanofabrication technology, the precise processing of micro lenses of arbitrary design can be realized. The error of the surface morphology can be controlled within a few tens of nanometers, fully meeting the application requirements. f. Ability to process lens with a small radius of curvature: High numerical aperture micro lenses can be produced to improve the imaging resolution. g. High uniformity: 3D Laser nanofabrication technology enables precise processing of each lens to achieve high uniformity. h. High yield: Based on high accuracy and high uniformity, precise control of the quality of micro lens arrays can be achieved and high yield can be realized. On this basis, 3D laser nanofabrication technology can not only fabricate traditional micro lens arrays, but also micro lens arrays composed of new pure flat superlenses (including graphene superlenses and super-surface lenses) to realize ultra-light and ultra-thin micro lens arrays.
