Manufacturing Of Freeform Micro-Optical Elements By Mask-Less Laser Direct Write Lithography And Replication By Imprinting

Today, freeform micro-optical structures are desired components in many photonic and optical applications such as lighting and detection systems due to their compactness, ease of system integration and superior optical performance. The high complexity of a freeform structure's arbitrary surface profile and the need for high throughput upon fabrication require novel approaches for their integration into a manufacturing process.For the fabrication of polymer freeform optics, in this contribution we discuss two principal technologies, mask-less laser direct write lithography ( MALA) and replication from the as-fabricated master by imprinting. We show the high flexibility in design and rapid-prototyping of freeform optical microstructures that can be achieved by such an approach. First, the original structures known as masters are fabricated using MALA. Because of the specific requirements on shape and height (> 50 mu m) of the microstructures, laser writing and photoresist processing have to be performed within a narrow range of fabrication parameters. Subsequently, UV-soft lithography based replication is used for serial production of the freeform micro-optical elements within a batch process.Aided by profilometry, optical microscopy and atomic force microscopy, the fidelity of the fabricated freeform micro-optical elements to the design is characterised. Finally, the light intensity distribution on a target plane caused by the freeform micro-optical element illuminated with an LED is determined and compared with the predicted one.