Fabrication of antireflection structures on the surface of optical lenses by using a liquid transfer imprint technique

Abstract

Antireflection (AR) films are useful for preventing the reflection of light from flat-panel displays, solar-cell panels, optical lenses, and similar structures. We previously reported the successful high-throughput fabrication of an AR structure (ARS) with less than 0.1% reflectivity by means of ultraviolet nanoimprint lithography (UV-NIL). However, this process tended to produce a thick residual layer that reduced transmittance and produced interfacial reflections at surfaces of lenses coated with the ARS. To reduce interfacial reflections, the thickness of the residual layer must be less than 100nm or so (roughly a quarter of the wavelength of visible light). Liquid transfer imprint lithography (LTIL) is an effective technique for reducing the thickness of the residual layer. In the LTIL process, residual resin is eliminated by separating the mold and substrate in the liquid phase. This process is also effective for curved surfaces, and it has been reported an ARS with a thin residual layer can be obtained by LTIL. However, the method that was used required a vacuum process and was time consuming. To obtain a thin residual layer at atmospheric pressure, we devised an LTIL process involving a roll-press method that does not require the presence of a vacuum. The technique permitted the fabrication of a high-performance ARS with improved reflectance and transmittance thickness, in which the thickness of the residual layer was less than a quarter of the wavelength of visible light. Furthermore, the technique could be used to produce a homogeneous ARS with a residual layer less than 100nm thick on a curved surface, such as that of a lens, in a reproducible and stable manner. The process is therefore suitable for fabricating ARSs that show a high performance with a thin residual layer on curved surfaces such as convex lenses.