Liquid tunable double-focus lens fabricated with diamond cutting and soft lithography

Single femtosecond pulse writing of a bifocal lens

In this Letter, a method for the fabrication of bifocal lenses is presented by combining surface ablation and bulk modification in a single laser exposure followed by the wet etching processing step. The intensity of a single femtosecond laser pulse was modulated axially into two foci with a designed computer-generated hologram (CGH). Such pulse simultaneously induced an ablation region on the surface and a modified volume inside the fused silica. After etching in hydrofluoric acid (HF), the two exposed regions evolved into a bifocal lens. The area ratio (diameter) of the two lenses can be flexibly adjusted via control of the pulse energy distribution through the CGH. Besides, bifocal lenses with a center offset as well as convex lenses were obtained by a replication technique. This method simplifies the fabrication of micro-optical elements and opens a highly efficient and simple pathway for complex optical surfaces and integrated imaging systems.

Universal membrane-based tunable liquid lens design for dynamically correcting spherical aberration over user-defined focal length range

A novel membrane-based tunable liquid aspherical lens design capable of dynamically reducing spherical aberration over certain focal length tuning range is presented. Different from conventional treatment using elastic membrane with uniform thickness, in current case, the membrane's cross-section is designed to be a plano-convex shape with well-defined aspherical contour. A brand new design flow combining optical ray-tracing and mechanical finite element analysis is especially developed, in which through properly selecting the initial focal length and the center membrane thickness with respect to particularly designed figure of merit (FOM), the membrane can be flexibly optimized to achieve dynamic spherical aberration correction capability over the desired focal length range. For proof of concept demonstration, a tunable aspherical lens with clear aperture of 4 mm is designed. Compared with conventional counterpart, after being individually optimized using current design strategy, lenses with distinctly reduced spherical aberration have been successfully achieved over different focal length tuning ranges. Besides, no special refractive index matching between the filling liquid and the membrane is required, making current design more practical in real applications.

Rapid optical μ-printing of polymer top-lensed microlens array

Microlenses have wide applications for light beam focusing or shaping in micro-optical systems. However, it remains challenging for conventional microfabrication methods to rapidly fabricate arrays of microlenses with complex profiles like lens-on-lens structures. In this paper, we present the rapid fabrication of polymer microlenses with lens-on-lens structures by using a digital optical μ-printing technology. An improved dynamic optical exposure method is developed to directly and precisely fabricate polymer top-lensed microlenses (TLMLs). Arrays of TLMLs with either elongated focal depth or two separate foci have been numerically investigated and experimentally demonstrated.

Solid electrically tunable dual-focus lens using freeform surfaces and microelectro-mechanical-systems actuator

In this Letter, a miniature solid tunable dual-focus (DF) lens, which is designed using freeform optical surfaces and driven by one microelectro-mechanical-systems rotary actuator, is reported. Such a lens consists of two optical elements, each having a flat surface and one freeform surface optimized by ray-tracing technology. By changing the relative rotation angle of the two lens elements, the lens configuration can form double foci with corresponding focal lengths varied simultaneously, resulting in a tunable DF effect. Results show that one of the focal lengths is tuned from about 30 to 20 mm, while the other one is varied from about 30 to 60 mm, with a maximum rotation angle of about 8.2 deg.

Lens-on-lens microstructures

Microlenses with multiple focal lengths play an important role in three-dimensional imaging and the real-time detection of unconfined or fluctuating targets. In this Letter, we present a novel method of fabricating lens-on-lens microstructures (LLMs) using a two-step femtosecond laser wet etching process. A 3×3 LLM array was made with a diameter of 129.0 μm. The fabricated LLM has two focal lengths, 80.4 and 188.7 μm, showing excellent two-level focusing and imaging abilities. Its size and focal length can be controlled by adjusting laser power and etching time. Its surface roughness remains about 61 nm. This simple and efficient method for large-scale production of LLMs has potential applications in diverse optical systems.

Liquid tunable lens integrated with a rotational symmetric surface for long depth of focus

A liquid tunable lens with an extended depth of focus (DOF) is proposed. By integrating a phase plate with rotational symmetric quartic function (QF) contour into the liquid lens cavity, the lens can achieve higher tolerance to the defocus aberration. The liquid lens was fabricated with a convenient and low-cost process that combined single-point diamond turning (SPDT) with soft lithography using polydimethylsiloxane (PDMS). Experimental results demonstrate that both focal length tunability and extended DOF can be achieved with the proposed liquid lens.