LIQUID LENS FOR AUTO FOCUS (AF)

Outstanding quality from digital pictures comes from a precise control of the focus: a good picture requires the main subject to be very sharp, and the rest of the picture more blurred. An effective AF capability is thus essential to obtain a superior photo. Varioptic’s liquid lens technology delivers fast, continuous and precise focus control. This is for use in all situations where the digital capture is critical:

• digital photography

• industrial data capture

• barcode reading (1D and 2D)

• biometric data acquisition

• videos with large amplitudes of object distance variations

 

THE FIRST LIQUID LENS USING THE CONCEPT OF ELECTROWETTING: ARCTIC SERIES

 

 

 

 

 

 

 

 

A sealed cell contains 2 liquids which are immiscible, oil and water. The shape of the oil drop is changed by electrowetting. Both liquids are transparent, with different indices of refraction but exactly the same density. The cell contains only those two liquids and this density matching makes the whole lens very stable against mechanical shocks. The liquid lens external shape is fixed, there is no moving part: only the internal liquids change shape. The Arctic lens is used for high performance Auto-Focus:

• Focus changes from -10 diopters to +30 diopters

• Continuous, highly reversible

• Fast changes, even for large steps of focus

 

IMAGING APPLICATIONS

AF Liquid lens is compatible with all the highest quality miniature camera modules, from small sensor formats to large ones (up to 1/2.5 inch), for all resolutions, from 3Mp to 10Mp and higher. Liquid lens optical quality is often close to the diffraction limit, thus not impacting the associated fix lens quality. The liquid lens is designed for visible light, but it is transparent as well in the near infrared.

The large focus range enables focus adjustment for a wide range of object distance, from a few centimeters to infinity.

The lens can be used for closed loop search of the focus (AF), or in open loop when object distance information can be obtained from another sensor. The unique stability of the liquid lens makes it the only actuator enabling this open loop mode.

Another unique property of the liquid lens is its ability to achieve very fast random steps: AF algorithms typically use a step by step approach of the best focus position. Varioptic liquid lens, being as fast in making big steps as small steps, enables smarter focus search with non-sequential algorithms.

Design rules for using a liquid lens into a camera module are simple and easily derived from the product’s datasheet. Optically the choice of liquid lens location comes from the overall system organization and function: for an optimal pure focus control, liquid lens should be placed as close as possible to the plane of the aperture stop: this can be in front of the lenses (add-on design), inside the optical stack or even behind it.

As the liquid lens has no moving parts, the mechanical design is much simpler, enabling a shorter design cycle: using the liquid lens for AF, complex actuator designs are unnecessary and replaced by straightforward electronics architecture and simple software programming.

 

 

 

 

 

LIQUID LENS APPLICATIONS

Electrowetting enables to manipulate the liquid interface shape, in order to create various optical functions or optical corrections.
Possible applications of liquid lenses are too many and too diverse to be all mentioned, but the list below can serve as a starting point for innovative thinking for new products, new applications or improved performance.

 

DIGITAL IMAGING APPLICATIONS

 

 

 

 

 

 

• Very fast image capture

• Very fast Auto Focus mode (non sequential algorithms)

• Capture of multiple images at different focus positions, for objects from infinity to a few cm

• Reconstruction of a 3D map from captured depth information

• Correction of handshake movements in real time

• Super-resolution

 

NON- IMAGING APPLICATIONS

 

 

 

 

• Laser focusing in X,Y and Z axes (with Baltic series)

• Laser de-cohering

• Wave front correction (adaptive optics, ophtalmology)

• Light dispersing for illumination

• Longitudinal spectrometry

• Feedback loops for fine optical adjustments

• Active control of beam deviations

 

MULTIPLE LENS CONFIGURATIONS IN A SINGLE BODY

The flexibility of liquid lens packaging allows having a single external body for several products, allowing very high flexibility in product design and evolution.

 

 

 

 

 

 

 

 

 

 

 

Inside the liquid lens, the different optical functions can be produced using different designs with specific electrodes patterns and different liquids.

 

A few examples:

 

 

 

 

 

 

Fast light focusing for imaging or beam control applications

                               

 

 

 

 

 

 

Fast light beam focusing and tilting for XYZ control of the optical rays.

                               

 

 

 

 

 

Arbitrary Zernike correction

 

                    Single electrode lens : Liquid interface is a sphere, with a variable radius as a function of voltage

                    Quad-electrode lens : The liquid interface is a sphere of adjustable radius and arbitrary tilts

                    Multiple electrode lens :With eight electrodes, the liquid interface can include Zernike corrections for:
                                                        - Sphere
                                                        - Tilt
                                                        - Cylinder (or astigmatism)

 

Electrowetting: a voltage variation induces a change in the contact angle of the fluid and effectively creates a lens with the precise desired properties.