CAMERA MODULE WITH TOLERANCE ADJUSTMENT USING EMBEDDED ACTIVE OPTICS
A focus free camera module uses fixed lenses within a housing that are combined with an electrically controllable active optical element, such as a tunable liquid crystal lens. The fixed lenses provide a desired amount of optical power, but the manufacturing tolerances of the module are insufficient to ensure a proper focus of an image on an image sensor. The active optical element is therefore used to compensate for any variations in the optical power to achieve the desired focus. To ensure an effective compensation, the module may be constructed so that, when the variation in optical power due to manufacturing tolerances is at a maximum, the desired focus is achieved when the active optical element is at zero optical power. All other variations may then be compensated by adjusting the active optical element to increase its optical power.
1 . A camera module comprising:
a fixed focus optical lens assembly through which an optical signal passes;
an electrically controllable active optical element, the active optical element changing its optical characteristics from a first state to a second state in response to an input electrical signal, such that the active optical element exerts a different optical influence on the optical signal in the first state than in the second state;
an image sensor; and
a mounting for the fixed focus optical lens assembly, the image sensor and the active optical element, wherein the camera module has a manufacturing tolerance insufficient to ensure a desired precision of focus of an image on said image sensor when said active optical element is at a nominal optical power, and wherein the optical characteristic of the active optical element may be adjusted to achieve said desired precision of focus of said image on the image sensor.
2 . A camera module according to claim 1 wherein the active optical element comprises a tunable liquid crystal lens for which the optical power changes in response to said input electrical signal.
3 . A camera module according to claim 2 wherein the nominal optical power of the active optical element is substantially zero diopters.
4 . A camera module according to claim 1 , wherein a potential variation in optical power of the camera module due to said manufacturing tolerance ranges between two predetermined extremes, and wherein the camera module is constructed such that, when said variation in optical power is at one of said extremes, said desired precision of focus is achieved with the active optical element at said nominal optical power.
5 . A camera module according to claim 1 wherein the fixed focus optical lens assembly comprises a plurality of fixed focus optical lenses.
6 . A camera module according to claim 5 wherein the active optical element is located between two fixed focus optical lenses of the fixed focus optical lens assembly.
7 . A camera module according to claim 5 wherein the active optical element is located at one end of the fixed focus optical lens assembly.
8 . A camera module according to claim 1 further comprising a mechanical adjustment mechanism that allows manual adjustment of a distance between the fixed focus optical lens assembly and the image sensor.
9 . A camera module according to claim 2 wherein the tunable liquid crystal lens has a tunable range to provide focusing power for near focus and infinity focus.
10 . A camera module according to claim 9 further comprising an autofocus processor for adjusting said input electrical signal, said autofocus processor having an offset value for infinity focus.
11 . A camera module according to claim 1 wherein said active optical element is a liquid crystal lens with liquid crystal polymerized while said lens is controlled to be between said first state and said second state.
12 . A method of manufacturing a fixed focus camera module comprising:
providing an image sensor, a fixed focus optical lens assembly and a tunable liquid crystal optical device;
mounting the image sensor and the fixed focus optical lens assembly in such a way that manufacturing tolerances of the camera module are insufficient to ensure a desired precision of focus of an image on the image sensor when said active optical element is at a nominal optical power; and
providing an electrical signal to the tunable liquid crystal optical device to modify the camera module and establish said desired precision of focus of the image on the image sensor.
13 . A method according to claim 12 wherein the active optical element comprises a tunable liquid crystal lens for which the optical power changes in response to said input electrical signal.
14 . A method according to claim 13 wherein the nominal optical power of the active optical element is substantially zero diopters.
15 . A method according to claim 12 , wherein a potential variation in optical power of the camera module due to said manufacturing tolerance ranges between two predetermined extremes, and wherein the method further comprises constructing the camera module such that, when said variation in optical power is at one of said extremes, said desired precision of focus is achieved with the active optical element at said nominal optical power.
16 . A method according to claim 15 wherein the nominal optical power of the active optical element is substantially zero diopters.
17 . A method according to claim 12 wherein providing a fixed focus optical lens assembly comprises providing a plurality of fixed focus optical lenses.
18 . A method according to claim 17 wherein the active optical element is located between two fixed focus optical lenses of the fixed focus optical lens assembly.
19 . A method according to claim 17 wherein the active optical element is located at one end of the fixed focus optical lens assembly.
20 . A method according to claim 12 further comprising adjusting a mechanical adjustment mechanism that changes a distance between the fixed focus optical lens assembly and the image sensor.
21 . A method according to claim 13 wherein the tunable liquid crystal lens has a tunable range to provide focusing power for near focus and infinity focus.
22 . A method according to claim 21 wherein said providing an electrical signal to the tunable liquid crystal optical device comprises using an autofocus processor for adjusting said electrical signal, said autofocus processor having an offset value for infinity focus.
23 . A method according to claim 13 further comprising including a monomer in a liquid crystal material of said liquid crystal lens and polymerizing said monomer once a desired optical power is set by said electrical signal.