Scanning optical systems
Scanning mechanisms that have application in confocal imaging use electromagnetic actuation to move elements in an optical system. An objective lens mounted to a flexure comprising a magnetic material is actuated in the axial direction by an electromagnet coil. An optical path may pass through the coil. Scanning in transverse directions may be provided using magnetically actuated flexible beams which move the tip of an optical fiber or other pinhole in one or more transverse directions. Actuators may be actuated using driving currents that include an AC component and a DC bias component. The scanning mechanisms may be miniaturized and may be constructed to provide real-time imaging.
1. An optical scanning device comprising:
a flexure comprising a ferromagnetic material, the flexure having a mounting portion movable in an axial direction;
a first lens mounted to the mounting portion of the flexure; and
an electromagnet adjacent to the flexure and spaced apart from the flexure in the axial direction;
wherein:
an optical path of the scanning device extends through a core of the electromagnet;
the optical scanning device comprises: one or more optical elements located within the core of the electromagnet, the one or more optical elements comprising a collimating lens arranged to deliver collimated light to the first lens; a pinhole located at a focal point of the collimating lens on a side of the collimating lens away from the first lens, the pinhole comprising a tip of an optical fiber; and a mechanism for scanning the pinhole in at least one dimension transverse to the axial direction;
the mechanism for scanning the pinhole comprises a second electromagnet spaced apart from a first cantilever beam in the transverse dimension,
the first cantilever beam projects from a support in the axial direction, and
the pinhole is mounted to the first cantilever beam, and the first cantilever beam comprises a magnetic material.
2. An optical scanning device according to claim 1 wherein the flexure comprises a plurality of folded beams coupling the mounting portion to a support.
3. An optical scanning device according to claim 2 wherein the folded beams extend between the mounting portion and a frame.
4. An optical scanning device according to claim 3 wherein the mounting portion, folded beams and frame are integrally formed in a sheet of material.
5. An optical scanning device according to claim 4 wherein the material is a ferromagnetic material.
6. An optical scanning device according to claim 5 wherein the material is nickel or a nickel alloy.
7. An optical scanning device according to claim 1 wherein the flexure comprises four folded beams coupled to the mounting portion at points equally spaced apart around a periphery of the mounting portion.
8. An optical scanning device according to claim 7 wherein the mounting portion is square.
9. An optical scanning device according to claim 1 wherein the mounting portion is formed with an aperture and the first lens is mounted in the aperture.
10. An optical scanning device according to claim 9 wherein an optical axis of the first lens is aligned in the axial direction.
11. An optical scanning device according to claim 10 wherein the first lens has a numerical aperture in the range of 0.1 to 0.7.
12. An optical scanning device according to claim 1 wherein the first cantilever beam has a ratio of width to thickness of at least 10:1 and the first cantilever beam is oriented so that a face of the first cantilever beam faces the second electromagnet.
13. An optical scanning device according to claim 12 wherein the first cantilever beam comprises a longitudinal groove and the optical fiber is affixed along the longitudinal groove.
14. An optical scanning device according to claim 12 wherein the first cantilever beam is made of nickel or a nickel alloy.
15. An optical scanning device according to claim 1 wherein the first cantilever beam is supported at an end of a second cantilever beam and the second cantilever beam has a bending axis aligned at right angles with a bending axis of the first cantilever beam.
16. An optical scanning device according to claim 15 comprising an electromagnetic actuator configured to flex the second cantilever beam about its bending axis, the electromagnetic actuator comprising a coil having windings extending around the second cantilever beam and a magnet mounted to the second cantilever beam at a point spaced apart from a fixed end of the second cantilever beam, the magnet having a pole spaced apart from a longitudinal axis of the second cantilever beam.
17. An optical scanning device according to claim 15 wherein the second cantilever beam has a stiffness about its bending axis that greater than a stiffness of the first cantilever beam about a bending axis of the first cantilever beam.
18. An optical scanning device according to claim 17 wherein the stiffness of the second cantilever beam is at least twice as great as the stiffness of the first cantilever beam.