Monolithic element and system for collimating or focusing laser light from or to an optical fiber
A monolithic optical element and system is used for collimating or focusing laser light from or to optical fibers. The optical fiber terminates in a tip that directly abuts against the first surface of the optical element. The optical element may provide a collimation or focusing function depending upon whether the abutting fiber delivers light for collimation or receives focused light from a collimated beam. The optical element may be a standard or modified barrel or drum lens, with the first and second surfaces being convex curved surfaces having the same or different radii of curvature. The end of the optical element to which the fiber abuts may have a diameter to match the inner diameter of a ferrule for positioning the fiber. A pair of the elements may be used for collimation and focusing in a Raman probehead or other optical detection system.
1. An optical system, comprising:
a monolithic, homogenous glass optical element defining an optical axis;
the optical element including a first cylindrical portion with a first end surface and a second cylindrical portion with an opposing end surface;
wherein the first cylindrical portion has a diameter that is smaller than that of the second cylindrical portion, and wherein the optical element further includes a stepped transition region between the first and second cylindrical portions;
wherein the diameter of the first cylindrical portion is dimensioned to mate with an existing optical fiber ferrule sleeve to align an optical fiber having a tip on-axis with optical element, and with the tip butted up against, and making intimate physical contact with, the first end surface of the optical element,
whereby the optical element provides a collimation function by receiving light from the tip of the fiber and transmitting the light as a collimated beam from the second surface, or the optical element provides a focusing function by focusing a collimated beam incident on the second end surface to the tip of the fiber; and
wherein the light being collimated or focused is confined substantially within the optical element, thereby reducing or eliminating the presence of unconfined high energy density light between the tip of the fiber and the first surface of the optical element.
2. The optical system of claim 1 , wherein:
the optical element is a barrel or drum lens; and
the first and second end surfaces are convex curved surfaces with the same radius of curvature.
3. The optical system of claim 1 , wherein:
the first and second end surfaces are convex curved surfaces; and
the radius of curvature of the first end surface is larger than the radius of curvature of the second end surface.
4. The optical system of claim 1 , wherein:
the diameter and curvature of the second end surface, the length of the optical element, and the refractive index of the glass are selected in combination to produce exact focusing/collimation to/from a point on the center of the fiber tip.
5. The optical system of claim 1 , wherein the optical element has a relatively high refractive index to minimize the spherical aberration.
6. The optical system of claim 1 , wherein the second end surface is aspheric.
7. The optical system of claim 1 , wherein the optical element forms a gradient index lens.
8. The optical system of claim 1 , including two of the optical elements, one acting as a light collimator, and the other acting as a light focusing element in a Raman measurement probe.