OPTICAL ASSEMBLIES

Abstract: This invention is directed to a method of supporting and locating optical elements in their axial location. Said method includes the steps of seperating optical elements by spacers (16) with matching surfaces (20) to the lenses. These spacers (16) have an optical axis similar to a lens which is positioned in coincidence with the mating lens optical axis (15). This is accomplished by rotating the spacer about its first surface center of curvature (C2) until the first lens (10) and the spacer (16) have a common axis. The second lens is then rotated about the center of curvature of the second surface (C3) of the spacer until all three have a common axis (15). Additional lenses and spacers can be added in a similar manner to build up the assembly.

Description: OPTICAL ASSEMBLIES Field of Invention This. invention relates to optical assemblies and more particularly to a method of supporting and locating optical elements in their axial position. Among many other possible uses, the method according to the invention, is particularly suited for constructing fine guidance sensors and optical control sensors for space telescopes. BACKGROUND OF INVENTION Optical assemblies require precise alignment of their individual elements. This is accomplished through the use of mechanical devices such as cells and spacers. The spacers provide a fixed non-adjustable axial space between elements which maintain the alignment. This invention performs this task and in addition eliminates element tilt, decenter, wedge and surface distortion. The invention also provides additional control of thermal performance. SUMMARY OF INVENTION The invention accomplishes this through the use of a spacer with spherical surfaces. Tho spacer surfaces are exact mates to the element surfaces the spacer separates. Thus a spacer with a convex surface is a mate for a concave lens with the same radius. The spacer has an optical axis similar to an optical element. This axis is defined as the line joining the centers of curvature of the two surfaces. Ideal alignment of the spacer places this axis coincident with the axis of the optical elements. Thus a common axis is formed. Any number of additional spaces and lenses may be added with each new piece aligned to the same axis. The precision of this alignment is only limited by our ability to locate the axis of each element or spacer. As a consequence, structural distortion of the optical surface is eliminated due to even distribution of load and selection of spacer material permit the control of thermal characteristics of each assembly. In view of the foregoing, objects of this invention include substantial elimination of the decenter error in optical element assemblies, substantial elimination of the tilt error in optical elements and substantial elimination of wedge in spacers and optical elements. Other objects include the provision for accurate and stable axial spacing of the optical elements, reduction or elimination of surface bending or deformation due to loads, and control of the thermal expansion character of spacers between elements. Briefly, the present invention is directed to a new and improved method of supporting and positioning optical elements, comprising the steps of: taking an optical lens element and a spherical spacer, and placing the two in contact so that their optical axes are coincident. The surfaces in contact are optically identical mating surfaces, generally spherical, with one surface concave and the mating surface convex with a common center of curvature. The alignment is controlled by rotating the spacer about the common surface center of curvature until the axes are coincident. The spacer has a central hole of sufficient diameter to pass the optical beam without vignetting. Further, according to one aspect of the invention, the last operation in the fabrication of the spacer is the removal of the central aperture, thereby providing a permanent record of the thickness of the spacer. There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description that follows may be better understood, and in order that the present contribution to the art may be better appreciated There are, of course, additional features of the invention which will he described more fully hereinafter. Those skilled in the art will appreciate that the conception on which this disclosure is based may readily be utilized as a basis for the designing of other methods for carrying out the several purposes of the invention. It is important, therefore, that this disclosure be regarded as including such equivalent methods that do not depart from the spirit and scope of the invention. Several embodiments of the invention have been chosen for purposes of illustration and description, and are shown in the accompanying drawings, forming a part of the specification. BRIEF DESCRIPTION OF THE DRAWINGS Figures 1 to 3 are schematic illustrations showing a series of steps in a method for supporting and locating optical elements in their axial location, according to the invention. DETAILED DESCRIPTION OF THE INVENTION In one embodiment of the invention, a method of supporting and locating optical elements in their axial location comprises the steps of taking an optical element 10, Figure 1 having a first center of curvature C1 for a first surface 12, and a second center of curvature C2 for a second surface 14, with the element's axis 15 passing through the two centers of curvature C1, C2. Next, the method comprises the steps of taking a spacer device 16, Figure 2, having a first surface 18 and a second surface 20, said first surface 18 being a matched mating surface with respect to the second surface 14 of the optical element 10. The spacer 16 is mounted as shown in Figure 2 so that the center of curvature of the spacer's first surface 18 is coincident at C2 with the second center of curvature of the optical element 10. The spacer's second center of curvature, indicated at C3 in Figure 2, is initially not on the optical element's axis 15. Thereafter, the spacer 16 is rotated about said second center of curvature C2 of the optical element 10 until the spacers second center of curvature C3 is coincident with the optical element's axis 15 as shown in Figure 3. As a result additional optical elements and spacers can be added by repeating the procedure and thus maintaining the alignment. The result is a lens assembly where all elements have a common axis, although each element has errors of centering and wedge. Thus, it is seen that the spacer devices, made of a suitable, stable material such as glass, for example, are inserted between optical elements as a means of supporting and locating the elements in their axial location. Material selection of the spacer is based upon thermal and manufacturing considerations. The surfaces of the spacer match the surfaces of the mating element and it has a large central aperture or hole 22, Figures 2 and 3, to permit light to pass through unimpeded. The aperture diameter is equal to or larger than the clear aperture of the mating element a The spacer, preferably with spherical surfaces, is made exactly like a lens. The same test plates are used to fabricate the spacer as are used to make the mating lenses. The radius match can be held to any level of precision desired. During the manufacturing process the center thickness of the spacer is monitored. This thickness is the distance specified by the optical designer for that optical system. The distance is measured directly and not inferred by calculation as is the case with prior conventional spacers. In addition, the last operation in the spacer manufacturing cycle is the removal of the center core. This core is saved and provides a permanent record of the thickness of that spacer. Occasionally, it is important to thermally control element-to-element spacing in an optical system. The use of metallic spacers provide the designer with one or two material choices for matching the coefficient of thermal expansion to that of glass. The use of glass spacers gives the designer a wide variety of choices in thermal expansion equal to or near that of the lenses in the assembly, and infact with the recent advent of non-expanding material the designer may choose a zero expansion coefficient if that is a desirable characteristic. While the advantages of using glass spacers are several, it should be pointed out that many of the advantages of the invention are independent of the material. Metallic spacers can provide many of t'le same advantages, and only in certain circumstances, such as that involving control of thermal expansion, for example, do they necessitate the use of glass. The making of a glass spacer, preferably with spherical surfaces, has the unique advantage that the radius of the spacer can be matched to its mating optical element to a very high degree of precision. This is due to the fact that parts can be made as a matched set. The spacer surface can he produced to optical tolerances, approximately one hundred times the tolerance of that of a machined part. It will thus be seen that the present invention does indeed provide a new and improved method of supporting and locating optical elements in their axial position, which effectively meets the objects mentioned hereinbefore. Although certain particular embodiments of the invention are herein disclosed for purposes of explanation, further modifications thereof, after study of this specification, will be apparent to those skilled in the art to which the invention pertains. Reference should accordingly be had to the appended claims in determining the scope of the invention.

Claims: WHAT IS CLAIMED: 1. A method of supporting and locating optical elements in their axial location comprising the steps of: taking an optical element having first and second surfaces with corresponding center of curvatures and an optical axis passing through the two centers of curvature; taking a spacer having a central aperture and first and second surfaces with corresponding center of curvatures and an optical axis passing through the two centers of curvature, said first surface being a matched mating surface with respect to the second surface of said optical element; ; mounting said spacer so that the spacer's first surface is in contact with the second surface of the optical element, subsequently adjusting the spacer position while maintaining contact between the two surfaces until the optical axis of the spacer is coincident with the optical axis of the element, whereby the optical element and the spacer are substantially perfectly aligned. 2. A method of supporting and locating optical elements in their axial location according to Claim 1 wherein said spacer is fabricated from glass. 3. A method of supporting and locating optical elements in their axial location according to Claim 1 wherein said spacer and said optical element have mating spherical surfaces. 4. A method of supporting and locating optical elements in their axial location according to Claim 1 wherein substantially the last operation in the fabrication of this spacer is forming said central aperture by removing a central core, thereby providing a permanent record of the thickness of the spacer.

Inventors: SELGER, KEN
Applicants: THE PERKIN-ELMER CORPORATION
Application year: 1984
Main classification: G02B7
IPC codes: G02B7