A diamond turning process has made possible a significant advance in the art of whispering-gallery- mode (WGM) optical resonators. By use of this process, it is possible to fashion crystalline materials into WGM resonators that have ultrahigh resonance quality factors (high Q values), are compact (ranging in size from millimeters down to tens of microns), and support single electromagnetic modes.

This development combines and extends the developments reported in "Few-Mode Whispering-Gallery-Mode Resonators" (NPO-41256), NASA Tech Briefs, Vol. 30, No. 1 (January 2006), page 16a and "Fabrication of Submillimeter Axisymmetric Optical Components" (NPO-42056), NASA Tech Briefs, Vol. 31, No. 5 (May 2007), page 10a. To recapitulate from the first cited prior article: A WGM resonator of this special type consists of a rod, made of a suitable transparent material, from which protrudes a thin circumferential belt of the same material. The belt is integral with the rest of the rod and acts as a circumferential waveguide. If the depth and width of the belt are made appropriately small, then the belt acts as though it were the core of a single-mode optical fiber: the belt and the rod material adjacent to it support a single, circumferentially propagating mode or family of modes.

Circumferential Belts were formed by diamond turning on the initially cylindrical surface of a CaF2 rod. The radial depths and axial widths of the belts were chosen to make some of the belts act as single-mode and some as multi-mode WGM resonators.
To recapitulate from the second cited prior article: A major step in the fabrication of a WGM resonator of this special type is diamond turning or computer numerically controlled machining of a rod of a suitable transparent crystalline material on an ultrahigh-precision lathe. During the rotation of a spindle in which the rod is mounted, a diamond tool is used to cut the rod. A computer program is used to control stepping motors that move the diamond tool, thereby controlling the shape cut by the tool. Because the shape can be controlled via software, it is possible to choose a shape designed to optimize a resonator spectrum, including, if desired, to limit the resonator to supporting a single mode. After diamond turning, a resonator can be polished to increase its Q.

By virtue of its largely automated, computer-controlled nature, the process is suitable for mass production of nominally identical single-mode WGM resonators. In a demonstration of the capabilities afforded by this development, a number of WGM resonators of various designs were fabricated side by side on the surface of a single CaF2 rod (see figure).

This work was done by Ivan Grudinin, Lute Maleki, Anatoliy Savchenkov, Andrey Matsko, Dmitry Strekalov, and Vladimir Iltchenko of Caltech for NASA's Jet Propulsion Laboratory.

In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:

Innovative Technology Assets Management

JPL

Mail Stop 202-233

4800 Oak Grove Drive

Pasadena, CA 91109-8099

(818) 354-2240

E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

Refer to NPO-43070, volume and number of this NASA Tech Briefs issue, and the page number.

Topics:
Computer software and hardware Fabrication Fiber optics Machining processes Manufacturing processes Optics Optimization Physical Sciences Production Turning
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Single-Mode WGM Resonators Fabricated by Diamond Turning

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NASA Tech Briefs Magazine

This article first appeared in the May, 2008 issue of NASA Tech Briefs Magazine (Vol. 32 No. 5).

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Overview

The document discusses advancements in the fabrication of single-mode whispering gallery mode (WGM) optical crystalline resonators using a diamond turning process. These resonators are significant for applications requiring minimal modes per free spectrum range (FSR), such as optical filtering. The motivation behind this research was to create a structure with a highly rarefied, ideally single-mode spectrum, and to develop a computer-controlled procedure for mass production of these devices.

The fabricated resonators are made from calcium fluoride crystal rods, featuring a single-mode optical resonator cut on their circumferential surfaces. The diamond turning process allows for deterministic and reproducible fabrication of these microstructures, resulting in resonators that are compact (ranging from tens to thousands of micrometers in diameter) and possess ultra-high optical Q factors. This new technology represents a significant improvement over existing resonators, which typically fall into three categories: Fabry-Perot cavities, ring resonators, and traditional whispering gallery mode resonators, all of which are inherently multi-mode.

The document highlights two filed NASA Technology Reports (NTRs) related to this technology: NTR#42056, which details the fabrication method for arbitrary axially symmetric optical crystalline components, and NTR#41256, which outlines the concept of single-mode dielectric WGM resonators. The current NTR combines and enhances these ideas, focusing on the automated mass production of single-mode resonators from any transparent optical material.

The novelty of this approach lies in its ability to produce single-mode resonators that are not only compact and efficient but also robust and versatile when made from optical crystals. This advancement opens up new possibilities for various applications in optics and photonics, particularly in fields that require precise control over optical modes.

For further inquiries or information regarding this technology, the document provides contact details for the Innovative Technology Assets Management at NASA's Jet Propulsion Laboratory. Overall, this document encapsulates a significant technological leap in the field of optical resonators, promising enhanced performance and broader applicability in scientific and commercial domains.