This patent application is assigned to
The following quote was obtained by the news editors from the background information supplied by the inventors: "Miniature resonant photonic devices as known in the art are created from coupled high Q-factor cavities (e.g., ring resonators, photonic crystal resonators or the like). The resonance is a result of circulating whispering gallery modes (WGMs) that are created within circular structures (such as around the circumference of an optical fiber), where the WGMs traveling around the circumference of the structure undergo repeated internal reflections at near-grazing incidence. The leakage of light can be very small in these structures, leading to high intrinsic quality factors (Q factors). The Q factor is generally defined as a measure of energy loss relative to the energy stored in a resonator (or any type of oscillating device), and can be characterized by the center frequency of a resonator divided by its bandwidth (a common value for a 'high Q' resonator is a value on the order of 10.sup.9 or more). The preferred 'high Q' resonator is therefore associated with a relatively narrow and sharp-peaked resonance feature.
"Conventional resonator structures are formed by creating features whose size is of the order of the wavelength of the propagating optical signal, or greater. For example, known rings or toroids or spheres are typically tens of microns in dimension. Such structures are commonly created using lithographic techniques (for example, etching a silicon material to create the feature pattern) with the undesirable result of surface roughness. The lithography-associated roughness leads to scattering of a propagating optical signal, reducing the Q factor of the device. In addition, the inaccuracies of the conventional fabrication process limit the precision with which multiple devices can be coupled together to form more complex structures. While it would be useful to create resonators with even smaller dimensions (i.e., sub-wavelength), which offers certain advantages in terms of performance, such smaller dimensions pose additional difficulties in fabrication.
"Previously, we have developed various complex, coupled photonic microdevices within and along an optical fiber, using sub-wavelength-sized perturbations of the fiber's radius to create resonance cavities. Multiple microstructures may be formed along a given length of optical fiber and coupled together to create complex photonic microdevices. Details of this device structure can be found in commonly-assigned US Publication 2012/0213474, dated
"However, when attempting to create relatively long chains of these devices, fabrication errors begin to impair their performance, with the errors growing with the length of the chain. One source of error may be nanometer-scale non-uniformities in radius of the fiber, which may then continue in cumulative fashion to affect all devices along the chain. Other sources of fabrication error in creating long chains of microresonators include, but are not limited to, surface contamination of the fiber, imperfections in system alignment (i.e., the system used to create the effective radius variations in the first instance), fluctuations of the beam power used to create effective radius variations, non-uniform doping profiles in photosensitive fibers and the like."
In addition to the background information obtained for this patent application, VerticalNews journalists also obtained the inventor's summary information for this patent application: "The needs remaining in the art are addressed by the present invention, which relates to a method of fabricating surface nanoscale axial photonic (SNAP) devices and, more particularly, to utilizing an in-line corrective process to locally modify the effective radius of a SNAP device along its length and create desired optical characteristics with sub-Angstrom accuracy.
"In accordance with one embodiment, the present invention describes a method of characterizing and correcting effective radius variations in a surface nanoscale axial photonic (SNAP) device that comprises a plurality of separate optical microdevices. The method includes the steps of: (1) characterizing an as-fabricated SNAP device to determine the local effective radius value of each optical microdevice, calibrating the as-fabricated SNAP device to determine an appropriate correction factor, defined as a change in effective radius associated with a predetermined 'treatment' (i.e., a time-dependent annealing process or UV radiation exposure); and then (3) correcting individual microdevices by the application of a number of treatments, the number of treatments applied to individual microdevices determined by the amount of correction required and the correction factor determined in the calibrating step. A number of iterations of the characterizing and correcting operations can be performed, achieving less than an Angstrom variation in effective radius variation. An apparatus for performing the method is also disclosed.
"In another embodiment, the present invention describes an apparatus for performing characterization and correction of the resonant characteristics of a surface nanoscale axial photonic (SNAP) device. The apparatus includes a characterization stage for measuring a local resonant wavelength value for each individual optical microdevice forming the SNAP device and an exposure stage for applying a predetermined number of treatments (annealing processes or UV radiation exposures) to individual optical microdevices, the predetermined number of treatments calculated based upon a known change in effective radius associated with a known annealing energy and duration, or UV radiation exposure.
"These and other embodiments of the present invention will become apparent during the course of the following discussion and by reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
"Referring now to the drawings, where like numerals represent like parts in several views:
"FIG. 1 illustrates an exemplary arrangement for supporting whispering gallery mode (WGM) resonances within a tapered section of optical fiber;
"FIG. 2 illustrates an alternative resonant structure created within a 'bottle'-like tapered region of an optical fiber;
"FIG. 3 depicts a surface nanoscale axial photonic (SNAP) device formed to include a plurality of microresonators distributed along a longitudinal extent of an optical fiber;
"FIG. 4 illustrates an exemplary annealing process that may be used to create the SNAP device of FIG. 3;
"FIG. 5 illustrates an exemplary UV radiation process that may be used to create the SNAP device of FIG. 3 in a photosensitive optical fiber;
"FIG. 6 illustrates an exemplary calibration (characterization) and correction (exposure) arrangement formed in accordance with the present invention to characterize and correct the resonant features of a SNAP device, such as the device shown in FIG. 3;
"FIG. 7 is an enlarged view of an exemplary portion of the calibration arrangement of FIG. 6;
"FIG. 8 includes a series of surface plots associated with a SNAP device containing a set of thirty resonators formed in accordance with the present invention, where FIG. 8(a) is a surface plot of the set of resonators subsequent to the initial formation of the SNAP device, FIG. 8(b) is a surface plot of the same SNAP device subsequent to the calibration operation; and FIG. 8© is a surface plot of the SNAP device after performing the individual correction operations on each microresonator, in accordance with the present invention; and
"FIG. 9 contains a series of plots of effective radius variation that are associated with the measured surface plots of FIG. 8, with plot 1 associated with FIG. 8(a), plot 2 associated with FIG. 8(b) and plot 3 associated with FIG. 8©."
URL and more information on this patent application, see: Sumetsky, Mikhail. Method of Fabricating Surface Nanoscale Axial Photonic Devices. Filed
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