Tri-layer ceramic optical fibers and method of making
US20260050117A1
Abstract
A method of forming a crystalline core/crystalline clad (C4) optical fiber. The method comprises coextruding a cladding mixture of a plasticizer and a binder with a yttrium aluminum garnet (YAG) core. The coextrusion dynamically clads a polycrystalline cladding onto the YAG core to yield a green C4 optical fiber. The C4 optical fiber is then densified, preferably in two steps sintering and hot isostatic pressing. The resulting optical C4 fiber has greater power capacity than a glass fiber labor host.
Description (excerpt)
CROSS REFERENCE TO RELATED APPLICATIONS This application is a continuation in part of and claims priority to and the benefit of pending application Ser. No. 18/802,679 filed Aug. 13, 2024, (Attorney Docket No. AFD-2361), and claims priority to and the benefit of pending application Ser. No. 18/802,701 filed Aug. 13, 2024 (Attorney Docket No. AFD-2363), and claim priority to expired provisional application Ser. No. 63/519,393 filed Aug. 14, 2023 and priority to expired provisional application Ser. No. 63/519,569 filed Aug. 15, 2023, all the disclosures of which are incorporated herein by reference. STATEMENT OF GOVERNMENT INTEREST The invention described and claimed herein may be manufactured, licensed and used by and for the Government of the United States of America for all government purposes without the payment of any royalty. FIELD OF THE INVENTION The present invention is related to cladded ceramic optical fibers and more particularly to such single crystal core/poly crystalline cladding optical fibers having an internal mechanism to reduce porosity. BACKGROUND OF THE INVENTION The principle of data transfer through optic fiber cables is based on the phenomenon of total internal reflection. When a light ray moves from a medium of higher refractive index into a medium of lower refractive index, the light ray bends away from the normal. The normal is a perpendicular to the surface boundary of the two media at the point at which the light ray meets the surface boundary. During optical signal transmission, light is shone along a thin glass fiber and as it hits the glass-air boundary at more than the critical angle it reflects along inside the fiber. A beam of light travels through one or more fibers and as long as the angle of incidence with the walls of a fiber is great enough, the light will be reflected along the fiber with multiple off-axis. Since the 1950's it has been known that cladding of a fiber urges the optical signals being transmitted to remain confined to the core and not be dissipated when the signal travels a long distance. Cladding is a layer of material with a lower refractive index that covers the core of a fiber optic cable. The core of the fiber optic cable has a higher refractive index than the cladding circumscribing the core. The refractive index of a medium is a ratio between the speed of light in a vacuum to the speed of light in that medium. Adding cladding increases the critical angle between the core and only those rays that are close to the axis of the fiber pass through. Additionally, with cladding the light rays travel roughly the same distance in the fiber, so that information input at one end of the fiber arrives at the other end with less time dispersion and increased fidelity. And there are fewer reflections along the fiber compared to the distance travelled without cladding, thereby reducing energy loss and the time of transmission. By confining the light within the core, the cladding reduces signal loss due to leakage of light, thereby maintaining the strength and fidelity of the transmitted signals over long distances. Cladding also provides the benefits of reduced dissipation of the optical signal due to irregularities in the core and overall reduced fiber diameter. The cladding also helps to prevent crosstalk between adjacent fibers by confining the light within the core of each fiber. Outside of the cladding may be a jacket for protection against environmental and mechanical hazards. According to prior art methods, when the ceramic powder that is compacted around a doped single crystal core at elevated temperatures, the single crystal core grows. During that growth, pores are trapped in the grown single crystal area and the dopant diffuses out of the doped core. However, porosity within either the core or cladding will cause reflection and diffusion of energy. As a crystalline core grows into the cladding, porosity occurs at the grain boundary between the core and cladding. Again, such porosity is inimical to optical signal transmission. This situation is particularly acute due to the high porosity of cladding powder, which is typically about 50 percent of the theoretical density. For example, a doped single crystal yttrium aluminum garnet crystal structure YAG (Y3Al5O12) fiber is a promising laser host for high power fiber laser. This fiber is cladded with a material having lower refractive index. Undoped YAG is believed to be a very suitable material for cladding on a doped single crystal YAG fiber, due to having a lower refractive index than doped YAG core with the same thermal conductivity and coeffi
Filing details
- Inventors
- Hyunjun Kim
- Assignee
- Government Of The United States As Represented By The Secretary Of The Air …
- Filed
- Sep 22, 2025
- Granted
- Application pending
Bibliographic data and excerpted text sourced from Google Patents (public record) as part of IP TechMatch's current-filings monitor. This filing is not part of the 2019 historical archive. For the authoritative full text, drawings, and legal status, see the source links above or consult USPTO records directly.