A fabrication method of the multi-core fiber Bragg grating (FBG) probe for measuring structures of a micro part based on the capillary self-assembly technique, wherein the diameter of the fiber (6) inscribed with FBG is reduced using a mechanical method or an etch method by the hydrofluoric acid; the fibers (6) inscribed with FBG, whose diameter has been reduced, are inserted into a tube (7) through its terminal with an inner taper angle; the FBG terminals of these fibers (6) are immersed into the UV adhesive (10) of a low viscosity and the UV adhesive (10) is raised in the gaps between the fibers (6); or the UV adhesive is dropped on the these fibers (6) and the capillary bridge between the fibers (6) is formed; a most compact structure of the fiber bundle is formed as a result of the capillary self-assembly; the fiber bundle is cured using a UV light and the multi-core FBG (11) is therefore formed; the terminal of the multi-core FBG (11) is polished with an optic fiber polishing machine and then a spherical tip is fabricated with the melting fiber method or the installation method of a micro ball; therefore, a multi-core FBG (11) probe can be achieved. The method features low crosstalk between signal of FBG, inexpensive and low insertion loss.

Provided is an optical waveguide with an inscribed Bragg grating, where the Bragg grating is stable at high temperature, has low scattering loss and high reflectivity. Also provided is a method for inscribing a Bragg grating in an optical waveguide, the method comprising irradiating the optical waveguide with electromagnetic radiation from an ultrashort pulse duration laser of sufficient intensity to cause a permanent change in an index of refraction within a core of the optical waveguide, where the irradiating step is terminated prior to erasure of a Bragg resonance, and heating the optical waveguide to a temperature and for a duration sufficient to substantially remove a non-permanent grating formed in the optical waveguide by the irradiating step.

Provided is an optical waveguide with an inscribed Bragg grating, where the Bragg grating is stable at high temperature, has low scattering loss and high reflectivity. Also provided is a method for inscribing a Bragg grating in an optical waveguide, the method comprising irradiating the optical waveguide with electromagnetic radiation from an ultrashort pulse duration laser of sufficient intensity to cause a permanent change in an index of refraction within a core of the optical waveguide, where the irradiating step is terminated prior to erasure of a Bragg resonance, and heating the optical waveguide to a temperature and for a duration sufficient to substantially remove a non-permanent grating formed in the optical waveguide by the irradiating step.

Provided is an optical waveguide with an inscribed Bragg grating, where the Bragg grating is stable at high temperature, has low scattering loss and high reflectivity. Also provided is a method for inscribing a Bragg grating in an optical waveguide, the method comprising irradiating the optical waveguide with electromagnetic radiation from an ultrashort pulse duration laser of sufficient intensity to cause a permanent change in an index of refraction within a core of the optical waveguide, where the irradiating step is terminated prior to erasure of a Bragg resonance, and heating the optical waveguide to a temperature and for a duration sufficient to substantially remove a non-permanent grating formed in the optical waveguide by the irradiating step.

A method for setting a heating condition for thermal aging of each of fiber Bragg gratings, includes: determining, based on a correspondence (Ed) between a temperature coefficient of each of the fiber Bragg gratings and a demarcation energy Ed of each of the fiber Bragg gratings, a first lower limit Ed.sub.min of the demarcation energy Ed such that the temperature coefficient is not more than a desired upper limit .sub.max; and setting the heating condition for thermal aging of each of the fiber Bragg gratings such that the demarcation energy Ed is not less than the first lower limit Ed.sub.min.

Provided is a cladded single crystal sapphire optical device (e.g., a s sapphire optical fiber or wafer). In one embodiment, the innovation provides a method for forming a cladding in a single crystal sapphire optical device by reactor irradiation. The reactor irradiation creates ions external to the optical device that enter the optical device, displace atoms in the optical device, and are implanted in the optical device, thus modifying the index of refraction of the optical device near the surface of the optical device and creating a cladding in the sapphire optical device.

A fabrication method of a multi-core fiber Bragg grating (FBG) probe for measuring structures of a micro part based on the capillary self-assembly technique, wherein the diameter of the fiber (6) inscribed with FBG is reduced using a mechanical method or an etch method by the hydrofluoric acid; the fibers (6) inscribed with FBG, whose diameter has been reduced, are inserted into a tube (7) through its terminal with an inner taper angle; the FBG terminals of these fibers (6) are immersed into the UV adhesive (10) of a low viscosity and the UV adhesive (10) is raised in the gaps between the fibers (6); or the UV adhesive is dropped on these fibers (6) and the capillary bridge between the fibers (6) is formed; a most compact structure of the fiber bundle is formed as a result of the capillary self-assembly; the fiber bundle is cured using a UV light and the multi-core FBG (11) is therefore formed; the terminal of the multi-core FBG (11) is polished with an optic fiber polishing machine and then a spherical tip is fabricated with the melting fiber method or the installation method of a micro ball; therefore, a multi-core FBG (11) probe can be achieved. The method features low crosstalk between signal of FBG, inexpensive and low insertion loss.

Provided is a cladded single crystal sapphire optical fiber. In one embodiment, the innovation provides a method for forming a cladding in a single crystal sapphire optical fiber by reactor irradiation. The reactor irradiation creates ions external to the fiber that enter the fiber, displace atoms in the fiber, and are implanted in the fiber, thus modifying the index of refraction of the fiber near the surface of the fiber and creating a cladding in the sapphire fiber.

Provided is an optical waveguide with an inscribed Bragg grating, where the Bragg grating is stable at high temperature, has low scattering loss and high reflectivity. Also provided is a method for inscribing a Bragg grating in an optical waveguide, the method comprising irradiating the optical waveguide with electromagnetic radiation from an ultrashort pulse duration laser of sufficient intensity to cause a permanent change in an index of refraction within a core of the optical waveguide, where the irradiating step is terminated prior to erasure of a Bragg resonance, and heating the optical waveguide to a temperature and for a duration sufficient to substantially remove a non-permanent grating formed in the optical waveguide by the irradiating step.

Provided is a cladded single crystal sapphire optical fiber. In one embodiment, the innovation provides a method for forming a cladding in a single crystal sapphire optical fiber by reactor irradiation. The reactor irradiation creates ions external to the fiber that enter the fiber, displace atoms in the fiber, and are implanted in the fiber, thus modifying the index of refraction of the fiber near the surface of the fiber and creating a cladding in the sapphire fiber.