Fabrication of graded index single crystal in glass

Abstract

Lithium niobate crystals were grown in 3D through localized heating by femtosecond laser irradiation deep inside 35Li2O-35Nb2O5-30SiO2 glass. Laser scanning speed and power density were systematically varied to control the crystal growth process and determine the optimal conditions for the formation of single crystal lines. EBSD measurements showed that, in principle, single crystals can be grown to unlimited lengths using optimal parameters. We successfully tuned the parameters to a growth mode where nucleation and growth occur upon heating and ahead of the scanning laser focus. This growth mode eliminates the problem reported in previous works of non-uniform polycrystallinity because of a separate growth mode where crystallization occurs during cooling behind the scanning laser focus. To our knowledge, this is the first report of such a growth mode using a fs laser. The crystal cross-sections possessed a symmetric, smooth lattice misorientation with respect to the c-axis orientation in the center of the crystal. Calculations indicate the observed misorientation leads to a decrease in the refractive index of the crystal line from the center moving outwards, opening the possibility to produce within glass a graded refractive index single crystal (GRISC) optically active waveguide.

Laser patterning of oriented LiNbO3 crystal particle arrays in NiO‐doped lithium niobium silicate glasses

“…In this study, the laser‐induced crystallization technique using cw Yb:YVO 4 fiber laser was applied to pattern LiNbO 3 crystals at the surface of NiO‐doped 40Li 2 O‐32Nb 2 O 5 ‐28SiO 2 glasses. The patterning of LiNbO 3 crystals in glasses by femtosecond (fs) laser irradiation has been also reported so far . For example, Cao et al reported the preferential nanocrystal orientation of LiNbO 3 using Yb‐doped fiber amplifier fs laser (λ = 1030 nm, pulse duration 300 fs, repetition rate 250 kHz, linearly polarized) in 32.5Li 2 O‐27.5Nb 2 O 5 ‐40SiO 2 glass.…”

“…They proposed an orientation mechanism based on the application of laser‐induced torques on the nanocrystal electric dipole . Recently, Veenhuizer et al patterned LiNbO 3 single crystal lines by controlling (optimal conditions) laser scanning speed and power density of fs laser (λ = 1026 nm, 175 fs, 200 kHz) in 35Li 2 O‐35Nb 2 O 5 ‐30SiO 2 glass and proposed a growth mode where nucleation and growth occur upon heating and ahead of the scanning laser focus. Even in the fs laser‐induced crystallization, particularly for the patterning of LiNbO 3 crystal lines with highly homogeneous morphologies, it is considered that moderate temperature and its spatial distribution being suitable for crystal growth must be highly controlled and designed.…”

Ferroelectric domain engineering of lithium niobate single crystal confined in glass

“…An extensive collection of work has been dedicated to the topic of laser-induced crystallization of glass [5][6][7][8][9][10] as it could aid in the creation of 2D and 3D photonic integrated circuits. The main idea is that the laser is focused with an objective on the surface or the interior of a glass sample, depositing energy via absorption, leading to heat accumulation and a rise to temperatures suitable for the nucleation and growth of crystals.…”

“…Continuous wave laser-induced crystallization of glass [5,6] relies on linear absorption of the incident laser and is thus limited to creating 2D crystal architectures on the glass surface. Femtosecond (fs) laser-induced crystallization of glass [7][8][9][10] is initiated by non-linear absorption of the incident beam. If the wavelength of the fs laser is chosen so that the material is transparent to the laser at low intensities, then only in the vicinity of the laser focus the intensity exceeds the threshold for non-linear absorption, allowing for the production of 3D crystal architecture deep inside the glass.…”

“…[8] Beyond passive optical waveguides, however, certain ferroelectric single-crystal-architecture-in-glass (SCAG) have the potential to be utilized for their electro-optic, non-linear optical, and piezoelectric response. In particular, significant effort has been expended to fabricate lithium niobate (LiNbO 3 ) SCAG within lithium niobosilicate glass, [9,10] due to its favorable electro-optic, [11] non-linear optical, [12] and piezoelectric [11] coefficients.…”