G.Y. Zhang

Faraday rotation spectra of bismuth-substituted rare-earth iron garnet crystals in optical communication band

Bismuth-substituted rare-earth iron garnet (REBIG) crystals are used in optical isolators for optical communication. However, the Faraday rotation (FR) spectra of REBIG crystals in the wavelength region of 1.3–1.6 μm have not yet been theoretically studied. To interpret the spectra, we assumed that the FR in this wavelength range was dominated by the contribution of the electric dipole transitions, and calculated the FR spectra. REBIG bulk crystals were grown from the Bi2O3 self-fluxed melt by the top-seeded solution growth method. The experimental results agreed with the theoretical calculation of FR in (HoBi)3Fe5O12, (YbBi)3Fe5O12, (YYbBi)3Fe5O12, and (TbBi)3Fe5O12. The results indicate that the theoretical analysis method of the FR spectra of REBIG in the visible range of wavelengths can be applied in the optical communication band.

Growth and optical properties of a new nonlinear optical lanthanum calcium borate crystal

The monoclinic lanthanum calcium borate La 2 CaB 10 O 19 (LCB) crystal was grown from its stoichiometric melt by the top-seeded pulling method. The unpolarized transmission spectrum of a 1-mm-thick (001)-cut LCB crystal was measured in the wavelength range of 190-3100nm. The crystal exhibited a high transmittance (>80%) and a short absorption edge (<190 nm). The phase-matched second-harmonic generation (SHG) properties within the (010) plane of a 1.7-mm-thick (001)-cut LCB crystal were studied for the first time with a Spectra-Physics 3900S Ti:sapphire CW tunable laser. The room-temperature phase-matching (PM) wavelength was found to be 869 nm when the light propagation and polarization directions of the fundamental beam were parallel to the [001] and [010] axes, respectively. The full width at half maximum (FWHM) of the wavelength-tuning curve was found to be about 6 nm. The phase-matched SHG of the LCB crystal exhibited a small temperature coefficient of 0.05nm/C between 24°C and 150°C and was quite stable for generating visible light upon temperature changes.

Vertical Bridgman growth of calcium lithium niobium gallium garnet crystals

The growth of calcium lithium niobium gallium garnet (CLNGG) crystal has been carried out using platinum crucibles in a vertical Bridgman (VB) furnace with three resistance-heating zones. Transparent CLNGG crystals grown from the congruent melts with and without weight loss compensation are different in color and are 25mm in diameter and about 70mm in length. The phase identification of the sintered raw materials, grown crystals and white compound formed on the side surface of the grown crystal has been done using the powder X-ray diffraction method. The formation of the white compound is related to the {100} facet growth near the side surface. The naturally selected growth direction of the CLNGG crystal grown without a seed is near 〈111〉, which is in good agreement with the morphological importance analysis according to the BFDH law. The VB-grown CLNGG also shows a cleavable feature parallel to {110} face and no absorption peaks in the wavelength range of 1100-1600nm. The linear thermal-expansion coefficient of the CLNGG crystal along 〈111〉 direction is also reported and compared with that of CNGG, GGG and platinum crucible.

Blue SHG characteristics and homogeneity of the TSSG grown potassium lithium niobate (KLN) crystal with high Li2O content

The high quality and crack-free KLN crystal with high Li 2 O content has been grown along the axis by the TSSG method from the melt of 31 mol% K 2 O, 26 mol% Li 2 O and 43 mol% Nb 2 O 5 . The size of the as-grown KLN crystal is about 6 x 9 x 29 mm 3 . The XRD analysis gives the lattice constant a = 12.583 A, and c = 4.041 A near the c value of the stoichiometric KLN. The Curie temperature of this crystal is determined to be 540°C by the dielectric constant measurement. The blue SHG characteristics of the KLN crystal are investigated by using a 3900S Ti: sapphire CW tunable laser. The FWHMs of the wavelength- and temperature-tuning curves for the NCPM SHG are determined to be 0.4 nm and 1.2°C, respectively. The blue laser light with 1.45mW output at 416.7 nm is achieved at room temperature by the single-pass SHG for 903 mW input power. The blue SHG conversion efficiency is estimated to be 0.25%/W that is the highest value obtained up to now. The temperature-tuned blue laser light with continuous output from 416.7 to 423.5 nm is obtained by increasing the crystal temperature from 23.5°C to 80°C. The temperature coefficient of the NCPM wavelength is 0.295 nm/°C. The investigated KLN crystal, especially its middle part, has a good homogeneity of the room temperature NCPM wavelength along the growth axis (<2 nm).

Second-Harmonic Generation of Ferroelectric Potassium Lithium Niobate Crystals.

The second-harmonic generation (SHG) properties of a potassium lithium niobate (KLN) crystal with the size of 8×20×43 mm3 were studied in detail. The KLN crystal was grown from a melt consisting of 32 mol% K2O, 24 mol% Li2O and 44 mol% Nb2O5 (denoted as the melt 32:24:44) by the top-seeded solution growth (TSSG) method. The ferroelectricity of the KLN crystal was revealed by the marked dielectric anomaly at the Curie temperature. The full-widths at half maximum (FWHMs) of the wavelength- and temperature-tuning curves of a 4-mm-long KLN crystal sample were found to be 0.6 nm and 2°C, respectively. The SHG conversion efficiency of this crystal was studied and estimated to be 0.03%/W for an input power of 748 mW. The CW tunable blue laser covering the range of 431.1–437.6 nm was achieved by tuning the crystal temperature in the range of 24–80°C. The crystal studied in this paper is more inhomogeneous and has lower SHG efficiency than the KLN crystal grown from the melt 31:26:43, which has higher Li2O content.