Wenrong Zeng

Computer‐Assisted Search for Nonlinear Optical Crystals

Based on anionic group theory, a computer-assisted material design system (CAMDS) has been developed. This method has proved to be a highly efficient means of discovering nonlinear optical crystals. In this method, important optical properties of the target compounds (borates, for example), such as the dij coefficients, refractive indices, and energy bandgap, are calculated so that a prior evaluation can be made before experiments. The results have given a meaningful guide to ensuing experiments, which have led to our discoveries of KBBF (KBe2BO3F2) and SBBO (Sr2Be2B2O7) in the past several years, followed by other members of the SBBO family in recent years. On the other hand, this system can also be used to evaluate the dij coefficients of the borate nonlinear optical (NLO) crystals discovered recently whose dij coefficients have not been determined experimentally.

New nonlinear optical crystal K 2 Al 2 B 2 O 7

The new nonlinear optical crystal K2Al2B2O7 is discovered with the molecular engineering approach on the basis of anionic group theory. An optically perfect single crystal with space group P321, free of moisture and hygroscopy, is readily grown by the top-seeding flux method. Its transparence range covers 180 to 3600 nm. The refractive indices are measured with the minimum-deviation method, based on which the Sellmeier equation is obtained. The measured nonlinear optical coefficient d11 is 0.45 pm/V. The moderate walk-off angle and angular bandwidth, together with the high optical homogeneity, make it a promising candidate for the fourth- and the fifth-harmonic generation of a Nd:YAG laser.

Two new nonlinear optical crystals: BaAl2B2O7 and K2Al2B2O7

The new nonlinear optical crystals BaAl2B2O7 and K2Al2B2O7 are readily grown by top-seeded flux method. BaAl2B2O7 crystallizes in the rhombohedral space group R32 (Z equals 3) in a cell of dimensions a equals b equals 5.001 angstrom, c equals 24.378 angstrom and V equals 528.01 angstrom3. K2Al2B2O7 crystallizes in the trigonal space group P321 (Z equals 3) in a cell of dimensions a equals b equals 8.530 angstrom, c equals 8.409 angstrom and V equals 529.9(2)angstrom3. The theoretical calculations and the measurement of nonlinear optical effect indicates that the two crystals are phase-matchable with the nonlinear optical coefficient d11 equals 0.75 pm/V for BaAl2B2O7 and d11 equals 0.48 pm/V for K2Al2B2O7. The birefringence of BaAl2B2O7 is (Delta) n equals 0.063 and 0.068 for K2Al2B2O7.

New development of nonlinear optical crystals for the ultraviolet region with molecular engineering

their frequency response were measured (Fig. 3). Frequency response improves with decreasing modulation-region length (e) , and large bandwidth (fMB: electrical) of 33 GHz is obtained for e = 50 p,m. In conclusion, we have proposed and demonstrated an MQW EA modulator integrated with waveguides. This modulator achieves a higher-speed modulation with a shorter modulation-region, while it is still long enough for easy fabrication and packaging. A fabricated 1-mm-long modulator with a 50-pm-long modulation-region showed a low insertion loss of 7 dB and a large bandwidth of 33 GHz.

Computer-assisted design for nonlinear optical crystals

Based on the anionic group theory, a computer-assisted material design system (CAMDS) has been developed and shown to be a highly efficient means for discovering nonlinear optical crystals. In this method, important optical properties of the target compounds (borates, for example), such as the dij coefficients, refractive indices and energy bandgap, are calculated so that a prior evaluation can be made before experiments. The results have given a meaningful guide to ensuring experiments, which have led to our discoveries of KBBF (KBe2BO3F2) and SBBO (Sr2Be2B2O7) in previous years followed by other members of the SBBO family in recent years. On the other hand, the system can also be used to evaluate the dij coefficients of the borate NLO crystals discovered recently whose dij coefficients have not been determined from experiment.