In 1998, Bender and Boettcher found that a wide class of Hamiltonians, even though non-Hermitian, can still exhibit entirely real spectra provided that they obey parity-time requirements or PT symmetry. Here we demonstrate experimentally passive PT-symmetry breaking within the realm of optics. This phase transition leads to a loss induced optical transparency in specially designed pseudo-Hermitian guiding potentials.

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The longitudinal (LO) and transverse (TO) A1 vibrational modes have been measured between 30 and 1200 cm−1 as a function of temperature (30–1240 K) for both KTiOPO4 (KTP) and KTiOAsO4 (KTA). KTP and KTA exhibit an obviously different Raman spectra in the frequency region 400–650 cm−1 (with respect to KTA). This middle-frequency difference is attributed to the substitution ions in XO4 group (X=P or As) modifing the force constant of crystal. The relative intensities of the low-frequency bands increase dramatically with increasing temperature due to high mobility of K+ ion. There is no typical soft-mode like behavior in the measured frequency range. A higher symmetric structure taking place above Tc has been confirmed by the disappearance of the A1g(LO) stretching modes of TiO6 group. Comparison of each frequency belonging to the symmetry A1, A2, B1, and B2 measured along the [110] phonon direction shows complex difference. The vibrational frequencies of various symmetries were also obtained.

We show how to transform multiple real-time photorefractive solitons into permanent two-dimensional single-mode waveguides impressed into the crystalline lattice of the host material. We experimentally demonstrate two specific configurations of such fixed multiple waveguides: directional couplers and multiple beam splitters.

The morphological and optical properties of In0.2Ga0.8As/GaAs quantum wells grown on various substrates are investigated for possible application to superluminescent diodes. The In0.2Ga0.8As/GaAs quantum wells are grown by molecular beam epitaxy on GaAs (100), (210), (311), and (731) substrates. A broad photoluminescence emission peak (~950 nm) with a full width at half maximum (FWHM) of 48 nm is obtained from the sample grown on (210) substrate at room temperature, which is over four times wider than the quantum well simultaneously grown on (100) substrate. On the other hand, a very narrow photoluminescence spectrum is observed from the sample grown on (311) with FWHM = 7.8 nm. The results presented in this article demonstrate the potential of high-index GaAs substrates for superluminescent diode applications.