Optical microresonators have recently attracted a growing attention in the photonics community. 1 Their applications range from quantum electro-dynamics to sensors and filtering devices for optical telecommunication systems, where they are likely to become an essential building block. 2 The integration of nonlinear and electro-optical properties in the resonators represents a very stimulating challenge, as it would incorporate new and more advanced functionality. Lithium niobate is an excellent candidate material, being an established choice for electro-optic and nonlinear optical applications. Here we report on the first realization of optical microring resonators in submicrometric thin films of lithium niobate. The high index contrast films are produced by an improved crystal ion slicing and bonding technique using benzocyclobutene. The rings have radius R = 100 µm and their transmission spectrum has been tuned using the electro-optic effect. These results open new perspectives for the use of lithium niobate in chip-scale integrated optical devices and nonlinear optical microcavities.The established use of wavelength division multiplexed (WDM) for local area network systems has raised the demand for new filtering and switching functions. 3 In order to integrate these devices on a wafer scale, whispering gallery mode microresonators represent the most compact and efficient solution. They consist of a bus waveguide evanescently coupled to a micrometer-size ring resonator; the characteristic size-dependent frequency spectrum of the ring allows only selected wavelength channels to be transmitted or shifted to another waveguide. Small radii allow a large free spectral range -i.e. large separation between the filtered channels -but increase the propagation bending losses, 4 which can compromise the quality factor Q -i.e. the wavelength selectivity -of the device. To overcome this limitation, high refractive index contrast between the ring core and the surrounding materials is mandatory. A second, very important, requirement relates to the tunability. The possibility to electrically control the transmission spectrum, via electro-optic effect, would allow extremely compact and ultrafast modulation and switching. By integrating arrays of microring resonators on a single optical chip, the realization of complex functions would be feasible. 5 Besides, large-Q resonators based on non centro-symmetric materials would exploit the high amount of stored energy for enhancing the efficiency of nonlinear optical phenomena. 6 Several examples of microring resonators have been proposed and successfully realized in the last years in a variety of materials like semiconductors, 7-10 silica 11 and polymers. 12,13 The advanced structuring technology in semiconductor materials enables the realization of very high-Q resonators even for radii as small as 10 µm. Silicon-based resonators can be tuned by electrically-driven carriers arXiv:0705.2392v1 [physics.optics]

No abstract

We report on a technique for the fabrication of ridge optical waveguides on top of β-BaB2O4 (BBO) crystals. The BBO crystals were first implanted by He+ ions to form planar optical waveguides. In the second step, the femtosecond laser ablation technique was employed for micromachining of ridge-type optical waveguides. A thorough study of material-specific ablation parameters for BBO has been performed in order to achieve ablated structures with smooth sidewalls. A further process of Ar+ ion smoothing in a plasma chamber was used to reduce the sidewall roughness of the ablated ridges from 75 to 35 nm root mean square. We demonstrated optical waveguiding in these femtosecond-ablated plasma-treated waveguides and measured total propagation losses of less than 10 dB∕cm at 532 nm, making them suitable for nonlinear- and electro-optical applications.

In this paper, numerical algorithms for extraction of optoelectronic material and device parameters in organic light-emitting devices (OLEDs) are presented and tested for their practical use. Of particular interest is the extraction of the emission profile and the source spectrum. A linear and a nonlinear fitting method are presented and applied to emission spectra from OLEDs in order to determine the shape of the emission profile and source spectrum. The motivation of the work is that despite the existence of advanced numerical models for optical and electronic simulation of OLEDs, their practical use is limited if methods for the extraction of model parameters are not well established. Two fitting methods are presented and compared to each other and validated on the basis of consistency checks. Our investigations show the impact of the algorithms on the analysis of realistic OLED structures. It is shown that both fitting methods p form reasonably well, even if the emission spectra to be analyzed are noisy. In some cases the nonlinear method performs slightly better and can achieve a perfect resolution of the emission profile. However, the linear method provides the advantage that no assumption on the mathematical shape of the emission profile has to be made.

We compare the photochemical stability of the nonlinear optical chromophore configurationally locked polyene 2-{3-[2-(4-dimethylaminophenyl)vinyl]-5,5-dimethylcyclohex-2-enylidene} malononitrile (DAT2) embedded in a polymeric matrix and in a single-crystalline configuration. The results show that, under resonant light excitations, the polymeric compound degrades through an indirect process, while the DAT2 crystal follows a slow direct process. We show that chromophores in a crystalline environment exhibit three orders of magnitude better photostability as compared to guest-host polymer composites.