In order to enable optical systems to operate with a high degree of compactness and reliability it is necessary to combine large number of optical functions in small monolithic structures. A development, somewhat reminiscent of that that took place in Integrated Electronics, is now beginning to take place in optics. The initial challenge in this emerging field, known appropriately as "Integrated Optics", is to demonstrate the possibility of performing basic optical functions such as light generation, coupling, modulation, and guiding in Integrated Optical configurations. The talk will review the main theoretical and experimental developments to date in Integrated Optics. Specific topics to be discussed include: Material considerations, guiding mechanisms, modulation, coupling and mode losses. The fabrication and applications of periodic thin film structures will be discussed.

Integrated optics

Almost three decades ago, the field of nonlinear optics evolved with the discovery of lasers. In the beginning, nonlinear optical (NLO) phenomena were investigated in inorganic materials, leading to the development of traditional NLO materials such as lithium niobate, potassium titanyl phosphate, quartz and gallium arsenide. In the 1970s, the importance of organic materials was realized because of the promise of large NLO responses, high laser damage thresholds, fast optical responses, architectural flexibility and ease of fabrication. Following work with organic materials, the scrutiny of organometallics also began recently. In organometallics, the metal-ligand bonding is expected to display large molecular hyperpolarizability because of the transfer of electron density between the metal atom and the conjugated ligand system. In organometallics, the diversity of central metals, oxidation states and ligands fosters in optimization of the charge-transfer interactions. Keeping this in view, second- and third-order NLO properties of organometallics have been reviewed here, highlighting new materials that are emerging. Organometallics may have a wide range of applications in opto-electronics including integrated optics, optical switching, telecommunications, bistability and modulation.

Organometallic materials for nonlinear optics

The photorefractive properties of single crystals of the organic material 2-cyclooctylamino-5-nitropyridine doped with 7,7,8,8-tetracyanoquinodimethane are investigated with two-wave mixing experiments. Refractive-index gratings with an amplitude of up to 1.8 × 10−6 could be recorded for grating vectors along the twofold axis. The phase gratings showed a phase shift of between 20° and 70° with respect to the intensity grating. An experimental procedure for determining phases and amplitudes of absorption and phase gratings is discussed in detail.

Photorefractive gratings in the organic crystal 2-cyclooctylamino-5-nitropyridine doped with 7,7,8,8-tetracyanoquinodimethane

A comparison is made between the second‐order polarizabilities of nitropyridine derivatives determined with two different methods: electric‐field‐induced second‐harmonic generation (EFISH) and a solvatochromic method. Both techniques yield the same values within the experimental errors, showing that the main contribution of the microscopic nonlinearity arises from a single intramolecular charge‐transfer transition. Based on the quantum‐mechanical two‐level model, the solvatochromic method also yields important molecular parameters, such as transition and excited‐state dipole moments. The second‐order polarizabilities determined with the EFISH method are shown to follow the theoretical two‐level dispersion.

Second‐order polarizabilities of nitropyridine derivatives determined with electric‐field‐induced second‐harmonic generation and a solvatochromic method: A comparative study

Photorefractive effects observed in the organic crystal 2-cyclooctylamino-5-nitropyridine doped with 7,7,8,8-tetracyanoquinodimethane

A new nonlinear optical crystal 2‐cyclooctylamino‐5‐nitropyridine (COANP) with point group symmetry mm2 has been grown by a temperature difference solution growth technique. Its linear and nonlinear optical properties have been investigated. The refractive indices na =1.702, nb =1.847, and nc =1.681 (λ=550 nm) and the nonlinear optical susceptibilities d31 and d33 (λω =1.06 μm) have been determined. Type I phase matching for Nd:YAG lasers (λ=1.06 μm) has been demonstrated for the configuration using a combination of d31 and d32 by angle tuning. A peak efficiency η=P2ω/Pω =3.6% has been observed with a 0.90‐mm‐thick crystal and a fundamental power Pω =560 W.

2‐cyclooctylamino‐5‐nitropyridine, a new nonlinear optical crystal with orthorhombic symmetry

2-Cyclooctylamino-5-nitropyridine (COANP) is a new nonlinear optical crystal with point group symmetry mm2. It has been grown by a temperature difference solution growth technique. Its linear and nonlinear optical properties have been investigated. The refractive indices na = 1.699, nb = 1.847 and nc = 1.681 (at ? = 550 nm) and the nonlinear optical susceptibilities d31 and d33 (kw = 1.06 p.m) have been determined. Type I phase matching is possible at 1.064 Ilm. A peak conversion efficiency 71 = P2co/Pco = 3.6% has been observed with a 0.90 mm thick crystal and a fundamental power Pw = 560 W.

D. Dobrowolski

Papers

2‐cyclooctylamino‐5‐nitropyridine, a new nonlinear optical crystal with orthorhombic symmetry

2-Cyclooctylamino-5-nitropyridine, a new nonlinear optical crystal with orthorhombic symmetry