Ilias Liakatas

Importance of intermolecular interactions in the nonlinear optical properties of poled polymers

A series of phenylbithiophene stilbenes and phenyltetraenes were synthesized and their first-order molecular hyperpolarizabilities determined. Optical nonlinearities up to μβo=9300×10−69 C m5/V were measured at 1907 nm. We show that intermolecular interactions have a large influence on the optical nonlinearity of the molecules in solution and in guest-host polymers with polymethylmethacrylate and polyquinoline as the host. We propose the use of a bulky donor group and a side chain perpendicular to the molecule’s conjugate bridge to reduce aggregation. Electro-optic coefficients as high as r33=30 pm/V at 1.55 μm in polymethylmethacrylate with 25 wt % chromophore loading were measured.

Second-Order Nonlinear Optical Organic Materials: Recent Developments

This chapter presents an overview of the current status of second-order nonlinear optical organic materials for their use in photonic applications such as optical frequency converters and electro-optic modulators. Special emphasis is placed on the material aspects and a thorough discussion of presently available substances. The potential of organic materials for third-order nonlinear optical applications has been presented in detail in Chap. 2. Earlier reviews of organic nonlinear optical materials covering different physical and material aspects can be found in [3.1–8].

Organic Materials for Second-Order Nonlinear Optics

Organic materials have become of great importance with regard to their nonlinear optical and electro-optic properties. They have attracted attention for applications in areas such as efficient frequency-conversion and high-speed light modulation. As a special feature their macroscopic properties arise from the properties of the constituent molecules. There are several possibilities to arrange these molecules macroscopically. The most common forms are single crystals [1-5], polymers [2, 6], and Langmuir-Blodgett films [7]. Besides these cases there exist other interesting concepts such as e.g. molecular beam deposition for the preparation of thin films. Since the macroscopic nonlinearity arises from the constituent molecules, the optimization of a material for a certain application consists of two steps. On the one hand, the nonlinear optical properties of the molecules have to be maximized and, on the other hand, the arrangement of these molecules in crystals or thin films has to be optimized.

Photochemical stability of highly nonlinear optical bithiophene chromophores

Abstract The photochemical stability of highly nonlinear optical bithiophene chromophores is investigated. Experiments in guest–host systems were performed in polymethylmethacrylate (PMMA) hosts for several differently modified bithiophenes and compared to Disperse Red 1 (DR1). The photochemical stability at visible wavelengths indicates that these chromophores are excellent candidates for electro-optic applications. Furthermore, one of the bithiophene chromophores was also investigated in the infrared region up to telecommunication wavelengths.

Stilbazolium based zwitterionic chromophores for electro-optic polymers

Abstract A series of stilbazolium based zwitterionic chromophores was synthesized. They have very large dipole moment (up to μ = 13x10-29 Cm) and high molecular hyperpolarizability (up to β = 135x10-40 m4V-1). Guest-host polymer thin films of the best molecules were prepared and poled by corona discharge. Values of the nonlinear optical coefficient (d31 = 0.7 pm/V. at γ = 1.545 nm) at molecular concentrations of 5x1019 m-3, comparable to that of Disperse Red 1, were obtained. The good molecular characteristics and macroscopic performance of these chromophores combined with their good thermal stability make them promising candidates for side-chain electro-optic polymers.

Polymer based electro-optic inline fiber modulator

Abstract Poled organic polymer films show great promise for use in integrated photonic devices such as amplitude or phase modulators for telecommunication. We use these polymers in a novel, low loss electro-optic inline fiber modulator. The modulator consists of a fiber half coupler, i.e. a curved fiber which is incorporated into a glass block and polished down close to the core. The coupler is coated with a semitransparent gold electrode, a thin film of our highly electro-optic polymer and an upper silver electrode. The light in the fiber can evanescently couple into the polymer overlay depending on the effective refractive index matching between polymer and fiber core which can be modulated through the electro-optical effect. Preliminary results of our first inline fiber modulators indicate a bandwidth of 100 MHz

Highly efficient and stable bithiophene-based nonlinear optical chromophores for polymer electro-optic applications

Summary form only given. The continuous interest in poled electro-optic polymers for device applications in information processing and telecommunications has resulted in the development of several types of second-order nonlinear optical chromophores that are highly efficient, as characterized by their large scalar product of dipole moment (/spl mu/) and the molecular first-order hyperpolarizability (/spl beta/). It has been shown that incorporation of thiophene rings into the conjugated units can greatly enhance /spl mu//spl beta/ while permitting a high thermal stability. According to the general guideline for optimization of /spl mu//spl beta/, we reason that using bithiophene moieties, having a longer conjugation length than the monothiophene ones, should further increase /spl mu//spl beta/ while maintaining the thermal, chemical, and photochemical stability.

Highly polar molecular crystals for electro-optic applications

Abstract We report on a series of new acentric 4-nitrophenylhydrazone derivatives which bear more than one hydroxy or methoxy electron donating group whose large molecular nonlinear optical properties were characterized with semi-empirical calculations and hyper-Rayleigh scattering. The second harmonic powder test results of several compounds showed large signals, two to three orders of magnitude larger than urea, which make these materials potentially interesting for nonlinear optics. Crystals of one of these new molecules (3,4-dihydroxybenzaldehyde-4-nitrophenylhydrazone, 3,4-DHNPH) are very promising for electro-optics. The properties are discussed in detail and a comparison with some of the best existing crystals for electro-optic applications is given