Peter M. Ranon

Efficient poling and thermal crosslinking of randomly bonded main‐chain polymers for stable second‐order nonlinearities

We report our second‐harmonic generation study of a new crosslinked main‐chain polymer system for second‐order nonlinear optics (NLO). In this unique polymer system, the rigid second‐order NLO chromophores are randomly bonded in the main chain with flexible links between the rigid chromophores to allow electric poling at or above the glass transition temperature. A thermal crosslinker is added to crosslink the polymer backbone during electric poling. The combination of the flexible chain segments and crosslinking allows us to achieve a high degree of alignment (〈cos3θ〉≊0.34) and long‐term (≳2500 h) temporal stability of the nonlinearities.

Photorefractivity in vanadium-doped ZnTe

We report on the observation of photorefractivity in vanadium‐doped zinc telluride in the 0.63–1.3‐μm‐wavelength range. Photorefractive two‐beam coupling, along with photoluminescence and absorption spectroscopy, are used to characterize a vapor‐phase transfer‐grown crystal. At 0.63 μm, we measure a grating‐formation time of 15 μs at an intensity of 4.7 W/cm2, which is comparable to GaAs at 1.06 μm, and is faster than photorefractive cubic and ferroelectric oxides.

Enhancement of the photorefractive gain at 1.3–1.5 μm in CdTe using alternating electric fields

We report large enhancement of the two-beam-coupling gain in vanadium-doped cadmium telluride. We used the applied-alternating-field method with square and sinusoidal waveforms. With nominally square waveforms gain coefficients in excess of 10 cm−1 have been measured, which significantly exceed the absorption coefficient of 2 cm−1 for our sample. The results agree well with theory when the major effects of the ac waveform shape, internal field screening, and large-signal effects are taken into account.

Improving the thermal stability by anchoring both ends of chromophores in the side‐chain nonlinear optical polymers

We report our study of a new side‐chain second‐order nonlinear optical polymer in which both ends of the chromophores are anchored by thermal crosslinking during electric field poling. A sizable second‐harmonic generation coefficient d33 of 60 pm/V was measured at 1064 nm fundamental wavelength with corona poling. After anchoring both ends of the chromophores, the thermal stability of the poling alignment was greatly improved and the nonlinear optical properties were shown to be stable at both 90 and 125 °C. Channel waveguides were defined in the polymer thin films by reactive ion etching.

Waveguide photonic devices made from thermally crosslinked second-order nonlinear optical polymers

A number of new thermally crosslinkable second-order nonlinear optical polymers have been developed and characterized. These polymers are designed for stable nonlinear optical activities since both ends of the rod-like chromophores are locked into a polymer matrix by covalent bonds. Sizable nonlinearities were measured in these polymers and the thermal stability of both main chain and side chain polymers were improved significantly by thermally induced crosslinking. These thermosetting polymers, with the chromophores either included in the main chain or as side chain pendants, have been used in a number of device applications. Waveguide structures can be defined in these polymers by reactive ion etching or ultraviolet bleaching. Thin film integrated optical devices, such as high frequency electro-optic modulators and birefringent directional couplers have been fabricated with reactive ion etching and photo bleaching methods. Waveguide fabrication techniques for multi-layer structures are discussed in detail.

Techniques for ultrastructure synthesis: stabilization of large second-order optical nonlinearities of poled polymers

Ultrastructure synthesis techniques for stabilization of large second order optical nonlinearities of poled polymers are reviewed. These techniques include covalent attachment of chromophores onto polyimide backbones, use of double-end crosslinkable chromophores, crosslinking of main-chain polymers with chromophores as polymer backbone components, and in-situ poling and polymerization of chromophores with multiple functionalities. By using these techniques, second harmonic generation coefficients, measured at 1064 nm wavelength, on the order of 10-7 esu and long term stability of optical nonlinearity at 90 - 125

New crosslinkable polymers with second-order nonlinear optical chromophores in the main chain

DEGC have been realized.

Stabilization of the dipole alignment of poled nonlinear optical polymers by ultrastructure synthesis

We have developed a new class of main-chain second-order nonlinear optical (NLO) polymers using well-developed condensation polymerization methods. In these polymers, the NLO chromophore dipoles are expected to be randomly arranged along the polymer backbone (i.e., the dipoles can be head-to-tail, head-to-head, or tail-to-tail). For comparison, a side-chain polymer having virtually the same chromophore as a pendant has also been prepared. The effect of variation in polymer structure on the second-order NLO properties and the effect of crosslinking on the stability of poling-induced macroscopic order are studied. Our results demonstrate that the random main-chain, second-order NLO polymers can be efficiently poled, yielding (chi) (2) as high as 300 pm/V. Long-term temporal stability of the poling- induced order (e.g., no significant NLO decay is observed for more than 2000 hours) can be realized by crosslinking the polymer backbone.