Gerald Meredith

Optical transitions and visible upconversion in Er3+ doped niobic tellurite glass

Er3+ doped Nb2O5–TeO2 (NT) glass suitable for developing optical fiber laser and amplifier has been fabricated and characterized. Intense and broad 1.53 μm infrared fluorescence and visible upconversion luminescence were observed under 975 nm diode laser and 798 nm laser excitation. For 1.53 μm emission band, the full width at half-maximum is 51 nm, the fluorescence lifetime is 2.6 ms, and the quantum efficiency is ∼100%. The maximum emission cross section is 8.52×10−21 cm2 at 1.532 μm, and is higher than the values in silicon and phosphate glasses. Under 798 nm excitation, efficient 531, 553, and 670 nm upconversion emissions are due to two-photon absorption processes. The “standardized” efficiency for the green upconversion light is 9.5×10−4, and this value is comparable to that reported for Er3+/Yb3+ codoped fluoride glasses. Intense visible upconversion fluorescence in Er3+ doped NT glass can be used in color display, undersea communication, and infrared sensor.

Hybrid electro-optic polymer and selectively buried sol-gel waveguides

An approach to utilizing electro-optically (EO) active polymers in hybrid waveguide structures is described and demonstrated. Buried sol-gel waveguides provide a robust basis for planar integrated circuitry, suitable for coupling with optical fibers. By selectively exposing the core of a buried channel guide, overcoating with an EO polymer, and using appropriately tapered transition zones, a guided mode can be made to undergo adiabatic transitions from sol-gel waveguide up into the EO polymer and back. Such a single-mode device was constructed. These transitions were proven via modulation of the emerging wave’s polarization ellipse by application of voltage to the EO polymer.

Photorefractive polymer composite operating at the optical communication wavelength of 1550 nm

A photorefractive polymer composite sensitized at 1550 nm through direct two-photon absorption has been developed. We show an external diffraction efficiency of 3% in four-wave-mixing experiments and perform holographic reconstruction of distorted images utilizing thin-film devices made of this polymer composite. Amongst other potential applications, the demonstration of accurate, dynamic aberration correction through holography in this all-organic photorefractive device presents an alternative to complex adaptive optics systems currently employed in through-air optical communication links.

Large-aperture switchable thin diffractive lens with interleaved electrode patterns

The authors report on a high-performance large-aperture switchable diffractive lens using nematic liquid crystal that can be used as an adaptive eyewear. The odd- and even-numbered ring electrodes are separated in two layers, avoiding the gaps between the neighboring electrodes and allowing high diffraction efficiency. It is easier to avoid shorts between neighboring conductive electrodes and fabricate lenses with larger aperture and smaller feature size. With a four-level phase modulation, a 15mm aperture, 2dpt lens with small aberrations and diffraction efficiency of above 75% could be demonstrated with low operating voltages. The thickness of the liquid crystal is only 5μm. The lens switching time is about 180ms. The on and off states of the electrically controlled lens allows near and distance vision, respectively. The focusing power of the lens can be adjusted to be either positive or negative. This structure can be extended to higher-level phase modulation with even higher efficiencies.

High-performance photorefractive polymer operating at 975 nm

A family of photorefractive polymer composites has been developed that enable high-performance device operation at a wavelength of 975nm. This constitutes a major extension into the near-infrared spectral region for the operation of all-organic photorefractive devices. Utilizing our photorefractive materials, we demonstrate large net two-beam coupling gain of more than 100cm−1, 60% diffraction efficiency in four-wave mixing experiments, and a fast response time of 33ms, at an irradiance of 1W∕cm2.

Hybrid electro-optic polymer/sol–gel waveguide modulator fabricated by all-wet etching process

A simple all-wet-etch process fabricates a hybrid electro-optic-polymer (EOP)/sol–gel waveguide modulator, confining the EOP laterally in the sol–gel overcladding. The structure enables an adiabatic transition between the passive sol–gel waveguides and the active EOP overlayers without lateral radiation. Intensity is confined well in a 0.9-μm-thick EOP overlayer, resulting in a low half-wave voltage (Vπ) due to the larger overlap integral. This lateral confinement technique allowed the reduction of Vπ (at 1550 nm) by a factor of 4.

Polarization-insensitive transition between sol-gel waveguide and electrooptic polymer and intensity modulation for all-optical networks

An intensity modulation using a hybrid electrooptic (EO) polymer/sol-gel straight channel waveguide, useful in the 1550-nm wavelength regime is demonstrated without using Mach-Zehnder interferometric waveguide. The sol-gel waveguide is selectively buried so that a vertical transition into and out of an EO polymer coated on the sol-gel waveguide is arranged. The throughput ratio for transverse electric (TE) and transverse magnetic (TM) modes of the light coupled out of the hybrid waveguide is improved up to 0.9 dB with the help of reduced birefringence of the EO polymer after corona poling. We show that the fabrication process of such hybrid-type waveguides enables production of a phase modulator operating at 1550-nm wavelength. The fabricated straight channel waveguide modulator exhibits stable- and high-intensity modulation efficiency (82%) using a simple cross-polarization setup after the polarization dependence is reduced. We demonstrate an all wet-etching process to fabricate polymeric EO modulators.

Video-rate compatible photorefractive polymers with stable dynamic properties under continuous operation

We report on photorefractive polymer composites that exhibit stable dynamic properties under continuous operation. These materials are based on a bis-triarylamine side-chain polymer matrix with a low ionization potential. The evolution of the response time for exposures up to 4kJ∕cm2 was studied and compared with that obtained in poly(n-vinylcarbazole) (PVK) based composites. In the composites, operational stability is combined with video-rate compatible dynamics, large dynamic range at moderate fields, and long shelf lifetimes.

Dynamic correction of a distorted image using a photorefractive polymeric composite

We demonstrate, for the first time, the dynamic correction of aberrated images in real-time using a polymeric composite with fast response times. The current novel experimental design is capable of restoring a phase aberrated, image carrying laser beam, to nearly its original quality. The ability to reconstruct images in real-time is demonstrated through the changing of the aberrating medium at various speeds. In addition, this technique allows for the correction of images in motion, demonstrated through the oscillatory movement of the resolution target. We also have demonstrated that important parameters of the materials in the study such as response times, diffraction efficiencies and optical gains all retain high figures of merit values under the current experimental conditions.

Fabrication and characterization of low-loss optical waveguides using a novel photosensitive polyimide

This paper presents simple fabrication of optical waveguides using a novel photosensitive polyimide (PSPI). PSPI has a glass transition temperature (Tg) of 330/spl deg/C and is directly patterned by ultraviolet (UV) exposure and wet-chemical development, lending itself to low-cost fabrication techniques. The fabricated waveguides possess low optical absorption at 1.3 and 1.5 /spl mu/m. Single and multimode buried ridge waveguides were made and tested, and a 0.4-dB/cm optical propagation loss is measured at 1.55 /spl mu/m.