There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

The theory of quasi-phase-matched second-harmonic generation is presented in both the space domain and the wave vector mismatch domain. Departures from ideal quasi-phase matching in periodicity, wavelength, angle of propagation, and temperature are examined to determine the tuning properties and acceptance bandwidths for second-harmonic generation in periodic structures. Numerical examples are tabulated for periodically poled lithium niobate. Various types of errors in the periodicity of these structures are then analyzed to find their effects on the conversion efficiency and on the shape of the tuning curve. This analysis is useful for establishing fabrication tolerances for practical quasi-phase-matched devices. A method of designing structures having desired phase-matching tuning curve shapes is also described. The method makes use of varying domain lengths to establish a varying effective nonlinear coefficient along the interaction length. >

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Quasi-phase-matched second harmonic generation: tuning and tolerances

The current status of lithium-niobate external-modulator technology is reviewed with emphasis on design, fabrication, system requirements, performance, and reliability. The technology meets the performance and reliability requirements of current 2.5-, 10-, and 40-Gb/s digital communication systems, as well as CATV analog systems. The current trend in device topology is toward higher data rates and increased levels of integration. In particular, multiple high-speed modulation functions, such as 10-Gb/s return-to-zero pulse generation plus data modulation, have been achieved in a single device.

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A review of lithium niobate modulators for fiber-optic communications systems

Domains in ferroelectrics were considered to be well understood by the middle of the last century: They were generally rectilinear, and their walls were Ising-like. Their simplicity stood in stark contrast to the more complex Bloch walls or N\'eel walls in magnets. Only within the past decade and with the introduction of atomic-resolution studies via transmission electron microscopy, electron holography, and atomic force microscopy with polarization sensitivity has their real complexity been revealed. Additional phenomena appear in recent studies, especially of magnetoelectric materials, where functional properties inside domain walls are being directly measured. In this paper these studies are reviewed, focusing attention on ferroelectrics and multiferroics but making comparisons where possible with magnetic domains and domain walls. An important part of this review will concern device applications, with the spotlight on a new paradigm of ferroic devices where the domain walls, rather than the domains, are the active element. Here magnetic wall microelectronics is already in full swing, owing largely to the work of Cowburn and of Parkin and their colleagues. These devices exploit the high domain wall mobilities in magnets and their resulting high velocities, which can be supersonic, as shown by Kreines' and co-workers 30 years ago. By comparison, nanoelectronic devices employing ferroelectric domain walls often have slower domain wall speeds, but may exploit their smaller size as well as their different functional properties. These include domain wall conductivity (metallic or even superconducting in bulk insulating or semiconducting oxides) and the fact that domain walls can be ferromagnetic while the surrounding domains are not.

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Domain wall nanoelectronics

Blue light was generated in a LiNbO/sub 3/ channel waveguide by frequency doubling radiation from a laser diode in a guided to guided wave interaction, utilizing first-order quasi-phase-matching in a periodically domain inverted structure. A fabrication method that does not depend on the use of titanium was used. A periodic pattern of silicon oxide on the positive c-face of LiNbO/sub 3/ was used in combination with a heat treatment to achieve a periodic outdiffusion and domain reversal in the surface layer. A channel guide was subsequently formed by proton exchange. >

Blue light generated by frequency doubling of laser diode light in a lithium niobate channel waveguide

The optical biaxial nature of crystals in the potassium titanyl phosphate (KTP) family result in anisotropic transmission that depends on the polarization direction of the transmitted radiation with respect to the fundamental crystal axes. Knowledge of the polarization-dependent crystal transmission is important for all wavelength-conversion applications and in particular is the only limitation on possible combinations of wavelengths when one uses the quasi-phase-matching techniques recently developed for the KTP family materials. In this study, polarized transmission spectra of KTiOPO4 (KTP), RbTiOPO4, RbTiOAsO4 (RTA), and KTiOAsO4 were measured over the 0.3–6-µm wavelength range with a spectrophotometer and a Fourier-transform infrared spectrometer. Seven crystal samples were studied, including four samples of KTP crystals of different origins. Variations in spectral transmission on the short- and long-wavelength edges, as well as visible-wavelength transmission and OH- absorption properties, are presented and discussed. The transmission of one sample of KTP and of RTA was also measured before and after periodic electric field poling.

Transmission measurements in KTP and isomorphic compounds

We show that the photodarkening resistivity of ytterbium-doped fiber lasers can be greatly improved by cerium codoping. It is suggested that the coexistence of the redox couple Ce(3+)/Ce(4+) in the glass provides means for trapping both hole- and electron-related color centers that are responsible for the induced optical losses in Yb-doped fiber lasers.

Improved photodarkening resistivity in ytterbium-doped fiber lasers by cerium codoping

A new strong erbium laser glass (SELG) based on a boro-alumo-phosphate composition is reported. We discuss the synthesis and chemical properties together with spectroscopic and thermo-mechanical da ...

Development and characterization of Yb-Er laser glass for high average power laser diode pumping

A method to produce periodically domain-inverted channel waveguides in LiNbO/sub 3/ is reported. With this type of waveguide, using quasi-phase matching (QPM), arbitrary wavelengths can be frequency doubled by choosing the appropriate period. It is concluded that, with improved fabrication methods, it will be possible to generate milliwatts of blue light with a diode laser as pump, which is of considerable interest. >

Fredrik Laurell

Papers

Blue light generated by frequency doubling of laser diode light in a lithium niobate channel waveguide

Transmission measurements in KTP and isomorphic compounds

Improved photodarkening resistivity in ytterbium-doped fiber lasers by cerium codoping

Development and characterization of Yb-Er laser glass for high average power laser diode pumping

Fabrication of periodically domain-inverted channel waveguides in lithium niobate for second harmonic generation