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

A new crystalline medium for 1.5 μm Yb-Er lasers is proposed: GdCa 4O(BO3)3 (GdCOB). Its melting point allows crystal growth using platinum instead of iridium crucibles. Spectroscopic and laser tes ...

New crystalline material for 1.5 μm lasers : Yb,Er - Activated GdCa 4O(BO3)3

We demonstrate self-compression of 173 fs pulses centered at 1030 nm down to 19.5 fs through electro-optic phase modulation by the phonon-polariton waves generated in a phase-matched intra-pulse difference-frequency mixing.

Self-Compression in Single-Domain KTP at 1 micron in a Normal Dispersion Regime

We investigate experimentally the spectral and angular degrees of freedom of multi-resonant optical parametric generation in hexagonally poled LiTaO 3 and demonstrate access to twin-beam output for either signal or idler waves by pump angle tuning.

Spectral and angular mapping of parametric generation in purely nonlinear lattices

The second-harmonic conversion efficiency within the PPKTP waveguide is investigated using two separate tunable CW Ti:sapphire lasers at 800 nm and 980 nm. Results show strong conversion efficiency which imply that the local damage-induced index modification does not adversely affect the periodic domain structure in the material.

Frequency doubling in femtosecond-written periodically-poled potassium titanyl phosphate waveguides

We demonstrate a tunable narrow-linewidth laser based on a semiconductor optical amplifier and a linearly chirped FBG. High tuning resolution and small power variation over 40 nm tuning range were achieved by optimizing the drive current. © 2019 The Author(s)

Fredrik Laurell

Papers

New crystalline material for 1.5 μm lasers : Yb,Er - Activated GdCa 4O(BO3)3

Self-Compression in Single-Domain KTP at 1 micron in a Normal Dispersion Regime

Spectral and angular mapping of parametric generation in purely nonlinear lattices

Frequency doubling in femtosecond-written periodically-poled potassium titanyl phosphate waveguides

Rapid and Continuously Tunable Narrow Linewidth Fiber Source Based on a SOA and a Linearly Chirped Fiber Bragg Grating