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 nitride semiconductor device including a light emitting device comprises a n-type region of one or more nitride semiconductor layers having n-type conductivity, a p-type region of one or more nitride semiconductor layers having p-type conductivity and an active layer between the n-type region and the p-type region. In such devices, there is provided with a super lattice layer comprising first layers and second layers which are nitride semiconductors having a different composition respectively. The super lattice structure makes working current and voltage of the device lowered, resulting in realization of more efficient devices.

Nitride semiconductor device

A lithographic apparatus configured to project a patterned beam of radiation onto a target portion of a substrate is disclosed. The apparatus includes a first radiation dose detector and a second radiation dose detector, each detector comprising a secondary electron emission surface configured to receive a radiation flux and to emit secondary electrons due to the receipt of the radiation flux, the first radiation dose detector located upstream with respect to the second radiation dose detector viewed with respect to a direction of radiation transmission, and a meter, connected to each detector, to detect a current or voltage resulting from the secondary electron emission from the respective electron emission surface.

Lithographic apparatus, and device manufacturing method

A nitride semiconductor laser device has an improved stability of the lateral mode under high output power and a longer lifetime, so that the device can be applied to write and read light sources for recording media with high capacity. The nitride semiconductor laser device includes an active layer, a p-side cladding layer, and a p-side contact layer laminated in turn. The device further includes a waveguide region of a stripe structure formed by etching from the p-side contact layer. The stripe width provided by etching is within the stripe range of 1 to 3 μm and the etching depth is below the thickness of the p-side cladding layer of 0.1 μm and above the active layer. Particularly, when a p-side optical waveguide layer includes a projection part of the stripe structure and a p-type nitride semiconductor layer on the projection part and the projection part of the p-side optical waveguide layer has a thickness of not more than 1 μm, an aspect ratio is improved in far field image. Moreover, the thickness of the p-side optical waveguide layer is greater than that of an n-side optical waveguide layer.

Nitride semiconductor laser device

A broadband wire grid polarizer (400) for the visible spectrum has a plurality of elongated elements (1240) supported on a substrate (1210). A region (1250) having a lower refractive index than the refractive index of the substrate is disposed between the elements and the substrate to reduce the longest wavelength at which resonance occurs.

Broadband wire grid polarizer for the visible spectrum

Frequency doubling of a 684 nm laser diode in a first-order periodically poled LiTaO3 is presented Controlling the side growth of the domain inverted region during high-voltage pulse application, a uniform nonlinear grating with a period of 17 μm and 50% duty cycle was fabricated over 10 mm interaction length in a 150 μm thick LiTaO3 substrate A 342 nm wavelength of harmonic ultraviolet light was generated in a single pass through the domain-inverted structure

Generation of ultraviolet light by frequency doubling of a red laser diode in a first-order periodically poled bulk LiTaO3

A light generating apparatus includes: a submount; a semiconductor laser chip mounted on the submount; a substrate which is mounted on the submount and includes an optical waveguide; and a substance having a predetermined thickness which is disposed between the semiconductor laser chip and the substrate. In an oscillation wavelength stabilizing apparatus for a light source, the light source is a semiconductor laser which includes: an active region for providing gain; and a distributed Bragg reflection (DBR) region for controlling an oscillation wavelength. The apparatus includes a control section which monotonously varies, in a first direction, a DBR current to be input to the DBR region while detecting the oscillation wavelength of an output light of the semiconductor laser so as to detect a DBR current value I o corresponding to a predetermined wavelength value, and then monotonously varies the DBR current in a second direction which is opposite the first direction beyond the detected value I o , and then monotonously varies the DBR current in the first direction again to set the DBR current at the detected value I o , thereby fixing the oscillation wavelength of the semiconductor laser chip at the predetermined wavelength value.

Optical apparatus and method for producing the same

We report high power and stable blue‐light generation by frequency doubling a laser diode, stabilized by a grating feedback technique, in a periodically domain‐inverted LiTaO3 waveguide. Due to the deep domain‐inverted regions and strong waveguide confinement formed by proton‐exchange and a quick heat treatment, high efficiency second harmonic generation (SHG) has been obtained. Locking the oscillation wavelength of a laser diode through the waveguide by a grating feedback technique, 8 mW of stable blue SHG has been demonstrated.

High power blue light generation by frequency doubling of a laser diode in a periodically domain‐inverted LiTaO3 waveguide

A theoretical analysis of the power spectra of diffusers with a series of pseudorandom phase sequences is presented. General equations describing three typical cases of power spectra are derived by making use of the constraints assumed. Profiles of the power spectra showed good agreement with the results of numerical computation using the fast-Fourier-transform algorithm. The images of the diffusers through a double-diffraction optical system were also evaluated by computer simulation. The advantage of pseudorandom phase sequences over random phase sequences is discussed from the viewpoint of signal-to-noise ratio.

Diffuser with pseudorandom phase sequence

A laser beam as fundamental waves which is emitted from a distribution Bragg reflection (DBR) semiconductor laser is incident on an optical waveguide of a light wavelength conversion device in which domain-inverted regions and the optical waveguide are formed in an LiTaO3 substrate. The wavelength of the incident laser beam is then converted so as to obtain higher harmonic waves such as blue light. In the conversion, a drive current to be applied to a DBR portion of the DBR semiconductor laser is changed so as to change an oscillating wavelength of the DBR semiconductor laser, thereby matching the oscillating wavelength with a phase-matched wavelength of the light wavelength conversion device. Thus, the generation of the harmonic waves to be output is stably controlled.

Makoto Kato

Papers

Generation of ultraviolet light by frequency doubling of a red laser diode in a first-order periodically poled bulk LiTaO3

Optical apparatus and method for producing the same

High power blue light generation by frequency doubling of a laser diode in a periodically domain‐inverted LiTaO3 waveguide

Diffuser with pseudorandom phase sequence

Method for stabilizing output of higher harmonic waves and short wavelength laser beam source using the same