An optical device for a quantum random number generator comprising: a source of phase randomised pulses of light, the source of phase randomised pulses of light further comprising a plurality of gain-switched lasers, each gain-switched laser having an output, and each gain-switched laser being configured to emit a stream of pulses such that the phase of each pulse in the stream of pulses is randomised, and an optical pulse combiner, the optical pulse combiner being configured to receive streams of pulses from the output of each gain-switched laser, combine the streams of pulses with one another into a combined stream of pulses and direct the combined stream of pulses into at least one output of the optical pulse combiner, the at least one output of the optical pulse combiner being the output of the source of phase randomised pulses of light; wherein the source of phase randomised pulses of light is configured such that the streams of pulses of light emitted by the plurality of gain-switched lasers are temporally offset relative to one another, a phase measurement element, the phase measurement element being configured to receive the combined stream of pulses from the output of the source of phase randomised pulses of light; and an optical detector, the optical detector being optically coupled to the phase measurement element.

An optical device is provided that includes an active waveguide having a top electrode and a plurality of layers including a gain layer. Configurations are disclosed for the active waveguide to enable amplification of a guided optical wave profile while preserving a shape of a lateral optical intensity profile of the guided optical wave as the guided optical wave is amplified along the waveguide. The top electrode and/or one or more layers of the active optical waveguide may be tailored to provide a tailored optical gain.

An embodiment semiconductor optical device includes an optical waveguide including a core, and an active layer extending in the waveguide direction of the optical waveguide for a predetermined distance and arranged in a state in which the active layer can be optically coupled to the core. The core and the active layer are arranged in contact with each other. The core is formed of a material with a refractive index of about 1.5 to 2.2, such as SiN, for example. In addition, the core is formed to a thickness at which a higher-order mode appears. The higher-order mode is an E.sub.12 mode, for example.

In an optical device, a first semiconductor layer and a second semiconductor layer are formed to be thinner than a core, an active layer has a shape with an end in a waveguide direction tapers toward a tip end, the first semiconductor layer having a trapezoidal shape with a width thereof decreases toward a side of a third semiconductor layer from a side of the core in a plan view and a width thereof decreases as one end in the waveguide direction recedes from a central portion of the active region, and the second semiconductor layer having a trapezoidal shape with a width thereof decreases toward a side of a fourth semiconductor layer from the side of the core in a plan view and a width thereof decreases as one end in the waveguide direction recedes from the central portion of the active region.

In some embodiments, a semiconductor structure includes: a first epitaxial oxide semiconductor layer; a metal layer; and a contact layer adjacent to the metal layer, and between the first epitaxial oxide semiconductor layer and the metal layer. The contact layer can include an epitaxial oxide semiconductor material. The contact layer can also include a region comprising a gradient in a composition of the epitaxial oxide semiconductor material adjacent to the metal layer, or a gradient in a strain of the epitaxial oxide semiconductor material over a region adjacent to the metal layer.

A direct modulation laser includes a distributed feedback type laser active region and an optical feedback region optically connected to one end of the laser active region in a waveguide direction. The direct modulation laser performs laser oscillation by using photon-photon resonance (PPR) that occurs depending on a frequency difference between a frequency of light generated (oscillated) in the laser active region and a frequency of an FP mode in the optical feedback region.

A semiconductor optical device includes a light emitting layer that emits light in a state of current injection; an optical waveguide in which a width or a thickness in an extending direction (y) of the light emitting layer varies along the extending direction; and a uniform diffraction grating having constant cycle, width and depth, wherein the light emitting layer, the optical waveguide and the uniform diffraction grating are arranged at positions where the light emitting layer, the optical waveguide, and the uniform diffraction grating are optically coupled to one another, the uniform diffraction grating is arranged above the light emitting layer, the optical waveguide is arranged below the light emitting layer, and the optical waveguide includes, in the extending direction, a first portion having a predetermined width, a second portion having a larger width than the width of the first portion, and a third portion having the same width as the width of the first portion.

A semiconductor structure can include a substrate comprising a first in-plane lattice constant, a graded layer on the substrate, and a first region of the graded layer comprising a first epitaxial oxide material comprising a second in-plane lattice constant. The graded layer on the substrate can include (Al.sub.x1Ga.sub.1−x1).sub.y1O.sub.z1, wherein x1 is from 0 to 1, wherein y1 is from 1 to 3, wherein z1 is from 2 to 4, and wherein x1 varies in a growth direction such that the graded layer has the first in-plane lattice constant adjacent to the substrate and a second in-plane lattice constant at a surface of the graded layer opposite the substrate. In some cases, a semiconductor structure includes a first region comprising a first epitaxial oxide material; a second region comprising a second epitaxial oxide material; and the graded region located between the first and the second regions.

The invention relates to a method for fabricating a semiconductor structure. The method comprises fabricating a photonic crystal structure of a first material, in particular a first semiconductor material and selectively removing the first material within a predefined part of the photonic crystal structure. The method further comprises replacing the first material within the predefined part of the photonic crystal structure with one or more second materials by selective epitaxy. The one or more second materials may be in particular semiconductor materials. The invention further relates to devices obtainable by such a method.

An optical device includes a first reflecting section, a second reflecting section, and a confining section. The first reflecting section is constituted of a thin-wire waveguide-type one-dimensional photonic crystal. The second reflecting section is constituted of a thin-wire waveguide-type one-dimensional photonic crystal of which a lattice constant differs from that of the first reflecting section. The confining section is sandwiched between the first reflecting section and the second reflecting section. A Fabry-Perot optical resonator is constituted by the first reflecting section, the confining section, and the second reflecting section.