A device includes two or more waveguide portions that are adjacent to each other, and each of the two or more waveguide portions includes a first n-doped semiconductor structure and a p-doped semiconductor structure in contact with the first n-doped semiconductor structure at a bottom surface and two lateral walls on opposite ends of the first n-doped semiconductor structure. The device includes an undoped semiconductor structure in contact with each of the p-doped semiconductor structures and free of contact with each of the first n-doped semiconductor structures, and the undoped semiconductor structure includes an optical waveguide core embedded within the undoped semiconductor structure. The device includes a second n-doped semiconductor structure in contact with the undoped semiconductor structure and free of contact with each of the first n-doped semiconductor structures and the p-doped semiconductor structures.

A photonic chip. In some embodiments, the photonic chip includes a waveguide; and an optically active device comprising a portion of the waveguide. The waveguide may have a first end at a first edge of the photonic chip; and a second end, and the waveguide may have, everywhere between the first end and the second end, a rate of change of curvature having a magnitude not exceeding 2,000/mm.sup.2.

A semiconductor optical device may include a semiconductor substrate; a compound semiconductor layer on the semiconductor substrate; an additional insulating film on the pedestal portion of the compound semiconductor layer, the additional insulating film having an upper surface and a side surface at an inner obtuse angle between them; a passivation film covering the compound semiconductor layer and the additional insulating film except at least part of the mesa portion, the passivation film having a protrusion raised by overlapping with the additional insulating film; a mesa electrode on the at least part of the mesa portion; a pad electrode on the passivation film within the protrusion; and an extraction electrode on the passivation film, the extraction electrode being continuous within and outside the protrusion, the extraction electrode connecting the pad electrode and the mesa electrode, the extraction electrode being narrower in width than the pad electrode.

In a semiconductor light modulator having a multiple quantum well structure, a light spot size converter element provided in a light input/output section is easily and accurately manufactured. At least one layer of a compound semiconductor layer containing a P element is inserted into a desired position in the multiple quantum well structure containing an Al element. This layer is smaller than a band gap of a compound semiconductor used in a bather layer of the multiple quantum well.

A cadmium free quantum dot including a semiconductor nanocrystal core and a semiconductor nanocrystal shell disposed on the core, wherein the quantum dot does not include cadmium and includes indium and zinc, the quantum dot has a maximum photoluminescence peak in a red light wavelength region, a full width at half maximum (FWHM) of the maximum photoluminescence peak is less than or equal to about 40 nanometers (nm), an ultraviolet-visible (UV-Vis) absorption spectrum of the quantum dot includes a valley between about 450 nm to a center wavelength of a first absorption peak, and a valley depth (VD) defined by the following equation is greater than or equal to about 0.2, a quantum dot polymer composite including the same, and a display device including the quantum dot-polymer composite:

(Abs.sub.first−Abs.sub.valley)/Abs.sub.first=VD.

An electrical-optical modulator may include one or more optical waveguides to propagate one or more optical signals in a direction of propagation. An optical waveguide of the one or more optical waveguides may include a time delay section, a first modulation section preceding the time delay section in the direction of propagation, and a second modulation section following the time delay section in the direction of propagation. The first modulation section and the second modulation section may be configured to be associated with opposite modulation polarities, and the time delay section may be configured to delay a phase of the one more optical signals relative to the first modulation section. The electrical-optical modulator may include one or more signal electrodes to propagate one or more signals in the direction of propagation in order to modulate the one or more optical signals through electrical-optical interaction.

An electrical-optical modulator may include a first section configured for a first electrical-optical interaction between one or more optical waveguides and one or more signal electrodes. The electrical-optical modulator may include a second section configured to increase or decrease a relative velocity of signals of the one or more signal electrodes to optical signals of the one or more optical waveguides relative to the first section. The electrical-optical modulator may include a third section configured for a second electrical-optical interaction between the one or more optical waveguides and the one or more signal electrodes according to an opposite modulation polarity relative to the first section.

An electro-absorption modulator (EAM) is configured to include an on-chip AC ground plane that is used to terminate the high frequency RF input signal within the chip itself. This on-chip ground termination of the modulation input signal improves the frequency response of the EAM, which is an important feature when the EAM needs to support data rates in excess of 50 Gbd. By virtue of using an on-chip ground for the very high frequency signal content, it is possible to use less expensive off-chip components to address the lower frequency range of the data signal (i.e., for frequencies less than about 1 GHz).

A photonic chip. In some embodiments, the photonic chip includes a waveguide; and an optically active device comprising a portion of the waveguide. The waveguide may have a first end at a first edge of the photonic chip; and a second end, and the waveguide may have, everywhere between the first end and the second end, a rate of change of curvature having a magnitude not exceeding 2,000/mm.sup.2.

A cadmium free quantum dot including a semiconductor nanocrystal core and a semiconductor nanocrystal shell disposed on the core, wherein the quantum dot does not include cadmium and includes indium and zinc, the quantum dot has a maximum photoluminescence peak in a red light wavelength region, a full width at half maximum (FWHM) of the maximum photoluminescence peak is less than or equal to about 40 nanometers (nm), an ultraviolet-visible (UV-Vis) absorption spectrum of the quantum dot includes a valley between about 450 nm to a center wavelength of a first absorption peak, and a valley depth (VD) defined by the following equation is greater than or equal to about 0.2, a quantum dot polymer composite including the same, and a display device including the quantum dot-polymer composite:

(Abs.sub.first−Abs.sub.valley)/Abs.sub.first=VD.