An optical modulator includes a first mesa waveguide extending in a first direction, and a second mesa waveguide. The first mesa waveguide includes a p-type first semiconductor layer disposed over a substrate, a core layer disposed over the first semiconductor layer, a p-type second semiconductor layer disposed over the core layer, and an n-type third semiconductor layer disposed over the core layer. The second semiconductor layer and the third semiconductor layer are arranged adjacent to each other in the first direction. An electrode is disposed over the third semiconductor layer. A joining surface between the second semiconductor layer and the third semiconductor layer is inclined with respect to a surface orthogonal to the first direction.

An optical device includes an optical waveguide, a buffer layer that is layered on the optical waveguide, and an opening that is formed at least in the buffer layer above a part near a side surface of the optical waveguide. The optical device further includes an electrode that is layered in the opening and that is configured to apply a signal to the optical waveguide and a silicon layer that is layered on the buffer layer excluding the opening.

Component errors prevent linear photonic circuits from being scaled to large sizes. These errors can be compensated by programming the components in an order corresponding to nulling operations on a target matrix X through Givens rotations X.fwdarw.T.sup.†X, X.fwdarw.XT.sup.†. Nulling is implemented on hardware through measurements with feedback, in a way that builds up the target matrix even in the presence of hardware errors. This programming works with unknown errors and without internal sources or detectors in the circuit. Modifying the photonic circuit architecture can reduce the effect of errors still further, in some cases even rendering the hardware asymptotically perfect in the large-size limit. These modifications include adding a third directional coupler or crossing after each Mach-Zehnder interferometer in the circuit and a photonic implementation of the generalized FFT fractal. The configured photonic circuit can be used for machine learning, quantum photonics, prototyping, optical switching/multicast networks, microwave photonics, or signal processing.

A balanced homodyne detection optical circuit according to the present disclosure is a planar optical waveguide circuit in which a circuit made of an optical waveguide including a dielectric or a semiconductor is formed on a substrate, the balanced homodyne detection optical circuit including an input port of local oscillator light and an input port of measurement light (squeezed light (including excitation light)), wherein a wavelength demultiplexing circuit which demultiplexes only the measurement light is arranged immediately after the input port of measurement light, a 50% multiplexing/demultiplexing circuit is arranged which causes squeezed light having been demultiplexed by the wavelength demultiplexing circuit and the local oscillator light to respectively branch at a branching ratio of 50% and to interfere with each other, and two output ports are arranged to which two outputs from the 50% multiplexing/demultiplexing circuit are guided.

Electro-optic (EO) modulators are disclosed. The EO modulators include a substrate and an EO material layer disposed over the substrate. The EO material layer and the substrate provide an optical waveguide having an optical group velocity (OGV). The EO modulators also include electrodes disposed over the EO material layer to provide a coplanar waveguide (CPW). The CPW has a radio-frequency (RF) phase velocity, and the electrodes have a gap therebetween. The EO modulators also include a superstrate disposed over the EO material layer and configured to be raised and lowered, or disposed and removed to tune the RF phase velocity to be substantially the same as the OGV, wherein a space exists between the superstrate and the EO material.

An optical modulator includes a substrate having a main surface including a first area and a second area, an optical modulation portion disposed on the first area, and an optical waveguide portion disposed on the second area. The optical modulation portion includes a first mesa waveguide and an electrode connected to the first mesa waveguide. The first mesa waveguide includes a p-type semiconductor layer, a first core layer, and an n-type semiconductor layer. The optical waveguide portion includes a second mesa waveguide. The second mesa waveguide includes a first cladding layer, a second core layer, and a second cladding layer. The second core layer is optically coupled to the first core layer. The first cladding layer contains a p-type dopant and protons. The second cladding layer contains an n-type dopant.

A polymer modulator including a waveguide core defined over an insulating layer and having a first passive region including a light input, a second passive region including a light output, and an active region optically coupling the passive regions into a continuous waveguide core between the input and output. The waveguide core in the first and second passive regions including one of sol-gel and SiO.sub.2 surrounded by cladding including one of sol-gel and SiO.sub.2. The cladding in the passive regions having a first refractive index, the waveguide core in both regions having a second refractive index at least 0.01 higher than the first refractive index. The waveguide core in the active region including sol-gel, a cladding layer of sol-gel positioned between the insulating layer and the waveguide core, the refractive index of the waveguide core is at least 0.01 higher than the refractive index of the cladding layer.

To prevent deterioration in an extinction ratio due to asymmetry between a pair of optical waveguides.

An optical modulator has a Mach-Zehnder optical waveguide including mutually parallel first and second waveguides and a signal electrode for controlling the phase of light propagating in the Mach-Zehnder optical waveguide. The first and second waveguides have a first section in which the second waveguide has a line width smaller than that of the first waveguide and a second section in which the first waveguide has a line width smaller than that of the second waveguide. The first section and the second section are replaced with each other in curved parts.

There is provided an optical waveguide device including a substrate, an optical waveguide formed on the substrate, and a working electrode that controls a light wave propagating through the optical waveguide, in which the working electrode includes a first base layer made of a first material, and a first conductive layer on the first base layer, and a conductor pattern including a second base layer made of a second material different from the first material and a second conductive layer on the second base layer is formed in a region other than a path from an input end to an output end of the optical waveguide, in a region on the substrate.

There is provided an optical waveguide device including: a substrate; an optical waveguide formed on the substrate; and a working electrode that controls a light wave propagating through the optical waveguide, in which the working electrode includes a first base layer made of a first material, a first conductive layer on the first base layer, a second base layer made of a second material different from the first material, which is on the first conductive layer, and a second conductive layer on the second base layer, and an edge of the second base layer is covered with the second conductive layer, in a cross-section perpendicular to an extending direction of the optical waveguide.