Methods and apparatus for etching a wafer. The wafer is positioned adjacent to a cathode within a vacuum chamber. The wafer includes a first layer stack, where the first layer stack includes a crystalline composition of a first element and a second element different from the first element. The crystalline composition may be BaTiO3 (BTO). A gas is received that includes a first partial gas and a second partial gas. The first and second partial gases may be HBr and Cl2, respectively. The gas is ionized, and the wafer is chemically etched by bombarding the layer stack with the ionized gas. The chemical etching includes reacting the first partial gas with the first element and reacting the second partial gas with the second element.

A method includes depositing a crystalline magnesium oxide (MgO) seed layer directly on an amorphous insulating cladding layer by a physical vapor deposition (PVD) process, and depositing a crystalline electro-optic layer directly on the crystalline MgO seed layer.

An expanded Bell state generator can generate a Bell state on four output modes of a set of m output modes, where m is greater than four. Some expanded Bell state generators can receive inputs on any four of a set of 2m input modes. Subsets of the m output modes can be multiplexed to reduce the number of modes to four. According to some embodiments, a set of 2×2 muxes can be used to rearrange the output modes prior to reducing the number of modes.

An apparatus for monitoring strain in an optical chip in silicon photonics platform. The apparatus includes a silicon photonics substrate shared with the optical chip. Additionally, the apparatus includes an optical input configured in the silicon photonics substrate to supply an input signal of a single wavelength. The apparatus further includes a first waveguide arm and a second waveguide arm embedded in the silicon photonics substrate to form an on-chip interferometer. The second waveguide arm forms a delay line being disposed at a region in or adjacent to the optical chip. The on-chip interferometer is configured to generate an interference pattern serving as an indicator of strain distributed at the region in or adjacent to the optical chip. The interference pattern is caused by a temperature-independent phase shift at the single wavelength of the interferometer between the first waveguide arm and the second waveguide arm.

An optical 90-degree hybrid includes two splitters, two combiners and four arm waveguides that connect output ports of the splitters and input ports of the combiners. Each of the splitters, the arm waveguides, and the combiners is a part of an optical waveguide. The optical waveguide is configured so that the phase error generated in the splitters due to wavelength change is suppressed by the phase error generated in the arm waveguides due to the wavelength change. The optical waveguide is further configured so that the phase error generated in the splitters due to deviation of a structure parameter from a certain value (e.g., design value) is suppressed by the phase error generated in the arm waveguides due to the deviation.

An integrated optical structure for multiplexing and/or demultiplexing an optical signal comprises a main waveguide having two parallel side surfaces, a first waveguide which meets the main waveguide at a first region on one of the two side surfaces, and a plurality of second waveguides which meet the main waveguide at a second region on one of the two side surfaces. The second region is spaced at a determined distance from the first region. The two side surfaces are arranged at a first angle relative to an extension direction of the first waveguide and a second angle relative to extension directions of the plurality of second waveguides. The optical structure further comprises one or more waveguide extension structures. Each waveguide extension structure is arranged adjacent to one of the two side surfaces of the main waveguide at a region that is different to the first and the second region.

A method includes receiving Bell pairs. Photons are obtained in a Greenberger-Horn-Zeilinger (GHZ) state by providing, to a first beam splitter, a photon from a first Bell pair and a photon from a second Bell pair. The first beam splitter is coupled with a first output channel and a second output channel. Obtaining the photons in the GHZ state further includes providing, to a second beam splitter, a photon from a third Bell pair and a photon from a fourth Bell pair. The second beam splitter is coupled with a third output channel and a fourth output channel. Obtaining the photons in the GHZ state further includes providing a photon output from the second output channel as a first input to a detector and a photon output in the third output channel a second input to the first detector.

An optical circuit module comprises a substrate with a first optical coupler connected to a first optical waveguide and a second optical coupler connected to a second optical waveguide on a substrate surface side; and a semiconductor photonic device mounted on the substrate, wherein the semiconductor photonic device has a third optical waveguide and a fourth optical waveguide extending to a first end face that faces the substrate surface, and wherein the third optical waveguide is optically connected to the first optical coupler and the fourth optical waveguide is optically connected to the second optical coupler.

A sensing system for characterizing analytes of interest in a sample comprises a photonic integrated circuit with an integrated interferometer. The integrated interferometer is configured for spectroscopic operation. The integrated interferometer comprises at least a sensing arm and a reference arm, both the sensing arm and the reference arm having an exposable segment available for interaction with the sample, whereby the exposable segment of the reference arm has an optical path length which is smaller than twice the optical path length of the exposable segment of the sensing arm. The exposable section of the sensing arm is selective to the analyte of interest, whereas the exposable section of the reference arm is not selective to the analyte of interest.

Electro-optical devices and methods for constructing electro-optical devices such as a switch or phase shifter. An electrode layer is deposited on a substrate layer, a waveguide structure is deposited on the electrode layer, a first cladding layer is deposited on the waveguide structure, and the first cladding layer is planarized and bonded to a wafer. The substrate layer is removed and the electrode layer is etched to split the electrode layer into a first electrode separated from a second electrode. A second cladding layer is deposited on the etched electrode layer. The first and second electrodes may be composed of a material with a large dielectric constant, or they may be composed of a material with a large electron mobility. The device may exhibit a sandwich waveguide architecture where an electro-optic layer is disposed between two strip waveguides.