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.

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 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 optical interferometer device is provided including a waveguide interferometer. The waveguide interferometer includes first and second waveguide arms in a waveguide plane, each waveguide arm including a n-type region and a p-type region forming a junction. The n-type region and the p-type region of the second waveguide arm are translationally symmetric with respect to the n-type region and the p-type region, respectively, of the first waveguide arm in the waveguide plane.

A disclosed optical device includes a first waveguide disposed between a branching portion and a multiplexing portion on a semiconductor substrate, and a second waveguide disposed between the branching portion and the multiplexing portion, the second waveguide being longer than the first waveguide. In the optical device, an optical confinement effect of the first waveguide is greater than an optical confinement effect of the second waveguide, the first waveguide has a curvature with a first curvature radius (Rs), the second waveguide has a curvature with a second curvature radius (Rl), and the first curvature radius is smaller than the second curvature radius.

A single mode waveguide with a straight portion and a curved portion, the curved portion having the shape of an adiabatic bend. The single mode waveguide has a curved portion that is shaped according to an adiabatic bend, with a curvature that varies continuously, and that vanishes at a point at which the curved portion is contiguous with a straight portion of the waveguide. The absence of curvature discontinuities avoids the coupling, within the waveguide, of optical power from a fundamental mode into a higher order mode and the curvature of the curved portion results in attenuation of optical power, in higher order modes, that may be coupled into the waveguide at either end.

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.

A self-equalizing photo-detector (SEPD) includes, in part, a multitude of optical splitters and photo detectors, and at least one optical delay element. The first optical splitter splits an optical signal into second and third optical signals. The optical delay element delays the second optical signal to generate a fourth optical signal. The second optical splitter splits a signal representative of the fourth optical signal to generate fifth and sixth optical signals. The first photo detector receives the third optical signal via a first optical path, has an anode terminal coupled to an output terminal of the detector and a cathode terminal coupled to a first supply voltage. The second photo detector receives the sixth optical signal via a second optical path, has an anode terminal coupled to a second supply voltage and a cathode terminal coupled to the output terminal of the detector.

Barium titanate thin film waveguides and related modulator and devices with photonic crystal structures to promote wide bandwidths, low operating voltages and small footprint.

An apparatus of polarization self-compensated delay line interferometer. The apparatus includes a first waveguide arm of a first material of a first length disposed between an input coupler and an output coupler and a second waveguide arm of the first material of a second length different from the first length disposed between the same input coupler and the same output coupler. The apparatus produces an interference spectrum with multiple periodic passband peaks where certain TE (transverse electric) and TM (transverse magnetic) polarization mode passband peaks are lined up. The apparatus further includes a section of waveguide of a birefringence material of a third length added to the second waveguide arm to induce a phase shift of the lined-up TE/TM passband peaks to a designated grid as corresponding polarization compensated channels of a wide optical band.