Provided is a photonic crystal element, which shows small delay of an electric signal, shows a small propagation loss, and has uniform characteristics over its entirety. The photonic crystal element includes a two-dimensional photonic crystal slab having holes periodically formed in a substrate made of a ceramics material, the photonic crystal element being configured to guide an electromagnetic wave having a frequency of 30 GHz or more and 20 THz or less.

Reflection between a Mach-Zehnder modulator and a termination resistor is suppressed. An optical modulator includes a differential drive open collector driver IC, a differential drive semiconductor Mach-Zehnder modulator, and a differential terminator. The Mach-Zehnder modulator includes waveguides and a differential high-frequency line. The differential terminator includes a differential high-frequency line and termination resistors. The differential high-frequency line includes a capacity provided at least one of between signal lines and between a signal line and a ground line.

An optical switch structure includes a substrate, a first electrical contact, a first material having a first conductivity type electrically connected to the first electrical contact, a second material having a second conductivity type coupled to the first material, and a second electrical contact electrically connected to the second material. The optical switch structure also includes a waveguide structure disposed between the first electrical contact and the second electrical contact and comprising a waveguide core coupled to the substrate and including a first material characterized by a first index of refraction and a first electro-optic coefficient and a waveguide cladding at least partially surrounding the waveguide core and including a second material characterized by a second index of refraction and a second electro-optic. The first index of refraction is greater than the second index of refraction the first electro-optic coefficient is less than the second electro-optic coefficient

An optical waveguide device includes an intermediate layer, a thin-film LN layer including X-cut lithium niobate, and a buffer layer stacked on a substrate; an optical waveguide formed in the thin-film LN layer; and an electrode for driving. The intermediate layer is formed by an upper first intermediate layer and a lower second intermediate layer, the second intermediate layer having a permittivity that is smaller than a permittivity of the first intermediate layer.

A phase shift keying modulator. The modulator comprises: a plurality of silicon waveguides provided in a device layer of a silicon-on-insulator platform, the silicon-on-insulator platform including one or more cavities; one or more III-V semiconductor based devices located within the one or more cavities of the silicon-on-insulator platform, each III-V semiconductor-based device including a III-V semiconductor based waveguide which is coupled at an input end to one of the plurality of silicon waveguides and coupled at an output end to another of the plurality of silicon waveguides, each III-V semiconductor based waveguide comprising an active phase modulating portion; and one or more contacts in electrical contact with each active phase modulating portion, such that the phase shift keying modulator is operable to modulate the phase of an optical wave passing through each active phase modulating portion.

An optical modulator includes a Mach-Zehnder interferometer including (i) a first optical waveguide including a first semiconductor junction diode, and (ii) a second optical waveguide including a second semiconductor junction diode. A semiconductor region connects the first and second semiconductor junction diodes such that a distance between the first and second optical waveguides is less than 2.0 .Math.m for at least a portion of a longitudinal direction of the optical modulator. In another aspect, a method of modulating an optical signal includes splitting input light into first and second optical transmission paths; modulating a phase difference between light in the first optical transmission path and light in the second optical transmission path without applying a bias voltage through an impedance less than 100 ohm between the first and second optical transmission paths; and combining light that is output from the first and second optical transmission paths.

A silicon-photonic optical modulator includes at least one optical input and at least one optical waveguide that is connected to the at least one optical input. The at least one optical waveguide is configured to propagate quasi-transverse-magnetic (quasi-TM) polarized light, where each of the at least one optical waveguide is configured as a rib waveguide that includes a rib arranged on a slab. The silicon-photonic optical modulator also includes at least one electrode configured to apply at least one electric field to the quasi-TM polarized light in the at least one optical waveguide. In some implementations, a height of the rib waveguide is greater than 0.85 λ/n, where A is a free-space wavelength of light and n is a refractive index of silicon in the silicon-photonic optical modulator, and a width of the rib waveguide is greater than a thickness of the slab.

An optical semiconductor chip of the present disclosure includes a high frequency line between an electrode pad receiving a modulation signal and a modulation electrode on the optical waveguide having a light absorption layer. The depletion layer capacitance generated in the light absorption layer is canceled by an inductor component of the high frequency line. When a portion directly below the high frequency line is embedded with a low-dielectric-constant material or is made hollow, the parasitic capacitance is further reduced. The high frequency line may have a zigzag shape as well as a linear shape. The electrode pad on the optical semiconductor chip can be connected to other substrates including RF lines for modulation signal input by bumps or wire bonding.

A segmented optical modulator includes two optical modulator segments located along a main face of a photonic chip, and two RF transmission lines connected to drive a corresponding one of the two optical modulator segments. A signal electrode of one of the transmission lines includes a segment that is vertically capacitively coupled to a plurality of spaced ground-connected metallic elements disposed in sequence along a length of the segment above or below thereof so as to be capacitively coupled thereto.

A capacitive electro-optical modulator includes a silicon layer having a cavity having sidewalls and a floor. A germanium or silicon-germanium strip overlies the silicon layer within the cavity. A silicon strip overlies the germanium or silicon-germanium strip within the cavity. The silicon strip is wider than the germanium or silicon-germanium strip. An insulator fills the cavity laterally adjacent the germanium or silicon-germanium strip and the silicon strip and extending between the sidewalls of the cavity. An upper insulating layer overlies the silicon strip and the insulator. A layer of III-V material overlies the upper insulating layer. The layer of III-V material formed as a third strip is arranged facing the silicon strip and separated therefrom by a portion of the upper insulating layer.