Abstract: A high frequency electrical signal control device comprises a transmitter for generating a high frequency electrical signal, a receiver, a transmission line for propagating the electrical signal, and a structure for radiating the electrical signal propagated through the transmission line to the space or receiving a signal from the space. The degree of coupling of the electrical signal between the space and the transmission line provided by the structure can be variably controlled.

Abstract: To reduce wavelength chirp and produce multi-valued signal light that can be readily demodulated on a receiver side, a Mach-Zehnder type optical modulator includes an incident waveguide that branches input light, a pair of optical waveguides that respectively transmit the branched light and exhibit an electro-optic effect, a pair of signal electrodes arranged along the optical waveguides, and an exit waveguide that outputs an interfered light of the light transmitted through the optical waveguides. Furthermore, at a boundary, the polarity of each of the optical waveguides reverses, and either the optical waveguides or the signal electrodes cross each other.

Abstract: Optical waveguides (A) and (B) of a Mach-Zehnder modulator is normally formed on a ?Z plane as an electric polarization non-inversion area. However, when the signal electrode 11 and the ground electrode 10 are provided asymmetrically on two waveguides, chirp occurs in output light, which is undesired. Therefore, these electrodes are provided symmetrically about the two waveguides. To effectively perform optical modulation, a part of the substrate in which an optical waveguide exists is to be electric polarization-inverted. As a result of the electric polarization inversion the optical waveguide is on the +Z plane. However, electric charge is accumulated on the +Z plane from unstable spontaneous electric polarization of an electric polarization inversion area, and has undesired influence on the performance of the optical modulator. Therefore, a conductive amorphous layer is formed on the surface of the electric polarization inversion area.

Abstract: A circuit for calibrating optoelectronic devices automatically trims a light sensor based upon a known light condition.

Abstract: An optical waveform shaping device includes a first waveguide portion, formed on a substrate, for transmitting the optical signal and simultaneously absorbing a portion of the optical signal, which has a signal level equal to or smaller than a predetermined value, so as to shape the optical signal; and a second waveguide portion, formed on the substrate, for transmitting the optical signal, which was transmitted through the first waveguide portion, and simultaneously amplifying the optical signal. The first waveguide portion may be formed using a saturable absorber. A first electrode for supplying electric current to the first waveguide portion so that the first waveguide portion is provided with a function of absorbing the optical signal; and a second electrode for supplying electric current to the second waveguide portion so that the second waveguide portion is provided with a function of amplifying the optical signal may also be provided.

Abstract: An optical device having a substrate having an electro-optical effect, an optical waveguide formed in the substrate, and an electric field emission electrode, and an electric field convergence electrode to which an electric field emitted from the electric field emission electrode converges. The optical waveguide is formed such that light propagating through the optical waveguide passes through an area under the electric field emission electrode or an area under the electric field convergence electrode and then passes through a remaining electrode. As a result, even when an interaction length is increased, the optical device acquires (increases) a modulation index appropriate to the increase in interaction length, thereby diminishing a drive voltage.

Abstract: An optical apparatus comprises an optical device formed on a device substrate, a first optical waveguide formed on the substrate or on the optical device, and a second, mechanically discrete optical waveguide assembled with the device substrate, optical device, or first optical waveguide. The first optical waveguide is arranged for transferring an optical signal between the optical device and the first optical waveguide. The first and second optical waveguides are arranged, when the second optical waveguide is assembled with the device substrate, optical device, or first optical waveguide, for transferring the optical signal therebetween via optical transverse coupling.

Abstract: A photoelectric circuit board includes a substrate, an optical waveguide and a core exposure surface. The substrate has an inspection opening. The optical waveguide includes a core and a clad formed around the core. The optical waveguide is formed on one surface side of the substrate, is exposed to the inspection opening, and has a portion curved toward the inspection opening. The core exposure surface is formed in the curved portion of the optical waveguide so that the core is exposed out of the clad.

Abstract: A connection member electrically connects an optical element configured to convert an electric signal to an optical signal or to convert an optical signal to an electric signal, a first substrate including an incident/releasing port of an optical transmission path for an optical signal at least one end portion thereof, and a second substrate to each other. The optical transmission path is optically coupled with the optical element to transmit the optical the connection. The connection member includes a connection unit connected to the second substrate and a holding unit having elasticity and holding the first substrate. The holding unit is provided with an electrode at a connecting position to the first substrate, and the holding unit holds the first substrate by connecting the first substrate to the electrode.

Abstract: An optical waveguide device includes a lower cladding layer, a high refractive index region provided on the lower cladding layer, a pair of cores provided on the lower cladding layer on both sides of the high refractive index region, and an upper cladding layer provided on the high refractive index region and the pair of cores. One of the upper and lower cladding layers has a pair of band-shaped parts disposed between the high refractive index region and the pair of cores.

Abstract: A coplanar waveguide line comprising a substrate; a central electrode strip on the substrate; first and second electrode strips disposed on opposite sides of the central electrode strip and extending parallel thereto; first and second optical waveguides on the substrate, the optical waveguides being positioned between the first and central electrode strips and extending parallel thereto; the central electrode comprising at least one T-rail extending proximate to the first optical waveguide; the first electrode comprising at least one T-rail extending proximate to the second optical waveguide; the substrate comprising an n+ electrically conducting layer extending between the optical waveguides; wherein the coplanar waveguide line further comprises an electrical connection between first and second electrode strips.

Abstract: An optical device includes optical layer and an electrode configured to reduce eddy currents. The electrode includes an electrically conductive base portion and a plurality of nanofilaments in connection with the electrically conductive base portion. The nanofilaments are configured to conduct an electric current between the optical layer and the base portion of the electrode.

Abstract: An optical device including (a) a substrate having an electro-optic effect; (b) an optical waveguide formed on a surface layer portion of said substrate and including an optical waveguide for performing optical modulation for light inputted to said substrate and an output optical waveguide and a monitoring optical waveguide branched from and connected to a downstream side portion of said modulating optical waveguide, said monitoring optical waveguide guiding light for monitoring optical modulation operation of said modulating optical waveguide; and (c) a reflecting portion being provided on the downstream side of said monitoring optical waveguide for reflecting light propagated along said monitoring optical waveguide, the width of a reflection face of said reflecting portion being substantially equal to the cut-out width of said monitoring optical waveguide.

Abstract: Various embodiments of the present invention are directed to modulators that can be operated electronically and used to modulate electromagnetic radiation. In one embodiment of the present invention, a modulator comprises a slot waveguide having a top semiconductor layer, a bottom semiconductor layer, and a transmission layer sandwiched between the top semiconductor layer and the bottom semiconductor layer. The slot waveguide also includes a plurality of holes forming a Bragg grating along the length of the slot waveguide.

Abstract: An optical transmission system which provides bandwidth restricted optical signal comprises an input terminal (10) for accepting an electrical binary signal, an amplifier (12) for amplifying said electrical binary signal to the level requested for operating an electrical-optical converter (16) such as a Mach Zehnder light modulator, a bandwidth restriction means (14) which is for instance a low pass filter for restricting bandwidth of said electrical binary signal, and an electrical-optical conversion means (16) such as a Mach Zehnder light modulator for converting electrical signal to optical signal. Because of the location of the low pass filter (14) between an output of the amplifier (12) and the Mach Zehnder light modulator (16), the amplifier (12) may operate in saturation region to provide high level output signal enough for operating the Mach Zehnder light modulator, and a signal shaped by the low pass filter (14) is applied to the Mach Zehnder light modulator (16) with excellent waveform.

Abstract: An optical device includes a phase modulator having a waveguide on a substrate. The phase modulator also includes an n-type region having a proximity to a p-type region that causes formation of a depletion region when a bias is not applied to the modulator. The depletion region is at least partially positioned in the light signal carrying region of the waveguide. The phase modulator is tuned by applying a reverse bias to the phase modulator. The reverse bias changes the size of the depletion region.

Abstract: In order to make it possible to suppress the influence of reflected light on a connection interface easily and with certainty, an optical waveguide device includes a first optical waveguide (1), a second optical waveguide (2) formed from a material or in a structure different from that of the first optical waveguide (1) and connected to the first optical waveguide (1), and a 1×1 multimode interference waveguide (3) formed by increasing the widths of the first optical waveguide (1) and the second optical waveguide (2) in the proximity of a connection interface between the first optical waveguide (1) and the second optical waveguide (2).

Abstract: The present invention provides an optical waveguide device having a configuration such that the optical waveguide is folded back on an end area of the optical waveguide substrate to widen the modulation band. The optical waveguide device 1A includes a substrate body 2 made of an electro-optical material, optical waveguide 6, and modulation electrodes 3, 4 and 5 for applying a voltage on the optical waveguide 6. The optical waveguide 6 includes first primary areas 6e and 6f, a first curved area 7A, first folding-back areas 6g and 6h provided between the first curved area 7A and a folding-back point 8, second primary areas 6m and 6n, a second curved area 7B, and second folding-back areas 6j and 6k provided between the second curved area 7B and the folding-back point 8. At least a part of the signal electrode is provided in a folding-back region extending from the first curved area 7A and the second curved area 7B to the folding-back point 8.

Abstract: A method of producing an optical connecting component in which three-dimensional electric wiring can be easily and accurately performed, and the optical connecting component are provided. A positioning projection 58 disposed on a second slide core 56 for positioning a core pin 54 disposed on a first slide core 55 is fitted in a positioning hole 34 disposed in a lead frame 30. The lead frame 30 is disposed in the vicinity of a lead pattern 31, so that the lead pattern 31 can be insert-molded while being positioned in an accurate position with respect to the second slide core 56. Therefore, it is possible to easily perform three-dimensional electric wiring in an accurate position.

Abstract: An optical device is disclosed which suppresses a bias shift which is a deviation of a phase relationship between output signal light and monitoring light. The optical device includes a substrate having an electro-optic effect, a modulating optical waveguide formed on a surface layer portion of the substrate and forming an interference optical modulator for modulating input light, and an output optical waveguide and a monitoring optical waveguide each formed on the surface layer portion of the substrate and branched from and connected to a downstream side portion of the modulating optical waveguide. The monitoring optical waveguide guides light for monitoring optical modulation operation of the modulating optical waveguide. The monitoring optical waveguide has a reduced width region which has a reduced waveguide width.

Abstract: An optical FSK modulator which can be used for an optical information communication is provided.

Abstract: An electrical connector to be electrically disposed between a first circuit board and a second circuit board to electrically couple the first circuit board with the second circuit board is disclosed. The electrical connector may have an electro-optic modulator to modulate optical signals based on electrical signals exchanged between the first and second circuit boards through the electrical connector. Systems incorporating such electrical connectors, and methods of using the electrical connectors and systems, such as for debug, are also disclosed.

Abstract: When a domain inversion part is produced by means of electric field polling process, damage in the vicinity of the forward end of a comb electrode and deviation of width of each domain inversion part are to be reduced. A polarization domain inversion structure has polarization domain inversion parts is produced by electric field poling process using a comb electrode formed on one surface of a substrate of a ferroelectric single crystal and of a single domain, and the comb electrode has a plurality of electrode portions and feeding portion. Each of the electrode portions corresponds with each domain inversion part of the domain inversion structure. The electrode portion has a plurality of low resistance pieces arranged in a direction “F” intersecting the longitudinal direction “E” of the electrode portion and spaced apart with each other.

Abstract: The invention relates to an electro-optic directional coupler suitable for use as a variable optical attenuator at reduced voltages compared to those known in the prior art. The present invention has found that by careful selection of an asymmetric directional coupler geometry, the transfer function of the device can be shifted so that it has an operating point between maximum and minimum transmission. Signal electrodes driven in push pull configuration advantageously use this operating point to achieve significant reduction in operating voltages for switching to maximum or minimum transmission. Asymmetry is created in the directional coupler by forming the waveguides to have different propagation constants by a difference in waveguide width, depth, index of refraction or index profile.

Abstract: Optical switches are described herein. In one embodiment, an exemplary optical switch includes, but is not limited to, a first waveguide, a second waveguide across with the first waveguide in an angle to form an intersection, and a pair of electrodes placed within a proximity of the intersection to switch a light traveling from the first waveguide to the second waveguide, where the intersection includes a geometry that supports single and multimode propagation. Other methods and apparatuses are also described.

Abstract: The present invention relates to an optical device including a branching unit for making branches of incident light in a first branch ratio, a phase adjusting unit for adjusting the relationship in phase among branched lights obtained by the branching unit and a combining/branching unit for combining the lights after the phase adjustment by the phase adjusting unit and for then making branches of the combined light in a second branch ratio, at least one of the first branch ratio and the second branch ratio being previously set at a branch ratio other than 1:1. This can realize an optical device capable of properly selecting output light with a different wavelength chirp quantity.

Abstract: In a dispersion compensation element 10X, a plurality of regions (I) and (II) mutually different in radius and interval of holes 24 are set, and voltages applied at electrodes 30A and 30B are controlled in respective regions (I) and (II) to make variable the sign and the absolute value of chromatic dispersion compensation. In a dispersion compensation system formed by using the dispersion compensation element 10X, an optical pulse picked up from an optical fiber transmission line is monitored, and the amount of voltage applied at the dispersion compensation element 10X is controlled based on its chromatic dispersion information to perform dispersion compensation of the optical pulse propagated through the optical fiber transmission line. Alternatively, dispersion compensation can be performed by varying the carrier density of the waveguide by applying a voltage to change the refractive index of the waveguide.

Abstract: An optical semiconductor device has a heater, an optical waveguide layer, a first electrode and a second electrode. The heater is provided on a first semiconductor region and has more than one heater segment coupled or separated to each other. The optical waveguide layer is provided in the first semiconductor region and receives heat from the heater. The first electrode is coupled to a connecting point of the heater segments adjacent to each other. The second electrodes are electrically common and are coupled to other ends of the heater segments in opposite side of the connecting point respectively.

Abstract: The present invention is a waveguide photodetector. In one embodiment, the waveguide photodetector includes a waveguide layer where light is guided or is confined and a detection layer formed on the waveguide layer where guided light is detected. Each of the waveguide layer and the detection layer allows for the guiding of no more than a single mode of light for a given polarization. In another embodiment, the waveguide photodetector includes a waveguide layer where light is guided or is confined, a detection layer formed on the waveguide layer where guided light is detected, a first electrical contact coupled to the detection layer, and a second electrical contact coupled to the detection layer. The first electrical contact and the second electrical contact are disposed in a spaced-apart, substantially parallel manner relative to each other.

Abstract: A periodically poled element comprises a ferroelectric substrate having a top surface, a bottom surface, a top electrode structure including at least one conductor positioned on the top surface, and a suppressing structure including at least one insulator positioned on the top surface and a gap separating the insulator from the conductor. The ferroelectric substrate has a predetermined polarization direction, the conductor is configured to form an inverted domain with an inverted polarization direction in the ferroelectric substrate as a predetermined voltage is applied during a poling process, and the suppressing structure is configured to suppress the spreading of the inverted domain during the poling process.

Abstract: An optical device wherein an optical waveguide is formed on a dielectric substrate, the optical device includes an input part and an output part where the optical waveguide and corresponding optical fibers are connected. A stress layer is provided for at least one of the input part and the output part. The stress layer applies a stress to the optical waveguide so that an index of refraction of the optical waveguide is reduced.

Abstract: A device 4 has a substrate 5, an optical waveguide 2 and modulation electrodes 1A, 1B, 1C. The substrate 5 is made of an electro-optic material and has a thickness of ?30 ?m at least in a region where the modulation electrode applies an electric field. The device has a ridge generated when the optical waveguide is formed, and the ridge has a height H (angstrom) and a width “W” (?m) whose product (H×W) is 7150 angstrom·?m or smaller to realize single mode propagation of light in the optical waveguide. The wave guide has branched parts in the region where the modulation electrode applied an electric field. The deviation of positions of peaks and bottoms in the extinction ratio curve can be reduced, by increasing the distance of the branched parts of the optical waveguide to ?46 ?m.

Abstract: An optical switch includes an optical waveguide to route an input optical beam. At least one polarization switch receives the input optical beam from the optical waveguide. At least one birefringent wedge is associated with the at least one polarization switch. The at least one polarization switch and at least one birefringent wedge operate to direct the input optical beam to two or more output locations through control of the polarization switch.

Abstract: The present invention provides an optical switch, an optical modulator, and a wavelength variable filter each of which has a simple configuration, which requires only a low driving voltage, which is independent of polarization, and which can operate at high speed. An optical switch according to the present invention includes a 3-dB coupler (16) placed on an input, a 3-dB coupler (17) placed on an output, and two optical waveguides connecting the input-side 3-dB coupler and the output-side 3-dB coupler together. The optical switch also includes a phase modulating section (18) that applies electric fields to one or both of the two optical waveguides. At least two optical waveguides are a crystal material including KTaxNb1-xO3 (0<x<1) and KxLi1-xTayNb1-yO3 (0<x<1, 0<y<1), or KTaxNb1-xO3 or KxLi1-xTayNb1-yO3.

Abstract: Optical couplers having attachment features are disclosed. A typical coupler according to the present invention couples an optical signal from an optical fiber to a channel waveguide by overlapping the cores of the optical fiber and channel waveguide along a portion of their waveguide lengths, with a spacing distance between the cores of not more than 20 microns for single-mode light coupling, and not more than 100 microns for multi-mode light coupling. This is in contrast to a prior art coupler, which seeks to position the ends of the two cores in a facing relationship. In embodiments according to the present invention, attachment films may be disposed in the overlapping regions to provide advantageous coupling arrangements and new types of opto-electric devices.

Abstract: An all-fiber, phase controlled interferometer device is disclosed as well as its method of manufacture. This device is suitable for use in an optical DPSK demodulation system. It is comprised of two optical fiber couplers, each having two input and two output ports and two branches between the couplers of unequal length. The couplers have a splicing ratio of 50% over the wavelength operating range of the device. The two branches between the couplers are shaped to provide one bit of delay between the branches and are also shaped to make a compact device. Also, the two branches are formed in such a manner as to minimize birefringence in the device. In addition, a fiber heater is provided to heat the longer branch so as to obtain phase control of the interferometer. The method of producing such a device is also disclosed.

Abstract: A method of forming an optical structure includes forming a circular grating resonator (CGR) on a substrate, the CGR including a center disc and a plurality of concentric rings spaced from one another; forming an input planar waveguide and an output planar waveguide on the substrate, the input planar waveguide and the output planar waveguide optically coupled to the CGR; and forming an electrode pair on the substrate, coplanar with the input and output planar waveguides, the electrode pair comprising an electrically conductive material in contact with opposing ends of the center disc of the CGR so as to render the CGR capable of electro-optical control.

Abstract: A method and arrangement of electrodes for increasing the resolution of a digital phase modulator for a fiber-optic signal transmission or measuring device. A predetermined total number m of electrodes of different lengths are arranged parallel and on both sides with respect to a light guiding path in or on an optical substrate. The electrodes are divided into two groups. A first group n of electrodes represents a coarse modulator with binary and more significant weighted electrodes of length ratio bn+0:bn=2, the longest electrode of which corresponds to the sum of lengths of all the remaining electrodes of the overall modulator. A second, smaller group of n0 non-binary and less significant weighted electrodes represents a fine modulator. The smallest output values are not formed by driving individual electrodes of the fine modulator, but rather by forming the difference, in each case, between two larger electrodes.

Abstract: The present invention relates to an acousto-optic device capable of extending the frequency band of SAWs being able to be generated by it, the acousto-optic device comprising: a light propagation unit for propagating light; a surface acoustic wave propagation unit capable of propagating a surface acoustic wave causing interaction with light which propagates in the light propagation unit; and a transducer electrode unit provided with a plurality of electrodes configured so as to correspond to a frequency band to be generated as the surface acoustic wave which propagates in the surface acoustic wave propagation unit.

Abstract: An optical modulator comprises a Z-cut lithium niobate substrate (21) on which is formed a Mach-Zehnder interferometer having two generally parallel waveguides (23, 25) lying beneath a buffer layer of dielectric material (27). First and second ground electrodes (29, 33) and a hot electrode (31) are disposed on the buffer layer (27), the first and second ground electrodes (29, 33) being spaced either side of the hot electrode (31), the hot electrode (31) and the first ground electrode (29) being proximate to at least apart of the respective waveguides (25, 23). The electrode structure is unsymmetrical in that (a) the hot electrode and the first ground electrode each have a width substantially less than that of the second ground electrode and or (b) the spacing between the first ground and hot electrodes is different from the spacing between the second ground and hot electrodes. whereby a range of chirp values can be obtained.

Abstract: An optical module has at least two optical elements mounted in parallel with each other. The module also has a first electrode pad which is formed between the paralleled optical elements and grounded to a ground potential and a second electrode pad which is arranged along a line that is intersected with a direction in which the optical elements are arranged, which faces the first electrode pad and is grounded to the ground potential. The module further has a conductive shield member which is connected to the first electrode pad and the second electrode pad and placed between electrical signal transmission paths each connected to the optical elements.

Abstract: A metal waveguide is coupled to a dielectric waveguide to obtain transmission of light in a plasmon mode along an edge of the metal waveguide. Efficient, broadband light transmission is obtained, achieving a low insertion loss, using standard processing tools. An efficient integrated optical circuit is obtained.

Abstract: An optical splitter/coupler has: a multimode waveguide having an electrooptic effect, and propagating light in a multimode; one incident waveguide propagating light in a single mode, and inputting the light to the multimode waveguide; one pair of emitting waveguides guiding-out, in a single mode, lights which have propagated-in through the multimode waveguide; at least one pair of individual electrodes provided so as to be positioned in vicinities of respective side edges on one surface of the multimode waveguide; and a ground electrode provided on another surface, wherein the multimode waveguide has a length such that 3(n+1) bright spots arise at a central portion and at both side edge portions due to incident light, the individual electrodes are provided at positions corresponding to an upstream-most one pair of the bright spots, and the emitting waveguides are connected to positions corresponding to a downstream-most one pair of the bright spots.

Abstract: A substantially straight beam in an unbuckled state is compressed to cause the beam to buckle using an adjustable compressor. The adjustable compressor applies force to one or both ends of the beam and limits compression on the beam to allow the beam to move between a first buckled state and a second buckled state. The first buckled state and the second buckled state comprise substantially equal magnitude and opposite direction buckling movements from the unbuckled state.

Abstract: An optical modulator includes a signal electrode for application of modulation signals whereby light propagated over an optical waveguide is modulated, and bias electrodes for application of a bias voltage for controlling an operating point for the modulation signals. A buffer layer is provided between a substrate exhibiting electro-optical effect and the bias electrodes, but at regions where no optical waveguide is formed beneath the bias electrodes, no buffer layer is provided, and the bias electrodes are provided directly upon the substrate. This configuration enables bias voltage to be reduced.

Abstract: A silicon-based optical modulator structure includes one or more separate localized heating elements for changing the refractive index of an associated portion of the structure and thereby providing corrective adjustments to address unwanted variations in device performance. Heating is provided by thermo-optic devices such as, for example, silicon-based resistors, silicide resistors, forward-biased PN junctions, and the like, where any of these structures may easily be incorporated with a silicon-based optical modulator. The application of a DC voltage to any of these structures will generate heat, which then transfers into the waveguiding area. The increase in local temperature of the waveguiding area will, in turn, increase the refractive index of the waveguiding in the area. Control of the applied DC voltage results in controlling the refractive index.

Abstract: A variable light controlling device comprising a substrate, an optical waveguide disposed on the substrate, a first heater and a second heater to change the optical waveguide's temperature is fabricated. And a total amount of the power supplied to the first and the second heater, or a total amount of heat emitted from both of the first and second heater, is maintained substantially constant. Then, the substrate is protected from temperature changes, thereby, stable and quick wavelength tuning operations are realized.

Abstract: A Mach-Zehnder optical modulator capable of feed-back compensating a change due to an optical coupling loss, and the characteristic change peculiar to functional devices, and a control method therefore, are provided. A control method for a semiconductor Mach-Zehnder optical modulator using a laser device as a light source includes modulating light emitted from the laser device, and extracting the light as output light; detecting monitor light separate from the output light, among the optically modulated light; and feed-back controlling an optical output intensity of the laser device based on the monitor light.

Abstract: Methods for optical isolation in high peak power fiber-optic systems prevent damage to a facet within a fiber-optic isolator caused by back-reflected light from, for example, an optical amplifier. Preventing damage to the facet may include expanding a mode area of the back-reflected light and/or reducing a change in refractive index.

Abstract: An electro-optic modulator having a substrate, one or more optical waveguides, at least one active electrode formed on the substrate and aligned over the optical waveguide, the active electrode operating to induce a refractive index change in the optical waveguide. The active electrode has a lower surface arranged facing the substrate, an upper surface arranged away from the substrate, substantially planar side walls, and rounded corners between the side walls and the lower surface of the active electrode. The electrode can be a bridge electrode, with two lower portions and an upper portion connected to the lower portions, the lower portions spaced apart from each other, each of the two lower portions of the active electrode extending over one of the optical waveguides. Each of the lower portions has rounded convex corners. The upper surface of the electrode can also have rounded corners or a completely rounded upper surface.