An optical transmitter includes: a splitter; a first optical modulator and a second optical modulator that modulate each of light beams split by the splitter; a first semiconductor optical amplifier (SOA) and a second SOA that are connected to a subsequent stage of the first optical modulator and a subsequent stage of the second optical modulator, respectively; a first detector and a second detector that detect light output intensity of the first SOA and light output intensity of the second SOA, respectively; a controller that sets gains of the first and second SOAs such that the first and second SOAs are equal in the light output intensity based on detection values of the first and second detectors; and a combiner that combines an output light beam of the first SOA and an output light beam of the second SOA.

An optical modulator element includes first and second optical modulators, an optical input terminal, and a branch coupler. Each of the first and second optical modulators includes a pair of Mach-Zehnder waveguides, a first optical coupler to split rays from the branch coupler into the pair of Mach-Zehnder waveguides, and a second optical coupler to combine rays transmitted through the pair of Mach-Zehnder waveguides. The first and second optical modulators are disposed in such a manner that a traveling direction of rays propagating through the pair of Mach-Zehnder waveguides of the first optical modulator and a traveling direction of rays propagating through the pair of Mach-Zehnder waveguides of the second optical modulator are angled toward each other.

A Mach Zehnder modulator operates by phase modulating split optical beams with a modulating signal to create dissimilarities in the optical characteristics between the split beams. When the beams are recombined, the dissimilarities gives rise to intensity modulations that are indicative of the modulating signal. One or both beams are modulated with an RF trimming signal. The trimming signal is applied asymmetrically across the two beams thereby reducing the intensity of the optical carrier frequency in one of the beams more than in the other. By selecting the size of the trimming signal the differences in the optical amplitude of the carrier frequency in the two beams can be nulled.

An optical waveguide device includes a substrate, an optical waveguide formed on the substrate, two electrodes disposed at positions sandwiching the optical waveguide from both sides in a plane of the substrate; and a dielectric layer covering a top of the optical waveguide, wherein the dielectric layer extends in a width direction of the optical waveguide to an extent including edges of the two electrodes, facing the optical waveguide, and is disposed to partially cover each of the two electrodes.

An optical waveguide element includes: a substrate; and a plurality of optical waveguides causing light to turn between a first direction and a second direction that is an opposite direction of the first direction in a plane of the substrate, the plurality of optical waveguides includes first portions extending in the first direction with a predetermined distance therebetween, second portions extending in a third direction that is different from the first direction, and third portions extending in the second direction, and each of the plurality of optical waveguides except for the optical waveguide in which the second portion extending in the third direction is located on an innermost side in the first direction intersects, at the third portion, another optical waveguide in which the second portion extending in the third direction is located further inward in the first direction.

An optical module and a method of assembling the optical module are disclosed. The optical module comprises a laser unit, a modulator unit, and a detector unit mounted on respective thermo-electric coolers (TECs). The modulator unit, which is arranged on an optical axis of the first output port from which a modulated beam is output, modulates the continuous wave (CW) beam output from the laser unit. On the other hand, the laser unit and the detector unit are arranged on another optical axis of the second output port from which another CW beam is output. The method of assembling the optical module first aligns one of the first combination of the laser unit and the modulator unit with the first output port and the second combination of the laser unit and the detector unit, and then aligns another of the first combination and the second combination.

Apparatus, circuits and methods for reducing mismatch in an electro-optic modulator are described herein. In some embodiments, a described optical includes: a splitter configured for splitting an input optical signal into a first optical signal and a second optical signal; a phase shifter coupled to the splitter; and a combiner coupled to the phase shifter. The phase shifter includes: a first waveguide arm configured for controlling a first phase of the first optical signal to generate a first phase-controlled optical signal, and a second waveguide arm configured for controlling a second phase of the second optical signal to generate a second phase-controlled optical signal. Each of the first and second waveguide arms includes: a plurality of straight segments and a plurality of curved segments. The combiner is configured for combining the first and second phase-controlled optical signals to generate an output optical signal.

Provided is a technique for reducing, using a simple circuit configuration, an amplitude difference between electric signals that are input to respective optical waveguide arms. An optical modulator includes: an optical demultiplexer that splits continuous wave light as received; first and second optical waveguide arms through which the continuous wave light as split propagates; an optical phase n shifter that introduces a phase shift of π to the continuous wave light as split; an optical multiplexer combines the continuous wave light propagating through the first and second optical waveguide arms; first and second signal electrodes that respectively input the electric signals to the first and second optical waveguide arms; a junction capacitance connected in shunt to at least one of the first and second signal electrodes; and a DC voltage source that applies a DC voltage to the junction capacitance.

Provided is an optical-waveguide-element module in which a common connecting substrate is used for different optical waveguide elements and deterioration of the propagation characteristics of electrical signals in a curved section of a signal electrode is suppressed. A control electrode in an optical waveguide element is consisted of a signal electrode SL and ground electrodes GD which put the signal electrode therebetween, a connecting substrate is provided with a signal line SL1 (SL2) and ground lines GD1 (GD2) which put the signal line therebetween, the signal electrode and the signal line, and, the ground electrodes and the ground lines are respectively connected to each other using wires (WR1, WR2, and WR20 to WR22) , the control electrode in which a space W1 between the ground electrodes GD at an input end or an output end of the control electrode is wider than a space W2 between the ground lines GD1 (GD2) on the optical waveguide element side in the connecting substrate, has a portion in which the space between the ground electrodes GD forms a space W3 which is narrower than the space W2 in a portion away from the input end or the output end, furthermore, the signal electrode SL in the control electrode has a curved section in a place from the input end or the output end to an operating part in which the control electrode applies an electric field to the optical waveguide, and suppression means (WR20 to WR32) for suppressing generation of a local potential difference between the ground electrodes which put the signal electrode therebetween in the curved section of the signal electrode is provided.

Disclosed herein is a traveling-wave Mach-Zehnder modulator and method of operating same that advantageously exhibits a reduced optical insertion loss as compared with contemporary Mach-Zehnder structures. Such advantage comes at the modest expense of increased modulator length and increased RF loss.