OPTICAL MODULATOR WITH FOLDED CAPACITIVE LOADING SLOW-WAVE ELECTRODE

Abstract

An optical waveguide modulator device includes two optical waveguides forming a Mach-Zehnder interferometer structure and two co-planar waveguide (CPW) traveling-wave electrodes (TWEs). Each optical waveguide includes a plurality of segmented phase tuning sections (phasers). The segmented phasers are folded multiple times and the segments are perpendicular to the TWE electrodes. The phase of the optical signal passing through the optical waveguide is electrically tunable by electrical signals applied to the optical modulator device through the two CPW TWE electrodes. The lengths of the connecting sections between adjacent phaser segments are design such that the wave fronts of microwave and optical wave can be matched after each phaser segment. The CPW TWE electrodes are connected by a plurality of capacitive loading phaser segments, which can effectively reduce the characteristic impedance of the TWE electrodes.

Claims

1. An optical waveguide modulator device comprising: two optical waveguides forming a Mach-Zehnder interferometer structure; and two co-planar waveguide (CPW) traveling-wave electrodes (TWEs); wherein each optical waveguide includes a plurality of segmented phase tuning sections (phasers), wherein a phase of the optical signal passing through the optical waveguide is electrically tunable by electrical signals applied to the optical modulator device through the two CPW TWE electrodes.

2. The optical waveguide modulator device of claim 1, wherein the segmented phasers are folded multiple times and the segments are perpendicular to the TWE electrodes.

3. The optical waveguide modulator device of claim 1, wherein each of the two CPW TWE electrodes has a predefined signal-ground distance to increase its characteristic impedance to higher than 50.

4. The optical waveguide modulator device of claim 1, wherein CPW TWE electrodes are connected by a plurality of capacitive loading phaser segments.

5. The optical waveguide modulator device of claim 1, wherein each optical waveguide further includes connecting sections between adjacent phaser segments, and wherein lengths of the connecting sections are configured to match wave fronts of microwave and optical wave after each phaser segment.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 is a top view chip layout illustrating an optical waveguide modulator using folded capacitive loading slow-wave electrode according to an embodiment of the present invention.

[0010] FIG. 2 is an enlarged view of a portion of the chip layout shown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The optical waveguide modulator devices according to embodiments of the present invention significantly reduce the overall chip size to solve the issues presented in the background section.

[0012] One embodiment is an optical waveguide modulator device. The optical device is an optical chip which comprises two optical waveguides with segmented phasers and forms a Mach-Zehnder interferometer by combining the two waveguides at their both ends respectively, and two co-planar waveguide (CPW) traveling-wave electrodes (TWEs) for applying electrical signal hence modulating the two phaser waveguides respectively. The segmented phasers are folded multiple times and the segments are perpendicular to the electrode. It can dramatically shorten the total length of the traveling wave while keeping the required length of the phaser waveguide. There are some challenges for designing such an optical waveguide modulator with good high speed performance which requires both 50 impedance matching of the traveling wave electrode and velocity matching between the electrical microwave signal and optical wave carrier, both of which are much easier to meet in a common straight and parallel waveguide-electrode design. In the present embodiment, a much wider than usual signal-ground distance of the CPW TWE is used to intentionally increase its characteristic impedance to much higher than 50 which is subsequently reduced by capacitive loading phaser segments. In some embodiments, without limitation, the signal-ground distance of the CPW TWE is in the range of 100-150 m, and the characteristic impedance is in the range of 80-120. The high impedance introduces another problem that the velocity of the microwave becomes much slower (slow-wave) than that of the optical wave. Whereas the folded and perpendicularly aligned phaser waveguide already introduce more waveguide length in a segment than the CPW TWE length for the same segment. By designing a proper waveguide length at the connecting section between two adjacent phaser segments the wave front of microwave and optical wave can be matched after each segment. The length of the segment is designed to be much less than the microwave wavelength therefore the segmented CPW transmission line can still be approximately treated as a continuous TWE. In the design of each specific device, careful and rigorous microwave simulation should be performed to ensure all above requirements are met.

[0013] It will be apparent to those skilled in the art that various modification and variations can be made in the optical waveguide modulator device of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover modifications and variations that come within the scope of the appended claims and their equivalents.