US 12,169,347 B2
Semiconductor Mach-Zehnder optical modulator and IQ modulator
Josuke Ozaki, Tokyo (JP); Yoshihiro Ogiso, Tokyo (JP); and Yasuaki Hashizume, Tokyo (JP)
Assigned to Nippon Telegraph and Telephone Corporation, Tokyo (JP)
Appl. No. 17/641,022
Filed by Nippon Telegraph and Telephone Corporation, Tokyo (JP)
PCT Filed Sep. 12, 2019, PCT No. PCT/JP2019/035886
§ 371(c)(1), (2) Date Mar. 7, 2022,
PCT Pub. No. WO2021/048972, PCT Pub. Date Mar. 18, 2021.
Prior Publication US 2022/0326587 A1, Oct. 13, 2022
Int. Cl. G02F 1/225 (2006.01); G02F 1/21 (2006.01); H04B 10/516 (2013.01)
CPC G02F 1/2257 (2013.01) [G02F 1/212 (2021.01); G02F 2202/102 (2013.01); H04B 10/516 (2013.01)] 9 Claims
OG exemplary drawing
 
1. An IQ modulator comprising:
two semiconductor Mach-Zehnder optical modulators;
an input waveguide on a semi-insulating semiconductor substrate; and
a branching filter on the semi-insulating semiconductor substrate and configured to separate light propogating through the input waveguide into two systems for input to the two semiconductor Mach-Zehnder optical modulators, wherein each of the two semiconductor Mach-Zehnder optical modulators comprises:
an optical waveguide on the semi-insulating semiconductor substrate, the optical waveguide comprising first and second arm waveguides;
a dielectric layer on the semi-insulating semiconductor substrate;
a first input-side lead-out line on the dielectric layer and a second input-side lead-out line on the dielectric layer adjacent to the first input-side lead-out line, the first and second input-side lead-out lines each having a first end and a second end;
first and second phase modulation electrode lines on the dielectric layer along the first and second arm waveguides, the first and second phase modulation electrode lines having first ends respectively connected to the second ends of the first and second input-side lead-out lines;
first and second electrodes respectively configured to apply modulation signals propagating through the first and second phase modulation electrode lines to the first and second arm waveguides, a first modulation signal of the modulation signals being input to the first end of the first input-side lead-out line, and a second modulation signal of the modulation signals that is complementary to the first modulation signal being input to the first end of the second input-side lead-out line;
a conductive layer between the semi-insulating semiconductor substrate and the optical waveguide;
a plurality of first wiring layers disposed intermittently in an extended direction of the optical waveguide so as to cross the optical waveguide, the first wiring layers being connected to the conductive layer;
a second wiring layer connecting the first wiring layers to an electrode pad configured to apply a voltage to the conductive layer;
first and second output-side lead-out lines on the dielectric layer, the first and second output-side lead-out lines having first ends respectively connected to second ends of the first and second phase modulation electrode lines;
a first ground line disposed in the extended direction of the optical waveguide on the dielectric layer outside the first input-side lead-out line, the first phase modulation electrode line, and the first output-side lead-out line; and
a second ground line disposed in the extended direction of the optical waveguide on the dielectric layer outside the second input-side lead-out line, the second phase modulation electrode line, and the second output-side lead-out line;
wherein a first semiconductor Mach-Zehnder optical modulator of the two semiconductor Mach-Zehnder optical modulators configured to receive an I modulation signal as an input and a second semiconductor Mach-Zehnder optical modulator of the two semiconductor Mach-Zehnder optical modulators configured to receive a Q modulation signal as an input are arranged such that the optical waveguides of the first and second semiconductor Mach-Zehnder optical modulators are positioned in parallel to each other;
wherein the second ground line of the first semiconductor Mach-Zehnder optical modulator and the first ground line of the second semiconductor Mach-Zehnder optical modulator adjacent thereto are integral portions of a common ground line common to the two semiconductor Mach-Zehnder optical modulators;
wherein a portion of the second wiring layer arranged in the extended direction of the optical waveguide is arranged under a centerline of the common ground line; and
wherein the first wiring layers each extend from a position under the first ground line of the first semiconductor Mach-Zehnder optical modulator to a position under the second ground line of the second semiconductor Mach-Zehnder optical modulator, and a distance from the second wiring layer to an end close to the first semiconductor Mach-Zehnder optical modulator and a distance from the second wiring layer to an end close to the second semiconductor Mach-Zehnder optical modulator are equal.