Semiconductor light emitting device and optical subassembly

An optical subassembly comprising:

• a semiconductor light emitting device comprising:
• a sub-mount with a conductive pattern on an upper surface of the sub-mount;
• an optical modulator with an upper electrode on a top surface of the optical modulator and a lower electrode on a bottom surface of the optical modulator,
• wherein the lower electrode is opposed and bonded to the conductive pattern;
• a termination resistor connected in parallel to the optical modulator;
• a microstrip substrate with a single-ended transmission line on a top surface of the microstrip substrate,
• wherein the single-ended transmission line extends from a first end portion to a second end portion of the microstrip substrate,
• wherein the microstrip substrate has a ground plane on a bottom surface of the microstrip substrate, and
• wherein the ground plane is opposed and bonded to the conductive pattern;
• and
• a wire that has a pair of ends,
• wherein one of the pair of ends is bonded to the upper electrode of the optical modulator, and another of the pair of ends is bonded to the second end portion of the single-ended transmission line,
• wherein:
• the single-ended transmission line includes a first section and a second section,
• wherein the second section extends from the first section and includes the second end portion, and
• wherein the second section is lower in characteristic impedance than the first section,
• a load circuit that includes the wire, the optical modulator, and the termination resistor is electrically connected between the second end portion and the conductive pattern, and
• the load circuit is equal to or lower in the characteristic impedance than the second section;
• and
• an electrical connector,
• wherein the electrical connector is electrically connected to the first end portion of the single-ended transmission line.