Transmitter optical subassembly and optical module

1. A transmitter optical subassembly comprising:

a light source;

an optical modulator for modulating output light from the light source, the optical modulator having a characteristic that a current depending on an amount of optical absorption has a positive correlation with an applied voltage thereto;

a transistor with a first terminal, a second terminal, and a third terminal, configured to pass a current between the second terminal and the third terminal based on a control signal input to the first terminal, wherein

the transistor at the second terminal is connected in series to the optical modulator,

a drive voltage applied to the optical modulator and the transistor is divided into a first voltage applied to the optical modulator and a second voltage applied to the transistor,

a drive current flowing through the optical modulator and the transistor depends on the control signal input to the first terminal,

the first voltage is based on the drive current and is subject to the characteristic of the optical modulator, and

the second voltage fluctuates based on the first voltage; and

a package that houses a submount,

wherein the optical modulator and the transistor are mounted on the submount, and

wherein the third terminal is adjacent to the optical modulator.

2. The transmitter optical subassembly according to claim 1 , wherein

the transistor is a field-effect transistor, and

the control signal is a voltage signal.

3. The transmitter optical subassembly according to claim 1 ,

wherein the light source is also mounted on the submount.

4. The transmitter optical subassembly according to claim 1 , wherein the light source and the optical modulator are monolithically integrated.

5. The transmitter optical subassembly according to claim 1 , wherein the package is made of material that is different than a material of the submount.

6. An optical module comprising;

a receiver optical subassembly; and

a transmitter optical subassembly comprising:

a light source;

an optical modulator for modulating output light from the light source;

a transistor with a first terminal, a second terminal, and a third terminal, configured to pass a current between the second terminal and the third terminal based on a control signal input to the first terminal,

wherein the transistor at the second terminal is connected in series to the optical modulator; and

a package that houses a submount,

wherein the light source, the optical modulator, and the transistor are mounted on the submount, and

wherein the third terminal is adjacent to the optical modulator.

7. The optical module according to claim 6 , wherein the transistor is an n-type metal-oxide-semiconductor field-effect transistor.

8. The optical module according to claim 6 , wherein the light source and the optical modulator are monolithically integrated.

9. The optical module according to claim 6 , wherein the control signal is a voltage signal.

10. The optical module according to claim 6 , wherein the package is made of a material that is different than a material of the submount.

11. The optical module according to claim 6 , wherein the submount includes a light source power line formed thereon for providing a light source power source to the light source.

12. The optical module according to claim 11 , wherein the third terminal is arranged between the light source power line and the second terminal.

13. A transmitter optical subassembly comprising:

a light source;

an optical modulator for modulating output light from the light source;

a transistor with a first terminal, a second terminal, and a third terminal, configured to pass a current between the second terminal and the third terminal based on a control signal input to the first terminal,

wherein the transistor at the second terminal is connected in series to the optical modulator; and

a package that houses a submount,

wherein the light source, the optical modulator, and the transistor are mounted on the submount, and

wherein the third terminal is adjacent to the optical modulator.

14. The transmitter optical subassembly according to claim 13 , wherein

a drive voltage applied to the optical modulator and the transistor is divided into a first voltage applied to the optical modulator and a second voltage applied to the transistor,

a drive current flowing through the optical modulator and the transistor depends on the control signal input to the first terminal,

the first voltage is based on the drive current, and

the second voltage fluctuates based on the first voltage.

15. The transmitter optical subassembly according to claim 13 , wherein the light source is a laser diode, the optical modulator is an electro-absorption optical modulator, and the transistor is a field-effect transistor.

16. The transmitter optical subassembly according to claim 15 , wherein the laser diode and the electro-absorption optical modulator are integrated into an electro-absorption optical modulator integrated laser.

17. The transmitter optical subassembly according to claim 13 , wherein the control signal is a voltage signal.

18. The transmitter optical subassembly according to claim 13 , wherein the light source and the optical modulator are monolithically integrated.

19. The transmitter optical subassembly according to claim 13 , wherein the package is made of a material that is different than a material of the submount.

20. The transmitter optical subassembly according to claim 13 , wherein the submount includes a light source power line formed thereon for providing a light source power source to the light source, and

wherein the third terminal is arranged between the light source power line and the second terminal.