Semiconductor laser and optical integrated light source including the same

1. A semiconductor laser, comprising:

an active layer;

a guide layer laminated on said active layer;

a diffraction grating formed along a light emission direction in said guide layer;

an upper electrode provided above said guide layer; and

a lower electrode provided below said active layer, wherein

said diffraction grating includes:

a current-injection diffraction grating; and

current-non-injection diffraction gratings provided both in front of and in back of said current-injection diffraction grating,

phase shifters are individually provided at a central portion of said current-injection diffraction grating and at boundaries between said current-injection diffraction grating and said current-non-injection diffraction gratings,

said upper electrode is provided above said current-injection diffraction grating and is not provided above said current-non-injection diffraction gratings, and

a product of a length of one of said current-non-injection diffraction gratings and a coupling coefficient of the one current-non-injection diffraction grating is equal to a product of a length of the other current-non-injection diffraction grating and a coupling coefficient of the other current-non-injection diffraction grating.

2. The semiconductor laser according to claim 1 , wherein a product of a length of each of said current-non-injection diffraction gratings and a coupling coefficient of the diffraction grating is 0.135 or less.

3. The semiconductor laser according to claim 1 , wherein each one of said phase shifters is a λ/4 phase shifter.

4. The semiconductor laser according to claim 1 , wherein both end surfaces of said diffraction grating are cleaved, and said both end surfaces are covered with anti-reflection coatings.

5. The semiconductor laser according to claim 1 , wherein the composition of a portion of said active layer provided under said current-injection diffraction grating is the same as the composition of a portion of said active layer provided under each of said current-non-injection diffraction gratings.

6. An optical integrated light source, comprising:

a semiconductor laser;

an optical modulator that is disposed at an output side of said semiconductor laser and modulates an intensity or a phase of a light output from said semiconductor laser; and

a semiconductor optical amplifier that amplifies the light output from said optical modulator, wherein

said optical integrated light source is capable of controlling an amplification factor of said semiconductor optical amplifier,

said semiconductor laser includes:

an active layer;

a guide layer laminated on said active layer;

a diffraction grating formed along a light emission direction in said guide layer;

an upper electrode provided above said guide layer; and

a lower electrode provided below said active layer,

said diffraction grating includes:

a current-injection diffraction grating; and

current-non-injection diffraction gratings provided both in front of and in back of said current-injection diffraction grating,

phase shifters are individually provided at a central portion of said current-injection diffraction grating and at boundaries between said current-injection diffraction grating and said current-non-injection diffraction gratings,

said upper electrode is provided above said current-injection diffraction grating and is not provided above said current-non-injection diffraction gratings, and

a product of a length of one of said current-non-injection diffraction gratings and a coupling coefficient of the one current-non-injection diffraction grating is equal to a product of a length of the other current-non-injection diffraction grating and a coupling coefficient of the other current-non-injection diffraction grating.

7. The optical integrated light source according to claim 6 , wherein the composition of a portion of said active layer provided under said current-injection diffraction grating is the same as the composition of a portion of said active layer provided under each of said current-non-injection diffraction gratings.

8. An optical integrated light source, comprising:

a plurality of semiconductor lasers;

a plurality of optical waveguides individually connected to outputs of said plurality of semiconductor lasers;

an optical multiplexing circuit that is connected to said plurality of optical waveguides and multiplexes laser lights that have propagated through said plurality of optical waveguides;

an output waveguide that propagates a light output from said optical multiplexing circuit; and

a semiconductor optical amplifier connected to said output waveguide, wherein

said optical integrated light source is capable of controlling an amplification factor of said semiconductor optical amplifier,

each of said plurality of semiconductor lasers includes:

an active layer;

a guide layer laminated on said active layer;

a diffraction grating formed along a light emission direction in said guide layer;

an upper electrode provided above said guide layer; and

a lower electrode provided below said active layer,

said diffraction grating includes:

a current-injection diffraction grating; and

current-non-injection diffraction gratings provided both in front of and in back of said current-injection diffraction grating,

phase shifters are individually provided at a central portion of said current-injection diffraction grating and at boundaries between said current-injection diffraction grating and said current-non-injection diffraction gratings,

said upper electrode is provided above said current-injection diffraction grating and is not provided above said current-non-injection diffraction gratings, and

a product of a length of one of said current-non-injection diffraction gratings and a coupling coefficient of the one current-non-injection diffraction grating is equal to a product of a length of the other current-non-injection diffraction grating and a coupling coefficient of the other current-non-injection diffraction grating.

9. The optical integrated light source according to claim 8 , wherein the composition of a portion of said active layer provided under said current-injection diffraction grating is the same as the composition of a portion of said active layer provided under each of said current-non-injection diffraction gratings.