Semiconductor optical devices with differential grating structure and method for manufacturing the same

1. A semiconductor optical device comprising:

a resonator having three regions comprising reflective, optical gain, and phase control regions,

wherein at least one region of the reflective and optical gain regions includes:

an n-type InP substrate;

a stack structure on the InP substrate including a waveguide and active layers;

a first grating formed under the stack structure and on the InP substrate; and

a second grating formed on the stack structure.

2. The semiconductor optical device of claim 1 , further comprising an n-type InP clad layer formed between the first grating and the stack structure.

3. The semiconductor optical device of claim 1 , further comprising a p-type InP clad layer formed between the stack structure and the second grating.

4. The semiconductor optical device of claim 1 , wherein the first grating is formed of InGaAsP.

5. The semiconductor optical device of claim 1 , wherein the second grating is formed of undoped InGaAsP or p-type InGaAsP.

6. The semiconductor optical device of claim 1 , wherein at least one of the first and second gratings is formed of a sampled grating.

7. The semiconductor optical device of claim 1 , wherein periods of the first and second gratings are different.

8. The semiconductor optical device of claim 1 , wherein the waveguide layer is formed of InGaAsP.

9. The semiconductor optical device of claim 1 , wherein the active layer is formed in a multi-quantum well structure including a well formed of an InGaAsP layer.

10. The semiconductor optical device of claim 1 , wherein the active layer is formed essentially of a bulk layer of InGaAsP.

11. The semiconductor optical device of claim 1 , wherein the stack structure includes a separation confinement hetero-structure (SCH) including a first and second optical waveguide layers formed on and under the active layer interposing the active layer therebetween.

12. The semiconductor optical device of claim 1 , wherein the first and second optical waveguide layers are formed of InGaAsP, respectively.

13. A method for manufacturing a semiconductor optical device comprising the acts of:

forming a first grating on an n-type InP substrate including three regions for forming reflective, optical gain, and phase control regions, respectively;

forming an n-type InP clad layer on the first grating;

forming a waveguide layer on the n-type InP clad layer;

forming an active layer on the waveguide layer;

forming a p-type InP clad layer on the active layer; and

forming a second grating on the p-type InP clad layer.

14. The method of claim 13 , wherein the first and second gratings are formed by a laser holography method, respectively.

15. The method of claim 13 , wherein the act of forming the first grating includes the acts of:

forming a first grating layer on the InP substrate;

forming an n-type InP layer on the first grating layer;

forming a first silicon nitride layer on the n-type InP layer;

forming a first photoresist pattern on the first silicon nitride layer by a laser holography method to expose a portion of the first silicon nitride layer;

forming a first silicon nitride pattern for exposing the n-type InP layer by dry etching the first silicon nitride layer while using the first photoresist pattern as an etch mask; and

forming the first grating by etching the n-type InP and first grating layers while using the first silicon nitride layer pattern as an etch mask.

16. The method of claim 15 , further including the act of forming a first sampled grating by removing the first grating from a portion of the InP substrate.

17. The method of claim 13 , wherein the act of forming the second grating further includes the acts of:

forming a second grating layer on the p-type InP clad layer;

forming a p-type InP layer on the second grating layer;

forming a second silicon nitride layer on the p-type InP layer;

forming a second photoresist pattern on the second silicon nitride layer by a laser holography method to expose a portion of the silicon nitride layer;

forming a second silicon nitride layer pattern for exposing the p-type InP layer by dry etching the second silicon nitride layer while using the second photoresist pattern as an etch mask; and

forming the second grating by etching the p-type InP and second grating layers while using the second silicon nitride layer pattern as an etch mask.

18. The method of claim 17 , further including the act of forming a second sampled grating by removing the second grating from a portion of the InP substrate.

19. The method of claim 13 , further comprising the act of removing the active layer from a region for forming the phase control region.