Optical spot size converter integrated laser device and method for manufacturing the same

Abstract

An optical spot size converter integrated laser device includes a substrate; a first waveguide laminated on the substrate and optically coupled to an optical fiber, the first waveguide being divided into a light source region having an active waveguide and an optical spot size converter region, and a trench formed on both lateral walls of the first waveguide on the substrate so that light emitted from the active waveguide interferes with light reflected by a wall surface of the first waveguide inside the first waveguide. By means of mutual interference between light emitted directly from the active waveguide of the laser device and light reflected by the interference waveguide, the optical spot size of a laser can be adjusted without affecting the single mode of the laser.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 briefly shows the structure of an LD integrated with an optical spot size converter according to an embodiment of the present invention;

FIG. 2 is a top view of the LD integrated with an optical spot size converter shown in FIG. 1;

FIGS. 3A to 3C show the spectrum of light outputted from the LD integrated with an optical spot size converter shown in FIG. 1;

FIG. 4 shows the NF and FF of a 1.3 μm wavelength DFB, which has an interference waveguide according to the present invention, and those of a conventional 1.3 μm wavelength DFB for comparison;

FIGS. 5A to 5B show the FFP of a 1.49 μm wavelength DFB LD, which has an interference waveguide according to the present invention, and that of a conventional 1.49 μm DFB LD for comparison;

FIGS. 6A to 6B show the change of FFP of an LD, which has an interference waveguide according to the present invention, as the temperature of the LD varies;

FIGS. 7A to 7E are sectional views taken along line A-A′ of FIG. 1 to show the steps of a method for manufacturing an LD integrated with an optical spot size converter according to an embodiment of the present invention; and

FIGS. 8 to 17 show the lateral structure of interference waveguides according to various embodiments of the present invention.

Claims

1. An optical spot size converter integrated laser device comprising: a substrate;a first waveguide laminated on the substrate and optically coupled to an optical fiber, the first waveguide being divided into a light source region having an active waveguide and an optical spot size converter region, the first waveguide having two lateral walls with corresponding surfaces; andtwo trenchs, each formed on a respective one of said lateral walls so that light emitted from the active waveguide interferes with light reflected inside the first waveguide by surface from among said corresponding surfaces.

2. The optical spot size converter integrated laser device as claimed in claim 1, wherein the first waveguide has a width within a range from 2-12 μm, said region being disposed, width-wise, inside a width extent of the active waveguide so that light emitted from the active waveguide undergoes interference horizontally.

3. The optical spot size converter integrated laser device as claimed in claim 1, wherein the first waveguide has a length within a range from 30-100 μm in an optical axis direction from an optical output surface of the active waveguide, a magnitude of said length causing light emitted from the active waveguide to undergo sufficient interference horizontally to achieve a desired amount of spot size conversion.

4. The optical spot size converter integrated laser device as claimed in claim 1, wherein the first waveguide has a height of 1.5-6 μm above the active waveguide in a direction perpendicular to an optical axis, so that light emitted from the active waveguide undergoes a desired amount of interference vertically.

5. The optical spot size converter integrated laser device as claimed in claim 1, wherein the first waveguide is made of a material having a refractive index within a range from 1.2-4.2, so that a near field of light emitted from the active waveguide is easily adjustable.

6. The optical spot size converter integrated laser device as claimed in claim 5, wherein the first waveguide is made of a combination of: a semiconductor selected from InP, GaAs, InGaAsP, InGaAs, Si, and Ge;a dielectric substance selected from SiO2, SiNx, and Al2O3 and formed by deposition or coating; anda polymer.

7. The optical spot size converter integrated laser device as claimed in claim 1, wherein a depth of a trench from among said trenches falls within a range from 7-15 μm so that sufficient reflection occurs on said surface to afford a desired amount of spot size conversion.

8. The optical spot size converter integrated laser device as claimed in claim 1, wherein the first waveguide has a dielectric layer laminated on the substrate so that total reflection occurs on a lower surface of the first waveguide.

9. The optical spot size converter integrated laser device as claimed in claim 1, comprising at least one of a DFB LD (Distributed Feedback LD), an FP LD, an EMLD (Electro-absorption Modulated LD), and a distributed Bragg reflector (DBR) LD.

10. The optical spot size converter integrated laser device as claimed in claim 1, wherein an optical output side section of the first waveguide has a rectangular cross-section perpendicular to a longitudinal direction of the first waveguide.

11. The optical spot size converter integrated laser device as claimed in claim 1, wherein an optical output side section of the first waveguide has a trapezoidal cross-section perpendicular to a longitudinal direction of the first waveguide.

12. The optical spot size converter integrated laser device as claimed in claim 1, wherein an optical output side section of the first waveguide has a saddle shape cross-section perpendicular to a longitudinal direction of the first waveguide, the cross-section having lateral sides indented at a level identical to a level of the active waveguide.

13. The optical spot size converter integrated laser device as claimed in claim 1, wherein the first waveguide has an optical output side section configured so that, in a cross-section perpendicular to a longitudinal direction of the first waveguide, said corresponding surfaces meet the substrate along curved lines, the substrate being positioned below said corresponding surfaces.

14. The optical spot size converter integrated laser device as claimed in claim 1, wherein the first waveguide has an optical output side section configured so that, in a cross-section perpendicular to a longitudinal direction of the first waveguide, said corresponding surfaces are slanted so as to intersect with each other at a level identical to a level of the active waveguide.

15. An optical spot size converter integrated laser device comprising: a substrate;a first waveguide laminated on the substrate and optically coupled to an optical fiber, the first waveguide being divided into a light source region having an active waveguide and an optical spot size converter region, the first waveguide having two lateral walls, each of the two having a corresponding surface; andtwo total reflection regions formed on the two lateral walls, respectively, each of the two total reflection regions having a refractive index different from a refractive index of the first waveguide so that light emitted from the active waveguide interferes with light reflected inside the first waveguide by a surface from among said corresponding surfaces.

16. The optical spot size converter integrated laser device as claimed in claim 15, wherein a given one of the total reflection regions comprises at least one of an ion implantation region, an ion diffusion region, and an air layer.

17. A method for manufacturing an optical spot size converter integrated laser device comprising the acts of: (a) laminating a lower clad layer, an active layer, and an upper clad layer successively on a semiconductor substrate;(b) forming a mask pattern in a predetermined active waveguide region on the upper clad layer and etching the upper clad layer, the active layer, the lower clad layer, and a part of the semiconductor substrate through a photolithography process to form a mesa structure that has a lateral wall;(c) forming an current interruption layer on said lateral wall; and(d) etching the current interruption layer on the lateral wall in the active waveguide region to form a first waveguide and a double trench, the first waveguide including an active waveguide.

18. The method for manufacturing an optical spot size converter integrated laser device as claimed in claim 17, wherein the act (a) comprises an act of forming a diffraction grating on the lower clad layer.

19. The method for manufacturing an optical spot size converter integrated laser device as claimed in claim 17, wherein the first waveguide extends 30-100 μm in an optical axis direction from an optical output surface of the active waveguide.

20. The method for manufacturing an optical spot size converter integrated laser device as claimed in claim 19, wherein the first waveguide has a width of 2-12 μm.

21. The method for manufacturing an optical spot size converter integrated laser device as claimed in claim 18, wherein the first waveguide has a height of 1.5-6 μm above the active waveguide in a direction perpendicular to an optical axis so that light emitted from the active waveguide undergoes a desired amount of interference vertically.

22. The method for manufacturing an optical spot size converter integrated laser device as claimed in claim 17, wherein the first waveguide is made of a material having a refractive index of 1.2-4.2 so that a near field of light emitted from the active waveguide is easily enlargeable.

23. The method for manufacturing an optical spot size converter integrated laser device as claimed in claim 22, wherein the first waveguide is made of a combination of a semiconductor selected from InP, GaAs, InGaAsP, InGaAs, Si, and Ge, a dielectric substance selected from SiO2, SiNx, and Al2O3 and formed by deposition or coating, and a polymer.

24. The method for manufacturing an optical spot size converter integrated laser device as claimed in claim 18, wherein the trench has a depth within a range from 7-15 μm.