Surface emitting laser with monolithic integrated lens

• US 4,935,939 A
• Filed: 05/24/1989
• Issued: 06/19/1990
• Est. Priority Date: 05/24/1989
• Status: Expired due to Term

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Liau, Zong-Long, Walpole, James N.
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): Wise, Robert E.
• Application Number:
  US07/356,881
• Time in Patent Office: 391 Days
• Field of Search: 372/98, 372/99, 372/101, 372/103, 350/96.15, 350/96.18
• US Class Current: 372/98
• CPC Class Codes: H01S 3/005 Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping shaping laser beam for working metal or other materials B23K26/06; optical elements, systems or apparatus in general G02B
• CPC Class Codes: H01S 5/005 Optical components external to the laser cavity, specially adapted therefor, e.g. for homogenisation or merging of the beams or for manipulating laser pulses, e.g. pulse shaping H01S5/026, H01S5/18388 take precedence
• CPC Class Codes: H01S 5/026 Monolithically integrated components, e.g. waveguides, monitoring photo-detectors, drivers stabilisation of output H01S5/06
• CPC Class Codes: H01S 5/0267 Integrated focusing lens H01S5/18388 takes precedence
• CPC Class Codes: H01S 5/14 External cavity lasers H01S5/18 takes precedence; mode locking H01S5/065
• CPC Class Codes: H01S 5/185 having only horizontal cavities, e.g. horizontal cavity surface-emitting lasers [HCSEL] comprising a photonic bandgap structure H01S5/11
• CPC Class Codes: H01S 5/42 Arrays of surface emitting lasers

Abstract

A surface emitting laser is described with a monolithic integrated lens formed in one side of an optical semiconductor substrate aligned with a parabolic light reflective mirror surface formed adjacent an edge emitting laser formed on, or in, the other side of the substrate. An optional optical feedback spherical mirror is formed concentric to the lens.

Claims

1. In a monolithic lens-laser device, the element comprising:

(a) a semiconductor substrate having first and second longitudinally extending opposed surfaces;

(b) a strip of lasing medium extending in a generally longitudinal plane formed on said first surface for emitting light out one end thereof;

(c) a lens having an optical axis and formed in said second surface for collimating light received from said lasing medium; and

(d) a laser light reflective surface formed adjacent one end of said strip and located at the intersection of the optical axis of the lens and the plane of the lasing medium.

2. The device of claim 1 further including an additional light reflective surface formed in said second surface concentric with said lens to reflect radiated light back to said lasing.

3. The device of claim 2 wherein the additional light reflective surface comprises a spherical mirror coaxial to said lens to reflect light back to said lasing medium to support light oscillation.

4. The device of claim 2 wherein the additional light reflective surface is a spherical mirror located radially inwardly concentric with said lens to reflect light back to said lasing medium.

5. The device of claim 1 wherein the lens is covered by a reflective coating such that light collimated by the lens is reflected back toward the first surface and partly transmitted out the first surface and partly reflected back to the lasing medium to sustain laser oscillation.

6. The device of claim 1 wherein the laser light reflective surface is an internally reflective surface formed at an angle of about 45°

to the plane of the strip.

7. The device of claim 1 wherein the laser light reflective surface is an internally reflective parabolic surface the focal point of which is located in the plane of the strip.

8. The device of claim 1 wherein the collimated light is directed toward an external cavity.

9. The device of claim 1 further including an additional partly light reflective surface formed in the path of said reflected light.

10. In an array of surface emitting laser devices wherein a plurality of laser structures are formed on a single substrate, each having lasing strips extending in the plane of the substrate, the improvement comprising:

(a) a lens, having an optical axis, formed in the substrate on a surface oppositely adjacent each laser in a plane parallel to the plane of the substrate; and

(b) a laser light reflective surface formed laterally adjacent each said laser for reflecting laser light from said laser toward said lens for collimation, said laser light reflective surface located at the intersection of the optical axis of the lens and the plane of the lasing strips.

11. The array of claim 10 wherein the laser light reflective surface is a paraboloid.

12. The array of claim 10 wherein the laser light reflective surface is a 45°

plane.

13. The array of claim 10 including a reflective mirror concentric to said lens.

14. The array of claim 10 wherein the lens is covered with a reflective material such that the collimated light is reflected back toward the substrate.

15. The method of forming a monolithic lens-laser device comprising the steps of:

(a) providing a semiconductor substrate having first and second planar opposed surfaces;

(b) forming a collimating lens, having an optical axis, in said first surface;

(c) forming a strip of active lasing material extending in the plane of said substrate surface over said second surface for emitting laser radiation out one edge of said strip; and

(d) forming a reflective surface located at the intersection of said optical axis and the plane of said strip.

16. The method of claim 15 wherein a reflective spherical mirror is formed concentric with the lens.

17. The method of claim 16 wherein the lens is located radially central to the mirror.

18. The method of claim 15 wherein, after the lens is formed, the reflective surface is located at the intersection by projecting light through the lens to form an image on the second surface, which image is used as an alignment reference to locate the reflective surface.

19. The method of claim 15 wherein the laser structure is formed of a buffer layer, active layer and cladding layer formed on a substrate of thickness H and in which the reflective surface is formed by a thermal mass transport process, in which stepped grooves are formed in the laser structure with a sidewall of a first step located a lateral distance s₁ from the optical axis of the lens and the active layer is undercut from the end wall a distance "u", and the buffer layer thickness is B, and wherein the focal length of the lens "F" equals:

H+B+s₁ +γ

.

20. The method of claim 19 wherein prior to forming the lens, an alignment mark is formed in the substrate to a depth "v" and prior to forming the laser structure, the substrate surface on the laser side is removed to a depth "M" and wherein the focal length of the lens "F" equals H-γ

-M+B+s₁ +γ

.

21. The method of claim 15 wherein the lens profile "Z" equals:

##EQU3## wherein "n" is the refractive index of the substrate

"τ

" is the radial distance from the lens axis to a point on the profile. and

"f" is the lens focal length.

22. The method of claim 15 wherein a spherical mirror is formed concentric to the lens and the radius of curvature of the spherical mirror "R" is:

##EQU4## wherein z'"'"'₃ is the lens thickness and

τ

'"'"'₃ is the axial radius of the lens.

23. In a monolithic mirror laser device, the improvement comprising:

(a) a semiconductor substrate having first and second longitudinally extending opposed surfaces;

(b) a strip of lasing medium for emitting light extending in a generally longitudinal plane formed over said first surface;

(c) a mirror formed in said substrate adjacent said second surface for reflecting and collimating light received from said lasing medium; and

(d) a laser light reflective surface formed adjacent one end of said strip and located at the intersection of the optical axis of the mirror and the plane of the lasing medium.

24. In an array of surface emitting laser devices wherein a plurality of laser structures are formed on a single substrate, each having lasing strips extending in the plane of the substrate, the improvement comprising:

(a) a mirror having an optical axis formed in the substrate on a surface oppositely adjacent each laser in a plane parallel to the plate of the substrate; and

(b) a laser light reflective surface formed laterally adjacent each said laser for reflecting laser light from said laser toward said mirror for reflection, said laser light reflective surface located at the intersection of the optical axis of the mirror and the plane of the lasing strips.

25. The array of claim 24 wherein the laser light reflective surface is a paraboloid.

26. The array of claim 24 wherein the laser light reflective surface is a 45°

plane.

27. In a monolithic lens-laser device, the improvement comprising:

(a) a semiconductor substrate having first and second longitudinally extending opposed surfaces;

(b) a strip of lasing medium for emitting light extending in a generally longitudinal plane formed over said first surface;

(c) a lens formed in said substrate adjacent said second surface for collimating light received from said lasing medium;

(d) a first laser light reflective surface formed adjacent one end of said strip and located at the intersection of the optical axis of the lens and the plane of the lasing medium;

(e) a second light reflective mirror surface formed in said substrate concentric to said lens.

28. The device of claim 27 wherein the second light reflective surface comprises a spherical mirror coaxial to said lens to reflect light back to said lasing medium to support light oscillation.

29. The device of claim 27 wherein the second light reflective surface is a spherical mirror located radially inwardly concentric with said lens to reflect light back to said lasing medium.

30. The device of claim 27 wherein the first laser light reflective surface is an internally reflective surface formed at an angle of about 45°

to the plane of the strip.

31. The device of claim 27 wherein the first laser light reflective surface is an internally reflective parabolic surface the focal point of which is located in the plane of the strip.