Mode control using transversal bandgap structure in VCSELs

• US 20020163947A1
• Filed: 03/08/2002
• Published: 11/07/2002
• Est. Priority Date: 03/09/2001
• Status: Active Grant

• Current Assignee: Alight Photonics ApS
• Original Assignee: Alight Technologies ApS
• Inventors: Birkedal, Dan, Ostergaard, John Erland
• Granted Patent: US 6,683,898 B2
• Time in Patent Office: Days
• US Class Current: 372/43
• CPC Class Codes: G02B 2006/1213 comprising photonic band-gap structures or photonic lattices
• CPC Class Codes: H01S 2301/166 Single transverse or lateral mode
• CPC Class Codes: H01S 5/11 Comprising a photonic bandgap structure
• CPC Class Codes: H01S 5/18311 using selective oxidation
• CPC Class Codes: H01S 5/18313 by oxidizing at least one of the DBR layers
• CPC Class Codes: H01S 5/18344 characterized by the mesa, e.g. dimensions or shape of the mesa
• CPC Class Codes: H01S 5/18355 having a defined polarisation
• CPC Class Codes: H01S 5/18369 based on dielectric materials
• CPC Class Codes: H01S 5/18377 comprising layers of different kind of materials, e.g. combinations of semiconducting with dielectric or metallic layers
• CPC Class Codes: H01S 5/18386 Details of the emission surface for influencing the near- or far-field, e.g. a grating on the surface
• CPC Class Codes: H01S 5/18394 Apertures, e.g. defined by the shape of the upper electrode

Abstract

A vertical cavity surface emitting laser (VCSEL) having a photonic band gap (PBG) region formed within or adjacent to a first and/or a second mirror, or within a spacer layer positioned between a gain region and at least one of the mirrors. The PBG region has a predetermined periodicity which substantially prevents the generated light from propagating the region, and defines a light aperture without the periodicity so as to allow the generated light to propagate through the aperture. The PBG region does not extend through the gain region, thereby allowing the full gain region to be used. Controls the efficiency of laser action by suppressing or preventing laser action in certain modes without losses, rather the modes are made forbidden. Energy from the forbidden modes is eventually coupled back to the allowed mode(s).

Provides a separation of the confinement of the gain region and the mode control without introducing energy losses.

Claims

1. A vertical cavity surface emitting laser comprising

a semiconductor material layer having a gain region adapted to generate light and to emit the generated light,

first and second at least substantially parallel mirrors forming a laser cavity comprising the gain region and at least one spacer layer being positioned between the gain region and the first and/or the second mirror, at least one of the mirrors being partially transparent to the generated light so as to allow the light generated in the gain region to be emitted through said at least one mirror, the laser cavity and the gain region supporting at least one transverse electromagnetic mode for the generated light, and

a photonic band gap region formed within or adjacent to the first and/or the second mirror, or within one of the at least one spacer layer(s), the photonic band gap region being positioned at least substantially parallel to the first and second mirror, the photonic band gap region having a predetermined periodicity which substantially prevents the generated light from propagating in said region, the photonic band gap region further defining a light aperture without the predetermined periodicity, so as to allow the generated light to propagate through said light aperture, the dimensions of the photonic band gap region and the light aperture being adapted to at least partly control an efficiency of laser action in each transverse electromagnetic mode, the dimension of the photonic band gap region in a direction being substantially normal to the first and second mirror being significantly smaller than the overall dimension of the vertical cavity surface emitting laser in said direction.

2. A vertical cavity surface emitting laser according to claim 1, wherein the photonic band gap region is positioned in such a way that it does not intersect the gain region.

3. A vertical cavity surface emitting laser according to claim 1, wherein the laser cavity and the gain region support a plurality of transverse modes for the generated light, and wherein each transverse electromagnetic mode can be defined by a distribution of wave-vectors k having transverse components k_T in the photonic band gap region, and wherein the dimensions of the photonic band gap region and the light aperture controls the laser action for each transverse electromagnetic mode by controlling a ratio between transverse components k_T lying within the light aperture and transverse components k_T lying within the photonic band gap region.

4. A vertical cavity surface emitting laser according to claim 3, wherein the ratio between transverse components k_T lying within the light aperture and transverse components k_T lying within the photonic band gap region determines a suppression or prevention of laser action in transverse electromagnetic modes so as to suppress or prevent laser action in modes having a low ratio in relation to modes having a high ratio.

5. A vertical cavity surface emitting laser according to claim 1, wherein the dimensions of the photonic band gap region and the light aperture are adapted to deteriorate laser action in higher order transverse electromagnetic modes in relation to laser action in a fundamental transverse electromagnetic mode of the cavity (TEM₀₀).

6. A vertical cavity surface emitting laser according to claim 1, further comprising current supply means for supplying an electric current to a predetermined region of the semiconductor material, said predetermined region defining the gain region, said predetermined region being characterised in that it, in a plane at least substantially parallel to the first and second mirror, has a substantial overlap with two or more transverse electromagnetic modes of the cavity.

7. A vertical cavity surface emitting laser according to claim 1, further comprising optical pumping means for supplying optical pumping to a predetermined region of the semiconductor material, said predetermined region defining the gain region, said predetermined region being characterised in that it, in a plane at least substantially parallel to the first and second mirror, has a substantial overlap with two or more transverse electromagnetic modes of the cavity.

8. A vertical cavity surface emitting laser according to claim 1, wherein the first and second parallel mirrors are distributed Bragg reflectors.

9. A vertical cavity surface emitting laser according to claim 1, wherein the light aperture has a three or more fold symmetry.

10. A vertical cavity surface emitting laser comprising

a semiconductor material body having a gain region adapted to generate light and to emit the generated light,

first and second parallel mirrors forming a laser cavity comprising the gain region and at least one spacer layer being positioned between the gain region and the first and/or the second mirror, at least one of the mirrors being partially transparent to the generated light so as to allow the light generated in the gain region to be emitted through said at least one mirror, the laser cavity and the gain region supporting at least one transverse electromagnetic mode for the generated light, and

a photonic band gap region formed within or adjacent to the first and/or the second mirror, or within one of the at least one spacer layer(s), the photonic band gap region being positioned at least substantially parallel to the first and second mirror, the photonic band gap region having a predetermined periodicity which substantially prevents the generated light from propagating in said region in the first plane, the photonic band gap region further defining an elongated light aperture without the predetermined periodicity, said elongated aperture having a dimension α

along a first axis and a dimension β

<

α

along a second axis perpendicular to the first axis, the dimensions of the photonic band gap region and the elongated light aperture being adapted to at least partly control an efficiency of laser action in each transverse electromagnetic mode and to suppress or prevent laser action in transverse electric modes which are not polarised at least substantially parallel to the first axis, the dimension of the photonic band gap region in a direction being at least substantially normal to the first and second mirror being significantly smaller than the overall dimension of the vertical cavity surface emitting laser in said direction.

11. A vertical cavity surface emitting laser according to claim 10, wherein the photonic band gap region is positioned in such a way that it does not intersect the gain region.

12. A vertical cavity surface emitting laser according to claim 10, wherein the elongated light aperture has a two fold symmetry.

14. A vertical cavity surface emitting laser according to claim 13, wherein the dimension of the photonic band gap region in a direction being substantially normal to the first and second mirror is significantly smaller than the overall dimension of the vertical cavity surface emitting laser in said direction.

15. A vertical cavity surface emitting laser according to claim 13, wherein the photonic band gap region is positioned in such a way that it does not intersect the gain region.

16. A vertical cavity surface emitting laser according to claim 13, wherein the light aperture has a three or more fold symmetry.

18. A phased array of vertical cavity surface emitting lasers according to claim 17, wherein the dimension of the photonic band gap region in a direction being substantially normal to the first and second mirror is significantly smaller than the overall dimension of the phased array of vertical cavity surface emitting lasers in said direction.

19. A phased array of vertical cavity surface emitting lasers according to claim 17, wherein the photonic band gap region is positioned in such a way that it does not intersect the gain region.

20. A phased array of vertical cavity surface emitting lasers according to claim 17, wherein the dimensions and positions of the light apertures are adapted to focus the emitted light at a distance from the laser.

30. A method of manufacturing an array of coupled vertical cavity surface emitting lasers with individual control of transverse electromagnetic modes, the method comprising the steps of performing the steps according to claim 16, wherein the step of forming the photonic band gap region comprises the step of forming the photonic band gap region so as to delimit two or more light apertures.

13. A vertical cavity surface emitting laser comprising

a semiconductor material body having a gain region adapted to generate light and to emit the generated light,

first and second parallel mirrors forming a laser cavity comprising the gain region and at least one spacer layer being positioned between the gain region and the first and/or the second mirror, at least one of the mirrors being partially transparent to the generated light so as to allow the light generated in the gain region to be emitted through said at least one mirror, the laser cavity and the gain region supporting at least one transverse electromagnetic mode for the generated light, and

a photonic band gap region formed within or adjacent to the first and/or the second mirror, or within one of the at least one spacer layer(s), the photonic band gap region being positioned at least substantially parallel to the first and second mirror, the photonic band gap region being formed by a periodic lattice of scattering centres having a periodicity which substantially prevents the generated light from propagating in said region, the scattering centres being elongated along a first axis, the photonic band gap region further defining a light aperture without the predetermined periodicity, wherein the dimensions of the photonic band gap region and the light aperture being adapted to at least partly control an efficiency of laser action in each transverse electromagnetic mode and the elongation of the scattering centres is adapted to suppress or prevent laser action in transverse electric modes which is not polarised at least substantially parallel to the first axis.

17. A phased array of vertical cavity surface emitting lasers comprising

a semiconductor material body having a gain region adapted to generate light and to emit the generated light,

first and second parallel mirrors forming a laser cavity comprising the gain region and at least one spacer layer being positioned between the gain region and the first and/or the second mirror, at least one of the mirrors being partially transparent to the generated light so as to allow the light generated in the gain region to be emitted through said at least one mirror, and

a photonic band gap region formed within or adjacent to the first and/or the second mirror, or within one of the at least one spacer layer(s), the photonic band gap region being at least substantially parallel to the first and second mirror, the photonic band gap region having a predetermined periodicity which substantially prevents the generated light from propagating in said region, the photonic band gap region further defining two or more separated light apertures positioned within a region defined by a projection of the gain region onto a plane being adjacent to or within the first or the second mirror, the two or more light apertures being regions without the predetermined periodicity forming two or more coupled laser resonators, the dimensions of the photonic band gap region and the two or more light apertures being adapted to at least partly control an efficiency of laser action in transverse electromagnetic modes in each laser resonator.

21. A method of manufacturing a vertical cavity surface emitting laser with control of transverse electromagnetic mode, the method comprising the steps of:

providing a substrate,

forming a first parallel stack of distributed Bragg reflectors on the substrate,

forming an active layer and a spacer layer on the first parallel stack,

forming a second parallel stack of distributed Bragg reflectors on the active layer and the spacer layer,

forming a photonic band gap region within or adjacent to the first and/or the second parallel stack, or within the spacer layer, by forming a periodic modulation in the permittivity of one or more layers of the first and/or the second parallel stack, or the spacer layer, said photonic band gap region being formed so as to delimit a light aperture for controlling the transverse electromagnetic mode, said light aperture being formed by a region in the photonic band gap region without said periodic modulation of the permittivity.

22. A method according to claim 21, wherein the photonic band gap region is formed and positioned in such a way that it does not intersect the gain region.

23. A method according to claim 21, wherein said periodic modulation of the permittivity is formed by forming a periodic lattice of holes in the first and/or the second parallel stack.

24. A method according to claim 21, wherein said periodic modulation of the permittivity is formed by depositing metallic pads in a periodic lattice on the second stack.

25. A vertical cavity surface emitting laser according to claim 21, wherein the light aperture has a three or more fold symmetry.

26. A method according to claim 25, wherein the light aperture at least substantially has the shape of a regular polygon.

27. A vertical cavity surface emitting laser according to claim 21, wherein the light aperture has a two fold symmetry and is elongated along a first axis defining a polarisation axis for the modes.

28. A method according to claim 21, further comprising the steps of:

forming a current aperture for defining a gain region in the active layer, and

forming charge injection means for providing current to the active layer.

29. A method according to claim 21, wherein the first parallel stack is formed by materials which are at least substantially transparent for radiation of wavelength λ

_p, and wherein the active layer at least substantially absorbs radiation of wavelength λ

_p.