Mode control using transversal bandgap structure in VCSELs

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.

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.

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.

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.