Fundamental transverse mode operation in solid state lasers

Claim 2

In a solid state laser, a monolithic body comprising: an active medium capable of producing stimulated coherent radiation of free space wavelength lambda in a plurality of transverse modes when suitably pumped, said active medium having a first reflective face forming one mirror of an optical resonator for sustaining said radiation and having a second face, opposite said first face, through which said radiation is transmitted; a passive portion disposed contiguous with said second face and in the path of said radiation, said passive portion having a third face, opposite said first face, forming another mirror of said resonator, at least one of said first and third faces being partially transmissive to permit the egress of said radiation from said resonator, said passive portion including an elongated dielectric region therein having a refractive index higher than the refractive index n2 of the remainder of said passive portion surrounding said dielectric region, said dielectric region having a cross-section perpendicular to the optic axis of said resonator which is substantially congruent with the shape of the crosssection of the active region of said active medium, the dimensions of the cross-section and refractive index of said dielectric region being adapted to support only fundamental transverse modes, and the length L2 of said dielectric region satisfying approximately the condition: L2 > OR = 2w2/ lambda n2 where w is the width of the higher order mode field in said active medium.

Claim 3

The body of claim 1 wherein said elongated dielectric region is a rectangular parallelepiped of width D axially aligned with said active region along the optic axis of said resonator and said remainder of said passive portion has a substantially uniform spatial distribution of refractive index n1 > n2, said dielectric region satisfying the condition that Delta about 3/4 (2 lambda /D)2 where Delta 1 - n2/n1 and (2 lambda /Dn1) << 1.

Claim 4

The body of claim 1 wherein said elongated dielectric region is a rectangular parallelepiped of width D axially aligned with said active region along the optic axis of said resonator, and said remainder of said passive portion is defined by four zones, upper and lower spaced zones of refractive index n2 < n1 which are contiguous with a pair of oppositely facing side surfaces of said dielectric region and a pair of lateral spaced zones of refractive index n3 < n1 which are contiguous with the other pair of oppositely facing side surfaces of said dielectric region.

Claim 5

The body of claim 1 wherein the refractive indices of said dielectric region and of said active region are substantially equal.

Claim 6

The body of claim 1 including an impedance matching layer formed on said second face between and contiguous with said active medium and said passive portion.

Claim 7

The body of claim 1 wherein said active medium comprises a double heterostructure including a pair of heterojunctions defining therebetween said active region of thickness d and a stripe geometry electrical contact of width S, said active region thereby being substantially a rectangular parallelepiped of cross-sectional dimensions: width S and height d.

Claim 8

The body of claim 6 wherein said active medium and said passive portion comprise AlGaAs.

Claim 9

The body of claim 6 wherein said active medium comprises AlGaAs, said passive portion comprises glass and including an impedance matching layer between and contiguous with said active medium and said passive portion.

Claim 10

The body of claim 1 including means for pumping said active medium to generate said radiation.

Claim 11

In a solid state laser adapted for fundamental transverse mode operation, a monolithic body comprising: a multilayered active medium including an epitaxial layer of n-AlxGa1 xAs, at least one epitaxial layer of AlyGa1 yAs, 0 < or = y < x, thereby forming a first heterojunction at the interface therebetween, and an epitaxial layer of p-AlzGa1 zAs, z > y, thereby forming a second heterojunction at the interface between said AlzGa1 zAs layer and said AlyGa1 yAs layer, said medium including a planar p-n junction between said heterojunctions and having a pair of spaced parallel cleavage surfaces one of which forms one mirror of an optical resonator, a stripe geometry electrical contact of length L2 and of width S formed on a major surface of said active medium and extending normal to said cleavage surfaces, thereby defining an active region in the shape of a rectangular parallelepiped of thickness d equal to the total thickness of said at least one AlyGa1 yAs layer, of width S, and of length L1, a Passive portion disposed contiguous with said second surface and having a third cleavage surface, parallel to said one mirror, forming another mirror of said resonator, at least one of said first and third surfaces being partially transmissive to radiation generated in said active region, said passive portion including a waveguide region in the shape of a rectangular parallelepiped axially aligned with said active region along the optic axis of said resonator, said waveguide region having length L2, height D, width W and refractive index n1, and the remainder of said passive portion having a refractive index n2 < n1, said waveguide region being designed so that Delta about 3/4 (2 lambda /D)2 where lambda is the free space wavelength of said radiation, Delta 1 - n2/n1) and (2 lambda /Dn1) << 1, thereby to support only fundamental transverse modes both parallel and perpendicular to the plane of said p-n junction and further being designed so that L2 > or = 2S2/ lambda n2 thereby to assure adequate spreading and hence attenuation of higher order modes, said waveguide region comprising AlpGa1 pAs and said remainder comprising AlqGa1 qAs, 0 < or = p < q, the parameters p and q being adapted to reduce reflections at said second surface.

Claim 12

In a solid state laser adapted for fundamental transverse mode operation, a monolithic body comprising: a multilayered active medium including an epitaxial layer of n-AlxGa1 xAs, at least one epitaxial layer of AlyGa1 yAs, 0 < or = y < x, thereby forming a first heterojunction at the interface therebetween, and an epitaxial layer of p-AlzGa1 zAs, z > y, thereby forming a second heterojunction at the interface between said AlzGa1 zAs layer and said AlyGa1 yAs layer, said medium including a planar p-n junction between said heterojunctions and having a pair of spaced parallel cleavage surfaces one of which forms one mirror of an optical resonator, a stripe geometry electrical contact of length L2 and of width S formed on a major surface of said active medium and extending normal to said cleavage surfaces, thereby defining an active region in the shape of a rectangular parallelepiped of thickness d equal to the total thickness of said at least one AlyGa1 yAs layer, of width S, and of length L1, a Passive portion disposed contiguous with said second surface and having a third cleavage surface, parallel to said one mirror, forming another mirror of said resonator, at least one of said first and third surfaces being partially transmissive to radiation generated in said active region, said passive portion including a waveguide region in the shape of a rectangular parallelepiped axially aligned with said active region along the optic axis of said resonator, said waveguide region having length L2, height D, width W and refractive index n1, and the remainder of said passive portion having a refractive index n2 < n1, said waveguide region being designed so that Delta about 3/4 (2 lambda /D)2 where lambda is the free space wavelength of said radiation, Delta 1 - n2/n1) and (2 lambda /Dn1) << 1, thereby to support only fundamental transverse modes both parallel and perpendicular to the plane of said p-n junction and further being designed so that L2 > or = 2S2/ lambda n2 thereby to assure adequate spreading and hence attenuation of higher order modes, said waveguide region comprising AlpGa1 pAs and said remainder comprising AlqGa1 qAs, 0 < or = p < q, the parameters p and q being adapted to reduce reflections at said second surface.