Second harmonic generator using a laser as a fundamental wave source

Claim 2

A second harmonic generator in accordance with claim 1, CHARACTERIZED IN THAT said quasi-phase matching element (50, 150) comprises an optical waveguide (54) having a periodical guide index distribution structure.

Claim 3

A second harmonic generator in accordance with claim 2, CHARACTERIZED IN THAT said semiconductor laser chip (30) has a first chip end (34) and a second chip end (36) each of which is capable of emitting a light; said second chip end (36) of said semiconductor laser chip (30) is an end on which said semiconductor laser chip (30) is optically coupled with said quasi-phase matching element (50, 150); and said first chip end (34) of said semiconductor laser chip (30) and said periodical guide index distribution structure of said quasi-phase matching element (50, 150) constitute an external optical resonator for lasing of said semiconductor laser chip (30).

Claim 4

A second harmonic generator in accordance with claim 2, CHARACTERIZED BY a structure for lasing of said semiconductor laser chip (30) utilizing feedback of a light from said periodical guide index distribution structure.

Claim 5

A second harmonic generator in accordance with claim 1, CHARACTERIZED IN THAT said semiconductor laser chip (30) has a first chip end (34) and a second chip end (36) each of which is capable of emitting a light; said second chip end (36) of said semiconductor laser chip (30) is an end on which said semiconductor laser chip (30) is optically coupled with said quasi-phase matching element (50, 150); and said first chip end (34) of said semiconductor laser chip (30) has provided thereon a first reflection coating film constituting an external optical resonator for lasing of said semiconductor laser chip (30); and said second chip end (36) of said semiconductor laser chip (30) has provided thereon a second reflection coating film free of contribution to said lasing of said semiconductor laser chip (30).

Claim 6

A second harmonic generator in accordance with claim 2, CHARACTERIZED IN THAT said periodical guide index distribution structure has a reflection effect on said fundamental wave light.

Claim 7

A second harmonic generator in accordance with claim 2, CHARACTERIZED IN THAT said periodical guide index distribution structure has a transmission effect on said second harmonic light.

Claim 8

A second harmonic generator in accordance with claim 2, CHARACTERIZED IN THAT said periodical guide index distribution structure has a period of variation of a guide index satisfying: (i) conditions of quasi-phase matching of said quasi-phase matching element (50, 150); (ii) conditions of reflection of said fundamental wave light; and (iii) conditions of transmission of said second harmonic light.

Claim 9

A second harmonic generator in accordance with claim 4, CHARACTERIZED IN THAT said semiconductor laser chip (30) and said quasi-phase matching element (50, 150) are arranged so that said feedback of said light is performed from said optical waveguide (54) to said active layer in said semiconductor laser chip (30).

Claim 10

A second harmonic generator in accordance with claim 1, CHARACTERIZED IN THAT said quasi-phase matching element (50, 150) comprises a LiNbO3 substrate (100) having a +C surface (118), an optical waveguide (54) formed on said +C surface (118) of said substrate (100) by a Li+ - H+ proton exchange method, and a periodical guide index distribution structure formed in said optical waveguide (54) by Ti diffusion.

Claim 11

A second harmonic generator in accordance with claim 8, CHARACTERIZED IN THAT said condition of quasi-phase matching is Λ/2 =Lc = (2s-1)λ(ω)/4{N(ω) - N(ω)}, where s is a positive integer, Λ is a period of variation of said guide index in said periodical guide index distribution structure, Lc is a length by an odd number as large as a coherence length of said fundamental light in said quasi-phase matching element (50, 150), λ(ω) is a wavelength of said fundamental wave light, N(ω) is an effective guide index of said optical waveguide (54) for said fundamental wave light, and N(2ω) is an effective guide index of said optical waveguide (54) for said second harmonic light.

Claim 12

A second harmonic generator in accordance with claim 8, CHARACTERIZED IN THAT said condition of said quasi-phase matching is Λ/2 = L(ω) = pλ(ω)/4N(ω), where p is a positive integer, Λ is a period of variation of said guide index in said periodical guide index distribution structure, λ(ω) is a wavelength of said fundamental wave light, L(ω) is odd times of the coherence length for the fundamental wavelength λ(ω), and N(ω) is an effective guide index of said optical waveguide (54) for said fundamental wave light.

Claim 13

A second harmonic generator in accordance with claim 8, CHARACTERIZED IN THAT said condition of transmission of said second harmonic light is Λ/2 =L(2ω) = (2q-1)λ(ω)/8N(2ω) where q is a positive integer, Λ is a period of variation of said guide index in said periodical guide index distribution structure, λ(2ω) is a wavelength of said second harmonic light, L(2ω ) is odd times of the coherence length for the wavelength λ(2ω) of said second harmonic light, and N(2ω) is an effective guide index of said optical waveguide (54) for said second harmonic light.

Claim 14

A second harmonic generator in accordance with claim 1, CHARACTERIZED IN THAT said quasi-phase matching element (50, 150) has a first element end (58, 158) capable of introduction and emission of said fundamental wave light and a second element end (60, 160) capable of introduction and emission of said second harmonic light, each of said first and second element ends (58, 158; 60, 160) having a second reflection coating film to keep reflection of said fundamental wave light and said second harmonic light to respective predetermined levels.

Claim 15

A second harmonic generator in accordance with claim 1, CHARACTERIZED IN THAT a 1/2 wavelength plate (72) is inserted between said semiconductor laser chip (30) and said quasi-phase matching element (50, 150).

Claim 16

A second harmonic generator in accordance with claim 1, CHARACTERIZED IN THAT said active layer of said semiconductor laser chip (30) and said optical waveguide (54) in said quasi-phase matching element (50, 150) are optically coupled with each other.

Claim 17

A second harmonic generator in accordance with claim 1, CHARACTERIZED IN THAT said quasi-phase matching element (50, 150) is of a planar type.

Claim 18

A second harmonic generator in accordance with claim 1, CHARACTERIZED IN THAT said quasi-phase matching element (50, 150) is of an optical fiber type.

Claim 19

A second harmonic generator in accordance with claim 1, CHARACTERIZED IN THAT said semiconductor laser chip (30) is adapted to be used under application of an operation current in a range free of lasing with said semiconductor laser chip (30) alone.

Claim 20

A second harmonic generator in accordance with claim 2, CHARACTERIZED IN THAT said quasi-phase matching element (50, 150) comprises a crystal substrate having a +C face (118) as a surface; said quasi-phase matching element (50, 150) has a first element end (58, 158) on a side of said semiconductor laser chip (30), said first element end (58, 158) being capable of introduction and emission of said fundamental wave light, and a second element end (60, 160) opposite to said first element end (58, 158) being capable of introduction and emission of said second harmonic light; said optical waveguide (54) extends between said first and second element ends (58, 158; 60, 160); said first and second element ends (58, 158; 60, 160) being inclined at interior angles Θ1 and Θ2, respectively, with respect to said +C face (118); and said semiconductor laser chip (30) and said quasi-phase matching element (50, 150) are arranged so that said fundamental wave light can be incident into said optical waveguide (54) at a Brewster angle or an angle approximate thereto.

Claim 21

A second harmonic generator in accordance with claim 20, CHARACTERIZED IN THAT said interior angles Θ1 and Θ2 satisfy Θ1 = Θ2.

Claim 22

A second harmonic generator in accordance with claim 20, CHARACTERIZED IN THAT said crystal substrate includes a substrate layer in which material of said crystal substrate remains unchanged; said optical waveguide (54) and said substrate layer define an interface therebetween which is parallel to said +C face(118); and said interior angle Θ1 is set up at a value at which said fundamental wave light and said second harmonic light in said optical waveguide (54) is allowed to enter said interface and said +C face (118) at a total reflection angle.

Claim 23

A second harmonic generator in accordance with claim 20, CHARACTERIZED IN THAT satisfied are conditions: ϑ1 = tan-1 n2; Θ1 > sin-1 (n3/n2)) - sin-1 {(1/n2)sin(tan-1 n2)}; and Θ1 < 180° - sin-1 (n3/n2) - sin-1 {(1/n2)sin(tan-1 n2)} where ϑ1 is said Brewster angle, n2 is a guide index of said optical waveguide (54) for said fundamental wave light; n3 is a guide index of said material of said crystal substrate for said fundamental light.

Claim 24

A second harmonic generator in accordance with claim 20, CHARACTERIZED IN THAT said interior angle Θ1 satisfies 49.2° < Θ1 < 83.3°, when said fundamental wave light has a wavelength of 830 nm.

Claim 25

A second harmonic generator in accordance with claim 20, CHARACTERIZED IN THAT said first and second element ends (58, 158; 60, 160) and said +C face (118) define respective edges substantially parallel to each other.