Semiconductor laser device

A semiconductor laser device comprising:

• a first-conductivity-type semiconductor substrate;
• a first-conductivity-type cladding layer, a first-conductivity-type-side optical guide layer, an active layer, a second-conductivity-type-side optical guide layer, a second-conductivity-type cladding layer, and a second-conductivity-type contact layer, which are laminated above the first-conductivity-type semiconductor substrate;
• a resonator formed of a front end surface and a rear end surface and allowing a round trip of a laser beam therebetween;
• and
• a ridge region in which the laser beam is guided between the front end surface and the rear end surface, the ridge region having a width of 2 W, wherein
• an oscillation wavelength is 2 and a high-order mode of a first order or higher is allowed in a lamination direction of the layers,
• the ridge region is composed of a ridge inner region of which a width is 2 Wi and an effective refractive index is nai, and ridge outer regions which are provided on both sides of the ridge inner region and of which a width is Wo and an effective refractive index is nao, the ridge outer regions having current non-injection structures,
• cladding regions in which at least the second-conductivity-type contact layer and the second-conductivity-type cladding layer are removed and an effective refractive index is nc, are provided on both sides of the ridge outer regions,
• an average refractive index nae in the ridge inner region and the ridge outer regions is represented by the following expression:
• [
• Mathematical
• ⁢
• 1
• ]
• (
• n
• a
• i
• ·
• W
• i
• +
• n
• a
• o
• ·
• W
• o
• )
• /
• (
• W
• i
• +
• W
• o
• )
• ,
• the following relationship is satisfied:
• [
• Mathematical
• ⁢
• 2
• ]
• 
• 2
• ⁢
• π
• λ
• ⁢
• n
• a
• e2
• -
• n
• c
• 2
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• (
• W
• i
• +
• W
• o
• )
• >
• π
• 2
• ,
• and
• the width Wo of each ridge outer region is greater than a distance from a lower end of each current non-injection structure to the active layer and is smaller than W which is ½ of the width of the ridge region.