Semiconductor laser

An optical module comprising at least an optical fiber for introducing light outside and a semiconductor laser that includes a semiconductor substrate;

• a core region defined by an active layer formed on one side of the semiconductor substrate;
• and a clad region defined by at least one clad layer overlaying the active layer,
• wherein the core region has a gain region with a length not smaller than 18 micrometers and not greater than 200 micrometers along an optical axis of at least the core region or the clad region;
• at least one of the core region and the clad region has a stripe shape and a stripe width modulated in a direction parallel with a surface of the substrate and perpendicular to the optical axis such that the center portion of the stripe, which works as a multi-mode interference waveguide enabling a lateral multi-mode, has a wider width than vicinity portions of the stripe, each of which works as a mono-mode waveguide,
• said multi-mode interference waveguide has a rectangular plane shape with a lateral width W and a waveguide length L which are decided so that a light intensity distribution at an output terminal of said multi-mode interference waveguide becomes a single-hill lowest order mode, and
• W, L, an effective refractive index n of a laser waveguide, and an operation wavelength λ are decided so as to satisfy a formula as follows:
• 0.9nW2/λ≦L≦1.1nW2/λ.

A semiconductor laser comprising:

• a semiconductor substrate;
• a core region defined by an active layer formed on one side of the semiconductor substrate;
• and a clad region defined by at least one clad layer at least overlaying the active layer,
• wherein the core region has a gain region with a length not smaller than 5 micrometers and not greater than 200 micrometers along an optical axis of at least the core region or the clad region;
• at least one of the core region and the clad region has a stripe shape and a strive width modulated in a direction parallel with a surface of the substrate and perpendicular to the optical axis such that the center portion of the stripe, which works as a multi-mode interference waveguide enabling a lateral multi-mode, has a wider width than vicinity portions of the stripe, each of which works as a mono-mode waveguide,
• said multi-mode interference waveguide has a rectangular plane shape with a lateral width W and a waveguide length L which are decided so that a light intensity distribution at an output terminal of said multi-mode interference waveguide becomes a single-hill lowest order mode, and
• W, L, an effective refractive index n of a laser waveguide, and an operation wavelength λ are decided so as to satisfy a formula as follows:
• 0.9nW2/λ≦L≦1.1nW2/λ.

An optical module comprising at least an optical fiber for introducing light outside and a semiconductor laser that includes a semiconductor substrate;

• a core region defined by an active layer formed on one side of the semiconductor substrate;
• and a clad region defined by at least one clad layer overlaying the active layer,
• wherein the core region has a gain region with a length not smaller than 5 micrometers and not greater than 200 micrometers along an optical axis of at least the core region or the clad region;
• at least one of the core region and the clad region has a stripe shape and a stripe width modulated in a direction parallel with a surface of the substrate and perpendicular to the optical axis such that the center portion of the stripe, which works as a multi-mode interference waveguide enabling a lateral multi-mode, has a wider width than vicinity portions of the stripe, each of which works as a mono-mode waveguide,
• said multi-mode interference waveguide has a rectangular plane shape with a lateral width W and a waveguide length L which are decided so that a light intensity distribution at an output terminal of said multi-mode interference waveguide becomes a single-hill lowest order mode, and
• W, L, an effective refractive index n of a laser waveguide, and an operation wavelength λ are decided so as to satisfy a formula as follows:
• 0.9nW2/λ≦L≦1.1nW2/λ.