Single-wavelength semiconductor laser

A single wavelength semiconductor laser comprising:

• laser cavity means, said laser cavity means including a multimode waveguide through which a plurality of transverse modes having different absolute values of propagation constants can be propagated, and means for imparting a periodical perturbation to said waveguide, so that the transverse modes can be coupled to each other when light of a predetermined wavelength is propagated in said waveguide, the two coupled transverse modes travelling forward and rearward along said waveguide to constitute two degenerate laser resonance modes;
• and
• mode selector means for selectively outputting a predetermined laser resonance mode as one of the two degenerate laser resonance modes, said mode selector means being structured so that light returning to said semiconductor laser from outside can be coupled only to the other of the two degenerate laser resonance modes.

A single wavelength semiconductor laser comprising:

• laser cavity means, said laser cavity means including a waveguide, and means for imparting a periodical perturbation to said waveguide so that transverse electric (TE) and transverse magnetic (TM) modes having different absolute values of propagation constants can be coupled to each other, accompanied with a mode conversion, when light of a predetermined wavelength is propagated in said waveguide, the coupled TE and TM modes travelling forward and rearward to constitute two degenerate laser resonance modes;
• and
• mode selector means for selectively outputting a predetermined laser resonance mode as one of the two degenerate laser resonance modes, said mode selector means being structured so that light returning to said semiconductor laser from outside can be coupled only to the other of the two degenerate laser resonance modes.

A single wavelength semiconductor laser comprising:

• laser cavity means, said laser cavity means including a waveguide and means for imparting a perturbation to said waveguide, so that two kinds of modes having different absolute values of propagation constants can be coupled to each other when light of a predetermined wavelength is propagated in said waveguide, the coupled modes respectively travelling in opposite directions to constitute two degenerate laser resonance modes;
• and
• mode selector means for selectively outputting a predetermined laser resonance mode as one of the two degenerate laser resonance modes, said mode selector means being structured so that light returning to said semiconductor laser from outside can be coupled only to the other of the two degenerate laser resonance modes.

A single wavelength semiconductor laser comprising:

• laser cavity means, said laser cavity means including a waveguide and means for imparting a perturbation to said waveguide, so that first and second modes having different absolute values of propagation constants can be coupled to each other when light of a predetermined wavelength is propagated in said waveguide, the coupled first and second modes respectively travelling in opposite first and second directions to constitute first and second laser resonance modes, the first laser resonance mode consisting of the first mode travelling in the first direction and the second mode travelling in the second direction, and second laser resonance mode consisting of the first mode travelling in the second direction and the second mode travelling in the first direction;
• and
• mode selector means for selectively outputting the first mode travelling in the first direction, said mode selector means being structured so that light returning to said semiconductor laser from outside can be coupled only to the the first mode travelling in the second direction.