Semiconductor optical device having a non-linear operational characteristic

A bistable laser diode, comprising:

• a gain region for amplifying optical radiation having a first wavelength to produce an output optical beam;
• a saturable absorption region for absorbing said optical radiation to suppress the amplification of the optical beam of the gain region said saturable absorption region reducing the absorption in response to irradiation of a control optical beam;
• said saturable absorption region comprising a quantum well layer having upper and lower major surfaces separated from each other by a first thickness, said quantum well layer comprising a first semiconductor material having a first band gap;
• a first quantum level pair formed in said quantum well layer in correspondence to said first thickness, said first quantum level pair comprising a first quantum level for electrons and a second quantum level for holes separated from each other by a first energy gap;
• said first thickness of the first material layer being determined such that said first energy gap corresponds to the first wavelength of the optical radiation that is amplified in the gain region;
• a first barrier layer having upper and lower major surfaces separated from each other by a second thickness chosen to allow the tunneling of electrons and holes through said first barrier layer, said first barrier layer comprising a second semiconductor material having a second band gap larger than the first band gap and disposed above said quantum well layer;
• a second barrier layer having upper and lower major surfaces separated from each other by a third thickness chosen to allow the tunneling of electrons and holes through said second barrier layer, said second carrier layer comprising a third semiconductor material having a third band gap larger than the first band gap and disposed below said quantum layer;
• said first and second barrier layers forming a potential well in the quantum well layer for confining electrons and holes;
• a carrier extinction layer having upper and lower major surfaces separated from each other by a fourth thickness larger than said first thickness, said carrier extinction layer being provided at least either of above the first barrier layer and below the second barrier layer;
• a second quantum level pair formed in said carrier extinction layer in correspondence to said third thickness, said second quantum level pair comprising a third quantum level for electrons and a fourth quantum level for holes separated from each other by a second energy gap that is smaller than said first energy gap;
• and
• carrier annihilating means for annihilating the electrons and holes from said third and fourth quantum levels by inducing a stimulated emission of light that has an energy identical with the second energy gap.

A laser diode, comprising:

• a first clad layer of a first conductivity type, said first clad layer having upper and lower major surfaces;
• a first electrode provided on the lower major surface of the first clad layer;
• an active layer having upper and lower major surfaces and provided on the upper major surface of the first clad layer;
• a second clad layer of a second, opposite conductivity type, said second clad layer having upper and lower major surfaces and provided on the upper major surface of the active layer;
• and
• a second electrode provided on the upper major surface of the second clad layer;
• said active layer comprising a material layer of a first material having a first band gap, said material layer having upper and lower major surfaces coincident to the upper and lower major surfaces of the active layer;
• a first quantum well wire of a second material having a second band gap that is smaller than said first band gap, said first quantum well wire extending in a direction parallel to the upper and lower major surfaces of said material layer, said first quantum well wire having a first size in a direction perpendicular to the elongating direction of the first quantum well wire when measured in a plane that is parallel to the upper and lower major surfaces of the material layer, said first size being set such that there are formed a pair of quantum levels, one for electrons and one for holes, in said first quantum well wire such that said quantum levels are separated from each other by a first energy gap corresponding to an energy of an optical beam that is produced by the laser diode;
• a second quantum well wire of a third material having a third band gap that is smaller than any of the first and second band gaps, said second quantum well wire extending parallel to said first quantum well wire at least one side of the first quantum well wire, such that the second quantum well wire is separated from the first quantum well wire by said first material forming the first material layer with a distance such that electrons and holes penetrate through the first material intervening between the first quantum well wire and the second quantum well wire, said second quantum well wire having a second size measured in the same direction as the first size, said second size being set such that there are formed a pair of quantum levels, one for electrons and one for holes, in said second quantum well wire such that the quantum levels in the second quantum well are separated from each other by a second energy gap that is substantially smaller than said first gap;
• said active layer being formed into a rectangular shape when viewed perpendicular to said upper major surface of the active layer, said active layer being defined by a first side wall pair comprising a pair of parallel and opposing side walls each extending in a direction perpendicular to the direction in which the first and second sizes are measured, said pair of opposing side walls being separated from each other with a first distance such that said opposing side walls form a cavity in the active layer that establishes a resonance with a light having an energy corresponding to the second energy gap, said active layer being further defined by a second side wall pair comprising a pair of parallel and opposing side walls each extending in a direction perpendicular to the side walls forming said first side wall pair and perpendicular to the upper and lower major surfaces of the active layer, said side walls forming said second side wall pair being separated from each other by a second distance such that said opposing side walls of the second side wall pair form a cavity in the active layer that establishes a resonance with the optical beam that is produced by the laser diode.

An optical semiconductor device for modulating an incident optical beam, comprising:

• a first material layer having upper and lower major surfaces, said first material layer having a first band gap and a first thickness, said first thickness being determined such that there are formed at least a first quantum level pair and a second quantum level pair, said first quantum level pair comprising a first quantum level for electrons and a second quantum level for holes separated from each other by a first energy gap, said first thickness being determined such that said first energy gap coincides with an energy of the incident optical beam, said second quantum level pair comprising a third quantum level for electrons and a fourth quantum level for holes separated from each other by a second energy gap that is smaller than said first energy gap;
• a second material layer having upper and lower major surfaces and provided on the upper major surface of the first material layer for confining electrons and holes in said first material layer, said second material layer having a second band gap that is substantially larger than the first band gap;
• said first and second material layers being stacked alternately to form an active layered body having upper and lower major surfaces;
• said active layered body being defined by a pair of opposing side walls that are separated from each other by a distance such that said opposing side walls form a cavity that establishes a resonance with an energy coincident to the first energy gap.

A semiconductor optical device having an optical transmittance and absorption changed in response to irradiation of an incident optical beam, comprising:

• a first material layer having a first band gap and a first thickness set so as to allow existence of two-dimensional excitons interacting with the incident optical beam, said first material layer having an optical absorption coefficient that is changed in response to the incident optical beam and characterized by electrons and holes that assume one or more quantum levels;
• a second material layer having a second band gap substantially larger than said first band gap and disposed at both sides of said first material layer, said second material layer having a second thickness for allowing a tunneling of the electrons in the first material layer therethrough;
• and
• a third material layer having a third band gap substantially smaller than said second band gap and provided at least on one side of the second material layer, said third material layer having a third thickness set such that the third material layer is characterized by electrons and holed that assume one or more quantum levels wherein all o the quantum levels of the electrons in the third material layer are energetically different from at least one of the quantum levels of the electrons in the first material layer, said third material layer having an optical absorption coefficient that is substantially smaller than the optical absorption coefficient of the first material layer.

A semiconductor optical device having a refractive index changed responsive to irradiation of an incident optical beam, comprising:

• a first material layer having a first band gap and a first thickness set so as to allow existence of a two-dimensional exciton interacting with the incident optical beam;
• a second material layer having a second band gap substantially larger than said first band gap and disposed at both sides of said first material layer, said second material layer having a second thickness for allowing a tunneling of electron therethrough;
• and
• a third material layer having a third band gap substantially smaller than said second band gap and provided at least on one side of the second material layer, said third material layer having a third thickness set such that there are formed one or more quantum levels of electron all of which being energetically different from at least one of those formed in the first material layer;
• said first thickness being chosen such that there is formed a quantum well structure wherein electrons and holes assume discrete quantum levels respectively at a conduction band and a valence band in the first material layer, said third thickness being chosen such that there is formed a quantum well structure wherein electrons and holes assume another discrete quantum levels respectively at the conduction band and the valence band in the third material layer and such that there exists at least one quantum level of electron in the third material layer of which energy is substantially lower than the that of one quantum level of electron interacting with the incident optical beam in the first material layer;
• said first and second material layers having respective thicknesses and compositions chosen such that there exists an energy difference between the quantum level of the holes in the first material layer and a top edge of the valence band of the second material layer which is substantially reduced as compared to that between a bottom edge of the conduction band in the second material layer and said quantum level of the electrons interacting with the incident optical beam in the first material layer, so that tunneling of electron from the first material layer to the third material layer through the second material layer is facilitated.

An optical device having a variable reflectivity comprising a stacked body of an alternate repetition of a first optical layer having a first refractive index and a second optical layer having a second refractive index, wherein either one of the first and second optical layers comprises:

• a first material layer having a first band gap and a first thickness set so as to allow existence of two-dimensional excitons interacting with the incident optical beam;
• a second material layer having a second band gap substantially larger than said first band gap and disposed at both sides of said first material layer, said second material layer having a second thickness for allowing a tunneling of electron therethrough;
• and
• a third material layer having a third band gap substantially smaller than said second bandgap and provided at least on one side of the second material layer, said third material layer having a thickness set such that there are formed on or more quantum levels of electrons all of which being energetically different from at least one of those formed in the first material layer.