Picosecond bistable optical switch using two-photon transitions

Claim 2

A bistable optical device with switching times in the picosecond range comprising: an optical resonator with an optical resonant cavity therein and including means for extracting a light output beam from said optical resonant cavity, a nonlinear material which is essentially optically transparent disposed in said optical resonant cavity, said nonlinear material having a conduction band and at least an upper and a lower valence bands with an energy spacing therebetween such that a two-hw photon transition can occur from a non-minimum energy location in said upper valence band to said conduction band, and a one-hw photon virtual transition at a non-minimum energy can occur between said upper and lower valence bands, said nonlinear material having an optical length which depends on the intensity of light in said optical resonant cavity; and means for pumping photon energy hw in the range 1/2Δ g <hw<Δ g into said optical resonant cavity in order to stimulate said virtual transition via the two-photon transition, where Δ g is the bandgap between the upper valence band and the conduction band of said nonlinear material.

Claim 3

A bistable optical device as defined in claim 1, wherein said optical resonator is a Fabry-Perot resonator.

Claim 4

A bistable optical device as defined in claim 2, wherein said nonlinear material is a semiconductor material.

Claim 5

A bistable optical switch as defined in claim 3, wherein said photon pumping means includes means for optically biasing said Fabry-Perot resonator with an input power such that the Fabry-Perot resonator has at least two stable transmission states at the optical bias.

Claim 6

A bistable optical device as defined in claim 4, wherein said semiconductor material is a direct bandgap semiconductor material.

Claim 7

A bistable optical device as defined in claim 5, wherein the lower and upper valence bands of said semiconductor material are the split-off valence band and the heavy hole valence band, respectively, and at approximately the two-photon absorption transition momentum location said semiconductor material has an energy gap E s between said split-off valence band and said heavy hole valence band which is less than the bandgap Δ g and greater than one-half the bandgap Δ g .

Claim 8

A bistable optical device as defined in claim 6, wherein said nonlinear semiconductor material is CdTe.

Claim 9

A bistable optical device as defined in claim 7, wherein said nonlinear semiconductor material is Hg 1-x Cd x Te, 0.7<<1.0.

Claim 10

A bistable optical switch with switching times in the picosecond range comprising: a Fabry-Perot resonator including an optical resonant cavity; a nonlinear semiconductor material disposed in said optical resonant cavity of said Fabry-Perot resonator, said semiconductor material having a conduction band, a heavy hole valence band, and at least one other valence band, and having a refractive index which depends on the intensity of light in said optical resonant cavity; and means for optically biasing said Fabry-Perot resonator with an optical input power such that the Fabry-Perot resonator has at least two stable transmission states, and for pumping photon energy hw in the range 1/2Δ g <hw<Δ g into said optical resonant cavity in order to stimulate a two-photon absorption transition between said heavy hole valence band and said conduction band and thus switch between said two stable transmission states in said Fabry-Perot resonator, where Δ g is the bandgap between the heavy hole valence band and the conduction band of said semiconductor material, wherein said semiconductor material has a band structure with a one-hw photon potential virtual transition between two valence bands thereof at a non-minimum energy.

Claim 11

A bistable optical switch with switching times in the picosecond range comprising: a Fabry-Perot resonator including an optical resonant cavity; a nonlinear semiconductor material disposed in said optical resonant cavity of said Fabry-Perot resonator, said semiconductor material having a conduction band, a heavy hole valence band, and at least one other valence band, and having a refractive index which depends on the intensity of light in said optical resonant cavity; and means for optically biasing said Fabry-Perot resonator with an optical input power such that the Fabry-Perot resonator has at least two stable transmission states, and for pumping photon energy hw in the range 1/2Δ g <hw<Δ g into said optical resonant cavity in order to stimulate a two-photon absorption transition between said heavy hole valence band and said conduction band and thus switch between said two stable transmission states in said Fabry-Perot resonator, where Δ g is the bandgap between the heavy hole valence band and the conduction band of said semiconductor material, wherein said semiconductor material has a band structure with a one-hw photon potential virtual transition between two valence bands thereof at a non-minimum energy.

Claim 12

A bistable optical switch as defined in claim 9, wherein said nonlinear semiconductor material is a direct bandgap semiconductor material.

Claim 13

A bistable optical switch as defined in claim 10, wherein said semiconductor material has a band structure such that the two-photon transition between the heavy hole valence band and the conduction band and the one-photon virtual transition between said two valence bands line up at approximately but not exactly the same momentum.

Claim 14

A bistable optical switch as defined in claim 11, wherein said at least one other valence band in said semiconductor material is the split-off valence band and said virtual transition is a one-hw photon virtual transition between said split-off valence band and said heavy hole valence band.

Claim 15

A bistable optical switch as defined in claim 11, wherein said semiconductor material is Hg 1-x Cd x Te, 0.7<x<1.0.

Claim 16

A bistable optical switch as defined in claim 12, wherein the photon energy pumped by said pumping means has its energy hw chosen such that ΔE h =E h -E h ' is a small positive energy, where E h ' is the energy of a hole created by the two-photon absorption transition in said heavy hole band and E h is the energy of a heavy hole near in energy to the hole created by the two photon transition and capable of said virtual transition between the heavy hole and split-off valence bands to thereby contribute to the susceptibility of the semiconductor material.

Claim 19

A bistable optical switch with switching times in the picosecond range comprising: a Fabry-Perot resonator including an optical resonant cavity; a nonlinear semiconductor material disposed in said optical resonant cavity of said Fabry-Perot resonator, said semiconductor material having a conduction band, a heavy hole valence band, and at least one other valence band and having a band structure with a direct bandgap between said heavy hole valence and conduction bands, and capable of having a 2-hw photon transition occur from a non-minimum energy location in said heavy hole band to said conduction band, and a 1-hw photon virtual transition occur at a non-minimum energy location between two of the valence bands, said semiconductor material also having a refractive index which depends on the intensity of light in said optical resonant cavity; means for optically biasing said Fabry-Perot resonator with an optical input power such that the Fabry-Perot resonator has at least two stable transmission states at this optical bias; and means for perturbing the populations of energy states with energies near the valence band energy states with virtual transitions that can give a contribution to the susceptibility to thereby switch between said two stable transmission states in said Fabry-Perot resonator, wherein said energy state perturbing means comprises means for pumping photon energy hw in the range 1/2Δ g <hw<Δ g into said optical resonant cavity in order to stimulate a two-photon absorption transition at said perturbed energy states, where Δ g is the bandgap between the heavy hole valence band and the conduction band of said semiconductor material.

Claim 20

A bistable optical switch with switching times in the picosecond range comprising: a Fabry-Perot resonator including an optical resonant cavity; a nonlinear semiconductor material disposed in said optical resonant cavity of said Fabry-Perot resonator, said semiconductor material having a conduction band, a heavy hole valence band, and at least one other valence band and having a band structure with a direct bandgap between said heavy hole valence and conduction bands, and capable of having a 2-hw photon transition occur from a non-minimum energy location in said heavy hole band to said conduction band, and a 1-hw photon virtual transition occur at a non-minimum energy location between two of the valence bands, said semiconductor material also having a refractive index which depends on the intensity of light in said optical resonant cavity; means for optically biasing said Fabry-Perot resonator with an optical input power such that the Fabry-Perot resonator has at least two stable transmission states at this optical bias; and means for perturbing the populations of energy states with energies near the valence band energy states with virtual transitions that can give a contribution to the susceptibility to thereby switch between said two stable transmission states in said Fabry-Perot resonator, wherein said energy state perturbing means comprises means for pumping photon energy hw in the range 1/2Δ g <hw<Δ g into said optical resonant cavity in order to stimulate a two-photon absorption transition at said perturbed energy states, where Δ g is the bandgap between the heavy hole valence band and the conduction band of said semiconductor material.

Claim 21

A bistable optical switch as defined in claim 16, wherein said at least one valence band in said semiconductor material comprises a split-off valence band and at approximately the two-photon absorption transition momentum location said semiconductor material has an energy gap E s between said split-off valence band and said heavy hole valence band which is less than the bandgap Δ g and greater than one-half the bandgap Δ g ; and the photon energy pumped by said pumping means has its energy hw chosen such that ΔE h =E h -E h ' is a small positive energy, where E h ' is the energy of the hole created by the two-photon absorption transition, and E h is the energy of a heavy hole near in energy to the hole created by the two-photon transition and capable of said virtual transition between the heavy hole and split-off valence bands to thereby contribute to the susceptibility of the semiconductor material.