Optical modulator
View Patent ↗Provided is an optical modulator for modulating light comprising: a superlattice structure having a plurality of interleaved narrow and wide bandgap semiconductor layers, wherein wave functions of energy states of electrons and holes in different narrow bandgap layers are coupled; and a power supply that applies voltage to the superlattice structure between a first non-zero voltage and a second non-zero voltage to modulate the light.
1. An optical modulator for modulating light comprising:
a superlattice structure having a plurality of interleaved narrow and wide bandgap semiconductor layers, wherein wave functions of energy states of electrons and holes in different narrow bandgap layers are coupled, said superlattice having an absorption spectrum characterized by an absorption edge; and
a power supply that applies voltage in a first range of voltages to the superlattice structure to modulate the light, which first voltage range is contiguous with a second lower voltage range and wherein in the first range the absorption edge red shifts and transmittance of the superlattice structure for the light decreases with increase in voltage and in the second range the absorption edge blue shifts and transmittance increases with increase in voltage.
2. An optical modulator according to claim 1 wherein in the first voltage range the wave functions are substantially decoupled and the absorption edge is determined by transitions between energy states in a same narrow bandgap layer.
3. An optical modulator according to claim 1 wherein following application of voltage in the first range, the power supply applies voltage in the second range to the modulator to remove electrons and holes generated therein by passage of the light therethrough.
4. An optical modulator according to claim 1 wherein substantially none of the narrow bandgap layers and at least one of the wide bandgap layers is seeded with non-radiative electron traps.
5. An optical modulator according to claim 4 wherein the at least one wide bandgap layers comprises all the wide bandgap layers.
6. An optical modulator according to claim 4 wherein the at least one wide bandgap layer comprises some but not all the wide bandgap layers.
7. An optical modulator according to claim 6 wherein the at least one wide bandgap layer comprises every other wide bandgap layer.
8. An optical modulator according to claim 6 wherein the at least one wide bandgap layer comprises every fourth wide bandgap layers.
9. An optical modulator according to claim 4 wherein the traps in a wide bandgap layer are generated by growing the wide bandgap layer at low temperature.
10. An optical modulator according to claim 1 wherein thickness of the narrow bandgap layers is less than or equal to 10 nanometers.
11. An optical modulator according to claim 10 wherein thickness of the narrow bandgap layers is substantially equal to 3 nanometers.
12. An optical modulator according to claim 1 wherein the thickness of the wide bandgap layers is less than or equal to 6 nanometers.
13. An optical modulator according to claim 12 wherein the thickness of the wide bandgap layers is substantially equal to 3 nanometers.
14. An optical modulator according to claim 1 wherein a ratio of thickness of a wide bandgap layer to a narrow bandgap layer is greater than or equal to one.
15. An optical modulator according to claim 14 wherein the ratio is greater than or equal to two.
16. An optical modulator according to claim 14 wherein the ratio is greater than or equal to three.
17. An optical modulator according to claim 1 wherein the number of narrow bandgap layers comprised in the superlattice structure is greater than 50.
18. An optical modulator according to claim 17 wherein the number of narrow bandgap layers comprised in the superlattice structure is substantially equal to 200.
19. An optical modulator according to claim 18 wherein the number of narrow bandgap layers comprised in the superlattice structure is substantially equal to 300.
20. A optical modulator according to claim 1 wherein the superlattice structure is formed in an intrinsic region of a pin diode.
21. An optical modulator according to claim 1 wherein the first range has a lower bound voltage less than 30 volts.
22. An optical shutter according to claim 21 wherein the lower bound of the first voltage range is less than 15 volts.
23. An optical modulator according to claim 22 wherein the lower bound of the first voltage range is between 5 and 10 volts.
24. An optical modulator according to claim 21 wherein the lower bound of the first voltage range is substantially equal to 25 volts.
25. An optical modulator according to claim 21 wherein the first voltage range is a voltage range between 25–55 volts.
26. An optical modulator according to claim 1 wherein the narrow bandgap layers are formed form GaAs.
27. An optical modulator according to claim 1 wherein the wide bandgap layers are formed from Al x Ga (1-x) As.
28. An optical modulator according to claim 27 wherein x is less than or equal to 0.7.
29. An optical modulator according to claim 28 wherein x is substantially equal to 0.3.
30. A method of modulating intensity of abeam of light comprising:
directing the beam of light so that it is incident on a superlattice structure having a plurality of interleaved narrow and wide bandgap semiconductor layers, wherein wave functions of energy states of electrons and holes in different narrow bandgap layers are coupled when voltage is not applied to the superlattice, said superlattice having an absorption spectrum characterized by an absorption edge; and
applying voltage in a first range of voltages to the superlattice structure to modulate the light, which first voltage range is contiguous with a second lower voltage range and wherein in the first range the absorption edge red shifts and transmittance of the superlattice structure for the light decreases with increase in voltage and in the second range the absorption edge blue shifts and transmittance increases with increase in voltage.
31. A method according to claim 30 wherein in the first voltage range the wave functions are substantially decoupled and the absorption edge is determined by transitions between energy states in a same narrow bandgap layer.
32. A method according to claim 30 and comprising, following application of voltage in the first voltage range, applying voltage in the second voltage range to the modulator to remove electrons and holes generated therein by the passage of the light beam therethrough.
33. An optical modulator comprising:
a multilayer heterojunction structure comprising a plurality of interleaved narrow and wide bandgap semiconductor layers; and
non-radiative traps located in at least one of the wide bandgap layers and substantially none of the narrow bandgap layers.
34. An optical modulator according to claim 33 wherein the at least one wide bandgap layers comprises all the wide bandgap layers.
35. An optical modulator according to claim 33 wherein the at least one wide bandgap layer comprises some but not all the wide bandgap layers.
36. An optical modulator according to claim 35 wherein the at least one wide bandgap layer comprises every other wide bandgap layer.
37. An optical modulator according to claim 35 wherein the at least one wide bandgap layer comprises every fourth wide bandgap layers.
38. An optical modulator according to claim 33 wherein the traps in a wide bandgap layer are traps generated by growing the wide bandgap layer at low temperature.