QUANTUM-CONFINED STARK EFFECT QUANTUM-DOT OPTICAL MODULATOR

• US 20040085612A1
• Filed: 10/30/2002
• Published: 05/06/2004
• Est. Priority Date: 10/30/2002
• Status: Active Grant

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Northrop Grumman Corporation
• Inventors: Holm, Steven R., Livingston, Peter M., Kunkee, Elizabeth T.
• Granted Patent: US 6,836,351 B2
• Time in Patent Office: Days
• US Class Current: 359/279
• CPC Class Codes: B82Y 10/00 Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
• CPC Class Codes: B82Y 20/00 Nanooptics, e.g. quantum optics or photonic crystals
• CPC Class Codes: G02F 1/01708 in an optical wavequide structure
• CPC Class Codes: G02F 1/01791 Quantum boxes or quantum dots
• CPC Class Codes: G02F 1/2257 the optical waveguides being made of semiconducting material
• CPC Class Codes: G02F 2201/126 push-pull
• CPC Class Codes: H01L 29/127 Quantum box structures

Abstract

A quantum-confined Stark effect quantum-dot optical modulator includes an interferometer having a beam splitter, first and second parallel optical branches fed by the beam splitter and a beam combiner fed by the first and second parallel optical branches and a laser for feeding a laser beam to the beam splitter. First and second optical phase shifters are provided in respective ones of the first and second parallel optical branches. Each optical phase shifter includes an intrinsic semiconductor crystalline planar layer and p-type and n-type planar semiconductor layers on opposite faces of the intrinsic semiconductor crystalline planar layer, the intrinsic layer lying in a plane parallel to a direction of propagation of the laser beam in the respective optical branch. The intrinsic layer has plural layers of planar arrays of quantum dots therein. A reverse bias D.C. voltage source is connected across the p-type and n-type layers.

Claims

1. An optical modulator for modulating a laser beam with a modulation signal, comprising:

an interferometer having a beam splitter, first and second parallel optical branches fed by said beam splitter and a beam combiner fed by said first and second parallel optical branches;

first and second optical phase shifters in respective ones of said first and second parallel optical branches, each one of said first and second optical phase shifters comprising;

(a) an intrinsic semiconductor crystalline planar layer and p-type and n-type planar semiconductor layers on opposite faces of said intrinsic semiconductor crystalline planar layer, said intrinsic layer lying in a plane parallel to a direction of propagation of said laser beam in the respective optical branch;

(b) plural layers of planar arrays of quantum dots in said intrinsic layer;

(c) a reverse bias D.C. voltage source connected across said p-type and n-type layers;

(d) a pair of modulation source terminals connected across said reverse bias D.C. voltage source whereby a modulation signal modulates the reverse bias voltage across said p-type and n-type layers.

2. The apparatus of claim 1 wherein said modulation source terminals of said first and second optical phase shifters are connected in opposite polarity to a common modulation source.

3. The apparatus of claim 2 wherein said intrinsic layer undergoes a change in refractive index sufficient to impose a quarter wavelength phase shift in response to a modulation signal increase by a quarter wavelength excursion voltage of said intrinsic layer.

4. The apparatus of claim 3 wherein said quantum dots in said intrinsic layer promote quantum-confined exciton states defining an exciton optical absorption line spectrum, said quantum-confined states decreasing in energy level upon increase of said reverse bias voltage.

5. The apparatus of claim 4 wherein a phase difference between said first and second optical phase shifters varies between zero and a half wavelength of said laser wavelength for a variation in the modulation signal between zero and the quarter wavelength excursion voltage.

6. The apparatus of claim 1 wherein each of said optical phase shifters produces a quarter wavelength phase shift whenever said reverse bias voltage is increased by a half wavelength excursion voltage, said first and second optical phase shifters being operated in push-pull mode whereby a quarter wavelength shift in each optical phase shifter produces a total phase shift of a half wavelength between said first and second phase shifter.

7. The apparatus of claim 1 wherein said p-type and n-type layers confine a major portion of said laser beam to said intrinsic layer.

8. The apparatus of claim 1 wherein said p-type and intrinsic layers are formed of a semiconductor material having a band gap greater than the photon energy of the laser beam, said quantum dots having a size such that excitons created in their vicinity are strongly confined.

9. The apparatus of claim 3 wherein said quantum dots have a diameter, height and layer-to-layer spacing sufficient to form potential wells capable of capturing exciton electron-hole pairs with sufficient binding energy to create optical-like transition energy spectra at an energy appropriate to the intended optical carrier frequency.

10. The apparatus of claim 9 wherein said transition energy spectra undergo a Stark effect downward shift in response to an increase in said reverse bias voltage with a corresponding shift in refractive index of said intrinsic layer, said shift in refractive index being sufficient to impose a phase shift on said laser beam in said intrinsic layer equal to a quarter wavelength of said laser wavelength whenever said increase in said reverse bias voltage reaches a half wavelength excursion voltage of said intrinsic layer.

11. An optical phase shifter capable of interacting with a light beam of a particular wavelength passing therethrough, comprising:

(a) an intrinsic semiconductor crystalline planar layer and p-type and n-type planar semiconductor layers on opposite faces of said intrinsic semiconductor crystalline planar layer, said intrinsic layer lying in a plane parallel to a direction of propagation of said light beam in the respective optical branch;

(b) plural layers of planar arrays of quantum dots in said intrinsic layer;

(c) a reverse bias D.C. voltage source connected across said p-type and n-type layers;

(d) a pair of modulation source terminals connected across said reverse bias D.C. voltage source whereby a modulation signal modulates the reverse bias voltage across said p-type and n-type layers.

12. The apparatus of claim 11 wherein said intrinsic layer undergoes a change in refractive index sufficient to impose a quarter wavelength phase shift in response to a modulation signal increase by a quarter wavelength excursion voltage of said intrinsic layer.

13. The apparatus of claim 11 wherein:

said quantum dots in said intrinsic layer anchor quantum-confined exciton states defining an exciton optical absorption line spectrum, said quantum-confined states decreasing in energy level upon increase of said reverse bias voltage; and

an exciton absorption line spectrum of one of said exciton states is offset from the wavelength of said light beam.

14. The apparatus of claim 11 wherein said optical phase shifter produces a quarter wavelength phase shift whenever said reverse bias voltage is increased by a half wavelength excursion voltage of said intrinsic layer.

15. The apparatus of claim 11 wherein said p-type and n-type layers confine a major portion of said light beam to said intrinsic layer.

16. The apparatus of claim 11 wherein said p-type, n-type and intrinsic layers are formed of a semiconductor material having a band gap corresponding at least generally to the wavelength of said light beam.

17. The apparatus of claim 16 wherein said quantum dots have a diameter, height and layer-to-layer spacing sufficient to form a potential wells capable of capturing exciton electron-hole pairs with sufficient binding energy to create optical-like transition energy spectra.

18. An optical modulator for modulating a laser beam with a modulation signal, comprising:

an interferometer having a beam splitter, first and second parallel optical branches fed by said beam splitter and a beam combiner fed by said first and second parallel optical branches;

first and second optical phase shifters in respective ones of said first and second parallel optical branches, each one of said first and second optical phase shifters comprising;

(a) an intrinsic semiconductor crystalline planar layer and p-type and n-type planar semiconductor layers on opposite faces of said intrinsic semiconductor crystalline planar layer, said intrinsic layer lying in a plane parallel to a direction of propagation of said laser beam in the respective optical branch;

(b) plural layers of planar arrays of quantum dots in said intrinsic layer, said quantum dots having a diameter, height and layer-to-layer spacing sufficient to form a potential wells capable of capturing exciton electron-hole pairs with sufficient binding energy to create optical-like transition energy spectra;

(c) a reverse bias D.C. voltage source connected to said p-type and n-type layers;

(d) a pair of modulation source terminals connected to said reverse bias D.C. voltage source whereby a modulation signal modulates the reverse bias voltage across said intrinsic layer, wherein said transition energy spectra undergo a Stark effect downward shift in wavelength in response to an increase in said reverse bias voltage with a corresponding shift in refractive index of said intrinsic layer, said shift in refractive index being sufficient to impose a phase shift on said laser beam in said intrinsic layer equal to a quarter wavelength of said laser beam whenever said increase in said reverse bias voltage reaches a half wavelength excursion voltage of said intrinsic layer.

19. The apparatus of claim 18 wherein said modulation source terminals of said first and second optical phase shifters are connected in opposite polarity (180°

out-of-phase) to a common modulation source.

20. The apparatus of claim 19 wherein said intrinsic layer undergoes a change in refractive index sufficient to impose a quarter wavelength phase shift in response to a modulation signal increase by a half wavelength excursion voltage of said intrinsic layer.

21. The apparatus of claim 20 wherein:

said quantum dots in said intrinsic layer promote quantum-confined exciton states defining an exciton optical absorption line spectrum, said quantum-confined states decreasing in energy level upon increase of said reverse bias voltage.

22. The apparatus of claim 21 wherein a phase difference between said first and second optical phase shifters varies between zero and a half wavelength of said laser for a variation in the modulation signal between zero and the quarter wavelength excursion voltage.

23. The apparatus of claim 18 wherein each of said optical phase shifters produces a quarter wavelength phase shift whenever said reverse bias voltage is increased by a quarter wavelength excursion voltage, said first and second optical phase shifters being operated in push-pull mode whereby a quarter wavelength shift in each optical phase shifter produces a total phase shift of a half wavelength between said first and second phase shifters.

24. The apparatus of claim 18 wherein said p-type and n-type layers confine a major portion of said laser beam to said intrinsic layer.

25. The apparatus of claim 18 wherein said p-type, n-type and intrinsic layers are formed of a semiconductor material having a band gap corresponding to and offset from the photon energy of said laser beam.

26. The apparatus of claim 18 further comprising a laser for furnishing said laser beam to said beam splitter, said laser, said interferometer and said optical phase shifters being formed as integrated semiconductor crystalline structures on a semiconductor substrate.