Patent
Infrared/optical imaging techniques using anisotropically strained doped quantum well structures
| العنوان: | Infrared/optical imaging techniques using anisotropically strained doped quantum well structures |
|---|---|
| Patent Number: | 5,748,359 |
| تاريخ النشر: | May 05, 1998 |
| Appl. No: | 08/754,004 |
| Application Filed: | November 21, 1996 |
| مستخلص: | An imaging system for transferring an infrared (IR) image to a visible image. The imaging system includes a polarization rotator that rotates the polarization of a visible light beam in response to absorptions of radiation from the IR image. A polarizer outputs components of the visible light beam as a function of the amount of absorbed radiation from the IR image. The polarization rotator is formed from a multiple quantum well structure grown on a semiconductor substrate with a thermally induced uniaxial, in-plane, compressive strain. The multiple quantum well structure includes a heterostructure of undoped barrier layers and doped quantum well layers. The strain causes the quantum well layers to have anisotropic radiation absorption characteristics. In particular, orthogonal components of the visible light parallel to and perpendicular to the strain will experience different degrees of absorption. The dopant in the quantum well layers is sufficient to bleach the lowest exciton resonances, thereby reducing absorption of the light beam. IR absorption from the image decreases the bleaching and increases the ability of the quantum well layers to promote exciton transitions. As such, the polarization of the light beam rotates as a function of the amount of IR absorbed from the image. |
| Inventors: | Shen, Paul H. (North Potomac, MD); Dutta, Mitra (Silver Spring, MD); Wraback, Michael (Rockville, MD); Pamulapati, Jagadeesh (Washington, DC) |
| Assignees: | The United States of America as represented by the Secretary of the Army (Washington, DC) |
| Claim: | What is claimed is |
| Claim: | 1. A polarization rotator comprising |
| Claim: | a semiconductor substrate; |
| Claim: | a multiple quantum well structure (MQW) mounted on said substrate, said MQW having a heterostructure of un-doped barrier layers and doped quantum well layers, and said MQW having a uniaxial compressive strain in the plane of said layers such that said doped quantum well layers have anisotropic radiation absorption characteristics at a first frequency; |
| Claim: | a first source of radiation at said first frequency directed normal to said layers and linerally polarized in the plane of said layers, and having radiation components directed parallel to and perpendicular to the direction of said strain; and |
| Claim: | a second source of radiation at a second frequency directed at said MQW such that radiation absorption at said second frequency lowers the free carrier population of said doped quantum well layers and increase radiation absorption at said first frequency. |
| Claim: | 2. The polarization rotator of claim 1 wherein said doped quantum well layers comprise means for promoting exciton transitions in response to radiation absorption at said first frequency. |
| Claim: | 3. The polarization rotator of claim 2 wherein said MQW comprise means, responsive to said radiation absorption at said second frequency, for exciting free carriers out of the lower levels of said doped quantum well layers to increase the ability of said doped quantum well layers to produce said exciton transitions. |
| Claim: | 4. The polarization rotator of claim 3 wherein said first source of radiation emits visible light and second source of radiation emits infrared radiation. |
| Claim: | 5. The polarization rotator of claim 3 wherein said doped quantum well layers contain P-type dopant and said means for exciting free carriers excites holes from the lower levels into the continuum of the valence band of said doped quantum well layers. |
| Claim: | 6. The polarization rotator of claim 3 wherein said doped quantum well layers contain N-type dopant and said means for exciting free carriers excites electrons from the lower levels into the continuum of the conduction band of said doped quantum well layers. |
| Claim: | 7. An imaging system comprising |
| Claim: | a radiation source emitting linerally polarized radiation at a first frequency; |
| Claim: | an image emitting radiation at a second frequency; |
| Claim: | a polarization rotator having input means for receiving said radiations from said radiation source and said image, output means for emitting said linerally polarized radiation at said first frequency, absorption means for absorbing said radiation at said second frequency, and rotation means for rotating the polarization of said radiation at said first frequency in response to absorption of said radiation at said second frequency; and |
| Claim: | a polarizer means for transmitting a polarized component of said radiation emitted from said output means. |
| Claim: | 8. The imaging system of claim 7 wherein said polarization rotator comprises a semiconductor substrate and a multiple quantum well structure (MQW) mounted on said substrate. |
| Claim: | 9. The imaging system of claim 8 wherein said MQW comprises a heterostructure of un-doped barrier layers and doped quantum well layers with a uniaxial compressive strain in the plane of said layers such that said doped quantum well layers have anisotropic radiation absorption characteristics at said first frequency. |
| Claim: | 10. The imaging system of claim 9 wherein said radiation source includes means for emitting said linerally polarized radiation normal to the plane of said layers. |
| Claim: | 11. The imaging system of claim 10 wherein said means for emitting said linerally polarized radiation emits said linerally polarized radiation with its polarization parallel to the plane of said layers and with orthogonal radiation components directed parallel to and perpendicular to the direction of said strain. |
| Claim: | 12. The imaging system of claim 11 wherein said quantum well layers include means for producing exciton transitions in response to radiation absorption by said quantum well layers at said first frequency. |
| Claim: | 13. The imaging system of claim 12 wherein said MQW include means, responsive to said radiation absorption at said second frequency, for varying the ability of said doped quantum well layers to produce said exciton transitions by exciting free carriers out of the lower levels of said doped quantum well layers. |
| Claim: | 14. The imaging system of claim 13 wherein said radiation source emits visible light and said image emits infrared radiation. |
| Claim: | 15. The imaging system of claim 13 wherein said doped quantum well layers contain P-type dopant and said radiation absorption at said second frequency excites holes from the lower levels into the continuum of the valence band of said doped quantum well layers. |
| Claim: | 16. The imaging system of claim 13 wherein said doped quantum well layers contain N-type dopant and said radiation absorption at said second frequency excites electrons from the lower levels into the continuum of the conduction band of said doped quantum well layers. |
| Claim: | 17. A method of fabricating a polarization rotator capable of rotating the polarization of radiation at a first frequency in response to absorption of radiation at a second frequency, said method comprising the steps of |
| Claim: | forming a semiconductor substrate; and |
| Claim: | growing a multiple quantum well structure (MQW) on said substrate in the form of a heterostructure of un-doped barrier layers and doped quantum well layers such that exciton transitions from the highest quantum levels in the valence band to the lowest quantum level in the conduction band correspond to said first frequency and carrier transitions to continuum levels correspond to said second frequency; and |
| Claim: | producing a uniaxial compressive strain in said MQW in the plane of said layers. |
| Claim: | 18. The method of claim 17 wherein said growing step includes forming said doped quantum well layers such that said exciton transitions correspond to visible light and said carrier transitions to said continuum levels correspond to infrared radiation. |
| Claim: | 19. The method of claim 17 wherein said growing step includes doping said doped quantum well layers such that bleaching of the lowest exciton resonances occurs. |
| Claim: | 20. The method of claim 19 wherein said doping step includes forming said doped quantum well layers with P-type dopant. |
| Claim: | 21. The method of claim 19 wherein said doping step includes forming said doped quantum well layers with N-type dopant. |
| Current U.S. Class: | 359/248; 359/245 |
| Current International Class: | G02F 103 |
| Patent References Cited: | 4879763 November 1989 Wood 5107307 April 1992 Onose et al. 5274247 December 1993 Dutta et al. 5381260 January 1995 Ballato et al. |
| Other References: | Shen et al, "Optical anisotropy in GaAs/Al.sub.x Ga.sub.1-x As multiple qtum wells under thermally induced uniaxial strain", Pysical Review B47 pp. 13933-13936, 15 May 1993. |
| Primary Examiner: | Font, Frank G. |
| Assistant Examiner: | Ratliff, Reginald A. |
| Attorney, Agent or Firm: | Zelenka, Michael Anderson, William H. |
| رقم الانضمام: | edspgr.05748359 |
| قاعدة البيانات: | USPTO Patent Grants |
| الوصف غير متاح. |