Optical modulator

• US 7,969,639 B2
• Filed: 02/06/2007
• Issued: 06/28/2011
• Est. Priority Date: 02/06/2006
• Status: Expired due to Fees

• Current Assignee: Qinetiq Limited (QinetiQ Group PLC)
• Original Assignee: Qinetiq Limited (QinetiQ Group PLC)
• Inventors: Scott, Andrew Maxwell, McNie, Mark Edward, Lewis, Keith Loder, Slinger, Christopher William, Brunson, Kevin Michael, Smith, Gilbert William
• Primary Examiner(s): Ben, Loha
• Application Number:
  US12/278,500
• Publication Number:
  US 20090052008A1
• Time in Patent Office: 1,603 Days
• Field of Search: 359290-295, 359/298, 359/245, 359/247, 359/248, 359/213.1, 359/321, 359/260, 359/282, 359/286, 345/85, 372/20, 372/23, 372/39, 372/92, 372/98, 356/248, 356/480, 356/506, 257/21, 385/28, 385/37, 385/39, 385/50
• US Class Current: 359/260
• CPC Class Codes: G02B 26/001 based on interference in an adjustable optical cavity interference filters G02B5/28; devices or arrangements using multiple reflections in spectrometry or monochromators G01J3/26
• CPC Class Codes: G02B 5/281 designed for the infrared light
• CPC Class Codes: G02B 5/284 of etalon type comprising a resonant cavity other than a thin solid film, e.g. gas, air, solid plates etalons for fibre optic multiplexing G02B6/29358; etalons for spectral measurement G01J3/26

Abstract

A micro-opto-electro-mechanical systems (MOEMS) electro optical modulator (2) having an electrically tuneable optical resonator comprising an asymmetric Fabry-Perot etalon incorporating a mirror (10) resiliency biased with respect to a substrate (13) and moveable in relation thereto in response to a voltage applied there-between. The optical modulator (2) is capable of modulating electromagnetic radiation having a plurality of wavelengths. The modulator is adapted to modulate the transmission of short wave infrared radiation (SWIR), medium wave infrared radiation (MWIR) and long wave infrared radiation (LWIR) and the reflection of visible radiation. A spatial optical modulator having a plurality of said MOEMS optical modulators (2). A method of addressing said spatial optical modulator.

Claims

1. A micro-opto-electro-mechanical systems (MOEMS) optical modulator having an optical resonator comprising an asymmetric Fabry-Perot etalon incorporating a mirror resiliently biased with respect to a substrate and moveable in relation thereto in response to a voltage applied there-between, wherein the optical modulator is adapted to modulate transmission of at least one of short wave infrared radiation (SWIR), medium wave infrared radiation (MWIR) and long wave infrared (LWIR).

2. An optical modulator according to claim 1 wherein the substrate is substantially transmissive to SWIR, MWIR and LWIR radiation.

3. An optical modulator according to claim 1 wherein the modulator is substantially transmissive to MWIR radiation in an optically open state and substantially non-transmissive to MWIR radiation in an optically closed state.

4. An optical modulator according to claim 3 having a maximum transmittance greater than 50% in the optically open state and a minimum transmittance of less than 5% in the optically closed state for MWIR radiation.

5. An optical modulator according to claim 1 having a multilayer stack comprising the following plurality of contiguous layers:

silicon moveable mirror layer, air gap, silicon layer, a first dielectric layer, and a silicon layer.

6. An optical modulator according to claim 5 wherein the first dielectric layer comprises one of silicon dioxide, silicon oxynitride, and silicon nitride.

7. An optical modulator according to claim 1 having a multilayer stack comprising the following plurality of contiguous layers:

silicon moveable mirror layer, air gap, a second dielectric layer, silicon layer, a first dielectric layer, and a silicon layer.

8. A optical modulator according to claim 7 wherein the second dielectric layer comprises one of silicon dioxide, silicon oxynitride, and silicon nitride.

9. An optical modulator according to claim 1 adapted to modulate reflection of visible radiation.

10. An optical modulator according to claim 1 wherein the mirror is moveable within the asymmetric Fabry-Perot etalon between a substantially stable first position distal to the substrate and a substantially stable second position proximate the substrate.

11. An optical modulator according to claim 10 wherein the mirror is adapted to respond to applied voltage to move non-linearly between the first and second positions.

12. An optical modulator according to claim 10 wherein the mirror is adapted to move from the first position upon application of a force thereto having a magnitude which exceeds a first threshold and is adapted to move from the second position upon reduction of the magnitude of the applied force below a second threshold, the two thresholds being arranged to be substantially different.

13. An optical modulator according to claim 12 wherein the force is an electrostatic force having a magnitude substantially proportional to the square of the applied voltage.

14. An optical modulator according to claim 12 wherein the mirror has a positional response which exhibits hysteresis.

15. An adaptive coded aperture imaging (ACAI) system comprising an aperture mask having at least one spatial optical modulator comprising a two-dimensional array of optical modulators according to claim 1, said at least one spatial optical modulator arranged so as to modulate electromagnetic radiation incident on a detector array.

16. An optical modulator according to claim 1 wherein said optical modulator is apodized.

17. An optical modulator according to claim 16 comprising a profiled mirror.