TUNABLE ELECTRO-OPTIC FILTER STACK

• US 20140354996A1
• Filed: 10/29/2011
• Published: 12/04/2014
• Est. Priority Date: 03/10/2010
• Status: Active Grant

• Current Assignee: Drexel University
• Original Assignee: Drexel University
• Inventors: Fontecchio, Adam K., Shriyan, Sameet K., Bellingham, Alyssa
• Granted Patent: US 9,752,932 B2
• Time in Patent Office: Days
• US Class Current: 356/416
• CPC Class Codes: G01J 3/0237 Adjustable, e.g. focussing
• CPC Class Codes: G01J 3/502 using a dispersive element, e.g. grating, prism
• CPC Class Codes: G01J 3/51 using colour filters
• CPC Class Codes: G02B 27/0103 comprising holographic elements
• CPC Class Codes: G02F 1/13342 Holographic polymer dispersed liquid crystals
• CPC Class Codes: G02F 1/13476 in which at least one liquid crystal cell or layer assumes a scattering state
• CPC Class Codes: G02F 2203/055 wavelength filtering
• CPC Class Codes: G03F 7/20 Exposure; Apparatus therefor photographic printing apparatus for making copies G03B27/00
• CPC Class Codes: G03F 7/26 Processing photosensitive materials; Apparatus therefor G03F7/12 - G03F7/24 take precedence

Abstract

A holographic polymer dispersed liquid crystal (HPDLC) tunable filter exhibits switching times of no more than 20 microseconds. The HPDLC tunable filter can be utilized in a variety of applications. An HPDLC tunable filter stack can be utilized in a hyperspectral imaging system capable of spectrally multiplexing hyperspectral imaging data acquired while the hyperspectral imaging system is airborne. HPDLC tunable filter stacks can be utilized in high speed switchable optical shielding systems, for example as a coating for a visor or an aircraft canopy. These HPDLC tunable filter stacks can be fabricated using a spin coating apparatus and associated fabrication methods.

Claims

1. A method comprising:

applying a layer of a conductive material to a surface of a substrate;

dispersing the conductive material along the surface of the substrate by applying a first rotational force to the substrate;

applying a mixture comprising a liquid crystal and a polymer to the dispersed first layer of conductive material;

dispersing the mixture along the first layer of conductive material by applying a second rotational force to the substrate; and

exposing the mixture to an interference pattern that causes the formation of at least one grating structure within the mixture.

2. The method of claim 1, wherein the substrate comes to rest between application of the first and second rotational forces.

3. The method of claim 1, wherein applying the first rotational force comprises rotating the substrate at a constant speed.

4. The method of claim 1, wherein applying the first rotational force comprises rotating the substrate at a first speed for a first interval of time, and rotating the substrate at a second speed for a second interval of time.

5. The method of claim 4, wherein the first speed is slower than the second speed.

6. The method of claim 1, wherein the interference pattern comprises a holographic interference pattern.

7. The method of claim 6, wherein the holographic interference is generated by a beam of laser light incident upon at least a portion of the mixture.

8. The method of claim 1, wherein the conductive material is applied to the substrate by an automated dispenser.

9. The method of claim 1, wherein the mixture is applied to the substrate by an automated dispenser.

10. The method of claim 1, wherein the conductive material and the mixture are applied to the substrate by respective automated dispensers.

11. The method of claim 1, further comprising:

applying a second layer of the conductive material to the exposed mixture;

dispersing the second layer of conductive material along the exposed mixture by applying a third rotational force to the substrate.

13. The method of claim 1, further comprising releasably securing the substrate to a rotatable component of a spin coating apparatus.

12. The method of claim 12, wherein applying the second layer of the conductive material comprises coating a grating structure formed in the mixture with the conductive material, such that an electric field can be applied to the mixture.

14. A hyperspectral imaging system comprising:

a hyperspectral imager that includes a holographic polymer dispersed liquid crystal tunable filter, the hyperspectral imager configured to spectrally multiplex hyperspectral imaging data acquired by the hyperspectral imager; and

a platform configured to carry the hyperspectral imager, the platform configured to facilitate airborne collection of the hyperspectral imaging data.

15. The hyperspectral imaging system of claim 14, wherein the holographic polymer dispersed liquid crystal tunable filter comprises a plurality of holographic polymer dispersed liquid crystal thin films.

16. The hyperspectral imaging system of claim 15, wherein a first holographic polymer dispersed liquid crystal thin film of the plurality abuts a first surface of an intervening conductive layer and a second holographic polymer dispersed liquid crystal thin film of the plurality abuts an opposed second surface of the intervening conductive layer.

17. The hyperspectral imaging system of claim 15, wherein each of the plurality of holographic polymer dispersed liquid crystal thin films abuts a surface of a conductive element disposed adjacent to the holographic polymer dispersed liquid crystal thin film.

18. The hyperspectral imaging system of claim 15, wherein the holographic polymer dispersed liquid crystal tunable filter comprises a stack of alternating holographic polymer dispersed liquid crystal thin films and conductive elements.

19. The hyperspectral imaging system of claim 15, wherein the conductive elements comprise respective discrete layers of PDOT:

PSS.

20. The hyperspectral imaging system of claim 15, wherein each of the holographic polymer dispersed liquid crystal thin films exhibits a respective switching time of no more than twenty microseconds.

21. The hyperspectral imaging system of claim 15, wherein each of the holographic polymer dispersed liquid crystal thin films comprises a film thickness of no more than twenty microns.

22. The hyperspectral imaging system of claim 14, wherein the holographic polymer dispersed liquid crystal tunable filter is capable of facilitating the acquisition of hyperspectral imaging data throughout a wavelength range of approximately 780 nm to approximately 3 μ

m.

23. The hyperspectral imaging system of claim 14, further comprising a transmitter configured to transmit the acquired hyperspectral imaging data.

24. A switchable optical shielding system comprising a visor integrated with a holographic polymer dispersed liquid crystal tunable filter, the holographic polymer dispersed liquid crystal tunable filter capable of switching between respective transparent and reflective states in no more than 20 microseconds.

25. The switchable optical shielding system of claim 24, wherein when in the reflective state, the holographic polymer dispersed liquid crystal tunable filter is capable reflecting light incident upon visor throughout a wavelength range of approximately 780 nm to approximately 3 μ

m.

26. The switchable optical shielding system of claim 24, further comprising an aviator helmet coupled to the visor.

27. The switchable optical shielding system of claim 26, further comprising a sensor communicatively coupled to the visor, the sensor configured to transmit a switching signal to the visor when light of a particular wavelength is sensed by the sensor, the sensor attached to the aviator helmet.

28. The switchable optical shielding system of claim 24, further comprising a sensor communicatively coupled to the visor, the sensor configured to transmit a switching signal to the visor when light of a particular wavelength is sensed by the sensor.

29. The switchable optical shielding system of claim 26, wherein when in the reflective state, the holographic polymer dispersed liquid crystal tunable filter is capable of reflecting light incident upon the visor throughout a wavelength range of approximately 780 nm to approximately 3 μ

m.

30. The switchable optical shielding system of claim 24, wherein the holographic polymer dispersed liquid crystal tunable filter is adhered to a surface of the visor.

31. The switchable optical shielding system of claim 24, wherein the holographic polymer dispersed liquid crystal tunable filter comprises a plurality of holographic polymer dispersed liquid crystal tunable filters disposed adjacent to one another along a surface of the visor.

32. A switchable optical shielding system comprising a canopy mounted to an aircraft, at least a portion of the canopy integrated with a holographic polymer dispersed liquid crystal tunable filter, the holographic polymer dispersed liquid crystal tunable filter capable of switching between respective transparent and reflective states in no more than 20 microseconds.

33. The switchable optical shielding system of claim 32, wherein when in the reflective state, the holographic polymer dispersed liquid crystal tunable filter is capable of reflecting light incident upon the canopy throughout a wavelength range of approximately 390 nm to approximately 12 μ

m.

34. The switchable optical shielding system of claim 33, further comprising at least one sensor communicatively coupled to the canopy, the at least one sensor configured to transmit a switching signal to the canopy when light of a particular wavelength is sensed by the sensor.

35. The switchable optical shielding system of claim 34, wherein the switching signal is indicative of switching at least a portion of the holographic polymer dispersed liquid crystal tunable filter from the transparent state to the reflective state or from the reflective state to the transparent state.

36. The switchable optical shielding system of claim 34, wherein the at least one sensor is attached to an aviator helmet worn by a pilot of the aircraft.

37. The switchable optical shielding system of claim 34, wherein the at least one sensor is integrated into the aircraft.

38. The switchable optical shielding system of claim 34, wherein the at least one sensor comprises an array of redundant sensors, at least a first sensor of the array attached to an aviator helmet worn by a pilot of the aircraft and at least a second sensor of the array integrated into the aircraft.

39. The switchable optical shielding system of claim 34, wherein when in the reflective state, the holographic polymer dispersed liquid crystal tunable filter is capable reflecting light incident upon visor throughout a wavelength range of approximately 780 nm to approximately 3 μ

m.

40. The switchable optical shielding system of claim 32, wherein the holographic polymer dispersed liquid crystal tunable filter is adhered to at least a portion of a surface of the canopy.

41. The switchable optical shielding system of claim 32, wherein the holographic polymer dispersed liquid crystal tunable filter comprises a plurality of holographic polymer dispersed liquid crystal tunable filters disposed adjacent to one another along at least a portion of a surface of the canopy.