Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2003-01-23
2004-09-28
Martinez, Joseph (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S270000, C359S267000, C359S269000, C359S273000
Reexamination Certificate
active
06798554
ABSTRACT:
DESCRIPTION
1. Technical Field
The present invention concerns a flexible electrochrome structure. It also concerns manufacturing methods for said structure.
The electrochrome structures of the present invention are modulable reflection systems operating in a wide spectral range going from the visible to the mid-infrared, in other words from wavelengths between 0.35 and 20 &mgr;m.
They therefore have numerous applications. For example, said structures are good flexible display devices operating both in the visible and infrared ranges. They also have a place, in particular, in the aerospace sector by making it possible to control thermal exchanges on space objects such as satellites.
2. State of the Prior Art
Electrochromism consists in modifying the optical properties of a material under the influence of an electric potential. Electrochrome structures allow electrochromism to be exploited, particularly in the aforementioned applications.
Overall, electrochrome structures may be broken down into two types: electrochrome structures operating in transmission and those operating in reflection.
In a device that operates in transmission, all of the incident radiation passes through the device and is attenuated in a modulable manner. In a device that operates in reflection, the device is firstly opaque, in other words no radiation passes through it, the incident radiation is then reflected in a modulable manner.
The present invention concerns structures of the second type.
Document WO-A-94/16356 by R. Bennett details two types of modulable reflection electrochrome devices. In the first type of device, the electrochrome layer is located on the metallic electrode, but towards the exterior of the device. It is therefore outside of the electric field created by the two electrodes. In order to allow the compensation of the charge in the electrochrome layer during electrochemical processes, a porous substance that is metallised and impregnated with electrolyte is used. The first device proposed is unsymmetrical, and the substrate of the counter electrode is located at the rear of the device. In the second device proposed, the device is symmetrical; the central porous substrate acts as a support for the working electrode and the counter electrode. The device can therefore operate on two sides.
It is stated, in this document, that the system operates over the whole spectral range, including infrared. However, for the two assemblies described, the position of the electrolyte in front of the active material and the reflective layer would imply the use of an electrolyte that is transparent in the infrared range. However this is not possible, since liquid and solid electrolytes are, by their vibration bands, absorbent in the mid-infrared range. The two assemblies proposed are therefore not suitable for use in the infrared.
Infrared electrochrome systems based on tungsten oxide WO
3
have recently been produced. An example of such a system is described, for example, in J. S. Hale, M. DeVries, B. Dworak and J. A. Woollam, Thin Solid Films 313-314, 205-209 (1998). The device proposed, based on the variation of optical indexes of WO
3
by electrochemical doping, nevertheless has the disadvantage of being rigid and unfortunately cannot be made flexible by replacing the substrate used by polymers. The design of the device remains conventional, since the electrochrome materials and the counter electrode remain in the electric field created by the two electrodes. A gold grid is used as electrode of the WO
3
in order to be transparent to infrared radiation. The device thus has an operation in which the active material (WO
3
) shows a contrast in reflectance. Moreover, it should be noted that the contrasts obtained in the mid-infrared range remain too low.
A similar device, in which tungsten trioxide is replaced by a conductive polymer, polyaniline, has been proposed in the document by P. Topart and P. Hourquebie, Thin Solid Films, 352, 243-2418 (1999). However, the device remains rigid and is based on a traditional battery type design, where the active material remains in the electric field.
The document U.S. Pat. No. 5,995,273 of P. Chandrasekhar describes a device that enables a contrast in absorbance of a layer of conductive polymer during its doping/undoping electrochemical process. The conductive polymer is deposited on a porous metallised substrate which plays the role of electrode, reflector and ionic conductor. Two designs of the system are proposed. In both cases, as in the case of the patent of Bennett cited above, the active layer of conductive polymer is situated outside of the electric field created by the two electrodes. The porous substrate impregnated with electrolyte then allows ionic conductivity between the two electroactive layers. The first design proposed by P. Chandrasekhar is very similar to that of R. Bennett with a PE film in intimate contact with a layer of conductive polymer. In the second design of the device proposed, the counter electrode is no longer, like in the first, parallel to the optically active electrode, but it is coiled up and placed on each side of the system.
However, producing the proposed structures is difficult and complex. In addition, the thickness of said structures is too high.
DESCRIPTION OF THE INVENTION
The present invention makes up for the aforementioned disadvantages of the prior art, by providing a flexible electrochrome structure operating in reflection at wavelengths of between 0.35 and 20 &mgr;m.
The electrochrome structure of the present invention comprises a microporous membrane including an electrolyte and, deposited on each of the surfaces of the microporous membrane, in a symmetrical manner in relation to said membrane, successively and in this order: an electrode formed from a reflecting and electronically conductive layer, a layer of electrochrome conductive polymer, and a flexible window transparent to wavelengths between 0.35 and 20 &mgr;m.
The basic principle of the structures of the present invention is therefore the total symmetry of the structure, the two faces of the structure having the same electrochrome properties.
According to a specific embodiment of the electrochrome structure of the present invention, the microporous membrane may be composed of a first and a second microporous membrane assembled surface against surface. This embodiment is described below in relation to the methods of the present invention and in the examples.
The microporous membrane is composed of one or several material(s) chosen as a function of the different elements that make up the electrochrome structure. For example, when the layer forming a reflecting electrode is a layer of metal, the microporous membrane is preferably composed of a material that may be metallised. Preferably, the material is compatible with the conductive polymer and the electrolyte, it has sufficient mechanical strength to play the role of a substrate, and it has a temperature resistance that allows it to withstand the temperature to which it may be subjected during the manufacture of the structure, for examples at temperatures near to 100° C. under pressure. Moreover, its porosity makes it possible for the electrolyte that is introduced into it to have sufficient ionic conductivity. In addition, once metallised, it has a high specular reflectance. To ensure this, the diameter of the pores is advantageously chosen in such a way as to remain substantially less that the wavelength of the radiation that one wishes to reflect. It should be noted that by modifying the size of the pores of the microporous membrane, it is possible to control the specular and diffuse parts of the reflected radiation.
Many polymers can meet the aforementioned specifications such as, for example, polymer films of any kind perforated mechanically or by laser ablation, fabrics, etc. According to the invention, the microporous may be composed, for example, of one or several of the following materials: a poly(propylene), a poly(ethylene terephthalate), a poly(methyl methacrylate), a poly(ethyl methacrylate),
Hourquebie Patrick
Pages Hubert
Topart Patrice
Commissariat a l'Energie Atomique
Martinez Joseph
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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