Compositions – Light transmission modifying compositions
Reexamination Certificate
2000-07-24
2001-10-16
Wu, Shean C. (Department: 1756)
Compositions
Light transmission modifying compositions
C252S589000, C252S299010, C428S001100
Reexamination Certificate
active
06303056
ABSTRACT:
BACKGROUND OF INVENTION
FIELD OF THE INVENTION
The present invention relates to composite films and more particularly to composite films employing a novel preparation process for nonlinear-optics applications.
BACKGROUND INFORMATION
Throughout this application, various publications and patents are referred to by an identifying citation. The disclosures of the publications and patents referenced in this application are hereby incorporated by reference into the present disclosure.
Liquid crystals exist in a phase intermediate between a crystalline solid and an isotropic liquid. The molecules of these compounds are usually rod-shaped with long molecular axes called the directors. Liquid crystal phases are characterized by the long-range order (i.e., in the sense of a solid) of the molecules. The nematic phase is the simplest, having only orientational ordering such that their directors are approximately parallel. The cholesteric liquid crystal phase originates from the presence of chirality in the nematic phase. Liquid crystals have many applications. They are used as displays in digital wristwatches, calculators, panel meters, thermometers, computer displays and industrial products. They may be used to record, store, and display images which may be projected onto a large screen. They also have potential use as television displays. Moreover, films may be prepared from liquid crystals, in which the molecular ordering is frozen, i.e. by polymerization, to provide desired optical properties. For example, nematic and cholesteric (chiral nematic) films may be prepared to exhibit wavelength- and circular-polarization-selective reflectance/transmission (for cholesteric liquid crystal (CLC) films), and phase-shift transmission (for nematic liquid crystal (NLC) films). A drawback of many of these devices, however, is that without further processing, liquid crystal materials tend to be relatively expensive and relatively temperature sensitive. Also, these materials tend to disadvantageously absorb other materials, which may alter the properties of the component, etc. Moreover, while polymerized LCs may address some of these drawbacks, such LCs may be undesirable for many applications, due to, for example, inadequate mechanical properties (rigidity) and/or optical properties, (indices of refraction, characteristic wavelengths, etc.).
Moreover, bandwidth has become increasingly pressing requirement of modern communications systems. As fiber optics replaces electrical cabling, WDM and DWDM techniques are used to exploit more and more of the available fiber optic bandwidth. Simultaneously, packet-switched signal architectures are gradually replacing TDM techniques in many application sectors. However, as billions of dollars are invested in these efforts to expand bandwidth, one significant bottleneck remains—switching node (interconnect) hardware. Current interconnection devices require the data to be first converted to an electrical signal, routed to the correct output, and then re-converted to an optical signal. This opto-electronic interface introduces latencies and substantially reduces the overall bandwidth of the system. All-optical (i.e., without opto-electronic conversion) switching technologies utilizing MEMS (microelectromechanical system) or polarization-based technologies preserve the fiber bandwidth but switch slowly, introducing latencies that limit their applicability.
Nonlinear optical (NLO) materials offer rapid switching speeds. However, a need exists for an improved performance while overcoming the drawbacks associated with current NLO materials. For example, devices using inorganic NLO crystals such as titanium-diffused lithium niobate (Ti:LiNbO
3
) tend to have inferior performance due to their weak NLO properties. In addition, temporal and thermal stability as well as radiation sensitivity are well-known problems. Furthermore, the inorganic crystal devices are difficult to integrate directly with electronics.
NLO devices based on thin films of poled organic polymers are viewed by many as a good solution, since such organic materials are low cost and readily processed. Hundreds of nonlinear organic materials have been synthesized and characterized, and devices using such materials have been demonstrated. However, these poled polymers have the following disadvantages: small second-order susceptibility, low optical damage threshold, high scattering losses, and limited temperature and temporal stability. Thus, poled NLO polymers still require a breakthrough in development to achieve practicality, despite the inherent advantages of the organic materials.
One way of taking advantage of thin film organics while overcoming these limitations is using NLO organic crystal films, which have a very high optical nonlinearity, higher damage threshold, and low scattering loss. U.S. Pat. No. 5,385,116 (Hattori et al, 1996) has reviewed various techniques for fabricating organic crystal films. However, significant manufacturability for practical devices remains. Until these problems are solved, the inherently superior organic NLO crystal materials cannot become useful.
Polymer composite containing NLO crystallites is another approach to obtain high-performance device materials. U.S. Pat. No. 4,759,820 (Calver et al, 1988) discloses processes to grow non-centro-symmetric crystallites, which can be either organic or inorganic, in a polymer matrix. The orientation of the crystallites is achieved by stretching, cold-drawing and other methods. A drawback of this technique is that it tends to be difficult to control the morphology, which is strongly dependent on the NLO material and the film processing.
Thus, a need exists for an improved optical film that exhibits large nonlinear optical effects while overcoming drawbacks of film devices.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, an ordered optical film structure is fabricated by the steps of:
(a) providing a first material and a second material which are substantially non-reactive relative to one another, at least one of the first material and the second material being a liquid crystal;
(b) combining the first material with the second material to form a blend;
(c) forming a film with the blend, the film having a molecular ordering defined by the liquid crystal;
(d) freezing the molecular ordering of the film;
(e) removing one of the first material and the second material to form a matrix having a plurality of sites interspersed therethrough and a liquid crystalline molecular ordering; and
(f) introducing a third material to the plurality of sites.
In a second aspect of the present invention, an ordered optical film structure comprises a substrate and a material disposed on the substrate, the material being a non-liquid crystal having a liquid crystalline molecular ordering.
In a third aspect of the present invention, an ordered optical film structure is fabricated by the steps of:
(a) providing a liquid crystal and a non-liquid crystal which are substantially non-reactive relative to one another;
(b) combining the liquid crystal with the non-liquid crystal to form a blend;
(c) forming a film with the blend, the film having a molecular ordering defined by the liquid crystal;
(d) freezing the molecular ordering of the film;
(e) removing one of the liquid crystal and the non-liquid crystal to form a matrix having a plurality of sites interspersed therethrough and a liquid crystalline molecular ordering.
The above and other features and advantages of this invention will be more readily apparent from a reading of the following detailed description of various aspects of the invention taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 4759820 (1988-07-01), Calvert et al.
patent: 5028109 (1991-07-01), Lawandy
patent: 5207952 (1993-05-01), Griffin, III
patent: 5224196 (1993-06-01), Khanarian
patent: 5256784 (1993-10-01), Francis et al.
patent: 5288426 (1994-02-01), Itoh et al.
patent: 5353247 (1994-10-01), Faris
patent: 5385116 (1995-01-01), Hattori et al.
patent: 5448382 (1995-09-01), Land et a
Fan Bunsen
Xu Jianjun
Sampson & Associates
Wu Shean C.
LandOfFree
Composite nonlinear optical film, method of producing the... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Composite nonlinear optical film, method of producing the..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Composite nonlinear optical film, method of producing the... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2565341