A. Diaz

Nanosphere dispersed liquid crystals for tunable negative-zero-positive index of refraction in the optical and terahertz regimes

An analysis of aligned nematic liquid crystal cells containing core-shell nanospheres shows that it is possible to devise a new type of metamaterial whose index of refraction is tunable from negative, through zero, to positive values. The design parameters for the constituents can be scaled for application in the optical as well as very long wavelength (e.g., terahertz and microwave) regions.

Supra-nonlinear photorefractive response of single-walled carbon nanotube- and C60-doped nematic liquid crystal

We have observed an extremely large electro-optically induced photorefractive effect in nematic liquid crystal doped with single-walled carbon nanotubes and fullerene C60. The effective refractive index change coefficient can be as large as 7 cm2/W, which is >1000 times larger than previous observations. We describe the basic mechanisms and conditions necessary for occurrence of such nonlinearities.

Nano-Dispersed Organic Liquid and Liquid Crystals for All-Time-Scales Optical Switching and Tunable Negative-and Zero- Index Materials

We present an overview of recent results obtained in nano-dispersed nonlinear neat organic liquids and liquid crystals. Experimental observations confirm the enhancement of nonlinear absorption in gold nano-spheres doped neat nonlinear liquids and extension of the bandwidth of efficient all-optical switching operation for visible-near infrared lasers in time scales ranging from sub-picoseconds through nanoseconds and microseconds and longer. Similar nano-particulate doped liquid crystal films also exhibit efficient all-optical switching capabilities for microseconds – cw lasers. Meta-materials fabricated with core-shell nano-spheres dispersed nematic liquid crystals show effective refractive indices that are tunable from negative through zero to positive values.

Recent Studies of Optical Limiting, Image Processing and Near-Infrared Nonlinear Optics with Nematic Liquid Crystals

The mechanisms for recently observed optically induced refractive index changes in nematic liquid crystals, and their use in novel optical limiting and image processing are reviewed, along with an assessment of their potentials for applications. We have also studied the optical nonlinearities of nematic liquid crystals in the near IR communication spectral region [1.55 µm]. Phase modulation of several πs can be generated with mW laser power in micron thick films.

Nonlinear Optical Effects in Nematic Liquid-Crystal Films in the 1.55 µm Spectral Region

We have studied the optical nonlinearities of nematic liquid crystals in the near IR communication spectral region [1.55 µm]. The origins of the refractive index changes are thermal indexing effect and director axis reorientations. Very large refractive index and phase modulation of several πs can be generated with mW laser power in micron thick dye-doped nematic liquid crystal films.

DESIGN AND TRANSMISSION-REFLECTION PROPERTIES OF LIQUID CRYSTALLINE OPTICAL METAMATERIALS WITH LARGE BIREFRINGENCE AND SUB-UNITY OR NEGATIVE-REFRACTIVE INDEX

The dispersion of nanoparticles in a nematic liquid crystal host medium provides an efficient way of designing tunable optical metamaterials that respond from the visible to the Terahertz and microwave regime. As studied in this article, these systems exhibit much larger birefringence than the nematic host and possess sub-unity, zero, and even negative refractive indices with unique reflection and transmission properties. These tunable optical metamaterials will enable a wide range of application possibilities in next-generation reflective, transmissive, modulation and switching elements and devices.

All-optical neural-net-like image processing with photosensitive nonlinear nematic film.

Received June 30, 2003 We demonstrate that some neural-net image-processing operations can be realized in an all-optical manner by use of the natural diffraction property of light in conjunction with the photosensitivity and optical nonlinearities of a transparent thin film. An example of image edge enhancement is illustrated with photosensitive supranonlinear nematic liquid-crystal films.

Liquid Crystal Nonlinear Optical Meta-Materials

We present an overview of metamaterials comprising nematic liquid crystals and nano-particulates or nano-structures. These metamaterials possess emergent properties such as electro-optically and all-optically tunable sub-unity, zero and negative refractive indices, and other properties not possible with conventional chemical synthesis methods. Optical wave mixing and self-action effects conducted with nano-particulate doped nematic liquid crystals have demonstrated fast optical field induced index modulation in micron- and sub-micron thin nematic films.

Liquid crystalline nonlinear optical metamaterials with low-loss tunable negative-zero-positive refractive indices

We describe a class of liquid crystalline photonic metamaterials that exhibit tunable negative-zero-positive refractive indices. As a result of the extreme sensitivity of the nematic liquid crystal constituent, these metamaterials also exhibit extraordinarily large optical nonlinearities associated with the optical field induced director axis reorientation and birefringence change. Incorporation of a gain medium such as laser dye reduces losses of the metamaterial.

Liquid crystal cladded metallo-dielectric and all-dielectric frequency selective surfaces for broadband tunable optical filters and planar negative index optics

We demonstrate how liquid crystal cladded metallo-dielectric and all-dielectric frequency selective surfaces (FSS) can perform as broadband tunable optical filters and planar negative index optical materials. Structures are designed using a genetic algorithm technique that takes into account the specifics of nanofabrication techniques to maximize the effective optical material response and minimize losses as the birefringent nematic liquid crystal (NLC) overlayer is tuned.