Ilkan Cokgor

Experimental characterization of a two-photon memory

We demonstrate the recording of 100 planes of digital images in a page-oriented two-photon memory and characterize the images in terms of signal-to-noise ratio and bit error rate. Possible error sources in the recording are discussed, and methods for compensating for some of these effects are presented. Looking at the distributions of the normalized bit intensities, we are able to estimate the minimum achievable bit error rate for this system.

Molecular transformation as a means for 3D optical memory devices

3D optical memory devices, capable of huge storage, very large bandwidth and amiable to parallel processing, are described. The 3D storage and accessing of information is based on non-linear absorption and emission by two different molecular structures.

Materials and systems for two photon 3-D ROM devices

The methods and systems used for storing and accessing information in three dimensions by means of two-photon absorption are described. The materials into which the information is stored are organic molecules dispersed in polymer matrices, which change structure and spectra after absorption of light. The writing and accessing of the information can be performed either bit-by-bit or in a two-dimensional (2-D) multibit plane format. Automated recording and readout three-dimensional (3-D) systems have been constructed and characterized. Channel error sources have been identified, and a custom spatial bit-error-rate test has been developed.

Two-photon absorption-based 3D optical memories

The rapid advance of image-dependent information processing and entertainment applications has accelerated the need for data storage solutions that offer high capacity and high data transfer rates while maintaining low system and media costs. Volume optical memories based on 2-photon absorption-induced photochromism enable random access writing and erasure to individual bits, lines, planes, or sets of planes within the volume of the memory media. The 3- dimensional nature of the storage enables high storage capacities (theoretically 1012 bits/cm2) and parallel readout for high data transfer rates (1-100 Gb/s). The customizable nature of the media (dye-doped plastic) and efficient fluorescent mechanism of the memory readout promise cost-effective system and media solutions. Characterization experiments for erasable and read-only media have been performed, and system experiments for automated recording, and portable read-only memories have been designed and constructed.

Two-photon-induced photochromic reactions in spirobenzopyran-doped poly(methyl methacrylate) thin-film waveguides.

We present experimental results of photochromic reactions induced by single- and two-photon excitations in a poly(methyl methacrylate) thin film doped with spirobenzopyran. We also demonstrate the operation of a spirobenzopyran-doped poly(methyl methacrylate) planar waveguide, prepared by cast spinning the media onto fused-quartz slides. The following phenomena were shown to take place in this waveguide: single-twophoton coloring, f luorescing, and bleaching. The results indicate that such devices may be suitable for many applications, including optical waveguides, volume optical storage, and optical sensors.

Two-photon optical data storage

The generation and application of information is rapidly evolving from text and graphics based to multimedia based, and it will shortly continue to evolve to virtual reality. The evolution between these stages introduces dramatic increases in the amount of data associated with the applications. For example, where text-based meeting notes have given way to emailed copies of vugraphs, future meeting documentation may require storing and communicating an entire collaborative virtual reality session. Even in the near term, the need to store, search for, and edit large numbers of images and digital video clips will drive data storage requirements forward in home, office, and network arenas, as shown in Fre 1 .

Multilayer disk recording using 2-photon absorption and the numerical simulation of the recording process

Two-photon absorption can be utilized to record multiple layers of bit-oriented data in inexpensive monolithic media offering an evolutionary path for high capacity volumetric storage. The feasibility of this approach has been demonstrated by recording 100 layers of data in 8 mm thick cube shaped polymer doped with a photochromic material. We report here the recording and read-out from 3-D optical disks made from similar materials. Multiple layer recording has been demonstrated by recording several data pages on three different layers within one of these disks.

Spyrobenzopyran-doped core PMMA fibers

Cylindrical PMMA filters with core regions doped with spirobenzopyran molecules have been fabricated. Spirobenzopyran is a photochromic molecule with two forms: spiropyran and merocyanine. In the fibers, one state could be reverted to the other either by a photo-initiated reaction or by thermal excitation. The fluorescence from the merocyanine form could be generated by exciting the core with a 543nm laser. For spirobenzopyran, higher temperatures favor the reaction form spiropyran form to merocyanine form, hence as temperature increases the merocyanine from concentration in the core increase causing the fluorescence intensity to increase. It was observed that the fluorescence increased fairly linearly over a certain range and started rolling off as the temperature approached to 60 degrees C. Refractive index and material dispersion characteristics of SP/PMMA was also measured. Fluorescence generation in the core by two-photon absorption from 40 ps pulses at 1064 nm has been demonstrated. The energy of the pulses was 1.8 uJ, which gave a peak intensity of 5GW/cm2 in 33um core. A portion of the emitted fluorescence was guided to the end of the fiber and a portion of it escaped the cladding and radiated into the air.

Two-photon-absorption-induced photochromic reactions in spirobenzopyran-doped PMMA waveguides

Multimode spirobenzopyran (SP) doped PMMA channel waveguides have been fabricated and one- and two-photon absorption induced photochromic reactions have been demonstrated in these waveguides. Bleaching of SP was performed by coupling a 0.75-mW, 543nm beam into these guides. Two-photon absorption based coloring was demonstrated using two counterpropagating pulses, one at 1064 nm and the other at 532 nm. We measured the coupling efficiency to be 0.168, which gave intensities inside the guide of 10.494 GW/cm2 and 7.765 GW/cm2 for the IR and the green beams, respectively. The ability to shift the colored spot via pulse delay in the counterpropagating pulse scheme was also demonstrated by moving a colored spot by approximately 30 micrometers . Finally, two-photon induced fluorescence was observed by exciting the waveguide with a single 1064-nm beam at an intensity of approximately 10 GW/cm2.

Computer simulation and optimization of a free-space optical interconnection system

The optical transpose interconnection system (OTIS) provides a good interconnection using only a pair of lenslet arrays. We have designed and optimized various OTIS systems based on refractive, spherical diffractive, and aspheric diffractive lenslets. The optimization goal is to maximize power coupling into the elements of a detector array. The various design approaches are compared and the optimal design is extracted; the parameters of the model are then to be used for the fabrication of the lenslet array. We also address system geometry, symmetry, and illumination issues relevant to the system design.