Muhsin Eralp

Photorefractive polymer composite operating at the optical communication wavelength of 1550 nm

A photorefractive polymer composite sensitized at 1550 nm through direct two-photon absorption has been developed. We show an external diffraction efficiency of 3% in four-wave-mixing experiments and perform holographic reconstruction of distorted images utilizing thin-film devices made of this polymer composite. Amongst other potential applications, the demonstration of accurate, dynamic aberration correction through holography in this all-organic photorefractive device presents an alternative to complex adaptive optics systems currently employed in through-air optical communication links.

Submillisecond response of a photorefractive polymer under single nanosecond pulse exposure

Individual nanosecond pulses at 532nm are applied to record gratings in photorefractive composite. At 4mJ∕cm2 illumination, maximum diffraction efficiencies of 56% have been reached with a build-up time of only 300μs (t1) demonstrating one order of magnitude faster recording compared to writing with continuous wave beams. This fast response enables applications in optical processing requiring frame rates of 100Hz or more. Due to the short duration of the writing pulses, the recording is insensitive to vibrations.

High-performance photorefractive polymer operating at 1550 nm with near-video-rate response time

The development of a high-performance photorefractive polymer composite operating at 1550 nm is reported. We show 40% internal diffraction efficiency with response time of 35 ms and a net gain of 20cm−1 in four-wave mixing and two-beam coupling experiments, respectively. This is more than an order of magnitude improvement in the diffraction efficiency and net two beam coupling gain and two orders of magnitude in the response time than the previously reported photorefractive polymer operating at this technologically important wavelength. The improvement in photorefractive characteristics is accomplished by an enhanced orientation of the nonlinear optical chromophore in the present composite.

High-performance photorefractive polymer operating at 975 nm

A family of photorefractive polymer composites has been developed that enable high-performance device operation at a wavelength of 975nm. This constitutes a major extension into the near-infrared spectral region for the operation of all-organic photorefractive devices. Utilizing our photorefractive materials, we demonstrate large net two-beam coupling gain of more than 100cm−1, 60% diffraction efficiency in four-wave mixing experiments, and a fast response time of 33ms, at an irradiance of 1W∕cm2.

All-optical dynamic correction of distorted communication signals using a photorefractive polymeric hologram

All-optical real-time dynamic correction of wave front aberrations for image transmission is demonstrated using a photorefractive polymeric hologram. The material shows video rate response time with a low power laser. High-fidelity, high-contrast images can be reconstructed when the oil-filled phase plate generating atmospheric-like wave front aberrations is moved at 0.3mm∕s. The architecture based on four-wave mixing has potential application in free-space optical communication, remote sensing, and dynamic tracking. The system offers a cost-effective alternative to closed-loop adaptive optics systems.

Photorefractive polymer device with video-rate response time operating at low voltages

The high-voltage bias required for video-rate compatible, efficient operation of a photorefractive polymer composite is reduced from 6-8 to 1.3 kV. At this low voltage, the device can hold erasable Bragg holograms with 80% efficiency in addition to having a video-rate response time. The transition of the holograms state from thick to thin is analyzed in detail.

Variation of Bragg condition in low-glass-transition photorefractive polymers when recorded in reflection geometry

Two low-glass transition photorefractive polymer composites were investigated in a symmetric reflection geometry. The holograms recorded in 105 mum thick devices have reached diffraction efficiencies as high as 60%. Unlike the gratings recorded in transmission geometry, holograms recorded in reflection geometry showed high angular selectivity and the Bragg condition was observed to be sensitive to the magnitude of the external bias field. We attribute this effect to poling-induced birefringence and give a theoretical analysis to describe the observed results.

Photorefractive polymers with sub-millisecond response time

We report the photorefractive properties of tetraphenyldiaminobiphenyl (TPD) based polymer composites that have been developed for single pulse laser operation at 532 nm. With an optimized composite, we demonstrate more than 50% diffraction efficiency using 4 mJ/cm2 single shot writing and 633 nm continuous wave (cw) beam reading. The present devices showed a 300 μs fast response time. This reveals the potential for these polymer devices in applications which require fast writing and erasure. Since the writing pulse-width is in nanosecond time scale, the recording is totally insensitive to vibrations. These devices can also be used as a stepping stone to realize all-color holography since they are sensitive to both green (532nm) and red (633nm) wavelengths. The holograms can be written with either of these two wavelengths and can be read by the same wavelength or the other wavelength with high diffraction efficiency. This demonstrates that these devices have the advantage of performing two-color holography, a step closer to a dynamic full-color holographic recording medium.

Photorefractive polymers based on bis-triarylamine side-chain polymers

We report on the photorefractive properties of two polymer composites that utilize a new bis-triarylamine side-chain polymer matrix. Correctly locating the frontier orbitals of the new transport manifold with respect to the HOMO levels of chromophores, allows stable continuous operation over exposure levels of more that 4 kJ/cm2 when samples are electrically biased at 57 V/μm. This operational stability is combined with video-rate compatible grating build-up times and a dynamic range that allows index modulations of 3 x 10-3 and gain coefficients on the order of 100 cm-1 at moderate fields. The thermal stability of one of the composites reported is excellent, showing no signs of phase separation even after one week at 60°C. A comparison with the stability of composites where the new matrix was replaced by PVK is also presented.

Efficient local fixing of photorefractive polymer holograms using a laser beam

We propose and demonstrate a novel technique for efficient local fixing of photorefractive polymer hologram using a laser beam. In the new technique, a CO2 laser beam is used to heat the sample and a local hologram can be fixed easily. By using glass and sapphire with particular thickness as the substrates for the photorefractive device, the hologram can be fixed efficiently and at much faster speed. The fixation efficiency can be greater than 80% and the hologram can be fixed in a few seconds. This technique is critical for dynamic holographic 3D display and holographic data storage.