Mikael Lindgren

Functionalized Fluorinated Hyperbranched Polymers for Optical Waveguide Applications

Fluorinated dendritic or hyperbranched polymers are demonstrated for the first time to be potentially useful for optical waveguide applications, for example in telecommunications. The required materials properties include the control of the refractive index over a wide range and UV-crosslinking for ease of processing and stable long-term mechanical properties. The authors report the synthesis of suitable functionalized fluorinated hyperbranched polymers and how the above requirements can be met by functionalization at the periphery of the polymers.

Fluorinated dendritic polymers and dendrimers for waveguide applications

Abstract Fluorinated hyperbranched polymers and dendrimers with low optical losses and functionality to modify refractive index and add a cross-linking unit were developed. The results of refractive index measurements indicate a tunability of the refractive index between approximately 1.5 and 1.6, and optical losses below 0.5 dB/cm at 1550 nm. Dendrimers with similar surface group structure and possibility to surface functionalization were prepared using a lanthanide cation as focal point. Results on luminescent properties in the NIR and IR regions were measured for lanthanide ions such as Nd3+ and Er3+, showing characteristic emission bands at 1.06, 1.3 and 1.5 μm. The associated absorption and excitation spectra were found similar to those of the corresponding ions in optical glasses.

Laser Beam Steering and Tracking using a Liquid Crystal Spatial Light Modulator

A linear one-dimensional, 1x4096 pixel, zero-twist nematic liquid crystal spatial light modulator (SLM) was evaluated for laser beam steering and tracking applications. The commercially obtained SLM is designed to operate at, λ = 850 nm, allowing more than 2 π phase modulation. Due to voltage leakage the phase modulation experienced by the wave front differed from the ideal calculated phase patterns. This cross talk between pixels reduces the diffraction efficiency. Different methods developed to compensate for this effect are presented. The usable steering range of the SLM was extended to ± 2 degrees using improved phase patterns. A simple model was developed to simulate the optical effects of the voltage leakage. Preliminary tracking experiments were carried out in a laboratory set-up using a moving corner cube retro reflector. The beam steering SLM was implemented in a transceiver for free-space optical communication. Initial results using the transceiver up to 180 m range are presented.

Novel passive polymer waveguides integrated with electro-optically active ferroelectric liquid crystals

We report the preparation and characterization of novel isotropic polymer slab waveguides made by photochemical crosslinking, and their integration with a ferroelectric liquid crystal in an integra ...

Intensity variations using a quantized spatial light modulator for nonmechanical beam steering

A liquid-crystal spatial light modulator (SLM) can be used to alter the phase of the wavefront to achieve a deflection or a change in the shape of a laser beam. Ideal blazed gratings have perfect diffraction efficiency, and all the light is deflected. Encoded onto a pixelated spatial light modulator, however, the spatial limitations and phase quantization result in a stepped, nonideal blazed grating and decreased diffraction efficiency. The far-field intensity distribution was measured for different deflection angles using 4 and 32 phase levels. The result has been analyzed and used to construct a simple model of the studied SLM. Simulations of the far field based on this model show good agreement with the experimental results.

Chiral dendritic polymers for photonic applications

Abstract We present chiral dendrons of different generations accomplished by reacting the hydroxyl groups at the chain ends with (−)menthoxyacetic acid. Subsequent deprotection of the carboxylic acid rendered acid functional chiral dendrons. The acid-functionalized chiral dendrons were doped with divalent cations Cu 2+ , Fe 2+ and Zn 2+ , and trivalent lanthanide cations Nd 3+ and Pr 3+ . We present results on their optical rotatory power along with circular dichroism spectroscopy and results of paramagnetic resonance. The chiral dendrons were shown to influence the electronic transitions of the metal ions (CD spectra). Attempts to characterize the circularly polarized luminescence of the Nd-dendrimer failed due to low quantum yield. The luminescence efficiency was found to be at least one order of magnitude lower than that of a fluorinated and non-chiral dendrimer structure of similar size and coordination structure.

Integrated Electro-Optic Switches Based on Ferroelectric Liquid Crystal Waveguides

Two integrated electro-optic switches based on smectic C * ferroelectric liquid crystal (FLC) planar waveguides oriented in the bookshelf geometry have been designed and realized. In order to test the first switch, a particular waveguide structure consisting of a three-stage device, having a thin FLC film middle stage and two glass waveguides as other stages, has been designed and realized. The second one is realized by a planar waveguide with a smectic C * ferroelectric liquid crystal overlayer. In this article the design, the realization, and the experimental characterization of electro-optical switches are reported. The electro-optical behavior and the response time of both devices have been studied for different configurations for both TE and TM polarization. Our main aim was to demonstrate the feasibility of an integrated electro-optic device based on a FLC waveguide, and our experimental results provide a number of interesting indications about device optimization and practical applications.

Characterization of a liquid crystal spatial light modulator for beam steering

The spatial light modulator (SLM) can be used to alter the phase of the wave front to achieve a deflection or a change in the shape of a laser beam. In this study a commercial nematic zero-twist liquid crystal SLM was evaluated. SLMs can be operated to produce pure phase modulation necessary for beam steering. For liquid crystals the relation between applied voltage and phase modulation is highly non-linear due to the relation between the voltage driven molecular tilt angle and extraordinary refractive index. To compensate for this effect we optimized and examined look-up tables (LUT) that realize the inverse of the phase response. It was found that the factory LUT improved the power ratio between the zero order and the first order peaks five times compared to the case without using an LUT, however, further improvement of this ratio of two was reached using an LUT optimized from the measured phase response of the SLM. The discrete phase modulation results in a stepped, non-ideal blazed grating that alters the relative power of the available steering angles. To obtain optimal performance these effects must be analyzed for different bit depths and preliminary results of such quantization effects are discussed.

Dendritic Polyesters for Optical Applications

In the protection against lasers, optical power limiting (OPL) is an area of interest. We have explored the effect of using dendritic molecules, based on bis-MPA (2,2-bis(methylol)-propionic acid), as encapsulants of porphyrine and thiophene dyes having OPL-properties. Preliminary results indicate that the OPL-effect of the porphyrine is increased approximately by a factor 2 if the porphyrine is decorated with dendritic wedges. This is thought to be a result of isolation of the dye leading to extended lifetimes for the excited states, increasing the probability for multi-photon absorption. For the thiophenes no OPL-effect was observed. This was probably due to the small size of the dendrons (first generation).

Characterization of fluorinated hyperbranched polymers and dendrimers for waveguide applications

We report on optical transmission properties and results of optical waveguide characterization of flourinated hyperbranched polymers and dendrimers (details on chemical synthesis were reported recently [1]). The polymers and dendrimers allow the introduction of additional functionality, such as cross-linking and refractive index tuneability. The dendrimers having a similar bulk structure as the hyperbranched polymer were also shown to house lanthanide cations for optical amplifying application. The fluorinated bulk structure results in a low contribution from vibration overtones in the absorption spectra in the NIR/IR region (800 - 2200 nm). The refractive index of the fundamental fluorinated hyperbranched polymer was found to be tuneable between ca 1.45 and 1.65 by incorporating various substituents. Optical losses were measured to be below ca 0.5 dB/cm at 1550 nm.