Anders Bjarklev

Strained silicon as a new electro-optic material.

For decades, silicon has been the material of choice for mass fabrication of electronics. This is in contrast to photonics, where passive optical components in silicon have only recently been realized. The slow progress within silicon optoelectronics, where electronic and optical functionalities can be integrated into monolithic components based on the versatile silicon platform, is due to the limited active optical properties of silicon. Recently, however, a continuous-wave Raman silicon laser was demonstrated; if an effective modulator could also be realized in silicon, data processing and transmission could potentially be performed by all-silicon electronic and optical components. Here we have discovered that a significant linear electro-optic effect is induced in silicon by breaking the crystal symmetry. The symmetry is broken by depositing a straining layer on top of a silicon waveguide, and the induced nonlinear coefficient, χ(2) ≈ 15 pm V-1, makes it possible to realize a silicon electro-optic modulator. The strain-induced linear electro-optic effect may be used to remove a bottleneck in modern computers by replacing the electronic bus with a much faster optical alternative.

Optical devices based on liquid crystal photonic bandgap fibres

Photonic Crystal Fibers (PCFs) have appeared as a new class of optical waveguides, which have attracted large scientific and commercial interest during the last years. PCFs are microstructured waveguides, usually in silica, with a large number of air holes located in the cladding region of the fiber. The size and location of these air holes opens up for a large degree of design freedom within optical waveguide design. Further, the existence of air holes in the PCF gives access close to the fiber core and by introducing new materials into the air holes, a high interaction between light and hole material can be obtained, while maintaining the microstructure of the waveguide. In this paper, we describe what we call Liquid Crystal Photonic Bandgap Fibers, which are PCFs infiltrated with Liquid Crystals (LCs) in order to obtain increased fiber functionality. We describe a thermo-optic fiber switch with an extinction ratio of 60dB and tunable PBGs using thermo-optic tuning of the LC. These devices operate by the PBG effect and are therefore highly sensitive to the refractive index distributions in the holes.

Highly birefringent index-guiding photonic crystal fibers

Photonic crystal fibers (PCFs) offer new possibilities of realizing highly birefringent fibers due to a higher intrinsic index contrast compared to conventional fibers. In this letter, we analyze theoretically the levels of birefringence that can be expected using relatively simple PCF designs. While extremely high degrees of birefringence may be obtained for the fibers, we demonstrate that careful design with respect to multimode behavior must be performed. We further discuss the cutoff properties of birefringent PCFs and present experimental results in agreement with theoretical predictions on both single- and multimode behavior and on levels of birefringence.

Gas sensing using air-guiding photonic bandgap fibers

We report on experimental studies of gas sensing using air-guiding photonic bandgap fibers. The photonic bandgap fibers have at one end been spliced to standard single mode fibers for ease of use and improved stability

Photonic crystal fiber based evanescent-wave sensor for detection of biomolecules in aqueous solutions

We demonstrate highly efficient evanescent-wave detection of fluorophore-labeled biomolecules in aqueous solutions positioned in the air holes of the microstructured part of a photonic crystal fiber. The air-suspended silica structures located between three neighboring air holes in the cladding crystal guide light with a large fraction of the optical field penetrating into the sample even at wavelengths in the visible range. An effective interaction length of several centimeters is obtained when a sample volume of less than 1 microL is used.

All-optical modulation in dye-doped nematic liquid crystal photonic bandgap fibers

Photonic crystal fibers (PCFs) have attracted significant attention during the last years and much research has been devoted to develop fiber designs for various applications, hereunder tunable fiber devices. Recently, thermally and electrically tunable PCF devices based on liquid crystals (LCs) have been demonstrated. However, optical tuning of the LC PCF has until now not been demonstrated. Here we demonstrate an all-optical modulator, which utilizes a pulsed 532nm laser to modulate the spectral position of the bandgaps in a photonic crystal fiber infiltrated with a dye-doped nematic liquid crystal. We demonstrate a modulation frequency of 2kHz for a moderate pump power of 2-3mW and describe two pump pulse regimes in which there is an order of magnitude difference between the decay times.

Electrically tunable photonic bandgap guidance in a liquid-crystal-filled photonic crystal fiber

Tunable bandgap guidance is obtained by filling the holes of a solid core photonic crystal fiber with a nematic liquid crystal and applying an electric field. The response times are measured and found to be in the millisecond range.

Selective detection of antibodies in microstructured polymer optical fibers

We demonstrate selective detection of fluorophore labeled antibodies from minute samples probed by a sensor layer of complementary biomolecules immobilized inside the air holes of microstructured Polymer Optical Fiber (mPOF). The fiber core is defined by a ring of 6 air holes and a simple procedure was applied to selectively capture either alpha-streptavidin or alpha-CRP antibodies inside these air holes. A sensitive and easy-to-use fluorescence method was used for the optical detection. Our results show that mPOF based biosensors can provide reliable and selective antibody detection in ultra small sample volumes.

The design of erbium-doped fiber amplifiers

An accurate model for the erbium-doped fiber amplifier is presented. The model is used to design the index profile of the doped fiber, optimizing with regard to efficiency for inline- and preamplifiers as well as for power booster amplifiers. The predicted pump efficiencies (maximum gain to pump power ratios) are in agreement with experimental results presented in the literature. The choice of codopant is shown to be very significant for the pump efficiency when pumping in the 0.98 mu m. The pump efficiency in the 0.98- mu m pump band is shown to be twice the pump efficiency in the 1.48- mu m pump band. >

Selective filling of photonic crystal fibres

A model for calculating the time necessary for filling one or more specific holes in a photonic crystal fibre is made. This model is verified for water, and its enabling potential is illustrated by a polymer application. Selective filling of the core in an air-guide photonic crystal fibre is demonstrated for a polymer and for water. Launching light into such a hybrid-material core proves to be very easily done. Finally, a scheme for enabling access to the core alone, by use of a fusion splicer, is presented.