Technical University of Denmark

Programmable Phase Optics









The Generalised Phase Contrast method Advanced optical micro-manipulation Phase-only optical encryption and decryption Spatial phase-only modulation by the reverse phase contrast method GPC implemented in plana-integrated micro-optics Complex field coupling to advanced optical fibers 2D polarization encoding using Spatial light modulators

Programmable complex field coupling to high-order guided modes of advance fibre optic waveguides

Advanced fibre optic waveguides have recently emerged as a promising technology for a wide range of applications. Micro-structured fibers, for example, are characterised by the presence of a periodic arrangement of low- and high-index microstructures that redefines the wave-guiding principle for such fibres. The unconventional optical properties arising from its distinctive wave-guiding scheme enable new possibilities such as endlessly single-mode propagation, broadband continuum generation, high-power transmission, reduced effects of dispersion, and more. Thus, the potentials of this new class of fibres are significant in optical telecommunications and sensors and are equally relevant to other fibre-based applications particularly in biomedical research.

Here, we generate tuneable complex field distributions for controllable coupling to high-order guided modes of advanced fibre optic waveguides. The optical Fourier transform of grating-based phase patterns, which are encoded on a computer-controlled spatial light modulator, generates complex field distributions for selective launching of a desired mode. Both the amplitude and the phase of the programmable fields are modulated by straightforward and fast adjustments of simple pre-defined binary phase-only diffractive patterns. Experiments demonstrate tuneable coupling to the second-order guided modes of a commercially available index-guiding silica fibre with a triangular lattice air-hole micro-structure.

Figure 1. Optical setup for coupling into the higher order guided modes of advanced optical fibers.

Figure 1 shows the setup for complex field coupling into the higher order guided modes of advanced fiber optic waveguides. The inset is a micrograph showing the cross-section of the index-guided micro-structured fibre (Crystal Fibre A/S, Denmark) with a silica-core diameter of approximately 14 mm.

We encode binary gratings (0 and pi) to generate a two-lobe complex field pattern for input into the fiber. The position of the input binary grating with respect to the optical axis sets the phase difference of the two first-diffraction order peaks. Moving the grating along the transverse direction enables selective launching of the first and second order guided mode. Moreover, changing the orientation angle of the grating allows rotation of the two peaks of the second-order mode.


Figure 2. Shifting the binary grating along the transverse direction

Figure 3. Rotating the binary grating.

Further Reading

Daria,V.R.; Rodrigo, P.J.; Glückstad, J., Programmable complex field coupling to high-order guided modes of micro-structured fibres. Opt. Commun. 232, 229-237 (2004) (Online access)

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Last update: 23-04-2009