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
Figure 3. Rotating the binary grating.
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