A tunable filter that can be integrated into an all-in-fibre Raman probe for remote in vivo measurements has been demonstrated. By exploiting the photonic bandgap effect in a filled solid-core photonic crystal fibre, researchers from Denmark have created a Rayleigh-rejection filter that can be tuned to operate at different wavelengths by simply heating the filling material.Anna Chiara Brunetti from the Department of Photonics Engineering at the Technical University of Denmark (DTU), who carried out the experimental work, said:“This work is part of a PhD project aiming at the development of an all-in-fibre Raman probe for real-time monitoring of yeast fermentation processes. The device will be integrated in a bioreactor currently under development at the department of Chemical and Biochemical Engineering, DTU. In general though, this device is suitable for all applications where a compact, tunable, low-loss and easy to operate probe is required, including lab-on-a-chip Raman devices.”