Micro- and nano-optical structures offer the possibility to control light on a wavelength scale. This allows further miniaturization of integrated optical circuits. Planar photonic crystal waveguides and microcavities are considered basic building blocks for applications such as microlasers, filters, multiplexers and optical switches. The possibility to tune or switch photonic crystal devices by various ways such as temperature, refractive index change using liquid crystals, free charge carrier density or non linear material effects increases their functionality to form multifunctional, intelligent devices. High-Q cavities in planar photonic crystals exhibit highly localised fields and narrow transmission bands. Due to their strong light confinement even a small perturbation of the localized field can change their transmission properties of the cavity. We present different ways of perturbing the optical environment near a photonic crystal cavity enabling tuning and modulation of the in-plane transmission. Optical switching and wavelength tuning is obtained by means of induced thermo and plasma dispersion effects when focusing a laser onto the cavity structure. The feasibility of high-speed optical integrated circuits based on silicon photonic crystal structures is shown. On the other hand, an AFM tip is used for mechanically tuning and damping the inplane transmission. A future challenge is the integration of more than one silicon tip to combine filter and tuning functionalities and to create a chip-based device.