Magnetic Imaging in Photonic Crystal Microcavities

We demonstrate the nonresonant magnetic interaction at optical frequencies between a photonic crystal microcavity and a metallized near-field microscopy probe. This interaction can be used to map and control the magnetic component of the microcavity modes. The metal coated tip acts as a microscopic conductive ring, which induces a magnetic response opposite to the inducing magnetic field. The resulting shift in resonance frequency can be used to measure the distribution of the magnetic field intensity of the photonic structure and fine-tune its optical response via the magnetic field components.

Figure 1

Scheme of the magnetic perturbation induced by the nanometric metallic tip. (a) The tip is positioned on the sample surface and the magnetic field lines enter the tip aperture. (b) The magnetic flux throughout the metallic ring of the tip aperture induces a magnetic moments.

Figure 2

Photoluminescence spectrum collected by the near-field probe during the scan. We label as M1 and M2 the two main modes of the cavity. In the inset a three-dimensional visualization of a scanning electron microscopy image of the investigated sample is reported.

Figure 3

(a),(b) Spatial distribution of the photoluminescence signal associated to the mode M1 and M2, respectively. (c),(d) Calculated electric field intensity associated to the mode M1 and M2, respectively. The different symbols indicate the position where the spectra in Fig. 4 are collected.

Figure 4

(a),(b) Near-field spectra collected in different position of the cavity for the mode M2, with an aluminum coated tip (a) and an uncoated tip (b). The inset reports a scanning electron microscope image of the studied cavity, the symbols indicate the positions where the spectra are collected.

Figure 5

(a),(b) Calculated intensity of the magnetic field component along the $z$ axis for the mode M1 and M2, respectively. The color scale indicates the intensity of the field. (c),(d) Experimental spectral shift map associated to the mode M1 and M2, respectively. In this case the color scale indicates the spectral position of the cavity modes.