Institut des
NanoSciences de Paris
insp
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Nanostructures et optique

Characterization of planar photonic crystals

A photonic crystal is a periodic dielectric structure which, in analogy with an electron in a crystal, creates a band structure of available photonic states. A well controlled way to fabricate a 2D photonic crystal is to create a lattice of holes in a thin layer. The versatility of this technique allows in particular to add a defect (hole vacancy) which constitutes a cavity.

We have collaborated with a group at the LAAS (Toulouse) in order to create such crystals with a cavity mode in the visible range so that it can couple to nanocrystal emission. We perform AFM and optical characterizations of the structures fabricated at the LAAS (fig. 1a). AFM measurements provide information on the surface roughness which is a key element for the quality factor of the cavity. We have established a protocol of characterization of the cavities by scattering of white light injected on the side of the sample. We showed that this method can be used to characterize the wavelength and width of the cavity modes and the results were in reasonable agreement with the values obtained by numerical simulations. With this method, we have studied the influence of the system geometry (holes diameter, shift of the side holes ...) on the cavity modes.

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Figure 1 : (a) AFM image of the surface of a silicon nitride planar photonic crystal with a vacancy of 3 holes fabricated at the LAAS. (b) White light cattering spectra from 3 cavities with different hole diameters, (a) experimental and (b) simulated (FDTD) (polarized orthogonal to the cavity long axis). For each cavity 1 or 2 modes can be seen, with a position well described by simulation, however with a systematic 20-nm shift related to uncertainty on the AFM determination of the holes sizes.

 

Collaborations :

- Olivier Gauthier-Lafaye, Sophie Bonnefont and Françoise Lozes-Dupuy at the LAAS (Toulouse)

- Emmanuelle Lacaze and Serge Berthier at the INSP respectively for AFM and optical characterizations

 

Communications :

- A. Avoine, C. Vion, J. Laverdant, C. Schwob, S. Bonnefont, O. Gauthier-Lafaye, L. Coolen, A. Maitre, Caractérisation des modes résonnants de cavités de cristaux photoniques dans le visible par spectroscopie de diffusion, Journées de la Matière Condensée, Troye (2010)

-  A. Avoine, C. Vion, J. Laverdant, S. Bonnefont, O. Gauthier-Lafaye, L. Coolen et A. Maître, Photonic crystal cavity modes in the visible range characterized by scattering spectroscopy, Phys. Rev. A 82, 063809 (2010)

-  C. Vion, A. Maître, O. Gauthier-Lafaye, S. Bonnefont, S. Hernandez, F. Lozes-Dupuy, Fabrication and optical characterization of photonic crystal cavities in the visible range, Spie Europe photonics (Starsbourg, avril 2008)