Arbitrary Spectral Shaping of Plasmonic Broadband Excitations

Yuval Tsur Physical Electronics, School of Electrical Engineering, Tel Aviv University, Tel Aviv University, Israel Itai Epstein Physical Electronics, School of Electrical Engineering, Tel Aviv University, Tel Aviv University, Israel Ady Arie Physical Electronics, School of Electrical Engineering, Tel Aviv University, Tel Aviv University, Israel

The ability to efficiently couple a spectrally broadband free-space beam with a plasmonic beam can open exciting new possibilities for on-chip communication and sensing. In order to enforce momentum preservation during the coupling, researchers often use prisms, periodic gratings or various slits. However, to the best of our knowledge arbitrary shaping of the SPP excitation spectrum had not yet been manifested.

To obtain this ability, we use computer-generated holograms as a tool to encode gratings which conserve momentum for an arbitrary coupling frequency spectrum. The theory stems from the notion that any binary periodic function could be represented by a Fourier series. This kind of holograms had been used in numerous research fields, such as non-linear optics, particle trapping and even electron microscopy. In our case, the binary function and the Fourier series are the coupling grating and the SPP spectrum, respectively.

In this work, we demonstrate numerically and experimentally the full control of both the spectral amplitude and the spectral phase of the SPP excitation, together with its transverse spatial profile, by means of plasmonic holographic gratings. We performed SPP coupling/decoupling experiments by focusing a transverse-magnetic polarized, spectrally-tunable, laser beam onto the plasmonic coupling grating, while recording the spectral reflection and the spectral de-coupled radiation from an adjacent simple out-coupling square grating. Specifically, we demonstrate the spectral shape of a 3rd-order Hermite-Gauss function (Fig. 1), and show that our experiments agree well with the theoretical predictions.

We believe that this demonstration can open new applications in broadband plasmonics, such as on-chip communication (wavelength division multiplexing) and chemical/bio-chemical SPP-based sensing.

Figure 1: Left: A schematic view of the interaction, showing broadband incoming and spectrally shaped outgoing radiation. Right: A comparison between experiment and simulation for a 3rd order Hermite-Gauss spectrum.

Figure 1: Left: A schematic view of the interaction, showing broadband incoming and spectrally shaped outgoing radiation.

Right: A comparison between experiment and simulation for a 3rd order Hermite-Gauss spectrum.

yuvaltsu@post.tau.ac.il









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