Electric field design of metallic sub-wavelength hole arrays for optical permittivity sensing

The transmission spectrum of metallic sub-wavelength hole arrays strongly depends on the shape, size, and material properties of structures and therefore enables the arrays to be used for sensing applications. We investigated hydrogen detection to prove the concept of permittivity sensing. Palladium (Pd) was used as the metallic material because of the large change in Pd permittivity upon hydrogen absorption. The fabricated Pd sub-wavelength hole arrays work as permittivity sensors having a strong main transmittance peak that show a redshift upon hydrogen exposure. The electric field distribution within the sub-wavelength holes was studied as a function of nanoplasmonic-based waveguide shape and length. The lower order optical modes within rectangular sub-wavelength holes in a thin metallic layer array were found to enhance the sensor response.