In this paper a beamforming network concept based on photonic technology for future array antenna systems for SAR applications is reported, covering from the optical signal distribution to the antenna, the true-time-delay control of the signal for each antenna element by using integrated photonics (PICs) both in transmission and reception, with broadband characteristics.
We study the electromagnetic behavior of a structure consisting of coupled aluminum nanodisks on a silicon waveguide
at telecom wavelengths. Numerical simulations show that the fundamental TE-like waveguide mode excites a localized
magnetic plasmon resonance between adjacent nanodisks with suitable dimensions, leading to transmission dips. For a
sufficient number of disks (periodically distributed along the propagation direction), the structure supports a magnetic
mode arising from a magneto-inductive coupling between neighboring nanodisks, as revealed by an Eigenmode analysis.
The transmission response of the samples was measured for both polarizations through an end-fire set-up, confirming
that the strong resonances are only present for TE polarization. Measurements and simulations are in good agreement,
showing that the resonances strength is maximized for three coupled nanodisks.
In this work, we show that closely-spaced gold nanohoops periodically distributed in a square lattice can provide
a strong magnetic response in the near infrared regime when illuminated under normal incidence (perpendicular
to the structure plane). Therefore, just a single metallic layer is needed to achieve the magnetic activity. A key
point to achieve this response is that the aspect ratio must be higher than 1. Transmission and reflection spectra
taken by means of a Fourier-Transform Infrared spectrometer show a strong absorbance peak at a wavelength that
can be tuned by modifying the hole radius of the nanohoops or the underlying dielectric substrate. Numerical
simulations show that at the resonance wavelength a virtual current loop is created, giving rise to a strong
magnetic moment and a large magnetic field enhancement in the space between nanohoops.
We prove theoretically that it is possible to build embedded reflectionless squeezers/expanders using transformation
optics. We illustrate the potential of this finding by proposing an application in which the squeezer is a key element: an
ultra-short perfect coupler for high-index nanophotonic waveguides.
Exploiting the concept of internal surface plasmon polariton (I-SPP) resonances, which appear at non-single metallic
film stacks, we have designed a metamaterial showing a negative effective refractive index within a large bandwidth.
The designed structure consists of an arrangement of several fishnet layers. By properly adjusting the lattice constant and
the thickness of the dielectric slab of the fishnet, an I-SPP mode can be excited at a certain frequency giving rise to a
negative effective refractive index. Thus, the combination of several fishnet layers, each one of them configured to
excite an I-SPP at a different frequency, enables us to extend the bandwidth at which a negative effective refractive
index is achieved, as long as the selected resonances are close enough. Specifically, from a subwavelength chain of two
fishnet layers, the retrieved effective parameters show a negative index behavior in a frequency span of about 44THz
centered at 210THz, owing to the fact that an I-SPP is excited in each fishnet layer at slightly different frequencies.