We demonstrate ultrafast tunable, near-infrared to ultraviolet frequency conversion in a chalcogenide glass metasurface based on Mie resonances and quasi-bound states in the continuum resonances, enabled by a phase-locking mechanism between the pump and the inhomogeneous portion of the third harmonic signal. Through phase locking, the pump pulse and the inhomogeneous harmonic component can co-propagate, resulting in the acquisition of the same refractive index and absorption coefficient as the pump. If this process occurs within a cavity, efficient frequency conversion can take place, even in the presence of strong material absorption at the wavelengths of the harmonics. As for all nonlinear processes, a resonant condition at the pump field boosts the nonlinear interactions. Finally, we experimentally show the simultaneous generation of phase-locked structured light beams, including optical vortices and Hopf-links at fundamental and tripled frequencies in all-dielectric nonlinear optical metasurfaces even though the tripled frequency corresponds to the region of high absorption of the dielectric material.
Optical beams with a phase term proportional to the azimuthal angle possess a singularity at the beam center and carry an orbital angular momentum (OAM). The OAM beams find important applications including the trapping and rotation of microscopic objects, atom-light interactions and optical communications. The OAM beams can be generated by spiral phase plates or spatial light modulators which are bulky. Recently, planar optical components including q-plates, arrays of nano-antennas and all-dielectric metasurfaces, have attracted significant attention. However, they lack reconfigurability, which means that once the components are fabricated, their functionality cannot be changed.
In this work, we experimentally demonstrate a nonlinear metasurface-based beam converter which is designed to transform a Hermite-Gaussian beam to a vortex beam with an OAM in a transmission mode. The proposed converter is built of an array of nano-cubes made of chalcogenide(As2S3) glass. Chalcogenides offer several advantages for designing all-dielectric, nonlinear metasurfaces, including high linear refractive index at near-infrared wavelengths, low losses, and relatively high third-order nonlinear coefficient. In particular, reconfigurability is enabled by the intensity-dependent refractive index or Kerr nonlinearity. Input Hermite-Gaussian beam at low intensity transmitting through the metasurface acquired an OAM, while at high intensity, remained its original intensity and phase profile. The parameters of the reconfigurable metasurface were optimized and its functionality was verified using numerical simulation and in laboratory experiments. Compared to conventional metasurfaces, their nonlinear counterparts are likely to enable a number of novel devices for all-optical switching and integrated circuits applications.
We propose and demonstrate a reliable and inexpensive tool for optical characterization of photonics metamaterials and metasurfaces. Existing characterization methods of metamaterials (or more precisely negative index metamaterials), including conventional interferometry and ellipsometry, are rather complex and expensive.
The “measurable” difference between, for example, positive index materials and negative index materials is that the former introduces a phase delay to transmitted light beam and the latter one introduces a phase advance. Here, we propose to use optical vortex interferometry to directly “visualize” phase delay or phase advance.
In the proposed setup a laser beams at the wavelength of 633 nm is separated in two by a beam splitter. One beam is transmitted through a spiral phase plate in order to generate a beam with an orbital angular momentum, and the second beam is transmitted through a nanostructured sample. Two beams are subsequently recombined by a beam splitter to form spiral interferogram. Spiral patterns are then analyzed to determine phase shifts introduced by the sample. In order to demonstrate the efficiency of the proposed technique, we fabricated four metasurface samples consisting of metal nano-antennas introducing different phase shifts and experimentally measured phase shifts of the transmitted light using the proposed technique. The experimental results are in good agreement with numerical simulations.
In summary, we report a novel method to characterize metasurfaces and metamaterials using optical vortex interferometry. The proposed characterization approach is simple, reliable and particularly useful for fast and inexpensive characterization of phase properties introduced by metamaterials and metasurfaces.
We show that unique optical properties of metamaterials open unlimited prospects to “engineer” light itself. For example, we demonstrate a novel way of complex light manipulation in few-mode optical fibers using metamaterials highlighting how unique properties of metamaterials, namely the ability to manipulate both electric and magnetic field components, open new degrees of freedom in engineering complex polarization states of light. We discuss several approaches to ultra-compact structured light generation, including a nanoscale beam converter based on an ultra-compact array of nano-waveguides with a circular graded distribution of channel diameters that coverts a conventional laser beam into a vortex with configurable orbital angular momentum and a novel, miniaturized astigmatic optical element based on a single biaxial hyperbolic metamaterial that enables the conversion of Hermite-Gaussian beams into vortex beams carrying an orbital angular momentum and vice versa. Such beam converters is likely to enable a new generation of on-chip or all-fiber structured light applications. We also present our initial theoretical studies predicting that vortex-based nonlinear optical processes, such as second harmonic generation or parametric amplification that rely on phase matching, will also be strongly modified in negative index materials. These studies may find applications for multidimensional information encoding, secure communications, and quantum cryptography as both spin and orbital angular momentum could be used to encode information; dispersion engineering for spontaneous parametric down-conversion; and on-chip optoelectronic signal processing.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.