In this work, partially etched amorphous silicon (a-Si) metasurface is designed and fabricated to enhance chiral THG from the a-Si nanodisks and SHG from integrated multilayer GaSe overlayers with spectrally tunable chirality. The metasurfaces are designed to support guided mode resonance in the 1500-1600 nm wavelength range. A minimum degree of circular polarization (DOCP) of -0.6 is obtained experimentally on-resonance for the inherent THG process from the silicon nanodisks with resonant enhancement of more than 5 orders. A spectrally tunable DOCP of -0.5 to 0.5 is obtained for the generated SHG from the GaSe layer on top of the silicon metasurface with resonant enhancement of more than 5 orders.
There is interest in studying nonlinear optical properties of monolayer and few-layer 2D materials due to the inherently strong nonlinear optical properties, interesting symmetry properties and polarization dependence. However, the inherent ultrathin 2D material limits the interaction length and efficiency of the nonlinear optical process studied. To overcome this limitation, 2D materials are integrated with resonant photonic structures to increase the overall nonlinear optical interaction strength. Such heterogeneously integrated structures offer the advantage of combining a range of 2D materials exhibiting diverse linear and nonlinear optical properties with prefabricated photonic structures using simple dry-transfer or chemical vapor deposition techniques. Here we will discuss some of the recent progress made in the area of heterogenous integration of 2D materials with dielectric resonant structures. We will also describe some of our recent effort in this direction in the resonant enhancement of second harmonic generation (SHG) from multi-layer Gallium Selenide coupled to silicon twodimensional resonant metasurface to achieve polarization independent SHG enhancement. We find that the designed 2D silicon resonant structures exhibit field depolarization at the resonance wavelength which needs to be accounted for when analyzing the nonlinear polarization. Furthermore, the second-harmonic signal radiated from the structure exhibits higher order diffraction effects with strong incident polarization angle dependence for the higher order diffraction components. Experimental studies on the above structures are also discussed with the observation of resonant enhancement of SHG and similar polarization dependence of the SHG on-/ off- the resonant metasurface when restricting the collection angles to the zeroth order diffracted nonlinear signal.
In this paper, we report demonstration of sub-wavelength high-index contrast gratings which exhibit guided mode resonances for enhancing nonlinear optical effects from 2D materials transferred on top of the structures. Twodimensional hexagonal arrays of c-Si nanodisks on a silicon-on-insulator wafer have been designed to have normal incidence resonance in the 1550-1650 nm wavelength region. Numerical simulations were performed to show resonance variations with structural parameters and corresponding field enhancements outside the structure to aid nonlinear optical response from materials placed on top of the structures. The fabricated structures were characterized for linear reflection using an external cavity tunable laser as the incident light source at close to normal incidence and compared with simulated reflection. As a proof-of-concept, we transferred few-layer Gallium Selenide (GaSe) flake on to the grating using a dry transfer method to examine second harmonic generation response of GaSe in presence of the grating. Second harmonic generation measurements showed strong SHG signal from the GaSe on top of the grating structure, with enhancement of ~ 15x observed at 1645 nm close to fundamental resonance wavelength. No SHG emission was observed from the silicon nanodisks withput the GaSe overlayer. Spectral and power of the SHG were also characterized. This work shows that the potential of heterogeneous integration of high nonlinearity 2D materials on to silicon based resonant optical structures to realize high efficiency nonlinear metasurfaces.
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.