Hybrid nanophotonic systems consisting of resonant dielectric nanostructures integrated with single or few layers of transition metal dichalcogenides (2D-TMDs) offer important opportunities for active nanophotonic systems featuring an actively tunable response. While the resonant nanophotonic structures serve to enhance the light-matter interaction in the atomically thin membranes, the 2D-TMDs exhibit tunable excitonic properties. However, the experimental realization and demonstration of active functionalities in such hybrid systems remains challenging.
Here, we experimentally realize resonant high-index dielectric meta-waveguides and metasurfaces integrated with various species of 2D-TMDs. We demonstrate voltage tuning of the systems’ transmittance and photoluminescent properties, as well as of their polarization dependence.
Our results show that hybridization with 2D-TMDs can serve to render resonant photonic nanostructures tunable and time-variant – important properties for practical applications in optical analog computers and neuromorphic circuits.
The excitation of quasi-bound states in the continuum (quasi-BIC) in symmetry broken all dielectric metasurfaces have been vastly explored in the last years. The high Q-factor of quasi-BIC resonances make them attractive in sensing, electromagnetic induced transparency or non-linear optics. The resonance wavelength is fixed by the geometry of the metasurface, which is a constraint for applications, which require the tuning of the resonances to different spectral regions. In this work, we demonstrate the use of temperature as a means to fine-tune the quasi-BIC resonance in hydrogenated amorphous silicon (a-Si:H) metasurfaces.
Bound states in the continuum (BICs) are a category of localized states that exist within the continuum of radiating modes. The high Q-factor exhibited by these states makes quasi-BICs interesting for enhancing the emission from quantum emitters. Quasi-BICs have been experimentally realized in silicon for applications in the infrared wavelength range. Instead of silicon, hydrogenated amorphous silicon (a-Si:H) has been used for achieving quasi-BIC resonance in parts of visible spectra. Titanium dioxide (TiO2) has emerged as an alternate material for fabricating dielectric metasurfaces with high Q-factor in the visible spectral range due to its lower absorptive losses and high refractive index. However, the fabrication process for TiO2 nanostructures presents challenges compared to the well-established fabrication processes in silicon. Our work focuses on the design and fabrication of TiO2 metasurfaces supporting a quasi-BIC mode around 795 nm, with a theoretical Q-factor of 353. Experimental results reveal a maximum Q-factor of 258 at 791 nm. We discuss encountered fabrication constraints and explore possibilities for improvement in both design and fabrication processes. This study contributes to the understanding of quasi-BIC resonance in TiO2 metasurfaces, and opens avenues for further exploration in the utilization of TiO2 for high-Q dielectric metasurfaces, offering insights into the design and optimization of these structures.
Realizing full-dimensional arbitrary manipulation of optical waves, which is known to be important for the implementation of optical devices with ondemand functionalities, still remains a challenge. Recently, Metasurfaces have shown unprecedented capabilities for the manipulation of optical waves at the subwavelength scale. Here, we demonstrated the use of chiral mirrors for the implementation of spin-selective multidimensional manipulation of optical waves. we validated that the three dimensions (amplitude, phase and operation wavelength) of optical waves is directly related to the three main structure variables of the designed chiral mirror. By simply and orderly changing the three structural variables of the designed chiral mirror, the spin-selective full and near independent manipulation of amplitude and phase of optical waves with a large and continuous wavelength agility can be implemented
Bound states in the continuum (BICs) represent dark modes trapped in the radiation continuum. BICs received significant attention in optics and photonics as a simple tool to achieve giant quality factors by transforming them into quasi-BICs. Here, we report the observation of high-harmonic generation in dielectric metasurfaces hosting BICs. The metasurface is composed of a square lattice with parallel Si bars of a slightly different width placed on a transparent substrate. The structure is engineered to support a quasi-BIC in the mid-IR with a high quality factor. We tune the metasurface asymmetry to enable the optimal coupling condition that provide the highest high-harmonic generation efficiency. In the experiment, we demonstrate the generation of odd optical harmonics from the 3rd to the 11th order in the BIC regime and study their polarization dependence. We measure the dependence of the high-harmonic signal on the input intensity. The concept of metasurfaces with highly localized light boosted by BIC resonances provides a new degree of freedom to control experimentally strong nonlinear optical response.
Photonic chip based Kerr frequency combs are transforming diverse applications including spectroscopy, telecommunication, signal processing and metrology among others. Integrated silicon nitride (SiN) waveguides with anomalous dispersion have the potential to bring practical nonlinear optics to mainstream photonic integrated circuits; however, high stress and high processing temperatures for SiN deposited by low pressure chemical vapour deposition (LPCVD) remain an obstacle to mass adoption. We successfully demonstrate fully CMOS-compatible high confinement SiN microring resonators based on reactive sputtering thin-films at a maximum processing temperature of 400°C. We deposit 0.85 μm thick SiN thin-films with a low stress value of 41.5 MPa and bulk material losses of 0.3 dB/cm. Linear waveguides losses of 0.7 dB/cm (Qint= 4.9 × 105) and 0.5 dB/cm (Qint= 6.6 × 105) have been achieved at 1560 nm and 1580 nm, respectively. We characterised the nonlinear properties of the waveguides and measured a nonlinear coefficient of Υ = 2.1 W-1 m-1 and a nonlinear refractive index n2 of 5.6 × 10-19 m2 W-1. Modulation-instability (MI) optical frequency combs are observed by pumping a 120 μm radius microring resonator at 1560 nm with an estimated on-chip pump power of 850 mW, showing a native FSR spaced frequency comb covering a >250 nm wide spectral range.
We present a new device platform which defines on-chip chalcogenide waveguide/resonators without directly etching chalcogenide. Using our platform, we have demonstrated chalcogenide ring resonators with record high Q-factor exceeding 1.1x107 which is 10 times larger than previous record on on-chip chalcogenide resonators. A ring cavity is designed and fabricated for Stimulated Brillouin lasing on our platform. Thanks to the high-Q factor, Brillouin lasing with threshold power of 1 mW is demonstrated. This value is more than an order of magnitude improvement than previous world record for on-chip chalcogenide Brillouin lasers. We also developed an efficient and flexible method for resonator waveguide coupling with our device platform. Coupling between a resonator and a waveguide can be varied from under coupled region to over-coupled region.
In this contribution, we demonstrate the deposition of low loss, CMOS-compatible SiN thin-films using plasma beam assisted reactive sputtering for photonic integrated circuits. Plasma beam assistance during the deposition process enabled us to achieve thin-film losses of below 0.1 dB/cm and a surface roughness of Rq of <0.1 nm, while keeping the processing temperatures below 400°C. Propagation losses of 0.9 dB/cm at 1550 nm have been achieved for waveguides with a cross section of 460× 2000 nm (height × width).
Hybrid integration of different materials will allow for different functionalities such as passive, amplifying, nonlinear, electro-optic, detection etc to build “system on a chip” devices. The vertically stacked layer design commonly proposed significantly increases the difficulty of the lithography process for the bottom-most layer due to the overlying topology. A methodology for significantly improving the fabrication tolerance of planar directional couplers is therefore presented. A parametric design study reveals that significant dimensional sensitivity improvements exist for certain center-to-center spacings for both power and wavelength splitters.
We review recent demonstration of stimulated Brillouin scattering in a chalcogenide photonic chip and its application to
optical and microwave signal processing tasks. The interaction between light and sound via stimulated Brillouin scattering
(SBS) was exploited in chalcogenide photonic circuits to achieve on-chip SBS slow and fast light, microwave photonic
filters, and dynamic gratings using travelling-wave geometry. Using a ring-resonator geometry, photonic-chip based
Brillouin laser was demonstrated.
The ability to control the speed of light on an optical chip is fundamental to the development of nanophotonic components for alloptical
signal processing and sensing [1-7]. However this is a significant challenge, because chip-scale waveguides require very large
changes in group index (Δng) to achieve appreciable pulse delays. Here, we use Stimulated Brillouin Scattering (SBS) to report the
demonstration of on-chip slow, fast and negative group velocities with Δng ranging from −44 to +130, and delays of up to 23ns at a
pump power of ~300mW and propagation length of 7cm. These results are obtained using a highly-nonlinear chalocogenide (As2S3)
rib waveguide, in which the confinement of both photons and phonons results in strong interaction. SBS can be used to achieve
controllable pulse delays at room temperature over a large wavelength and signal-bandwidth [5]. These results open up a new set of
photonic applications ranging from microwave photonics [8] to spectrometry [4].
We report the first demonstration of on-chip stimulated Brillouin scattering (SBS). SBS is characterized in a
chalcogenide (As2S3) photonic chip where the measured Brillouin shift and full-width at half-maximum (FWHM)
linewidth are 7.7 GHz and 34 MHz respectively. The measured Brillouin gain coefficient (gB) is 0.715 x 10-9 m/W, consistent with the theoretical estimate.
As the bit rates of optical networks increase, the ability of accurate monitoring of optical waveforms has become
increasingly important. In recent years, optical sampling has emerged as a technique to perform time-resolved
measurements of optical data signals at high data rates with a bandwidth that cannot be reached by conventional
photodetectors and oscilloscopes. In an optical sampling system, the optical signal is sampled in the optical
domain by a nonlinear optical sampling gate before the resulting samples are converted to an electrical signal.
This avoids the need for high bandwidth electronics if the optical sampling gate is operated with a modest
repetition frequency.
In this paper, we present an optical sampling system using the optical Kerr effect in a highly nonlinear
chalcogenide device, enabling combined capability for femtosecond resolution and broadband signal wavelength
tunability. A temporal resolution 450-fs is achieved using four-wave mixing (FWM) in dispersion-engineered
chalcogenide waveguides: on one hand a 7-cm long planar waveguide (integrated on a photonic chip) and on the
other hand a 5-cm long tapered fiber. The use of a short length, dispersion-shifted waveguide with ultrahigh
nonlinearity (10000/W/km) enables high-resolution optical sampling without the detrimental effect of chromatic
dispersion on the temporal distortion of the signal and sampling pulses, as well as their phase mismatch (which
in turn would degrade the FWM efficiency and the sensitivity of the measurement). Using these chalcogenide
devices, we successfully monitor a 640-Gb/s optical time-division multiplexing (OTDM) datastream, showcasing
its potential for monitoring of signals at bitrates approaching and beyond Tb/s. We compare the advantages
and disadvantages of both approaches and discuss fundamental limitations as well as potential improvements.
In this review, we discuss the progress and prospects offered by chalcogenide glass photonic crystals. We show that by
making photonic crystals from a highly-nonlinear chalcogenide glass, we have the potential to integrate a variety of
active devices into a photonic chip. We describe the testing of two-dimensional Ge33As12Se55 chalcogenide glass
photonic crystal membrane devices (waveguides and microcavities). We then demonstrate the ability to not only post-tune
the devices properties but also create high Q cavities by using the material photosensitivity.
Device parameters, like center frequency, polarization dependent loss (PDL), and optical crosstalk in silica-based waveguide device, are determined by the refractive index (RI) and its uniformity across the wafer, thermal expansion coefficient (TCE), and biaxial elastic modulus of silica film. In this study the optical and thermo-mechanical properties of plasma enhanced CVD silica films with different compositions were investigated before and after thermal annealing. RI of deposited films decreased sharply with N2O/SiH4 ratio up to 40, and increased slowly when this ratio was larger than 60. The minimum RI of deposited film was found slightly higher than that of thermal oxide. CTE and elastic modulus of silica film were obtained by measuring the film stress with temperature. Growth stresses of deposited films were increased with N2O/SiH4 ratio. Due to the porous structure, the CTE and elastic modulus of deposited films at low temperature range (<400°C) were different from those of pure silica. Sharp rise in stress due to gas evolution from film was observed around 500°C. The amount of stress increase and the origin of evolved gas are dependent on the film composition. When silica films were fully annealed (1100°C for 4hour), their CTE and elastic modulus were the same as those of thermal oxide. Upon annealing at high temperature (~800°C), however, cracks were generated on sub-oxide film, which was deposited at low N2O/SiH4 ratio. RI of annealed films changed with the composition of deposited film, the annealing temperature, and the cooling rate after anneal.
The objective of this study was to find the relationship between process parameters and responses in deep silica etching for hybrid integration. The process parameters were the wafer temperature, oxygen addition, clamp material and process pressure. The responses to these parameters were sidewall roughness, profile of etched waveguide, the morphology of etched surface and critical dimension change. When the process parameters were varied, the change in responses could be interpreted by analyzing sidewall polymer thickness and selectivity. Polymer thickness and selectivity also have positive correlation. To investigate which parameter is dominant in determining the coupling efficiency between waveguide end facet and active device in application for hybrid integration, the propagation loss of waveguide with or without deep trenches were measured and analyzed.
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