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Register a new userHigh dispersive and monolithic 100% efficiency grisms
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We present a type of grism, a series combination of transmission grating and prism, in which we reduce the number of diffraction orders and achieve a configuration with very high angular dispersion. The grism can be fabricated from a single dielectric material and requires no metallic or dielectric film layers for high transmission diffraction efficiency. One can reach 100% in the -1st transmission diffraction order and the equal damage threshold as the dielectric bulk material. We realized such an element in fused silica with an efficiency of more then 99%. The bevel backside reflection is reduced by a statistical antireflective structure, so we measured an efficiency of the entire grism of 95% at a single wavelength.
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We demonstrate that the phase-matched dispersive wave (DW) emission within the resonance band of a 25-cm-long gas-filled hollow-core photonic crystal fiber (HC-PCF) can be strongly enhanced by the photoionization effect of the pump pulse. In the experiments we observe that as the pulse energy increases, the pump pulse gradually shifts to shorter wavelengths due to soliton-plasma interactions. When the central wavelength of the blueshifting soliton is close to the resonance band of the HC-PCF, high-efficiency energy transfer from the pump light to the DW in the visible region can be obtained. During this DW emission process, we also observe that the spectral center of the DW gradually shifts to longer wavelengths leading to a slightly-increased DW bandwidth, which can be well explained as the consequence of phase-matched coupling between the pump pulse and the DW. In particular, at an input pulse energy of 6 uJ, the spectral ratio of the DW at the fiber output is measured to be as high as ~53% together with a conversion efficiency of ~19%. These experimental results, explained by numerical simulations, pave the way to high-brightness light sources based on high-efficiency frequency-upconversion processes in gas-filled HC-PCFs.
The emission of dispersive waves (DWs) by temporal solitons can be described as a cascaded four-wave mixing process triggered by a pair of monochromatic continuous waves (CWs). We report experimental and numerical results demonstrating that the efficiency of this process is strongly and non-trivially affected by the frequency detuning of the CW pump lasers. We explain our results by showing that individual cycles of the input dual-frequency beat signal can evolve as higher-order solitons whose temporal compression and soliton fission govern the DW efficiency. Analytical predictions based on the detuning dependence of the soliton order are shown to be in excellent agreement with experimental and numerical observations.
Recently, an achromatic metasurface was successfully demonstrated to deflect light of multiple wavelengths in the same direction and it was further applied to the design of planar lenses without chromatic aberrations [Science, 347, 1342(2015)]. However, such metasurface can only work for normal incidence and exhibit low conversion efficiency. Here, we present an ultrawide-angle and high-efficiency metasurface without chromatic aberration for wavefront shaping in visible range. The metasurface is constructed by multiple metallic nano-groove gratings, which support enhanced diffractions for an ultrawide incident angle range from 10o to 80o due to the excitations of localized gap plasmon modes at different resonance wavelengths. Incident light at these resonance wavelengths can be efficiently diffracted into the same direction with complete suppression of the specular reflection. This approach is applied to the design of an achromatic flat lens for focusing light of different wavelengths into the same position. Our findings provide a facile way to design various achromatic flat optical elements for imaging and display applications.
We demonstrate an approach for automated Kerr comb generation in the normal group-velocity dispersion (GVD) regime. Using a coupled-ring geometry in silicon nitride, we precisely control the wavelength location and splitting strength of avoided mode crossings to generate low-noise frequency combs with pump-to-comb conversion efficiencies of up to 41%, which is the highest reported to date for normal-GVD Kerr combs. Our technique enables on-demand generation of a high-power comb source for applications such as wavelength-division multiplexing in optical communications.
We report temporal and spectral domain observation of regenerative oscillation in monolithic silicon heterostructured photonic crystals cavities with high quality factor to mode volume ratios (Q/V). The results are interpreted by nonlinear coupled mode theory (CMT) tracking the dynamics of photon, free carrier population and temperature variations. We experimentally demonstrate effective tuning of the radio frequency (RF) tones by laser-cavity detuning and laser power levels, confirmed by the CMT simulations with sensitive input parameters.
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