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Authors
Robin Pierron
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We report on the rst evidence of direct micropeak machining using a photonic jet (PJ) with nanosecond laser pulses. PJ is a high concentrated propagative light beam with a full width at half maximum (FWHM) smaller than the diraction limit. In our case, PJs are generated with a shaped optical ber tip. Micropeaks with a FWHM of around 1 $mu$m, a height until 590 nm and an apex radius of 14 nm, were repeatability achieved on a silicon wafer. The experiments have been carried out in ambient air using a 100/140 multimode silica ber with a shaped tip along with a 35 kHz pulsed laser emitting 100 ns pulses at 1064 nm. This study shows that the phenomenon occurs only at low energies, just under the ablation threshold. Bulk material appears to have moved around to achieve the peaks in a selforganized process. We hypothesize that the matter was melted and not vaporized; hydrodynamic ow of molten material governed by surfacetension forces may be the causes. This surface modication has many applications. For example, this paper reports on the decrease of wettability of a textured silicon wafer.
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We demonstrate a photonic radio frequency (RF) transversal filter based on an integrated optical micro-comb source featuring a record low free spectral range of 49 GHz yielding 80 micro-comb lines across the C-band. This record-high number of taps, or wavelengths for the transversal filter results in significantly increased performance including a QRF factor more than four times higher than previous results. Further, by employing both positive and negative taps, an improved out-of-band rejection of up to 48.9 dB is demonstrated using Gaussian apodization, together with a tunable centre frequency covering the RF spectra range, with a widely tunable 3-dB bandwidth and versatile dynamically adjustable filter shapes. Our experimental results match well with theory, showing that our transversal filter is a competitive solution to implement advanced adaptive RF filters with broad operational bandwidths, high frequency selectivity, high reconfigurability, and potentially reduced cost and footprint. This approach is promising for applications in modern radar and communications systems.
We demonstrate significantly improved performance of a microwave true time delay line (TTDL) based on an integrated micro-ring resonator (MRR) Kerr optical comb source with a channel spacing of 49GHz, corresponding to 81 channels over the C-band. The broadband microcomb, with a record low free spectral range of 49GHz, results in a large number of comb lines for the TTDL, greatly reducing the size, cost, and complexity of the system. The large channel count results in a high angular resolution and wide beam steering tunable range of the phased array antenna (PAA). The enhancement of PAA performance matches well with theory, corroborating the feasibility of our approach as a competitive solution towards implementing compact low-cost TTDL in radar and communications systems.
We demonstrate the key role of the laser injection into a multimode fiber to obtain a photonic jet (PJ). PJ, a high concentrated propagating beam with a full width at half maximum smaller than the diffraction limit, is here generated with a shaped optical fiber tip using a pulsed laser source (1064~nm, 100~ns, 35~kHz). Three optical injection systems of light are compared. For similar etched marks on silicon with diameters around 1~$mu$m, we show that the required ablation energy is minimum when the injected light beam is close to the fundamental mode diameter of the fiber. Thus, we confirm experimentally that to obtain a PJ out of an optical fiber, light injection plays a role as important as that of the tip shape, and therefore the role of the fundamental mode in the process.
A simple procedure is demonstrated for fabrication of waveplates which can be released from substrate by laser cutting. Oblique angle deposition, chemical etching and laser inscription steps were used for the final lift-off and release of micro-waveplates in HCl solution.
Drawing inspiration from bilayer graphene, this paper introduces its photonic analog comprising two stacked graphene-like photonic crystals, that are coupled in the near-field through spoof surface plasmons. Beyond the twist degree of freedom that can radically alter the band structure of the bilayer photonic graphene, the photonic dispersion can be also tailored via the interlayer coupling which exhibits an exponential dependence on the distance between the two photonic crystals. We theoretically, numerically, and experimentally characterize the band structures of AA- and AB-stacked bilayer photonic graphene, as well as for twisted bilayer photonic graphene with even and odd sublattice exchange symmetries. Furthermore, we numerically predict the existence of magic angles in bilayer photonic graphene, which are associated with ultra-flat bands resulted from interlayer hybridization. Finally, we demonstrate that the bilayer photonic graphene at a particular twist angle satisfying even sublattice exchange symmetry is a high-order photonic topological insulator. The proposed bilayer photonic graphene could constitute a useful platform for identifying new quantum materials and inspiring next-generation photonic devices with new degrees of freedom and emerging functionality.
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