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Integrated wavelength filters with high optical rejection are key components in several silicon photonics circuits, including quantum photon-pair sources and spectrometers. Non-coherent cascading of modal-engineered Bragg filters allows for remarkable optical rejections in structures that only support transverse-electric (TE) polarized modes such as uncladded 220-nm-thick silicon. However, the restriction to TE-only platforms limits the versatility of the non-coherent cascading approach. Here, we propose and experimentally demonstrate a new, to the best of our knowledge, approach for high-rejection filters in polarization-diverse platforms by combining non-coherent cascading of modal-engineered Bragg filters and anisotropy-engineered metamaterial bends. Bragg filters provide a high rejection of the TE mode, while the metamaterial bends remove any residual power propagating in the transverse-magnetic (TM) mode, without any penalty in terms of insertion loss or device footprint. Based on this strategy, we demonstrate optical rejection exceeding 60 dB in 300-nm-thick, cladded silicon waveguides.

4 pags., 4 figs., 1 tab., Silicon nitride (SiN) waveguides provide a substantially lower index contrast, thermo-optic coefficient, and reduced birefringence compared to silicon-on-insulator waveguides. These properties make SiN a prominent candidate for implementation of ultra-wideband dual-polarization photonics circuits with a great potential for datacom applications. State-of-the-art SiN power splitters are still hampered in terms of either bandwidth or single-polarization operation. Here, we propose to overcome these limitations by exploiting modal and waveguide symmetry engineering in a single-mode slot waveguide. This topology prevents mode-beating, while granting symmetric power splitting for both polarizations. Experimental characterization of the fabricated device shows low loss (, Spanish Ministry of Science, Innovation and Universities (MICINN) (IJCI-2016-30484, RTI2018- 097957-B-C33, TEC2015-71127-C2-1-R with FPI scholarship BES-2016-077798); Comunidad de Madrid - FEDER funds (S2018/NMT-4326); Horizon 2020 Framework Programme (Marie Sklodowska-Curie 734331); H2020 European Research Council (ERC POPSTAR 647342); European Commission (H2020-ICT-26127-2017 COSMICC 688516); French Industry Ministry (Nano2022 project under IPCEI program); Agence Nationale de la Recherche (ANR-MIRSPEC-17-CE09-0041).

We demonstrated a class of highly nonlinear hybrid waveguide structures based on infiltration of As2S3 chalcogenide glass into silicon slot waveguides. The nonlinear properties of the hybrid waveguides were precisely quantified via a bidirectional top-hat D-scan method, enabling a direct comparison between properties measured using different device geometries. We experimentally demonstrate hybrid As2S3-Si slot waveguides with a two-photon absorption (TPA) figure of merit exceeding 2 at near infrared wavelengths. These waveguides largely satisfy the critical criterion for efficient nonlinear integrated photonics (FOMTPAwg>1), allowing phase shifts greater than π with minimal overall losses. These results pave the way for efficient and robust ultrafast all-optical devices and circuits in large-scale silicon photonics technology.

A polarization tolerant optical receiver is a key building block for the development of wavelength division multiplexing based high-speed optical data links. However, the design of a polarization independent demultiplexer is not trivial. In this Letter, we report on the realization of a polarization tolerant arrayed waveguide grating (AWG) on a 300-mm silicon nitride (SiN) photonic platform. By introducing a series of individual polarization rotators in the middle of the waveguide array, the polarization dependence of the AWG has been substantially reduced. Insertion losses below 2.2 dB and a crosstalk level better than − 29 d B has been obtained for transverse electric and transverse magnetic polarizations on a four-channel coarse AWG. The AWG temperature sensitivity has also been evaluated. Thanks to the low thermo-optical coefficient of SiN, a thermal shift below 12 pm/°C has been demonstrated.

[EN] Waveguide Bragg grating filters with narrow bandwidths and high optical rejections are key functions for several advanced silicon photonics circuits. Here, we propose and demonstrate a new, to the best of our knowledge, Bragg grating geometry that provides a narrowband and high rejection response. It combines the advantages of subwavelength and modal engineering. As a proof-of-concept demonstration, we implement the proposed Bragg filters in 220-nm-thick Si technology with a single etch step. We experimentally show flexible control of the filter selectivity, with measured null-to-null bandwidths below 2 nm, and strength of 60 dB rejection with a null-to-null bandwidth of 1.8 nm., Agence Nationale de la Recherche (ANR-MIRSPEC-17-CE09-0041, ANR-SITQOM-15-CE24-0005); European Research Council (ERC POPSTAR 647342).

[EN] Bragg filters stand as key building blocks of the silicon-on-insulator (SOI) photonics platform, allowing the implementation of advanced on-chip signal manipulation. However, achieving narrowband Bragg filters with large rejection levels is often hindered by fabrication constraints and imperfections. Here, we show that the combination of single-side corrugation asymmetry and subwavelength engineering provides a narrowband response with large corrugations, overcoming minimum feature size constraints of conventional Si Bragg filters. We comprehensively study the impact of the corrugation asymmetry in conventional and subwavelength single-etched SOI Bragg filters, showing their potential for bandwidth reduction. Finally, we experimentally demonstrate novel subwavelength geometry based on shifted corrugation teeth, achieving null-to-null bandwidths and rejections of 0.8 nm and 40 dB for the symmetric configuration and 0.6 nm and 15 dB for the asymmetric case. (c) 2018 Optical Society of America, Agence Nationale de la Recherche (ANR) (Project SITQOM DS0710).

We demonstrate low-loss Ge-rich Si

Vertical slot waveguide micro-ring resonators in silicon photonics have already been demonstrated in previous works and applied to several schemes, including sensing and hybrid nonlinear optics. Their performances, first quantified by the reachable Q-factors, are still perceived to be restrained by larger intrinsic propagation losses than those suffered by simple Si wire waveguides. In this Letter, the optical loss mechanisms of slot waveguide micro-ring resonators are thoroughly investigated with a special focus on the coupler loss contribution that turns out to be the key obstacle to achieving high Q-factors. By engineering the coupler design, slotted ring resonators with a 50 μm radius are experienced with a loaded Q-factor up to 10 times improvement from Q=3,000 to Q=30,600. The intrinsic losses due to the light propagation in the bent slot ring itself are proved to be as low as 1.32±0.87 dB/cm at λ=1,550 nm. These investigations of slot ring resonators open high performance potentials for on-chip nonlinear optical processing or sensing in hybrid silicon photonics.

International audience; Polymer-sorted semiconducting single-walled carbon nano-tubes (SWNTs) provide room-temperature emission at near-infrared wavelengths, with potential for large volume production of high-quality solutions and wafer-scale depo-sition. These features make SWNTs a very attractive material for the realization of on-chip light sources. Coupling SWNT into optical microcavities could enhance and guide their emission, while enabling spectral selection by cavity resonance engineering. This could allow the realization of bright, narrowband sources. Here, we report the first demonstration of coupling SWNTs into the resonant modes of Si hollow-core photonic crystal cavities. We exploit the strong evanescent field in these resonators to interact with SWNT emission, coupling it into an integrated access wave-guide. Based on this concept, we demonstrate narrowband SWNT emission resonantly coupled into a Si bus wave-guide with a full width at half-maximum of 0.34 nm and an off-resonance rejection exceeding 5 dB. Single-walled carbon nanotubes (SWNTs) are a versatile material with outstanding electrical [1,2] and optical properties [3,4]. Indeed, the same SWNT-based device can be reconfigured to perform as a light emitter, detector, or transistor, just by changing the applied voltage [5]. Hence, they have an immense potential to serve as an efficient connection bridge between the electrical and optical planes in future silicon optoelectronic circuits. In the optical domain, semiconducting SWNTs are a direct bandgap material exhibiting room-temperature electro-and photolumi-nescence in the visible and near-infrared [6,7]. Recent advances in solution processing [8] and wafer-scale selective deposition [9] have opened a new path toward the realization of on-chip light sources for the Si photonic platform, based on the use of SWNTs. These could become a cost-effective alternative to current solutions relying on III-V materials. However, the emission from SWNTs has a low quantum efficiency [10] and a wide spectrum that hinder their use as narrowband sources [11]. These two drawbacks could be circumvented by integrating the SWNTs into Si photonic microcavities. The resonant light confinement in small volumes in those cavities could be used to enhance light emission through the Purcell effect [12], while their high quality factors could be exploited to spectrally narrow the wideband SWNT emission. Spectral narrowing has been demonstrated for the emission of individual SWNTs coupled to suspended 1D photonic crystal microcavities [11,13]. This configuration has shown very promising results for quantum photonic applications relying on single-photon sources [14]. However, the intensity of a single emitter could not suffice for datacom or sensing applications. One possible solution to increase the emission intensity is to use a network of SWNTs [7,15–18]. Networks of high-purity polymer-sorted semiconducting SWNTs have shown room-temperature photoluminescence [7] and intrinsic gain [15]. It is worth noting that this sorting technique results in polymer wrapped semiconducting SWNTs. This precludes photo-luminescence quenching when the SWNTs are in contact with a silicon substrate, obviating the need to suspend them in air. Hence, polymer-sorted SWNTs allow cost-effective and large volume on-chip deposition based on drop casting or spin coating techniques. In this context, remarkably narrowband emission with quality factors of Q ˆ 3800 has been demonstrated for networks of polymer-sorted SWNTs in 2D silicon photonic crystal microcavities [16]. Still, no coupling between cavity-enhanced SWNT emission and on-chip waveguides has been reported for this kind of structure. Resonant enhancement of the emission from SWNT networks and coupling to Si pho-tonic waveguides has been shown for Si micro-ring resonators [19]. Nevertheless, these traveling wave resonators have comparatively large mode volumes that limit their potential for Purcell emission enhancement.

The use of a birefringent graded photonic crystal (GPhC) is proposed for the realization of an efficient polarization beam splitter. This approach allows decoupling the two functions of efficient light injection for both polarizations and TE/TM beam splitting. A smooth light polarization splitting is naturally achieved due to the different curved trajectories followed within the graded medium by the TE and TM waves. A 160 nm operating bandwidth with insertion loss around 1 dB and interpolarization crosstalk below −15 dB is predicted by a finite difference time domain simulation. The unusually exploited electromagnetic phenomena are experimentally evidenced by scanning near-field optical measurements performed on samples fabricated using the silicon on insulator photonics technology. These experimental works open perspectives for the use of birefringent GPhCs to manage polarization diversity in silicon photonic circuits.

A flexible design of slot photonic crystal waveguide with a wide comb is investigated. Introduction of a carefully designed comb within the photonic crystal waveguide allows an accurate dispersion engineering in order to achieve slow light and increase the optical confinement within the comb. The strong light confinement results in an extremely small nonlinear effective area around 0.015 μm2. We report experimental realization of a comb photonic crystal waveguide with measured group indices higher than 100 in a Mach-Zehnder interferometer configuration and extract losses limited to 3.7 dB for a 100 μm device at n(g)=37.

Room-temperature quantum-confined Stark effect in a Ge/SiGe quantum-well structure is reported at the wavelength of 1.3 μm. The operating wavelength is tuned by the use of strain engineering. Low-energy plasma-enhanced chemical vapor deposition is used to grow 20 periods of strain-compensated quantum wells (8 nm Ge well and 12 nm Si(0.35)Ge(0.65) barrier) on Si(0.21)Ge(0.79) virtual substrate. The fraction of light absorbed per well allows for a strong modulation around 1.3 μm. The half-width at half-maximum of the excitonic peak of only 12 meV allows for a discussion on physical mechanisms limiting the performances of such devices.

A star coupler-based beam splitter for rib waveguides is reported. A design method is presented and applied in the case of silicon-on-insulator rib waveguides. Experimental results are in good agreement with simulations. Excess loss lower than 1 dB is experimentally obtained for star coupler lengths from 0.5 to 1 μm. Output balance is better than 1 dB, which is the measurement accuracy, and broadband transmission is obtained over 90 nm.