We propose and demonstrate an on-chip 1*N power splitter based on topological photonic crystal (TPC) on a monolithic silicon photonic platform. Benefiting from the valley-locked propagation mode at the interface of TPCs with different topological phases, the proposed power splitter has negligible backscattering around the sharp bendings and good robustness to fabrication defects, which therefore enable lower insertion loss, better uniformity, and more compact footprint than the conventional designs. For the fabricated 1*2 (8) power splitter, the uniformity among the output ports is below 0.35 (0.65) dB and the maximum insertion loss is 0.38 (0.58) dB with compact footprint of 5*5 um2 (10*12 um2) within a bandwidth of 70 nm. In addition, the topological power splitter only requires simple configurations of TPCs with different topological phases, which is more reliable in design and fabrication compared with the conventional designs.
Two-dimensional materials are attractive for constructing high-performance photonic chip-integrated photodetectors because of their remarkable electronic and optical properties and dangling-bond-free surfaces. However, the reported chip-integrated two-dimensional material photodetectors were mainly implemented with the configuration of metal-semiconductor-metal, suffering from high dark currents and low responsivities at high operation speed. Here, we report a van der Waals PN heterojunction photodetector, composed of p-type black phosphorous and n-type molybdenum telluride, integrated on a silicon nitride waveguide. The built-in electric field of the PN heterojunction significantly suppresses the dark current and improves the responsivity. Under a bias of 1 V pointing from n-type molybdenum telluride to p-type black phosphorous, the dark current is lower than 7 nA, which is more than two orders of magnitude lower than those reported in other waveguide-integrated black phosphorus photodetectors. An intrinsic responsivity up to 577 mA/W is obtained. Remarkably, the van der Waals PN heterojunction is tunable by the electrostatic doping to further engineer its rectification and improve the photodetection, enabling an increased responsivity of 709 mA/W. Besides, the heterojunction photodetector exhibits a response bandwidth of ~1.0 GHz and a uniform photodetection over a wide spectral range, as experimentally measured from 1500 to 1630 nm. The demonstrated chip-integrated van der Waals PN heterojunction photodetector with low dark current, high responsivity and fast response has great potentials to develop high-performance on-chip photodetectors for various photonic integrated circuits based on silicon, lithium niobate, polymer, etc.
We report a waveguide-integrated MoS2 photodetector operating at the telecom band, which is enabled by hot-electron-assisted photodetection. By integrating few-layer MoS2 on a silicon nitride waveguide and aligning one of the two Au electrodes on top of the waveguide, the evanescent field of the waveguide mode couples with the Au–MoS2 junction. Though MoS2 cannot absorb the telecom-band waveguide mode, the Au electrode could absorb it and generate hot electrons, which transfer to the beneath MoS2 channel due to the low Au–MoS2 Schottky barrier and generate considerable photocurrent. A photoresponsivity of 15.7 mA W–1 at a wavelength of 1550 nm is obtained with a low bias voltage of −0.3 V, which is also moderately uniform over the wide telecom band. A 3 dB dynamic response bandwidth exceeding 1.37 GHz is realized, which is limited by the measurement instrument. The demonstrated MoS2-based hot-electron photodetector not only outperforms other waveguide-integrated hot-electron photodetectors but also provides a strategy to extend the photodetection spectral range of two-dimensional materials. With the maturity of high-quality large-scale growth and flexible transfer of two-dimensional materials, their hot-electron photodetectors could be integrated on various photonic integrated circuits, including silicon, lithium niobate, polymers, etc.
We report a high-responsive hot-electron photodetector based on the integration of an Au–MoS2 junction with a silicon nitride microring resonator (MRR) for detecting telecom-band light. The coupling of the evanescent field of the silicon nitride MRR with the Au–MoS2 Schottky junction region enhances the hot-electron injection efficiency. The device exhibits a high responsivity of 154.6 mA W−1 at the wavelength of 1516 nm, and the moderately uniform responsivities are obtained over the wavelength range of 1500–1630 nm. This MRR-enhanced MoS2 hot-electron photodetector offers possibilities for integrated optoelectronic systems.
We report an indium phosphide nanowire (NW)-induced cavity in a silicon planar photonic crystal (PPC) waveguide to improve the light–NW coupling. The integration of NW shifts the transmission band of the PPC waveguide into the mode gap of the bare waveguide, which gives rise to a microcavity located on the NW section. Resonant modes with Q factors exceeding 103 are obtained. Leveraging on the high density of the electric field in the microcavity, the light–NW interaction is enhanced strongly for efficient nonlinear frequency conversion. Second-harmonic generation and sum-frequency generation in the NW are realized with a continuous-wave pump laser in a power level of tens of microwatts, showing a cavity-enhancement factor of 112. The hybrid integration structure of NW-PPC waveguide and the self-formed microcavity not only opens a simple strategy to effectively enhance light–NW interactions, but also provides a compact platform to construct NW-based on-chip active devices.
Microring resonators, as a fundamental building block of photonic integrated circuits, have been well developed into numerous functional devices, whose performances are strongly determined by microring's resonance lineshapes. We propose a compact structure to reliably realize Lorentzian, Fano, and electromagnetically induced transparency (EIT) resonance lineshapes in a microring. By simply inserting two air-holes in the side-coupled waveguide of a microring, a Fabry-Perot (FP) resonance is involved to couple with microring's resonant modes, showing Lorentzian, Fano, and EIT lineshapes over one free spectral range of the FP resonance. The quality factors, extinction ratios, and slope rates in different lineshapes are discussed. At microring's specific resonant wavelength, the lineshape could be tuned among these three types by controlling the FP cavity's length. Experiment results verify the theoretical analysis well and represent Fano lineshapes with extinction ratios of about 20 dB and slope rates over 280 dB/nm. The reliably and flexibly tunable lineshapes in the compact structure have potentials to improve microring-based devices and expand their application scopes.
We achieve Fano-like resonances in an all-in-fiber structure embedded with an in-line Mach-Zehnder interferometer (MZI).A fiber Bragg grating is inserted into MZI's one arm to form a resonance, which functions as the discrete state of the Fano-like resonance to couple with the continuum propagating mode of MZI in the fiber core.A theoretical model predicts the controllable resonance lineshape by changing the phase difference between the MZI's two interference pathways.Fano-like resonances with an extinction ratio over 20 dB are experimentally observed, which are reliably tuned into Lorentzian and electromagnetically induced transparency-like resonances by versatile methods.The realization of Fano-like resonances with broad tunability in this all-in-fiber structure holds potentials in fiber-based applications of sensing, signal processing and nonlinear optics.
Resonance lineshapes of a side-coupled waveguide-microring resonator (MRR) is crucial for the performances of MRR-based on-chip photonic devices. Much efforts have been made to modify the resonance lineshapes to other types, such as asymmetric Fano profiles. However, complex photonic structures are required to integrate with waveguide-MRR. Here, we model the light propagation in a waveguide-MRR into the interactions of a discrete resonance mode and a continuum waveguiding mode and propose the phase delay between the two states plays great roles in controlling the resonance lineshape into symmetric Lorentzian dips, Lorentzian peaks, and Fano lineshapes with arbitrary asymmetric factors. We experimentally verify this by fabricating silicon waveguide-MRR with an air-hole inserted in the bus-waveguide section coupled with the MRR, where the air-hole with varied dimensions could control the phase delay. The results not only have potentials to strengthen the performances of MRR-based devices, but also provide a simple strategy to control resonance lineshapes in other optical resonators, including photonic crystal cavity, microtoroid, etc.
We report a simple and facile integration strategy of a laser source in passive photonic integrated circuits (PICs) by deterministically embedding semiconductor nanowires (NWs) in waveguides. InP NWs laid on a SiN slab are buried by a polymer layer which also acts as an electron-beam resist. With electron-beam lithography, hybrid polymer-SiN waveguides are formed with precisely embedded NWs. The lasing behavior of the waveguide-embedded NWs is confirmed, and more importantly, the NW lasing mode couples into the hybrid waveguide and forms an in-plane guiding mode. Multiple waveguide-embedded NW lasers are further integrated in complex photonic structures to illustrate that the waveguiding mode supplied by the NW lasers could be manipulated for on-chip signal processing, including power splitting and wavelength-division multiplexing. This integration strategy of an on-chip laser is applicable to other PIC platforms, such as silicon and lithium niobate, and the top cladding layer could be changed by depositing SiN or SiO2, promising its CMOS compatibility.
We propose and experimentally demonstrate, by simply inserting an air-hole or two air-holes in the waveguide side-coupled with a microring, the transmission spectrum could present Fano lineshapes at all of the resonant modes.
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