Polarization entanglement generation in silicon nitride waveguide-coupled dual microring resonators.

Polarization-entangled photon pair sources exhibiting nonlocal quantum correlations are crucial to developments of quantum computing, quantum communications, quantum cryptography, and quantum sensing technologies. On-chip polarization entanglement generation thus constitutes one enabling component for integrated quantum photonic circuits. Here, we present to our knowledge the first polarization-entangled photon pair sources in a silicon nitride platform for integrated quantum photonic circuits.

Parallel wavelength-division-multiplexed signal transmission and dispersion compensation enabled by soliton microcombs and microrings.

The proliferation of computation-intensive technologies has led to a significant rise in the number of datacenters, posing challenges for high-speed and power-efficient datacenter interconnects (DCIs). Although inter-DCIs based on intensity modulation and direct detection (IM-DD) along with wavelength-division multiplexing technologies exhibit power-efficient and large-capacity properties, the requirement of multiple laser sources leads to high costs and limited scalability, and the chromatic dispersion (CD) restricts the transmission length of optical signals. Here we propose a scalable on-chip parallel IM-DD data transmission system enabled by a single-soliton Kerr microcomb and a reconfigurable microring resonator-based CD compensator.

Continuously tunable silicon optical true-time delay lines with a large delay tuning range and a low delay fluctuation.

On-chip switchable optical true-time delay lines (OTTDLs) feature a large group delay tuning range but suffer from a discrete tuning step. OTTDLs with a large delay tuning range and a continuous tuning capability are highly desired. In this paper, we propose and experimentally demonstrate a silicon-based broadband continuously tunable OTTDL comprising a 7-bit delay line and a switch-based continuously tunable delay line.

On-chip passive pump-rejection long-pass filters for integrated SiC-based nonlinear and quantum photonic chips.

We present an on-chip passive pump-rejection filter on an integrated silicon carbide (SiC)-on-insulator photonic platform. Our filters exploit the optical absorption from an amorphous silicon (α-Si) thin-film layer deposited on the top surface and on the sidewalls of the SiC waveguide to reject light with a wavelength below 1.0 µm.

A 3C-SiC-on-Insulator-Based Integrated Photonic Platform Using an Anodic Bonding Process with Glass Substrates.

Various crystalline silicon carbide (SiC) polytypes are emerging as promising photonic materials due to their wide bandgap energies and nonlinear optical properties. However, their wafer forms cannot readily provide a refractive index contrast for optical confinement in the SiC layer, which makes it difficult to realize a SiC-based integrated photonic platform. In this paper, we demonstrate a 3C-SiC-on-insulator (3C-SiCoI)-based integrated photonic platform by transferring the epitaxial 3C-SiC layer from a silicon die to a borosilicate glass substrate using anodic bonding.

Integrated SiN microresonator-based quantum light sources with high brightness using a subtractive wafer-scale platform.

The silicon nitride (SiN) platform, demonstrating a moderate third-order optical nonlinearity and a low optical loss compared with those of silicon, is suitable for integrated quantum photonic circuits. However, it is challenging to develop a crack-free, wafer-scale, thick SiN platform in a single deposition run using a subtractive complementary metal-oxide-semiconductor (CMOS)-compatible fabrication process suitable for dispersion-engineered quantum light sources. In this paper, we demonstrate our unique subtractive fabrication process by introducing a stress-release pattern prior to the single SiN film deposition.

Stress-released SiN fabrication process for dispersion-engineered integrated silicon photonics.

We develop a stress-released stoichiometric silicon nitride (SiN) fabrication process for dispersion-engineered integrated silicon photonics. To relax the high tensile stress of a thick SiN film grown by low-pressure chemical vapor deposition (LPCVD) process, we grow the film in two steps and introduce a conventional dense stress-release pattern onto a ∼400nm-thick SiN film in between the two steps. Our pattern helps minimize crack formation by releasing the stress of the film along high-symmetry periodic modulation directions and helps stop cracks from propagating.

An optofluidic "tweeze-and-drag" cell stretcher in a microfluidic channel.

The mechanical properties of biological cells are utilized as an inherent, label-free biomarker to indicate physiological and pathological changes of cells. Although various optical and microfluidic techniques have been developed for cell mechanical characterization, there is still a strong demand for non-contact and continuous methods. Here, by combining optical and microfluidic techniques in a single desktop platform, we demonstrate an optofluidic cell stretcher based on a "tweeze-and-drag" mechanism using a periodically chopped, tightly focused laser beam as an optical tweezer to trap a cell temporarily and a flow-induced drag force to stretch the cell in a microfluidic channel transverse to the tweezer.

Photoresponsive spiro-polymers generated in situ by C-H-activated polyspiroannulation.

The development of facile and efficient polymerizations toward functional polymers with unique structures and attractive properties is of great academic and industrial significance. Here we develop a straightforward C-H-activated polyspiroannulation route to in situ generate photoresponsive spiro-polymers with complex structures. The palladium(II)-catalyzed stepwise polyspiroannulations of free naphthols and internal diynes proceed efficiently in dimethylsulfoxide at 120 °C without the constraint of apparent stoichiometric balance in monomers.

Optical lattice generation using vertically embedded multimode-interference square-core polymer waveguides on a silicon chip.

We demonstrate two-dimensional optical lattice generation at 1064nm wavelength using vertically embedded multimode-interference (MMI) square-core polymer waveguides on a silicon chip. We demonstrate tuning of the effective waveguide length by longitudinally offsetting the waveguide input end-face from the input beam waist. Our measurement results of the waveguides with different cross-sectional dimensions at different effective waveguide lengths exhibit lattice patterns spanning from 4 × 4 to 10 × 10 arrays at the waveguide output end-face.

Actively stabilized silicon microrings with integrated surface-state-absorption photodetectors using a slope-detection method.

We propose and experimentally demonstrate actively stabilized silicon microrings with integrated surface-state-absorption (SSA) photodetectors using a slope-detection method. Our proof-of-concept experiments reveal that the active stabilization using multiple discrete-step slope thresholds can effectively reduce the microring transmitted intensity variations upon various temperature modulation conditions. We demonstrate an actively stabilized microring transmission with intensity modulations within ~2.

Active resonance wavelength stabilization for silicon microring resonators with an in-resonator defect-state-absorption-based photodetector.

We propose and demonstrate active resonance wavelength stabilization for silicon microring resonators with an in-resonator defect-state-absorption (DSA)-based photodetector (PD) for optical interconnects. We integrate an electro-optic (EO) tuner and a thermo-optic (TO) tuner on the microring, which are both feedback-controlled following a photocurrent threshold-detection method. Our BF(2)-ion-implanted DSA-based PIN PD exhibits a cavity-enhanced sub-bandgap responsivity at 1550 nm of 3.

Silicon coupled-resonator optical-waveguide-based biosensors using light-scattering pattern recognition with pixelized mode-field-intensity distributions.

Chip-scale, optical microcavity-based biosensors typically employ an ultra-high-quality microcavity and require a precision wavelength-tunable laser for exciting the cavity resonance. For point-of-care applications, however, such a system based on measurements in the spectral domain is prone to equipment noise and not portable. An alternative microcavity-based biosensor that enables a high sensitivity in an equipment-noise-tolerant and potentially portable system is desirable.

Silicon nitride three-mode division multiplexing and wavelength-division multiplexing using asymmetrical directional couplers and microring resonators.

We demonstrate silicon nitride mode-division multiplexing (MDM) and wavelength-division multiplexing (WDM) using asymmetrical directional couplers and microring resonators. Our experiments reveal three-mode multiplexing and demultiplexing. We demonstrate 30Gb/s open eye diagrams with an extinction ratio of ~9 dB for each of the three modes.

Unfolding a design rule for microparticle buffering and dropping in microring-resonator-based add-drop devices.

We propose an intuitive and quantitative design rule to determine the microparticle transport processes, including buffering and dropping, on microring-resonator-based add-drop devices at cavity resonances in an integrated optofluidic chip. The design rule uses the splitting ratio, S, of the optical-field intensity at the microring feedback-arc just after the output-coupling region to that at the drop-waveguide as a figure-of-merit for particle transport to determine between particle buffering (S > 1) and dropping (S < 1). The particle transport, however, becomes probabilistic in the case that S is close to 1.

Direct-modulated waveguide-coupled microspiral disk lasers with spatially selective injection for on-chip optical interconnects.

We investigate direct-modulated waveguide-coupled microspiral disk lasers for on-chip optical interconnects. Microspiral resonators, with a rotationally asymmetric shape and a waveguide directly gapless coupled to the notch, offer a compact unidirectional-emission on-chip laser source. We employ spatially selective injection by means of a ring-shaped p-contact on top of the microdisk rim region to selectively inject current to the whispering-gallery-like modes and thus enhance the laser performance.

Sub-bandgap linear-absorption-based photodetectors in avalanche mode in PN-diode-integrated silicon microring resonators.

We report a sub-bandgap linear-absorption-based photodetector in avalanche mode at 1550 nm in a PN-diode-integrated silicon microring resonator. The photocurrent is primarily generated by the defect-state absorption introduced by the boron and phosphorous ion implantation during the PN diode formation. The responsivity is enhanced by both the cavity effect and the avalanche multiplication.

Silicon-on-insulator multimode-interference waveguide-based arrayed optical tweezers (SMART) for two-dimensional microparticle trapping and manipulation.

We demonstrate two-dimensional optical trapping and manipulation of 1 μm and 2.2 μm polystyrene particles in an 18 μm-thick fluidic cell at a wavelength of 1565 nm using the recently proposed Silicon-on-insulator Multimode-interference (MMI) waveguide-based ARrayed optical Tweezers (SMART) technique. The key component is a 100 μm square-core silicon waveguide with mm length.

Epitaxial III-V-on-silicon waveguide butt-coupled photodetectors.

We report silicon waveguide butt-coupled p-i-n InGaAs photodetectors epitaxially grown on silicon-on-insulator substrates by metalorganic chemical vapor deposition. The InGaAs absorption layer that is lattice-matched to InP is selectively grown on patterned SOI substrates, employing metamorphic growth of GaAs and InP buffer layers. We measure a dark current of 2.

Optical trapping of microparticles using silicon nitride waveguide junctions and tapered-waveguide junctions on an optofluidic chip.

We study optical trapping of microparticles on an optofluidic chip using silicon nitride waveguide junctions and tapered-waveguide junctions. We demonstrate the trapping of single 1 μm-sized polystyrene particles using the evanescent field of waveguide junctions connecting a submicrometer-sized input-waveguide and a micrometer-sized output-waveguide. Particle trapping is localized in the vicinity of the junction.

Planar optical tweezers using tapered-waveguide junctions.

We demonstrate planar optical tweezers using the evanescent field of a silicon nitride tapered-waveguide junction between a singlemode waveguide and a multimode waveguide. Our experiments show that the junction embedded in a fluidic channel holds up to one and two polystyrene particles of sizes of 2.2 μm and 1 μm, respectively.

Modeling of coupled-resonator optical waveguide (CROW) based refractive index sensors using pixelized spatial detection at a single wavelength.

We model and analyze coupled-resonator optical waveguide (CROW) based refractive index (RI) sensors using pixelized spatial detection. Our modeled cascaded Fabry-Perot (FP) CROWs reveal that the intra-band states mode-field distributions vary upon effective RI change at a single wavelength. The spatial Fourier transform of the CROW mode-field distributions, with each cavity field intensity integrated as a pixel, shows spatial frequency peak shift, which constitutes the basis of such a spatial domain sensor.

Optical manipulation of microparticles using whispering-gallery modes in a silicon nitride microdisk resonator.

We demonstrate optical manipulation of 1 μm sized polystyrene microparticles on silicon nitride microdisk resonator devices using whispering-gallery modes in an integrated optofluidic chip. We demonstrate multiple trapping tracks and extended trapping ranges within single wavelengths through exciting high-order modes. We observe various sets of trapping tracks and ranges through exciting various resonance modes.

Electro-optical tunable time delay and advance in a silicon feedback-microring resonator.

We report the demonstration of electro-optical tunable time delay and advance using a silicon feedback-microring resonator integrated with p-i-n diodes. By controlling the feedback and round-trip phase shifts through the carrier-injection-based free-carrier dispersion effect, we obtain a large dynamic time tuning range (-88 ps to 110 ps) upon dc bias voltage change in the range of few tens of millivolts at a given resonance wavelength. We also demonstrate tunable time delay and advance at different resonance wavelengths within 0.

Electro-optical tunable time delay and advance in silicon microring resonators.

We demonstrate electro-optical tunable time delay and advance in a silicon-microring-resonator-based notch filter integrated with a lateral p-i-n diode. We tune the time delay and advance by controlling the coupling regimes from over- to under-coupling through carrier-injection-based free-carrier dispersion effect. We measure maximum time delay and advance of approximately -95 and approximately 96 ps near critical coupling, with bandwidths of approximately 3.