Silicon photonics is becoming the leading technology for photonic integrated circuits (PICs) due to large-scale integration, low cost, and high-volume productions enabled by complementary ...metal-oxide-semiconductor (CMOS) fabrication process. Thanks to various material and optical characteristics of crystalline silicon, the silicon-on-insulator platform has become the dominant material platform for silicon photonics. Meanwhile, monolithic or heterogeneous integration of other materials on silicon photonic chips, including the silicon nitride (SiN)-on-insulator platform and the III-V-on-silicon platform, are under rapid developments to enhance the functionalities of silicon photonics. Among the myriad of silicon photonic structures for passive and active components, integrated microresonators are promising for a broad range of applications due to their strong resonance field enhancement, narrowband wavelength selectivity, and compact footprints. In this paper, we review the state of the art and our perspectives on emerging technologies based on integrated silicon photonic microresonators in the technology domains of intradatacenter optical interconnects, integrated nonlinear and quantum photonics, and lab-on-a-chip optical biosensing. We specifically review recent progress and our original work in SOI microring-based crossbar switch fabrics; III-V-on-silicon microresonator lasers; silicon-based microresonator nonlinear and quantum sources; and SiN microresonator-based optical biosensors.
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. A series of functional polymers with multisubstituted spiro-segments and absolute molecular weights of up to 39,000 are produced in high yields (up to 99%). The obtained spiro-polymers can be readily fabricated into different well-resolved fluorescent photopatterns with both turn-off and turn-on modes based on their photoinduced fluorescence change. Taking advantage of their photoresponsive refractive index, we successfully apply the polymer thin films in integrated silicon photonics techniques and achieve the permanent modification of resonance wavelengths of microring resonators by UV irradiation.
Silicon nitride (SiN) is a promising material platform for integrating photonic components and microfluidic channels on a chip for label-free, optical biochemical sensing applications in the visible ...to near-infrared wavelengths. The chip-scale SiN-based optofluidic sensors can be compact due to a relatively high refractive index contrast between SiN and the fluidic medium, and low-cost due to the complementary metal-oxide-semiconductor (CMOS)-compatible fabrication process. Here, we demonstrate SiN-based integrated optofluidic biochemical sensors using a coupled-resonator optical waveguide (CROW) in the visible wavelengths. The working principle is based on imaging in the far field the out-of-plane elastic-light-scattering patterns of the CROW sensor at a fixed probe wavelength. We correlate the imaged pattern with reference patterns at the CROW eigenstates. Our sensing algorithm maps the correlation coefficients of the imaged pattern with a library of calibrated correlation coefficients to extract a minute change in the cladding refractive index. Given a calibrated CROW, our sensing mechanism in the spatial domain only requires a fixed-wavelength laser in the visible wavelengths as a light source, with the probe wavelength located within the CROW transmission band, and a silicon digital charge-coupled device (CCD) / CMOS camera for recording the light scattering patterns. This is in sharp contrast with the conventional optical microcavity-based sensing methods that impose a strict requirement of spectral alignment with a high-quality cavity resonance using a wavelength-tunable laser. Our experimental results using a SiN CROW sensor with eight coupled microrings in the 680nm wavelength reveal a cladding refractive index change of ~1.3 × 10^-4 refractive index unit (RIU), with an average sensitivity of ~281 ± 271 RIU-1 and a noise-equivalent detection limit (NEDL) of 1.8 ×10^-8 RIU ~ 1.0 ×10^-4 RIU across the CROW bandwidth of ~1 nm.
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. Our method leverages the advantages of non-contact optical forces and a microfluidic flow for both cell stretching and continuous cell delivery. We demonstrate the stretcher for mechanical characterization of rabbit red blood cells (RBCs), with a throughput of ∼1 cell per s at a flow rate of 2.5 μl h
−1
at a continuous-wave laser power of ∼25 mW at a wavelength of 1064 nm (chopped at 2 Hz). We estimate the spring constant of RBCs to be ∼14.9 μN m
−1
. Using the stretcher, we distinguish healthy RBCs and RBCs treated with glutaraldehyde at concentrations of 5 × 10
−4
% to 2.5 × 10
−3
%, with a strain-to-concentration sensitivity of ∼−1529. By increasing the optical power to ∼45 mW, we demonstrate cell-stretching under a higher flow rate of 4 μl h
−1
, with a higher throughput of ∼1.5 cells per s and a higher sensitivity of ∼−2457. Our technique shows promise for applications in the fields of healthcare monitoring and biomechanical studies.
An optofluidic cell stretcher using a periodically chopped optical tweezer and a microfluidic flow for non-contact, continuous cell mechanical characterization.
We propose a controlled-NOT (CNOT) gate based on two-photon quantum interference in cascaded silicon dual-ring resonators with Mach-Zehnder interferometer-assisted coupling. We illustrate the working ...principle and the design parameters of the device by theoretical modeling.
Lithium niobate modulators have primarily been fabricated on chip-level or 4/6-inch wafers. Here, thin-film lithium niobate (TFLN) electro-optic Mach-Zehnder modulators (MZM) are demonstrated for the ...first time on an 8-inch silicon substrate. The fabricated LN modulator has an on-chip loss of less than 1 dB with a waveguide loss of lower than 0.5 dB/cm. The half-wave voltage- length product (V<inline-formula> <tex-math notation="LaTeX">\pi \cdot </tex-math></inline-formula> L) is 3.12 V<inline-formula> <tex-math notation="LaTeX">\cdot </tex-math></inline-formula> cm in the C-band at a 0.5 cm modulation length, and the corresponding 3-dB bandwidth of the electro-optic response is beyond 67 GHz. All specifications are state-of-the-art. These results provide the basis for the industrialization of the TFLN platform with better balance between performance and cost.
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. Our theoretical analysis reveals that the offset causes additional mode-dependent phase changes. Our numerical modeling results using the three-dimensional beam-propagation method are consistent with our experimental results and theory.
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. Here, we demonstrate the proof-of-concept of such a biosensor using a coupled-resonator optical-waveguide (CROW) on a silicon-on-insulator chip. The sensing scheme is based on measurements in the spatial domain, and only requires exciting the CROW at a fixed wavelength and imaging the out-of-plane elastic light-scattering intensity patterns of the CROW. Based on correlating the light-scattering intensity pattern at a probe wavelength with the light-scattering intensity patterns at the CROW eigenstates, we devise a pattern-recognition algorithm that enables the extraction of a refractive index change, Δn, applied upon the CROW upper-cladding from a calibrated set of correlation coefficients. Our experiments using an 8-microring CROW covered by NaCl solutions of different concentrations reveal a Δn of ~1.5 × 10(-4) refractive index unit (RIU) and a sensitivity of ~752 RIU(-1), with a noise-equivalent detection limit of ~6 × 10(-6) RIU.
We demonstrate an on-chip optical cell stretcher using optical lattices generated from SU8-filled vertically embedded multimode-interference waveguides in a silicon substrate. We extract the shear ...modulus of ~2 μN/m from swollen rabbit red blood cells.
We report on-chip optical lattice generation using SU8-filled vertically embedded multimode-interference waveguides in a silicon substrate. We show stretching of rabbit red blood cells using the ...generated optical lattices in a fluidic channel.
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