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A multiport thermo-optic switch based on parallel polymer waveguides and microheater array is proposed. The basic unit is a $1\times3$ switch for Up Transfer, Isolation, and Down Transfer operations. By introducing refractive index perturbation along the selected waveguides through microheaters, the Transfer /Isolation condition can be switched locally, and light is then steered into different paths. A $1\times5$ switch is demonstrated experimentally as an example. Colorless ( $1.50~\mu \text{m}$ to $1.62~\mu \text{m}$ ) and polarization independent operation is achieved with crosstalk suppression ratio larger than 10 dB, which can be further optimized. The design requires less waveguides and tuning sections than conventional Mach-Zehnder interferometer-based switches. 6 microheaters are placed but only 3 need to be powered on simultaneously to reach any of the 5 output ports. The maximal heater power is 33.8 mW over a coupling length of $1331.6~\mu \text{m}$ . This design can easily scale up to form an arbitrary cascaded M $\times1$ and $1\times $ N switch network for high-density photonic integration.

We propose and experimentally demonstrate a fiber spectrum analyzer based on a planar waveguide chip butt-coupled with an input fiber and aligned to a standard camera without any free-space optical elements. The chip consists of a single-mode waveguide to connect with the fiber, a beam broadening area, and a waveguide array in which the lengths of the waveguides are designed for both wavelength separation and beam focusing. The facet of the chip is diced open so that the outputs of the array form a near-field emitter. The far field are calculated by the Rayleigh-Sommerfeld diffraction integral. We show that the chip can provide a focal depth on the millimeter scale, allowing relaxed alignment to the camera without any fine-positioning stage. Two devices with 120 and 220 waveguides are fabricated on the polymer waveguide platform. The measured spectral width are 0.63 nm and 0.42 nm, respectively. This simple and practical approach may lead to the development of a spectrum analyzer for fiber that is easily mountable to any commercial camera, thereby avoiding the complication for customized detectors as well as electronic circuits afterwards.

In this article, we demonstrate a push-pull silicon dual-ring modulator based on two cascaded rings which are coupled with each other through two parallel bus waveguides. In the transmission spectrum of the modulator, a narrow transparency peak exists in the center of the broad dip based on the electromagnetically induced transparency (EIT)-like effect. Benefiting from both the EIT-like effect and push-pull drive configuration, a low insertion loss (IL) of 1.4 dB and an extinction ratio (ER) over 6.4 dB are obtained at a bit rate of 10 Gb/s with a peak-to-peak driving voltage (Vpp) of 5 V. The corresponding maximum optical modulation amplitude (OMA) is 0.56, which is almost twice that of a single micro-ring modulator with the same driving voltage. Moreover, the maximum OMA is 0.47 at 20 Gb/s, which is 81% larger than that of a single micro-ring modulator.

Astrophotonics aims to apply photonic technology to manipulate light from a telescope and process it for astronomical research purposes in an efficient and cost-effective way. In particular, using planar dispersive device for astronomical spectroscopic research is a promising method, as the compact and lightweight device could replace at least some of the bulky parts in the modern spectrograph. However, the migration of arrayed waveguide gratings from optical communication to astronomy must go through new designs with tailored properties. In this work, we first demonstrate an arrayed waveguide grating with over 100-nm free spectral range and further propose a new design of an integrated photonic spectrograph without any free-space optics. The design merges the wavefront modulation of a conventional lens into the length/phase variation in the waveguide array, in addition to the required difference to form the grating effect. The end effect is that the output light from the facets of the arrayed waveguides is not only separated by wavelength, but also focused onto a camera at a fixed distance. Simulation shows this design can reach high resolving power (> 7,000) with more compact size and most importantly, it eliminates the need to add any conventional lens in the optical path, in the sense of a truly integrated photonic spectrograph.

As a classic immunoregulatory cytokine, interleukin-10 (IL-10) can provide in vivo and in vitro neuroprotection respectively during cerebral ischemia and after the oxygen-glucose deprivation (OGD)-induced injury. However, its role in cortical neuronal survival at different post-ischemic phases remains unclear. The current study found that IL-10 had distinct effects on the neuronal apoptosis at different OGD stages: at an early stage after OGD, IL-10 promoted the OGD-induced neuronal apoptosis in the cultured primary cortical neurons by activating p65 subunit, which up-regulated Bax expression and down-regulated Bcl-xL expression; at a late OGD stage, however, it attenuated the OGD-induced neuronal apoptosis by activating c-Rel, which up-regulated Bcl-xL expression and down-regulated Bax expression. The early-stage pro-apoptosis and late-stage anti-apoptosis were both partly abolished by PDTC, an NF-κB inhibitor, and promoted by PMA, an NF-κB activator. The optimal anti-apoptotic effect appeared when the cultured neurons were treated with IL-10 at 9-24 h after OGD. Taken together, our findings suggest that IL-10 exerts a dual effect on the survival of the cultured neurons by activating the NF-κB pathway at different stages after OGD injury and that PMA treatment at a late stage can facilitate the IL-10-conferred neuroprotection against OGD-induced neuronal injury.

We propose and experimentally demonstrate a microwave photonic phase shifter based on a tunable silicon photonic interleaver. This device consists of a microring resonator, a tunable interleaver, and a $2\,\times \,1$ multimode interferometer (MMI). By thermally tuning the interleaver, a linear phase shift of 188° is realized with a linearity of 0.08 and a radio-frequency (RF) power variation within 1 dB for a 40-GHz signal.

Background: Transplantation of bone marrow-derived mesenchymal stem cells (BMSCs) is a potential therapy for cerebral ischemia. However, the underlying protective mechanism remains undetermined. Here, we tested the hypothesis that transplantation of BMSCs via intravenous injection can alleviate neurological functional deficits through activating PI3K/AKT signaling pathway after cerebral ischemia in rats. Methods: A cerebral ischemic rat model was established by the 2 h middle cerebral artery occlusion (MCAO). Twenty-four hours later, BMSCs (1 × 106 in 1 ml PBS) from SD rats were injected into the tail vein. Neurological function was evaluated by modified neurological severity score (mNSS) and modified adhesive removal test before and on d1, d3, d7, d10 and d14 after MCAO. Protein expressions of AKT, GSK-3β, CRMP-2 and GAP-43 were detected by Western-bolt. NF-200 was detected by immunofluorescence. Results: BMSCs transplantation did not only significantly improve the mNSS score and the adhesive-removal somatosensory test after MCAO, but also increase the density of NF-200 and the expression of p-AKT, pGSK-3β and GAP-43, while decrease the expression of pCRMP-2. Meanwhile, these effects can be suppressed by LY294002, a specific inhibitor of PI3K/AKT. Conclusion: These data suggest that transplantation of BMSCs could promote axon growth and neurological deficit recovery after MCAO, which was associated with activation of PI3K/AKT /GSK-3β/CRMP-2 signaling pathway.

Mode- and polarization-division multiplexing are new promising options to increase the transmission capacity of optical communications. On-chip silicon polarization and mode handling devices are key components in integrated mode- and polarization-division multiplexed photonic circuits. In this paper, we review our recent progresses on silicon-based polarization beam splitters, polarization splitters and rotators, mode (de) multiplexers, and mode and polarization selective switches. Silicon polarization beam splitters and rotators are demonstrated with high extinction ratio, compact footprint and high fabrication tolerance. For on-chip mode multiplexing, we introduce a low loss and fabrication tolerant three-mode (de)multiplexer employing sub-wavelength grating structure. In analogy to a conventional wavelength selective switch in wavelength-division multiplexing, we demonstrate a selective switch that can route mode- and polarization-multiplexed signals.

We propose and experimentally demonstrate an automated resonance wavelength alignment scheme for an O-band 4 × 4 thermo-optic optical switch using dual-ring resonators. In this scheme, a new control algorithm based on saddle point searching is employed to align dual-input switching elements (SEs) and therefore the 4 × 4 switch. The proposed scheme is proven effective by demonstrating eight routing configurations for two 10-Gb/s data channels. The insertion losses of the three-stage SEs are ≤6.9 dB, and the crosstalk values are below -13.6 dB. Besides, the tolerance of the switch to the wavelength misalignment between the two optical input signals is measured. Negligible performance degradations are observed when the two channels are spaced by 0.05 nm.

We present the design and experimental demonstration of a compact tunable silicon photonic interleaver with a wide spectral range. The interleaver consists of an interfering loop containing a Fabry–Perot cavity formed by two Sagnac loops. The transmission coefficients of the directional couplers are calculated based on the maximally flat criterion. The impacts of the transmission coefficient variations on the extinction ratio and filter sharpness are investigated. The wavelength dependences of the directional couplers are analyzed to increase the spectral range of the interleaver. The device was fabricated on a silicon-on-insulator platform. The spectral ranges of the measured transmission and reflection spectra are increased to 60 nm. By thermal tuning the waveguide connecting the two Sagnac loops, the central wavelength can be shifted over one free spectral range with a wavelength-tuning efficiency of ∼0.08 nm/mW.

We experimentally demonstrate a multi-stage wavelength locking scheme based on saddle point searching in a dual-ring based $4\times 4$ electro-optic switch. Three-stage switching elements can be aligned to the signal wavelength with initial $\leq 2-nm$ wavelength misalignments.

A generic multiport optical switch capable of generating all-logic outputs is demonstrated by altering the mode profiles and propagation characteristics in a multimode waveguide through a combination of microheaters. The principles and design rules are introduced. As proof of concept, a 3-bit all-logic switch is fabricated on a polymer waveguide platform. The experimental results are in good agreement with the simulations based on a heat solver and the eigenmode expansion method. The device shows polarization insensitive and colorless operation from 1520 to 1600 nm with an extinction ratio between “On” and “Off” states larger than 11.9 dB in all cases. The maximum heat power is 43.9 mW (for (1, 0, 0) state). The simple, compact, and easily scalable device can be used to construct 1 × N and M × N switch networks, showing promising applications in on-chip photonic signal processing and computation.

We demonstrate a real-time holographic display using quantum-dot doped liquid crystal with a build-up time of several to tens of milliseconds, and the maximum diffraction efficiency is measured up to 30%. Holographic videos of red, green, and blue colors at a refresh rate of 60 Hz are realized. The dependences of response time on the recording intensity, applied voltage, and grating period are investigated.

We present a 3D integrated wavelength demultiplexer using a square-core fiber (SCF) and matched dual-layer arrayed waveguide gratings (AWGs). The SCF works as a 3D fiber multimode interference device, which splits the input light into symmetric four spots. The spots are then coupled to a pitch-matched 4-waveguide network, each connecting an AWG. Interface waveguides are designed to improve the coupling efficiency between the SCF and the dual-layer chip. The four AWGs are designed with different central wavelengths and a large free spectral range (FSR) of 120 nm. To reach a small and uniform insertion loss among different channels, only the central channels of each AWG are used for demultiplexing. The device is fabricated on a polymer platform. The upper and lower layers of the chip are fabricated using the same photolithography mask but rotated 180° so that 4 different AWG designs can be mapped to a single chip. The measured transmission spectra of the four AWGs cover a bandwidth of 112 nm. The insertion loss variation is smaller than 1.4 dB. The designed device can find applications in fiber optic sensing, communication, and astronomy.

We present our recent work on thermal-optical switching on silicon chips, including two nanobeam switches with wavelength tuning, and a mode and polarization selective switch having a 748-Gb/s capacity on a single wavelength.

A silicon dual-ring modulator with 10-dB bandwidth of 0.08 nm and low insertion loss of 1.1 dB is experimentally demonstrated. The modulation speed of the dual-ring modulator can be as high as 20 Gb/s.

We propose and experimentally demonstrate a compact silicon photonic interleaver based on an interfering loop containing a 1D Fabry–Perot (FP) cavity for coarse wavelength division multiplexing (CWDM) applications. The interleaver consists of a directional coupler and a FP cavity designed to minimize the channel crosstalk. Instead of using an off-chip optical circulator, the reflection light of the interleaver can be separated from the input by placing two identical interleavers in a Mach–Zehnder interferometer (MZI) structure for practical applications. We also study the impacts of fabrication errors of the MZI structure. The fabricated device has a footprint of 64 μm×70 μm and a channel spacing of ∼19 nm. The maximum crosstalk is −16 dB in a wavelength range from 1508 nm to 1590 nm.

We propose and experimentally demonstrate an on-chip all-optical differential-equation solver capable of solving second-order ordinary differential equations (ODEs) characterizing continuous-time linear time-invariant systems. The photonic device is implemented by a self-coupled microresonator on a silicon-on-insulator platform with mutual coupling between the cavity modes. Owing to the mutual mode coupling within the same resonant cavity, the resonance wavelengths induced by different cavity modes are self-aligned, thus avoiding precise wavelength alignment and unequal thermal wavelength drifts as in the case of cascaded resonators. By changing the mutual mode coupling strength, the proposed device can be used to solve second-order ODEs with tunable coefficients. System demonstration using the fabricated device is carried out for 10-Gb/s optical Gaussian and super-Gaussian input pulses. The experimental results are in good agreement with theoretical predictions of the solutions, which verify the feasibility of the fabricated device as a tunable second-order photonic ODE solver.

We demonstrate an automated wavelength calibration scheme for a dual-ring based silicon electro-optic switch. By using an improved saddle point searching algorithm, the calibration over a full free spectral range of 6 nm is achieved.

We review recent progress on silicon photonic devices for optical signal processing, including nanobeam devices for wavelength filtering and switching, directional couplers for polarization/mode processing, and subwavelength grating devices for multi-dimensional processing.

An enhanced four-wave mixing in a silicon-graphene hybrid slot waveguide is proposed and experimentally demonstrated. The conversion efficiency is −48.8 dB, showing 3.2-dB and 0.5-dB improvements relative to silicon slot waveguide and strip waveguide, respectively.

A compact silicon bandpass filter with high sidelobe suppression is proposed and experimentally demonstrated using an apodized subwavelength grating (SWG) coupler. The device is implemented by placing a SWG waveguide next to a strip waveguide, and apodization is employed with a Gaussian profile to taper the gap between the two waveguides. A high sidelobe suppression ratio of 27 dB can be obtained with a 3-dB bandwidth of 8.8 nm and an insertion loss of 2.5 dB. Owing to the large optical phase mismatch between the two waveguides and the presence of the SWG waveguide, the coupling length of the device is reduced to 100.3 μm. The experimental results validate our proposed apodized-SWG-based contradirectional coupler (contra-DC) as a promising device in suppressing out-of-band components in coarse wavelength division multiplexed (CWDM) optical communication systems.

We experimentally demonstrate a compact silicon contradirectional coupler with high sidelobe suppression by using apodized subwavelength grating waveguide. A suppression ratio of higher than 20 dB is achieved with a ∼100-pm coupling length.

We propose and experimentally demonstrate a reconfigurable ultrawideband (UWB) pulse generation scheme by using a dual-drive Mach-Zehnder modulator (DDMZM). In the proposed method, two phase modulators of the DDMZM are respectively driven by properly designed electrical signals. By carefully setting the parameters of the two electrical signals and the bias voltage of the DDMZM, different UWB pulses can be achieved at the interference output of the DDMZM. A proof-of-concept experiment verifies the feasibility of the proposed method. Photonic generations of UWB monocycle, doublet, triplet, and quintuple pulses have been successfully demonstrated, with central frequencies of 4.69, 4.69, 5.47, and 6.25 GHz and fractional bandwidths of 150%, 133%, 186%, and 75%, respectively.

We propose and experimentally demonstrate a new method to generate a 3-D ultrawideband (UWB) signal by utilizing a dual-drive Mach-Zehnder modulator (DDMZM). Three degrees of freedom of the generated 3-D UWB signal are pulse position, pulse phase, and pulse amplitude. In this scheme, each radio frequency (RF) port of the DDMZM is modulated by a combination of two encoded signals with different amplitudes. By properly adjusting the amplitudes of the encoded signals and the bias voltages of the two RF ports, a 5-Gb/s 3-D UWB signal with a central frequency of 3.5 GHz and a 10-dB fractional bandwidth of 163% is successfully generated by using only a single DDMZM.

In this paper, we propose and demonstrate a 2 × 2 optical Benes switching unit based on two nested silicon microring resonators (MRRs) monolithically integrated on a silicon-on-insulator (SOI) wafer. High extinction ratios (ERs) of about 44.7/38.0 dB and low crosstalk values of about −37.5/−45.2 dB at cross/bar states are obtained with the fabricated device. The operation principle is theoretically studied and the switching function is verified by system demonstration experiments with 10 and 12.5 Gb/s non-return-to-zero (NRZ) signals. The switching speed on the order of gigahertz based on free carrier effect in silicon is also experimentally demonstrated.

In this paper, we propose and demonstrate an all-optical second-order differentiator based on a two-stage self-coupled optical waveguide on a silicon-on-insulator platform. The transmission spectrum of the fabricated device has a parabola-like filtering notch with a 3-dB bandwidth of up to ~ 100 GHz and a depth of ~ 12 dB. Experiments are carried out for 10-, 20-, and 40-Gb/s optical time-domain multiplexing (OTDM) picosecond pulse trains, and the second-order differentiations are achieved using the fabricated device.

The temperature dependence of diffraction efficiency and response time in two holographic systems using doped liquid crystals (LC) is investigated. For dye-doped LCs, the response time is generally robust to temperature variation but the diffraction efficiency is temperature-sensitive; whereas, the QDdoped LC remains robust for both characteristics around room temperature.