Xin Fu

Experimental demonstration of an ultracompact Si-nanowire-based reflective arrayed-waveguide grating (de)multiplexer with photonic crystal reflectors

An ultracompact reflective arrayed-waveguide grating (AWG) (de)multiplexer based on Si nanowires is demonstrated for the first time (to our knowledge). Each waveguide in the array has an individual photonic crystal (PhC) reflector at its end, making the AWG layout design very flexible. An eight-channel AWG (de)multiplexer with a channel spacing of 400 GHz is demonstrated experimentally. The total size of the fabricated AWG is as small as 134mumx115mum. The excess loss of the fabricated reflective AWG (de)multiplexer is about 3-4 dB, and the crosstalk is about -12dB.

Narrow-linewidth short-pulse III-V-on-silicon mode-locked lasers based on a linear and ring cavity geometry

Picosecond-pulse III-V-on-silicon mode-locked lasers based on linear and ring extended cavity geometries are presented. In passive mode-locked operation a 12 kHz -3dB linewidth of the fundamental RF tone at 4.7 GHz is obtained for the linear cavity geometry and 16 kHz for the ring cavity geometry. Stabilization of the repetition rate of these devices using hybrid mode-locking is also demonstrated.

Compact Dense Wavelength-Division (De)multiplexer Utilizing a Bidirectional Arrayed-Waveguide Grating Integrated With a Mach–Zehnder Interferometer

A compact wavelength-division (de)multiplexer is proposed and demonstrated experimentally to achieve doubled channel number and halved channel spacing by utilizing a bidirectional arrayed-waveguide grating integrated with an Mach-Zehnder interferometer optical interleaver. As an example, an 18-channel wavelength-division (de)multiplexer with a channel spacing of 200 GHz is designed and fabricated. The measured excess loss is about 8 dB and the channel crosstalk is -15 ~ -18 dB. The footprint of this fabricated (de)multiplexer is about 520 μm × 190 μm.

5 x 20 Gb/s heterogeneously integrated III-V on silicon electro-absorption modulator array with arrayed waveguide grating multiplexer

We present a five-channel wavelength division multiplexed modulator module that heterogeneously integrates a 200 GHz channel-spacing silicon arrayed-waveguide grating multiplexer and a 20 Gbps electro-absorption modulator array, showing the potential for 100 Gbps transmission capacity on a 1.5x0.5 mm² footprint.

5-hydroxymethylcytosine loss is associated with poor prognosis for patients with WHO grade II diffuse astrocytomas

Currently, the reliable prognostic biomarkers for WHO grade II diffuse astrocytomas (DA) are still limited. We investigated the relations between the level of 5-Hydroxymethylcytosine (5hmC), an oxidated production of 5-methylcytosine (5mC) by the ten eleven translocated (TET) enzymes, and clinicopathological features of glioma patients. With an identified anti-5hmC antibody, we performed immunohistochemistry in 287 glioma cases. We detected that 5hmC variably reduced in most gliomas and 5hmC reduction was closely associated with higher pathological grades and shortened survival of glioma patients. In multivariate analysis, 5hmC had no independent prognostic value in the entire patient cohort. However, multivariate analysis within subtypes of gliomas revealed that 5hmC was still a prognostic marker confined to DA. In addition, we detected that IDH1 mutation by DNA sequencing was associated with favorable survival within DA. Lastly, we detected that the combination of 5hmC/KI67 was a useful prognostic marker for restratification of DA.

Design and fabrication of a 200 GHz Si-nanowire-based reflective arrayed-waveguide grating (de)multiplexer with optimized photonic crystal reflectors.

A compact Si-nanowire-based reflective arrayed-waveguide grating (AWG) for dense wavelength-division multiplexing is proposed. At the end of each waveguide in the array, there is an individual photonic crystal (PhC) reflector, which makes the AWG layout design very flexible. All the PhC reflectors are with the same design. With such a design, the total size of the AWG (de)multiplexer is reduced by more than a half. The reflection efficiency of the used PhC reflectors is enhanced by optimizing the taper between the arrayed waveguides and the PhC reflector. A 200 GHz AWG (de)multiplexer is designed and fabricated as an example. The total size is only about 193 μm × 168 μm.

Optical bistability in a high-Q racetrack resonator based on small SU-8 ridge waveguides

A racetrack resonator with a high Q value (~34,000) is demonstrated experimentally based on small SU-8 optical ridge waveguides, which were fabricated with an improved etchless process. Optical bistability is observed in the present racetrack resonator even with a low input optical power (5.6-7.3 mW), which is attributed to the significant thermal nonlinear optical effect due to the high Q value and the large negative thermo-optical coefficient of SU-8. Theoretical modeling for the optical bistability is also given, and it agrees well with the experimental result.

Low driving voltage band-filling-based III-V-on-silicon electroabsorption modulator

In this paper, a method for realizing a low driving voltage electroabsorption modulator based on the band-filling effect is demonstrated. The InP-based electroabsorption modulator is integrated using divinylsiloxane-bis-benzocyclobutene adhesive bonding on a silicon-on-insulator waveguide platform. When the electroabsorption modulator is forward biased, the band-filling effect occurs, which leads to a blue shift of the exciton absorption spectrum, while the absorption strength stays almost constant. In static operation, an extinction ratio of more than 20 dB with 100 mV bias variation is obtained in an 80 μm long device. In dynamic operation, 1.25 Gbps modulation with a 6.3 dB extinction ratio is obtained using only a 50 mV peak-to-peak driving voltage. The band-filling effect provides a method for realizing ultra-low-driving-voltage electroabsorption modulators.

High-Q Microring Resonators With 2

High Q-factor microring resonators (MRRs) with 2×2 angled multimode interference (MMI) couplers are realized based on SU-8 polymer strip waveguides, which has an SU-8 polymer core, an SiO2 buffer, and an air cladding. The present MRR has a small radius (150 μm) because of the high-index contrast of the SU-8 optical waveguides. The coupling ratio of the angled MMI couplers is adjusted to achieve a high-loaded Q-factor MRR by modifying the bending angle. When this bending angle is chosen as 3.25°, the Q-factor of the fabricated MRR is about 25 000.

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We design, fabricate and measure an all shallowly etched reflection-type silicon arrayed waveguide gratings(R-AWG) with one stigmatic point, which contributes to reducing the crosstalk of R-AWG.