A dual-polarization 10-channel mode (de)multiplexer is proposed and realized with cascaded dual-core adiabatic tapers on a silicon-on-insulator (SOI) platform. The mode demultiplexer has a 2.3 μm-wide multimode bus waveguide, which supports six mode-channels of TE polarization and four mode-channels of TM polarization. These ten mode-channels are (de)multiplexed with five cascaded dual-core adiabatic tapers based on SOI nanowires. The widths for these dual-cores are chosen optimally according to the dispersion curves of the dual-core SOI nanowire, so that the desired highest-order modes of TE-and TM-polarizations are extracted simultaneously. These two extracted mode-channels are coupled very efficiently to the fundamental modes of TE-and TM-polarizations (TE 0 and TM 0 ) in the narrow waveguide, respectively, which are then separated by using a polarization beam splitter based on bent directional couplers. A chip consisting of a pair of 10-channel mode (de)multiplexers is fabricated and then tested with data transmission of 30Gbps/channel. The measurement results show that all TM-and TE mode-channels have low crosstalks (-15ß-25 dB) and low excess losses (0.2ß1.8 dB) over a broad wavelength band of ß90 nm, which makes it WDM (wavelength-division-multiplexing)-compatible and thus suitable for high capacity on-chip optical interconnects.
Multimode silicon photonics is attracting more and more attention because the introduction of higher-order modes makes it possible to increase the channel number for data transmission in mode-division-multiplexed (MDM) systems as well as improve the flexibility of device designs. On the other hand, the design of multimode silicon photonic devices becomes very different compared with the traditional case with the fundamental mode only. Since not only the fundamental mode but also the higher-order modes are involved, one of the most important things for multimode silicon photonics is the realization of effective mode manipulation, which is not difficult, fortunately because the mode dispersion in multimode silicon optical waveguide is very strong. Great progresses have been achieved on multimode silicon photonics in the past years. In this paper, a review of the recent progresses of the representative multimode silicon photonic devices and circuits is given. The first part reviews multimode silicon photonics for MDM systems, including on-chip multichannel mode (de)multiplexers, multimode waveguide bends, multimode waveguide crossings, reconfigurable multimode silicon photonic integrated circuits, multimode chip-fiber couplers, etc. In the second part, we give a discussion about the higher-order mode-assisted silicon photonic devices, including on-chip polarization-handling devices with higher-order modes, add-drop optical filters based on multimode Bragg gratings, and some emerging applications.
Mode‐division multiplexing (MDM) is attractive to enhance the link capacity of optical interconnects by using multiple mode‐channels in multimode bus waveguides. As sharp waveguide bends are very important for realizing dense photonic integrated circuits, here ultra‐sharp multimode waveguide bends for MDM systems are proposed and demonstrated by using subwavelength grating waveguide structures on silicon. An ultra‐sharp S‐bend with a radius of 10 µm is realized for the first time to enable a low‐loss and low‐crosstalk MDM optical interconnect with three mode‐channels. For this proposed ultra‐sharp subwavelength grating multimode waveguide bend (SMWB) with a 90° bending angle, the theoretical excess losses for the TE0, TE1, and TE2 modes are 0.1–0.3 dB, 0.18–0.22 dB, and 0.3–0.5 dB, respectively, in a wavelength band of 1500–1600 nm. Meanwhile, inter‐mode crosstalks are very low (less than −30 dB) for all mode‐channels. For the fabricated 90°‐SMWB, the excess losses for the TE0, TE1, and TE2 modes are 0.1–0.3 dB, 0.2–0.4 dB, and 0.3–0.7 dB while the inter‐mode crosstalk is approximately −22 dB in a wavelength band of 1520–1600 nm. The proposed SMWB is also extended for more than three mode‐channels.
Time-energy entangled-photon pair generation is shown from a Q > 1 million AlGaAs-on-insulator microring resonator with an internal generation rate greater than 20×109 pairs sec
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1 mW
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2, heralded single photon purity > 99%, and a visibility > 97%.
A polarization beam splitter (PBS) is proposed and realized for silicon photonic integrated circuits with a 340-nm-thick silicon core layer by introducing an asymmetric directional coupler (ADC), which consists of a silicon-on-insulator (SOI) nanowire and a subwavelength grating (SWG) waveguide. The SWG is introduced to provide an optical waveguide which has much higher birefringence than a regular 340-nm-thick SOI nanowire, so that it is possible to make the phase-matching condition satisfied for TE polarization only in the present design when the waveguide dimensions are optimized. Meanwhile, there is a significant phase mismatching for TM polarization automatically. In this way, the present ADC enables strong polarization selectivity to realize a PBS that separates TE and TM polarizations to the cross and through ports, respectively. The realized PBS has a length of ∼2 μm for the coupling region. For the fabricated PBS, the extinction ratio (ER) is 15-30 dB and the excess loss is 0.2-2.6 dB for TE polarization while the ER is 20-27 dB and the excess loss is 0.3-2.8 dB for TM polarization when operating in the wavelength range of 1520-1580 nm.
8 is highly efficient at degrading feather keratin. We observed integrated feather degradation over the course of 48 h in basic culture medium while studying the entire process with scanning electron microscopy. Large amounts of ammonia, sulfite, and -cysteic acid were detected in the fermented liquid. In addition, four enzymes (gamma-glutamyltranspeptidase, peptidase T, serine protease, and cystathionine gamma-synthase) were identified that play an important role in this degradation pathway, all of which were verified with molecular cloning and prokaryotic expression. To the best of our knowledge, this report is the first to demonstrate that cystathionine gamma-synthase secreted by 8 is involved in the decomposition of feather keratin. This study provides new data characterizing the molecular mechanism of feather degradation by bacteria, as well as potential guidance for future industrial utilization of waste keratin.
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