分类： 光学 >> 量子光学 提交时间： 2023-02-19
Long Zhang
Shihan Hong
Yi Wang
Hao Yan
Yiwei Xie
Tangnan Chen
Ming Zhang
Zejie Yu
Yaocheng Shi
Liu Liu
Daoxin Dai
摘要： The singlemode condition is one of the most important design rules for optical waveguides in guided-wave optics. The reason following the singlemode condition is that higher-order modes might be excited and thus introduce some undesired mode-mismatching loss as well as inter-mode crosstalk when light propagates along an optical waveguide beyond the singlemode regime. As a result, multimode photonic waveguides are usually not allowed. In this paper, we propose the concept of silicon photonics beyond the singlemode regime, developed with low-loss and low-crosstalk light propagation in multimode photonic waveguides with broadened silicon cores. In particular, silicon photonic waveguides with a broadened core region have shown an ultra-low-loss of ~0.1 dB/cm for the fundamental mode even without any special fabrication process. A micro-racetrack resonator fabricated with standard 220-nm-SOI MPW-foundry processes shows a record intrinsic Q-factor as high as 1.02*107 for the first time, corresponding to ultra-low waveguide propagation loss of only 0.065 dB/cm. A high-performance microwave photonic filter on silicon is then realized with an ultra-narrow 3-dB bandwidth of 20.6 MHz as well as a tuning range of ~20 GHz for the first time. An on-chip 100-cm-long delayline is also demonstrated by using the present broadened SOI photonic waveguides with compact Euler-curve bends, the measured propagation loss is ~0.14 dB/cm. The proposed concept of silicon photonics beyond the singlemode regime helps solve the issue of high propagation loss and also significantly reduces the random phase errors of light due to the random variations of waveguide dimensions. In particularity it enables silicon photonic devices with enhanced performances, which paves the way for new-generation silicon photonics realizing the large-scale photonic integration.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
Lijia Song
Tangnan Chen
Weixi Liu
Hongxuan Liu
Yingying Peng
Zejie Yu
Huan Li
Yaocheng Shi
Daoxin Dai
摘要： Silicon photonic Mach-Zehnder switches (MZSs) have been extensively investigated as a promising candidate for practical optical interconnects. However, conventional 2{\times}2 MZSs are usually prone to the size variations of the arm waveguides due to imperfect fabrication, resulting in considerable random phase imbalance between the two arms, thereby imposing significant challenges for further scaling up NN MZSs. Here we propose a novel design towards calibration-free 2{\times}2 and N{\times}N MZSs, employing optimally widened arm waveguides, enabled by novel compact tapered Euler S-bends with incorporated mode filters. With standard 180-nm CMOS foundry processes, more than thirty 2{\times}2 MZSs and one 4{\times}4 Benes MZS with the new design are fabricated and characterized. Compared with their conventional counterparts with 0.45-{\mu}m-wide arm waveguides, the present 2{\times}2 MZSs exhibit ~370-fold reduction in the random phase imbalance. The measured extinction ratios of the present 2{\times}2 and 4{\times}4 MZSs operating in the all-cross state are ~30 dB and ~20 dB across the wavelength range of ~60 nm, respectively, even without any calibrations. This work paves the way towards calibration-free large-scale N{\times}N silicon photonic MZSs.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Optical modulators are required to have high modulation bandwidths and a compact footprint. In this paper we experimentally demonstrate a novel Si/In$_2$O$_3$ hybrid plasmonic waveguide modulator, which is realized by an asymmetric directional coupler (ADC) consisting of a silicon photonic waveguide and a Si/In$_2$O$_3$ hybrid plasmonic waveguide. The optical signal is modulated by radio-frequency (RF) signal applied on the Au electrodes at the top of MOS capacitor and contacting the In$_2$O$_3$ thin film. The record-high modulation bandwidth of >40 GHz is realized by a silicon-doping-free metal-oxide-In$_2$O$_3$ capacitor integrated in a 3.5-$\mu$m-long asymmetric directional coupler (ADC) for the first time.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： The realization of ultra-compact passive silicon photonic devices is becoming more and more important for the future large-scale photonic integration as desired for many systems. Although some compact silicon photonic devices have been demonstrated by using inverse design, the device performance is still insufficient for real applications. Here, we propose and realize several representative ultra-compact advanced passive silicon photonic devices with decent performances by introducing subwavelength-grating (SWG) structures developed by our high-efficiency inverse design method. These devices are designed by optimally manipulating the multimode excitation and the multimode interference in a region defined with SWG structures. These SWG structures with excellent feature-size uniformity are more fabrication-friendly than those random nano-structures used in previous inverse-designed photonic devices. The high-efficiency of our inverse design method is attributed to a novel search-space-dimension control strategy and the efficient problem-oriented electromagnetic-field solvers available for SWG structures. Specifically, we present the realization of a 6-channel mode (de)multiplexer, a broadband 90{\deg}-hybrid, and a two-channel flat-top wavelength demultiplexer as some examples, which can hardly be realized by previously reported inverse design approaches. These devices exhibit ultra-compact footprints as well as decent performances when compared to the counterparts developed by the classical theory.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Two-dimensional materials (2DMs) meet the demand of broadband and low-cost photodetection on silicon for many applications. Currently, it is still very challenging to realize excellent silicon-2DM PDs. Here we demonstrate graphene-silicon-graphene waveguide PDs operating at the wavelength-bands of 1.55 {\mu}m and 2 {\mu}m, showing the potential for large-scale integration. For the fabricated PDs, the measured responsivities are respectively ~0.15 mA/W and ~0.015 mA/W for the wavelengths of 1.55 {\mu}m and 1.96{\mu}m. In particular, the PDs exhibit a high bandwidth of ~33 GHz, an ultra-low dark current of tens of pico-amperes, a high normalized photo-to-dark-current ratio (NPDR) of 1.63x10^6 W^-1, as well as a high linear dynamic range of 3 {\mu}W-1.86 mW (and beyond) at 1.55 {\mu}m. According to the measurement results for the wavelength-bands of 1.55/2.0 {\mu}m and the theoretical modeling for the silicon-graphene heterostructure, it is revealed that internal photo-emission and photo-assisted thermionic field emission dominantly contribute to the photoresponse in the graphene-silicon Schottky junctions, which helps the future work to further improve the performance.
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