In this paper we report TE-mode phase modulation obtained by inducing a capacitive charge on graphene layers embedded in the core of a waveguide.There is a biasing regime in which graphene absorption is negligible but...In this paper we report TE-mode phase modulation obtained by inducing a capacitive charge on graphene layers embedded in the core of a waveguide.There is a biasing regime in which graphene absorption is negligible but large index variations can be achieved with a voltage–length product as small as V_(π)L_(π)≃0.07 V cm for straight waveguides and V_(π)L_(π)≃0.0024 V cm for 12μm radius microring resonators.This phase modulation device uniquely enables a small signal amplitude<1 V with a micrometer-sized footprint for compatibility with CMOS circuit integration.Examples of phase-induced changes are computed for straight waveguides and for microring resonators,showing the possibility of implementing several optoelectronic functionalities as modulators,tunable filters,and switches.展开更多
We propose a new type of dispersion flattening technology, which can generate an ultra-flat group velocity dispersion profile with five and six zero-dispersion wavelengths(ZDWs). The dispersion value varies from-0.15 ...We propose a new type of dispersion flattening technology, which can generate an ultra-flat group velocity dispersion profile with five and six zero-dispersion wavelengths(ZDWs). The dispersion value varies from-0.15 to 0.35 ps/(nm·km) from 4 to 8 μm, which to the best of our knowledge is the flattest one reported so far, and the dispersion flatness is improved by more than an order of magnitude. We explain the principle of producing six ZDWs. Mode distribution in this waveguide is made stable over a wide bandwidth. General guidelines to systematically control the dispersion value, sign, and slope are provided, and one can achieve the desired dispersion by properly adjusting the structural parameters. Fabrication tolerance of this waveguide is also examined.展开更多
As silicon photonics transitions from research to commercial deployment,packaging solutions that efficiently couple light into highly compact and functional sub-micrometer silicon waveguides are imperative but remain ...As silicon photonics transitions from research to commercial deployment,packaging solutions that efficiently couple light into highly compact and functional sub-micrometer silicon waveguides are imperative but remain challenging.The 220 nm silicon-on-insulator(SOI)platform,poised to enable large-scale integration,is the most widely adopted by foundries,resulting in established fabrication processes and extensive photonic component libraries.The development of a highly efficient,scalable,and broadband coupling scheme for this platform is therefore of paramount importance.Leveraging two-photon polymerization(TPP)and a deterministic free-form micro-optics design methodology based on the Fermat’s principle,this work demonstrates an ultraefficient and broadband 3-D coupler interface between standard SMF-28 single-mode fibers and silicon waveguides on the 220 nm SOI platform.The coupler achieves a low coupling loss of 0.8 dB for the fundamental TE mode,along with 1 dB bandwidth exceeding 180 nm.The broadband operation enables diverse bandwidthdriven applications ranging from communications to spectroscopy.Furthermore,the 3-D free-form coupler also enables large tolerance to fiber misalignments and manufacturing variability,thereby relaxing packaging requirements toward cost reduction capitalizing on standard electronic packaging process flows.展开更多
The high-temperature sensitivity of the silicon material index limits the applications of silicon-based micro-ring resonators in integrated photonics. To realize a low but broadband temperature-dependent-wavelength-sh...The high-temperature sensitivity of the silicon material index limits the applications of silicon-based micro-ring resonators in integrated photonics. To realize a low but broadband temperature-dependent-wavelength-shift microring resonator, designing a broadband athermal waveguide becomes a significant task. In this work,we propose a broadband athermal waveguide that shows a low effective thermo-optical coefficient of1 × 10^(-6)∕K from 1400 to 1700 nm. The proposed waveguide shows a low-loss performance and stable broadband athermal property when it is applied to ring resonators, and the bending loss of ring resonators with a radius of >30 μm is 0.02 dB/cm.展开更多
Optical pulses are fundamentally defined by their temporal and spectral properties.The ability to control pulse properties allows practitioners to efficiently leverage them for advanced metrology,high speed optical co...Optical pulses are fundamentally defined by their temporal and spectral properties.The ability to control pulse properties allows practitioners to efficiently leverage them for advanced metrology,high speed optical communications and attosecond science.Here,we report 11×temporal compression of 5.8 ps pulses to 0.55 ps using a low power of 13.3 W.The result is accompanied by a significant increase in the pulse peak power by 9.4×.These results represent the strongest temporal compression demonstrated to date on a complementary metal–oxide–semiconductor(CMOS)chip.In addition,we report the first demonstration of on-chip spectral compression,3.0×spectral compression of 480 fs pulses,importantly while preserving the pulse energy.The strong compression achieved at low powers harnesses advanced on-chip device design,and the strong nonlinear properties of backend-CMOS compatible ultra-silicon-rich nitride,which possesses absence of two-photon absorption and 500×larger nonlinear parameter than in stoichiometric silicon nitride waveguides.The demonstrated work introduces an important new paradigm for spectro-temporal compression of optical pulses toward turn-key,on-chip integrated systems for all-optical pulse control.展开更多
Microresonator-based Kerr frequency combs have attracted a great deal of attention in recent years, in which mode locking of the generated combs is associated with bright or dark cavity soliton formation. In this pape...Microresonator-based Kerr frequency combs have attracted a great deal of attention in recent years, in which mode locking of the generated combs is associated with bright or dark cavity soliton formation. In this paper, we show a unique that, different from soliton propagation along a waveguide, cavity solitons can be robustly formed under dispersion profile with four zero-dispersion wavelengths. More importantly, such a dispersion profile exhibits much smaller overall dispersion, thus making it possible to greatly reduce the pump power by five to six times.展开更多
We report an above-band-gap radiative transition in the photoluminescence spectra of single crystalline Ge in the temperature range of 20-296 K. The temperature-independence of the peak position at -0.74 eV is remarka...We report an above-band-gap radiative transition in the photoluminescence spectra of single crystalline Ge in the temperature range of 20-296 K. The temperature-independence of the peak position at -0.74 eV is remarkably different from the behavior of direct and indirect gap transitions in Ge. This transition is observed in n-type, p-type, and intrinsic single crystal Ge alike, and its intensity decreases with the increase of temperature with a small activation energy of 56 meV. Some aspects of the transition are analogous to III-V semiconductors with dilute nitrogen doping, which suggests that the origin could be related to an isoelectronic defect.展开更多
Octave-spanning frequency comb generation in microresonators is promising, but strong spectral losses caused by material absorption and mode coupling between two polarizations or mode families can be detrimental. We e...Octave-spanning frequency comb generation in microresonators is promising, but strong spectral losses caused by material absorption and mode coupling between two polarizations or mode families can be detrimental. We examine the impact of the spectral loss and propose robust comb generation with a loss of even 300 dB/cm.Cavity nonlinear dynamics show that a phase change associated with spectral losses can facilitate phase matching and Kerr comb generation. Given this unique capability, we propose a novel architecture of on-chip spectroscopy systems.展开更多
文摘In this paper we report TE-mode phase modulation obtained by inducing a capacitive charge on graphene layers embedded in the core of a waveguide.There is a biasing regime in which graphene absorption is negligible but large index variations can be achieved with a voltage–length product as small as V_(π)L_(π)≃0.07 V cm for straight waveguides and V_(π)L_(π)≃0.0024 V cm for 12μm radius microring resonators.This phase modulation device uniquely enables a small signal amplitude<1 V with a micrometer-sized footprint for compatibility with CMOS circuit integration.Examples of phase-induced changes are computed for straight waveguides and for microring resonators,showing the possibility of implementing several optoelectronic functionalities as modulators,tunable filters,and switches.
基金National Natural Science Foundation of China(61775164,61225005,61775165)
文摘We propose a new type of dispersion flattening technology, which can generate an ultra-flat group velocity dispersion profile with five and six zero-dispersion wavelengths(ZDWs). The dispersion value varies from-0.15 to 0.35 ps/(nm·km) from 4 to 8 μm, which to the best of our knowledge is the flattest one reported so far, and the dispersion flatness is improved by more than an order of magnitude. We explain the principle of producing six ZDWs. Mode distribution in this waveguide is made stable over a wide bandwidth. General guidelines to systematically control the dispersion value, sign, and slope are provided, and one can achieve the desired dispersion by properly adjusting the structural parameters. Fabrication tolerance of this waveguide is also examined.
基金National Science Foundation(ITE-2236093,NSF ITE Convergence Accelerator)Ministry of Education-Singapore(International Postdoctoral Fellowship)。
文摘As silicon photonics transitions from research to commercial deployment,packaging solutions that efficiently couple light into highly compact and functional sub-micrometer silicon waveguides are imperative but remain challenging.The 220 nm silicon-on-insulator(SOI)platform,poised to enable large-scale integration,is the most widely adopted by foundries,resulting in established fabrication processes and extensive photonic component libraries.The development of a highly efficient,scalable,and broadband coupling scheme for this platform is therefore of paramount importance.Leveraging two-photon polymerization(TPP)and a deterministic free-form micro-optics design methodology based on the Fermat’s principle,this work demonstrates an ultraefficient and broadband 3-D coupler interface between standard SMF-28 single-mode fibers and silicon waveguides on the 220 nm SOI platform.The coupler achieves a low coupling loss of 0.8 dB for the fundamental TE mode,along with 1 dB bandwidth exceeding 180 nm.The broadband operation enables diverse bandwidthdriven applications ranging from communications to spectroscopy.Furthermore,the 3-D free-form coupler also enables large tolerance to fiber misalignments and manufacturing variability,thereby relaxing packaging requirements toward cost reduction capitalizing on standard electronic packaging process flows.
基金National Basic Research Program of China(973)(2014CB340104/3)National Natural Science Foundation of China(NSFC)(61775164,61335005,61377076,61575142,61431009)Tianjin University
文摘The high-temperature sensitivity of the silicon material index limits the applications of silicon-based micro-ring resonators in integrated photonics. To realize a low but broadband temperature-dependent-wavelength-shift microring resonator, designing a broadband athermal waveguide becomes a significant task. In this work,we propose a broadband athermal waveguide that shows a low effective thermo-optical coefficient of1 × 10^(-6)∕K from 1400 to 1700 nm. The proposed waveguide shows a low-loss performance and stable broadband athermal property when it is applied to ring resonators, and the bending loss of ring resonators with a radius of >30 μm is 0.02 dB/cm.
基金supported by the National Research Foundation Competitive Research Grant(NRF-CRP18-2017-03)the MOE ACRF Tier 2 Grant.
文摘Optical pulses are fundamentally defined by their temporal and spectral properties.The ability to control pulse properties allows practitioners to efficiently leverage them for advanced metrology,high speed optical communications and attosecond science.Here,we report 11×temporal compression of 5.8 ps pulses to 0.55 ps using a low power of 13.3 W.The result is accompanied by a significant increase in the pulse peak power by 9.4×.These results represent the strongest temporal compression demonstrated to date on a complementary metal–oxide–semiconductor(CMOS)chip.In addition,we report the first demonstration of on-chip spectral compression,3.0×spectral compression of 480 fs pulses,importantly while preserving the pulse energy.The strong compression achieved at low powers harnesses advanced on-chip device design,and the strong nonlinear properties of backend-CMOS compatible ultra-silicon-rich nitride,which possesses absence of two-photon absorption and 500×larger nonlinear parameter than in stoichiometric silicon nitride waveguides.The demonstrated work introduces an important new paradigm for spectro-temporal compression of optical pulses toward turn-key,on-chip integrated systems for all-optical pulse control.
基金National Basic Research Program of China(973)(2014CB340104/3)National Natural Science Foundation of China(NSFC)(61775164,61335005,61575142,61431009)Advanced Integrated Optoelectronics Facility at the Tianjin University,China
文摘Microresonator-based Kerr frequency combs have attracted a great deal of attention in recent years, in which mode locking of the generated combs is associated with bright or dark cavity soliton formation. In this paper, we show a unique that, different from soliton propagation along a waveguide, cavity solitons can be robustly formed under dispersion profile with four zero-dispersion wavelengths. More importantly, such a dispersion profile exhibits much smaller overall dispersion, thus making it possible to greatly reduce the pump power by five to six times.
基金supported by the Si-Based Laser Initiative of the Multidisciplinary University Research Initiative (MURI)sponsored by the Air Force Office of Scientific Research (AFOSR), USAsupervised by Dr. Gernot Pomrenke.
文摘We report an above-band-gap radiative transition in the photoluminescence spectra of single crystalline Ge in the temperature range of 20-296 K. The temperature-independence of the peak position at -0.74 eV is remarkably different from the behavior of direct and indirect gap transitions in Ge. This transition is observed in n-type, p-type, and intrinsic single crystal Ge alike, and its intensity decreases with the increase of temperature with a small activation energy of 56 meV. Some aspects of the transition are analogous to III-V semiconductors with dilute nitrogen doping, which suggests that the origin could be related to an isoelectronic defect.
基金National Basic Research Program of China(973)(2014CB340104/3,61775164,61335005,61377076,61575142,61431009)Advanced Integrated Optoelectronics Facility at the Tianjin University
文摘Octave-spanning frequency comb generation in microresonators is promising, but strong spectral losses caused by material absorption and mode coupling between two polarizations or mode families can be detrimental. We examine the impact of the spectral loss and propose robust comb generation with a loss of even 300 dB/cm.Cavity nonlinear dynamics show that a phase change associated with spectral losses can facilitate phase matching and Kerr comb generation. Given this unique capability, we propose a novel architecture of on-chip spectroscopy systems.
