A horizonless ultracompact object can have a stable antiphoton sphere,which causes the photons inside the unstable photon sphere to strongly deflect,thereby leading to the formation of distinctive inner photon rings.I...A horizonless ultracompact object can have a stable antiphoton sphere,which causes the photons inside the unstable photon sphere to strongly deflect,thereby leading to the formation of distinctive inner photon rings.In this study,we present analytical descriptions for the shape,thickness,and interference pattern of higher-order inner photon rings.By taking the static spherically symmetric Schwarzschild star with a photon sphere as an example,we find that its inner photon rings can be more non-circular and thicker than the outer ones and show that the inclusion of the inner photon rings can result in new features in the interferometric pattern.Further,our formulae can be applied to other ultracompact objects,providing a convenient approach for studying the observational properties of their higher-order photon rings.展开更多
Silicon carbide(SiC)has great potential for optomechanical applications due to its outstanding optical and mechanical properties.However,challenges associated with SiC nanofabrication have constrained its adoption in ...Silicon carbide(SiC)has great potential for optomechanical applications due to its outstanding optical and mechanical properties.However,challenges associated with SiC nanofabrication have constrained its adoption in optomechanical devices,as embodied by the considerable optical loss or lack of integrated optical access in existing mechanical resonators.In this work,we overcome such challenges and demonstrate a low-loss,ultracompact optomechanical resonator in an integrated 4H-SiC-on-insulator(4H-SiCOI)photonic platform for the first time,to our knowledge.Based on a suspended 4.3-μm-radius microdisk,the SiC optomechanical resonator features low optical loss(<1 dB∕cm),a high mechanical frequency f m of 0.95×10^(9)Hz,a mechanical quality factor Q_(m)of 1.92×10^(4),and a footprint of<1×10^(−5)mm^(2).The corresponding f_(m)·Q_(m)product is estimated to be 1.82×10^(13)Hz,which is among the highest reported values of optomechanical cavities tested in ambient environment at room temperature.In addition,the strong optomechanical coupling in the SiC microdisk enables coherent regenerative optomechanical oscillations at a threshold optical dropped power of 14μW,which also supports efficient harmonic generation at increased power levels.With such competitive performance,we envision a range of chip-scale optomechanical applications to be enabled by the low-loss 4H-SiCOI platform.展开更多
Reflectors are an essential component for on-chip integrated photonics. Here, we propose a new method for designing reflectors on the prevalent thin-film-on-insulator platform by using genetic-algorithm optimization.I...Reflectors are an essential component for on-chip integrated photonics. Here, we propose a new method for designing reflectors on the prevalent thin-film-on-insulator platform by using genetic-algorithm optimization.In simulation, the designed reflector with a footprint of only 2.16 μm× 2.16 μm can achieve ~97% reflectivity and 1 dB bandwidth as wide as 220 nm. The structure is composed of randomly distributed pixels and is highly robust against the inevitable corner rounding effect in device fabrication. In experiment, we fabricated on-chip Fabry–Perot(FP) cavities constructed from optimized reflectors. Those FP cavities have intrinsic quality factors of>2000 with the highest value beyond 4000 in a spectral width of 200 nm. The reflectivity fitted from the FP cavity resonances is >85% in the entire wavelength range of 1440–1640 nm and is beyond 95% at some wavelengths.The fabrication processes are CMOS compatible and require only one step of lithography and etch. The devices can be used as a standard module in integrated photonic circuitry for wide applications in on-chip semiconductorlaser structures and optical signal processing.展开更多
Primordial black holes have been considered attractive dark matter candidates,whereas some of the predictions rely heavily on the near-horizon physics that remains to be tested experimentally.As a concrete alternative...Primordial black holes have been considered attractive dark matter candidates,whereas some of the predictions rely heavily on the near-horizon physics that remains to be tested experimentally.As a concrete alternative,thermal 2-2-holes closely resemble black holes without event horizons.Being a probable endpoint of gravitational collapse,they provide a solution to the information loss problem but also naturally result in stable remnants.Previously,we have considered primordial 2-2-hole remnants as dark matter.Owing to the strong constraints from a novel phenomenon associated with remnant mergers,only small remnants with mass approximate to the Planck mass can constitute all dark matter.In this paper,we examine the scenario in which the majority of dark matter consists of particles produced by the evaporation of primordial 2-2-holes,whereas the remnant contribution is secondary.The products with sufficiently light mass may contribute to the number of relativistic degrees of freedom in the early universe,which we also calculate.Moreover,2-2-hole evaporation can produce particles that are responsible for the baryon asymmetry.We observe that baryogenesis through direct B-violating decays or through leptogenesis can both be realized.Overall,the viable parameter space for the Planck remnant scenario is similar to that of primordial black holes with Planck remnants.However,heavier remnants result in different predictions,and the viable parameter space remains large even when the remnant abundance is small.展开更多
基金Supported by the National Natural Science Foundation of China(12447143,12273116,62394350,and 62394351)science research grants from the China Manned Space Project(CMS-CSST-2021-A12 and CMS-CSST-2021-B10)+1 种基金Strategic Priority Research Program of the Chinese Academy of Sciences(XDA0350302)Opening Project of National Key Laboratory of Aerospace Flight Dynamics of China(KGJ6142210220201)。
文摘A horizonless ultracompact object can have a stable antiphoton sphere,which causes the photons inside the unstable photon sphere to strongly deflect,thereby leading to the formation of distinctive inner photon rings.In this study,we present analytical descriptions for the shape,thickness,and interference pattern of higher-order inner photon rings.By taking the static spherically symmetric Schwarzschild star with a photon sphere as an example,we find that its inner photon rings can be more non-circular and thicker than the outer ones and show that the inclusion of the inner photon rings can result in new features in the interferometric pattern.Further,our formulae can be applied to other ultracompact objects,providing a convenient approach for studying the observational properties of their higher-order photon rings.
文摘Silicon carbide(SiC)has great potential for optomechanical applications due to its outstanding optical and mechanical properties.However,challenges associated with SiC nanofabrication have constrained its adoption in optomechanical devices,as embodied by the considerable optical loss or lack of integrated optical access in existing mechanical resonators.In this work,we overcome such challenges and demonstrate a low-loss,ultracompact optomechanical resonator in an integrated 4H-SiC-on-insulator(4H-SiCOI)photonic platform for the first time,to our knowledge.Based on a suspended 4.3-μm-radius microdisk,the SiC optomechanical resonator features low optical loss(<1 dB∕cm),a high mechanical frequency f m of 0.95×10^(9)Hz,a mechanical quality factor Q_(m)of 1.92×10^(4),and a footprint of<1×10^(−5)mm^(2).The corresponding f_(m)·Q_(m)product is estimated to be 1.82×10^(13)Hz,which is among the highest reported values of optomechanical cavities tested in ambient environment at room temperature.In addition,the strong optomechanical coupling in the SiC microdisk enables coherent regenerative optomechanical oscillations at a threshold optical dropped power of 14μW,which also supports efficient harmonic generation at increased power levels.With such competitive performance,we envision a range of chip-scale optomechanical applications to be enabled by the low-loss 4H-SiCOI platform.
基金Hong Kong Research Grants Council Early Career Scheme(24208915)Hong Kong Research Grants Council Joint Research Scheme(N_CUHK415/15)National Natural Science Foundation of China(NSFC)
文摘Reflectors are an essential component for on-chip integrated photonics. Here, we propose a new method for designing reflectors on the prevalent thin-film-on-insulator platform by using genetic-algorithm optimization.In simulation, the designed reflector with a footprint of only 2.16 μm× 2.16 μm can achieve ~97% reflectivity and 1 dB bandwidth as wide as 220 nm. The structure is composed of randomly distributed pixels and is highly robust against the inevitable corner rounding effect in device fabrication. In experiment, we fabricated on-chip Fabry–Perot(FP) cavities constructed from optimized reflectors. Those FP cavities have intrinsic quality factors of>2000 with the highest value beyond 4000 in a spectral width of 200 nm. The reflectivity fitted from the FP cavity resonances is >85% in the entire wavelength range of 1440–1640 nm and is beyond 95% at some wavelengths.The fabrication processes are CMOS compatible and require only one step of lithography and etch. The devices can be used as a standard module in integrated photonic circuitry for wide applications in on-chip semiconductorlaser structures and optical signal processing.
基金Work of U.A.is supported in part by the Chinese Academy of Sciences President's International Fellowship Initiative(PIFI)(2020PM0019)the Institute of High Energy Physics,Chinese Academy of Sciences(Y9291120K2).J.R.is supported by the Institute of High Energy Physics(Y9291120K2)。
文摘Primordial black holes have been considered attractive dark matter candidates,whereas some of the predictions rely heavily on the near-horizon physics that remains to be tested experimentally.As a concrete alternative,thermal 2-2-holes closely resemble black holes without event horizons.Being a probable endpoint of gravitational collapse,they provide a solution to the information loss problem but also naturally result in stable remnants.Previously,we have considered primordial 2-2-hole remnants as dark matter.Owing to the strong constraints from a novel phenomenon associated with remnant mergers,only small remnants with mass approximate to the Planck mass can constitute all dark matter.In this paper,we examine the scenario in which the majority of dark matter consists of particles produced by the evaporation of primordial 2-2-holes,whereas the remnant contribution is secondary.The products with sufficiently light mass may contribute to the number of relativistic degrees of freedom in the early universe,which we also calculate.Moreover,2-2-hole evaporation can produce particles that are responsible for the baryon asymmetry.We observe that baryogenesis through direct B-violating decays or through leptogenesis can both be realized.Overall,the viable parameter space for the Planck remnant scenario is similar to that of primordial black holes with Planck remnants.However,heavier remnants result in different predictions,and the viable parameter space remains large even when the remnant abundance is small.
