A wideband,high-resolution vector spectrum analyzer for integrated photonics

The analysis of optical spectra—emission or absorption—has been arguably the most powerful approach for discovering and understanding matter.The invention and development of many kinds of spectrometers have equipped us with versatile yet ultra-sensitive diagnostic tools for trace gas detection,isotope analysis,and resolving hyperfine structures of atoms and molecules.With proliferating data and information,urgent and demanding requirements have been placed today on spectrum analysis with ever-increasing spectral bandwidth and frequency resolution.These requirements are especially stringent for broadband laser sources that carry massive information and for dispersive devices used in information processing systems.In addition,spectrum analyzers are expected to probe the device’s phase response where extra information is encoded.Here we demonstrate a novel vector spectrum analyzer(VSA)that is capable of characterizing passive devices and active laser sources in one setup.Such a dual-mode VSA can measure loss,phase response,and dispersion properties of passive devices.It also can coherently map a broadband laser spectrum into the RF domain.The VSA features a bandwidth of 55.1 THz(1260–1640 nm),a frequency resolution of 471 kHz,and a dynamic range of 56 dB.Meanwhile,our fiber-based VSA is compact and robust.It requires neither high-speed modulators and photodetectors nor any active feedback control.Finally,we employ our VSA for applications including characterization of integrated dispersive waveguides,mapping frequency comb spectra,and coherent light detection and ranging(LiDAR).Our VSA presents an innovative approach for device analysis and laser spectroscopy,and can play a critical role in future photonic systems and applications for sensing,communication,imaging,and quantum information processing.

Foundry manufacturing of tight-confinement,dispersion-engineered,ultralow-loss silicon nitride photonic integrated circuits

The foundry development of integrated photonics has revolutionized today’s optical interconnect and datacenters.Over the last decade,we have witnessed the rising of silicon nitride(Si_(3)N_(4)) integrated photonics,which is currently transferring from laboratory research to foundry manufacturing.The development and transition are triggered by the ultimate need for low optical loss offered by Si_(3)N_(4),which is beyond the reach of silicon and III-V semiconductors.Combined with modest Kerr nonlinearity,tight optical confinement,and dispersion engineering,Si_(3)N_(4) has today become the leading platform for linear and Kerr nonlinear photonics,and it has enabled chip-scale lasers featuring ultralow noise on par with table-top fiber lasers.However,so far all the reported fabrication processes of tight-confinement,dispersion-engineered Si_(3)N_(4) photonic integrated circuits(PICs)with optical loss down to few dB/m have only been developed on 4-inch(100 mm diameter)or smaller wafers.Yet,to transfer these processes to established CMOS foundries that typically operate 6-inch or even larger wafers,challenges remain.In this work,we demonstrate the first foundry-standard fabrication process of Si_(3)N_(4) PICs with only 2.6 dB/m loss,thickness above 800 nm,and near 100%fabrication yield on 6-inch(150 mm diameter)wafers.Such thick and ultralow-loss Si_(3)N_(4) PIC enables low-threshold generation of soliton frequency combs.Merging with advanced heterogeneous integration,active ultralow-loss Si_(3)N_(4) integrated photonics could pave an avenue to addressing future demands in our increasingly information-driven society.

Optical microcombs in whispering gallery mode crystalline resonators with dispersive intermode interactions

Soliton microcombs have shown great potential in a variety of applications ranging from chip-scale frequency metrology to optical communications and photonic data center,in which light couplings among cavity transverse modes,termed as intermode interactions,are long-existing and usually give rise to localized impacts on the soliton state.Of particular interest are whispering gallery mode-based crystalline resonators,which with dense mode families,potentially feature interactions of all kinds.While effects of narrowband interactions such as spectral power spikes have been well recognized in crystalline resonators,those of broadband interactions remain unexplored.Here,we demonstrate microcombs with broadband and dispersive intermode interactions,in homedeveloped magnesium fluoride microresonators with an intrinsic Q-factor approaching 10 billion.In addition to conventional soliton comb generation in the single-mode pumping scheme,comb states with broadband spectral tailoring effect have been observed,via an intermode pumping scheme.Remarkably,footprints of both constructive and destructive interference on the comb spectrum have been observed,which as confirmed by simulations,are connected to the dispersive effects of the coupled mode family.Our results would not only contribute to the understanding of dissipative soliton dynamics in multi-mode or coupled resonator systems,but also extend the access to stable soliton combs in crystalline microresonators where mode control and dispersion engineering are usually challenging.

Universal dynamics and deterministic motion control of decoherently seeded temporal dissipative solitons via spectral filtering effect

Temporal dissipative solitons have been widely studied in optical systems,which exhibit various localized structures and rich dynamics,and have shown great potential in applications including optical encoding and sensing.Yet,most of the soliton states,as well as the switching dynamics amongst,were fractionally captured or via self-evolution of the system,lacking of control on the soliton motion.While soliton motion control has been widely investigated in coherently seeded optical cavities,such as microresonator-based dissipative solitons,its implementation in decoherently seeded systems,typically the soliton mode-locked lasers,remains an outstanding challenge.Here,we report the universal dynamics and deterministic motion control of temporal dissipative solitons in a mode-locked fibre laser by introducing a scanned spectral filtering effect.We investigate rich switching dynamics corresponding to both the assembly and the disassembly of solitons,revealing a complete and reversible motion from chaotic states to soliton and soliton-molecule states.Significant hysteresis has been recognized in between the redshift and blueshift scan of the motorized optical filter,unveiling the nature of having state bifurcations in dissipative and nonlinear systems.The active soliton motion control enabled by filter scanning highlights the potential prospects of encoding and sensing using soliton molecules.