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.

Frequency-comb-linearized, widely tunable lasers for coherent ranging

Tunable lasers,with the ability to continuously vary their emission wavelengths,have found widespread applications across various fields such as biomedical imaging,coherent ranging,optical communications,and spectroscopy.In these applications,a wide chirp range is advantageous for large spectral coverage and high frequency resolution.Besides,the frequency accuracy and precision also depend critically on the chirp linearity of the laser.While extensive efforts have been made on the development of many kinds of frequency-agile,widely tunable,narrow-linewidth lasers,wideband yet precise methods to characterize and linearize laser chirp dynamics are also demanded.Here we present an approach to characterize laser chirp dynamics using an optical frequency comb.The instantaneous laser frequency is tracked over terahertz bandwidth at 1 MHz intervals.Using this approach we calibrate the chirp performance of 12 tunable lasers from Toptica,Santec,New Focus,EXFO,and NKT that are commonly used in fiber optics and integrated photonics.In addition,with acquired knowledge of laser chirp dynamics,we demonstrate a simple frequency-linearization scheme that enables coherent ranging without any optical or electronic linearization unit.Our approach not only presents novel wideband,highresolution laser spectroscopy,but is also critical for sensing applications with ever-increasing requirements on performance.

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.

Portable atomic gravimeter operating in noisy urban environments

The gravimeter based on atom interferometry has potential wide applications on building gravity networks and geophysics as well as gravity assisted navigation. Here, we demonstrate experimentally a portable atomic gravimeter operating in the noisy urban environment. Despite the influence of noisy external vibrations, our portable atomic gravimeter reaches a sensitivity as good as 65 μGal/√Hz and a resolution of 1.1 μGal after 4000 s integration, being comparable to state-of-the-art atomic gravimeters. Our achievement paves the way for bringing the portable atomic gravimeter to field applications.