Ultra-high extinction ratio optical pulse generation with a thin film lithium niobate modulator for distributed acoustic sensing

We experimentally demonstrate ultra-high extinction ratio(ER)optical pulse modulation with an electro-optical modulator(EOM)on thin film lithium niobate(TFLN)and its application for fiber optic distributed acoustic sensing(DAS).An interface carrier effect leading to a relaxation-tail response of TFLN EOM is discovered,which can be well addressed by a small compensation component following the main driving signal.An ultrahigh ER>50 dB is achieved by canceling out the tailed response during pulse modulation using the EOM based on a cascaded Mach–Zehnder interferometer(MZI)structure.The modulated optical_(√)pulses are then utilized as a probe light for a DAS system,showing a sensitivity up to-62.9 dB·rad∕Hz~2(7 pε/Hz)for 2-km single-mode sensing fiber.Spatial crosstalk suppression of 24.9 dB along the fiber is also obtained when the ER is improved from 20 dB to 50 dB,clearly revealing its importance to the sensing performance.

Highly efficient fiber to Si waveguide free-form coupler for foundry-scale silicon photonics

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.

Mid-infrared chalcogenide microfiber knot resonators

A novel type of mid-IR microresonator,the chalcogenide glass(ChG)microfiber knot resonator(MKR),is demonstrated,showing easy fabrication,fiber-compatible features,resonance tunability,and high robustness.ChG micro fibers with typical diameters around 3μm are taper-drawn from As2S3 glass fibers and assembled into MKRs in liquid without surface damage.The measured Q factor of a typical 824μm diameter ChG MKR is about 2.84×104 at the wavelength of 4469.14 nm.The free spectral range(FSR)of the MKR can be tuned from2.0 nm(28.4 GHz)to 9.6 nm(135.9 GHz)by tightening the knot structure in liquid.Benefitting from the high thermal expansion coefficient of As2S3 glass,the MKR exhibits a thermal tuning rate of 110 pm·℃^-1 at the resonance peak.When embedded in polymethyl methacrylate(PMMA)film,a 551μm diameter MKR retains a Q factor of 1.1×10^4.The ChG MKRs demonstrated here are highly promising for resonator-based optical technologies and applications in the mid-IR spectral range.

Real-time,in situ probing of gamma radiation damage with packaged integrated photonic chips

Integrated photonics is poised to become a mainstream solution for high-speed data communications and sensing in harsh radiation environments,such as outer space,high-energy physics facilities,nuclear power plants,and test fusion reactors.Understanding the impact of radiation damage in optical materials and devices is thus a prerequisite to building radiation-hard photonic systems for these applications.In this paper,we report real-time,in situ analysis of radiation damage in integrated photonic devices.The devices,integrated with an optical fiber array package and a baseline-correction temperature sensor,can be remotely interrogated while exposed to ionizing radiation over a long period without compromising their structural and optical integrity.We also introduce a method to deconvolve the radiation damage responses from different constituent materials in a device.The approach was implemented to quantify gamma radiation damage and post-radiation relaxation behavior of SiO2-cladded SiC photonic devices.Our findings suggest that densification induced by Compton scattering displacement defects is the primary mechanism for the observed index change in SiC.Additionally,post-radiation relaxation in amorphous SiC does not restore the original pre-irradiated structural state of the material.Our results further point to the potential of realizing radiation-hard photonic device designs taking advantage of the opposite signs of radiation-induced index changes in SiC and SiO2.

Two-photon lithography for integrated photonic packaging

Photonic integrated circuits(PICs)have long been considered as disruptive platforms that revolutionize optics.Building on the mature industrial foundry infrastructure for electronic integrated circuit fabrication,the manufacturing of PICs has made remarkable progress.However,the packaging of PICs has often become a major barrier impeding their scalable deployment owing to their tight optical alignment tolerance,and hence,the requirement for specialty packaging instruments.Two-photon lithography(TPL),a laser direct-write three-dimensional(3-D)patterning technique with deep subwavelength resolution,has emerged as a promising solution for integrated photonics packaging.This study provides an overview of the technology,emphasizing the latest advances in TPL-enabled packaging schemes and their prospects for adoption in the mainstream photonic industry.