Broadband picometer-scale resolution on-chip spectrometer with reconfigurable photonics

Miniaturization of optical spectrometers is important to enable spectroscopic analysis to play a role in in situ,or even in vitro and in vivo characterization systems.However,scaled-down spectrometers generally exhibit a strong trade-off between spectral resolution and operating bandwidth,and are often engineered to identify signature spectral peaks only for specific applications.In this paper,we propose and demonstrate a novel global sampling strategy with distributed filters for generating ultra-broadband pseudo-random spectral responses.The geometry of all-pass ring filters is tailored to ensure small self-and cross-correlation for effective information acquisition across the whole spectrum,which dramatically reduces the requirement on sampling channels.We employ the power of reconfigurable photonics in spectrum shaping by embedding the engineered distributed filters.Using a moderate mesh of MZls,we create 256 diverse spectral responses on a single chip and demonstrate a resolution of 20 pm for single spectral lines and 30 pm for dual spectral lines over a broad bandwidth of 115 nm,to the best of our knowledge achieving a new record of bandwidth-to-resolution ratio.Rigorous simulations reveal that this design will readily be able to achieve single-picometer-scale resolution.We further show that the reconfigurable photonics provides an extra degree of programmability,enabling user-defined features on resolution,computation complexity,and relative error.The use of SiN integration platform enables the spectrometer to exhibit excellent thermal stability of±2.0℃,effectively tackling the challenge of temperature variations at picometer-scale resolutions.

Advances in cost-effective integrated spectrometers

The proliferation of Internet-of-Things has promoted a wide variety of emerging applications that require compact,lightweight,and low-cost optical spectrometers.While substantial progresses have been made in the miniaturization of spectrometers,most of them are with a major focus on the technical side but tend to feature a lower technology readiness level for manufacturability.More importantly,in spite of the advancement in miniaturized spectrometers,their performance and the metrics of real-life applications have seldomly been connected but are highly important.This review paper shows the market trend for chip-scale spectrometers and analyzes the key metrics that are required to adopt miniaturized spectrometers in real-life applications.Recent progress addressing the challenges of miniaturization of spectrometers is summarized,paying a special attention to the CMOS-compatible fabrication platform that shows a clear pathway to massive production.Insights for ways forward are also presented.

Bridging the gap between resonance and adiabaticity:a compact and highly tolerant vertical coupling structure

We present a compact,highly tolerant vertical coupling structure,which can be a generic design that bridges the gap between conventional resonant couplers and adiabatic couplers for heterogeneously integrated devices.We show insights on relaxing the coupler alignment tolerance and provide a detailed design methodology.By the use of a multisegmented inverse taper structure,our design allows a certain proportion of the odd supermode to be excited during the coupling process,which simultaneously facilitates high tolerance and compactness.With a total length of 87μm,our coupler is almost threefold shorter than the state-of-the-art alignment-tolerant adiabatic couplers and outperforms them by demonstrating a more than 94%coupling efficiency(for<0.3 d B coupling loss)with±1μm misalignment tolerance,which,to our best knowledge,is a new record for III-V-on-silicon vertical couplers.Furthermore,our design has high tolerance to fabrication-induced structural deformation and ultrabroad bandwidth.These features make it particularly suitable for building densely integrated III-V-onsilicon photonic circuits with commercially available microtransfer printing assembly tools.The proposed design can be widely adopted in various integration platforms.