Flexible Integrated Photonics for On-Chip Quasi-Distributed Sensing

“Zero change” platform for monolithic back-end-of-line integration of phase change materials in silicon photonics

Abstract Monolithic integration of novel materials for unprecedented device functions without modifying the existing photonic component library is the key to advancing heterogeneous silicon photonic integrated circuits. To achieve this, the introduction of a silicon nitride etching stop layer at selective area, coupled with low-loss oxide trench to waveguide surface, enables the incorporation of various functional materials without disrupting the reliability of foundry-verified devices. As an illustration, two distinct chalcogenide phase change materials (PCM) with remarkable nonvolatile modulation capabilities, namely Sb2Se3 and Ge2Sb2Se4Te1, were monolithic back-end-of-line integrated into silicon photonics. The PCM enables compact phase and intensity tuning units with zero-static power consumption. Taking advantage of these building blocks, the phase error of a push-pull Mach-Zehnder interferometer optical switch could be trimmed by a nonvolatile phase shifter with a 48% peak power consumption reduction. Mirco-ring filters with a rejection ratio >25dB could be applied for >5-bit wavelength selective intensity modulation, and waveguide-based >7-bit intensity-modulation photonic attenuators could achieve >39dB broadband attenuation. The advanced “Zero change” back-end-of-line integration platform could not only facilitate the integration of PCMs for integrated reconfigurable photonics but also open up the possibilities for integrating other excellent optoelectronic materials in the future silicon photonic process design kits.

Integrated Flexible Microscale Mechanical Sensors Based on Cascaded Free Spectral Range-Free Cavities

Scalable On‐Chip Microdisk Resonator Spectrometer

AbstractOn‐chip micro‐spectrometers are sought after with great effort owing to extensive potential applications in mobile optical sensing and imaging. By multiplexing more physical channels, the reconstructive spectrometers based on the spectral‐to‐spatial mapping technique can improve the spectral range. However, this method is challenging to implement and sustain due to the increase in system complexity and the decrease of dynamic range or spectral resolution. Here, a micro‐spectrometer utilizing a single tunable microdisk resonator (MDR) is demonstrated. Such a single MDR spectrometer has only one physical channel to receive all spectral components with a compact size, overcoming the trade‐off among spectral resolution, spectral range, and dynamic range. Leveraging the wavelength and temperature‐dependent response matrix, unknown spectra are reconstructed from their corresponding output light intensity vector. The fabricated device illustrates a high resolution of 0.01 nm for a dual peak and a medium resolution of 0.2 nm in the 20 nm spectral range. A wide variety of complex input spectra, including narrowband and broadband spectral signals, can be well recovered, exhibiting the robustness of the spectral reconstruction approach. Moreover, this proposed spectrometer exhibits ease of scalability and flexible configuration to a spectrometer array covering a set of desired and even discrete spectral ranges.

Integrated Microring Spectrometer with In‐Hardware Compressed Sensing to Break the Resolution‐Bandwidth Limit for General Continuous Spectrum Analysis

AbstractMicrospectrometers have numerous applications in mobile optical sensing due to their dramatic advantages of compact size, light weight, and low power consumption. Reconstructive spectrometers, based on computational algorithms, have garnered considerable interest as they exhibit superior resolution or spectral bandwidth. However, existing reconstructive spectrometer designs face challenges in spectral applicability, algorithm robustness, and the resolution‐bandwidth limit. Here, a reconstructive spectrometer that utilizes a microring resonator (MRR) is proposed to achieve compressed sensing in hardware by decomposing an arbitrary continuous spectrum into a series of simple comb spectra. Owing to the presparse operation of the MRR, one needs to construct the comb spectra with a known line shape, only leaving the amplitude to be solved. Consequent random gratings measure the comb spectra, which are reconstructed with high robustness. Thanks to the independent engineering of spectral resolution and bandwidth, the approach breaks the traditional resolution‐bandwidth limit. A narrowband signal of a dual peak at 0.2 nm and a broadband spectrum with a large spectral bandwidth of 60 nm and 300 spectral channels using only eight physical channels is retrieved, achieving an ultrahigh reconstructive compression ratio of 37.5. This work opens up the possibility of on‐site spectral spectroscopy applications for the lab‐on‐a‐chip system.

Electrically programmable phase-change photonic memory for optical neural networks with nanoseconds in situ training capability

Waveguide-integrated PdSe2 photodetector with high responsivity and speed in the near-infrared range across the O+E+S+C bands

Abstract Hybrid integration of two-dimensional (2D) materials on a silicon photonic platform enables diverse exploration of novel active functions and significant improvement in device performance for next-generation silicon integrated photonic circuits. 2D transition metal dichalcogenide materials (TMDCs) have attracted extensive attention for photodetectors, but developing high-performance waveguide-integrated photodetectors based on conventionally investigated 2D TMDCs at the telecom C-band is still a big challenge because of their large optical bandgap and slow carrier mobility. Here, we propose PdSe2, a new type of 2D TMDC, to be integrated with silicon photonic components for on-chip photodetection with high responsivity and speed in the datacom and telecom optical bands ranging from the O-band to the C-band. The obtained waveguide-integrated photodetectors show a high responsivity of 1190.2 mA W−1 at 1550 nm and a low noise-equivalent power of 4.0 pW Hz-0.5 at 5V. The 3 dB bandwidth reaches up to 1.5 GHz, and the measured data rate is 2.5 Gbit s−1. The achieved PdSe2 photodetectors provide new insights to explore the integration of novel 2D TMDCs with silicon photonics and demonstrate the potential of integrated photodetectors for applications in diverse areas, including optical communications, on-chip spectroscopy, and sensing.

Tunable narrow-band single-channel add-drop integrated optical filter with ultrawide FSR

Abstract Free-spectral-range (FSR)-free optical filters have always been a critical challenge for photonic integrated circuits. A high-performance FSR-free filter is highly desired for communication, spectroscopy, and sensing applications. Despite significant progress in integrated optical filters, the FSR-free filter with a tunable narrow-band, high out-of-band rejection, and large fabrication tolerance has rarely been demonstrated. In this paper, we propose an exact and robust design method for add-drop filters (ADFs) with an FSR-free operation capability, a sub-nanometer optical bandwidth, and a high out-of-band rejection (OBR) ratio. The achieved filter has a 3-dB bandwidth of < 0.5 nm and an OBR ratio of 21.5 dB within a large waveband of 220 nm, which to the best of our knowledge, is the largest-FSR ADF demonstrated on a silicon photonic platform. The filter exhibits large tunability of 12.3 nm with a heating efficiency of 97 pm/mW and maintains the FSR-free feature in the whole tuning process. In addition, we fabricated a series of ADFs with different periods, which all showed reliable and excellent performances.

A universal approach for photonic integration on flexible substrates

De-multiplexing free on-chip low-loss multimode switch enabling reconfigurable inter-mode and inter-path routing

AbstractSwitching and routing are critical functionalities for a reconfigurable bandwidth-dense optical network, and great efforts had been made to accommodate mode-division multiplexing technology. Although the reconfigurable routing for spatial-mode groups between different optical paths was realized recently, a demultiplexing-switching-multiplexing process is necessary. Here we present a simplified and compact on-chip 2×2 multimode switch that can be easily upgradable to a larger scale. Fully and reconfigurable routing between not only optical paths but also spatial modes is achieved. To obtain a low loss multimode processing, a novel structure free from demultiplexing and re-multiplexing operations is adopted. The switch enables minimum and maximum insertion losses of 0.3 and 1.2 dB, with a compact footprint of 433 μm×433 μm and low crosstalk of <−16.6 dB for all channels. It is further extended to two types of 4×4 switch fabrics with cross-bar and ring-bus architectures, as demonstrations of high-level integration. System characterization with 32 Gb/s high-speed modulated signals is also carried out, reaching up to 256 Gb/s aggregate throughput. These results verify a general solution of 2×2 multimode switch for reconfigurable inter-mode and inter-path routing applicable in large-scale and high-density multimode optical network.

Crossing-Free On-Chip <tex>$2\times 2$</tex> Polarization-Diverse Switch

Crossing-free on-chip 2  ×  2 polarization-transparent switch with signals regrouping function

Ultra-compact bent multimode silicon waveguide with ultralow inter-mode crosstalk

Ultra-Compact Silicon Multimode Bent Waveguide with Ultralow Inter-Mode Crosstalk

On-chip switch for reconfigurable mode-multiplexing optical network