Preparation of magnetic chitosan corn straw biochar and its application in adsorption of amaranth dye in aqueous solution

In this study, the magnetic chitosan biochar (MCB) was magnetized by chemical coprecipitation after loading chitosan with Schiff base reaction. The prepared MCB was used to remove amaranth dye in solution. The synthesized MCB was characterized to define its surface morphology and specific elements. The amaranth dye adsorption system was optimized by varying the contact time, pH, and initial concentration. The adsorption of MCB on amaranth dye was measured in a wide pH range. According to Zeta potential, the surface of MCB was positively charged in the acidic pH region, which was more conducive to the adsorption of anionic amaranth dye. In addition, the adsorption data was fitted with the pseudo-first-order model and Langmuir adsorption model and the maximum adsorption capacity reached 404.18 mg/g. The adsorption efficiency of MCB was still above 95% after three cycles of adsorption and desorption. The removal percentage in the real sample of amaranth dye by MCB was within 94.5–98.6% and the RSD was within 0.14–1.08%. The MCB adsorbent with advantages of being easy to prepare, easy to separate from solution after adsorption, has good adsorption performance for amaranth dye and is effective potential adsorbent to remove organic anionic dye in wastewater

High-Speed and Energy-Efficient Non-Volatile Silicon Photonic Memory Based on Heterogeneously Integrated Memresonator

Recently, interest in programmable photonics integrated circuits has grown as a potential hardware framework for deep neural networks, quantum computing, and field programmable arrays (FPGAs). However, these circuits are constrained by the limited tuning speed and large power consumption of the phase shifters used. In this paper, introduced for the first time are memresonators, or memristors heterogeneously integrated with silicon photonic microring resonators, as phase shifters with non-volatile memory. These devices are capable of retention times of 12 hours, switching voltages lower than 5 V, an endurance of 1,000 switching cycles. Also, these memresonators have been switched using voltage pulses as short as 300 ps with a record low switching energy of 0.15 pJ. Furthermore, these memresonators are fabricated on a heterogeneous III-V/Si platform capable of integrating a rich family of active, passive, and non-linear optoelectronic devices, such as lasers and detectors, directly on-chip to enable in-memory photonic computing and further advance the scalability of integrated photonic processor circuits

Non-volatile Phase-only Transmissive Spatial Light Modulators

Free-space modulation of light is crucial for many applications, from light detection and ranging to virtual or augmented reality. Traditional means of modulating free-space light involves spatial light modulators based on liquid crystals and microelectromechanical systems, which are bulky, have large pixel areas (~10 micron x 10 micron), and require high driving voltage. Recent progress in meta-optics has shown promise to circumvent some of the limitations. By integrating active materials with sub-wavelength pixels in a meta-optic, the power consumption can be dramatically reduced while achieving a faster speed. However, these reconfiguration methods are volatile and hence require constant application of control signals, leading to phase jitter and crosstalk. Additionally, to control a large number of pixels, it is essential to implement a memory within each pixel to have a tractable number of control signals. Here, we develop a device with nonvolatile, electrically programmable, phase-only modulation of free-space infrared radiation in transmission using the low-loss phase-change material (PCM) Sb2Se3. By coupling an ultra-thin PCM layer to a high quality (Q)-factor (Q~406) diatomic metasurface, we demonstrate a phase-only modulation of ~0.25pi (~0.2pi) in simulation (experiment), ten times larger than a bare PCM layer of the same thickness. The device shows excellent endurance over 1,000 switching cycles. We then advance the device geometry, to enable independent control of 17 meta-molecules, achieving ten deterministic resonance levels with a 2pi phase shift. By independently controlling the phase delay of pixels, we further show tunable far-field beam shaping. Our work paves the way to realizing non-volatile transmissive phase-only spatial light modulators

Non-volatile programmable photonics based on phase-change materials

Thesis (Ph.D.)--University of Washington, 2023Programmable photonics can enable a plethora of exciting applications from next-generation optical interconnects to quantum information technologies. Conventionally, photonic systems are tuned by mechanisms such as thermos-optic effect, free carrier dispersion, electro-optic effect, or mechanical movement. Although these physical effects allow either fast (> 100GHz) or large contrast (> 60dB) switching, they are not optimal for programmability which does not require frequent switching. Phase-change materials (PCMs) can offer an ideal solution thanks to their reversible switching, large index contrast, and non-volatile behavior, enabling a truly ‘set-and-forget’ switch element with no static power consumption. Recent years, we have indeed witnessed the fast adoption of PCMs in programmable photonic systems, from photonic integrated circuits (PICs) to meta-optics. Despite the tremendous progress in the field, a few remaining challenges must be addressed before the technology can be scalable and ultimately commercialized. For example, the high optical loss of the traditional PCMs, such as Ge2Sb2Te5 (GST), is prohibitive for large-scale PICs. Secondly, the energy required to electrically switch PCMs remains to be high (~tens of nano-joules), and the device footprint is still large (> 64µm). Lastly, so far there has not been an ideal solution towards non-volatile phase-only control in the free-space due to the high loss of the PCMs and microheaters. In this dissertation, we aim to circumvent these limitations. First, we demonstrated non-volatile phase modulation (\Delta\phi~0.17\pi) with near zero insertion loss in both Si and SiN integrated photonics using a low-loss PCMs Sb2S3. Through device engineering, an ultra-compact (33µm coupling length) directional coupler switch was realized based on Sb2Se3. Individual control of the phase and coupling in racetrack resonator was achieved. We further showed that ultra-low switching energy down to 8.7±1.4aJ/nm3 can be achieved using graphene microheaters for tuning the PCMs with excellent endurance over 1,000 cycles. Finally, leveraging a high-Q metasurface, we demonstrated non-volatile phase-only modulation of free-space light with ~0.2π phase shift and near zero change in intensity. Our work represents a crucial step in the development of disruptive non-volatile photonic technologies based on PCMs