Engineering Dispersive-Dissipative Modal Coupling in Hybrid Optical Microresonators.

Hybrid microresonators have served an intriguing platform for fundamental research and applied photonics. Here, we study the plasmonics-engineered coupling between degenerate optical whispering gallery modes, which can be tuned in a complex space featuring the dissipative strong, dispersive strong, and weak coupling regimes. Experimentally, the engineering of a single plasmonic resonance to a cavity mode family is examined in a waveguide-integrated high-Q microdisk, from which the complex coupling coefficients are extracted and agree well with theoretical predictions. The coupling strength over 10 GHz is achieved for both dissipative and dispersive interactions, showing a remarkable enhancement compared to that induced by a dielectric scatterer. Furthermore, the far fields of hybridized cavity modes are measured, revealing the coherent interference between the radiative channels. Our results shed light on the engineering of whispering gallery modes through plasmonic resonances, and provide fundamental guidance to practical microcavity devices.

Lactic acid production with two types of feedstocks from food waste: Effect of inoculum, temperature, micro-oxygen, and initial pH.

Lactic acid (LA) is an important chemical with broad market applications. To optimize LA production, food waste has been explored as feedstock. Due to the wide variety of food waste types, most current research studies have obtained different conclusions. This study focuses on carbohydrate-rich fruit and vegetable waste (FVW) and lipid-rich kitchen waste (KW), and the effect of inoculum, temperature, micro-oxygen, and initial pH were compared. FVW has a greater potential for LA production than KW. As an inoculum, lactic acid bacteria (LAB) significantly increased the maximum LA concentration (27.6 g/L) by 50.8 % compared with anaerobic sludge (AS). FVW exhibited optimal LA production at 37 °C with micro-oxygen. Adjustment of initial pH from 4 to 8 alleviated the inhibitory effect of accumulated LA, resulting in a 46.2 % increase in maximum LA production in FVW. The expression of functional genes associated with metabolism, genetic information processing, and environmental information processing was higher at 37 °C compared to 50 °C.

Enzyme enhanced lactic acid fermentation of swine manure and apple waste: Insights from organic matter transformation and functional bacteria.

Anaerobic co-fermentation is a favorable way to convert agricultural waste, such as swine manure (SM) and apple waste (AW), into lactic acid (LA) through microbial action. However, the limited hydrolysis of organic matter remains a main challenge in the anaerobic co-fermentation process. Therefore, this work aims to deeply understand the impact of cellulase (C) and protease (P) ratios on LA production during the anaerobic co-fermentation of SM with AW. Results showed that the combined use of cellulase and protease significantly improved the hydrolysis during the enzymatic pretreatment, thus enhancing the LA production in anaerobic acidification. The highest LA reached 41.02 ± 2.09 g/L within 12 days at the ratio of C/P = 1:3, which was approximately 1.26-fold of that in the control. After a C/P = 1:3 pretreatment, a significant SCOD release of 45.34 ± 2.87 g/L was achieved, which was 1.13 times the amount in the control. Moreover, improved LA production was also attributed to the release of large amounts of soluble carbohydrates and proteins with enzymatic pretreated SM and AW. The bacterial community analysis revealed that the hydrolytic bacteria Romboutsia and Clostridium_sensu_stricto_1 were enriched after enzyme pretreatment, and Lactobacillus was the dominant bacteria for LA production. This study provides an eco-friendly technology to enhance hydrolysis by enzymatic pretreatment and improve LA production during anaerobic fermentation.

Non-Hermitian Chiral Heat Transport.

Exceptional point (EP) has been captivated as a concept of interpreting eigenvalue degeneracy and eigenstate exchange in non-Hermitian physics. The chirality in the vicinity of EP is intrinsically preserved and usually immune to external bias or perturbation, resulting in the robustness of asymmetric backscattering and directional emission in classical wave fields. Despite recent progress in non-Hermitian thermal diffusion, all state-of-the-art approaches fail to exhibit chiral states or directional robustness in heat transport. Here we report the first discovery of chiral heat transport, which is manifested only in the vicinity of EP but suppressed at the EP of a thermal system. The chiral heat transport demonstrates significant robustness against drastically varying advections and thermal perturbations imposed. Our results reveal the chirality in heat transport process and provide a novel strategy for manipulating mass, charge, and diffusive light.

Trapping photons with optical black hole.

An optical black-hole cavity based on transformation optics enables Q-factor enhancement and strong field confinement, by eliminating the intrinsic radiation loss of the conventional whispering-gallery modes, holding potential for applications in energy harvesting and optoelectronics.

Revealing mechanism of micro-aeration for enhancing volatile fatty acids production from swine manure.

Micro-aeration is considered a new strategy for improving volatile fatty acids (VFAs) production of agricultural waste. This study investigated the effect and mechanism of micro-aeration of air and oxygen (O2) on VFAs production from swine manure. The results showed that Air-micro-aeration had the most significant improvement effect, with the highest VFAs of 8.21 g/L, which was increased by 22.4%. Moreover, the mixing effects of different micro-aeration were limited, and the microbial communities significantly varied. Firmicutes and Bacteroidota were the dominant hydrolytic and acidogenic bacteria, and Air-micro-aeration preferentially promoted electron transfer activity and energy generation. Methanosarcina, Methanocorpusculum, and Methanobrevibacter can adapt to environmental changes according to their different oxygen tolerance, and the consumption and conversion of VFAs by methanogens were slow under Air-micro-aeration condition. This study revealed mechanism of micro-aeration for improving VFAs production from swine manure, providing a theoretical basis for micro-aeration regulation optimization.

Antibiotic removal potential for low greenhouse gas emission process of anaerobic digestion (AD) producing volatile fatty acids (VFAs).

This study aimed to investigate the antibiotic of sulfachloropyridazine (SCP) reduction and its effects on volatile fatty acids (VFAs) accumulation and microbial community structures during the process of anaerobic digestion (AD) producing VFA. Results showed that initial SCP concentrations have a positive correlation with reduction of SCP and accumulation of VFAs. The removal rates of SCP were 22.21%, 30.00%, 39.31% and 42.59% and the maximum production of VFAs were 3947, 6180, 6462 and 6032 mg/L for initial SCP concentrations of 25, 50, 75 and 100 mg/kg·TS, respectively. SCP only altered bacterial composition by hastening growth of specific bacterial taxa, but didn't increase bacterial α-diversity.

Improving production of lactic acid and volatile fatty acids from dairy cattle manure and corn straw silage: Effects of mixing ratios and temperature.

Anaerobic co-fermentation (AcoF) of dairy cattle manure (DCM) and corn straw silage (CSS) for producing lactic acid (LA) and volatile fatty acids (VFAs) was investigated. Batch experiments were conducted at seven different DCM/CSS ratios and at mesophilic and thermophilic temperatures. Results indicated that the highest concentration of LA was 17.50 ± 0.70 g/L at DCM:CSS ratio of 1:3 and thermophilic temperature, while VFAs was 18.23 ± 2.45 g/L at mono-CSS fermentation and mesophilic temperature. High solubilization of thermophilic conditions contributed to LA accumulation in AcoF process. Presence of the CSS increased the relative abundance of Lactobacillus for LA production at thermophilic. Meanwhile, the abundance of Bifidobacterium was increased when CSS was added at mesophilic, which could conduce to VFAs production. This study provides a new route for enhancing the biotransformation of DCM and CSS into short-chain fatty acids, potentially bringing economic benefits to agricultural waste treatment.

Produce individual medium chain carboxylic acids (MCCA) from swine manure: Performance evaluation and economic analysis.

Environmental issues caused by untreated animal manure require the development of resource recovery from waste through a circular economy approach. Producing medium chain carboxylic acids (MCCA) with higher value than biogas from manure has become promising. The objective of this study was to develop an effective individual MCCA produce process utilizing manure. In this study, animal manure was firstly anaerobic fermentation into short chain fatty acids (SCFA), then acidified manure and ethanol were fed into the chain elongation reactor with gradually increasing the organic loading rate (OLR) from 7.0 to 18.5 gCOD/L/d, and the mixed MCCA was separated individually via a fractional distillation process. The SCFA fermentation occurred mainly at the first 10 days, and the optimum concentrations of SCFA for treatments at 2 %VS, 4 %VS and 6 %VS were 6.58, 10.40 and 14.10 g/L, respectively. For the chain elongation reactor, the maximum concentrations of n-caproate and n-caprylate were 10.25 and 0.63 g/L, respectively, which were comparable with that obtained from other complex wastes. Over 90% MCCA can be recovered from the fermentation broth via the optimized extractant of methyl tert-butyl ether (MTBE) and the fractional distillation system. Preliminary economic analysis shows that this MCCA production process presented a higher economic benefit (9.25 $/m3 manure) than traditional biogas production (2.65 $/m3 manure), making MCCA production from swine manure economically competitive. This work provides a new route for manure resource recovery besides the biogas process.

Vibrational Kerr Solitons in an Optomechanical Microresonator.

Kerr soliton microcombs in microresonators have been a prominent miniaturized coherent light source. Here, for the first time, we demonstrate the existence of Kerr solitons in an optomechanical microresonator, for which a nonlinear model is built by incorporating a single mechanical mode and multiple optical modes. Interestingly, an exotic vibrational Kerr soliton state is found, which is modulated by a self-sustained mechanical oscillation. Besides, the soliton provides extra mechanical gain through the optical spring effect, and results in phonon lasing with a red-detuned pump. Various nonlinear dynamics is also observed, including limit cycle, higher periodicity, and transient chaos. This work provides a guidance for not only exploring many-body nonlinear interactions, but also promoting precision measurements by featuring superiority of both frequency combs and optomechanics.

Roles of micro-aeration on enhancing volatile fatty acids and lactic acid production from agricultural wastes.

Micro-aeration was proven to be an environmentally friendly strategy for efficiently enhancing volatile fatty acids (VFAs) and lactic acid (LA) production. The roles of micro-aeration on mono-digestion of swine manure (SM) for VFAs production and co-digestion of SM with corn silage (CS) for LA production were investigated, respectively. In this study, micro-aeration increased the maximum VFAs concentration by 20.3% to 35.71 g COD/L, and shortened the time to reach the maximum from 18 days to 10 days. Micro-aeration limited the conversion of LA into VFAs, leading to LA accumulation effectively to be 26.08 g COD/L. Microbial community analysis suggested that Clostridium and Terrisporobacter were always the dominant bacteria with or without micro-aeration for VFAs production, but the relative abundance increased notably during the same period. However, Bifidobacterium, which could use the higher productivity metabolism pathway, i.e., Bifidum pathway to produce LA, increased from lower than 1% to 22.9% by micro-aeration.

Operando monitoring transition dynamics of responsive polymer using optofluidic microcavities.

Optical microcavities have become an attractive platform for precision measurement with merits of ultrahigh sensitivity, miniature footprint and fast response. Despite the achievements of ultrasensitive detection, optical microcavities still face significant challenges in the measurement of biochemical and physical processes with complex dynamics, especially when multiple effects are present. Here we demonstrate operando monitoring of the transition dynamics of a phase-change material via a self-referencing optofluidic microcavity. We use a pair of cavity modes to precisely decouple the refractive index and temperature information of the analyte during the phase-transition process. Through real-time measurements, we reveal the detailed hysteresis behaviors of refractive index during the irreversible phase transitions between hydrophilic and hydrophobic states. We further extract the phase-transition threshold by analyzing the steady-state refractive index change at various power levels. Our technology could be further extended to other materials and provide great opportunities for exploring on-demand dynamic biochemical processes.

Single-mode characteristic of a supermode microcavity Raman laser.

Microlasers in near-degenerate supermodes lay the cornerstone for studies of non-Hermitian physics, novel light sources, and advanced sensors. Recent experiments of the stimulated scattering in supermode microcavities reported beating phenomena, interpreted as dual-mode lasing, which, however, contradicts their single-mode nature due to the clamped pump field. Here, we investigate the supermode Raman laser in a whispering-gallery microcavity and demonstrate experimentally its single-mode lasing behavior with a side-mode suppression ratio (SMSR) up to 37 dB, despite the emergence of near-degenerate supermodes by the backscattering between counterpropagating waves. Moreover, the beating signal is recognized as the transient interference during the switching process between the two supermode lasers. Self-injection is exploited to manipulate the lasing supermodes, where the SMSR is further improved by 15 dB and the laser linewidth is below 100 Hz.

Optimization of lactate production from co-fermentation of swine manure with apple waste and dynamics of microbial communities.

Co-anaerobic fermentation (co-AF) of swine manure (SM) and apple waste (AW) has been proved to be beneficial for lactic acid (LA) production. In order to further improve the LA production, three important parameters, namely AW in feedstock, temperature, volatile solids (VS) of feedstock, were evaluated using Box-Behnken design and response surface methodology. The quadratic regression model was developed and interactive effects was found between the three parameters. Results showed that the maximum concentration, 31.18 g LA/L (with LA yield of 0.62 g/g VS), was obtained under optimum conditions of 60.4% AW in feedstock, 34.7 ℃, and 5.0% VS. At the optimum conditions, the solubilization of organic matter was enhanced compared with mono-fermentation of SM. Microbial community structure of the reactor diverged greatly with fermentation time. Clostridium and Lactobacillus were dominant bacteria in the fermentation process, resulting in a remarkably LA accumulation.

Short chain carboxylic acids production and dynamicity of microbial communities from co-digestion of swine manure and corn silage.

Short chain carboxylic acids (SCCAs) have attracted much attention due to their wide application and benefit of high economy. This study investigated the influence of organic load rates (OLRs) on short-chain carboxylic acids (SCCAs) production and microbial communities for co-digestion of swine manure (SM) and corn silage (CS) during four different OLRs stages in a semi-continuous mode. The results showed that relatively stable SCCAs concentration of 10.5-13.6 g COD/L and SCCAs yield of 0.42 mg COD/mg VS was achieved at OLR of 3.0 g VS/L·d. The maximum concentration of 19.1 g COD/L was achieved at 3.5 g VS/L·d. Volatile fatty acids (VFAs) (include acetic, n-butyric and caproic acids) accounted for approximately 80% of SCCAs. Hydrolysis bacteria (HB) including Clostridium, Terriporobacter, Intestinibacter, and Turiibacter decreased with the increase of OLR, while acidogenic bacteria (AB) including Acetobacter, Lactobacillus, Aeriscardovia, and Pseudomonas increased, resulting in insufficient degradation of CS.

Regulated Photon Transport in Chaotic Microcavities by Tailoring Phase Space.

Manipulating light dynamics in optical microcavities has been made mainly either in real or momentum space. Here we report a phase-space tailoring scheme, simultaneously incorporating spatial and momentum dimensions, to enable deterministic and in situ regulation of photon transport in a chaotic microcavity. In the time domain, the chaotic photon transport to the leaky region can be suppressed, and the cavity resonant modes show stronger temporal confinement with quality factors being improved by more than 1 order of magnitude. In the spatial domain, the emission direction of the cavity field is controlled on demand through rerouting chaotic photons to a desired channel, which is verified experimentally by the far-field pattern of a quantum-dot microlaser. This work paves a way to in situ study of chaotic physics and promoting advanced applications such as arbitrary light routing, ultrafast random bit generation, and multifunctional on-chip lasers.

Enhanced lactic acid production from the anaerobic co-digestion of swine manure with apple or potato waste via ratio adjustment.

The valorization of organic waste into lactic acid (LA) via co-digestion has attracted tremendous research interests in recent years. This study investigated the feasibility of intensifying the LA accumulation from anaerobic digestion (AD) of swine manure (SM) by adding apple waste (AW) or potato waste (PW). Results indicated that AW or PW obviously enhanced the accumulation of LA, and when the optimal mixing ratio of AW or PW to SM of 75:25, the maximum concentrations of LA were 27.61 and 8.91 g COD/L, which were around 3.53- and 1.14-folds of that of the mono-digestion of SM, respectively. Meanwhile, the co-digestion of SM and AW showed significantly higher LA production than that of SM and PW (p < 0.05). High reducing sugar content of AW contributed to LA accumulation in AD process. In addition, AW increased the relative abundance of Lactobacillus and Clostridium, thus benefited the production of LA.

Bioconversion of swine manure into high-value products of medium chain fatty acids.

This research proposes and demonstrates, for the first time, the utilization of swine manure as a complex feedstock to produce high-value medium chain fatty acids (MCFA). The two-stage anaerobic digestion (AD) carboxylates platform was adopted for the conversion of swine manure to short chain fatty acids (SCFAs) and then SCFAs to MCFA (n-caproate, n-heptanoate, and n-caprylate) with ethanol supplementation. We defined the appropriate initial pH of 10.0 for SCFAs production with a carbon conversion rate of 71.2%, and acetate, propionate were the main products, which accounted for around 72.9% of the total SCFAs in the primary stage (I). Through the addition of ethanol, 61.3% of the converted carbon in the complex SCFAs solution was converted into MCFA (C6-C8) in the chain elongation stage (II), while only 6.7% was attributed to methane formation. The concentrations of n-caproate, n-heptanoate, and n-caprylate reached 8.6 g COD/L (3.9 g/L), 6.4 g COD/L (2.7 g/L), and 2.6 g COD/L (1.07 g/L), respectively. This study achieved a relatively higher concentration of n-heptanoate compared with past studies of MCFA from other feedstock. These findings demonstrated a new route for resource recovery and the operating parameters for producing MCFA from swine manure.

Chaos-assisted two-octave-spanning microcombs.

Since its invention, optical frequency comb has revolutionized a broad range of subjects from metrology to spectroscopy. The recent development of microresonator-based frequency combs (microcombs) provides a unique pathway to create frequency comb systems on a chip. Indeed, microcomb-based spectroscopy, ranging, optical synthesizer, telecommunications and astronomical calibrations have been reported recently. Critical to many of the integrated comb systems is the broad coverage of comb spectra. Here, microcombs of more than two-octave span (450 nm to 2,008 nm) is demonstrated through χ(2) and χ(3) nonlinearities in a deformed silica microcavity. The deformation lifts the circular symmetry and creates chaotic tunneling channels that enable broadband collection of intracavity emission with a single waveguide. Our demonstration introduces a new degree of freedom, cavity deformation, to the microcomb studies, and our microcomb spectral range is useful for applications in optical clock, astronomical calibration and biological imaging.

Reconfigurable symmetry-broken laser in a symmetric microcavity.

The coherent light source is one of the most important foundations in both optical physics studies and applied photonic devices. However, the whispering gallery microcavity, as a prime platform for novel light sources, has the intrinsically chiral symmetry and severely rules out access to directional light output, all-optical flip-flops, efficient light extraction, etc. Here, we demonstrate a reconfigurable symmetry-broken microlaser in an ultrahigh-Q whispering gallery microcavity with the symmetric structure, in which a chirality of lasing field is empowered spontaneously by the optical nonlinear effect. Experimentally, the ratio of counter-propagating lasing intensities is found to exceed 160:1, and the chirality can be controlled dynamically and all-optically by the bias in the pump direction. This work not only presents a distinct recipe for coherent light sources with robust and reconfigurable performance, but also opens up an unexplored avenue to symmetry-broken physics in optical micro-structures.