Search

Magneto-optical (MO) effects have a pivotal role in modern photonic devices for light manipulation and sensing, but the study of these effects has so far been limited to the MO Faraday and Kerr effects. Conventional MO systems encounter considerable intrinsic losses, markedly hampering their ability to amplify the MO effects. Here we introduce a loss-enhanced MO effect to sublinearly amplify the frequency response of a non-Hermitian optical cavity under different background magnetic fields. This exceptional MO effect relies on an architecture of MO material embedded in a Fabry–Pérot cavity, accompanied by a polarization-dependent optical absorption, that is, linear dichroism, to construct a reconfigurable exceptional point. The experimental results show that two eigenmodes of the Fabry–Pérot cavity exhibit sublinear frequency splitting. By electrically reconfiguring the absorber, the eigenfrequency shift can be adaptively enhanced under different background magnetic fields. Using this effect, we demonstrate the detection of subtle magnetic field variations in a strong background, with the system’s response magnified by a factor exceeding 10 and sensitivity increased threefold compared with its conventional Hermitian counterpart. Our study leverages exceptional physics to study the MO effect and develops a new class of reconfigurable MO devices equipped with enhanced sensitivity for potential integration with photonic systems.

The integrated gate commutated thyristor (IGCT) is promising in dc grids nowadays. However, to meet the increasing demands for handling high fault currents, the turn-off capability of IGCT still needs to be optimized, which is affected by transient turn-off current redistribution significantly. This article proposes an experiment method based on an isolated anode design for detecting the turn-off current redistribution characteristics of IGCT. Influences of ON-state current density and commutation impedance distribution on IGCT’s turn-off current redistribution characteristics are explored in detail. The results show that when IGCT’s turn-off process satisfies the “hard” gate drive condition, the anode current redistribution gets changed mainly in the current commutation period and the anode voltage rising period of the turn-off process, before IGCT’s dynamic avalanche phenomenon happens. Though the anode current distribution experiences large fluctuations during the commutation period, it will achieve a new balancing state at the end of this period, which almost does not affect the following periods. When IGCT goes into the anode voltage rising period, the ON-state current density distribution will affect the turn-off current redistribution. Under the effects of carrier extraction speed differences, the current density distribution throughout the chip tends to reduce its initial difference, which leads to the phenomenon of “current self-balancing.” Meanwhile, the region with the highest ON-state current density dominates the anode voltage’s building-up speed. To increase IGCT’s turn-off capability, improving the ON-state anode current density uniformity utilizing an optimized layout or cell structure is one of the effective methods.

Chirality, defined by Lord Kelvin, refers to the geometric symmetry property of an object that cannot be superposed onto its mirror image using rotations and translations. The material’s chirality can be probed with light as the optical activity: optical rotary dispersion (ORD) and circular dichroism (CD). It is still challenging to yield extremely sensitive ORD and CD for very weak chirality and measure both simultaneously. Cavity ringdown polarimetry has been reported to improve ORD detection sensitivity with the absence of equally important CD signature, at the price of high cavity finesse near 400, frequency-locking sophistication, and large magnetic field. Here, we report a unique recipe to demonstrate the simultaneous measurement of ORD and the CD by separately observing the chiral eigenmode spectra from a bowtie optical cavity with a finesse about 30, without resorting to frequency locking or magnetic field. We obtain a sensitivity of ∼2.7×10-3deg/Hzfor ORD, ∼8.1×10-6/Hzfor CD, and a spectral resolution of 0.04pmwithin a millisecond-scale measurement. We present a cost-effective yet ultrasensitive account for chiral chromatography, the conformational dynamics and chiroptical analysis of biological samples which particularly exhibit weak and narrow spectral signals.

High-voltage direct current voltage source converter (HVdc-VSC) technology is an important solutions for large-scale renewable sources. The MMC is one of the most popular topologies for the HVdc-VSC system. The extreme faults affect the safety and reliability of the MMC greatly. This article gives comprehensive analysis and experiment of extreme faults in the MMC based on an IGCT. Causes and characterization of the extreme faults are analyzed in detail. A new protection solution based on the CP-IGCT and fast recovery diode with HS-FRD is proposed. The surge current capability of HS-FRD is validated via experiment successfully. Theoretical calculation shows that the protection solution based on CP-IGCT, and HS-FRD can help reduce the maximum fault current below 50% when the anode inductor is 0.8 μH in the extreme shoot-through fault. Test results show that the protection solution can realize the discharge of the dc capacitor below 4.5 kV in the extreme shoot-through fault. The maximum fault current in the MMC based on the IGCT is only about 600 kA, while the maximum fault current in the MMC based on the IGBT is over 1100 kA. Explosion proof of CP-IGCT is validated during the tests, which is similar to that of the protection thyristor. However, the IGBT cannot guarantee the stability of the package and may cause severe safety problem. The failed CP-IGCT has the short-circuit failure mode and can be used for bypass of the faulty MMC submodule. Via comparison, the proposed protection solution has lowest cost and complexity, as well as the highest safety.

A scheme to enhance the optical delay in Rydberg atoms is proposed. In the linear case, the optical delay in a four-level system can be significantly enhanced compared to that of the three-level system. However, the width of the transparent window will decrease with an increase in the optical delay. In the nonlinear case, the nonlinear dispersion becomes steep around the transparency window. The enhanced cross-Kerr nonlinearity mainly contributes to the effective dispersion, which dramatically increases the optical delay. The simulation result shows that the optical delay of the system could be enhanced tens of times; moreover, the wide transparency window remains. So the delay-bandwidth product could be significantly improved due to nonlinear dispersion. We further examine Gaussian pulse propagation in the Rydberg atoms.

A white light cavity (WLC) scheme is proposed to achieve broadband response in the terahertz (THz) region by enhanced nonlinear dispersion in a magnetized graphene system. In the weak probe field limit, the cavity linewidth is narrowed due to electromagnetically induced transparency, and then it becomes nearly as broad as the empty-cavity linewidth under the condition of Autler–Towns splitting. It is interesting to find that the cavity linewidth can be further broadened by enhanced nonlinear dispersion. The simulation result shows that the response range of the cavity is from 6.273 THz to 6.308 THz under the given condition, which is nearly 11 times larger than the empty-cavity linewidth. Furthermore, the improvement in cavity transmission and the response of WLC at different frequencies are investigated.

An active-Raman-gain (ARG) spectrum of Rydberg atoms is investigated and proposed to measure a microwave (MW) electric (E) field. A strong Raman field couples the ground-state transition with large frequency detuning, and a probe field drives the metastable transition, whose transmission shows a large gain. When a MW field couples the Rydberg transition, the gain peak splits. It is interesting to find that the frequency splitting of gain peaks shows a linear relationship with the MW-field strength, which can be used to measure the MW E field. Moreover, the ARG spectrum has a large peak value that is about 10 times larger than that of common electromagnetically induced transparency schemes. For weak MW fields, the Doppler effect will greatly narrow the gain spectrum if the probe and Raman fields copropagate through the atomic cell, which increases the probe sensitivity dramatically. After the Doppler averaging, the probe sensitivity is enhanced by about 10 times, and the linewidth is narrowed to 1/10 compared to the case without the Doppler effect.

Current guidelines recommend adjuvant chemotherapy (ACT) for stage II colorectal cancer (CRC) patients by using clinical high risk factors, with which circulating tumor cells (CTCs) were not considered. Here, an assessment to detect CTCs based on subtraction enrichment mediated by magnetic beads conjugated with CD45, immunofluorescence staining of CK, and fluorescence in situ hybridization of CEP8 is established. Both CEP8- and CK-positive CTCs have the potential to improve the risk stratification of stage II CRC patients. Patients with preoperative CTCs of ≥4 had a significantly higher recurrence risk than those with preoperative CTCs of <4 in two external validation cohorts (P< 0.0001). In the subgroup with clinical high risk, when preoperative CTCs were <4, patients did not benefit from ACT (P= 0.5764); however, when preoperative CTCs were ≥4, patients received benefit from ACT (P= 0.0064). Additionally, regardless of clinical risk status and preoperative CTC levels, if postoperative CTC levels were ≥4 for more than three consecutive time points (monitoring time interval, 2–6 months), the recurrence rate was 100%. Our findings suggested that the subtraction enrichment of CTCs could provide a reliable method to stratify the recurrence risk and make therapeutic decisions after surgery in stage II CRC patients.

MicroRNAs have been reported to play an important role in diverse biological processes and progression of various cancers. MicroRNA-29a has been observed to be downregulated in human lung cancer tissues, but the function of microRNA-29a in lung cancer has not been well investigated. In this study, we demonstrated that the expression levels of microRNA-29a were significantly downregulated in 38 pairs of lung cancer tissues when compared to adjacent normal tissues. Overexpression of microRNA-29a inhibited the activity of cell proliferation and colony formation of lung cancer cells, H1299 and A549. Furthermore, microRNA-29a targeted NRAS proto-oncogene in lung cancer cells. In human clinical specimens, NRAS proto-oncogene was highly expressed in human lung cancer tissues compared to normal tissues. More interestingly, microRNA-29a also sensitizes lung cancer cells to cisplatin (CDDP[Please replace “CDDP” with its expansion in the abstract and also provide expansion for the same in its first occurrence in text, if appropriate.]) via its target, NRAS proto-oncogene. Thus, our results in this study demonstrated that microRNA-29a acted as a tumor suppressor microRNA, which indicated potential application of microRNAs for the treatment of human lung cancer in the future.