Linear-space-variant model for Fourier ptychographic microscopy.

Fourier ptychographic microscopy (FPM) needs to realize well-accepted reconstruction by image segmentation and discarding problematic data due to artifacts caused by vignetting. However, the imaging results have long suffered from uneven color blocks and the consequent digital stitching artifacts, failing to bring satisfying experiences to researchers and users over the past decade since the invention of FPM. In fact, the fundamental reason for vignetting artifacts lies in that the acquired data does not match the adopted linear-space-invariant (LSI) forward model, i.e., the actual object function is modulated by a quadratic phase factor during data acquisition, which has been neglected in the advancement of FPM. In this Letter, we rederive a linear-space-variant (LSV) model for FPM and design the corresponding loss function for FPM, termed LSV-FPM. Utilizing LSV-FPM for optimization enables the efficient removal of wrinkle artifacts caused by vignetting in the reconstruction results, without the need of segmenting or discarding images. The effectiveness of LSV-FPM is validated through data acquired in both 4f and finite conjugate single-lens systems.

Near-zero beam drift laser tracking and measurement system with two-stage compression structures.

This paper introduces a scheme of near-zero beam drift tracking technology with two-stage compression structures for the coordinate accuracy measurement of a laser tracker. The Galileo telescope system, with a magnification of 21.43, is designed to compress the beam drift in a dual-frequency interferometer. The azimuth and pitch of the beam drift are compressed to 2.41 in. and 2.92 in., and the compression rates are 95.0% and 91.9%, respectively. The improved four degrees of freedom position-sensitive detector system is used to further compress the beam drift. The peak-to-peak value of the beam drift is 0.9 in. in the azimuth direction and 2.1 in. in the pitch direction. The standard deviation of azimuth is within 0.15 in, and the pitch is within 0.43 in. The coordinate accuracy of the laser tracker can be improved 6.85 parts per million by simulation. The developed two-stage compression near-zero beam drift system can be used in the laser tracker to realize large-scale precision instrument geometric measurement.

High-velocity measurement method in dual-frequency laser interference tracker based on beam expander and acousto-optic modulator.

The laser tracker, as a new large-scale measuring instrument of combining conventional measurement technology and modern control technology, has the advantages of intelligence, portability, large measurement space, high measurement accuracy and short detection period. However, the laser tracker has strict requirements on the moving speed of the spherically mounted retroreflector. This deficiency not only limits the application of the measuring instrument in the field of high-velocity measurement, but also greatly reduces the measurement efficiency. In this work, we analyze the factors that affect the tracking velocity of the laser tracker, and propose for the first time to use the beam expander device to improve the transverse tracking measurement velocity of the instrument. The experimental results show that the laser tracker miss distance can reach 2.25 mm. The transverse tracking velocity and acceleration can reach 4.34 m/s and 2.4 g, respectively. Additionally, the acousto-optic modulator is used to increase the frequency difference between the reference beam and the measuring beam, so that the value is greater than 19 MHz. The radial tracking measurement velocity can reach 6.2 m/s. The high-velocity laser interference tracker developed by this new method can be used in the field of large-scale space precision measurement such as nuclear power, medical treatment and rail transit.

Cognitive reserve disorder in age-related hearing loss: cognitive cortical compensatory to auditory perceptual processing.

The aim of this study is to ascertain the mechanisms of cognitive reserve disorder in age-related hearing loss (ARHL), to study the correlation between ARHL and cognitive decline via EEG, and to reverse the adverse remodeling of auditory-cognitive connectivity with hearing aids (HAs). In this study, 32 participants were enrolled, including 12 with ARHLs, 9 with HAs, and 11 healthy controls (HCs), to undergo EEG, Pure Tone Average (PTA), Montreal Cognitive Assessment (MoCA), and other general cognitive tests. There were the lowest MoCA in the ARHL group (P = 0.001), especially in language and abstraction. In the ARHL group, power spectral density of the gamma in right middle temporal gyrus was significantly higher than HC and HA groups, while functional connectivity between superior frontal gyrus and cingulate gyrus was weaker than HC group (P = 0.036) and HA group (P = 0.021). In the HA group, superior temporal gyrus and cuneus had higher connectivity than in the HC group (P = 0.036). In the ARHL group, DeltaTM_DTA (P = 0.042) and CTB (P = 0.011) were more frequent than in the HC group, while there was less DeltaTM_CTA (P = 0.029). PTA was found to be associated with MoCA (r = -0.580) and language (r = -0.572), DeltaTM_CTB had a likewise correlation with MoCA (r = 0.483) and language (r = 0.493), while DeltaTM_DTA was related to abstraction (r = -0.458). Cognitive cortexes compensate for worse auditory perceptual processing in ARHL, which relates to cognitive decline. The impaired functional connectivity between auditory and cognitive cortexes can be remodeled by HAs. DeltaTM may serve as a biomarker for early cognitive decline and decreased auditory speech perception in ARHL.

Few-Layer Bismuthene for Coexistence of Harmonic and Dual Wavelength in a Mode-Locked Fiber Laser.

Bismuthene, as a novel two-dimensional (2D) material, has attracted extensive attention because of its outstanding properties including narrow band gap, stability at room temperature, nonlinear optical transmission, and so on. In this paper, the physical characteristic, nonlinear optical response, and ultrafast photonics application of few-layer bismuthene are studied experimentally. By the balanced twin-detector measurement method, the saturable absorption property of few-layer bismuthene with a modulation depth of 2.5% and saturable intensity of 110 MW/cm2 at the optical communication band (C-band) is illustrated. Dependent on a few-layer bismuthene saturable absorber, an all-fiber ultrashort pulse laser is fabricated and the proposed fiber laser can operate with coexistence of harmonic mode-locking and dual-wavelength mode-locking. The different laser generations of harmonic and dual wavelength depend on the saturable absorption of few-layer bismuthene, the suitable birefringence and nonlinearity strength in the laser cavity. The results suggest that the ultrashort pulse laser obtained based on few-layer bismuthene could be applied to the field of pump-probe experiments and tunable terahertz radiation generation potentially.

Efficacy of an Integrative Treatment for Tinnitus Combining Music and Cognitive-Behavioral Therapy-Assessed With Behavioral and EEG Data.

Chronic tinnitus is a prevalent condition that could cause severe negative impact on an individual's life. However, there has not been an established treatment due to a limited understanding of the pathophysiology of this multifarious disorder. In this study, we tested the efficacy of an integrative treatment, combining music therapy with cognitive-behavioral therapy (CBT). We collected three groups of patients receiving three different treatments: Music-CBT, music therapy and CBT. We used both subjective (i.e., questionnaires) and objective (i.e., resting-state EEG data) measurements to assess the behavioral and neural changes brought upon by the treatments. Analyses of the subjective measurements found a significant improvement of scale scores in Music-CBT and CBT, but not in the Music group. Analysis of the EEG data further showed increased powers in alpha and theta band after the Music-CBT treatment, and increased gamma power after CBT, whereas no significant difference was found for the music therapy. Further source localization analysis of alpha and theta changes in the Music-CBT group found that primary sources of the changes were located at auditory processing regions such as superior temporal gyrus, and higher emotional and cognitive processing regions such as ventromedial prefrontal cortex (vMPFC), lateral prefrontal cortex and parahippocampus. These results indicated that Music-CBT was effective in improving tinnitus symptoms on both a behavioral and neural level, which is more robust than the music therapy or CBT alone.

Fe3O4 nanoparticle-enabled mode-locking in an erbium-doped fiber laser.

In this paper, we have proposed and demonstrated the generation of passively mode-locked pulses and dissipative soliton resonance in an erbium-doped fiber laser based on Fe3O4 nanoparticles as saturable absorbers. We obtained self-starting mode-locked pulses with fundamental repetition frequency of 7.69 MHz and center wavelength of 1561 nm. The output of a pulsed laser has spectral width of 0.69 nm and pulse duration of 14 ns with rectangular pulse profile at the pump power of 190 mW. As far as we know, this is the firsttimethatFe3O4 nanoparticles have been developed as low-dimensional materials for passive mode-locking with rectangular pulse. Our experiments have confirmed that Fe3O4 has a wide prospect as a nonlinear photonics device for ultrafast fiber laser applications.

Bismuthene Nanosheets for 1 µm Multipulse Generation.

Bismuthene, as a new two-dimensional material made up of diazo metal elements, has drawn massive attention for its unique electronic, mechanical, quantum, and nonlinear optical properties. In recent years, researchers have increasingly turned their attention to the ultrafast photonics fields based on bismuthene. However, the internal ultrashort pulse dynamics has seldom been explored yet. In this work, the nonlinear optical properties of bismuthene nanosheets have been studied and applied in a passively mode-locked fiber laser. The saturation intensity and modulation depth of a saturable absorber (SA) device are about 2.4 MW/cm2 and 1%, respectively. Thanks to the narrow band gap of bismuthene and tapered fiber structure, a special kind of noise-like multipulses has been obtained. The evolution of the pulsed laser is also studied. This proposed pulsed fiber laser based on a bismuthene SA device is well suitable for some applications such as material processing, optical logics, and so forth.

Lead sulfide nanoparticles for dual-wavelength ultrashort pulse generation.

Nanoparticle materials have many potential applications in the area of electronics and optoelectronics due to their unique and versatile properties. In particular, lead sulfide nanoparticles (PbS NPs) have shown excellent ultrafast photonics and can be applied to communication systems because of their low bandgap, high thermal damage threshold and stability. The wavelength division multiplexor (WDM) technique is vital to fiber optical communication, which allows the transmission of many different-wavelength signals in one fiber cable. However, PbS NPs for multi-wavelength pulse generation has not been reported until now. In this work, PbS NPs have been investigated and successfully applied in an Er-doped fiber laser as a saturable absorber (SA) to generate a dual-wavelength short pulse for the first time. A picosecond-level ultrashort pulse at center wavelengths of 1545 and 1585 nm can be achieved simultaneously or respectively. It is worth mentioning that the two wavelengths are separated up to 40 nm, which can significantly expand the optical communication capacity. The result suggests that PbS NPs as smart nonlinear optical components have wide applications in optical communications, short-pulse lasers, and even high-performance photodectors.

SnSe2 Nanosheets for Subpicosecond Harmonic Mode-Locked Pulse Generation.

Tin diselenide (SnSe2 ) nanosheets as novel 2D layered materials have excellent optical properties with many promising application prospects, such as photoelectric detectors, nonlinear optics, infrared photoelectric devices, and ultrafast photonics. Among them, ultrafast photonics has attracted much attention due to its enormous advantages; for instance, extremely fast pulse, strong peak power, and narrow bandwidth. In this work, SnSe2 nanosheets are fabricated by using solvothermal treatment, and the characteristics of SnSe2 are systemically investigated. In addition, the solution of SnSe2 nanosheets is successfully prepared as a fiber-based saturable absorber by utilizing the evanescent field effect, which can bear a high pump power. 31st-order subpicosecond harmonic mode locking is generated in an Er-doped fiber laser, corresponding to the maximum repetition rate of 257.3 MHz and pulse duration of 887 fs. The results show that SnSe2 can be used as an excellent nonlinear photonic device in many fields, such as frequency comb, lasers, photodetectors, etc.

Few-layer bismuthene for robust ultrafast photonics in C-Band optical communications.

The ultrafast photonics of different conventional two-dimensional (2D) materials have been studied intensively. Few-layer structure bismuthene has been reported as a new type of 2D material with high efficient electronics, strong mechanics and outstanding photonics properties. In this paper, a robust ultrafast pulse generation in communications-Band (C-Band) based on few-layer bismuthene has been reported. The characteristics and the ultrafast optical nonlinear properties of few-layer bismuthene have been investigated experimentally. The optical induced deposition method is employed to fabricate the saturable absorber based on bismuthene (BiSA). Most importantly, we also utilize BiSA for the ultrafast photonics, which demonstrates that a high-splitting-threshold robust ultrafast fiber laser with 1.3-ps pulse duration at 1531 nm has been obtained in the experiments. Even though we increase the pump power from the self-starting threshold (i.e. 86 mW) to 314 mW, the soliton pulse does not split. Moreover, the high-splitting-threshold laser operation can be achieved stably even if the lasers are exposed in air for at least half a year. It is demonstrated that the proposed bismuthene nonlinear components can be potentially applied to the optical communications with C-Band (i.e. 1530-1565 nm wavelength) to broaden the communications window.

Clinical Findings in Patients With Persistent Positional Nystagmus: The Designation of "Heavy and Light Cupula".

Objective: Direction-changing positional nystagmus (DCPN) had been observed as persistent horizontal apogeotropic and was considered as "cupulolithiasis or heavy cupula. " Recently, the concept of "light cupula" exhibiting persistent geotropic DCPN has been introduced. However, the light cupula is not systematically described, while the identification and diagnosis of "light cupula" should be improved. Here we investigated the underlying characteristics and therapeutic options designed to the "light" and "heavy" cupula, respectively; and summarized the clinical characteristics and therapeutic effect in the two groups. Methods: A total of 359 cases with vertigo and bilateral DCPN were found in the supine roll test. Only 25 patients with persistent DCPN were enrolled and followed up. According to the direction of nystagmus, we further divided the patients into "heavy cupula" (apogeotropic) and "light cupula" (geotropic) groups. We compared the incidence, characteristics of nystagmus and the efficacy of repositioning maneuver in the two groups. Results: Nine patients with persistent horizontal geotropic DCPN were confirmed as "light cupula," other 16 patients with persistent horizontal ageotropic DCPN were confirmed as heavy cupula. All 25 patients had null plane; the mean value and standard deviation of the null plane in light cupula and heavy cupula was 25.67 ± 9.31° and 27.06 ± 6.29°, respectively. The mean value and standard deviation of the termination plane in light cupula was 28.78 ± 10.00°, and 30.25 ± 6.53° in heavy cupula. There was no statistical significance between the two groups. We found that the direction of evoked nystagmus in the supine position was toward the intact side in light cupula, while in heavy cupula, it was toward the lesion side. The null plane appeared on the lesion side. For light cupula patients, the effect was not obvious at Day-7 after the treatment, however, treatment for most heavy cupula patients were effective. All patients recovered after 30 days of treatment. Conclusion: The null plane is crucial in determining the lesion side for light or heavy cupula. Although the short-term therapeutic effect of the light cupula is not as promising as the effect seen in heavy cupula, the long-term prognosis in both groups is comparable; with all patients recovered after 30 days of treatment. Study design: This is a retrospective cohort study.

Few-layer bismuthene for femtosecond soliton molecules generation in Er-doped fiber laser.

Bismuthene, a mono-elemental two-dimensional material with a novel kind of few-layer structure purely consisting of bismuth, has been predicted to have a prominent optical response and enhanced stability in theory. In this paper, few-layer bismuthene is employed as the saturable absorber. The mode-locker is fabricated by dropping bismuthene on a microfiber in a passively mode-locked, Er-doped fiber laser. The single pulse can be obtained at 122.1 mW, with 621.5 fs pulse duration at 1557.5 nm central wavelength, 10.35 nm spectral width and fundamental repetition of 22.74 MHz. Thanks to the outstanding nonlinear effect and semimetal of the bismuthene, dual-pulses, octonary-pulses and fourteen-pulses soliton molecules with tightly and loosely temporal separation can be achieved for the first time, to the best of our knowledge. The preceding indicates that bismuthene will have wide potential in many applications, such as optical fiber communications, optical logical gate, and laser materials processing, etc.

Few-layer bismuthene for ultrashort pulse generation in a dissipative system based on an evanescent field.

Bismuthene has attracted a great deal of attention because of its unique electronic and optical properties. However, there are few reported applications of bismuthene in nonlinear optical applications. In this research, a dissipative soliton ytterbium-doped mode-locked fiber laser at 1 µm regime with a bismuthene saturable absorber (SA) by using evanescent field interaction for the first time is demonstrated. The nonlinear optical absorption of microfiber-based bismuthene SA is shown experimentally by using a homemade ultrafast fiber laser, whose saturation intensity and modulation depth are about 13 MW cm-2 and 2.2%, respectively. Relying on the excellent nonlinear optical property of the bismuthene SA, the typical dissipative solitons with a repetition rate of 21.74 MHz are generated at a center wavelength of 1034.4 nm. The time-bandwidth product of the pulse is about 23.07 with a pulse width of 30.25 ps. The results demonstrate that bismuthene is a good candidate for application in a 1 µm wave-breaking-free mode-locked fiber laser and nonlinear photonic components.