Multiplexable all-optical nonlinear activator for optical computing.

As an alternative solution to surpass electronic neural networks, optical neural networks (ONNs) offer significant advantages in terms of energy consumption and computing speed. Despite the optical hardware platform could provide an efficient approach to realizing neural network algorithms than traditional hardware, the lack of optical nonlinearity limits the development of ONNs. Here, we proposed and experimentally demonstrated an all-optical nonlinear activator based on the stimulated Brillouin scattering (SBS). Utilizing the exceptional carrier dynamics of SBS, our activator supports two types of nonlinear functions, saturable absorption and rectified linear unit (Relu) models. Moreover, the proposed activator exhibits large dynamic response bandwidth (∼11.24 GHz), low nonlinear threshold (∼2.29 mW), high stability, and wavelength division multiplexing identities. These features have potential advantages for the physical realization of optical nonlinearities. As a proof of concept, we verify the performance of the proposed activator as an ONN nonlinear mapping unit via numerical simulations. Simulation shows that our approach achieves comparable performance to the activation functions commonly used in computers. The proposed approach provides support for the realization of all-optical neural networks.

Quantum Light Generation Based on GaN Microring toward Fully On-Chip Source.

An integrated quantum light source is increasingly desirable in large-scale quantum information processing. Despite recent remarkable advances, a new material platform is constantly being explored for the fully on-chip integration of quantum light generation, active and passive manipulation, and detection. Here, for the first time, we demonstrate a gallium nitride (GaN) microring based quantum light generation in the telecom C-band, which has potential toward the monolithic integration of quantum light source. In our demonstration, the GaN microring has a free spectral range of 330 GHz and a near-zero anomalous dispersion region of over 100 nm. The generation of energy-time entangled photon pair is demonstrated with a typical raw two-photon interference visibility of 95.5±6.5%, which is further configured to generate a heralded single photon with a typical heralded second-order autocorrelation g_{H}^{(2)}(0) of 0.045±0.001. Our results pave the way for developing a chip-scale quantum photonic circuit.

High-precision angular rate detection based on an optomechanical micro hemispherical shell resonator gyroscope.

Cavity optomechanics with picometer displacement measurement resolution has shown vital applications in high-precision sensing areas. In this paper, an optomechanical micro hemispherical shell resonator gyroscope (MHSRG) is proposed, for the first time. The MHSRG is driven by the strong opto-mechanical coupling effect based on the established whispering gallery mode (WGM). And the angular rate is characterized by measuring the transmission amplitude changing of laser coupled in and out from the optomechanical MHSRG based on the dispersive resonance wavelength shift and/or dissipative losses varying. The detailed operating principle of high-precision angular rate detection is theoretically explored and the fully characteristic parameters are numerically investigated. Simulation results show that the optomechanical MHSRG can achieve scale factor of 414.8 mV/ (°/ s) and angular random walk of 0.0555 °/ h1/2 when the input laser power is 3 mW and resonator mass is just 98 ng. Such proposed optomechanical MHSRG can be widely used for chip-scale inertial navigation, attitude measurement, and stabilization.

Towards a photonic integrated all-optical phase regenerator.

All-optical phase regeneration aims at restoring the phase information of coherently encoded data signals directly in the optical domain so as to compensate for phase distortions caused by transceiver imperfections and nonlinear impairments along the transmission link. Although it was proposed two decades ago, all-optical phase regeneration has not been seen in realistic networks to date, mainly because this technique entails complex bulk modules and relies on high-precision phase sensitive nonlinear dynamics, both of which are adverse to field deployment. Here, we demonstrate a new, to the best of our knowledge, architecture to implement all-optical phase regeneration using integrated photonic devices. In particular, we realize quadrature phase quantization by exploring the phase-sensitive parametric wave mixing within on-chip silicon waveguides, while multiple coherent pump laser tones are provided by a chip-scale micro-cavity Kerr frequency comb. Multi-channel all-optical phase regeneration is experimentally demonstrated for 40 Gbps QPSK data, achieving the best SNR improvement of more than 6 dB. Our study showcases a promising avenue to enable the practical implementation of all-optical phase regeneration in realistic long-distance fiber transmission networks.

Discrete frequency-bin entanglement generation via cascaded second-order nonlinear processes in Sagnac interferometer.

Discrete frequency-bin entanglement is an essential resource for applications in quantum information processing. In this Letter, we propose and demonstrate a scheme to generate discrete frequency-bin entanglement with a single piece of periodically poled lithium niobate waveguide in a modified Sagnac interferometer. Correlated two-photon states in both directions of the Sagnac interferometer are generated through cascaded second-order optical nonlinear processes. A relative phase difference between the two states is introduced by changing the polarization state of pump light, thus manipulating the two-photon state at the output of the Sagnac interferometer. The generated two-photon state is sent into a fiber polarization splitter, and then a pure discrete frequency-bin entangled two-photon state is obtained by setting the pump light. The frequency entanglement property is measured by a spatial quantum beating with a visibility of 96.0±6.1%. The density matrix is further obtained with a fidelity of 98.0±3.0% to the ideal state. Our demonstration provides a promising method for the generation of pure discrete frequency-bin entanglement at the telecom band, which is desired in quantum photonics.

Very high-frequency, gate-tunable CrPS4 nanomechanical resonator with single mode.

Two-dimensional (2D) antiferromagnetic semiconductor chromium thiophosphate (CrPS4) has gradually become a major candidate material for low-dimensional nanoelectromechanical devices due to its remarkable structural, photoelectric characteristics and potentially magnetic properties. Here, we report the experimental study of a new few-layer CrPS4 nanomechanical resonator demonstrating excellent vibration characteristics through the laser interferometry system, including the uniqueness of resonant mode, the ability to work at the very high frequency, and gate tuning. In addition, we demonstrate that the magnetic phase transition of CrPS4 strips can be effectively detected by temperature-regulated resonant frequencies, which proves the coupling between magnetic phase and mechanical vibration. We believe that our findings will promote the further research and applications of the resonator for 2D magnetic materials in the field of optical/mechanical signal sensing and precision measurement.

Gate-tunable bolometer based on strongly coupled graphene mechanical resonators.

Bolometers based on graphene have demonstrated outstanding performance with high sensitivity and short response time. In situ adjustment of bolometers is very important in various applications, but it is still difficult to implement in many systems. Here we propose a gate-tunable bolometer based on two strongly coupled graphene nanomechanical resonators. Both resonators are exposed to the same light field, and we can measure the properties of one bolometer by directly tracking the resonance frequency shifts, and indirectly measure the other bolometer through mechanical coupling. We find that the sensitivity and the response bandwidth of both bolometers can be independently adjusted by tuning the corresponding gate voltages. Moreover, the properties of the indirectly measured bolometer show a dependence on the coupling between the two resonators, with other parameters being fixed. Our method has the potential to optimize the design of large-scale bolometer arrays, and open new horizons in infrared/terahertz astronomy and communication systems.

Coherent phonon dynamics in spatially separated graphene mechanical resonators.

Vibrational modes in mechanical resonators provide a promising candidate to interface and manipulate classical and quantum information. The observation of coherent dynamics between distant mechanical resonators can be a key step toward scalable phonon-based applications. Here we report tunable coherent phonon dynamics with an architecture comprising three graphene mechanical resonators coupled in series, where all resonators can be manipulated by electrical signals on control gates. We demonstrate coherent Rabi oscillations between spatially separated resonators indirectly coupled via an intermediate resonator serving as a phonon cavity. The Rabi frequency fits well with the microwave burst power on the control gate. We also observe Ramsey interference, where the oscillation frequency corresponds to the indirect coupling strength between these resonators. Such coherent processes indicate that information encoded in vibrational modes can be transferred and stored between spatially separated resonators, which can open the venue of on-demand phonon-based information processing.

Wavelength-division multiplexing communications using integrated soliton microcomb laser source.

In this Letter, we report an investigation of the feasibility and performance of wavelength-division multiplexed (WDM) optical communications using an integrated perfect soliton crystal as the multi-channel laser source. First, we confirm that perfect soliton crystals pumped directly by a distributed-feedback (DFB) laser self-injection locked to the host microcavity has sufficiently low frequency and amplitude noise to encode advanced data formats. Second, perfect soliton crystals are exploited to boost the power level of each microcomb line, so that it can be directly used for data modulation, excluding preamplification. Third, in a proof-of-concept experiment, we demonstrate seven-channel 16-quadrature amplitude modulation (16-QAM) and 4-level pulse amplitude modulation (PAM4) data transmissions using an integrated perfect soliton crystal as the laser carrier; excellent data receiving performance is obtained for various fiber link distances and amplifier configurations. Our study reveals that fully integrated Kerr soliton microcombs are viable and advantageous for optical data communications.

Phase noise of Kerr soliton dual microcombs.

Dissipative Kerr soliton microcombs are believed to be a promising technique to build a dual-comb source for applications including precision laser metrology, fast laser spectroscopy, and high-speed optical signal processing. In this Letter, we conduct a detailed experimental investigation on the phase coherence between two on-chip Kerr soliton microcombs, where the underlying physical and technical origins that lead to the mutual phase noise between microcombs are analyzed. Moreover, the techniques of 2-point locking and optical frequency division are explored to enhance the dual-microcomb phase coherence, and we demonstrate the best phase noise down to -50 dBc/Hz at 1-Hz offset, -90 dBc/Hz at 1-kHz offset, and -120 dBc/Hz at 1-MHz offset. Our study provides a basic reference for both fundamental studies and practical applications of Kerr soliton dual microcombs that entail high mutual phase coherence.

Mid-infrared spectrally-uncorrelated biphotons generation from doped PPLN: a theoretical investigation.

We theoretically investigate the preparation of mid-infrared (MIR) spectrally-uncorrelated biphotons from a spontaneous parametric down-conversion process using doped LN crystals, including MgO doped LN, ZnO doped LN, and In2O3 doped ZnLN with doping ratio from 0 to 7 mol%. The tilt angle of the phase-matching function and the corresponding poling period are calculated under type-II, type-I, and type-0 phase-matching conditions. We also calculate the thermal properties of the doped LN crystals and their performance in Hong-Ou-Mandel interference. It is found that the doping ratio has a substantial impact on the group-velocity-matching (GVM) wavelengths. Especially, the GVM2 wavelength of co-doped InZnLN crystal has a tunable range of 678.7 nm, which is much broader than the tunable range of less than 100 nm achieved by the conventional method of adjusting the temperature. It can be concluded that the doping ratio can be utilized as a degree of freedom to manipulate the biphoton state. The spectrally uncorrelated biphotons can be used to prepare pure single-photon source and entangled photon source, which may have promising applications for quantum-enhanced sensing, imaging, and communications at the MIR range.

Phonon lasing with an atomic thin membrane resonator at room temperature.

Graphene has been considered as one of the best materials to implement mechanical resonators due to their excellent properties such as low mass, high quality factors and tunable resonant frequencies. Here we report the observation of phonon lasing induced by the photonthermal pressure in a few-layer graphene resonator at room temperature, where the graphene resonator and the silicon substrate form an optical cavity. A marked threshold in the oscillation amplitude and a narrowing linewidth of the vibration mode are observed, which confirms a phonon lasing process in the graphene resonator. Our findings will stimulate the studies on phononic phenomena, help to establish new functional devices based on graphene mechanical resonators, and might find potential applications in classical and quantum sensing fields, as well as in information processing.

Linking doctor-patient relationship to medical residents' work engagement: The influences of role overload and conflict avoidance.

BACKGROUND: Chinese residents' practical work experiences are different from those described in Western studies. To explore potential mechanisms underlying the effects of doctor-patient relationships on medical residents' work engagement, verifying a posited mediating effect of role overload, and moderating effect of conflict avoidance, in the Chinese context. METHODS: Based on the conservation of resources theory, a composite model was constructed. This study's data were collected from four different Chinese tertiary hospitals; 195 residents undergoing regularization training took this survey. Hierarchical moderated and mediated regression analyses were utilized. RESULTS: Doctor-patient relationship were found to be positively related to residents' work engagement (ß=0.31, p≤0.001). Role overload partially mediated the effect of these relationships on work engagement, and the moderating role of conflict avoidance in the relationship between doctor-patient relationship and conflict avoidance was negative. CONCLUSION: Maintaining good doctor-patient relationship can prompt residents to increase their engagement in work in order to meet their patients' needs. Furthermore, role overload has a particular influence in early career stages. Not only is it necessary for residents to gain a sense of recognition and support while they carry out their job responsibilities, especially while dealing with complex doctor-patient relationship, but it is also important to create work environments that can help residents shape their professional competency.

Enhancing the long-term stability of dissipative Kerr soliton microcomb.

A temporal dissipative Kerr soliton (DKS) frequency comb can be generated in an optical micro-cavity relying on the rigid balance between cavity decay (dispersion) and parametric gain (nonlinear phase modulation) induced by an intense pump laser. In practice, to maintain such delicate double balances experienced by the intracavity soliton pulses, it requires precise control of the pump laser frequency and power, as well as the micro-cavity parameters. However, to date there still lacks experimental demonstration that simultaneously stabilizes all these key parameters to enhance the long-term DKS stability. Here, we demonstrate continuous working of a on-chip DKS microcomb for a record-breaking 14 days without showing any sign of breakdown. Such improved microcomb stability is enabled mainly by robust pump power coupling to the micro-cavity utilizing packaged planar-lightwave-circuit mode converters, and faithful locking of the pump frequency detuning via an auxiliary laser heating method. In addition to superior stability, the demonstrated DKS microcomb system also achieves favorable compactness, with all the accessory modules being assembled into a standard 4U case. We hope that our demonstration could prompt the practical utilization of Kerr microcombs in real-world applications.

Quantum random number generator based on single-photon emitter in gallium nitride.

We experimentally demonstrate a real-time quantum random number generator by using a room-temperature single-photon emitter from the defect in a commercial gallium nitride wafer. Due to the brightness of our single-photon emitter, the raw bit generation rate is about 1.8 MHz, and the unbiased bit generation rate is about 420 kHz after the von Neumann's randomness extraction procedure. Our results show that the commercial gallium nitride wafer has great potential for the development of integrated high-speed quantum random number generator devices.

Stimulated Brillouin laser-based carrier recovery in a high-Q microcavity for coherent detection.

We demonstrate all-optical carrier recovery exploring a stimulated Brillouin laser (SBL) in a high-Q whispering-gallery-mode microcavity, to achieve coherent data detection without requiring an independent local oscillator laser. An ultra-high optical signal-to-noise ratio better than 70 dB is achieved for the recovered carrier, thanks to the fact that the generated SBL counter-propagates with the incoming data signal and experiences high SBS efficiency. High-frequency stability is obtained between the recovered carrier tone and the original data signal, enabling high-performance coherent detection without the need of electrical frequency drift compensation. This Letter offers a low complexity, high energy efficiency, and high robust carrier recovery solution.

Dispersion independent long-haul photon-counting optical time-domain reflectometry.

Photon-counting optical time-domain reflectometry (PC-OTDR) based on single photon detection is an effective scheme to attain the high spatial resolution for optical fiber fault monitoring. Currently, due to the spatial resolution of PC-OTDR being proportional to the pulse width of a laser beam, short laser pulses are essential for a high spatial resolution. However, short laser pulses have a large bandwidth, which would be widened by the dispersion of fiber, causing inevitable deterioration in the spatial resolution, especially for long-haul fiber links. In this Letter, we propose a scheme of dispersion independent PC-OTDR based on an infinite backscatter technique. Our experimental results-with more than 45 km long fiber-show that the spatial resolution of the PC-OTDR system is independent with the total dispersion of the fiber under test. Our method provides an avenue for developing long-haul PC-OTDR with high performance.

Wavelength-tunable passively mode-locked all-fiber laser at 1.5 µm.

We have experimentally demonstrated a wavelength-tunable passively mode-locked all-fiber laser at 1.5 µm wavelength by using an erbium-doped fiber amplifier, a fiber-pigtailed semiconductor saturable absorber mirror, and a tunable birefringence Sagnac filter. In our work, by properly setting the polarization state of the propagating light in the birefringence Sagnac filter, the mode-locked lasing wavelength can be continuously tuned from 1544.1 to 1560.8 nm, corresponding to a tuning range of 16.7 nm. At a central wavelength of 1548.5 nm, the fiber laser delivers pulses as short as 713.2 fs with a repetition rate of 4.65 MHz, a 3 dB bandwidth of 5.7 nm, and an average output power of 4.86 mW. Our results show that such a mode-locked all-fiber laser has great potential in applications in nonlinear optics at the 1.5 µm band.

Improvement of the taper degree of laser-drilled holes via a double-pulse train.

Laser drilling has been widely used in various application fields because of advantages such as environmental friendliness, scalability, non-contact, etc. Nevertheless, it still has some drawbacks. One of the most concerning is the taper degree caused by the ablation process resulting from a laser Gaussian beam. In this study, we utilize a nanosecond double-pulse laser (at 532 nm) to experimentally acquire a series of holes on stainless thin plates. With the double-pulse train, the taper degree of a drilled hole becomes half of that drilled by using a single-pulse train. Different combinations of the power component of the two pulses for the double-pulse laser have been investigated to earn the optimum power ratio of the two pulses. For instance, by using a double-pulse laser train with a repetition rate of 5 kHz and a total power of 8 W, we observe that the optimized combination of the two pulses is 2 W and 6 W. Furthermore, we theoretically analyze the variations of the density, temperature, and pressure around the processing area during both the double-pulse and single-pulse laser processing based on a constrained interpolation profile procedure. The theoretical results show that drilled holes with smaller taper degree can be realized by using the double-pulse approach. Our results have great potential in laser drilling and precision laser machining.

Strategic elements of residency training in China: transactional leadership, self-efficacy, and employee-orientation culture.

BACKGROUND: The standardized training of resident physicians in China is significant and robust. During the training, clinical teachers act as leaders. The training taking place in public hospitals requires a transactional leadership style (TLS), but existing research studies seldom analyze how to promote residents' performance from this perspective. METHODS: Two hundred and ninety six new residents undertaking standardized training were recruited from five tertiary hospitals in two provinces of China. Hierarchical moderated and mediated regression analyses were used to test the hypotheses. The hypotheses include that TLS is positively related to the training performance; mediating effect of self-efficacy and moderating effect of employee-orientation organizational culture (EOC) are significant. RESULTS: (1) Two kinds of teachers' TLS, punishment and reward, have significant positive influence on residents' performance. (2) Self-efficacy of residents partly mediates the positive relationship. (3) EOC moderates the relationship between the punitive behavior of clinical teachers with TLS and the self-efficacy of the residents. CONCLUSIONS: Empirical evidence has shown the positive relationship between teachers' TLS and residents' performance outcomes in China. Teachers can enhance training performance by promoting self-efficacy of residents. This study also advances our understanding of EOC by examining the demonstrated moderating effects of cultural background in the relationship between teachers' TLS and the self-efficacy of residents.