Highly confining waveguides (Δne>0.1) without a degraded nonlinear coefficient and low propagation losses have been fabricated in lithium niobate (LN) by a new process that we called high vacuum vapor-phase proton exchange (HiVac-VPE). Index contrast, index profile, nonlinearity, and crystallographic phases are carefully investigated. Original analysis of index profiles indicates that the waveguides contain sub-layers whose depths depend on the exchange durations. Propagation behavior, propagation losses, and second-harmonic generation response of HiVac-VPE channel waveguides are investigated at telecom wavelength. The results recommend HiVac-VPE as a very promising technique for fabricating efficient nonlinear photonic integrated circuits in LN crystals.

The famous demonstration of optical rogue waves (RWs), a powerful tool to reveal the fundamental physics in different laser scenarios, opened a flourishing time for temporal statistics. Random fiber laser (RFL) has likewise attracted wide attention due to its great potential in multidisciplinary demonstrations and promising applications. However, owing to the distinctive cavity-free structure, it is a scientific challenge to achieve temporal localized RWs in RFLs, whose feedback arises from multiple scattering in disordered medium. Here, we report the exploration of RW in the highly skewed, transient intensity of an incoherently pumped RFL for the first time, to our knowledge, and unfold the involved kinetics successfully. The corresponding frequency domain measurements demonstrate that the RW event arises from a crucial sustained stimulated Brillouin scattering process with intrinsic stochastic nature. This investigation highlights a novel path to fully understanding the complex physics, such as photon propagation and localization, in disordered media.

We demonstrate for the first time to our knowledge the use of Fe3O4 nanoparticles for Q-switching a tunable mid-infrared (Mid-IR) Dy3+-doped ZBLAN fiber laser around 3 μm. The Q-switcher was fabricated by depositing the prepared Fe3O4 nanoparticles solution onto an Au mirror. Its nonlinear optical response was characterized using a mode locked Ho3+/Pr3+-codoped ZBLAN fiber laser at 2.87 μm, and showed a modulation depth of 11.9% as well as a saturation intensity of 1.44 MW/cm2. Inserting the device into a tunable Dy3+-doped ZBLAN fiber laser, stable Q-switched pulses within the tunable range of 2812.4–3031.6 nm were obtained. When tuning the wavelength to 2931.2 nm, a maximum Q-switching output power of 111.0 mW was achieved with a repetition rate of 123.0 kHz and a pulse width of 1.25 μs. The corresponding pulse energy was 0.90 μJ. This demonstration suggests that Fe3O4 nanoparticles are a promising broadband saturable absorption material for mid-infrared operation.

Metasurfaces have been used to realize optical functions such as focusing and beam steering. They use subwavelength nanostructures to control the local amplitude and phase of light. Here we show that such control could also enable a new function of artificial neural inference. We demonstrate that metasurfaces can directly recognize objects by focusing light from an object to different spatial locations that correspond to the class of the object.

The mid-infrared spectrum can be recorded from almost any material, making mid-infrared spectroscopy an extremely important and widely used sample characterization and analysis technique. However, sensitive photoconductive detectors operate primarily in the near-infrared (NIR), but not in the mid-infrared, making the NIR more favorable for accurate spectral analysis. Although the absorption cross section of vibrational modes in the NIR is orders of magnitude smaller compared to the fundamental vibrations in the mid-infrared, different concepts have been proposed to increase the detectability of weak molecular transitions overtones. Yet, the contribution of magnetophotonic structures in the NIR absorption effect has never been explored so far. Here we propose high-Q magnetophotonic structures for a supersensitive detection of weak absorption resonances in the NIR. We analyze the contributions of both magnetic and nonmagnetic photonic crystal configurations to the detection of weak molecular transitions overtones. Our results constitute an important step towards the development of highly sensitive spectroscopic tools based on high-Q magnetophotonic sensors.

A multifunctional photo-thermal therapeutic nano-platform Y2O3: Nd3+/Yb3+/Er3+@SiO2@Cu2S (YR-Si-Cu2S) was designed through a core–shell structure, expressing the function of bio-tissue imaging, real-time temperature detection, and photo-thermal therapy under 808 nm light excitation. In this system, the core Y2O3: Nd3+/Yb3+/Er3+ (YR) takes the responsibility of emitting optical information and monitoring temperature, while the shell Cu2S nano-particles carry most of the photo-thermal conversion function. The temperature sensing characteristic was achieved by the fluorescence intensity ratio using the thermally coupled energy levels (TCLs) S3/24/H211/2 of Er3+, and its higher accuracy for real-time temperature measurement in the bio-tissue than that of an infrared thermal camera was also proved by sub-tissue experiments. Furthermore, the photo-thermal effect of the present nano-system Y2O3: Nd3+/Yb3+/Er3+@SiO2@Cu2S was confirmed by Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) ablation. Results indicate that YR-Si-Cu2S has application prospect in temperature-controlled photo-thermal treatment and imaging in bio-tissues.

Bipolar phototransistors have higher optical responsivity than photodiodes and play an important role in the field of photoelectric conversion. Two-dimensional materials offer a good optical responsivity and have the potential advantages of heterogeneous integration, but mass-production is difficult. In this study, a bipolar phototransistor is presented based on a vertical Au/graphene/MoS2 van der Waals heterojunction that can be mass-produced with a silicon semiconductor process using a simple photolithography process. Au is used as the emitter, which is a functional material used not just for the electrodes, MoS2 is used for the collector, and graphene in used for the base of the bipolar phototransistor. In the bipolar phototransistor, the electric field of the dipole formed by the Au and graphene contact is in the same direction as the external electric field and thus enhances the photocurrent, and a maximum photocurrent gain of 18 is demonstrated. A mechanism for enhancing the photocurrent of the graphene/MoS2 photodiode by contacting Au with graphene is also described. Additionally, the maximum responsivity is calculated to be 16,458 A/W, and the generation speed of the photocurrent is 1.48×10?4 A/s.

We present, to the best of our knowledge, the first implementation of full-field quantum optical coherence tomography (FF-QOCT). In our system, we are able to obtain full three-dimensional (3D) information about the internal structure of a sample under study by relying on transversely resolved Hong–Ou–Mandel (HOM) interferometry with the help of an intensified CCD (ICCD) camera. Our system requires a single axial scan, obtaining full-field transverse single-photon intensity in coincidence with the detection of the sibling photon for each value of the signal-idler temporal delay. We believe that this capability constitutes a significant step forward toward the implementation of QOCT as a practical biomedical imaging technique.

Diverse ultrafast dynamics have been reported on different graphene prepared by different methods. Chemical-vapor-deposited (CVD) growth is regarded as a very promising method for highly efficient production of graphene. However, CVD-grown graphene usually presents only one of the diverse ultrafast dynamics. Thus, control of the ultrafast photo-electronic dynamics of CVD-grown graphene is vital to present the diversity for different photodetection applications of CVD-grown graphene. In this paper, we report on the first realization to our knowledge of control of the ultrafast dynamics of CVD-grown graphene and the manifestation of diverse ultrafast dynamics on sole CVD-grown graphene. We study the ultrafast photoelectronic dynamics of CVD-grown graphene with different degrees of oxidation caused by ozone oxidation using femtosecond time-resolved transient differential transmission spectroscopy, and we find that the ultrafast dynamics can evolve obviously with the time of ozone oxidation. The diverse ultrafast dynamics reported previously on different monolayer graphenes prepared by different methods are achieved on the sole CVD-grown graphene by controlling oxidation time. The mechanism for manipulation of the ultrafast dynamics by ozone oxidation is revealed by Raman spectroscopy as the control of the Fermi level of CVD-grown graphene. Simulations of dynamics based on the optical conductivity model of graphene and Fermi level change well reproduce the observed diverse ultrafast dynamics. Our results are very important for the diverse applications of graphene and open a new path toward the diverse ultrafast dynamics on the sole graphene prepared by any method.

While the performance of mode-locked fiber lasers has been improved significantly, the limited gain bandwidth restricts them from generating ultrashort pulses approaching a few cycles or even shorter. Here we present a novel method to achieve few-cycle pulses (～5 cycles) with an ultrabroad spectrum (～400 nm at ?20 dB) from a Mamyshev oscillator configuration by inserting a highly nonlinear photonic crystal fiber and a dispersion delay line into the cavity. A dramatic intracavity spectral broadening can be stabilized by the unique nonlinear processes of a self-similar evolution as a nonlinear attractor in the gain fiber and a “perfect” saturable absorber action of the Mamyshev oscillator. To the best of our knowledge, this is the shortest pulse width and broadest spectrum directly generated from a fiber laser.

The year 2019 marks the 10th anniversary of the first report of ultrafast fiber laser mode-locked by graphene. This result has had an important impact on ultrafast laser optics and continues to offer new horizons. Herein, we mainly review the linear and nonlinear photonic properties of two-dimensional (2D) materials, as well as their nonlinear applications in efficient passive mode-locking devices and ultrafast fiber lasers. Initial works and significant progress in this field, as well as new insights and challenges of 2D materials for ultrafast fiber lasers, are reviewed and analyzed.

The collective oscillation of electrons located in the conduction band of metal nanostructures being still energized, with the energy up to the bulk plasmon frequency, are called nonequilibrium hot electrons. It can lead to the state-filling effect in the energy band of the neighboring semiconductor. Here, we report on the incandescent-type light source composed of Au nanorods decorated with single Ga-doped ZnO microwire (AuNRs@ZnO:Ga MW). Benefiting from Au nanorods with controlled aspect ratio, wavelength-tunable incandescent-type lighting was achieved, with the dominating emission peaks tuning from visible to near-infrared spectral regions. The intrinsic mechanism was found that tunable nonequilibrium distribution of hot electrons in ZnO:Ga MW, injected from Au nanorods, can be responsible for the tuning emission features. Apart from the modification over the composition, bandgap engineering, doping level, etc., the realization of electrically driving the generation and injection of nonequilibrium hot electrons from single ZnO:Ga MW with Au nanostructure coating may provide a promising platform to construct electronics and optoelectronics devices, such as electric spasers and hot-carrier-induced tunneling diodes.