A convenient and versatile scheme to generate continuously adjustable cylindrical vector (CV) and vortex beams by multiplexing and cascading passive vortex half-wave plates (VHPs) is proposed. (−24)–24 order CV or vortex beams are generated only based on VHPs with m = 1, 3, and 8. The coaxial and small-angle interference are introduced to detect orders. For coaxial interference of $l_1$-order and $l_2$-order vortex beams, the intensity distribution is spirally fan shaped. The partition number is N = |$l_2$− $l_1$|, and the spiral direction can distinguish the sign of topological charge with higher value. Fork-shaped fringes appear in the center for small-angle interference between vortex beams with incident angle ${\beta }_1$ and ${\beta }_2$. The forking number between two fringes meets N = |$l_2$− $l_1$|, and the forks face upward when ($l_2$− $l_1$)(${\beta }_2$− ${\beta }_1$) < 0, and face downward when ($l_2$− $l_1$)(${\beta }_2$− ${\beta }_1$) > 0. Particularly, when one of the beams is a Gaussian beam, such as $l_1$ = 0, the value and sign of the topological charge $l_2$ can be directly detected. And for the interference between CV and Gaussian plane beams, the partition number N is positively correlated with the polarization order P, with N = |P| or N = 2|P| for coaxial or small-angle interference, respectively, and corresponding sign can be identified by the polarization azimuth distributions measured by Stokes parameters. It is experimentally demonstrated that the proposed scheme can effectively generate continuously adjustable CV and vortex beams by programming limited VHPs, greatly expanding order numbers with low cost, low energy consumption, and high utilization, and the coaxial and small-angle interference method can conveniently detect the corresponding orders without borrowing redundant devices.

We design a novel slow-light silicon photonic crystal waveguide which can operate over an extremely wide flat band for ultrafast integrated nonlinear photonics. By conveniently adjusting the radii and positions of the second air-holes rows, a flat slow-light low-dispersion band of 50 nm is achieved numerically. Such a slow-light photonic crystal waveguide with large flat low-dispersion wideband will pave the way for governing the femtosecond pulses in integrated nonlinear photonic platforms based on CMOS technology.

Strictly uniform time interval between adjacent channels is a crucial requirement for the multi-wavelength interleaved (MWI) pulse sources, which difficult alignment can be easily solved by what we believe to be our novel method based on frequency-resolved optical gating (FROG). By utilizing highly precise measurements from FROG, which provide fully two-dimensional information of the pulses in time and frequency domain, we can intuitively identify the time mismatches between different channels in the MWI pulse sources. This enables us to directly align the timing of each channel with sub-picosecond resolution at the first time. MWI pulse sources with total repetition rate of 20.8 GHz (four wavelengths) and 41.6 GHz (eight wavelengths) are precisely aligned by the proposed method, this achievement will pave the way for advancements in photonic analog-digital converters (PADC), high-speed optical communications and so on.

The effects of optical sampling pulse power, RF power, and electronic back-end bandwidth on the performance of time- and wavelength-interleaved photonic analog-to-digital converter (PADC) with eight-channel 41.6 GHz pulses have been experimentally investigated in detail. The effective number of bits (ENOB) and peak-to-peak voltage (V_pp) of converted 10.6 GHz electrical signals were used to characterize the effects. For the 1550.116 nm channel with 5.2 G samples per second, an average pulse power of 0 to −10 dBm input to the photoelectric detector (PD) has been tested. The V_pp increased with increasing pulse power. And the ENOB for pulse power −9~−3 dBm was almost the same and all were greater than four. Meanwhile, the ENOB decreased either when the pulse power was more than −2 dBm due to the saturation of PD or when the pulse power was less than −10 dBm due to the non-ignorable noise relative to the converted weak signal. In addition, RF powers of −10~15 dBm were loaded into the Mach–Zehnder modulator (MZM). The V_pp increased with the increase in RF power, and the ENOB also showed an increasing trend. However, higher RF power can saturate the PD and induce greater nonlinearity in MZM, leading to a decrease in ENOB, while lower RF power will convert weak electrical signals with more noise, also resulting in lower ENOB. In addition, the back-end bandwidths of 0.2~8 GHz were studied in the experiments. The V_pp decreased as the back-end bandwidth decreased from 8 to 3 GHz, and remained nearly constant for the bandwidth between the Nyquist bandwidth and the subsampled RF signal frequency. The ENOB was almost the same and all greater than four for a bandwidth from 3 to 8 GHz, and gradually increased up to 6.5 as the back-end bandwidth decreased from the Nyquist bandwidth to 0.25 GHz. A bandwidth slightly larger than the Nyquist bandwidth was recommended for low costs and without compromising performance. In our experiment, the −3 to −5 dBm average pulse power, about 10 dBm RF power, and 3 GHz back-end bandwidth were recommended to accomplish both a high ENOB more than four and large V_pp. Our research provides a solution for selecting optical sampling pulse power, RF power, and electronic back-end bandwidth to achieve low-cost and high-performance PADC.

We designed a tellurite microstructure fiber (TMF) and proposed a broadband optical frequency comb generation scheme that was based on electro-optical modulation and cascaded sign-alternated dispersion TMF (CSAD-TMF). In addition, the influence of different nonlinear effects, the ultrashort pulse evolution in the CSAD-TMF with the anomalous dispersion (AD) zones and the normal dispersion (ND) zones were analyzed based on the generalized nonlinear Schrodinger equations (GNLSE) modelling. According to the simulations, when the input seed comb had a repetition rate of 20 GHz and had an input pulse peak power of 30 W, the generation scheme could generate optical frequency combs with a 6 dB spectral bandwidth spanning over 170 nm centered at 1550 nm. Furthermore, the generated combs showed good coherence in performance over the whole 6 dB spectral bandwidth. The highly coherent optical frequency combs can be used as high-repetition-rate, multi-wavelength light sources for various integrated microwave photonics and ultrafast optical signal processing applications.

The heat fluxes on the lower outer divertor plate were calculated using the DFLUX code with the surface temperature measured by the IR camera on the experimental advanced superconducting tokamak. The analyzed discharges were lower single-null divertor configuration discharges with different auxiliary heating: lower hybrid wave current drive (LHCD) combined with neutral beam injection (NBI) and LHCD combined with ion cyclotron resonant heating (ICRH). The surface temperature of the lower outer divertor target plate was about 170 °C in the LHCD + NBI H-mode, with the high temperature mostly distributed in the location near the joint of the dome and the outer target plate. The temperature increased as the NBI was turned on and fluctuated due to edge localized modes (ELMs). The heat flux reached nearly 4 MW/m ² when ELMs appeared and declined to less than 1 MW/m ² when the NBI was turned off. Temperature distribution with extreme toroidal asymmetry was observed in the selected LHCD + ICRH H-mode discharge. The surface temperature on the lower outer divertor target plate was up to 220 °C in one region with broader temperature distribution. During the LHCD + ICRH H-mode, the peak heat flux was not seen during the period of ICRH injection, though a brief spike in heat flux was observed at the beginning of the ICRH injection. The full-width at half-maximum of the heat flux profile as a function of divertor target plate location of the LHCD + ICRH H-mode is three times that of the LHCD + NBI H-mode.