Qi Sun

In this Letter, we present a compact scattering spectrometer system based on fluorosilicate glass ceramics. By the algorithmic spectral calibration and reconstruction, we achieve wavelength detection with a resolution of 0.1 nm. Numerous nanocrystals embedded in the glass host in the glass ceramics result in a significant natural multilayer scattering medium, which can provide a 60% scattering efficiency for incident light while increasing the optical path of incident light transmitting in the medium. The glass ceramics scattering medium with a rather compact physical size is integrated with a low-cost camera to compose an optical spectral system, which has potential application in lab-on-a-chip optical spectroscopy.

Random scattering of light in disordered media can be used for highly sensitive speckle-based wavemeters and spectrometers. However, the multiple scattering events that fold long optical paths within a compact space also make such devices exceedingly sensitive to vibrations and small disturbances to the disordered media. Here, we show how scattering can be engineered so that it can be used for a compact computational spectrometer that is largely insensitive to environmental factors. We designed and fabricated a three-dimensional pseudo-random nano-void pattern with 62% scattering efficiency. The controlled amount of multiple scattering ensured a sufficiently long optical path for the target resolution of 100 pm, with optimal long-term stability. The 200-μm-thick scattering silica substrate was integrated in a compact assembly with a low-cost camera sensor. The target resolution was achieved for full spectrum measurements while single wavelengths could be determined with 50 pm resolution. Such tailored scattering systems can improve the trade-off among cost, size, stability, and spectral resolution in computational spectrometers.

With the continuous increase of the amount of power grid data, the traditional method is to remotely transmit data to the cloud for equipment fault classification and detection. When a fault occurs on the equipment side, it is often unable to respond and deal with it in time, which brings security risks to power grid equipment. The current variable selection research on network connectivity data is mainly aimed at homogeneous samples, that is, the individual effects α of the samples are the same, but in reality, the individual effects of most samples are heterogeneous, without considering the heterogeneity. will cause a large deviation in the estimation and prediction of the model. Therefore, when there is group heterogeneity in the individual effect in the network data, this paper proposes a new variable selection method. Using the network cohesion effect, we analyze the variable coefficients and connected sample individuals At the same time, the isolated forest algorithm is used to solve the problem, and the convergence of the algorithm is proved. Numerical simulation and empirical analysis show that our method improves the accuracy of variable selection and reduces the prediction error.

Laser irradiation of silica glass is shown to trigger redistribution of material resulting in accumulation of stress and refractive index modification, and the rearrangement of the glass network has a significant impact on the quality of laser written optical components. We propose an alternative laser writing approach for achieving the desired refractive index and optical phase profiles through improved material stress control, demonstrated using both Gaussian and Bessel writing beams. The new material processing strategy is successfully adapted for implementing photonic circuits and diffractive elements with greater efficiency due to improved uniformity and symmetry of the induced index modification.

The influence of nonlinear phase modulations on third-harmonic (TH) conversion in silica microfibers is experimentally demonstrated. By utilizing such influence, enhanced narrow-bandwidth ultraviolet TH is generated at a high signal-to-noise ratio (33 dB) and an average power of several hundred nanowatts. Detailed trends of TH power against input pump power were characterized with peak pump power up to 2.5 kW, and the results agree with predicted features, confirming that harmonic output could be optimized with adaptive control of the phase mismatch.

While recent advances in femtosecond writing have allowed rapid and flexible realization of lab-on-chip and integrated optics systems in various media, miniaturisation of such fs-written waveguide architectures remains hampered by high bend loss α b . Despite efforts to reduce bend loss, e.g. by annealing the waveguides [1] or writing stress structures [2], the minimum bend radius at telecommunications wavelengths remains large (> 16mm) in silica [1]. To overcome this, we demonstrate a novel bend loss reduction method by inducing stress to fabricate a microcrack on the outer bend edge of the waveguide. The large index difference at the core-microcrack interface (1.45 vs 1.0) enhances modal confinement and inhibits radiation loss. Laser induced stress cracking is often used for dicing glass sheets with excellent smoothness (roughness < 30nm) [3]; hence such cracks will not exacerbate scattering losses when integrated alongside a waveguide.

The femtosecond laser writing technique has been widely exploited for transparent materials processing. One of the useful features following laser irradiation is refractive index modification. The sign of refractive index change depends on irradiation conditions. Negative refractive index change can be 10 ⁻² , but it is accompanied with strong optical scattering. The laser induced positive refractive index change is about 10 ⁻³ . For diffractive optics this is relatively small change and thus requires to modify a large physical thickness for inducing a significant optical phase delay. This can be achieved with Bessel beams [1]. However, an extended Bessel zone leads to higher stress around the laser affected zone, which can induce structural cracks with a high energy deposition level [2]. The large stressed region also distorts subsequent writing pulses which detriments the overall uniformity of the inscribed structure limiting the performance of the written diffractive element. Here, we report a method for controlling stress accumulated during the inscription with a femtosecond Bessel beam inside silica, and demonstrate its benefits for improving structural uniformity and preventing crack formation.

A 3-layer Fresnel lens with 52% diffraction efficiency was inscribed with a femtosecond Bessel beam in silica, with each layer being ~80 μm. An anomalous dispersion property was characterized with an RGB LED source.