Search

Silica microspheres have been demonstrated as the optical micro-cavity for laser generation based on whispering-gallery modes (WGM). They can achieve a high-quality factor (Q) within a tiny volume. Traditionally, complex processes are needed to process a coating containing photoluminescent elements, with enough thickness and uniformity, for laser generation. We developed a novel sol-gel fabrication method of Er3+/Yb3+doped silica microspheres with a homogeneous doping concentration over the entire microsphere volume. The sol-gel precursors were doped with 1–2 mol% Er3+ and/or Yb3+. The viscosity of the precursor was controlled at around 4000 cP, and gel fibers can be conveniently drawn from the precursor. After firing at 1000 °C for 1 h, transparent fibers with diameters of 40–180 µm were obtained. The fiber tips were quickly melted into microspheres using a CO2 laser. The diameters of microspheres were determined by the fiber diameter and laser parameters, such as laser power and irradiation time duration. Typically, the microspheres had diameters between 90 to 160 µm. The emission spectrum under 357 nm and 527 nm excitation showed characteristic Er3+ emission peaks, that match the literature well. The UV-VIS spectra confirm the photoluminescence results and showed both Er3+ and Yb3+ characteristic absorptions. The optical behaviors of the microspheres indicate that the Er3+ and Yb3+ were well dispersed in the silica matrix and the microspheres had typical optical activities of Er3+/Yb3+ glasses. Highlights: Silica microspheres, fabricated using laser melting, with homogeneously doped Er3+/Yb3+. No need for multiple layers of Er3+/Yb3+ sol-gel coatings. Microspheres demonstrated strong optical activities with Er3+/Yb3+ doping. [ABSTRACT FROM AUTHOR]

Happiness plays an important role in human emotion and one’s growth. In this paper, we use the data from the World Happiness Report, Countries of the World, and Countries Dataset 2020 to discern the relationship the happiness score has with the economy, family, health, freedom, trust, perception of corruption, generosity, and residual. In our research, we used the regression approach to find the most important factors that affect the happiness score in the past five years. Since we observed a positive and moderate relationship between the residual and happiness score, we then looked for other factors that contribute to the residual, the unexplained factor. Finally, we verified the main factors to the happiness score.

An optical approach to implement radio-frequency (RF) self-interference cancellation using an integrated dual-parallel Mach–Zehnder modulator (DP-MZM) is proposed and demonstrated experimentally. The received signals and the reference signal are converted into optical domain via the sub-MZMs (MZM1 and MZM2) in the DP-MZM, which are biased at the quadrature point and the minimum point with the output of double sideband with carrier signal and double sideband with carrier-suppressed signal, respectively. It avoids the optical interference at the combining Y branch waveguide. The time and the amplitude matching conditions for cancellation between the reference signal and the interference signal are completed by the electrical tunable time delay line and the phase shifter in the MZM2 path. A cancellation depth larger than 80 dB is obtained for the single-frequency signal of 2.4, 5, 8, and 10 GHz. For the bandwidth of 100 MHz, cancellation depths as high as 35.8, 33.1, and 38.3 dB are realized at frequencies of 2.4, 5, 8, and 10 GHz, respectively. [ABSTRACT FROM PUBLISHER]

Self-homodyne detection (SHD) is a promising approach to realize high-capacity short-reach optical transmission systems with low cost and low power consumption. We experimentally demonstrate single-carrier net 800-Gb/s SHD transmission with low-cost ∼MHz linewidth distributed feedback (DFB) laser over 2 km, 10 km, 25 km, and 40 km single-mode fiber (SMF) using three different quadrature amplitude modulation (QAM) formats, including 80-Gbaud dual-polarization (DP) 64QAM, 100-Gbaud DP-32QAM, and 120-Gbaud DP-16QAM. Among them, net 800-Gb/s DP-64QAM SHD transmission over 25 km SMF using an uncooled DFB laser with a linewidth of 2.6 MHz is experimentally verified. The detailed experimental performance evaluation of net 800Gb/s SHD system is performed, in which various configurations are considered, such as different laser linewidths, three QAM formats, and different transmission distances. DFB lasers with linewidths of 1 MHz and 2.6 MHz lead to negligible penalty when compared to the same SHD system but using an external cavity laser (ECL) with a linewidth of 26kHz in back-to-back (BTB) case. 80-Gbaud DP-64QAM obtains the highest optical signal-to-noise ratio (OSNR) requirement and the highest bit-error rate (BER) floor but the best tolerance of chromatic dispersion (CD). 120-Gbaud DP-16QAM achieves the lowest OSNR requirement and the lowest BER floor but the worst tolerance of CD. The detailed experimental investigation is conducive to promote the practical application of SHD in different short-reach scenarios.