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We propose and study a method of optical crosstalk suppression for silicon photomultipliers (SiPMs) using optical filters. We demonstrate that attaching absorptive visible bandpass filters to the SiPM can substantially reduce the optical crosstalk. Measurements suggest that the absorption of near infrared light is important to achieve this suppression. The proposed technique can be easily applied to suppress the optical crosstalk in SiPMs in cases where filtering near infrared light is compatible with the application.Ultratrace molecular detections are vital for precancer diagnosis, forensic analysis, and food safety. Superhydrophobic (SH) surface-enhanced Raman scattering (SERS) sensors are regarded as an ideal approach to improve detection performance by concentrating analyte molecules within a small volume. However, due to the low adhesion of SH surfaces, the analyte droplet is prone to rolling, making it hard to deposit molecules on a predetermined position. Furthermore, the sediment with a very small area on the SH-SERS surface is difficult to be captured even with a Raman microscope. In this study, femtosecond laser fabricated hybrid SH/hydrophobic (SH/HB) surfaces are successfully applied to realize a rapid and highly sensitive SERS detection. By modulating dual surface structures and wetting behaviors, the analyte molecules can be enriched at the edge of HB pattern. This improves the convenience and speed of Raman test. On a hybrid SH/HB SERS substrate with a circular HB pattern at 300-µm-diameter, a femtomolar level (10-14 M) of rhodamine 6G can be detected by using analyte volumes of just 5 µL. The SERS enhancement factor can reach 5.7×108 and a good uniformity with a relative standard deviation of 6.98% is achieved. Our results indicate that the laser fabrication of hybrid SERS sensor offers an efficient and cost-effective approach for ultratrace molecular detection.Athermalisation is a procedure in which the wavelength of a semiconductor laser remains unchanged even as the temperature is altered. This is achieved by altering the currents that flow through the laser so as to maintain the wavelength and avoid mode hops. In this study, we demonstrate that lasers operating with a large red-shift with respect to the gain peak yield the best performance in terms of the highest temperature operation and also in terms of the widest athermal operating range. In particular, a device with red detuning of approximately 25 nm yields the best results. This device is athermalised continuously (without mode hops) from 5 to 106 oC, and discontinuously to 115 oC while maintaining wavelength stability of $pm$0.4 GHz/0.003 nm and side mode suppression ratio of above 40 dB in most of the continuous range and above 30 dB in the discontinuous regime. Operating in this manner will enable semiconductor lasers to be used without a thermoelectric cooler in applications where the temperature changes substantially.We propose and demonstrate using the DIALux software with our proposed linear-regression machine-learning (LRML) algorithm for designing a practical indoor visible light positioning (VLP) system. Experimental results reveal that the average position errors and error distributions of the model trained via the DIALux simulation and trained via the experimental data match with each other. This implies that the training data can be generated in DIALux if the room dimensions and LED luminary parameters are available. The proposed scheme could relieve the burden of training data collection in VLP systems.In this work, we present a packaged whispering gallery mode (WGM) device based on an optical nanoantenna as the coupler and a glass microsphere as the resonator. The microspheres were fabricated from either SiO2 fiber or Er3+-doped fiber, the latter creating a WGM laser with a threshold of 93 µW at 1531 nm. The coupler-resonator WGM device was packaged in a glass capillary. The performance of the packaged microlaser was characterized, with lasing emission both excited in and collected from the WGM cavity via the nanoantenna. The packaged system provides isolation from environmental contamination, a small size, and unidirectional coupling while maintaining a high quality (Q-) factor (∼108).In recent years, sensing and communication applications have fueled important developments of group-IV photonics in the mid-infrared band. In the long-wave range, most platforms are based on germanium, which is transparent up to ∼15-µm wavelength. However, those platforms are limited by the intrinsic losses of complementary materials or require complex fabrication processes. To overcome these limitations, we propose suspended germanium waveguides with a subwavelength metamaterial lateral cladding that simultaneously provides optical confinement and allows structural suspension. These all-germanium waveguides can be fabricated in one dry and one wet etch step. A propagation loss of 5.3 dB/cm is measured at a wavelength of 7.7 µm. These results open the door for the development of integrated devices that can be fabricated in a simple manner and can potentially cover the mid-infrared band up to ∼15 µm.Passive daytime radiative cooling has recently become an attractive approach to address the global energy demand associated with modern refrigeration technologies. One technique to increase the radiative cooling performance is to engineer the surface of a polar dielectric material to enhance its emittance at wavelengths in the atmospheric infrared transparency window (8-13 µm) by outcoupling surface-phonon polaritons (SPhPs) into free-space. click here Here we present a theoretical investigation of new surface morphologies based upon self-assembled silica photonic crystals (PCs) using an in-house built rigorous coupled-wave analysis (RCWA) code. Simulations predict that silica micro-sphere PCs can reach up to 73 K below ambient temperature, when solar absorption and conductive/convective losses can be neglected. Micro-shell structures are studied to explore the direct outcoupling of the SPhP, resulting in near-unity emittance between 8 and 10 µm. Additionally, the effect of material composition is explored by simulating soda-lime glass micro-shells, which, in turn, exhibit a temperature reduction of 61 K below ambient temperature. The RCWA code was compared to FTIR measurements of silica micro-spheres, self-assembled on microscope slides.The transition dipole moment (TDM) orientation in the emission layer (EML) of organic light-emitting diodes (OLEDs) have attracted increasing attention from many researchers. But the study point at the molecular orientation in the hole transport layer (HTL) and electron transport layer (ETL) was not reported widely. In this paper, the molecular orientation of HTLs and ETLs were controlled by the deposition rate. The angle-dependent PL spectra and the variable angle spectroscopic ellipsometry (VASE) were used for evaluating the molecular orientation of B3PYMPM and TAPC, respectively. We found that fast deposition rate can boost preferentially vertical molecular orientation in both molecules and facilitate the hole and electron mobility, which was tested by the current density-voltage and capacitance-voltage curves of HODs and EODs. Moreover, the HTLs and ETLs were employed in OLED devices to verify the influence of molecular orientation on charge carrier mobility, which determined the performance of OLEDs significantly.Owing to the increasing demand for information transmission, the information capacity of free-space optical communications must be increased without being significantly affected by turbulence. Herein, based on a radially-polarized vector field array, analytical formulae for three parameters are derived average intensity, degree of polarization, and local states of polarization (SoPs). Propagation properties varying with propagation distance, strength of turbulence, beam waist, and beamlet number are investigated. In particular, the results show that the sign of local SoPs on different receiver planes is consistent with that of the source field, and that the SoPs remain constant at specific locations as the propagation distance increases; hence, the effect of turbulence on local SoPs is slight. Meanwhile, three different SoPs, i.e., linear, right-handed, and left-handed rotation polarizations, appear at corresponding locations, thereby enabling the channel capacity to be increased. This study may not only provide a theoretical basis for vector beam array propagation in a turbulent environment, but also propose a feasible solution for increasing the channel capacity and reliability to overcome challenges in a free-space link. Additionally, this study may benefit potential applications in laser lidar and remote sensing.This paper proposes optical carrier microwave interferometry (OCMI)-based optical fiber interferometers for sensing applications with improved measurement sensitivity with the assistance of the Vernier effect. Fabry-Perot interferometers (FPIs) are employed in the proof of concept. A single-FPI-OCMI system is first demonstrated for measurements of variations of temperatures by tracking the spectral shift of the interferogram in microwave domain. By cascading two FPIs with slightly different optical lengths, the Vernier effect is generated in the magnitude spectrum of the system with a typical amplitude-modulated signal. By tracking the shift of the envelope signal, temperature measurements are experimentally demonstrated with greatly enhanced sensitivity. The amplification factor for the measurement sensitivity can be easily adjusted by varying the length ratio of the two cascaded FPIs. In addition to the experimental demonstration, a complete mathematical model of the FPI-OCMI system and the mechanism for the amplified sensitivity due to Vernier effect is presented. Numerical calculations are also performed to verify the analytical derivations.The description of deformable mirror (DM) surface, which is usually a complex freeform surface, affects the measurement speed and accuracy in a real-time interferometric measurement system with a DM as the dynamic compensator. We propose an accurate and fast description method with automatically configurable Gaussian radial basis function. The distribution and shape factors of GRBFs are related to the complexity of the surface with sufficient flexibility to improve the accuracy, and the fitting results are automatically obtained using a traversal optimization algorithm, which can improve the fitting speed by reducing the number of time-consuming calculations. The feasibility is verified by numerical and practical experiment.We use a model to investigate both the temporal and spectral characteristics of a signal lightwave which has been spectrally broadened through phase modulation with a maximal-length sequence (MLS), which is a common type of pseudo-random bit sequence. The enhancement of the stimulated Brillouin scattering (SBS) threshold of the modulated lightwave in a fiber system is evaluated by numerically simulating the coupled three-wave SBS interaction equations. We find that SBS can build up on a nanosecond-level time scale in a short fiber, which can reduce the SBS suppressing capability of MLS modulation waveforms with GHz-level clock rate, if the sub-sequence ("run") lengths with the same symbol (zero or one) of the MLS extend over several nanoseconds. To ensure the SBS buildup is perturbed and thus suppressed also during these long sub-sequences, we introduce a low-pass filter to average the signal over several bits so that the modulation waveform changes gradually even during long runs and amplify the RF modulation waveforms to the level required for sufficient spectral broadening and carrier suppression of the optical signal.
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