Nitrogen-vacancy (NV) centers in diamond are progressively favored for room-temperature magnetic field measurement. The signal to noise ratio (SNR) optimization for NV diamond magnetometry generally concentrates on signal amplitude enhancement rather than efficient noise processing. Here, we report a compound filter system combining a wavelet denoising method and an adaptive filter for the realization of an efficient weak magnetic measurement with a high SNR. It allows enhanced magnetic field measurement with an average SNR enhancement of 17.80 dB at 50 nT within 500 mHz to 100 Hz and 14.76 dB at 500 mHz within 50 nT to 1100 nT. The introduction of this system in NV diamond magnetometry is aimed to improve signal quality by effectively eliminating the noise and retaining ideal signals.

Fluorescence detection is widely used in biology and medicine, while the realization of on-chip fluorescence detection is vital for the portable and point-of-care test (POCT) application. In this Letter, we propose an efficient fluorescence excitation and collection system using an integrated GaN chip consisting of a slot waveguide and a one-dimensional photonic crystal (1D PC) waveguide. The slot waveguide is used to confine the excitation light for intense light–sample interaction, and the one-trip collection efficiency at the end of slot waveguide is up to 14.65%. More interestingly, due to the introduction of the 1D PC waveguide, the fluorescence signal is directly filtered out, and the excitation light is reflected to the slot waveguide for multiple excitations. Its transmittances for the designed exciting wavelength of 520 nm and the fluorescent wavelength of 612 nm are 0.2% and 85.4%, respectively. Finally, based on numerical analysis, the total fluorescence collection efficiency in our system amounts to 15.93%. It is the first time, to our knowledge, that the concept of an all-in-one-chip fluorescence detection system has been proposed, which paves the way for on-chip fluorescence excitation and collection, and may find potential applications of miniaturized and portable devices for biomedical fluorescence detection.

We propose a method for reconstructing non-diffuse surfaces based on the π-phase-shifted two-plus-one phase-shifting method. First, we introduce a 2f_H + a + 2f_M + 2f_L method for unwrapped phase extraction. Subsequently, we introduce a new set of π-phase-shifted 2f_H + a/2 + 2f_M + 2f_L fringe patterns with halved background intensity. The saturated pixels will be replaced with the unsaturated pixels in the π-phase-shifted fringe patterns. Finally, we analyze eight fringe replacement cases and give the corresponding phase calculation, and further give the general formulas. Experiments confirm that the sum of the phase error of the proposed method is 81.4% lower than that of the traditional method, and 61.5% lower than that of the adaptive fringe projection method.

In this Letter, we propose a simple structure of an orthogonal type double Michelson interferometer. The orthogonal detection method overcomes the problems of uneven ranging sensitivity and the inability of traditional interferometers to determine the displacement direction. The displacement measurement principle and signal processing method of the orthogonal double interferometer are studied. Unlike the arctangent algorithm, the displacement analysis uses the arc cosine algorithm, avoiding any pole limit in the distance analysis process. The minimum step size of the final experimental displacement system is 5 nm, which exhibits good repeatability, and the average error is less than 0.12 nm.

Aiming at coherence degradation during target detection, a suppressing method based on frequency-modulated continuous wave coherent lidar is proposed. Combined with a random iteration algorithm, a long-pulse echo signal with coherent degradation is matched with random phase noise of a certain frequency and achieves coherence restoration. Simulation and field experiment results show that this proposed method can recover the intrapulse coherence in long-pulse echo signals. In addition, for the real target echo signal at 4.2 and 19.8 km, the peak signal-to-noise ratio processed by this method is increased by 0.35 times and 4 times after pulse compression, respectively.

Overlay (OVL) for patterns placed at two different layers during microchip production is a key parameter that controls the manufacturing process. The tolerance of OVL metrology for the latest microchip needs to be at nanometer scale. This paper discusses the influence on the accuracy and sensitivity of diffraction-based overlay (DBO) after developing inspection and after etching inspection by the asymmetrical deformation of the OVL mark induced by chemical mechanical polishing or etching. We show that the accuracy and sensitivity of DBO metrology can be significantly improved by matching the measuring light wavelength to the thickness between layers and by collecting high-order diffraction signals, promising a solution for future OVL metrology equipment.

In the femtosecond two-photon polymerization (2PP) experimental system, optical aberrations degrade the fabrication quality. To solve this issue, a multichannel interferometric wavefront sensing technique is adopted in the adaptive laser processing system with a single phase-only spatial light modulator. 2PP fabrications using corrected high-order Bessel beams with the above solution have been conducted, and high-quality microstructure arrays of microtubes with 20 µm diameter have been rapidly manufactured. The effectiveness of the proposed scheme is demonstrated by comparing the beam intensity distributions and 2PP results before and after aberration corrections.

Modulation of a vector light field has played an important role in the research of nanophotonics. However, it is still a great challenge to accurately measure the three-dimensional vector distribution at nanoscale. Here, based on the interaction between the light field and atomic-sized nitrogen-vacancy (NV) color center in diamonds, we demonstrate an efficient method for vectorial mapping of the light-field distribution at nanoscale. Single NV centers with different but well-defined symmetry axes are selected and then interact with the same tightly focused light field. The excitation of a single NV center is related to the angle between the NV center axis and the polarization of the light field. Then the fluorescence patterns of different NV centers provide the information on the vectorial light field distribution. Subsequently analyzing the fluorescence patterns with the help of a deep neural network, the intensity and phase of the light-field vectorial components are fully reconstructed with nanometer resolution. The experimental results are in agreement with theoretical calculations. It demonstrates that our method can help to study light–matter interaction at nanoscale and extend the application of vector light fields in research on nanophotonics.

We proposed and experimentally demonstrated an all-fiber sensor for measuring bend with high sensitivity based on a ring core fiber (RCF) modal interferometer. The sensor was fabricated by splicing a segment of RCF between two pieces of multimode fiber (MMF) and single-mode fiber (SMF) at the ends of the MMF as lead-in and lead-out. Due to the first segment of the MMF, the transmitted light is coupled into the ring core, silica center, and cladding of the RCF, exciting multiple modes in the RCF. By the modal interferences in the structure, bending sensing can be realized by interrogating the intensity of the interference dip. Experimental results show a high bending sensitivity of -25.63dB/m-1 in the range of 1.0954m-1 to 1.4696m-1. In addition, the advantages of the bend sensor, such as small size, low temperature sensitivity, and simple fabrication process, can be used for curvature measurement in building health monitoring.

Usually, a multilens optical system is composed of multiple undetectable sublenses. Wavefront of a multilens optical system cannot be measured when classical transmitted phase measuring deflectometry (PMD) is used. In this study, a wavefront measuring method for an optical system with multiple optics is presented based on PMD. A paraxial plane is used to represent the test multilens optical system. We introduce the calibration strategy and mathematical deduction of gradient equations. Systematic errors are suppressed with an N-rotation test. Simulations have been performed to demonstrate our method. The results showing the use of our method in multilens optical systems, such as the collimator and single-lens reflex camera lenses show that the measurement accuracy is comparable with those of interferometric tests.