Multimodal biometric sensing and processing systems can significantly improve the success rate of identification and authentication compared to traditional unimodal biometric authentication techniques. We propose a Flexible micro-nanofiber (MNF) multimodal sensor for fingerprint recognition. We used PDMS as the sensor substrate and placed the MNF in s-shape on the PDMS. The surface of the PDMS is covered with a film with a thickness of only 2 μm to package the MNF. A ridge-shaped sensing area is formed on the sensor surface. Such structure protects the NMF from damage at the same time. It also greatly preserves the sensitivity of the NMF. This method realizes the simultaneous measurement of the fingerprint signal and the touch dynamics signal. We tested the stability of the sensors when measuring friction and pressure as well as temperature changes. We performed the recognition of 400 sets of fingerprint signals with an accuracy of 95.75%. Such method has great potential for applications in communication, computing, commercial purposes, and financial transactions.

We have explored a new way to achieve ultrasensitive detection of acoustic waves in an aqueous environment based on fiber-optic tweezers technology. Silicon dioxide particle trapped by the piconewton scale's light force is used as underwater acoustic wave sensors. When the acoustic signal propagates in water, it will cause microscale vibration of the particle in the light trap, resulting in small changes in the distance between the particle and the tip of the fiber optic and a change in the light range difference between the reflected beams, and the original underwater acoustic wave signals are obtained based on the resulting double-beam interference effect. Experiments show that, by collecting the movement information of particle in the optical trap under the influence of acoustic waves, it is possible to listen to acoustic signals with sound power as low as -67.135 dB and real-time monitoring of acoustic signals within the frequency range of 5-4 kHz, with a signal-to-noise ratio (SNR) of up to 72.073 dB. The new underwater acoustic sensing mode proposed in this article can overcome the existing acoustic sensing technology's limitations and provide a new direction for the sensing field of optical fiber tweezers technology.

This article proposes a dual fiber-optic microphone (DFOM) based on coherent synthesis technology, in which the sound pickup module mainly consists of two optical fibers and a reflection film, constituting two identical Fabry–Perot (FP) interferometric cavities as the acoustic sensing structure. The use of dual fiber-optic can increase the light intensity of the reflected light received by the photodetector (PD), while offsetting signal distortion caused by factors such as fiber length and temperature variations, and reducing signal interference, thereby improving the purity and accuracy of the signal. The DFOM exhibits strong fault tolerance, in case one of the optical fibers fails, the other one can still perform normal sound collection, thus enhancing the reliability of the microphone. Acoustic tests show that the sound pressure sensitivity of this DFOM at a frequency of 250 Hz is 64.8 mV/Pa. The signal-to-noise ratio (SNR) is as high as 62.45 dB under the action of a 6-kHz sound pressure signal. It maintains a linear sound pressure response and a flat frequency response in the range of 10 Hz–20 kHz. These results indicate that the DFOM has high sensitivity and a wide frequency response range, making it suitable for acoustic detection within the audible range.

This paper presents and experimentally validates a highly sensitive fiber-optic Fabry-Perot interferometer sound sensor based on a fiber-optic spherical structure. The Fabry-Perot interferometer comprises an aluminum foil diaphragm and a fused fiber-optic microsphere end face, both sealed in a structure made of a glass tube. An optical fiber microsphere structure is used for the first time in acoustic sensing. Based on the strong focusing capability of the microsphere, the high coupling ef-ficiency to the reflected beam, and the extensive range of the focused convergent optical field formed, the focused convergent optical fields facilitate the sensing of an extensive range of motion or deformation of the cavity compared to the divergent optical field of a flat fiber end face, i.e., the acoustic signals at more minor sound pressures can also be well sensed, thus compared to a flat fiber end face fiber The acoustic sensor can monitor acoustic signals over a more extensive frequency range and a larger range of acoustic pressure variations, and the output voltage signal is of a larger amplitude at the same acoustic signal, which allows the monitoring of acoustic signals at acoustic frequencies within the hearing range of the human ear. Experimental results show that the sensor shows a flat frequency response in the range of 20 Hz-20 kHz, covering all frequency components of the human ear hearing range, and the signal-to-noise ratio of the proposed acoustic sensor in the range of 20 Hz-20 kHz is greater than that of the flat fiber end-surface based acoustic sensor and the reference electroacoustic sensor, especially The sensor has the advantages of good high sensitivity, excellent linearity, wide planar response range, and simple manufacturing process. It can potentially be used as a highly sensitive, high acoustic quality fiber optic microphone in practical applications.

Bridging optical tweezers and microfluidics can form a multifunctional platform, which can overcome the difficulties of precise manipulation in hydrodynamic flow in a noninvasive method. However, when integrated into a microfluidic chip, the fiber optic tweezer loses its flexibility. Here, we propose a compact single fiber optical tweezer–micropipette system. It can sort particles by differences in shape and refractive index in a completely noninvasive way while retaining the flexibility, high selectivity, and precision of a fiber optical tweezer. Compact microfluidic channels are formed by combining two different-diameter micropipettes. The internal diameter of the circular microfluidic channel is less than 30 μm. Furthermore, we calculated the trapping and pushing regions of Yeast and Chlorella and achieved the separation of Yeast from Chlorella in the experiments. We did 90 sets of tests on the sorting accuracy of single fiber optical tweezer (SFOT). SFOT was able to distinguish between two types of particles in each test. With the advantages of high selectivity, high accuracy, low optical power consumption, and compact structure, such methods can be used in the fields of optical separation, cell transportation, cell sorting, and single-cell analysis.

We propose a near-field picometer vibration detection method based on a dielectric microsphere probe. Using an optical fiber combined with a dielectric microsphere to form a near-field probe. When parallel light is injected into the dielectric microsphere, interaction occurs between the surface of the microsphere and the focused beam in the near field, and at the front end of the dielectric microsphere will generate a highly localized electromagnetic beam, i.e., a photonic nanojet (PNJ). The nanojet of the probe in the near-field can enhance the scattered light of the object under the test surface. We used a differential structure that was formed by two optical fiber probes to detect the picometer vibration in the near field. From the experimental results, we know that the method can detect the picometer vibration signal, while the minimum vibration signal of 20 pm can be detected. The method has the potential to apply in cellular diagnostics, single-molecule detection, and in situ measurements.

We propose a microsphere-assisted Fabry-Perot interferometry (MAFPI) for microstructure measurement. We stretch the single-mode fiber and combine it with microspheres of different sizes and refractive indices, which can form super-focused spots with different characteristics, that is, a photonic nanojet phenomenon. As a proof of principle, we performed scanning imaging of optical discs and holographic gratings by MAFPI. The optical disc image obtained by MAFPI is consistent with the result obtained by a scanning electron microscope, and the obtained grating image is consistent with the actual result.