Kaichuan Xu

We report a monolithically integrated distributed feedback multiwavelength laser array (DFB-MLA) photonic chip for large capacity interrogation of weak fiber Bragg grating (WFBG) arrays. The chip integrates multiwavelength generation, optical power combining, power equalization, and pulse gating on a single InP platform. Based on the reconstruction-equivalent-chirp (REC) technique, the 8 × 3 laser array exhibits an adjacent-channel wavelength spacing of approximately 2.5 nm and a total tuning range of 60 nm. In the photonic chip, the outputs of different channels are combined through an on-chip three-stage Y-branch combiner and subsequently pass through two functionally separated semiconductor optical amplifiers (SOAs). The power-equalization SOA (PE-SOA) compensates for wavelength-dependent power variations, reducing the interchannel power variation from approximately 10 to 0.3 dB. The pulse-gating SOA (PG-SOA) converts the continuous wavelength-swept output into optical pulses for time-domain addressing. Based on a time- and wavelength-division multiplexing (TWDM) scheme, the chip-based demodulation system successfully demodulated 100 WFBGs with a spatial interval of 0.2 m between adjacent gratings. These results demonstrate the potential of the integrated photonic source for compact, large-capacity optical fiber sensing systems.

A large-capacity ultra-weak fiber Bragg grating (UW-FBG) array interrogation system is proposed and implemented. The system utilizes time- and wavelength-division multiplexing methods, based on a large-range tunable laser source (TLS) with fast tuning capability. The TLS consists of a distributed feedback multi-wavelength laser array (DFB-MLA) with a wavelength tuning range of 40 nm, which is realized using the reconstruction-equivalent-chirp (REC) technique. An external SOA modulator is used to modulate the output light from the TLS into nanosecond pulsed light. We establish an experimental system and successfully achieve 50 UW-FBGs interrogation. We perform temperature, strain, and vibration sensing experiments with a interrogation linearity of above 0.9995 and an error of less than 4 pm. Theoretically, the system is estimated to have an interrogation capability of more than 10,000 UW-FBGs, and the minimum spacing of adjacent UW-FBGs is 0.4 m. This research has made significant advancements in the multiplexing capability and spatial resolution of the UW-FBG array interrogation technology, offering important application potential in fields such as battery pack, structural health monitoring, and aerospace.

We develop a novel broadband comb light source for sensing multiple fiber Bragg gratings (FBGs). This broadband light source is realized through a Fabry-Pérot laser with intracavity saturable absorbers (FP-SA), which is a new type of low-cost and highly integrated semiconductor laser solution. The laser chip measures 1500 μm in length and 300 μm in width. Based on a waveform shaper and the FP-SA laser, we successfully generated the output of a broadband comb light source. By adjusting the filter bandwidth, laser gain voltage, and reverse voltage, we were able to tune the output bandwidth of the light source across a wide range from 2.5 nm to 25 nm. We propose a fitting method that leverages peak value extraction, tailored to the unique output characteristics of this source. Experimental results demonstrate that, when utilizing the FP-SA laser with a comb wavelength spacing of 0.23 nm, the demodulation repeatability achieves ±3.5 pm, and the demodulation linearity exceeds 0.9996. To the best of our knowledge, this work presents a new high-performance integrated broadband light source option for quasi-distributed FBGs array sensing systems.

A novel fiber Bragg grating (FBG) sensing system with a core laser source comprising a high-density integrated distributed feedback (DFB) laser array based on the reconstruction-equivalent-chirp (REC) technique is presented and demonstrated. This study proposes a fast and wideband wavelength-swept laser (WSL) based on a DFB laser array. 24 lasers are monolithically integrated with an 8 × 3 matrix structure with a wavelength spacing of 2.1 nm. The REC technique is used to simplify the grating fabrication and enhance the precise control of the wavelength spacing. Furthermore, a high-speed FBG sensing system using field-programmable gate arrays (FPGA) is proposed and demonstrated, achieving stable high-speed sweeping with a wavelength coverage of 50.4 nm and a sweeping frequency of up to 5.85 kHz without mode hopping. The FBG sensing system has a solid-state design without moving parts, allowing real-time, high-speed, and stable monitoring of temperature, pressure, strain, and displacement. It maintains superior stability even under challenging vibration and shock environments. Additionally, the system is cost-effective and is anticipated to have diverse industrial applications.

In this study, we propose a novel adjustable rotational half-dome mode conversion for a single-mode fiber(SMF) to generate Linearly Polarized First Order Mode(LP ₁₁ mode) and Orbital Angular Momentum(OAM) mode from Linearly Polarized Fundamental Mode(LP ₀₁ mode). The mode conversion system consists of two modules: the Fiber Rotation Traction (FRT) Module, which achieves LP ₀₁ -LP ₁₁ mode conversion by adjusting the rotational angles of θ =45°/135°/225°/270°.Then elongate it and cut off the optical fiber terminal to form a flat port; And the Fiber Half-Dome Lens (FHDL) Module, which converts the OAM mode from LP ₁₁ mode by fabricating a half-dome lens at the terminal of the FRT module output, introducing two light spots of the LP ₁₁ mode with corresponding rotational orthogonal angles. Theoretical and experimental results demonstrate that LP ₀₁ -LP ₁₁ mode conversion can be obtained through our FRT Module,and LP ₁₁ -OAM mode conversion can be generated through our FHDL Module.The Precise control of the equipment, the model conversion experiment can be made with good robustness and experimental repeatability. Comparing with existing conversion, this mode conversion technique enables the conversion of a single SMF into multiple modes, highlighting its simplicity of operation, which eliminates the necessity for fiber coupling or modulation with optical components. Furthermore, the potential applications of this method extend to optical tweezers particle manipulation experiments. In our future work, we plan to apply this method to enhance the efficiency of particle capture in optical tweezers experiments, leveraging its simplicity and effectiveness.

We present a microsphere-based microsensor that can measure the vibrations of the miniature motor shaft (MMS) in a small space. The microsensor is composed of a stretched fiber and a microsphere with a diameter of 5 μm. When a light source is incident on the microsphere surface, the microsphere induces the phenomenon of photonic nanojet (PNJ), which causes light to pass through the front. The PNJ’s full width at half maximum is narrow, surpassing the diffraction limit, enables precise focusing on the MMS surface, and enhances the scattered or reflected light emitted from the MMS surface. With two of the proposed microsensors, the axial and radial vibration of the MMS are measured simultaneously. The performance of the microsensor has been calibrated with a standard vibration source, demonstrating measurement errors of less than 1.5%. The microsensor is expected to be used in a confined space for the vibration measurement of miniature motors in industry.

In the field of biomedicine, the non-destructive and label-free detection of individual living cells has been long pursued. We propose a tapered fiber optic biosensor (TFOB), and perform theoretical and simulation analyses of the optical intensity distribution of the fiber tip, which gradually becomes thinner to expose the evanescent field around it. The fiber tip becomes a highly sensitive sensing element that acts as a transduction mechanism for the evanescent field. It translates the intensity change of the evanescent field around the tapered fiber into changes in output power. Experimental results show that the developed TFOB can detect vibration signals with amplitudes as low as 3 nm and achieve nondestructive, label-free measurements of respiratory vibrations of pasta yeast cells. Results show the periodic motion of yeast cells in the range of 300–550 Hz. Meanwhile, inactivated yeast cells have no characteristic frequencies evident in the spectrum. This nanoscale fiber optic sensor offers potential technical support for cell activity detection and pathological analysis.