Zhenguo Jing

All-solid, open-cavity fiber optic Fabry–Perot etalon (FPE) sensors possess a wide static pressure detection range, yet their low sensitivity significantly restricts their application. This study proposes a programmable Vernier effect to improve the gas pressure sensitivity of FPE sensors substantially. By effectively modulating the emission spectrum of a widely tunable laser using a variable optical attenuator (VOA), the emission spectrum at different modulation lengths is expected to produce an optical beating in conjunction with the transmission spectrum of the FPE sensor, thereby realizing the Vernier effect. Experimental results indicate that by utilizing the proposed programmable Vernier effect, the pressure sensitivity of the FPE sensor has increased to −612.21 pm/kPa, demonstrating an amplification in sensitivity of approximately −153 times, consistent with the theoretical results. Owing to the programmable Vernier effect, which flexibly enhances the sensitivity of the FPE sensor, this sensor demonstrates considerable potential for gas pressure monitoring under various extreme conditions.

Inspired by the demodulation algorithm of Fabry–Perot composite sensors in the field of fiber-optic sensing, this paper proposes a method based on a widely tunable modulated grating Y-branch (MG-Y) laser combined with the cross-correlation algorithm to achieve a highly precise measurement of the optical thickness of each layer of a multilayer optical sample. A sample consisting of a double glass stack was selected, and the interference spectrum of the stacked sample was acquired using a widely tunable MG-Y laser. A fast Fourier transform (FFT) algorithm combined with a finite impulse response (FIR) bandpass filter was utilized to separate the different frequency components of the multilayer optical sample. The normalized spectra of each layer were reconstructed using the Hilbert transform. Subsequently, a cross-correlation algorithm was employed to process the normalized spectrum and determine the optical thickness of each layer with high precision. The samples were measured at predetermined locations, with 150 consecutive measurements performed to assess the repetition of the thickness. The standard deviation of these measurements was found to be lower than 1.5 nm. The results show that the cross-correlation algorithm is advantageous in the optical thickness measurement of multilayer films.

In this paper, a cost-effective and miniaturized instrument is proposed, which is based on a tunable modulated grating Y-branch (MG-Y) laser for rapid temperature measurement using a Fabry-Perot interferometer (FPI) sensor. The FPI sensor with a 1 463-µm cavity length is a short segment of a capillary tube sandwiched by two sections of single-mode fibers (SMFs). This system has a broad tunable range (1 527 nm–1 567 nm) with a wavelength interval of 8 pm and a tuning rate of 100 Hz. Temperature sensing experiments are carried out to investigate the performance of the system by demodulating the absolute cavity length of the FPI sensor using a cross-correlation algorithm. Experimental results show that the sensor can reach the response time as short as 94 ms with the sensitivity of 802 pm/°C. Benefiting from the homemade and integrated essential electrical circuits, the entire system has the small size, low cost, and practical application potential to be used in the harsh environment for rapid temperature measurement.

In this paper, a new method for manufacturing flexible and repeatable sensors made of silicon solar cells is reported. The method involves depositing the noble metal film directly onto the Si template and stripping out the substrate with a pyramid morphology by using an adhesive polymer. In order to evaluate the enhancement ability of the substrate, Rhodamine 6G (R6G) were used as surface-enhanced Raman scattering (SERS) probe molecules, and the results showed a high sensitivity and stability. The limit of detection was down to 10⁻¹² M for R6G. The finite-difference time domain (FDTD) was used to reflect the distribution of the electromagnetic field, and the electric field was greatly enhanced on the surface of the inverted pyramidal substrate, especially in pits. The mechanism of Raman enhancement of two types of pyramidal SERS substrate, before and after stripping of the noble metal film, is discussed. By detecting low concentrations of plasmid DNA, the identification of seven characteristic peaks was successfully realized using a noble metallic pyramidal substrate.

We present a novel, to the best of our knowledge, white light interferometric fiber-optic gyroscope (IFOG) scheme using a fiber-optic rhombic optical path difference (OPD) bias structure to interrogate with a sensing coil to realize rotation rate measurement without a phase modulator. The OPD bias structure composed of four ( 2 × 1 ) 3 dB single-mode fiber couplers was constructed to implement non-reciprocal OPD bias. White light interferometric demodulation was utilized to acquire the change in OPD due to the Sagnac-phase shift. Absolute linear output can be obtained. We produced the principle prototype of rhombic OPD bias white light IFOG without utilizing a phase modulator. An experimental demonstration of the IFOG prototype system achieves linear output with respect to the OPD difference in detecting rotation rate.

In this paper, we propose a hybrid time and wavelength division multiplexed (TWDM) active quadrature demodulation technique for fiber-optic Fabry—Perot acoustic sensor network. A modulated grating Y-branch (MG-Y) laser is utilized to achieve fast and programmable wavelength tuning. For each sensing channel, two operating wavelengths with quadrature phase difference are determined by the initial cavity length of the sensor. According to the DC voltages of the detected signal, the operating wavelength is feedback-controlled to locate on the spectral slope, maintaining the high sensitivity of the sensing system. Compared with traditional passive quadrature demodulation and quadrature point intensity demodulation methods, the feedback control logic is simple and flexible. Moreover, the proposed active quadrature demodulation scheme is easily applicable to sensors with different cavity lengths. Combined with a hybrid TWDM technology, simultaneous multi-point acoustic detection can be achieved, requiring only one tunable laser and one photodetector. A two-point sound velocity sensing system and a four-point sound source localization system are constructed. Experimental results show that different sensing channels can work effectively without crosstalk.

When the cavity changes during spectrum acquisition process, Doppler phenomena will occur and cause conventional scanning white-light interferometry (WLI) to fail. To address this problem, a novel laser frequency modulated phase-shifting WLI (PS-WLI) is proposed. Two phase-shifted spectra can be obtained by introducing a fixed phase-shift after each scanning frequency. The phase results containing modulations of frequency scanning and dynamic signals are retrieved based on quadrature demodulation. Although the full-spectrum acquisition frequency of the proposed PS-WLI is only 50 Hz, 0.5~20 kHz vibration signals can be demodulated. It combines the advantages of frequency-switched two-step phase shifting interferometry (PSI) and scanning WLI to achieve absolute measurement of dynamic low-finesse Fabry-Perot sensors. Numerical simulations and experiments verify its effectiveness.

Drift of Quadrature operating point (Q-point) due to variations in ambient temperature restricts the demodulation accuracy of fiber-optic extrinsic Fabry-Perot interferometer (EFPI) sensors. To overcome this challenge, in this paper, we propose and demonstrate a self-stabilizing Q-point system based on Vernier-tuned distributed Bragg reflectors (VT-DBR) laser, the laser wavelength is locked to a point with the maximum slope on the interference spectrum of fiber-optic EFPI sensor. Taking advantage of large-tuning range (40nm) and fast wavelength switching capability (<20ns), we develop a robust EFPI acoustic sensor system with stable Q-point operation. When the EFPI sensor is subject to ambient temperature variations, we use an FPGA to implement the fast laser wavelength switching of the laser and automatic Q-point locking that ensure Q-point stability. The operating point drift from Q-point is obtained by dc voltage output changes. Experimental results indicate that stabilizing Q-point of the EFPI sensor is effectively realized during the temperature changes between 27-320C. Without the stabilization method, the deviation is up to 85.5% of dc voltage output at operating point from Q-point value. With the stabilization method, the deviation is less than 0.68%. This self-stabilizing Q-point method based on VT-DBR laser has a strong ability to resist ambient temperature variations, and provides a novel solution to Q-point drift of fiberoptic EFPI sensors.