In this paper, we report a fiber-optic pressure sensor fabricated by three-dimensional (3D) printing of glass using direct laser melting method. An all-glass fiber-housing structure is 3D printed on top of a fused silica substrate, which also serves as the pressure sensing diaphragm. And an optical fiber can be inserted inside the fiber housing structure and brought in close proximity to the diaphragm to form a Fabry-Perot interferometer. The theoretical analysis and experimental verification of the pressure sensing capability are presented.

Benefitting from the advancement of digital electronics in the 20th century, sensors have also gradually evolved from analog to digital. As semiconductor components are required in digital sensors, a power supply is still needed for the sensor. To eliminate the need for a power supply on the sensor, a concept of passive digital sensing is proposed. Different from the semiconductor-based electrical digital sensing method, the parameter to be measured is first converted to a mechanical signal, then the mechanical signal is encoded to multiple digital bits by a passive digitizer, where each bit is identified as open or short state that is detectable by general IO ports. To demonstrate the proposed sensing concept, a passive RFID temperature sensor is implemented using a bimetallic coil as the temperature sensing unit. The 6-bit binary codes are acquired and transmitted by a passive RFID that is powered by an energy harvester. The test results show that the temperature sensor has a measurement sensitivity of 1.32 °C/bit and a working distance over 10 meters.

A novel fiber optic Fabry-Perot acoustic sensor based on a grooved diaphragm has been proposed, avoiding the decrease of resonant frequency due to the enhanced sensitivity of the sensor based on conventional circular diaphragm. The effect of the structural parameters on sensitivity and resonant frequency is investigated by finite element simulation, and the designed diaphragm is fabricated by a digital light processing 3D printer. Experimental results indicate that the sensor based on the grooved diaphragm has an acoustic pressure sensitivity of 37.44 mV/Pa @2 kHz and a resonant frequency of 2.12 kHz, where the sensitivity is about 2.07 times that of the sensor based on the conventional circular diaphragm and the resonant frequency is almost unchanged. It is shown that the proposed sensor has the advantages of simple fabrication process, high consistency, and excellent applicability for weak acoustic signal detection.

A high-sensitive curvature sensor based on the negative curvature hollow core fiber (NCHCF) is proposed and demonstrated. The graded index fiber (GIF) is introduced between single mode fiber (SMF) and NCHCF for the cascaded structure of SMF-GIF-NCHCF-GIF-SMF. Compared to the structure without GIF, the coupling efficiency is improved by 16.5%. For the cascaded structure, multi-mode interference (MMI) and anti-resonance (AR) mechanisms coexist in the transmission spectra. The experimental results show that MMI-based dips have a blue shift as curvature increases while AR is not sensitive to its variation. As such, the self-referencing approach is employed for improving the performance of curvature sensor with the sensitivity up to -5.27 nm/m ^-1 . Furthermore, the temperature sensitivity of the sensor is -0.003 nm/°C, indicating a negligible temperature crosstalk. With advantages of compactness, efficient coupling, high sensitivity and negligible temperature crosstalk, the curvature sensor shows prospects in structural security monitoring, aviation industry, energy exploration and other fields.

This article presents a signal processing method to demodulate the optical interference phase of cascaded individual optical fiber intrinsic Fabry-Perot interferometric (IFPI) sensors in a coherent microwave-photonic interferometry (CMPI) distributed sensing system. The new method utilizes the chirp effect of electro-optic modulator (EOM) to create a quasi-quadrature optical interference phase shift between two adjacent pulses which correspond to two adjacent reflection points in the time domain. The phase shift can be controlled by adjusting the bias voltage that is applied to the EOM. The interference phase is calculated by elliptically fitting the phase shift. The interference phase change is proportional to the optical path difference (OPD) change of the interferometer, and the sign can be used to differentiate the increase or decrease of the OPD. The method is demonstrated for distributed strain sensing, showing good linearity, high resolution and large dynamic range.

A dielectric filter using a shared cavity with a quasi-box-like topology is proposed. In the shared cavity, four TE $_{\mathbf{101}}$ mode resonators with a dispersive coupling are cascaded to obtain a quasi-ellipse response. A coupling iris is employed to isolate cross coupling and provide source-load coupling based on the absorption effect of dispersive coupling on cross coupling while not on source-load coupling. This design offers a controllable transmission zero (TZ) which extends the stopband up to 1.85 $f_{\mathbf{0}}$ with rejection greater than $-$ 20 dB. A design example is fabricated and measured. The simulated and the measured results show good consistency for validating the wide out-of-band suppression characteristics of the proposed filter.