High-sensitivity fiber-optic X-ray detectors employing gadolinium oxysulfide composites.

Radiation detection technologies have been applied in broad fields such as security inspection, medical diagnosis, environment monitoring and scientific analysis. Fiber-optic radiation detectors exhibit unique advantages including miniaturization, resistance to water, remote monitoring, and distributable detection. However, the low sensitivity and the high limit-of-detection limit its practical applications. Herein we demonstrated high-performance fiber-optic X-ray detectors with scintillating composites consisting of UV glue and uniformly distributed gadolinium oxysulfide (GADOX) powders. The impacts of the length, thickness and GADOX weight ratio of the composite coating upon the detector performance, were systematically investigated in terms of the generation and the coupling efficiency of radio-luminescence. Besides the high-performance scintillator, the scattering loss and the geometric factor greatly affected the detector performance. A higher sensitivity and lower limit-of-detection could be achieved by increasing the GADOX weight ratio and decreasing the thickness simultaneously. The optimal detector with the highest GADOX weight ratio (70%), exhibited a linear sensitivity to the X-ray dose rate within 31-1575 µGyair/s, and a low limit-of-detection of ∼0.26 µGyair/s at a tube voltage of 120 kV. The mechanism discussed here will provide insightful guidance for further development of fiber-optic radiation detectors and these promising results demonstrate the potential applications of fiber-optic detectors.

Mach-Zehnder Interferometer Biochemical Sensor Based on Silicon-on-Insulator Rib Waveguide with Large Cross Section.

A high-sensitivity Mach-Zehnder interferometer (MZI) biochemical sensing platform based on Silicon-in-insulator (SOI) rib waveguide with large cross section is proposed in this paper. Based on the analyses of the evanescent field intensity, the mode polarization and cross section dimensions of the SOI rib waveguide are optimized through finite difference method (FDM) simulation. To realize high-resolution MZI read-out configuration based on the SOI rib waveguide, medium-filled trenches are employed and their performances are simulated through two-dimensional finite-difference-time domain (2D-FDTD) method. With the fundamental EH-polarized mode of the SOI rib waveguide with a total rib height of 10 µm, an outside rib height of 5 µm and a rib width of 2.5 µm at the operating wavelength of 1550 nm, when the length of the sensitive window in the MZI configuration is 10 mm, a homogeneous sensitivity of 7296.6%/refractive index unit (RIU) is obtained. Supposing the resolutions of the photoelectric detectors connected to the output ports are 0.2%, the MZI sensor can achieve a detection limit of 2.74 × 10(-6) RIU. Due to high coupling efficiency of SOI rib waveguide with large cross section with standard single-mode glass optical fiber, the proposed MZI sensing platform can be conveniently integrated with optical fiber communication systems and (opto-) electronic systems, and therefore has the potential to realize remote sensing, in situ real-time detecting, and possible applications in the internet of things.

Design of a High-Performance Micro Integrated Surface Plasmon Resonance Sensor Based on Silicon-On-Insulator Rib Waveguide Array.

Based on silicon-on-insulator (SOI) rib waveguide with large cross-section, a micro integrated surface plasmon resonance (SPR) biochemical sensor platform is proposed. SPR is excited at the deeply etched facet of the bend waveguide by the guiding mode and a bimetallic configuration is employed. With the advantages of SOI rib waveguide and the silicon microfabrication technology, an array of the SPR sensors can be composed to implement wavelength interrogation of the sensors' output signal, so the spectrometer or other bulky and expensive equipment are not necessary, which enables the SPR sensor to realize the miniaturization and integration of the entire sensing system. The performances of the SPR sensor element are verified by using the two-dimensional finite-different time-domain method. The parameters of the sensor element and the array are optimized for the achievement of high performance for biochemical sensing application. As a typical example, a single bimetallic SPR sensor with 3 nm Au over 32 nm Al possesses a high sensitivity of 3.968 × 104 nm/RIU, a detection-accuracy of 14.7 µm(-1). For a uniparted SPR sensor, it can achieve a detection limit of 5.04 × 10(-7) RIU. With the relative power measurement accuracy of 0.01 dB, the refractive index variation of 1.14 × 10(-5) RIU can be detected by the SPR sensor array.